9. DRAFT FLOODPLAIN RISK MANAGEMENT PLAN · 9. DRAFT FLOODPLAIN RISK MANAGEMENT PLAN ... of design flood levels from current conditions. ... 4 installation of ‘flood proof’ doors

TOWRADGI CREEK, WOLLONGONG 169 BEWSHER CONSULTING PTY LTDFLOODPLAIN RISK MANAGEMENT STUDY June 2003 J829final-Vol1.doc

9. DRAFT FLOODPLAIN RISK MANAGEMENTPLAN

This chapter presents the draft Floodplain Risk Management Plan, showing thepreferred floodplain risk management measures, for the Towradgi Creek catchment.

The preferred measures have been determined from the range of available measuresdiscussed in Chapter 8, after an assessment of the impacts on flooding, as well asenvironmental, social, and economic considerations.

The total cost of the draft Floodplain Risk Management Plan, which involves more than40 different elements, would be in the order of $14.5 million. Implementation of theentire draft Plan would result in about a 40% saving of average annual flood damagesin the catchment (a saving in the order of $500,000 per annum) and would equate to anoverall benefit–cost ratio of about 0.4.

About $6.5 million of the $14.5 million total would involve extensive upgrading works inthe vicinity of the Corrimal Retail Area to protect at least 8 residential properties, 9commercial properties and 12 shops from flooding above floor level in a 100 year flood.

The remaining $8 million would involve works that would ultimately protect a further 61residences from flooding above floor level in a 100 year flood. These works include:

4 voluntary purchase of 9 properties at a cost of $2.6 million;

4 voluntary house raising of 16 properties at a cost of $640,000;

4 voluntary redevelopment of 12 properties at a cost of $720,000;

4 construction of 9 debris control structures at a cost of $860,000;

4 removal of the Colgong Crescent footbridge in the Towradgi Creek (Branch 1)catchment and construction of a raised single-span structure in the same locationat a cost of about $200,000;

4 enlargement of The Avenue culvert in the South Corrimal Creek (Branch 4)catchment at a cost of about $550,000;

4 enlargement of the Lemrac Avenue culvert in the North Corrimal Creek(Branch 5) catchment at a cost of about $700,000;

4 enlargement of the Railway Street culvert and associated works at the accessroad to the Coke Works site in the North Corrimal Creek (Branch 5) catchmentat a cost of about $1.4 million;

4 a variety of other smaller studies and works with a total cost of about $300,000.


One of the key components of the draft Floodplain Risk Management Plan is therecommendation of planning and building controls — these controls will be sensitive tothe flood problems in the catchment and reduce the future flood risk to the catchmentcommunity. The draft Floodplain Risk Management Plan also contains importantrecommendations relating emergency management and community flood awareness.

The costs for implementation of elements relating to floodplain planning, emergencymanagement and community awareness would be borne mainly by Council staff. Mostof these elements have been assigned either an urgent or a high priority because theyare essential for ensuring that flood risks in the Towradgi Creek catchment are notincreased in the future.

It should be noted that even with the completion of all the elements of the draftFloodplain Risk Management Plan, there would not be a significant change in the heightof design flood levels from current conditions. However, the most importantconsideration is that there would be a significant reduction in the amount of flood risk tothe people of the Towradgi Creek catchment.

Some of the reasons for this are as follows:

4 Council’s planning controls and policies, emergency management andcommunity flood awareness programs, would not reduce the current heights ofdesign flood levels. Rather, these types of options control the increase of floodrisks in the future;

4 measures such as voluntary house purchase, voluntary house raising andvoluntary reconstruction and redevelopment would not reduce the current heightsof design flood levels. Rather, these types of options help to reduce current floodrisks by reducing the number of people living in flood prone houses;

4 calculations would show that options involving the enlargement of a pipe orculvert would reduce flood levels upstream of the works. However, thesereductions would only occur if the culvert remained unblocked during a floodevent. In accordance with Council’s Conduit Blockage Policy, the upgradedculverts would still have to be assumed to be completely blocked (if the newculvert had a diagonal dimension of less than 6m). Therefore, there would be noreportable reduction in the height of design flood levels with installation of largerculverts. Therefore, options that involve upgrading of culverts have beenrecommended primarily on the basis of the ‘reduction of flood risk potential’ thatthey would offer the catchment community.

Therefore, flood levels and flood damages quoted for existing conditions in Appendix Bof this report and the Flood Damages Data Base would remain applicable followingimplementation of the entire strategy.

Table 9.1 provides a summary of each recommended element of the draft FloodplainManagement Plan for the Towradgi Creek catchment.


The following information is presented in Table 9.1 about each element of the Plan:

4 estimates of capital cost, together with annual maintenance cost if applicable;

4 reduction in the number of properties that would be flooded in a 100 year flood,assuming no blockage of culverts;

4 benefit–cost ratio where appropriate;

4 indicative priority (urgent, high, medium and low) — priority rankings for each ofthe options were discussed and adopted by the Floodplain Risk ManagementCommittee as part of the draft Plan. However, as situations change, it may beappropriate for Council to review these priorities;

4 likely sources of funding.

Each of the elements of the draft Floodplain Risk Management Plan is presented onFigure 9.1.

Once the draft Plan is adopted by Council, Council can then apply for funding tocommence the works.

The principal components of the Plan are discussed in this chapter, as follows:

4 catchment-wide measures — Section 9.1;4 Towradgi Creek (Branch 1) — Section 9.2;4 South Angels Creek (Branch 2) — Section 9.3;4 North Angels Creek (Branch 3) — Section 9.4;4 South Corrimal Creek (Branch 4) — Section 9.5;4 North Corrimal Creek (Branch 5) — Section 9.6;4 Carr Creek (Branch 6) — Section 9.7;4 Parker Creek (Branch 7) — Section 9.8.


TABLE 9.1: RECOMMENDED MEASURES FOR DRAFT FLOODPLAIN RISK MANAGEMENT PLAN

ESTIMATED COST (3)ITEM(Plan

SectionNo.)

DESCRIPTION

Reduction ofproperties

floodedabove floor

level (1)

Benefit–Cost

Ratio (2) CAPITAL MAINTENANCE(per annum)

FUNDINGSOURCES PRIORITY

9.1 CATCHMENT-WIDE MEASURES9.1.1 Planning Controls and Policy Issues:

4 draft Development Control Plan4 graded planning controls — Planning Matrix4 amendments to Local Environmental Plan4 adoption of Foreshore Building Line4 notions on Section 149(2) Certificates4 amendments to Conduit Blockage Policy

na na Council staffcosts

Council staffcosts

Current CouncilResponsibility High

9.1.2 Riverine Corridor Strategy, including:4 preparation of a Vegetation Management Plan;4 study of stream geomorphology;4 investigation into restoration of creek systems;4 investigation into rectification of in-stream and creek

bank erosion;4 identification of options for managing illegal

structures;4 preparation of a Riverine Corridor Maintenance

Program;

na na $80,000 Dependent onrecommendations

Council, DIPNR,National Landcare

ProgramHigh

9.1.3 Flood proofing:4 development of Flood Proofing Guidelines4 installation of ‘flood proof’ doors

naDependent on

recommendationsna Staff costs

Dependent onrecommendations

Staff costsnil

CouncilCouncil, residents

HighHigh

9.1.4 Improved Emergency Management Planning na na Council staffcosts

Council staffcosts SES High



SectionNo.)

DESCRIPTION


floodedabove floor

level (1)

Benefit–Cost



9.1.5 Improved Community Flood Awareness4 Update of Council GIS data base4 Issuing of Flood Certificates4 Production of book about August 1998 flood4 Commemoration activities

4 Brochure on Flood Risk Precincts4 production of brochure on how local community

can care for creek environment4 Installation of flood markers

na na

Staff costsStaff costs$20,000

Dependent onrecommendations

Staff costs

Staff costs$5,000 each

(allow 4 markers)

Staff costsStaff costs nil

nil

nilStaff costs

Staff costsStaff costs

CouncilCouncil

Council, VolunteersCouncil, SES

Council, SESCouncil, DIPNRCouncil, DIPNR

High

9.1.6 Policy for Management of Escarpment Runoff na na Council staffcosts

Council staffcosts Council High

9.2 TOWRADGI CREEK (BRANCH 1)9.2.1 Voluntary house purchase — 5 properties 5 0.4 $1,600,000 nil Council, DIPNR High

9.2.2 Voluntary reconstruction/redevelopment — 3properties 3 0.4–0.5 $180,000 net nil Council, DIPNR High

9.2.3 Removal and raising of Colgong Crescent footbridge inits current location 10 3.0 $200,000 nil Council, DIPNR Urgent

9.2.4 Embankment along eastern Creek Bank behindCassell Avenue 0 na $20,000 Council staff

costs Council, DIPNR Medium

9.2.5 Debris control structures — 3 locations na na $285,000 $9,000 Council, DIPNR High

9.2.6

Management of ocean entrance4 policy to dig pilot channel/breach beach berm4 access to telemetered water levels at Pioneer

Road gauge4 design ocean levels for 100 year flood and PMF

na na Council staffcosts

Council staffcosts Council Medium

9.2.7 Prosser Close Erosion Study na na $20,000 nil Council, DIPNR Urgent9.2.8 Caldwell Avenue Local Area Flood Assessment na na $15,000 nil Council, DIPNR Low

9.3 SOUTH ANGELS CREEK (BRANCH 2)9.3.1 Voluntary reconstruction/redevelopment — 1 property 1 0.4 $60,000 net nil Council, DIPNR High9.3.2 Works at Tarrawanna Soccer Complex and Corrimal St 0 na $20,000 nil Council, DIPNR Low



SectionNo.)

DESCRIPTION


floodedabove floor

level (1)

Benefit–Cost



9.4 NORTH ANGELS CREEK (BRANCH 3)9.4.1 Voluntary house raising — 1 property 1 0.8 $40,000 nil Council, DIPNR High9.4.2 Voluntary reconstruction/redevelopment — 1 property 1 0.9 $60,000 net nil Council, DIPNR Medium9.4.3 Debris control structures — 1 location na na $95,000 $3,000 Council, DIPNR High9.4.4 Bellambi Street Flood Assessment na na na na Council, DIPNR current9.4.5 Tarrawanna Road channel works 0 na $40,000 nil Council, DIPNR Low

9.5 SOUTH CORRIMAL CREEK (BRANCH 4)9.5.1 Enlargement of The Avenue culvert up to 5 (4) 0.7 $550,000 nil Council, DIPNR Medium

9.5.2 Controls to maintain overland flow paths wherefloodwaters spilt off roads into lower lying properties na na Council staff

costsCouncil staff

costs Council Urgent

9.5.3 Debris control structure — 1 location na na $95,000 $3,000 Council, DIPNR High

9.6 NORTH CORRIMAL CREEK (BRANCH 5)9.6.1 Voluntary house purchase — 4 properties 4 0.3–0.6 $1,000,000 nil Council, DIPNR High9.6.2 Voluntary reconstruction/redevelopment — 1 property 1 0.7 $60,000 net nil Council, DIPNR High9.6.3 Enlargement of Lemrac Avenue culvert up to 5 (4) 0.3 $700,000 nil Council, DIPNR High9.6.4 Enlargement of Railway Street culvert up to 4 (4) 0.2 $1,400,000# nil Council, DIPNR Medium

9.6.5Formalisation of overland flow path through CorrimalRetail Area between No.81 Collins Street and PrincesHighway (including downstream compensatory works)

9 commercial+ 12 shops

+ 8 residential0.2–0.3

$6,500,000(includes pipe upgrade

works, propertypurchase, downstreamcompensatory works

and studies)

nil Council, DIPNR,private developer High

9.6.6 Lower ground levels near Collins Street sag point 0 na $10,000 nil Council, DIPNR Low


costsCouncil staff


9.6.8 Debris control structures — 4 locations na na $380,000 $12,000 Council, DIPNR High9.6.9 Installation of bollards on roadways — 3 locations 0 na $15,000 nil Council, DIPNR High9.6.10 Additional pipe inlet capacity at No.81 Collins Street na na $20,000 nil Council, DIPNR High



SectionNo.)

DESCRIPTION


floodedabove floor

level (1)

Benefit–Cost



9.7 CARR CREEK (BRANCH 6)9.7.1 Voluntary house raising — 13 properties 13 1.1–1.3 $520,000 nil Council, DIPNR High


9.7.3 Maintaining 2 overland flow paths between Carr Creek(Branch 6) and Towradgi Creek (Branch 1) na na Council staff

costsCouncil staff


9.8 PARKER CREEK (BRANCH 7)9.8.1 Voluntary house raising — 2 properties 2 0.6 & 1.1 $80,000 nil Council, DIPNR High



costsCouncil staff


TOTALS 69 residential 0.41 $14.45 million $30,000Notes:(1) Reduction in the number of properties currently flooded above floor level in a 100 year flood.(2) Refer to Section 7.2.3 or information on how benefit–cost ratios have been calculated, particularly with regard to Council’s Conduit Blockage Policy.(3) When a range of costs has been provided in the text, only the highest cost has been presented in this table(4) With application of Council’s Conduit Blockage Policy, the number of properties ‘protected’ would be zero. If culverts were assumed to unblocked, the number of houses protected are shown.



9.1 CATCHMENT-WIDE MEASURES

9.1.1 Planning Controls and Policy Issues

Priority: HighCapital Cost: Council staff costsMaintenance Cost: Council staff costs

Recommendations: Development Control Plan — adoption of a Development ControlPlan (DCP) that outlines appropriate measures to be applied todevelopment in the floodplain. Appendix A3 provides a suggestedDraft Development Control Plan entitled “Managing our FloodRisks” for consideration and adoption in accordance with theprocess required under the Environmental Planning andAssessment Act. Flood related controls within existing DCPsshould be replaced with a reference to this issue specific DCP.

Council would also need to review its current provisions for exemptand complying development (as outlined in DCPs No.99/1 and99/2) to ensure they are consistent with the new DCP.

Planning Matrix — the consideration of the application of a gradedset of planning controls for different land uses relative to differentlevels of flood hazard within the study area (see Table 8.4). Thiswould involve the adoption of the High, Medium and Low FloodRisk Precincts, as described in Section 4.5.

Wollongong Local Environmental Plan — the consideration, byCouncil, of the following for inclusion within the Wollongong LEP:

– standard definitions, objectives and standard clauses generallyas outlined in Appendix A2;

– the identification of the extent of the “flood prone land” onCouncil’s LEP maps.

Foreshore Building Line — a resolution by Council to adopt aforeshore building line (FSBL) along all creeks within the study areain accordance with the boundaries of the High Flood Risk (andInterim Riverine Corridor) Precinct, and other criteria (includingerosion potential, stream integrity and floodway provision) relatingto an interim setback of 10m from the tops of creek banks. Thissetback could be made greater if documented environmental basedata existed to allow for a more site-specific setback.


The FSBL should be identified on Council’s LEP maps and shouldinvolve consultation with other agencies including PlanningNSW(formerly the Department of Urban Affairs and Planning (DUAP)),National Parks and Wildlife Service and DIPNR regarding theintegration of Riparian Corridor Management Studies currentlybeing prepared by the Illawarra Escarpment Project CoordinationTeam.

This process should also involve a review of the appropriatenessof the zoning of individual land parcels, should the combined floodrisk and environmental criteria result in a foreshore building linethat substantially affects reasonable development expectations.

Section 149(2) Certificates — the incorporation by Council ofnotations upon Section 149(2) Certificates that identify the floodaffectation by the DCP.

Conduit Blockage Policy — amendments to the Policy to:

– ensure that potential flow diversions, which may be initiated bya blockage, are considered and designed for. It is important inthese situations to determine which would create the worstflood situation and hence the maximum flood levels for aparticular section of the creek system;

– incorporate the requirements for economic appraisal forassessment of culvert upgrading works and the like as outlinedby the then DLWC (2001).

9.1.2 Riverine Corridor Strategy

Priority: HighCapital Cost: $80,000Maintenance Cost: Dependent on recommendations made.Implementation Cost: Dependent on recommendations made.

Recommendations: The preparation and implementation of a Riverine Corridor Strategyby Council for the creek corridors within the study area, to improvecorridor linkages, to restore their ecological value and to replaceinappropriate vegetation (that impedes the flow of water or couldprovide a source of debris, thereby exacerbating flood impacts)with more appropriate flood compatible native species. Keycomponents of the Strategy would include:

– preparation of a Vegetation Management Plan;– study of stream geomorphology;– investigation into restoration of creek systems;– investigation into rectification of in-stream and bank erosion;– identification of options for managing illegal structures;– preparation of a Riverine Corridor Maintenance Program;


9.1.3 Flood Proofing

Priority: HighCapital Cost: Council staff costs and private residents’ costs for any works

undertakenMaintenance Cost: Nil

Recommendations: The development of some ‘Flood Proofing Guidelines’ isrecommended for inclusion in the draft Floodplain RiskManagement Plan. Some examples of some flood compatiblematerials and building techniques are included in Schedule 1 of thedraft Development Control Plan (see Appendix A3 of AppendixA).

Individual properties, particularly commercial properties, can bemodified to reduce the impacts of flooding by a number of floodproofing techniques. These techniques include, but not limited to,the following:

– construction of small flood-retaining walls around the immediateperimeter of the house or around a small proportion of theproperty. These types of walls are similar to levees in functionand so if walls are to be extended beyond the immediateperimeter of the house, the same issues as levees need to beconsidered before they are installed (see Section 8.3.1). Generally it must be ensured that the walls would not adverselyaffect the flood situation at neighbouring properties.

– fitting waterproof doors and/or waterproofing walls of houses.There appears to be a number of opportunities for replacing‘standard’ doors with flood-proof doors at the lowermost unitsof some of the multi-unit developments;

– locating shelves and storage areas at a height above the likelyflood level for the storage of electronic equipment and personaleffects (particularly photographs, diaries, clothes and othermemorabilia).

Flood proofing measures are a private cost and so could beimplemented with minimal cost to Council.


9.1.4 Improved Emergency Management Planning

Priority: HighCapital Cost: mainly limited to training of SES staff and volunteersMaintenance Cost: minimal

Recommendations: Unfortunately, there is limited scope to improve the flood warningin the Towradgi Creek catchment as this relatively short, steepcatchment experiences ‘flash flooding’. As such, the Met. Bureauwould be unable to provide a specific flood warning service to thiscatchment. Therefore, improved emergency management planningand support for the continued development of the Local Flood Planis considered to be an important component of the draft FloodplainRisk Management Plan.

It is recommended that the existing SES Flood Plan be updatedwith the new flood intelligence data now available via the currentstudy. It is important that the plan be endorsed by all organisationsthat have responsibilities for activities prior to and during floods. The Floodplain Risk Management Committee would be an idealgroup to assist the SES with the continued development of theLocal Flood Plan, and to enlist the support of other authorities.

9.1.5 Improved Community Flood Awareness

Priority: HighCapital Cost: Council staffing costs for all items except book about 1998 flood

($20,000) and simple flood markers ($5,000 each).Maintenance Cost: Council staffing costs

Recommendations: – updating of Council’s GIS with flood damages data base;– issuing of flood certificates;– production of a book about the August 1998 flood;– organisation of commemorative activities;– production of brochure on Flood Risk Precincts;– production of brochure on how community can care for the local

creek environment;– installation of flood markers.

The Floodplain Risk Management Committee and Council woulddetermine exact details of the Community Flood AwarenessStrategy in more detail at a later stage.


9.1.6 Policy for Management of Escarpment Runoff

Priority: HighCapital Cost: Council staffing costsMaintenance Cost: Council staffing costs

Recommendations: There were several locations in the upper reaches of the TowradgiCreek catchment during the August 1998 flood where houses andproperties where flooded when floodwaters flowed directly off thesteep escarpment behind them. In some areas, residents havetried to manage this type of runoff themselves by constructing smallwalls and excavating small channels.

It is recommended that Council develop a policy so thatescarpment runoff can be managed in a coordinated way.

9.2 TOWRADGI CREEK (BRANCH 1)

9.2.1 Voluntary House Purchase

Priority: HighCapital Cost: $1.6 millionMaintenance Cost: nil

Recommendations: It is recommended that the following 4 single dwellings and 1 smallunit block be included on Council’s Voluntary House PurchaseScheme:

– Nos. 130, 132, 133, 134 and 137 Pioneer Road.

9.2.2 Voluntary Reconstruction/Redevelopment

Priority: HighCapital Cost: $180,000 net costMaintenance Cost: nil

Recommendations: It is recommended that the following 3 houses be included onCouncil’s Voluntary House Reconstruction/RedevelopmentScheme:

– Nos 54 and 56 Caldwell Avenue;– No.2 Cassell Avenue.


9.2.3 Removal/Relocation of Colgong Crescent Footbridge

Priority: UrgentCapital Cost: $200,000Maintenance Cost: minimal

Recommendations: It is recommended that the Colgong Crescent footbridge and theadjacent creek ‘weir’ be urgently removed and a higher structurebuilt at the same location.

The replacement of the existing footbridge with a new and higherstructure (Option E), which would have a single span across thecreek (rather than relocating the structure nearby to near therailway line), was clearly the preferred solution for the footbridgefrom the community submissions received during the publicexhibition of the Study and Plan and by the Floodplain RiskManagement Committee.

To achieve no increase in 100 year flood levels the minimum levelof the new deck would have to be about RL5.1 mAHD (based onthe underside of the deck matching the 100 year level ofRL4.6 mAHD). This level of RL5.1 mAHD would be about 1mhigher than the adjacent Colgong Crescent road level and alsoabout 0.6m higher than the existing floor levels at adjacentproperties (Nos. 4 and 6). This required height of a new footbridgewould have to examined from a privacy perspective.

9.2.4 Embankment along Eastern Creek Bank behind Cassell Avenue

Priority: MediumCapital Cost: $20,000Maintenance Cost: Council staff costs

Recommendations: This option is recommended subject to a study undertaken byCouncil to confirm its feasibility.

This option was raised in the community submissions receivedduring the public exhibition of this Study and Plan. The area wherethis embankment could be built is currently being surveyed byCouncil to confirm its feasibility. It is possible that this option willprovide useful flood protection in the more frequent flood events,for several adjacent properties in Cassell Avenue. In larger floodevents, the embankment would be overtopped. Local drainageissues would have to be carefully considered with such anembankment.


9.2.5 Debris Control Structures

Priority: HighFeasibility Study: $45,000 (includes Hydraulic Investigation of $10,000 and

Environmental Investigation of $5,000 for each structure)Capital Cost: $240,000Maintenance Cost: $9,000 p.a.

Recommendations: It is recommended that the following 3 locations are examined todetermine their suitability for siting a debris control structure:

– adjacent to the corner of Foothills Road and Caldwell Avenue,– adjacent to the end of Pringle Road,– upstream of the railway line bridge (with access off the end of

Carr Street).

9.2.6 Management of Ocean Entrance

Priority: MediumCapital Cost: Council staff costsMaintenance Cost: Council staff costs

Recommendations: Because the beach berm can quite easily reach levels in excess ofRL3.0 mAHD, it is recommended that a policy be developed to diga pilot channel once a water level of RL2.0 mAHD is reachedbehind the berm at the ocean entrance. It is suggested that Councilreceives direct access to the telemetered Pioneer Road levels andwhenever the water level reaches RL2.0 mAHD, a starter channelis excavated.

It is also recommended that the following design ocean levels beadopted at the outlet of Towradgi Creek (these include anallowance of 0.3m for potential ‘Greenhouse’ impacts):

– 100 year level of 2.7 mAHD;– probable maximum flood level of 3.7 mAHD.

9.2.7 Prosser Close Erosion Study

Priority: UrgentCapital Cost: $20,000Maintenance Cost: nil

Recommendations: Although some stabilisation works have been completed, it isrecommended that a specific study be undertaken to determine themost appropriate works that should be undertaken to address thesevere erosion that occurred during the August 1998 flood.


9.2.8 Caldwell Avenue Local Area Flood Assessment

Priority: LowCapital Cost: $15,000Maintenance Cost: nil

Recommendations: The depression through Nos. 54–58 Caldwell Avenue conveysexcess local catchment flows to Towradgi Creek (Branch 1). Thisflowpath lies beyond the limit of the MIKE-11 hydraulic modelhowever it is apparent that in the August 1998 flood there weresubstantial overland flows passing along this overland flow path.There is therefore an opportunity to create a more suitable overlandflow path and so keep floodwaters away from the houses. It shouldbe noted that such works would not alleviate the significant floodproblems caused by flooding from the main creek experienced byNos. 54 and 56.

It is recommended that a Local Area Flood Assessment beundertaken for these Caldwell Avenue properties.

9.3 SOUTH ANGELS CREEK (BRANCH 2)



Recommendations: It is recommended that the following house be included on Council’sVoluntary House Reconstruction/Redevelopment Scheme (it isnoted that Council currently owns this property):

– No.51 Meadow Street.

9.3.2 Works at Tarrawanna Soccer Complex and Corrimal Street

Priority: LowCapital Cost: $20,000Maintenance Cost: minimal

Recommendations: Minor works, to further control runoff from the Tarrawanna soccerclub complex, are recommended. This would include adjustmentsto levels of the southern access track and grading to direct localrunoff into the adjacent detention basin rather than spilling acrossCorrimal Street and adversely affecting the garage at No 13Corrimal Street.


9.4 NORTH ANGELS CREEK (BRANCH 3)

9.4.1 Voluntary House Raising

Priority: HighCapital Cost: $40,000Maintenance Cost: nil

Recommendations: It is recommended that the following house be included on Council’sVoluntary House Raising Scheme:

– No 47 Tarrawanna Road.



Recommendations: It is recommended that the following house be included on Council’sVoluntary House Reconstruction/Redevelopment Scheme:

– No.32 Meadow Street.

9.4.3 Debris Control Structure


Environmental Investigation of $5,000)Capital Cost: $80,000Maintenance Cost: $3,000 p.a.

Recommendations: It is recommended that the following location is examined as todetermine its suitability for siting a debris control structure:

– near the top of the spillway chute of the upper “Foothills Estatedetention basin above Bellambi Street.

9.4.4 Bellambi Street Flood Assessment

Priority: CurrentCapital Cost: not applicableMaintenance Cost: nil

Recommendations: This area is currently being assessed in detail as part of a separateinvestigation. A draft report was submitted to Council early in 2002and Council is currently assessing the implications of the report’srecommendations. It is anticipated that this assessment will allowbroader guidelines to be developed regarding provisions for runoffentering properties that back onto the escarpment slopes.


9.4.5 Tarrawanna Road Channel Works


Recommendations: It is recommended that works including an energy dissipaterstructure be considered at the outlet of the gabion-lined channeldownstream of Tarrawanna Road to control erosion problems asoccurred in the August 1998 flood. The gabion-lined channel itselfis also in need of repair. The cost of the works could be partlycovered by the Section 94 contributions from development of thenew subdivision.

9.5 SOUTH CORRIMAL CREEK (BRANCH 4)

9.5.1 Enlargement of The Avenue Culvert

Priority: MediumCapital Cost: $400,000Maintenance Cost: nil

Recommendations: It is recommended that this culvert be enlarged to a 3,000mm wideby 1,800mm high box culvert that would convey the 100 year floodflow in South Corrimal Creek (Branch 4) of 15.2m3/s under theroadway (while the 100 year floodwaters received from UnderwoodStreet would still travel overland). The works would need tosupplemented with upstream and downstream transition works.The downstream works would need to address existing stabilityproblems with the western channel bank and the scour hole at theexisting pipe outlet.

If the upgraded culverts remained unblocked during major floods,the works would achieve a major reduction in overland flows withan associated reduction in flood risk and flood damages.

Subject to a separate assessment, the culvert upgrade worksshould be supplemented by a debris control structure located justupstream of The Avenue, (see Section 9.5.3).


9.5.2 Controls to Maintain Overland Flow Paths where Floodwaters Spilt offRoads into Lower Lying Properties

Priority: UrgentCapital Cost: Council staff costsMaintenance Cost: Council staff costs

Recommendations: Research undertaken following the August 1998 flood revealed thatat the following location, the local road not only acted as overlandflowpaths but floodwaters spilt off the road and into lower lyingproperties:

– the southern side of Francis Street, between Collins Street andUnderwood Street.

It is recommended that any redevelopment proposals for thesouthern properties in the locations listed above should not obstructor prevent these spills from entering the properties. This willensure each property continues to accept its portion of the overlandflow from the roadway. Council will need to consider these issueswhen considering development proposals in the area in order toavoid local flood problems within the site. In particular, propertyfrontage fences should not obstruct these spills from entering theproperties, otherwise neighbouring properties would potentiallyexperience more significant flood problems.

9.5.3 Debris Control Structure


Environmental Investigation of $5,000)Capital Cost: $80,000Maintenance Cost: $3,000 p.a.

Recommendations: It is recommended that the following location is examined as todetermine its suitability for siting a debris control structure:

– upstream of The Avenue (subject to negotiation of a ‘right-of-way’ through an adjoining property).


9.6 NORTH CORRIMAL CREEK (BRANCH 5)

9.6.1 Voluntary House Purchase

Priority: HighCapital Cost: $1,000,000Maintenance Cost: nil

Recommendations: It is recommended that the following 4 houses be included onCouncil’s Voluntary House Purchase Scheme:

– Nos. 1,3 and 5 Willow Grove;– No.112 Collins Street.



Recommendations: It is recommended that the following houses be included onCouncil’s Voluntary House Reconstruction/RedevelopmentScheme:

– No.69 Cross Street.

9.6.3 Enlargement of Lemrac Avenue Culvert


Recommendations: In the vicinity of Lemrac Avenue, North Corrimal Creek (Branch 5)currently consists of a single 1,500mm diameter conduit thatfollows the Lemrac Avenue alignment before reaching the rear ofthe drainage reserve next to No.5 Lemrac Avenue. With the aimof eliminating above-floor flooding of up to 5 properties in a 100year flood in the vicinity of this culvert, a new and larger culvert withdimensions in the order of 6,000mm wide and 1,800mm high isrecommended.

Its construction would also involve significant upstream and somedownstream transition works. The construction of downstreamtransition works would ensure that there would be no adverseimpacts on downstream properties because of the works.


As the length of the diagonal of such a culvert would exceed 6m,the Council’s Conduit Policy states that only 25% blockage of thepipe needs to be assumed when calculating design flood levels.

The scheme would achieve a major reduction in overland flows andresult in the associated reduction in flood risk and damages.

It is recognised that the works would require the construction of anupstream debris control structure (see Section 9.6.8).

9.6.4 Enlargement of Railway Street Culvert

Priority: MediumCapital Cost: $1.4 millionMaintenance Cost: nil

Recommendations: The pipes under Railway Street currently consist of twin 1,800mmdiameter concrete pipes and these receive flows from the muchlarger capacity multi-cell box culverts (3 x 3,000mm wide x1,700mm high) under the Northern Distributor. Because of thesignificant differences in the capacities of the two culvert structures,there is the potential for relatively frequent and major surchargingof floodwaters to occur at the transition structure between the twoculverts.

It is recommended that the Northern Distributor box culverts beextended under Railway Street and beyond the access roadwayservicing the medium density development at No.29 RailwayStreet.

With application of Council’s Conduit Blockage Policy and becauseof the ‘backwater’ impact from the road culvert that accesses theCoke Works, there would not be any significant reduction in depthsof floodwaters in major floods across Railway Street.

The value of these works would greatly improve if downstreamworks were also carried out at the access road to the Coke Works(downstream of Railway Street). With this culvert downstreamaccess road assumed to be fully blocked, this causes a backwatereffect that extends as far upstream as Railway Street. If the levelsof the access road roadway levels were lowered (or there wassignificant upgrading of the culvert), this would reduce the depth offloodwaters Railway Street. Consequently, these works have beenincluded as part of this option.

The construction of a debris control structure on the upstream sideof the Northern Distributor is also recommended as part of theseworks (see Section 9.6.8). The construction of downstreamtransition works would ensure that there would be no adverseimpacts on downstream properties because of the works.


9.6.5 Formalisation of Overland Flow Path through Corrimal Retail Area betweenNo.81 Collins Street and Princes Highway

Priority: HighCapital Cost: $6.5 million (including culvert upgrade works, property purchase,

downstream compensatory works and investigation/feasibilitystudies)

Maintenance Cost: nil

Recommendations: The single worst location for flood damages in the Towradgi Creekcatchment in the August 1998 flood was the retail area at Corrimalbetween the sag points in Underwood Street and the PrincesHighway. This was confirmed with the hydraulic modelling of aseries of design flood events. At this location there is nowatercourse. Instead there are twin large diameter pipes that carryNorth Corrimal Creek storm flows under the medium densitydevelopment at No.81 Collins Street, under Underwood Street,under the local shops (which includes the former ‘Coles New World’shopping complex) and under the Princes Highway and theadjoining Council park.

Despite the very substantial costs associated with implementing aflood mitigation scheme at this location, Option 2 is stronglyrecommended for detailed investigation given the very substantialflood mitigation benefits that would accrue. Because of this, thedevastating nature of the flooding that occurred in the August 1998and because of the strong community support for a solution to befound, works in the area of the Corrimal Retail Area have beenincluded as high priority works in this draft Plan.

Overall viability of the works, however, is dependent on the costsinvolved and the nature of redevelopment proposed by the privatesector in this area. If a large portion of the costs need to be met byCouncil, the project may not be viable. Discussions withdevelopers are proceeding. Preliminary indications are that theacquisition costs to be met by Council would be large and theproject may not be able to proceed.

The recommended works (Option 2) would involve undertakingworks between No.81 Collins Street and downstream of the PrincesHighway. The works would address both the retail area problemsand the residential area flood problems at and upstream ofUnderwood Street. It was assumed that the scheme would bedesigned to cope with the 100 year design flows and that the workswould accommodate the existing ‘Coles’ development betweenUnderwood Street and Bertram Lane.


The following elements are recommended for these works:

– extension of the floodway through No.81 Collins Street toUnderwood Street. This would require the purchase of No.29AUnderwood Street (and the demolition of its single dwelling),the purchase of the south-western corner of No.29 UnderwoodStreet and the excavation of a floodway. This floodway wouldhave similar dimensions to the current floodway. It isanticipated that a portion of No.29A, which would be surplus tothe floodway requirements could be used to providereplacement parking spaces, etc for No.29;

– construction of culverts under Underwood Street that wouldconvey the floodway flows under the roadway;

– extension of the culverts through the ‘Coles’ car park (south ofthe current building footprint);

– development of an overland flow path through the ‘Coles’ siteto convey overland flows to No.203 Princes Highway, which iscurrently a private car park. Floodwaters would then bedirected into a new underground conduit that would carry theflows under the highway and the park to where the watercoursere-commences at the outlet of the existing twin pipes.

This scheme has the attractions of not disrupting the shoppingprecinct at the highway sag point and of substantially reducinghazardous flow conditions at the highway. However, the requiredconduit size would be very large and potential blockage at the inletwould need to be carefully considered. There may also beproblems with services and utilities that run parallel to the highway.

An important component of this project would be to include thefollowing compensatory works to ensure the works would notincrease flood levels and damages downstream of the workscompared with current day conditions:

– some widening of the channel (in the vicinity of the creekoverbanks) between the twin pipe outlet below the highway andthe Northern Distributor;

– modification of the entry conditions at the Northern Distributormultiple culvert (for example, the construction of a ‘hood’ at theinlet to improve its efficiency);

– extension of the Northern Distributor culvert under RailwayStreet (see Section 9.6.4);

– works at the twin culvert at the Coke Works access road (assee Section 9.6.4).


9.6.6 Lower Ground Levels near Collins Street Sag Point


Recommendations: At the Collins Street sag point near the Willow Grove intersection,the ground levels immediately downslope of the roadway areslightly elevated. There is the opportunity to lower those levels andso formalise an overland flowpath. These works are thereforerecommended and would lower local flood levels, especially inCollins Street itself.



Recommendations: Research undertaken following the August 1998 flood revealed thatat the following location, the local road not only acted as overlandflowpaths but floodwaters spilt off the road and into lower lyingproperties:

– the southern side of Coxs Avenue, between Parmenter Avenueand Lemrac Avenue.


9.6.8 Debris Control Structures


Environmental Investigation of $5,000 for each structure)Capital Cost: $320,000Maintenance Cost: $12,000 p.a.


Recommendations: It is recommended that the following 4 locations are examined asto their suitability for siting debris control structures:

– upstream of Lemrac Avenue (with access via the PublicReserve fronting Coxs Avenue;

– upstream of No.81 Collins Street– upstream of access road bridge off Railway Street (near the

scout hall);– upstream of the Coke Works access road twin culvert (subject

to negotiation to build an access track and to provide access forongoing maintenance).

9.6.9 Installation of Bollards on Roadways


Recommendations: During the August 1998 flood, vehicles were swept off roadways attwo locations in the North Corrimal Creek (Branch 5) catchment —at Lemrac Avenue and Railway Street. Together with a thirdlocation within the catchment at Collins Street, it is recommendedthat bollards be erected on the downstream side of the roadwaysto prevent vehicles from being swept into the creek channel.

9.6.10 Additional Pipe Inlet Capacity at No.81 Collins Street


Recommendations: Within the Corrimal Retail area, there is no water course to conveythe North Corrimal Creek (Branch 5) flows. Instead there are twinlarge diameter pipes that carry flows under the medium densitydevelopment at No.81 Collins Street and downstream through theCorrimal retail centre. When the capacity of the culverts isexceeded, flood flows are conveyed firstly along a formalisedoverland flowpath, which only extends through No.81 Collins StreetEast (that is downstream) of Underwood Street, there is noflowpath available for excess flows. In the August 1998 flood, flowdiversions occurred and the local area flooding was exacerbated bydebris effectively fully blocking the entrance to the twin 1,800mmdiameter pipes at No.81 Collins Street.


The large diameter pipes at No.81 Collins Street haveconsiderable, yet under-utilised, capacity. It is thereforerecommended that works be undertaken downstream of the pipeinlets to provide for additional and/or alternative capacity. Thiscould be achieved by installing large open grates on the top of thepipes. This would provide additional opportunities for floodwatersto enter the pipe should the inlet be blocked. The preferredlocation for large grates such as these would be at the downstreamend of the floodway within the property itself.

9.7 CARR CREEK (BRANCH 6)



Recommendations: It is recommended that the following 13 houses be included onCouncil’s Voluntary House Raising Scheme:

– Nos. 11, 13, 15, 17 and 19 Dalton Street;– Nos. 24, 26, 28, 30, and 34– Nos. 38, 40 and 42 Carr Street.



Recommendations: It is recommended that the following 2 houses be included onCouncil’s Voluntary House Reconstruction/RedevelopmentScheme:

– No.25 Carr Street;– No.33 Colgong Crescent.

9.7.3 Maintaining Two Overland Flow Paths between Carr Creek (Branch 6) andTowradgi Creek (Branch 1)



Recommendations: In accordance with Council’s Conduit Blockage Policy within CarrCreek (Branch 6), the culverts at both the Northern Distributor andIllawarra Railway need to be assessed assuming that they wouldbe fully blocked. As a result of this potential blockage, localcatchment flows would be diverted towards the Towradgi Creek(Branch 1) floodplain.

It is important that existing local ground levels not be raised alongthese potential flowpaths within the Northern Distributor andIllawarra Railway corridors. This could cause design flood levelsin the area to also be raised.

9.8 PARKER CREEK (BRANCH 7)



Recommendations: It is recommended that the following 2 houses be included onCouncil’s Voluntary House Raising Scheme:

– No.39 Parker Road;– No.138 Cawley Street.



Recommendations: It is recommended that the following houses be included onCouncil’s Voluntary House Reconstruction/RedevelopmentScheme:

– No.32 Lake Parade;– Nos.32 and 41 Parker Road;– No.136 Cawley Street.




Recommendations: Research undertaken following the August 1998 flood revealed thatthe local road not only acted as overland flowpaths but floodwatersspilt off the road and into lower lying properties at:

– the southern side of Lake Parade, in the vicinity of Carroll Roadand Parker Road.



10. REFERENCES

Bewsher, D. and P. Grech. 2000, ‘Development of Flood Prone Areas’, 40th AnnualConference, NSW Floodplain Management Authorities, Parramatta, NSW. May 2000.

Bewsher Consulting Pty Ltd. 2003. Addendum to Towradgi Creek Flood Study followingAugust 1998 Flood. Final Report. Report prepared for Wollongong City Council.

Department of Land and Water Conservation. 2001. Blockage Issues for ManagementStudy Option Appraisals. Internal Memorandum between then DLWC Sydney/SouthCoast Region (Wollongong) and Wollongong City Council dated 28 September 2001.

Don Fox Planning Pty Ltd. 2003. Towradgi Creek Floodplain Risk Management Study. Report on Planning Issues. Report prepared for Bewsher Consulting Pty Ltd andWollongong City Council.

Emergency Management Australia. 1995. Flood Warning — An Australian Guide.

Forbes Rigby Pty Ltd. August 1995. Review of Flooding Issues – Sandon Point LESCommissioned by Wollongong City Council.

Katherine Region of Writers. 1999. The Katherine’s Comin’ Down. Katherine Region ofWriters. Katherine, Northern Territory.

Lord, D. and M. Kulmar. July 2000 The 1974 Storms Revisited: 25 Years Experiencein Ocean Wave Measurement Along the South-East Australian Coast. Proceedings of27th International Conference on Coastal Engineering (pp559-572). Sydney, Australia.

New South Wales Government. 1986. Floodplain Development Manual.

New South Wales Government. January 2001. Floodplain Management Manual: TheManagement of Flood Liable Land.

New South Wales Treasury. 1997. NSW Government Guidelines for Economic Appraisal.Prepared by Office of Financial Management. Treasury Policy and Guidelines PaperTPP97-2.

New South Wales Treasury. 1999. Economic Appraisal — Principles and ProceduresSimplified. Prepared by Office of Financial Management. Policy and Guidelines PaperTPP99-1.


Public Works Department. 1989. Little Lake Flood Data Preliminary Assessment Study.Internal Report by Supervising Engineer, South Coast. Dated 21 September 1989.

Public Works Department. 1992. Towradgi and Collins Creek Flood Study. Compendiumof Data. Report No. PWD92037.

Snowy Mountains Engineering Corporation. 1998. Towradgi Creek Flood Study. (in draft)Report prepared for Wollongong City Council.

Rawlhouse Publishing Pty Ltd. 1999. Rawlinsons Australian Construction Handbook. Rawlhouse Publishing Pty Ltd, Perth.

Taylor, J.A., M.A. Greenaway and D.I. Smith. 1987. ANUFLOOD — Programmer'sGuide and User's Manual. Centre for Resource and Environmental Studies.

Water Studies Pty Ltd. 1992. User Manual ‘FLDAMAGE’. Water Studies Pty Ltd.

Wollongong City Council. 2002. Conduit Blockage Policy (Section 7.3 of WollongongCouncil Drainage Design Code).

Wollongong City Council. 2003. Towradgi Creek Floodplain Management Committee. Minutes of Meeting Wednesday, 19 February 2003. Council Chambers.

Wyllie, S.J., M.A. Kulmar and P.J. Davidson. c1994. Development of Design OffshoreWave and Ocean Level Conditions for the New South Wales Coastal Zone.


11. GLOSSARYNote that terms shown in bold are described elsewhere in this Glossary.

100 year flood A flood that occurs on average once every 100 years. Also known as a 1%flood. See annual exceedance probability (AEP) and average recurrenceinterval (ARI).



afflux The increase in flood level upstream of a constriction of flood flows. A roadculvert, a pipe or a narrowing of the stream channel could cause theconstriction.

annual exceedanceprobability (AEP)

AEP (measured as a percentage) is a term used to describe flood size. AEPis the long-term probability between floods of a certain magnitude. Forexample, a 1% AEP flood is a flood that occurs on average once every 100years. It is also referred to as the ‘100 year flood’ or 1 in 100 year flood’. Theterms 100 year flood, 20 year flood, 5 year flood etc, have been used in thisstudy. See also average recurrence interval (ARI).

Australian Height Datum(AHD)

A common national plane of level approximately equivalent to the height abovesea level. All flood levels, floor levels and ground levels in this study havebeen provided in metres AHD.

average annual damage(AAD)

Average annual damage is the average flood damage per year that wouldoccur in a nominated development situation over a long period of time.

average recurrenceinterval (ARI)

ARI (measured in years) is a term used to describe flood size. It is a meansof describing how likely a flood is to occur in a given year. For example, a 100year ARI flood is a flood that occurs or is exceeded on average once every 100years. The terms 100 year flood, 20 year flood, 5 year flood etc, have beenused in this study. See also annual exceedance probability (AEP).

catchment The land draining through the main stream, as well as tributary streams.

design flood A theoretical flood likely to occur, on average, every “x” years, eg a 100 yearARI flood is a design flood likely to occur, on average, every 100 years. seeaverage recurrence interval (ARI) and annual exceedance probability(AEP). The height of the design flood is called the ‘design flood level’.

designated flood The size of flood selected for planning purposes. Traditionally only one‘designated flood’ has been adopted for a particular locality. However, morethan one ‘designated flood' can be used for planning, building and developmentcontrols. Unless the designated flood is a probable maximum flood (PMF),floods larger than the designated flood can occur. This term is now referred toas the flood planning level (FPL).

Development ControlPlan (DCP)

A DCP is a plan prepared in accordance with Section 72 of the EnvironmentalPlanning and Assessment Act, 1979 that provides detailed guidelines for theassessment of development applications.


DIPNR Department of Infrastructure, Planning and Natural Resources. In April 2003,the new name for the DLWC became the Department of Infrastructure,Planning and Natural Resources (DIPNR). DIPNR has been used whereverapplicable in this report.

discharge The rate of flow of water measured in terms of volume per unit time, forexample, cubic metres per second (m3/s). Discharge is different from thespeed or velocity of flow, which is a measure of how fast the water is moving.

DLWC Department of Land and Water Conservation. Since May 1995, this was thename for the Department of Water Resources (DWR), the Department ofConservation and Land Management (CALM) and flood sections of the PublicWorks Department (PWD). In April 2003, the new name for the DLWC becamethe Department of Infrastructure, Planning and Natural Resources (DIPNR).DIPNR has been used wherever applicable in this report.

DUAP Department of Urban Affairs and Planning (NSW). This department becamethe Department of Planning (NSW) (PlanningNSW) and became a majorcomponent of the Department of Infrastructure, Planning and NaturalResources (DIPNR) from April 2003.

DWR Department of Water Resources. This department became a major componentof the Department of Land and Water Conservation (DLWC) in May 1995 andthe new Department of Infrastructure, Planning and Natural Resources(DIPNR) in April 2003.

ecologically sustainabledevelopment (ESD)

Using, conserving and enhancing natural resources so that ecologicalprocesses, on which life depends, are maintained, and the total quality of life,now and in the future, can be maintained or increased. A more detaileddefinition is included in the Local Government Act 1993.

effective warning time The time available after receiving advice of an impending flood and before thefloodwaters prevent appropriate flood response actions being undertaken. Theeffective warning time is typically used to move farm equipment, move stock,raise furniture, evacuate people and transport their possessions.

emergency management A range of measures to manage risks to communities and the environment. Inthe flood context it may include measures to prevent, prepare for, respond toand recover from flooding.

EP&A Act Environmental Planning and Assessment Act, 1979.

extreme flood An estimate of the probable maximum flood (PMF), which is the largest floodlikely to occur.

flood A relatively high stream flow that overtops the natural or artificial banks in anypart of a stream, river, estuary, lake or dam, and/or local overland floodingassociated with major drainage before entering a watercourse, and/or coastalinundation resulting from super-elevated sea levels and/or waves overtoppingcoastline defences excluding tsunami.

flood awareness An appreciation of the likely effects of flooding and a knowledge of the relevantflood warning, response and evacuation procedures.

flood hazard The potential for damage to property or risk to persons during a flood. Floodhazard is a key tool used to determine flood severity and is used for assessing thesuitability of future types of land use.


flood level The height of the flood described either as a depth of water above a particularlocation (e.g. 1m above a floor, yard or road) or as a depth of water related toa standard level such as Australian Height Datum (e.g the flood level was 7.8mAHD). Terms also used include flood stage and water level.

flood liable land Land susceptible to flooding up to the probable maximum flood (PMF). Alsocalled flood prone land. Note that the term flood liable land now covers thewhole of the floodplain, not just that part below the flood planning level, asindicated in the superseded Floodplain Development Manual (NSWGovernment, 1986).

flood planning level(FPL)

The combination of flood levels and freeboards selected for planningpurposes, as determined in floodplain risk management studies andincorporated in floodplain risk management plans. Formerly called thedesignated flood or the flood standard.

flood prone land Land susceptible to flooding up to the probable maximum flood (PMF). Alsocalled flood liable land.

flood proofing A combination of measures incorporated in the design, construction andalteration of individual buildings or structures subject to flooding, to reduce oreliminate damages during a flood.

flood stage see flood level.

Flood Study A study that identifies the flood levels for a range of flood sizes.

floodplain The area of land that is subject to inundation by floods up to and including theprobable maximum flood event, that is, flood prone land or flood liable land.

Floodplain RiskManagement Plan

The outcome of a Floodplain Risk Management Study.

Floodplain RiskManagement Study

The current study. These studies are carried out in accordance with theFloodplain Management Manual (NSW Government, 2001) and assess optionsfor minimising the danger to life and property during floods. These measures,referred to as ‘floodplain risk management measures/options’, try to achieve anequitable balance between environmental, social, economic, financial andengineering considerations. The outcome of a Floodplain Risk ManagementStudy is a Floodplain Risk Management Plan.

floodway Those areas of the floodplain where a significant discharge of water occursduring floods. Floodways are often aligned with naturally defined channels. Floodways are areas that, even if only partially blocked, would cause asignificant redistribution of flood flow, or a significant increase in flood levels.

flow see discharge

freeboard A factor of safety expressed as the height above the design flood level.Freeboard provides a factor of safety to compensate for uncertainties in theestimation of flood levels across the floodplain, such and wave action,localised hydraulic behaviour and impacts that are specific event related, suchas levee and embankment settlement, and other effects such as “greenhouse”and climate change.


high flood hazard For a particular size flood, usually at the flood planning level, there would bea possible danger to personal safety, able-bodied adults would have difficultywading to safety, evacuation by trucks would be difficult and there would be apotential for significant structural damage to buildings;.

hydraulics Term given to the study of water flow in waterways; in particular, the evaluationof flow parameters such as water level and velocity.

hydrology Term given to the study of the rainfall and runoff process; in particular, theevaluation of peak discharges, flow volumes and the derivation ofhydrographs (graphs that show how the discharge or stage/flood level at anyparticular location varies with time during a flood).

km kilometres. 1km = 1,000m = 0.62 miles.

km2 square kilometres. 1km2 = 1,000,000m2 = 100ha = 250 acres.

Local Government Area(LGA)

All of the Towradgi Creek catchment is within the Wollongong LocalGovernment Area (LGA).

Local EnvironmentalPlan (LEP)

A Local Environmental Plan is a plan prepared in accordance with theEnvironmental Planning and Assessment Act, 1979, that defines zones,permissible uses within those zones and specifies development standards andother special matters for consideration with regard to the use or developmentof land.

low flood hazard For a particular size flood, usually at the flood planning level, able-bodiedadults would generally have little difficulty wading and trucks could be used toevacuate people and their possessions should it be necessary.

m metres. All units used in this report are metric.

m AHD metres Australian Height Datum (AHD).

m/s metres per second. Unit used to describe the velocity of floodwaters. 10km/h= 2.7m/s.

m2 square metres. 1m2 = 10.8 square feet.

m3/s Cubic metres per second or 'cumecs'. A unit of measurement for creek flowsor discharges. It the rate of flow of water measured in terms of volume per unittime.

merit approach The principles of the merit approach are embodied in the FloodplainManagement Manual (NSW Government, 2001) and weigh up social,economic, ecological and cultural impacts of land use options for different floodprone areas together with flood damage, hazard and behaviour implications,and environmental protection and well being of the State’s rivers andfloodplains.

MIKE-11 The software program used to develop a computer model that analyses thehydraulics of the waterways within a catchment and calculates water levels(flood levels) and flow velocities. Known as a hydraulic model (seeSection 4.2).

mm millimetres. 1m = 1,000mm


overland flow path The path that floodwaters can follow if they leave the confines of the main flowchannel. Overland flow paths can occur through private property or alongroads. Floodwaters travelling along overland flow paths, often referred to as‘overland flows’, may or may not re-enter the main channel from which they left— they may be diverted to another water course.

peak discharge The maximum flow or discharge during a flood.

PlanningNSW Formerly the Department of Urban Affairs and Planning (NSW). Thisdepartment became the Department of Planning (NSW) (PlanningNSW) andbecame a major component of the Department of Infrastructure, Planning andNatural Resources (DIPNR) in April 2003.

present value In relation to flood damage, is the sum of all future flood damages that can beexpected over a fixed period (usually 20 years) expressed as a cost in today’svalue.

probable maximumflood (PMF)

The largest flood likely to ever occur. The PMF defines the extent of floodprone land or flood liable land, that is, the floodplain. The extent, natureand potential consequences of flooding associated with the PMF event areaddressed in this Floodplain Risk Management Study.

RAFTS The software program used to develop a computer model that analyses thehydrology (rainfall–runoff processes) of the catchment and calculateshydrographs and peak discharges. Known as a hydrological model (seeSection 4.1).

reliable access During a flood, reliable access means the ability for people to safely evacuatean area subject to imminent flooding within effective warning time, havingregard to the depth and velocity of floodwaters, the suitability of the evacuationroute, and other relevant factors.

risk Chance of something happening that will have an impact. It is measured interms of consequences and likelihood. In the context of this study, it is thelikelihood of consequences arising from the interaction of floods, communitiesand the environment.

runoff The amount of rainfall that ends up as flow in a stream, also known as rainfallexcess.

SES State Emergency Service of New South Wales.

SMEC Snowy Mountains Engineering Corporation.

stage–damage curve A relationship between different water depths and the predicted flood damageat that depth.

velocity the term used to described the speed of floodwaters, usually in m/s (metres persecond). 10km/h = 2.7m/s.

water level see flood level.

water surface profile A graph showing the height of the flood (flood stage, water level or floodlevel) at any given location along a watercourse at a particular time.

WCC Wollongong City Council. This Floodplain Risk Management Study and Planhas been undertaken for Wollongong City Council.

TOWRADGI CREEK, WOLLONGONG BEWSHER CONSULTING PTY LTDFLOODPLAIN RISK MANAGEMENT STUDY June 2003 J829final-Vol1.doc

APPENDIX A

REPORT ON PLANNING ISSUES(INCLUDING PROPOSED

DEVELOPMENT CONTROL PLAN)

BY DON FOX PLANNING PTY LTD

TOWRADGI CREEK FLOODPLAIN RISK MANAGEMENT STUDY Don Fox PlanningREPORT ON PLANNING ISSUES June 2003, 4147-AppA-Planning Document.doc

Wollongong City Council

TOWRADGI CREEKFLOODPLAIN RISK MANAGEMENT STUDY

APPENDIX A

REPORT ON PLANNING ISSUES

MARCH 2002(Final Amendments June 2003)

Prepared by:

Don Fox PlanningP O Box 230 Pennant Hills NSW 1715

Telephone (02) 9980 6933Facsimile (02) 9980 6217

Email [email protected]: www.donfoxplanning.com.au

ACN 002 263 998


TABLE OF CONTENTS___________________________________________________________________

1.0 INTRODUCTION .........................................................................................................11.1 Background and Study Scope .............................................................................................. 11.2 Study Area ............................................................................................................................ 1

2.0 THE PLANNING CONTEXT .......................................................................................32.1 Characteristics of the Study Area ........................................................................................ 3

2.1.1 Topography .................................................................................................................. 32.1.2 Existing Vegetation....................................................................................................... 42.1.3 Existing Land Use ....................................................................................................... 52.1.4 Heritage ....................................................................................................................... 7

2.2 Population and Development Trends................................................................................... 82.2.1 Changing Population and Characteristics and Projections ......................................... 82.2.2 Recent Development Activity and Strategic Planning Directions.............................. 10

2.3 Existing Planning and Development Controls.................................................................... 112.3.1 Introduction................................................................................................................ 112.3.2 State Environmental Planning Policies ..................................................................... 112.3.3 Regional Environmental Plans (REP’s)..................................................................... 122.3.4 Advisory Circulars ..................................................................................................... 132.3.5 Local Environmental Plans (LEP’s)........................................................................... 142.3.6 Development Control Plans (DCP’s)......................................................................... 152.3.8 Council Policies ......................................................................................................... 192.3.9 Development Application Assessment...................................................................... 212.3.10 Section 149 Certificates ............................................................................................. 222.3.11 Section 94 Contributions Plans ................................................................................. 23

3.0 PROPOSED APPROACH TO FLOODPLAIN PLANNING .......................................243.1 General Philosophy............................................................................................................ 24

3.1.1 Traditional Approach to Floodplain Planning ............................................................ 243.1.2 Objectives of Floodplain Planning............................................................................. 253.1.3 Flood Planning Levels (FPL’s) .................................................................................. 273.1.4 The Planning Matrix Approach.................................................................................. 27

3.2 Preparing a Planning Matrix................................................................................................ 293.2.1 Step 1 — Categorising the Floodplain ....................................................................... 293.2.2 Step 2 — Prioritising Land Uses in the Floodplain..................................................... 303.2.3 Step 3 – Controls to Modify Building Form and Community Response..................... 31

3.3 Implementation of the Planning Matrix Approach ............................................................... 324.0 REVIEW OF PLANNING OPTIONS ..........................................................................34

4.1 General ............................................................................................................................... 344.2 State Environmental Planning Policies (SEPP’s) .............................................................. 344.3 Regional Environmental Plans (REP’s) ............................................................................. 344.4 Local Environmental Plans (LEP’s).................................................................................... 34

4.4.1 Objectives................................................................................................................... 354.4.2 Definitions................................................................................................................... 354.4.3 Zoning Changes ................................................................................................................. 37

4.5 Development Control Plans (DCP’s).................................................................................. 384.5.1 Floor Area................................................................................................................... 384.5.2 Flood Compatible Building Components.................................................................... 384.5.3 Structural Soundness ................................................................................................. 394.5.4 External Flood Effects ................................................................................................ 394.5.5 Evacuation/Access ..................................................................................................... 394.5.6 Flood Awareness........................................................................................................ 394.5.7 Management and Design ........................................................................................... 39

4.6 Policies................................................................................................................................ 404.7 Section 94 Contributions Plans.......................................................................................... 404.8 Section 149 Certificates ..................................................................................................... 40

5.0 RECOMMENDED PLANNING MEASURES .............................................................42


LIST OF ILLUSTRATIONS___________________________________________________________________

1 Regional Location

2 Study Area

3 Typical View of Flood Hazard Currently Held by the Community

4 Current Floodplain Planning

5 Distributing Land Uses Under the Planning Matrix Approach

6 The Planning Matrix Approach to Floodplain Planning

LIST OF APPENDICES___________________________________________________________________

A1 Census Data

A2 Standard Inclusions for LEP's

A3 Recommended Development Control Plan


1

1.0 INTRODUCTION

1.1 Background and Study Scope

Don Fox Planning Pty Ltd has been engaged by Bewsher Consulting Pty Ltd toform part of a consultant team to prepare a Floodplain Risk Management Study(FRMS). The FRMS is to be prepared for the Towradgi Creek Catchmentfloodplain within the Wollongong Local Government Area (LGA).

The purpose of this component of the study is to undertake the following tasks:

• Describe the characteristics of the study area with regard to land use,building form, population characteristics, vegetation and appearance withparticular regard to implications for the management of the flood risks.

• Discuss the role of planning in the preparation of the FRMS and theimplications and the choice of an appropriate flood planning level (FPL)standard or standards.

• Review the existing framework of planning and development controls that arerelevant to the formulation of planning instruments and the assessment ofdevelopment applications within the study area.

• Discuss the proposed approach and philosophy to floodplain planning andhow it may be implemented within the study area, particularly having regardto the planning responsibility of Council and planning controls emanatingfrom this FRMS.

• Discuss options and review strategic planning issues to guide the formulationof appropriate planning controls ultimately for inclusion within a FloodplainRisk Management Plan (FRMP).

• To make specific planning recommendations in regard to the above,including an outline of suggested planning controls.

It is recognised that the flood hazard is one component for consideration in anytown planning exercise. It is not considered appropriate to recommend a varietyof planning controls for inclusion within a FRMP, which responds to theplanning hazard identified by hydraulic studies in isolation to this strategicplanning context. Accordingly, this component of the FRMS considers thestrategic planning context for the study area as a prelude to formulatingplanning recommendations for the FRMP.

1.2 Study Area

The study area comprises the Towradgi Creek catchment as depicted uponIllustrations 1 and 2.


2

The study area lies approximately 5.5 kilometres to the north of Wollongongand drains a catchment area of about 7.2 square kilometres. The catchmentrises from Corrimal Beach, to its upper most reaches at the Illawarraescarpment in the west. The Towradgi Creek catchment contains 6 maintributaries, which pass through the suburbs of Tarrawanna, Towradgi, Corrimaland Fernhill. As outlined by the study brief, the study area includes the whole ofthe Towradgi Catchment inclusive of the main arm of Towradgi Creek and its 6tributaries as defined by the brief.


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2.0 THE PLANNING CONTEXT

2.1 Characteristics of the Study Area

2.1.1 Topography

The western extent of the study area, the Illawarra escarpment, comprises verysteep slopes with a few defined watercourses.

That section of study area between the foothills of the escarpment to thePrinces Highway is comprised of extremely irregular undulating topography.This area comprises a combination of short steep slopes, moderate slopes andsome flat areas (see Photograph 1).

Photograph 1: View of Branch No. 5 from Coxs Avenue

That part of the study area between the Princes Highway and the Pacific Oceanis comprised of generally gentle slopes and flat terrain. Within this area thetributaries converge with Towradgi Creek and the course of the creek becomesmore defined and in parts is contained within steep banks (see Photograph 2).

Photograph 2: View of Towradgi Creek South of the Railway Line


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2.1.2 Existing Vegetation

The top end (western extent) of the study area comprises dense escarpmentvegetation. The remainder of the study area, from the foothills of theescarpment to the Pacific Ocean has been generally urbanised. This urbanarea, consistent with other areas is devoid of the majority of the originalvegetation and now contains a vast array of domesticated exotic species.

The watercourses are generally devoid of natural vegetation, although somerehabilitation has occurred within public open space areas, particularly withinthe lower reaches of Towradgi Creek near to its outlet with the Pacific Ocean.

Some sections of the watercourses in the study area are substantially weedinfested. Weeds species along the watercourses include larger trees such aswillows, which have proven to be unstable in flood times and a potential sourceof debris and a consequent potential obstruction to the flow of flood waters (seefor example the section of Branch No. 5 near the corner of Meadow Street andFoothills Road – refer to Photographs 3 and 4).

Photograph 3: Branch No. 4 viewed from Foothills Road

Photograph 4: Branch No. 5 viewed from Collins Street


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A Vegetation Management Plan for the watercourses within the study area, andthe interface which fringes between the urban area and the foothills of theescarpment, may be beneficial in contributing to restoring the ecological valueof the watercourses as well as minimising erosion and debris whichexacerbates the flooding problem.

2.1.3 Existing Land Use

The western extent of the study area, being the escarpment lands is generallydevoid of development. While the study area comprises primarily residentialdevelopment, there are a variety of other uses, summarised as follows:

a) Development nearest to the foothills of the escarpment comprises mainlydwelling houses mostly constructed within the last 20 to 30 years, many ofwhich are of 2 to 3 storeys and/or elevated structures due to theundulating topography. The remainder of the study area comprisesprimarily one storey older dwellings of various standards, many of whichhave undergone renovations and/or alterations and extensions.

b) There is a scattering of medium density development within the studyarea, comprising mainly villas and/or townhouses (see Photograph 5).Corner stores are located throughout the study area, and a number ofsmall neighbourhood shopping complexes, such as that near the corner ofMeadow Street and Caldwell Avenue (refer to Photograph 2). This latestshopping centre is located adjacent to the upper reaches of TowradgiCreek.

Photograph 5: A recent townhouse development in James Road, Backing onto Branch No. 4

c) The main centre within the study area is the Corrimal Shopping locatedbetween the Princes Highway, Underwood Street, Tarrawanna Road andRussell Street. Branch No. 5 traverses through the centre of this shoppingcentre (refer to Photograph 6) and flooding from this watercoursesignificantly affects the car park area and a number of shops.


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Photograph 6: Car parking at rear of shops along Railway Street, backing onto Branch No. 5

d) There are other non-residential land uses including the Corrimal BowlingClub on Francis Street and a timber yard, car wrecking yard and wroughtiron manufacturers within Bellambi and Meadow Streets. These uses areaffected by Branch 4 and Branch 3 respectively (refer to Photograph 7).Activities such as the timber yard give rise to issues such as the externalstorage of materials, which may be hazardous during periods of flood.The car wrecking yard has similar issues, but with a greater emphasisupon water quality impacts particularly as vehicles are stored on unsealedsurfaces.

Photograph 7: Timber Yard in Bellambi Street – affected by Branch No. 3

e) A large portion of the study area between the Princes Highway and therailway line is occupied by a large industrial use. This use is adjacent tothe confluence of Branches No. 4 and 5 Towradgi Creek.

f) There are occasional vacant properties within the study area (eg. 22 to 28Francis Street, cnr Collins Street) the majority of which appear to beconstrained from development due to issues such as flooding.

g) There are a number of pockets of public open space land within the studyarea, the majority of which appear to be located along the major


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watercourses. Notwithstanding, these open space lands do not form acontiguous open space system and indeed the watercourses oftentraverse land held in private ownership with no easement to formalise theirdrainage function.

The last point gives rise to issues associated with possible illegal structures andactivities occurring along the watercourses in the study area. Additionally, theremay be minor ancillary structures such as fences and outbuildings in suchlocations, which may or may not have approval, but are constructed in amanner which could constrain the flow of flood waters or create a hazard duringperiods of flood. Examples include fences constructed as de facto levees, theconstruction of bunds to deflect the natural flow of flood water, fence typeswhich potentially disintegrate and become active debris during periods of flood,and other similar structures such as domestic pedestrian bridges overwatercourses, cubby houses, outbuildings, etc.

Such structures would not normally be a concern outside of the floodplain, butcreate problems by diverting or increasing the depth of floodwaters, orgenerating sources of debris, which become hazardous during periods of flood.Measures to police and rectify inappropriate structures, and prevent theiroccurrence in the future, would represent an appropriate planning response inthe FRMP.

2.1.4 Heritage

The issue of heritage is of significance in regard to the forming andunderstanding of the social and cultural context of the floodplain and to ensurethat any flood mitigation measures do not impact upon the heritage of the studyarea. The Wollongong LEP 1990 (as amended) identify a number of heritageitems within the study area, inclusive of the following.

• The “Escarpment Area” being the escarpment lands in the western extent ofthe study area.

• Part of Corrimal Public School, Wilga Street (Item No. 6205).

• The Catholic Cemetery, Princes Highway, Corrimal (Item No. 6360).

• House and Garden, Underwood, The Avenue and Francis Street (Item No.6208).

• The War Memorial (Railway Street) (Item No. 6210).

• House “The Ridge” Corrimal Street, Tarrawanna (Item No. 5986).

• Corrimal Hotel, 264 – 268 Princes Highway (Item No. 6464).

• Towradgi Creek Corridor, Tarrawanna and Corrimal (Item No. 6207).

• Ziem’s shops and outbuildings, 330 Princes Highway (Item No. 6463).


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The inclusion of the Towradgi Creek Corridor is an interesting reflection on thehistorical significance placed on this watercourse, for the local area. It is notedthat the heritage corridor includes more than just the permanent watercourseand extends out in some cases to include adjacent residential and other urbanproperties as well as open space lands and public roads. That is, this heritageitem reflects more closely the actual floodplain as opposed to just the creekcorridor.

2.2 Population and Development Trends

2.2.1 Changing Population and Characteristics and Projections

A summary of Census data for the Towradgi Catchment study area is providedat Appendix A1. Due to changes in Census collector district boundaries, thecomparison of data between 1986 and 1991 is excellent, but between the 1991and 1996 Censuses, the comparison is poor. Accordingly, the table provided atAppendix A1 should be regarded as an indicator of general trends, as opposedto an expression of absolute numbers. With this qualification, the following is adiscussion of salient findings from an analysis of this data.

The population of the Towradgi study area decreased by nearly 300 personsbetween the 1986 and 1991 Censuses, but increased marginally between the1991 and 1996 Censuses. This corresponded to close to nil dwelling growth,but declining dwelling occupancy ratios between the 1986 and 1991 Censuses.Conversely, between the 1991 and 1996 Censuses, dwelling growth wassubstantial (in the order of over 200 to 300 new dwellings) which provided fornett population growth, regardless of a continuance in the decline of thedwelling occupancy ratio.

Generally, it is observed that dwelling growth in the study area has acceleratedduring the 1990’s, primarily in the form of multi-unit housing. At the same time,household sizes are declining, with dwelling occupancy ratios falling from 2.75persons per dwelling in 1986 to 2.50 persons per dwelling in 1996. This isconsistent with the trends throughout the Wollongong LGA, NSW and Australiagenerally.

Total population growth within the study area is below that occurring across theWollongong LGA overall. The compound rate of population growth for theWollongong LGA between 1986 and 1991 was 0.7% and between 1991 and1996, was 0.4%, with the corresponding compound rate of growth in the studyarea being –0.6% and 0.2% for the same periods, respectively. This is reflectiveof the study area being predominantly an established older urban area, withgrowth potential being limited to mainly redevelopment with multi-unit housing.Such redevelopment has been occurring within the 1990’s, as evidenced by theCensus data described above.

While median household incomes in the study area rose between 1986 and1996 from $20,000 to $26,500, effective indexed household incomes (based onCPI standardised figures) declined within the same period from $31,700 to$26,500. This trend was similar for median individual incomes and medianfamily incomes for the study area. The median household income for the study


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area is below the average for NSW overall, as at the 1996 Census ($34,000 formedian household incomes in NSW).

Consistent with trends throughout NSW and Australia, the population of theTowradgi study area is also ageing. The population of the study area is slightly“older” than NSW overall, with 24%, 25% and 26% of the study area populationbeing aged 55 or greater at the 1986, 1991 and 1996 Censuses. In comparison,the NSW population aged 55 and over represented 21%, 21% and 21% of thetotal NSW population, within the same periods respectively. The population ofthe study area is also “older” than the Wollongong LGA overall, which had 21%,22% and 22% of its total population aged 55 or greater, respectively, within thesame Census periods.

Dwellings in the Towradgi study area are predominantly owned or beingpurchased (59%) with 35% being rented (the remainder being “other” or notstated) as at the 1996 Census. This is similar to the situation for NSW overall(59% being owned or being purchased and 35% being rented), while marginallydifferent to the Wollongong LGA (64% being owned or being purchased and30% being rented). It must be noted, that accurate comparison of dwellingsowned/being purchased or rented within NSW overall is difficult, due todifferences in undeclared responses. However, median mortgage and rentalrates are relatively higher in the Towradgi study area ($933 and $117respectively at the 1996 Census) in comparison to NSW overall ($906 and $143respectively at the 1996 Census) and the Wollongong LGA ($908 and $122respectively at the 1996 Census).

The relevance of the above statistics, apart from providing an understanding ofthe nature of the population subject to potential flood risk, can be summarisedas follows:

• Stabilised or declining population growth and relatively low dwelling growthrates reflects the situation where the study area is relatively established withminimal expectations for further growth. Therefore, the need andexpectation of further development in the floodplain may be outweighed bythe risk to property and persons. Therefore, higher standards andrestrictions on development in that part of the study area which is floodaffected, is unlikely to result in any significant social impact to thecommunity as a whole.

• Higher rents and mortgages coupled with low and declining householdincomes relative to NSW and the Wollongong LGA overall, is an indicatorthat the study area population would be expected to be less likely to be ableto financially recover from flood damages and losses.

• The older and ageing population of the Towradgi study area would likely beless mobile and physically capable of coping with the trauma of floods.Further, households with the main income of earner in the older age cohortare likely to be in a life cycle stage where the ability to financially recoverfrom flood damages and losses would be more difficult.


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• Dwelling growth in the study area has occurred mainly due toredevelopment in the form of multi-unit housing. Analysis undertakenelsewhere in this study has revealed that the form of multi-unit housing ismostly townhouses and villas which is a form of residential developmentwhich can result in increased flood damages due to the increased extent offloor area near to ground level, as opposed to other forms of housing suchas lower density detached dwellings, or residential flat buildings with areduced footprint.

In regard to the latter issue identified above, appropriate controls on residentialdevelopment would need to be imposed to ensure that any future developmentpermitted by Council’s planning controls, does not give rise to unreasonableincreases in flood damages. Such controls are outlined and discussed laterwithin this report.

2.2.2 Recent Development Activity and Strategic PlanningDirections

The majority of the study area is substantially developed and minimal potentialexists for further new development. Having regard to other planningconsiderations, there would also appear to be variable potential forredevelopment. Redevelopment and infill development is occurring in adispersed fashion dependent of land availability, rather than being concentratedin any particular section of the study area.

Some forms of medium density residential development are permissible withinthe residential zones of the study area. Such development is occurring mainlyin the form of townhouses on diminishing parcels of vacant land oramalgamated parcels of older housing properties. Some potential exists toencourage redevelopment adjacent to watercourses in a manner whichimproves the flood compatibility of housing (see Bewsher & Grech, 2000). Assuch development is permissible generally within the residential zones of thestudy area, an important outcome of this study will be to formulate planningcontrols which facilitate development which encourages and achieves areduction in potential damages.

As part of this redevelopment, there is the potential for developers to seekpermission to fill their allotments, mainly to reduce the height differencebetween the natural ground level and the minimum floor level required by flood-related building controls. An area where future requests for filling are likely is inthe Parker Creek (Branch 7) floodplain. In locations where redevelopment(including filling) would reduce the flood risk potential and/or the risk to life,such redevelopment may even be encouraged, provided the development isconsistent with the 2001 Floodplain Management Manual or other planningconsiderations.

The cumulative impacts of filling in the floodplain near to a level of the 100 yearflood, in terms of flood storage, have been assessed as part of this study. Ithas been found that the impacts on flood storage from filling in the floodplain upto a level close to the 100 year flood level would be acceptable, and would notcause significant increases in flood levels elsewhere in the catchment.


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It has therefore been considered to be appropriate to allow filling in thefloodplain up to a maximum height of 300mm below the 100 year flood level.Minimal additional fill above this level to provide for, for example, drivewayaccess to garages or to fill under floor areas, was also examined in the terms ofcumulative impacts, and was considered to be acceptable.

The impacts of filling on flood storage therefore would not need to be assessedfor each individual Development Application (DA). However, other potentialhydraulic impacts such as loss of conveyance (that is, the obstruction of flowingwater), changes in local drainage, changes to overland flow paths, etc., wouldstill need to be assessed before filling could be approved on an individual lot.Other non-flooding issues, such as amenity, overshadowing and environmentalconsiderations would also need to be addressed in the assessment.

Redevelopment of parts of the main Corrimal Shopping Centre is also possible.Significant potential for flood damages exists within the centre at present.Consequently, issues for any future development would include the requirementof an appropriate minimum floor level — one that would balance accessibilitywith reduced flood damages and the provision of a suitable flow path forfloodwaters. The planning controls that are recommended by this study wouldneed to address these issues.

2.3 Existing Planning and Development Controls

2.3.1 Introduction

This section of the report identifies and examines various forms of planninginstruments and associated controls which apply to the study area and mayhave potential for use for the purposes of implementing planning controls toguide future development within the study area. Not all of these planninginstruments will be applicable, but are reviewed for the purposes ofcompleteness and to provide a general overview of planning controls andstrategic planning direction for the area.

2.3.2 State Environmental Planning Policies

A State Environmental Planning Policy (SEPP) is a planning documentprepared in accordance with the Environmental Planning & Assessment Act(EPA Act) by the Department or Urban Affairs & Planning and eventuallyapproved by the Minister, which deals with matters of significance forenvironmental planning for the State. Examples of SEPP’s that have beenprepared include SEPP No. 19 - Bushland in Urban Areas, and SEPP No. 35 -Maintenance Dredging of Tidal Waterways. No State Environmental PlanningPolicy has been prepared dealing specifically with the issue of flooding.

State Environmental Planning Policy No. 5 – Housing For Older Persons orPersons with a Disability (SEPP 5) applies to urban land or land adjoining urbanland where dwellings, hospitals and similar uses are permissible. SEPP 5 wouldapply to the majority of the study area, and would effectively override Council’splanning controls to permit residential development for older and disabled


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persons to a scale permitted by SEPP 5. Notwithstanding, Clause 4(2)(a) of thisPolicy restricts its application to land identified as floodways or high floodhazard in another environment planning instrument such as a REP or LEP (asdescribed below).

2.3.3 Regional Environmental Plans (REP’s)

A Regional Environmental Plan (REP) is prepared in accordance with EPA Actby the planningNSW and eventually approved by the Minister. An REPprovides objectives and controls for environmental planning for a region, or partof a region. The extent of a region will vary depending upon the issue to beaddressed but normally refers to more than one LGA. Illawarra RegionalEnvironmental Plan No. 1 is one such REP, and this has the followingimplications in regard to the FRMS:

(a) Clause 28 of the REP requires that any draft LEP proposed to controldevelopment on rural land which has a history of flooding, requiresCouncil to obtain sufficient information to introduce appropriate controls tominimise the affect of flooding on any potential development. This FRMS,prepared in accordance with State Government policy, would provide anappropriate basis for addressing the provisions of Clause 28 in the studyarea, if ever required.

(b) Clause 65 of the REP stipulates that a draft LEP shall not rezone landfrom rural to urban unless Council has consulted with the DIPNR,prepared a plan of management and is satisfied that the potential for floodlosses is "contained". Again, the ultimate outcome of this FRMS is toproduce an FRMP for the floodplain of the Towradgi Catchment, which isprepared in consultation with the DIPNR and effectively provides amanagement plan to minimise flood damages and risk to life. The FRMPwill, therefore, be an important consideration for any future urbanrezonings in the study area. Compliance with the ultimate FRMP will alsobe important for the purposes of maintaining Council's indemnity fromliability pursuant to Section 733 of the Local Government Act, 1993.

(c) Clause 66 of the REP provides the following provisions in regard to themanagement of land subject to flooding:

"66.(1) A draft Local Environmental Plan to controldevelopment on land in existing urban areas which has ahistory of flooding shall be prepared only when theconsent authority has identified the flood behaviour onthat land and associated flood risk.

66.(2) A plan of management for the land referred insubclause (1) shall indicate appropriate controls ordevelopment standards relating to floor height, buildingmaterials, access, infill, land clearing and the like toensure the effects of any flooding on the developmentshall be minimal."


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As above, it is considered that a FRMP prepared in accordance with StateGovernment flood policy and the Floodplain Development Manual (FPDM)would satisfy the provisions of Clause 66 in regard to the requirement for aplan of management. It is important to note that such a plan ofmanagement is a necessary prerequisite to any LEP on land covered bythe REP, inclusive of the study area, which has the effect of controllingdevelopment in existing urban areas and has a "history" of flooding.

It is important to note that the REP does not define terms such as "flood liableland", "land subject of flooding", "plan of management", etc. Consistent with thetraditional flood planning approach, Council has adopted a designated flood (orflood planning level - FPL) to be the 100 year average recurrence interval (ARI)which seeks to regulate development with only a defined section of thefloodplain. Floods greater than the 100 year ARI can occur, with the ultimateupper limit being the probable maximum flood (PMF). A more flexible approachto dealing with the issue of flooding across the full range of flood extents isoutlined and discussed at Section 3.0 of this report.

2.3.4 Advisory Circulars

planningNSW is responsible for providing advice to local councils to ensure thatbest practice is maintained in the planning process. A Planning andEnvironment Commission (PEC) Circular was issued in 1977 advocatingprescriptive floodplain planning controls and the adoption of the 100 year ARIflood standard. Subsequently, a Departmental Circular (No. 122) was issued bythe former Department of Planning (DOP) and more recently as Circular No. C9to assist Councils to relate the current flood policy of the State Government andthe earlier Floodplain Development Manual (FPDM) (now superseded by the‘Floodplain Management Manual’), to the requirements of the EPA Act and theDepartment’s general approach to floodplain planning.

The current State Flood Policy (1984) disbanded the 100 year ARI floodstandard and requires local Councils to implement floodplain managementbased on a merits based approach. The Circular states that in accordance withthe FPDM, Councils should prepare single comprehensive local environmentalplans to implement their Floodplain Risk Management Plans, and so avoid anad hoc, piecemeal approach to planning within floodplains.

In recognition that the preparation of such LEP’s may take some time, Councilswere advised that in the interim, adequate supporting data for decision makingshould be obtained inclusive of:

• any relevant Floodplain Risk Management Plan or interim policy;

• details of flooding in the area;

• social and economic impact of flooding;

• environmental impacts of development in the floodplain (eg. on water quality,flood behaviour, etc);


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• the availability of alternative flood free sites and reasonable alternative usesfor the subject site;

• cumulative adverse impacts;

• matters of state and regional significance (eg. the impact of development ona floodplain beyond local government boundaries); and

• increased risk of flood damage to regional infrastructure, reduction in floodstorage capacity, etc.

2.3.5 Local Environmental Plans (LEP’s)

A Local Environmental Plan (LEP) is a plan prepared in accordance with theEPA Act which defines zones, permissible uses within those zones and specificdevelopment standards and other special matters for consideration with regardto the use or development of land. LEP’s are normally, and in this case, specificto individual LGA's and the relevant LEP is outlined and discussed below.

The study area is affected by the provisions of The City of Wollongong LocalEnvironmental Plan 1990 (WLEP). This LEP has no specific references toflooding. The objectives of the plan do not include any references to minimisingflood risk, no definitions are provided which clarify terms associated withfloodplain management, and no provisions are provided which specificallycontrol development for the purposes of minimising damages and risk to lifeassociated with flooding. An outcome of the FRMP could appropriately be theintroduction of additional provisions within WLEP to clarify terms used, providean objective which relates to floodplain management and outline specificmatters for consideration when dealing with applications on flood affected land.

Notwithstanding the above, Clause 19 of WLEP indirectly provides a potentialmechanism to minimise the effects of flooding. This clause provides the abilityfor Council to fix a foreshore building line from creeks, by way of a resolution.Due to the nature of flooding within the study area, this clause could beemployed as an effective mechanism to restrict development within the morehazardous flood affected zone bordering the numerous creeks traversing thestudy area.

Part 3(a) of the Foreshore and Rivers Improvement Act requires that theapproval of the DIPNR be obtained by way of the granting of a permit, for anyworks or excavation within 40 metres of the bank of a watercourse. Where suchapproval is required, development proposals are deemed to be “integrateddevelopment” for the purposes of the Environmental Planning and AssessmentAct, 1979. While Council’s planning controls may permit substantialdevelopment within 40 metres of a watercourse, the DIPNR may in many casesrefuse to grant a Section 3A Permit at variable setbacks from the watercoursedue to environmental and hydraulic considerations.


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Discussions are presently proceeding between the DIPNR and Council in orderto establish appropriate guidelines, to provide some certainty to developers,and a systematic basis for assessing applications adjacent to watercourses,which satisfies appropriate environmental and hydraulic considerations. Thesetback required by the DIPNR with regard to the issuing of Section 3APermits, may in some cases be more or less than setbacks required havingregard to flooding considerations. Nonetheless, in order to provide anappropriate and coordinated basis for the assessment of developmentproposals adjacent to watercourses, a foreshore building line could be fixedwhich identifies the maximum setbacks required by all criteria.

There are a number of different zones within the subject floodplain, none ofwhich are specific flood-related zones. These zones are:

• 2(a) Residential Low Density;• 2(b) Residential Medium Density;• 3(a) General Business;• 3(b) Neighbourhood Business;• 4(a) Industrial Light;• 5(b) Special Uses - Railways;• 6(a) Public Recreation;• 6(b) Private Recreation;• 7(a) Environmental Protection – Special;• 7(b) Environmental Protection – Conservation;• 7(c) Environmental Protection – Residential;• 8(b) State Recreation Areas;• 9(b) Main Roads;• 9(c) Local Roads.

The majority of the urban section of the study area is zoned 2(a) ResidentialLow Density, while the large proportion of the study area, being the non-urbanescarpment, is mostly zoned 7(a) Environmental Protection – Special.

2.3.6 Development Control Plans (DCP’s)

A Development Control Plan (DCP) is a plan prepared in accordance withSection 72 of the Environmental Planning & Assessment Act which providesdetailed guidelines for the assessment of development applications. There area number of relevant DCP's with references to the issue of flooding. Thefollowing are relevant to this study.

DCP 9 - Part 1 Residential Standards

• Conventional dwellings are required to have a maximum height of twostoreys (or 7 metres to the topmost ceiling) while residential flats can have aheight of between two storeys (or 7 metres to allow garages under dwellingson steep land) up to four storeys (including parking above ground level)depending upon the zoning of the land. The restrictions on height areimportant when considering the appropriateness of elevating structures as ameans of minimising the impact of flooding.


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• The issue of drainage generally is dealt with as follows (Page 13):

"Surface and roof water must be disposed of to the satisfaction ofCouncil and so designed that the rate of discharge off the siteafter the development has been completed does not exceed thatcurrently discharging from the site. If drainage of the site needsto be across private property, proof of the owners consent mustbe furnished.

Natural watercourses may be modified only with prior consentfollowing a detailed hydrological study showing that there will beno adverse affect on any other properties."

The modification of watercourses and the building on previous watercoursepaths was a major issue of debate in the assessment of the effects of the1998 floods (refer to Lustig & Irish, 1999).

• The provisions for subdivision include the following requirements for thedesign of roads (Page 17):

"Full crossfalls are appropriate in streets up to 5 metres in width.In all cases it must be demonstrated that downhill properties areprotected from overflow drainage and that footpaths can beprovided on through roads."

• Subdivision controls also include standard requirements for drainage, suchas minimum width for easements (see Page 17).

• Further within the controls relating to subdivision, under the sub-heading"Open Space" (Page 18) the following is stated:

"In all subdivisions on the foreshores of the ocean, lakes andinlets and major watercourses, a strip of at least 30 metres wide,or adequate width to carry maximum flood flow, is expected to bededicated to Public Reserve unless there are specialcircumstances.

Major watercourses within new development should be dedicatedto Council."

The situation in the study area is that the majority of the land has alreadybeen subdivided. Indeed, one of the issues within the study area is thatearlier subdivisions have not provided for the identification and dedication ofboth major and minor watercourses as public open space or easements.This has resulted in some cases, in unrealistic expectations for thedevelopment of land and difficulties in implementing drainage improvementworks.

• The issue of drainage is again dealt with under the headings "SensitiveSites", "Environmental Zones" and "Drainage" (Page 22). However, the


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provisions in this section are related primarily to water quality and notflooding.

• Under the heading "Sensitive Sites", "Land Constraints", "Flood Control"(Page 23), specific statements are made in regard to Council's policy inregard to floodplain management, being as follows:

"Council has adopted the State Government's policy regardingdevelopment of flood affected land as set out in their "FloodplainDevelopment Manual" - Public Works Department. WhereCouncil records show, or there is reasons to suspect, that theland is susceptible to flood, then a detailed flood study preparedby a recognised consultant must establish the impact of thedevelopment on flooding."

This section then goes on to describe the six types of floodplain categoriesreferred to within the FPDM, and confirms that Council's current designatedflood standard (FPL) is the 100 year ARI. Specific implications fordevelopment include the following:

• A detailed flood study may be required to determine the extent of floodaffectation;

• The area of land classed as "floodway: or "high hazard flood fringe" (asper the FPDM categories) should be excluded from gross site areawhen calculating FSR's;

• Habitable floor areas should be 0.5 metres above the designated flood;

• Garages should be at or above the designated flood;

• The level of parking areas should be determined based on theappropriate standard provided by the FPDM for the product of velocityand flood depth.

The FPDM was prepared by the Government to assist Council inimplementing the State Government Flood Policy, being a merits basedapproach. The policy basically requires that Council prepares their ownFRMP's for individual floodplains having regard to the economic, socialand environmental circumstances of each area. This provides a process ofbalancing the risks associated with flooding against the economic andsocial value of using the floodplain, to provide a management plan whichmeets the level of risk and expectations of the community. Accordingly, allthese measures contained within Council's DCP will need to be reviewedas part of the FRMS and FRMP process.

• New fences are limited to open fences.

Wollongong DCP No. 6 – Commercial and Industrial Developments

Page 7 of this document outlines the information that Council will require to besubmitted with a development application, which includes a flood study of the


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land could potentially flood. Page 50 of this document, under the headingsLand Constraints and Flood, outlined the same controls as those containedwithin the Residential DCP under the same heading.

Wollongong Draft DCP No. 49 - Draft Multi Dwelling ResidentialDevelopment

This document is a draft DCP to replace existing DCP No. 49. The Draft DCP(dated August 2000) is presently on public exhibition and is not expected to bereported back to Council until early in 2001. The thrust of the changes with theDraft DCP 49 is to provide better urban design outcomes, and accordingly floodrelated issues have not in the main been redressed as would be expected.

The parts of the Draft DCP which have any major relevance to the issue offlooding are outlined as follows:

• A site analysis is to be required for development which requires theidentification of flood affected areas, overland flow paths and drainage(Page 25).

• Under the heading of Natural Land Constraints, the following provision isprovided:

“4.1.2.b Flooding

Where Council’s records show or there are other reasons to suspect thata site is susceptible to flood, then the development must comply withCouncil’s Flood Policy. Consideration must be made of drainageeasement and flood-ways should not be built over but utilise as positiveopen space opportunities”.

This is an important principle which is obviously lacking from olderdevelopments in the area and can be reinforced through the provisions of anappropriate flood policy. As recommended later, this flood policy can take theform of a DCP to provide appropriate status for its consideration in theassessment of development applications.

In Section 4.3.2.d, which provide provisions regarding fences, the Draft DCPstates that fences are not encouraged within floodways.

In regard to stormwater management (Clause 4.9.2.a) the Draft DCP requirescompliance with Council’s Drainage Design and On-Site Detention Policy.Applicants are encouraged to minimise stormwater impacts through adoptingsystems such as OSD, rain water storage tanks and infiltration trenches.

Wollongong DCP No. 99/1 (Complying Development) and DCP No. 99/2(Exempt Development)

All minor development which is ancillary or incidental to dwellings (includingcarports, garages, sheds and the like) has been excluded from being complyingdevelopment, where located in an area marked “flood assessment” on a seriesof maps held by Council or located within the area affected by a 100 year ARI


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storm event. For those ancillary developments which fall within the ambit ofcomplying development, some general criteria are specified, such as the needto ensure that fences do not prevent the natural flow of stormwater drainageand runoff. Certain minor development may be exempt development only if aPart 3A Permit under the Rivers and Foreshores Improvement Act has beenissued for development involving excavation in or within 40 metres of the bankof a watercourse or erection of a building or structure within 20 metres of thebank of a watercourse. In many cases, this would preclude a proposal beingexempt development.

The eventual recommendations of the FRMP should include a need to reviewthe exempt and complying development provisions of Council, to ensure thatthey both remain consistent. For example, any agreement reached with theDIPNR regarding the appropriate setbacks from watercourses which wouldachieve an automatic Part 3A approval may allow the exempt developmentprovisions of Council to be refined. Also, the FRMP may produce standarddefinitions of flood prone land and similar terms which can be adopted by theabove described DCP’s.

Controls on fencing within the floodplain are also a likely outcome of the FRMP,and therefore fencing on flood prone land should not be complying or exemptdevelopment, and the planning controls recommended by the FRMP couldthereby provide the relevant criteria for the assessment of fencing applicationsin the floodplain. Alternatively, some fence types could be permitted withoutconsent provided Council’s exempt and complying development provisionsestablished specific design criteria which address hydraulic issues.

2.3.8 Council Policies

In addition to formal regulations such as a DCP or an LEP, Councils may fromtime to time adopt specific policies with regard to their long term vision fordevelopment within the floodplain or to deal with specific matters such asflooding. Normally, such policies are translated into DCP’s or other planninginstruments such as an LEP.

Wollongong City Council adopted an interim Flood Prone Land Policy for theLGA which adopts the 100 year ARI as the flood standard (flood planning level).

Council has also adopted a policy regarding design flood levels and culvertblockages. This policy requires that for the purposes of hydraulic design andflood level calculations certain criteria be adopted assuming blockages andobstructions and associated implications of such blockages. The need for thisdraft policy has arisen from data obtained during the major floods of August 17,1998 and October 24, 1999 where the blockage of drainage structures andchannels were found to contribute substantially to increase flood impacts.Depending on Council’s preference, such detailed specifications could beappended to the Draft DCP recommended within the conclusion of this report,for the purposes of having a complete comprehensive document dealing withthe issue of flooding.


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The State Government Flood Policy introduced in 1984 specifically abandonedthe application of the 100 year ARI flood standard as the designated floodstandard for the State of New South Wales, and required each LGA todetermine their flood standard or standards based on merit. The FPDMintroduced in 1986 and the more recent FMM released in 2001 provideguidelines to assist councils in determining the relevant standards and policies,through the preparation of FRMS’s and FRMP’s.

Until the adoption of an FRMP, Councils under the 1986 FPDM were requiredto produce interim flood policies, an example which would be the policy referredto above. The ability to rely on interim policies was removed from the 2001FMM which increases the urgency to prepare FRMP’s for flood affected areasin the LGA.

The procedures now outlined within the 2001 FMM provide Council withindemnity pursuant to the limitations provided by Section 733 of the LocalGovernment Act 1993, and accordingly is very important to Council’s overallrisk management procedures. The eventual outcome of all FRMP’s, includingthis FRMP will be to translate relevant planning recommendations of thesedocuments into the instruments available through the EP & A Act, principallythe LEP and DCP. Recommendations for translating relevant recommendationsof these documents into these instruments are made later within this report.

In addition to the above Wollongong City Council has introduced a “BlockagePolicy” to be applied in planning and design where the flow of flood waters maybe constrained by a blockage. A major contributor to the devastation caused bythe August 1998 flood, was the extensive blockage of culvert and bridgestructures. In many cases, the hydraulic capacity of culverts, bridges andunderground pipe systems was completely eliminated or severely restricted asa result of the blockages. This in turn resulted in excessive overland floodingproblems.

In 2000, in response to these problems, which were widespread throughout theWollongong City Council local government area, Council amended itsprocedures and policies for the assessment of flood behaviour at culvert andbridge structures to allow for the potential effects of blockage. Prior to this time,it was not generally the policy of the then Department of Land and WaterConservation (now Department of Infrastructure, Planning and NaturalResources) to consider blockage in the preparation of flood studies andfloodplain risk management studies throughout NSW. Consequently,Wollongong Council had no formal policy that considered such blockage ofculvert and bridge structures.

The Floodplain Risk Management Committee formally adopted the new‘Conduit Blockage Policy’, early in 2001, as part of the Council’s DrainageDesign Code. The policy was formally adopted by Council in November 2002(Wollongong City Council, 2002).


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2.3.9 Development Application Assessment

Development applications for proposals which are permissible with consentmust have regard to the relevant ‘Matters for Consideration’ contained inSection 79C of the Environmental Planning and Assessment Act 1979.

Section 79C(1)(a)(i) of the Act requires the consent authority to take intoconsideration, when determining a development application, the provisions ofany environmental planning instrument. Accordingly, Council is required to haveregard to the provisions of the applicable LEP’s which specify various mattersto consider with respect to flood liable land.

Section 79C(1)(a)(iii) requires that Council also consider any DCP in force.While no DCP is presently in force which deals specifically with the issue offlooding, such an instrument would provide a desirable mechanism for Councilto comprehensively assess development applications with respect to the issueof flooding.

The Environmental Planning and Assessment Act 1979 and accompanyingRegulations 2000 also identify certain developments which are deemed to be“designated development”. Designated developments are generally large scaledevelopments which have been identified as potentially causing greater impactson the environment. Hence, designated development proposals require thepreparation of an Environmental Impact Statement (EIS) and more specialisedassessment procedures including statutory notification of the developmentapplication with third party rights of appeal for any objectors.

Schedule 3 of the Environmental Planning and Assessment Regulation 2000identifies those developments which are designated development by virtue oftheir processing capacity, site requirements or location near environmentallysensitive features. Developments such as certain industries, local works,extractive industries, mines and the like are permissible in the zoning of thestudy area and adjoining land. Some of these developments may be regardedas designated development when located within a certain distance of a naturalwater body or wetlands or on flood prone land or a floodplain.

Schedule 3 of the EPA Regulation 1994 defines floodplain as follows:

“Floodplain means the floodplain level nominated in aLocal Environmental Plan or those areas inundated asa result of a 100 year flood event if no level has beennominated.”

Accordingly, there are a number of potential outcomes of the FRMP processwhich may have implications in regard to the manner in which DevelopmentApplications are dealt with.

2.3.10 Section 149 Certificates

A Section 149 Certificate is basically a zoning certificate issued under theprovisions of the EPA Act, and must be attached to a contract prepared for the


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sale of property. The matters to be contained within the Section 149(2)Certificate are prescribed within Schedule 4 of the Environmental Planning andAssessment Regulation, 1994, which includes the following specific matters inregard to flooding.

“12. Whether or not the Council has by resolution adopted apolicy to restrict the development of land because of thelikelihood of landslip, bushfire, flooding, tidal inundation,subsidence or any other risk”. [Our emphasis]

The wording of the above prescribed matter is such that inconsistencies arisebetween local councils in regard to the extent of information they provide onflooding. It has been argued that on literal interpretation, councils are onlyrequired to provide a ‘yes’ or ‘no’ answer as to whether such a policy exists.Further, there is potential equivocation when a council is aware of a flood risk,(eg. that a property is known to be located between the 100 year ARI and PMFextents), and there are no policies restricting development subject to the risk. Aprincipal issue which arises is whether there is a legal or moral obligation forcouncil to advise of the risk (Mawson J, Prior N, and Bewsher D, 1994).

A certificate issued under Section 149(5) of the Act simply requires that Council“include advice on such other relevant matter affecting the land of which it maybe aware”. While this certificate type would necessitate Council advising of allflood information it holds, it is a more expensive certificate and is not mandatoryattached to property sale contracts.

Council has a number of standard notations for inclusion on Section 149Certificates which relate to both land known to be affected or not affected byflooding. The notations relating to land not known to be flood affected advisethat Council’s maps do not indicate flooding, however these may not becomplete and where at any doubt exist the services of a suitable qualifiedengineer should be obtained.

Council also has a number of notations for Section 149 Certificates on floodaffected land. These notations advise that Council’s flood maps identify theland as being located in an area where flooding has occurred or is suspected.Advice is given that the services of a suitably qualified engineer should besought to ascertain the likely affect, if any, on the land. There are notationswhich also provide advice in regard to associated considerations such asexistence of a piped watercourse and potential ponding.

These Section 149 notices should ultimately be reviewed upon adoption of theFRMP, to recognise the existence of the FRMP and any policies emanatingfrom that document, as well as the findings of the flood study preceding theFRMP. Generally, the recommendations of this study are to advise all persons,through the use of Section 149 Certificates (and other methods) of all potentialflooding (ie. up to the PMF).


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2.3.11 Section 94 Contributions Plans

Section 94 Contributions Plans under the EPA Act provide a basis for thelevying of development contributions to construct drainage and flood mitigationworks required as a result of future development. Section 94 contributions canonly be applied to fund works associated with the new development and cannotbe applied for purposes of rectifying past inadequacies.

As structural flood mitigation options are limited and potential developmentgrowth is also minimal, it is unlikely that a Section 94 Contributions Plan wouldbe a feasible fund raising mechanism for such measures. This should howeverbe monitored by Council and reviewed should expected development ratesincrease or if large individual developments would warrant a site specificSection 94 Contributions Plan.


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3.0 PROPOSED APPROACH TO FLOODPLAINPLANNING

3.1 General Philosophy

The various floodplains which forms the basis of the subject study area, arerelatively narrow and as a consequence, the range of issues normallyaccounted in a FRMS do not arise in this case. In the context of this study,primary issues relate to appropriate setbacks of development from identifiedflood flow paths (mainly creeks and tributaries whether piped, in formedchannels or not) and appropriate floor levels. Notwithstanding, Council willneed to ensure that the planning outcomes derived from this study areintegrated with all other FRMP’s currently under preparation in the WollongongCity LGA (4 others which are under preparation at this time) to provide aconsistent platform for dealing with the issue of flooding with futuredevelopment.

Accordingly, it is considered appropriate to provide a general discussionregarding an appropriate approach to floodplain planning generally which canbe adopted by Council, before identifying how the Towradgi Creek floodplainspecifically fits into this framework. The following sub-sections of this reportdescribe both the traditional approach to floodplain planning and an alternatepreferred approach which could apply to the Wollongong City LGA as a whole.

3.1.1 Traditional Approach to Floodplain Planning

In general terms, the real flood hazard within floodplains is poorly understoodand appreciated by the community.

Often the community considers there to be a flood hazard only on land belowthe flood planning level (FPL) which is the level below which councils placerestrictions on development. This FPL is commonly the 100 year ARI flood. Infact, floods can occur well above this level within the study area. A 100 yearARI is a probability determined for any 12 month period - it is not a measure ofhazard. For planning purposes we can identify the existence of varioushazards such as bushfire and landslip and when identified proceed to managetheir potential consequences. Ironically, because probabilities are able to becalculated for flooding, planners have traditionally only selectively managed thehazard based on a nominal FPL.

Illustration 3 presents the view of flood hazard generally held by thecommunity. The flood hazard extent relates only to the FPL (in this case the100 year ARI flood). In the community’s mind, there is no flood hazard abovethe 100 year ARI flood level.


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Illustration 3: Typical View of Flood Hazard Currently Held by Community

Confusion over the nature of the flood hazard has not been helped by thecurrent procedures for flood notations on Section 149 Certificates under theEPA Act. As previously discussed, the certificates are often misinterpreted bythe community as a statement of whether or not a flood hazard exists at theproperty. Most importantly, when a council does not mention flooding on acertificate, the community may incorrectly assume that there is no flood hazardwhen in fact (eg. for properties just above the FPL), the flood hazard may besignificant in dimension albeit slightly more rare in occurrence.

3.1.2 Objectives of Floodplain Planning

Floodplain risk management is about occupying the floodplain and optimisingits use in a manner which is compatible with the flood hazard and at a level ofrisk which is accepted by the community.

Floodplain risk management involves more than setting a FPL. It is aboutcomprehensively managing the risk to people and assets (both below andabove the FPL) by applying and integrating a range of available measures.

There are different types of flood risks and a range of ways in which each typeof flood risk can be managed. This includes floor level controls, floodawareness and warning, evacuation facilities, building design, distributing landuses in a flood compatible manner, subdivision design (eg. road layouts),structural works, etc.

Traditional floodplain planning has relied almost entirely on the definition of asingular FPL, which has usually been the 100 year ARI flood level for thepurposes of applying floor level controls. While such an approach has oftenbeen adequate, the approach has not worked well everywhere and has led to anumber of problems including:

• creation of a ‘hard edge’ to development at the FPL;


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C distribution of development within the floodplain in a manner which doesnot recognise the risks to life or the economic costs of flood damage;

C unnecessary restriction of some land uses from occurring below the FPL,while allowing other inappropriate land uses to occur immediately abovethe FPL;

C polarisation of the floodplain into perceived ‘flood prone’ and ‘flood free’areas;

C lack of recognition of the significant flood hazard that may exist above theFPL (and as a result, there are very few measures in place to manage theconsequences of flooding above the FPL);

C creation of a political climate where the redefinition of the FPL (due to theavailability of more accurate flood behaviour data, or for other reasons) isfiercely opposed by some parts of the community, due to concern aboutsignificant impacts on land values - ie. land which was previouslyperceived to be ‘flood free’ will now be made ‘flood prone’ - (despite thelikelihood that such concerns may only be short term).

Accordingly, continuation of the sole reliance on the 100 year ARI FPL isinappropriate if a generic flood risk management approach is to be developedfor both Towradgi Creek Floodplain and the overall Wollongong City LGA.

The current approach to floodplain planning discussed above may be typifiedby the example shown in Illustration 4, which flows from the inappropriate viewof flood hazard presented in Illustration 3. No development is permitted belowthe FPL (ie. 100 year ARI flood) because of an acknowledgment of somedegree of flood hazard. Above the FPL, no flood hazard is perceived andtherefore there are no flood-related controls on development. Thus an abruptchange in development control occurs at the FPL.

Illustration 4: Current Floodplain Planning(Derived from an inappropriate view of flood hazard and the use of a singular flood planninglevel)


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In addition, it is rare to find councils which have determined their FPL using theprocedures suggested in the State Government’s FMM (2001) or previousFPDM (1986). That is, by balancing the social, economic and ecologicalconsiderations against the consequences of flooding, with a view to minimisingthe potential for property damage and the risk to life and limb.

By default, most councils have adopted the 100 year ARI FPL, given that thisFPL has been widely used across the State and that councils have been unableto carry out the assessment necessary to establish appropriate alternatives.The process suggested in the Manual, being complex and without detailedguidelines for town planners, has been difficult for councils to follow.

3.1.3 Flood Planning Levels (FPL’s)

The flood planning level (FPL) is the level below which Council placesrestrictions on development due to the hazard of flooding. FPL is the currentpreferred terminology in place of the flood standard or the designated flood,which were previously used by the previous FPDM (1986).

Consistent with the above philosophy, the danger in adopting FPL’s below thePMF is that they are recognised by the community as definitive advice as towhether a flood hazard exists or not. Further, there has traditionally been anapproach where a singular FPL (or flood standard) has been chosen whichcreates significant limitations on a holistic approach to managing the flood riskin the floodplain. The reality is that various land uses are subject to alternateconsequences (risks) from the flood hazard (eg. the risks of the flooding of ahospital is much different to the consequences of the flooding of an amenitiesblock in parkland). Accordingly, there needs to be a simplistic approach ofreflecting the different flood risk to different land uses within the floodplain,while maintaining an understanding that flood risks still occur, regardless thatflood controls may not be imposed. The planning matrix approach discussedbelow is one such methodology of addressing these issues.

3.1.4 The Planning Matrix Approach

Given that some floodplains have an extensive flood range, and given thedifficulty in addressing the associated variability in flood risks with simple rules,the use of the planning matrix approach (D. Bewsher and P.Grech, 1997) isrecommended.

The approach distributes land uses within the floodplain and controlsdevelopment to minimise the flood consequences as depicted in Illustration 5below.


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Illustration 5: Distributing Land Uses under the Planning Matrix Approach

Using this approach, a matrix of development controls, based on the floodhazard and the land use, can be developed which balances the risk exposureacross the floodplain. This approach has been adopted as part of the recentHawkesbury–Nepean Flood Management Strategy. It has also been previouslyapplied within the Blacktown, Narrabri, Cabramatta Creek, Patterson River,North Wentworthville and Molong Floodplain Management Studies, and theresulting matrix has been pivotal in the new draft DCPs and LEP’srecommended for implementation as part of these Floodplain Risk ManagementPlans (see Illustration 6).

The approach is summarised in Illustration 6. It is fully consistent with theFloodplain Management Manual.

Illustration 6: The Planning Matrix Approach to Floodplain Planning


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3.2 Preparing a Planning Matrix

3.2.1 Step 1 — Categorising the Floodplain

The first stage in developing a “planning matrix” is to identify each of thefloodplains to which the overall policy document is to be applied, while thesecond stage is to divide the floodplains into different areas subject to similarlevels of hazard.

In regard to the first stage, it is noted that this FRMS relates only to theTowradgi Creek Floodplain. Notwithstanding, it is our approach that Councilwould benefit considerably by having a singular policy document which appliesto all floodplains within its LGA.

The approach intended to be adopted to satisfy the above objective, is toprepare a singular DCP which has a common preamble, objectives and generalpolicies, while specific controls for each floodplain are reflected within aplanning matrix prepared for each individual floodplain and annexed to theprincipal document. This approach has been adopted and recommendedelsewhere for the management of floodplains jointly administered by more thanone local council (eg. Cabramatta Creek FRMS where its management is jointlythe responsibility of Fairfield and Liverpool City Councils), or where Councilshave a number of floodplains with their LGA.

The second stage in the preparation of the planning matrix is to identify differentflood risk precincts (FRP’s), reflective of the variable flood hazard within each ofthe separate floodplains. In regard to the subject study, the following threeFRP’s are proposed:

• High Flood Risk (andInterim RiverinePrecinct)

This has been defined as the area within theenvelop of land subject to a high hydraulic hazard(in accordance with the provisional criteria outlinedin the Floodplain Management Manual) in a 100year flood event together with all land within acorridor 10m from the top of the creek bank. Thehigh flood risk precinct is where high flooddamages, potential risk to life, or evacuationproblems would be anticipated. Most developmentshould be restricted in this precinct. In this precinct,there would be a significant risk of flood damageswithout compliance with flood related building andplanning controls.

• Medium Flood Risk This has been defined as land below the 100 yearflood level (plus 0.5m freeboard) subject to lowhydraulic hazard (in accordance with theprovisional criteria outlined by the FloodplainManagement Manual). In this precinct there wouldstill be a significant risk of flood damage, but thesedamages can be minimised by the application ofappropriate development controls.


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• Low Flood Risk This has been defined as all other land within thefloodplain (ie within the extent of the probablemaximum flood) but not identified as either a highflood risk or medium flood risk Flood Risk Precinct,where risk of damages are low for most land uses.The low flood risk precinct is that area above the100 year flood (plus 0.5m freeboard) and most landuses would be permitted within this precinct.

The FRP’s delineated above have been formulated to provide a basis forstrategic planning and development control having regard to the specificcharacteristics of the Towradgi Creek Floodplain.

The High FRP is inclusive of the area of a riverine corridor from whichdevelopment should be setback for ecological reasons. The riverine corridorsalong each of the seven branches within the Towradgi Creek catchment arepotentially of significant environmental value and need to be restored andmaintained. At the time of preparation of this study, the then DLWC (nowDIPNR) was in the process of commencing a Riparian Corridor ManagementStrategy. This management strategy is being steered by the IllawarraEscarpment Project Coordination Team as part of the implementation ofrecommendations from the Commission of Inquiry into “The long-term planningand management of the Illawarra Escarpment”.

Whether it is through the DIPNR's work or other Council studies, it is importantthat the riparian/riverine corridors are clearly identified and that Councildevelops a strategy for management of the riparian/riverine corridors.

The FRP is that area above the 100 year ARI flood which is potentially subjectto flooding, but is not included in any of the other FRP’s. This area is stillsubject to some flood-related risk and those uses which may be consideredcritical or should be afforded maximum protection against risk from flooding, areto be identified as undesirable land uses in this precinct. The other majorpurpose for this FRP is to identify and recognise the potential flood risk for allpersons and properties affected by the PMF, regardless of whether any specificdevelopment controls are to be applied. This provides a basis for floodawareness programs, evacuation and emergency planning and to maximise thepreparedness of the community.

3.2.2 Step 2 — Prioritising Land Uses in the Floodplain

The next component in the preparation of the planning matrix is to prioritiseland uses within the floodplain. This is achieved by identifying discreetcategories of land uses, of similar levels of sensitivity to the flood hazard. Inthis case the following categories have been adopted:

• Essential community facilities• Critical utilities• New Residential Subdivisions• Established Residential Areas


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• Commercial or industrial• Tourist related development• Recreation or agriculture• Minor development.

Defined land uses, as specified by the relevant LEP’s, SEPP’s or REP’s areincluded within each of the above categories (and further described wherenecessary) depending on relevance having regard to the issue of flooding.Many of these land uses will be irrelevant to the Towradgi Creek Floodplain, butmay be considerations for other floodplains in the Wollongong City LGA.

These categories are subsequently listed under each FRP in the planningmatrix dependent upon the level of flood risk which is considerable acceptable.This provides a basis to specifying whether certain categories are unsuitableland uses in different parts of the floodplain or whether they are suitable subjectto varying degrees of development control. This approach is basically theapplication of the philosophy previously described within this report.

To assist in determining the land use priorities throughout the floodplain, thequestionnaire survey distributed to residents within the floodplain wasspecifically tailored to provide answers which have been used in balance withother criteria (such as orderly and efficient planning) to determine the finaldistribution of land uses categories. The land use categories referred to in thequestionnaire survey were ranked by respondents according to which theythought were the most important to protect from flooding, these were ranked asfollows:

1. Residential (most important)

2. {Critical utilities{Essential community facilities

3. {Commercial and industrial development{New residential subdivisions

4. {Minor development and additions{Recreation or agricultural land (least important)

As stated previously, the results of the questionnaire need to be balanced withother criteria to produce the final matrix. (Note, the separate category of "touristfacilities" was not considered as part of the original survey process).

3.2.3 Step 3 – Controls to Modify Building Form and CommunityResponse

The next component in the preparation of the planning matrix is to assigndifferent planning controls to seek to modify building form and the ability of thecommunity to respond in times of flooding, depending upon the type of land useand the location of that land use within the floodplain. The type of controls canbe categorised under seven main headings, being:


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• Floor levels• Flood compatible building components• Structural soundness• Flood effect on others (impact on flood behaviour)• Evacuation/access• Flood awareness• Management and design.

The resident survey revealed that a high percentage of respondents (48%)believe the Council should prohibit all development on land with any potentialfor flooding. Fewer respondents (44%) considered that development should berestricted in extremely hazardous parts of the floodplain, and only 37% statedthat new development could be managed by imposing restrictions such asminimum floor levels or use of flood compatible building materials. A proportionof respondents (51%) also believe that individuals should be advised about theflood risk, and allowed to choose for themselves whether or not to undertakenew development. A high percentage (55%) believe that prospectivepurchasers of property, or other people who inquire of Council, should receivesuitable notifications concerning flooding.

There should be variance to the stringency of development controls reflectingthe attitudes of the community, the sensitivity of the land use category to theflood hazard, and the location of the land use within the floodplain.

3.3 Implementation of the Planning Matrix Approach

The most appropriate mechanism for the implementation of the proposed floodpolicy is its adoption by Council as a DCP. This DCP could also include generalpolicies of Council such as their criteria for rezoning applications within thefloodplain, which while not specifically relevant to the assessment ofdevelopment applications, provides a holistic approach to Council’s policies forthe management of the floodplain. There would be no legal impediment to theinclusion of such additional matters within the DCP document.

A singular planning matrix will be prepared as a component of this FRMS forthe Towradgi Creek Floodplains. Council could incorporate a separate matrixfor floodplains for which other FRMP’s are being prepared and residualfloodplains. The residual floodplains, being those floodplains for which FRMP’shave not been prepared to date, should be the subject of interim guidelinesincorporated into the DCP. Notwithstanding, we note that the current FMM doesnot now recognise interim policies adopted while awaiting the preparation of aFRMP and Council should seek further legal advice regarding the status ofsuch guidelines for the purposes of Section 733 of the Local Government Act,1993.

In addition to the preparation of the DCP’s, Council will need to undertakediscreet changes to its LEP in order to ensure consistency with definitions,special flood development control clauses, and to modify boundaries whichestablish appropriate setbacks from creeks through the use of foreshorebuilding line provisions. These changes are outlined and discussed further in alater section of this report.


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4.0 REVIEW OF PLANNING OPTIONS

4.1 General

There are a number of alternate mechanisms by which land use planning mayhave a role in implementing non-structural measures for the control ofdevelopment within the floodplain. These measures may vary from a fairlybroad strategic overview of future and intended development or detailedbuilding and development controls applicable to various forms of developmentin different zones.

Town planning can also have an input in regard to providing appropriatemechanisms for the implementation of structural measures, such as theadoption of a Section 94 contributions plan to provide developer fundingtowards broader scale flood mitigation works (although not likely to be aworthwhile mechanism in this case). Town planning can also assist in regard toflood awareness initiatives through notations on Section 149 Certificates(zoning information certificates).

The following is an outline of planning measures considered appropriate forconsideration for the study area.

4.2 State Environmental Planning Policies (SEPP’s)

As the State Government's FMM is aimed at encouraging a merit basedapproach to floodplain planning for individual areas, it is unlikely to be desirableto establish a global policy for floodplain development through the application ofa SEPP. Accordingly, the pursuance of this option is not discussed further.

4.3 Regional Environmental Plans (REP’s)

A review of Illawarra REP No. 1, is an option that would need to be pursued byplanningNSW in consultation with relevant government authorities. Councilcould refer this FRMS to the Department to initiate consideration of a review toreframe its flood related provisions to accord with the principles of modern-dayfloodplain planning and to consistently define terminology.

4.4 Local Environmental Plans (LEP’s)

There are various aspects of Council=s LEP which can be appropriatelystructured to form a component in the application of the FRMP. It is noted thatthe structure of the LEP should be such that it provides the necessary flexibilityfor the adoption of other FRMP=s and their associated planningrecommendations which may be prepared from time to time elsewhere withinthe LGA. In this regard, the importance of the LEP can be summarised asfollows.

• To provide objectives for the application of floodplain managementprinciples in the assessment of development applications.


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• To appropriately identify areas subject to flooding in order that developmentapplications in such areas may be specially considered and that Council hasa basis for notifying the public of the potential for flooding on individualparcels of land in accordance with Section 149 Certificates issued under theAct.

• To outline general matters for consideration with more detailed controlsbeing the subject of a DCP in accordance with accepted practice.

• To clearly define terminology used in the LEP, which are related tofloodplain management. Terminology in the LEP should be consistent withthe FMM.

• To ensure that the permissibility and prohibition of uses is consistent withthe FRMP, in order that flood sensitive land uses are clearly prohibitedwithin areas subject to significant and hazardous levels of flooding. In thisregard we note that the prohibition of land uses is a matter which must beclearly outlined within the LEP as this function cannot legally be transferredto a DCP.

4.4.1 Objectives

The Wollongong LEP presently provides specific objectives for each zone andsix broad aims for the overall LEP. It would not be appropriate to providefloodplain management related objectives for each of the zones within the studyarea, due to the vast number of zones, and the existence of these zones welloutside of the floodplains of the LGA. The aims of the overall LEP provided thatClause 4 could be expanded to include a floodplain management objective,although having regard to the nature of the existing aims of the LEP, it may bepreferable to structure this definition to more broadly apply to all natural, andpossibly man-made, hazards. Such an objective is provided within AppendixA2 for further consideration and adaptation by Council

4.4.2 Definitions

It is considered preferable that the consideration of the flood hazard beapplicable to the whole of the floodplain (ie. up to the PMF) albeit that theconsiderations will vary considerably across the floodplain depending upon thesensitivity of individual land uses and the extent of the flood hazard in anyparticular area. Accordingly, it is considered appropriate that a definition of“Flood Prone land” consistent with the intent of the Floodplain ManagementManual be adopted. Defining of a singular flood standard or FPL is irrelevantdue to the proposal to apply a graded set of planning controls applicable to thewhole of the floodplain. That is the package of planning controls effectivelyprovides various flood standards which vary with different land uses (eg.Residential, commercial/industrial, etc), location within the floodplain (ie. WhichFRP), and that part of the development to be controlled (eg. Floor levels, floodcompatible materials, evacuation, etc).


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Identifying “Flood Prone Land” as the whole of the floodplain (ie, up to the PMF)would allow the acknowledgement of all potential flood risks. This is data nowavailable for the whole of the study area and can be progressively compiled ona map for other catchments as information becomes available. This does notnecessarily mean that it is proposed to reduce development potential in thefloodplain. A detailed DCP will provide a gradation of planning controls relativeto the position of land in the floodplain and consequent flood risk. VariousFRP’s are to be identified in the floodplain, as previously described. OtherFRP’s may be identified as part of other FRMS’s and FRMP’s.

In the consideration of adopting appropriate definitions regard must be made toother FRMP=s which may be undertaken in the same LGA in the future. That is,the structure of the definitions must allow for the logical application of two ormore FRMP=s and must not complicate Council=s duties in regard to areaswhich are not covered by a FRMP. The standard definitions provided atAppendix A2 are considered to achieve the aim.

It would be preferable to identify the extent of the PMF on the DCP Map (orpossibly as a separate map series), in order that there would be clearrecognition of potential flood risk and an understanding of the application of theLEP. The identification of the PMF would also provide context to the definitionsto be recommended for inclusion within the LEP.

It is also considered desirable that the component of flood prone land which isclearly unsuitable to the majority of specific uses due to the extent of thehazard, be identified and defined in order to provide a basis to restrictinappropriate land uses encroaching within this area. This hazardouscomponent of the flood prone land would be that defined as the “High FloodRisk Area” in the DCP. The LEP could give effect to restricting the majority ofland uses within this area by Council resolving to adopt a foreshore building line(FSBL) for the creeks within the study area, which extends at a minimum to theboundaries of this High Flood Risk area. As discussed previously, the FSBLmay also be set to have regard to other environmental criteria such asenvironmental and erosion considerations.

It is recognised that the changes to the LEP will need to occur gradually asother FRMP's for the remaining floodplains of the Wollongong City LGA areprepared. The ultimate course of action in regard to amending the LEP mayinclude the following actions:

• Introduce a standard clause for the consideration of developmentapplications on flood prone land.

• The adoption of a FSBL along all creeks in the study area based generallyon the extent of the High Flood Risk precinct (or equivalent). The FSBL mayalso be extended to include other environmental considerations such aserosion risk or riparian corridors requiring preservation by the DIPNR underthe provisions of their legislation. (We do not believe that the HydraulicMaps should be solely relied on for this as the implications in the LEP couldbe significant in certain cases. A review would need to be undertaken toinvestigate the extent of affectation on all allotments to determine whether


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there are any cases where existing properties are wholly affected by theproposed FSBL restrictions. Where this occurs, such properties will requirefurther assessment regarding future use.

• Introduce standard definitions.

In addition to the above, it is proposed that Council would adopt a developmentcontrol plan for the detail associated with the management of flood risk, asdiscussed below.

4.4.3 Zoning Changes

Following adoption of the planning matrix and formalisation of the flood riskprecinct boundaries, Council would then have all the necessary information,with regard to flooding, to assess applications for all types of development,including rezoning of land, in the floodplain. In relation to flood risk alone, itdoes not appear necessary to rezone any land within the Towradgi Creekcatchment floodplains. However, if rezoning applications were received forallotments within the floodplain, there are a range of issues, in addition toflooding, that would need to be considered.

As part of redevelopment within the floodplain, there is the potential fordevelopers to seek permission to fill their allotments. In locations whereredevelopment (including filling) would reduce the flood risk potential and/or therisk to life, such redevelopment may even be encouraged, provided thedevelopment is consistent with the 2001 Floodplain Management Manual orother planning considerations.

The cumulative impacts of filling in the floodplain near to a level of the 100 yearflood, in terms of flood storage, have been assessed as part of this study. Ithas been found that the impacts on flood storage from filling in the floodplain upto a level close to the 100 year flood level would be acceptable, and would notcause significant increases in flood levels elsewhere in the catchment.

It has therefore been considered to be appropriate to allow filling in thefloodplain up to a maximum height of 300mm below the 100 year flood level.Minimal additional fill above this level to provide for, for example, drivewayaccess to garages or to fill under floor areas, was also examined in the terms ofcumulative impacts, and was considered to be acceptable.

The impacts of filling on flood storage therefore would not need to be assessedfor each individual Development Application (DA). However, other potentialhydraulic impacts such as loss of conveyance (that is, the obstruction of flowingwater), changes in local drainage, changes to overland flow paths, etc., wouldstill need to be assessed before filling could be approved on an individual lot.Other non-flooding issues, such as amenity, overshadowing and environmentalconsiderations would also need to be addressed in the assessment.


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4.5 Development Control Plans (DCP’s)

The appropriate mechanism for specifying detailed controls to be applied fornew development would be a DCP. This document could form an overallcomprehensive flood management policy for Council and a suggested draftDCP is included as Appendix AB. The DCP should be accompanied by a mapwhich identifies all FRP's.

There are seven areas of development control consideration relevant tofloodplain planning which may be applied to development in the study area. Thefollowing provides a discussion of the controls that would be appropriatelyconsidered under each of these headings.

4.5.1 Floor Area

All habitable floor levels of dwellings should be no lower than the 100 year ARIflood level plus freeboard (0.5 metres). Additionally, where practical, extendedfloors associated with minor additions to existing development should beprovided at the 100 year ARI flood level plus freeboard but should never be at alevel lower than the existing floor level where that does not comply with thestandard. Higher floor levels (i.e. above the PMF level may be required whererelied upon to satisfy evacuation criteria.

Less “flood sensitive” land uses such as buildings associated with recreationareas or non-urban uses (where permitted outside of the High FRP) could havebuildings located with floor levels at the 20 year ARI flood level sufficient toavoid nuisance flooding. (In some circumstances, it may be appropriate to varythis requirement and where a site specific analysis was carried). Critical utilitiesshould have floor levels above the PMF as these will be essential to ensuringminimal disruption to the community during major floods. Essential communityfacilities (such as public halls, etc) should be located outside of the floodplain toprovide for potential refuge during major floods and minimal impact to thecommunity.

4.5.2 Flood Compatible Building Components

All structures below the design flood level for individual land uses should beconstructed of flood compatible materials. With regard to the identification ofappropriate flood compatible materials, an appropriate general list of materialsand fittings is provided within the recommended DCP. However, we note thatthe Department of Land & Water Conservation is currently having a detailedstudy undertaken by the CSIRO and the University of Newcastle, which willidentify appropriate flood compatible materials (including methods ofconstruction) applicable to Australian conditions (in particular, the Hawkesbury-Nepean Floodplain). The CSIRO study is understood to not yet be completedbut is expected to be completed some time during this year. It is recommendedthat the DCP be reviewed upon completion and availability of this CSIRO study.


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4.5.3 Structural Soundness

An engineer’s report is considered to be appropriate to ensure structureslocated within high FRP’s are capable of withstanding the forces of floodsincluding debris and buoyancy factors. The issue of structural soundnessshould be considered elsewhere within the floodplain, but it is not consideredthat an engineering report would be necessary in each case.

4.5.4 External Flood Effects

An appropriate principle in floodplain management is to ensure thatdevelopment within the floodplain does not directly or cumulatively increase theflood affectation or hazard upon other properties, the environment or persons.Hence, it is recommended that an engineer’s report is provided for anydevelopment within the High FRP or for any subdivision works and filling in theMedium FRP to prove that the development will not increase flood affectationelsewhere. This matter will also need to be considered with regard to other landuses in the floodplain but an engineering report may not be necessary in eachcase.

4.5.5 Evacuation/Access

Having regard to the short warning time and the relatively narrow floodplaincorridors throughout the study area, regional evacuation is not as pertinent anissue as is site and local evacuation. Accordingly, the structure of the DCPprovides for regional evacuation to be addressed within other floodplains asappropriate, and more specific matters associated with site and local accessare addressed within appropriate controls.

4.5.6 Flood Awareness

The planning mechanisms available to assist in increasing flood awarenessinclude the provision of notations upon Section 149(2) Certificates (zoningcertificates) and imposition of restrictions on titles of new allotments createdthrough subdivision advising of minimum floor levels relative to the flood leveland of Council’s flood prone land policy. Such mechanisms are recommendedas outlined later in this report.

4.5.7 Management and Design

Special consideration of the design and management of individual proposalscan also reduce the flood risk and potential damage to property and persons.These measures may involve the provision of a flood plan for individual siteswhich ensures that individuals consider and plan means to minimise thelikelihood of flood damage, including providing for the movement of goodsabove the flood level within the likely available flood warning time. Otherspecific considerations are for the storage of certain goods above the designflood level and requiring the implementation of mitigating measures to preventpollution of the floodplain potentially occurring during floods.


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4.6 Policies

In addition to formal regulations such as the DCP, Council may wish to identifyand adopt specific policies with regard to their long term vision for developmentwithin the floodplain. This may be a stand alone document cross-referencingthe LEP and DCP and integrated into Council’s current Policy documentframework. Such general policy considerations have been included in the draftDCP, for Council’s adaptation as desired.

4.7 Section 94 Contributions Plans

A Section 94 Contributions Plan includes detail in regard to anticipated increaseof demand for public services and amenities arising from projected newdevelopment and provides calculations for developer contributions in order tofund the additional public services and amenities in accordance with anidentified schedule of works. Section 94 Contributions Plans have animplication in regard to the FRMS, where it is necessary or appropriate to fundflood mitigation works through such plans.

As outlined previously, due to the limited development potential in the studyarea and the lack of any major structural flood mitigation option, the use ofSection 94 Contributions Plans to implement the FRMP is considered anunlikely requirement. This should, however, be monitored by Council andreviewed should expected development rates increase or if large individualdevelopments would warrant a site specific Section 94 Contributions Plan.

4.8 Section 149 Certificates

Consistent with recommendations regarding Council’s LEP maps, it isrecommended that all areas located within the known PMF extent (Flood Pronelands) be advised of the applicability of Council=s Flood Risk ManagementPolicy and DCP. The proposed DCP Policy will provide controls fordevelopment within the floodplain (up to the PMF). The controls will notnecessarily provide an outright restriction to development, but will providevarying degrees of development control measures required to ensure that landuses are acceptable having regard to their sensitivity to the flood hazard, andtheir location within the floodplain.

In addition to identifying flood prone land (the extent of the PMF) upon the LEP,it is also recommended that the FRP’s be identified and recognised as part ofthe DCP. This will be important for interpreting how the DCP applies in regardto individual properties. As the accuracy of the flood level data dictates theFRP’s within the matrix, which determines the severity of controls to be applied,it is important to confirm such information by detail survey. It is recommendedthat this be achieved through the provision of flood certificates issued byCouncil.

Inadequate or non-comprehensive flood risk information on Section 149Certificates operates as a strong force against increasing public awareness ofthe known flood risk which has flow on effects in regard to flood preparedness


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and ease of implementing appropriate building strategies, being importantfactors in floodplain risk management. There are also liability issues withCouncil not fully advising of known flood risks, due to legal requirementsgenerally, and the provisions of Section 733 of the Local Government Act,specifically.


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5.0 RECOMMENDED PLANNING MEASURES

Having regard to the above discussion, the following planning measures arerecommended:

(a) That consideration be given to the application of a graded set of planningcontrols for different land uses relative to different levels of flood hazardwithin the study area.

(b) That the planning implications for each of the structural flood mitigationoptions be addressed, having regard to the issues outlined within thisreport, should any of these options be seriously considered in the future.

(c) That Council considers the following for inclusion within the WollongongLEP:

• Inclusion of the standard definition, objectives and standard clausesgenerally as outlined in Appendix A2.

• Identify on Council=s LEP maps the extent of the “flood prone land”.

(d) That in accordance with Clause 19 of the Wollongong LEP 1990, Councilresolve to adopt a foreshore building line (FSBL) along all creeks withinthe study area which accords with the boundaries of the High Flood RiskFRP, and other environmental and erosion risk criteria necessitatingsetbacks from creeks. (This should involve consultation with the DIPNRregarding Part 3A Permit approval criteria.) The FSBL should be identifiedon Council’s LEP maps. This process should also involve a review of theappropriateness of the zoning of individual land parcels, should thecombined flood risk and environmental criteria result in a FSBL, whichsubstantially affects reasonable development expectations.

(e) That Council initiates a program of identifying, and seeking the removal of,all illegal structures (i.e. unlawfully constructed and unlikely to be able toobtain development consent due to their consequent impact on flooding)within the High FRP.

(f) A Development Control Plan be adopted outlining appropriate measuresto be applied to development in the floodplain. In this regard, AppendixA3 provides a suggested Draft Development Control Plan forconsideration and adoption in accordance with the process required underthe EPA Act. Flood related controls within other existing DCP’s should bereplaced with a reference to the issue specific DCP.


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(g) That in accordance with the Policy, Council incorporates notations uponSection 149(2) Certificates, which identify the affectation by the DCP.

(h) That Council prepare and implement a Riverine Corridor Strategy for thecreek corridors within the study area, to improve corridor linkages andrestore their ecological value and remove inappropriate vegetation whichimpedes the flow of water or forms a source of debris which exacerbatesflooding impacts. This should be undertaken in consultation with theDIPNR, being the State Government’s leading expert in streammanagement.

(i) That Council reviews its current exempt and complying developmentprovisions (as outlined in DCPs No. 99/1 and 99/2) to ensure they areconsistent with the above recommendations.

(j) That Council investigates the feasibility of a policy of formalising the creekcorridors within publicly owned land or with drainage easements held tothe benefit of Council when dealing with development applicationsinvolving the development or redevelopment of flood affected lands. Thiswill require further research of the extent of easement of land acquisitionrequired, the likelihood of redevelopment in areas where such acquisitionis required, the impact on the functioning of individual properties and thepotential costs to Council.

It is considered that the above recommendations provide appropriateresponses to the issues raised and evaluated within the context of the FRMSand the legislative framework associated with planning. The planning controlsby their nature provide measures to address the flooding issue associated withnew development, and other measures may be recommended elsewhere withinthe FRMP dealing with existing development.


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REFERENCES

Bewsher Consulting Pty Ltd and Don Fox Planning Pty Ltd, October 1997,‘Land Use Planning and Development Control Measures’, Hawkesbury-Nepean Flood Management Strategy, prepared for the Hawkesbury-NepeanFlood Management Advisory Committee.

Bewsher Consulting Pty Ltd in association with Don Fox Planning Pty Ltd andothers, 1996, ‘Blacktown Floodplain Risk Management Study’, prepared forBlacktown City Council.

Bewsher Consulting Pty Ltd in association with Don Fox Planning Pty Ltd andothers, 1996, ‘Narrabri Floodplain Risk Management Study’, prepared forNarrabri Council.

Bewsher Consulting Pty Ltd in association with Don Fox Planning Pty Ltd andothers, 1997, ‘Molong Floodplain Risk Management Study’, prepared forCabonne Shire Council.

Bewsher Consulting Pty Ltd in association with Don Fox Planning Pty Ltd andothers, 1996, ‘Assessment of Floodplain Controls, Carinya Road, Picnic Point’,prepared for Bankstown City Council.

Bewsher, D., P. Grech, May 2000, ‘Development of Flood Prone Areas’, 40th

Annual Conference, NSW Floodplain Management Authorities, Parramatta,NSW.

Bewsher, D., P. Grech & J. Maddocks, May 1998, ‘Using Flood Certificates toRaise Flood Awareness’, 38th Annual Floodplain Management Conference,Moama, NSW.

Bewsher, D. & P. Grech, May 1997, ‘A New Approach to the Development ofFloodplain Controls for Floodplains’. Paper presented to the 37th AnnualFloodplain Management Conference - Maitland.

Hunt, I. & P. Kofod, May 2000, ‘Wollongong Floods’, 40th Annual Conference,NSW Floodplain Management Authorities, Parramatta, NSW.

Lustig, T. & J. Irish, May 2000, ‘What Caused the Losses from the WollongongFloods of August 1998?’, 40th Annual Conference, NSW FloodplainManagement Authorities, Parramatta, NSW.

Mawson, J., Prior, N. and Bewsher, D., 1994. ‘Flooding and StormwaterInundation Notations C The Section 149 Dilemma’. Paper presented to the 3rdAnnual Conference of the Municipal Engineers, Australia.

NSW Government, December 1986, ‘Floodplain Development Manual’,Department of Water Resources, Sydney.


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NSW Government, 1984, ‘Review of Flood Prone Land Policy’, discussionpaper, Floodplain Management Review Committee, Sydney.

NSW Government, May, 1997, ‘Draft Floodplain Management Manual’, Sydney.

Ribbons, S., July 1997, ‘The Risk of Flooding - What Are the People of theHawkesbury B Nepean Willing to Accept?’, Kingswood, NSW.

Smith, D., ‘Beyond the Design Flood - Implications for Urban Floodplains’.


APPENDIX A1

ANALYSIS OF CENSUS INFORMATION1986 TO 1996

Appendix A1Towradgi Floodplain Risk Management Study

ANALYSIS OF CENSUS INFORMATION : 1986 TO 1996

AREA: Towradgi Change %ChangeCompound Rate of

Change

1986 1991 1996 1986-96 1986-96 1986-91 1991-96

DEMOGRAPHIC SUMMARY

Total personsMales 4825 4610 4650 -175 -4 -0.9% 0.2%

Females 4740 4657 4723 -17 0 -0.4% 0.3%

Persons 9565 9267 9373 -192 -2 -0.6% 0.2%

Aged 15 years and overMales 3779 3601 3687 -92 -2 -1.0% 0.5%

Females 3745 3695 3765 20 1 -0.3% 0.4%

Persons 7524 7296 7452 -72 -1 -0.6% 0.4%

Aborig. & Torres St. Is.Males 26 48 46 20 77 13.0% -0.8%

Females 16 34 55 39 244 16.3% 10.1%

Persons 42 82 101 59 140 14.3% 4.3%

AGE SUMMARY

Age 0-4 682 672 687 5 1 -0.3% 0.4%

Age 5-14 1351 1284 1233 -118 -9 -1.0% -0.8%

ge 15-24 1568 1351 1288 -280 -18 -2.9% -1.0%

ge 25-54 3705 3685 3720 15 0 -0.1% 0.2%

ge 55-64 1206 991 836 -370 -31 -3.9% -3.3%

Age 65 or more 1045 1334 1592 547 52 5.0% 3.6%

Age Group as a Percentage of the Population

Age 0-4 7 7 7 0 3 0.3% 0.2%

Age 5-14 14 14 13 -1 -7 -0.4% -1.0%

ge 15-24 16 15 14 -3 -16 -2.3% -1.2%

ge 25-54 39 40 40 1 2 0.5% 0.0%

ge 55-64 13 11 9 -4 -29 -3.2% -3.6%

Age 65 or more 11 14 17 6 55 5.7% 3.4%

Median Age

Males 31 33 34 3 10Females 33 35 36 3 9Persons 32 34 35 3 9

0%

20%

40%

60%

80%

100%

1986 1991 1996

YEAR

CHANGING AGE STRUCTURE

Age 0-4 Age 5-14Age 15-24 Age 25-54Age 55-64 Age 65 or more

0

500000

1000000

1500000

2000000

2500000

1986 1991 1996

DWELLING FORMS CHANGE

Separate Houses (OPD) Other Dwg Structures (OPD)

June 2003App A1 Census Data 1 Don Fox Planning

AREA: TowradgiChange %Change of Change

ETHNICITY SUMMARY 1986 1991 1996 1986-96 1986-96 1986-91 1991-96

Australian Born 7106 6895 6876 -230 -3 -0.6% -0.1%

Overseas Born: ESC 1008 993 910 -98 -10 -0.3% -1.7%

Overseas Born: NESC 1354 1227 1235 -119 -9 -2.0% 0.1%

Total Overseas Born 2362 2220 2145 -217 -9 -1.2% -0.7%

Birthplace Group as a Percentage of the Population

Australian Born 74 74 73 -1 -1Overseas Born: ESC 11 11 10 -1 -8Overseas Born: NESC 14 13 13 -1 -7Total Overseas Born 25 24 23 -2 -7

OSB Poor English speakers 202 187 177 -25 -12OSB Poor Eng % of pop 2 2 2 0 -11OSB Poor Eng % of 5+ pop 2 2 2 0 -10

LABOUR FORCE SUMMARY

Employed 3618 3512 3490 -128 -4

Unemployed 559 545 484 -75 -13

Not in the Labour Force 3254 3063 3325 71 2

Unemployment Rate 13 13 12 -1 -9Participation Rate 56 56 53 -2 -4

INCOME SUMMARY

Median Individual Income $8,000 $11,700 $12,200 4200 53Median Family Income $22,500 $31,200 $33,300 10800 48Median Household Income $20,000 $25,600 $26,500 6500 33Standardised Medians (CPI)

Median Individual Income $12,800 $13,300 $12,200 -600 -5Median Family Income $35,700 $35,300 $33,300 -2400 -7Median Household Income $31,700 $29,000 $26,500 -5200 -16

AREA: TowradgiChange %Change

DWELLINGS SUMMARY 1986 1991 1996 1986-96 1986-96

Occupied Pvte Dwgs (OPD) 3445 3462 3732 287 8Occupancy Ratio 2.75 2.65 2.50 0 -9

H'holds Owned/purch'g 2162 2198 2197 35 2H'holds Renting 1162 1140 1299 137 12% Hlds Owned/purch'g 63 63 59 -4 -6% Hlds Renting 34 33 35 1 3

Average Number bedrooms 3 3 n/av n/av n/avAverage Number vehicles 1 1 1 0 -7

Separate Houses (OPD) 2680 2679 2548 -132 -5Other Dwg Structures (OPD) 765 783 1184 419 55% Separate Houses 78 77 68 -10 -12% Other Dwg Structures 22 23 32 10 43

Median Mortgage $343 $635 $933 590 172Median Rent $64 $99 $117 53 83Standardised Medians (CPI)

Median Mortgage $544 $718 $933 389 72Median Rent $101 $112 $117 16 15

EXPLANATORY NOTESOSB: ESC Overseas born: Main English Speaking Countries. This is an approximation only, as Canada is not included

OSB: NESC Overseas born: Other than Main English Speaking Countries

OSB Poor English speaOverseas born people who speak English "Not well" or " Not at All" - Note 1986 measures OSB NESC only.

June 2003App A1 Census Data 2 Don Fox Planning


APPENDIX A2

STANDARD INCLUSIONS FOR LEPs


A2-1

APPENDIX A2

STANDARD INCLUSIONS FOR LEP’s

DEFINITIONS

Flood Prone land means land indicated on the map marked “Flood Prone land” heldin the office of Council as amended from time to time.

OBJECTIVES

To minimise the risk to human life and damage to property caused by naturalhazards such as land instability and flooding and to allow for more detailed controlsfor development on flood prone land to be implemented within a DevelopmentControl Plan.

STANDARD CLAUSE

Development in Flood Prone land

.... (1) Notwithstanding any other provisions of this plan, the Council may refuseconsent to the carrying out of any development on flood prone land where, in itsopinion, the development may:

(a) be inconsistent with any interim flood policy adopted by Council in accordancewith the principles contained in the Manual entitled “Floodplain DevelopmentManual” dated December 1986 (Reference No. PWD86010) or any floodplainrisk management plan adopted by Council in accordance with the Manualentitled “Floodplain Management Manual” dated 2001 (as published by theState Government);

(b) detrimentally increase the potential flood affectation on other development orproperty;

(c) result, to a substantial degree, an increased risk to human life;

(d) be likely to result in additional economic and social cost which could notreasonably be managed by potentially affected persons and the generalcommunity; or

(e) adversely affect the environment of the floodplain by causing avoidableerosion, siltation, unnecessary destruction of river bank vegetation, a reductionin the stability of the river bank;

....(2) For the purposes of this plan, the Council may consult with and take intoconsideration, any advice of the Department Infrastructure, Planning and NaturalResources and the State Emergency Service in relation to the nature of the floodhazard, the necessity and capacity to evacuate persons, and the consequence andsuitability of the development.


APPENDIX A3

MANAGING OUR FLOOD RISKSWOLLONGONG CITY COUNCIL

DRAFT DEVELOPMENT CONTROL PLAN

APPENDIX A3

DRAFT

MANAGING OUR FLOOD RISKS Wollongong City Council Development Control Plan (DCP) No. ….. (Environmental Planning and Assessment Act, 1979)

Prepared by

Don Fox Planning

December 2002 (Final Amendments June 2003)

E:\PROJECTS\4147 Towradgi FRMP\Reports\4147-AppA3-DCP.doc

Draft DCP Managing Our Flood Risks June 2003 Wollongong City Council E:\PROJECTS\4147 Towradgi FRMP Final\4147-AppA3-DCP.doc

________________________________________________________________ Don Fox Planning

TABLE OF CONTENTS

Page

1.0 GENERAL ...................................................................................................................1

1.1 What is the Plan?.............................................................................................. 1

1.2 Why is This Plan Required? .............................................................................. 1

1.3 To Which Applications Does the Plan Apply?................................................... 1

1.4 Where Does the Plan Apply?............................................................................ 2

1.5 How Does the Plan Relate to Other Legislation and Regulations?...................... 2

1.6 How to Use this Plan? ...................................................................................... 2

1.7 What are the Aims and Objectives of the Plan?................................................. 3

1.8 Glossary........................................................................................................... 5 2.0 WHAT ARE THE CRITERIA FOR DETERMINING APPLICATIONS? .......................7

2.1 General............................................................................................................ 7

2.2 Land Use Categories......................................................................................... 7

2.3 Flood Risk Precincts ......................................................................................... 7

2.4 Which Controls Apply to Proposed Developments? .......................................... 8

2.5 Are There Special Requirements for Fencing? .................................................. 9

2.6 Special Considerations ................................................................................... 10 3.0 WHAT INFORMATION IS REQUIRED WITH AN APPLICATION TO ADDRESS

THIS PLAN?..............................................................................................................11


________________________________________________________________ Don Fox Planning

LIST OF ATTACHED SCHEDULES

1 Flood Compatible Materials 2 Land Use Categories 3 Prescriptive Controls –Towradgi Floodplain 4 Prescriptive Controls – Hewitts/Slacky/Woodlands/Tramway/Tomas Gibson

Creeks Floodplain 5 Prescriptive Controls - Allans Creek Floodplain (to be completed) 6 Prescriptive Controls - Fairy/Cabbage Tree Creeks Floodplain (to be completed) 7 Prescriptive Controls – Mullet/Brooks Creeks Floodplain (to be completed) 8 Prescriptive Controls - Minnegang Creek Floodplain (to be completed) 9 Prescriptive Controls - Collins/Wharton/Bellambi Creek Floodplain (to be

completed) 10 Prescriptive Controls - Northern Suburbs Floodplain (to be completed) 11 Prescriptive Controls – All other floodplains


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1.0 GENERAL 1.1 What is the Plan? This document is to be known as the “Wollongong Flood Risk Management Development Control Plan” (DCP) No. …... This Plan has been adopted by Council at its meeting of .................. in accordance with Section 72 of the Environmental Planning and Assessment Act, 1979 (Development Control Plans). 1.2 Why is This Plan Required? In 1984, the State Government introduced the current flood prone land policy applicable to New South Wales. The first Floodplain Development Manual (FDM) was published in 1986, providing guidelines for the implementation of the government’s flood prone land policy and the merit approach which underpins its application. Revised guidelines were released in 2001 and are now embodied in the Floodplain Management Manual (FMM). The FMM continues to support the NSW Government’s Flood Prone Land Policy. The primary objective of the policy is:

“to reduce the impact of flooding and flood liability on individual owners and occupiers of flood prone property, and to reduce private and public losses resulting from floods, utilising ecologically positive methods wherever possible.”

To achieve this objective the FMM acknowledges a broad risk management hierarchy of: • avoidance of flood risk; • minimisation of flood risk using

appropriate planning controls; and • flood risk mitigation.

Flood risk mitigation is the least preferred option, being costly and most likely to adversely affect the natural environment. Avoidance and minimisation of flood risk are the options most likely to be acceptable and are primarily reliant on land use planning and development control for implementation.

Local Government is the primary authority responsible for both flood risk management and land use planning in New South Wales. The State Government’s flood policy provides for a flexible merit based approach to be followed by local government when dealing with planning, development and building matters on flood prone land, in order to facilitate development wherever practicable. For Council to fully carry out its responsibilities for management of flood prone land, it is necessary to prepare a local “Floodplain Risk Management Plan” (FRMP). The FMM requires that Councils prepare Floodplain Risk Management Studies (FRMS) as a prelude to the formulation of a FRMP which, among other things, would control development and other activity within the floodplain. The process for preparing a FRMS and FRMP is depicted by Figure 1. This Plan is consistent with the State Government’s “Flood Prone Land Policy” and the FMM. This Plan is an application of the State Policy which reflects local circumstances, as identified for some floodplains, through the preparation of FRMS’s and FRMP’s. 1.3 To Which Applications Does the Plan Apply? Council will take into consideration this Plan when determining development applications received in accordance with the Environmental Planning and Assessment Act, 1979.


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Figure 1: Floodplain Risk Management Process (FMM, 2001) This Plan does not propose to exempt any applications from the necessity to obtain a particular approval of the Council or other government agencies, where such a requirement would otherwise exist. 1.4 Where Does the Plan Apply? The Plan applies to whole of the Local Government area, as depicted upon the DCP Map. There are a number of floodplains within the LGA, and this DCP will provide general provisions relating to all the floodplains and specific provisions relating to individual floodplains. 1.5 How Does the Plan Relate to Other Legislation and Regulations? This Plan should be read in conjunction with the relevant provisions of the NSW Government Flood Prone Lands Policy and Floodplain Management Manual (FMM 2001), the Environmental Planning and Assessment Act, 1979, and Regulations thereto, applicable Environmental Planning Instruments (in particular Wollongong Local Environmental Plan (LEP) 1990, Wollongong LEP 38, and the Illawarra Planning Scheme and Illawarra and

Illawarra Regional Environmental Plan No. 1) and other relevant Development Control Plans and policies adopted by Council. 1.6 How to Use this Plan Please read this document carefully and seek assistance from Council officers as required. The following is a summary of the major steps you should address: (a) Check the proposal is permissible

in the zoning of the land by reference to any applicable Environmental Planning Instrument (eg. Wollongong Local Environment Plan 1998).

(b) Read this document fully. (c) Consider any other relevant

planning controls of Council (eg. controls in any other applicable DCP which governs the size and setback of development).

(d) Determine the floodplain (eg.

Towradgi Creek, Fairy Cabbage Tree Creek, etc.) and flood risk precinct (low, medium or high) within which your site is situated. Enquire with Council regarding existing flood risk mapping or whether a site specific


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assessment may be warranted in your case.

(e) Determine the land use category

relevant to your development proposal, by firstly confirming how it is defined by the relevant environmental planning instru-ment and secondly by ascertaining the land use category from Schedule 2 of this Plan.

(f) Assess and document how the

proposal will achieve the performance criteria for development and associated fencing provided by Clauses 2.4.2 and 2.5.2 of this Plan.

(g) Check if the proposal will satisfy

the prescriptive criteria for different land use categories in different flood risk precincts, as specified in Schedule 4 to 10 of this Plan depending on which floodplain the site is located.

If the proposal does not comply with the prescriptive controls, determine whether the performance criteria are nonetheless achieved. The assistance of Council staff or an experienced floodplain consultant may be required at various steps in the process to ensure that the requirements of this Plan are fully and satisfactorily addressed. 1.7 What are the Aims and Objectives of the Plan? This Plan aims to:- (a) To minimise the potential impact

of development and other activity upon the aesthetic, recreational and ecological value of the waterway corridors.

(b) Increase public awareness of the

hazard and extent of land affected by all potential floods, including floods greater than the 100 year

average recurrence interval (ARI) flood and to ensure essential services and land uses are planned in recognition of all potential floods.

(c) Inform the community of Council's

policy for the use and development of flood prone land.

(d) Reduce the risk to human life and

damage to property caused by flooding through controlling development on land affected by potential floods.

(e) Provide detailed controls for the

assessment of applications lodged in accordance with the Environmental Planning and Assessment Act 1979 on land affected by potential floods.

(f) Provide different guidelines, for the

use and development of land subject to all potential floods in the floodplain, which reflect the probability of the flood occurring and the potential hazard within different areas.

(g) Apply a “merit-based approach” to

all development decisions which takes account of social, economic and ecological as well as flooding considerations.

(h) To control development and other

activity within each of the individual floodplains within the LGA having regard to the characteristics and level of information available for each of the floodplains, in particular the availability of FRMS’s and FRMP’s prepared in accordance with the FMM and its predecessor, the FDM.

(i) Deal equitably and consistently

with applications for development on land affected by potential floods, in accordance with the principles contained in the FMM, issued by the NSW Government.


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DCP MAP

INSERT LGA BOUNDARY MAP FROM COUNCIL


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1.8 Glossary

For the purpose of this Plan, the following definitions have been adopted:

Australian Height Datum (AHD) is a common national plain of level corresponding approximately to mean sea level. Average Recurrence Interval (ARI) means the long-term average number of years between the occurrence of a flood as big as, or larger than, the selected event. For example, floods with a discharge as great as, or greater than, the 20 year ARI flood event will occur on average once every 20 years. ARI is another way of expressing the likelihood of occurrence of a flood event. Design floor level or ground level means the level specified in this Plan which applies to the relevant land use type within the relevant Flood Risk Precinct. Ecologically sustainable development (ESD) is using, conserving and enhancing natural resources so that ecological processes, on which life depends, are maintained, and the total quality of life, now and in the future, can be maintained or increased. A more detailed definition is included in the Local Government Act 1993. Effective warning time is the time available after receiving advice of an impending flood and before the floodwaters prevent appropriate flood response actions being undertaken. The effective warning time is typically used to move farm equipment, move stock, raise furniture, evacuate people and transport their possessions. Extreme flood means an estimate of the probable maximum flood, which is the largest flood likely to ever occur. Flood is a relatively high stream flow which overtops the natural or artificial banks in any part of a stream, river, estuary, lake or dam, and/or local overland flooding associated with major drainage as

defined by the FMM before entering a watercourse, and/or coastal inundation resulting from super-elevated sea levels and/or waves overtopping coastline defences excluding tsunami. Flood awareness is an appreciation of the likely effects of flooding and a knowledge of the relevant flood warning and evacuation procedures. Flood compatible building components means a combination of measures incorporated in the design and/or construction and alteration of individual buildings or structures subject to flooding, and the use of flood compatible materials for the reduction or elimination of flood damage. Flood compatible materials include those materials used in building which are resistant to damage when inundated. A list of flood compatible materials is attached in Schedule 1. Flood evacuation strategy means the proposed strategy for the evacuation of areas within effective warning time during periods of flood as specified within any policy of Council, the FRMP, the relevant State government disaster plan, by advices received from the State Emergency Services (SES) or as determined in the assessment of individual proposals. Flood prone land (being synonymous with flood liable and floodplain) is the area of land which is subject to inundation by the probable maximum flood (PMF). Floodplain Management Manual (FMM) refers to the document dated January 2001, published by the New South Wales Government and entitled “Floodplain Management Manual: the management of flood liable land”.


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Floodplain Risk Management Plan (FRMP) means a plan prepared for one or more floodplains in accordance with the requirements of the FMM or its predecessor.

Floodplain Risk Management Study (FRMS) means a study prepared for one or more floodplains in accordance with the requirements of the FMM or its predecessor. Freeboard is a factor of safety expressed as the height above the design flood level. Freeboard provides a factor of safety to compensate for uncertainties in the estimation of flood levels across the floodplain, such and wave action, localised hydraulic behaviour and impacts that are specific event related, such as levee and embankment settlement, and other effects such as “greenhouse” and climate change. Habitable floor area means:

• in a residential situation: a living or working area, such as a lounge room, dining room, rumpus room, kitchen, bedroom or workroom;

• in an industrial or commercial situation: an area used for offices or to store valuable possessions susceptible to flood damage in the event of a flood.

Hazard is a source of potential harm or a situation with a potential to cause loss. In relation to this plan, the hazard is flooding which has the potential to cause harm or loss to the community. Local overland flooding means inundation by local runoff rather than overbank discharge from a stream, river, estuary, lake or dam. Merit approach is an approach, the principles of which are embodied in the FMM which weighs social, economic, ecological and cultural impacts of land use options for different flood prone areas together with flood damage, hazard and behaviour implications, and environmental protection and well being of the State’s rivers and floodplains.

Outbuilding means a building which is ancillary to a principal residential building and includes sheds, garages, car ports and similar buildings. Probable maximum flood (PMF) is the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation. Probable maximum precipitation (PMP) is the greatest depth of precipitation for a given duration meteorologically possible over a given size storm area at a particular location at a particular time of the year, with no allowance made for long-term climatic trends (World Meteorological Organisation, 1986). It is the primary input to the estimation of the probable maximum flood. Probability is a statistical measure of the expected chance of flooding (see ARI). Reliable access during a flood means the ability for people to safely evacuate an area subject to imminent flooding within effective warning time, having regard to the depth and velocity of flood waters, the suitability of the evacuation route, and without a need to travel through areas where water depths increase. Risk means the chance of something happening that will have an impact. It is measured in terms of consequences and probability (likelihood). In the context of this plan, it is the likelihood of consequences arising from the interaction of floods, communities and the environment. Survey plan is a plan prepared by a registered surveyor which shows the information required for the assessment of an application in


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accordance with the provisions of this Policy. 2.0 WHAT ARE THE CRITERIA FOR DETERMINING APPLICATIONS? 2.1 General The criteria for determining applications for proposals potentially affected by flooding are structured in recognition that different controls are applicable to different land uses and levels of potential flood inundation and hazard. The procedure to determine what controls apply to proposed development involves: • firstly, identifying the land use category

of the development (from Schedule 2); • secondly, determine which floodplain

and which part of that floodplain the land is located within (refer to Clause 2.3 and relevant flood risk mapping); and

• then apply the controls outlined under

Clause 2.4. Clause 2.5 provides specific requirements for fencing in the floodplain, while Clause 2.6 identifies special considerations which will apply only to some development in specific circumstances. Clauses 2.4 and 2.5 which provide controls for development and fencing in the floodplain contain objectives, performance criteria and prescriptive controls, with the following purpose: • The objectives represent the

outcomes that the Council wishes to achieve from each control.

• The performance criteria represent a

means of assessing whether the desired outcomes will be achieved.

• The prescriptive controls are

preferred ways of achieving the outcome. While adherence to the prescriptive controls may be important,

it is paramount that the objectives and the performance criteria are clearly satisfied.

2.2 Land Use Categories Eight major land use categories have been adopted. The specific uses, as defined by the applicable Environmental Planning Instruments, which may be included in each category, are listed in Schedule 2. 2.3 Flood Risk Precincts Each of the floodplains within the local government area can be divided based on different levels of potential flood risk. The relevant Flood Risk Precincts (FRP’s) for each of the floodplains are outlined below. Towradgi Creek Floodplain High Flood Risk (and Interim

Riverine Corridor) Precinct This has been defined as the area within the envelop of land subject to a high hydraulic hazard (in accordance with the provisional criteria outlined in the Floodplain Management Manual) in a 100 year flood event together with all land within a corridor 10m from the top of the creek bank. The high flood risk precinct is where high flood damages, potential risk to life, evacuation problems would be anticipated or development would significantly and adversely effect flood behaviour. Most development should be restricted in this precinct. In this precinct, there would be a significant risk of flood damages without compliance with flood related building and planning controls. Medium Flood Risk Precinct

This has been defined as land below the 100 year flood level (plus 0.5m


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freeboard) that is not within the High Flood Risk (and Interim Riverine Corridor) Precinct. It is land subject to low hydraulic hazard (in accordance with the provisional criteria outlined by the Floodplain Management Manual). In this precinct there would still be a significant risk of flood damage, but these damages can be minimised by the application of appropriate development controls. Low Flood Risk Precinct

This has been defined as all other land within the floodplain (ie. within the extent of the probable maximum flood) but not identified within either the High Flood Risk (and Interim Riverine Corridor) or the Medium Flood Risk Precinct, where risk of damages are low for most land uses. The Low Flood Risk Precinct is that area above the 100 year flood (plus 0.5m freeboard) and most land uses would be permitted within this precinct. 2.4 Which Controls Apply to Proposed Developments? The development controls apply to all land within a Flood Risk Precinct described above. The type and stringency of controls have been graded relative to the severity and frequency of potential floods, having regard to categories determined by the relevant Floodplain Risk Management Study and Plan or, if no such study or plan exists, council’s interim considerations. The categories applicable to each floodplain are depicted on the planning matrices contained in the following schedules: • Schedule 3 –Towradgi Creek

Floodplain • Schedule 4 –

Hewitts/Slacky/Woodlands/Tramway/ Tomas Gibson Creeks Floodplain

• Schedule 5 – Allans Creek Floodplain (to be completed)

• Schedule 6 – Fairy/Cabbage Tree Creeks Floodplain (to be completed)

• Schedule 7 – Mullet/Brooks Creeks Floodplain (to be completed)

• Schedule 8 – Minnegang Creek Floodplain (to be completed)

• Schedule 9 – Collins/Wharton/Bellambi Creek Floodplain (to be completed)

• Schedule 10 – Northern Suburbs Floodplain (to be completed)

• Schedule 11 – All other floodplains.

[Council to insert controls for other floodplains as FRMP’s are prepared] 2.4.1 Objectives (a) To ensure the proponents of

development and the community in general are fully aware of the potential flood hazard and consequent risk associated with the use and development of land within the floodplain.

(b) To require developments with

high sensitivity to flood risk (eg. critical public utilities) be sited and designed such that they are subject to no or minimal risk from flooding and have reliable access.

(c) Allow development with a

lower sensitivity to the flood hazard to be located within the floodplain, subject to appropriate design and siting controls, provided that the potential consequences that could still arise from flooding remain acceptable having regard to the State Government’s Flood Policy and the likely expectations of the community in general

(d) To prevent any intensification

of the use of High Flood Risk Precinct or floodways, and wherever appropriate and possible, allow for their conversion to natural waterway corridors.


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(e) To ensure that design and siting

controls required to address the flood hazard do not result in unreasonable impacts upon the amenity or ecology of an area.

(f) To minimise the risk to life by

ensuring the provision of appropriate access from areas affected by flooding up to extreme events.

2.4.2 Performance Criteria (a) The proposed development should

not result in any increased risk to human life.

(b) The additional economic and social

costs which may arise from damage to property from flooding should not be greater than that which can reasonably be managed by the property owner and general community.

(c) The proposal should only be

permitted where effective warning time and reliable access is available for the evacuation of an area potentially affected by floods. Evacuation should be consistent with any relevant or flood evacuation strategy where in existence.

(d) Development should not

detrimentally increase the potential flood affectation on other development or properties either individually or in combination with the cumulative impact of development that is likely to occur in the same floodplain.

(e) Development should not result in

significant impacts upon the amenity of an area by way of unacceptable overshadowing of adjoining properties, privacy impacts (eg. by unsympathetic house-raising) or by being incompatible with the streetscape or character of the locality.

(f) Proposed development must be consistent with ESD principles.

2.4.3 Prescriptive Controls Schedules 3 to 11 outline the controls relevant to each of the floodplains to which this Plan applies. 2.5 Are There Special Requirements for Fencing? 2.5.1 Objectives (a) To ensure that fencing does

not result in the undesirable obstruction of the free flow of floodwaters.

(b) To ensure that fencing does

not become unsafe during floods and potentially become moving debris which threatens the integrity of structures or the safety of people.

2.5.2 Performance Criteria (a) Fencing is to be constructed

in a manner which does not affect the flow of floods so as to detrimentally increase flood affection on surrounding land.

(b) Ability to be certified by a

suitably qualified engineer, that the proposed fencing is adequately constructed so as to withstand the forces of floodwaters, or collapse in a controlled manner to prevent the undesirable impediment of flood waters.


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2.5.3 Prescriptive Controls 2.5.3.1 Fencing within a floodway or

High FRP will not be permissible except for security/ permeable/ open type/safety fences of a type approved by Council.

2.5.3.2 Council will require a

Development Application for all new solid (non-porous) and continuous fences above 0.6m high, in the High and Medium FRP’s unless otherwise stated by exempt and complying development provisions which may be incorporated into Council=s Environmental Planning Instruments from time to time.

2.5.3.3 An applicant will need to demonstrate that the fence would create no impediment to the flow of floodwaters. Appropriate fences must satisfy the following:-

(a) An open collapsible hinged fence

structure or pool type fence; (b) Other than a brick or other masonry

type fence (which will generally not be permitted); or

(c) A fence type and siting criteria as

prescribed by Council. 2.5.3.4 Other forms of fencing will be

considered by Council on merit. 2.6 Special Considerations When assessing proposals for development or other activity within the area to which this Policy applies, Council will take into consideration the following specific matters. (a) The proposal does not have a

significant direct or cumulative detrimental impact on:

i) water quality;

ii) native bushland vegetation;

iii) riparian vegetation; iv) estuaries, wetlands,

lakes or other water bodies;

v) aquatic and terrestrial ecosystems;

vi) indigenous flora and fauna; or

vii) fluvial geomorphology. (b) Development pursued to

mitigate the potential impact of flooding (eg. house raising) must be undertaken in a manner which minimises the impact upon the amenity and character of the locality.

(c) The proposal must not

constrain the orderly and efficient utilisation of the waterways for multiple purposes.

(d) The proposal must not

adversely impact upon the recreational, ecological, aesthetic or utilitarian use of the waterway corridors, and where possible, should provide for their enhancement, in accordance with ESD principles.

(e) Proposals for house raising

must provide appropriate documentation including a report from a suitably qualified engineer to demonstrate the raised structure will not be at risk of failure from the forces of floodwaters and the provision of details such as landscaping and architectural enhancements which ensure that the resultant structure will not result in significant adverse impacts upon the amenity and character of an area.


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3.0 WHAT INFORMATION IS REQUIRED WITH AN APPLICATION TO ADDRESS THIS PLAN?

3.1 Applications must include

information which addresses all relevant controls listed above, and the following matters as applicable.

3.2 Applications for Concessional

Development (see Schedule 2) to an existing dwelling on Flood Prone Land shall be accompanied by documentation from a registered surveyor confirming existing floor levels.

3.3 Development applications affected

by this plan shall be accompanied by a survey plan showing:-

(a) The position of the existing

building/s or proposed building/s; (b) The existing ground levels to

Australian Height Datum around the perimeter of the building and contours of the site; and

(c) The existing or proposed floor levels

to Australian Height Datum. 3.4 Applications for earthworks, filling of

land and subdivision shall be accompanied by a survey plan (with a contour interval of 0.25m) showing relative levels to Australian Height Datum.

3.5 For large scale developments, or

developments in critical situations, particularly where an existing catchment based flood study is not available, a flood study using a fully dynamic one or two dimensional computer model may be required. For smaller developments the existing flood study may be used if available and suitable (eg it contains sufficient local detail), or otherwise a flood study prepared in a manner consistent with the “Australian Rainfall and Runoff” publication, Council’s Drainage Design Code and the Floodplain Management

Manual, will be required. From this study, the following information shall be submitted in plan form:

i) water surface contours;

ii) velocity vectors; iii) velocity and depth product

contours; iv) delineation of flood risk

precincts relevant to individual floodplains; and

v) show both existing and proposed flood profiles for the full range of events for total development including all structures and works (such as revegetation/enhancements).

This information is required for the pre-developed and post-developed scenarios. 3.6 Where the controls for a

particular development proposal require an assessment of structural soundness during potential floods, the following impacts must be addressed:

i) hydrostatic pressure; ii) hydrodynamic pressure;

iii) impact of debris; and

iv) buoyancy forces. Foundations need to be included in the structural analysis.


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SCHEDULE 1 FLOOD COMPATIBLE MATERIALS

BUILDING COMPONENT

FLOOD

COMPATIBLE MATERIAL

BUILDING

COMPONENT

FLOOD

COMPATIBLE MATERIAL

Flooring and Sub-floor Structure

" concrete slab-on-ground monolith construction " suspension reinforced concrete slab.

Doors

" solid panel with water proof adhesives " flush door with marine ply filled with closed cell foam " painted metal construction " aluminium or galvanised steel frame

Floor Covering

" clay tiles " concrete, precast or in situ " concrete tiles " epoxy, formed-in-place " mastic flooring, formed-in-place " rubber sheets or tiles with chemical-set adhesives " silicone floors formed-in-place " vinyl sheets or tiles with chemical-set adhesive " ceramic tiles, fixed with mortar or chemical-set adhesive " asphalt tiles, fixed with water resistant adhesive

Wall and Ceiling Linings

" fibro-cement board " brick, face or glazed " clay tile glazed in waterproof mortar " concrete " concrete block " steel with waterproof applications " stone, natural solid or veneer, waterproof grout " glass blocks " glass " plastic sheeting or wall with waterproof adhesive

Wall Structure

" solid brickwork, blockwork, reinforced, concrete or mass concrete

Insulation Windows

" foam (closed cell types) " aluminium frame with stainless steel rollers or similar corrosion and water resistant material.

Roofing Structure (for Situations Where the Relevant Flood Level is Above the Ceiling)

" reinforced concrete construction " galvanised metal construction

Nails, Bolts, Hinges and Fittings

" brass, nylon or stainless steel " removable pin hinges " hot dipped galvanised steer wire nails or similar


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Electrical and Mechanical Equipment For dwellings constructed on land to which this Policy applies, the electrical and mechanical materials, equipment and installation should conform to the following requirements.

Heating and Air Conditioning Systems Heating and air conditioning systems should, to the maximum extent possible, be installed in areas and spaces of the house above the relevant flood level. When this is not feasible every precaution should be taken to minimise the damage caused by submersion according to the following guidelines.

Main power supply - Subject to the approval of the relevant authority the incoming main commercial power service equipment, including all metering equipment, shall be located above the relevant flood level. Means shall be available to easily disconnect the dwelling from the main power supply.

Fuel - Heating systems using gas or oil as a fuel should have a manually operated valve located in the fuel supply line to enable fuel cut-off.

Wiring - All wiring, power outlets, switches, etc., should, to the maximum extent possible, be located above the relevant flood level. All electrical wiring installed below the relevant flood level should be suitable for continuous submergence in water and should contain no fibrous components. Earth core linkage systems (or safety switches) are to be installed. Only submersible-type splices should be used below the relevant flood level. All conduits located below the relevant designated flood level should be so installed that they will be self-draining if subjected to flooding.

Installation - The heating equipment and fuel storage tanks should be mounted on and securely anchored to a foundation pad of sufficient mass to overcome buoyancy and prevent movement that could damage the fuel supply line. All storage tanks should be vented to an elevation of 600 millimetres above the relevant flood level.

Equipment - All equipment installed below or partially below the relevant flood level should be capable of disconnection by a single plug and socket assembly.

Ducting - All ductwork located below the relevant flood level should be provided with openings for drainage and cleaning. Self draining may be achieved by constructing the ductwork on a suitable grade. Where ductwork must pass through a water-tight wall or floor below the relevant flood level, the ductwork should be protected by a closure assembly operated from above relevant flood level.

Reconnection - Should any electrical device and/or part of the wiring be flooded it should be thoroughly cleaned or replaced and checked by an approved electrical contractor before reconnection.


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SCHEDULE 2 LAND USE CATEGORIES

Sensitive Uses and

Facilities Critical Utilities and

Uses Subdivision Residential

Community centre which may provide an important contribution to the notification or evacuation of the community during flood events; Hospitals; and Nursing Homes.

Hazardous or offensive industry or storage establishment; Housing for older persons or persons with a disability; institutions; Educational establishments; Liquid fuel depot; Public utility (including generating works) undertakings which are essential to evacuation during periods of flood or if affected would unreasonably affect the ability of the community to return to normal activities after flood events; and Telecommunication facilities.

Subdivision of land which involves the creation of new allotments, with potential for further development.

Boarding houses; Camp or caravan park site – long-term sites only (1); Cottage industry; Dual occupancy development; Dwelling; Dwelling house; Granny flat; Health consulting rooms; Home employment; Group homes; Residential flats; Serviced apartments; and Utility installations (other than critical utilities)

(1) As defined by the Local Government (Caravan Park and Camping Grounds) Transitional

Regulation 1993.


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Commercial or

Industrial Tourist Related Development

Recreation or Non-urban Uses

Concessional Development

Brothels; Bulky goods salesroom or showroom; Commercial facilities; Hazardous industry; Heliports; Heavy Industry; Light Industry; Licensed premises; Light industrial retail outlet; Motel; Offensive or hazardous storage establishment; Place of worship; Recreation facility; Registered club; Restaurant; Service station; Sex shop; Shop; Transport terminal; Truck or heavy machinery sale; and Warehouse

Camp or caravan site – short term sites (1) only

Agriculture; Extractive industry; Forestry; Helicopter landing site; Intensive agriculture; Leisure area; Mine; Recreation areas and minor ancillary structures (eg. toilet blocks or kiosks); and Turf farming.

(a) In the case of residential development:

(i) An addition or

alteration to an existing dwelling of not more than 10% or 30m2 (whichever is the lesser) of the habitable floor area which existed at the date of commencement of this Plan;

(ii) The construction of an outbuilding with a maximum floor area of 20m2; or

(iii) Redevelopment for the purposes of substantially reducing the extent of flood affectation to the existing building

(1) As defined by the Local Government (Caravan Park and Camping Grounds) Transitional

Regulation 1993.


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3 2 2or5 2 1 2,4 1 2,42 1 1 1 1 1 1 13 2 2 2 2 2 2 2 1 1

2 2 2 2 1 2 2 2 2 2 1 12,4 * 3,4 4 3,4 * 3,4 1,4 3,4 3 1or3 3 1or34,5 1 1 2,3,5 2,3,5 2,3,5 2,3,5 2,3,5 2,3,5

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Floor Level123

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Flood Affectation1

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Management and Design

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2345

Schedule 3

Management & Design

Planning Consideration

Low Flood Risk High Flood Risk

Floor LevelBuilding Components

Flood AffectationEvacuation

Towradgi Creek FloodplainPlanning & Development Controls

Engineers report to certify that any structure can withstand the forces of floodwater, debris & buoyancy up to & including a 100 year flood plus freeboard

Structural Soundness

(& Interim Riverine Corridor)Medium Flood Risk

All structures to have flood compatible building components below or at the 100 year flood level plus freeboard

All Floor Levels to be equal to or greater than the 20 year flood level plus freeboard unless justified by site specific assessment

Structural Soundness

Freeboard equals an additional height of 500mm

Reliable access for pedestrians required during a 100 year flood

Evacuation

Refer to 'Management & Design' planning consideration for subdivision

Applicant to demonstrate that area is available to store goods above the 100 year flood level plus freeboard

Floor levels of shops to be as close to the design floor level as practical. Where the below the design floor level , more than 30% of the floor area to be above the design floor level or premises to be flood proofed below the design floor level

Building Components & Method

All structures to have flood compatible building components below or at the PMF level plus freeboard

Habitable floor levels to be equal to or greater than the 100 year flood level plus freeboardAll Floor Levels to be equal to or greater than the PMF flood level plus freeboard

Floor levels to be as close to the design floor level as practical & no lower than the existing floor level when undertaking alterations or additions

Applicant to demonstrate that area is available to store goods above the PMF level plus freeboardNo external storage of materials below the design floor level which may cause pollution or be potentially hazardous during any flood

Flood Risk Precincts (FRP's)

Engineers report required to certify that the development will not increase flood affectation elsewhere

The impact of the development on flooding elsewhere to be considered

Applicant to demonstrate that potential development as a consequence of a subdivision proposal can be undertaken in accordance with this PlanSite Emergency Response Flood plan required (except for single dwelling-houses) where floor levels are below the design floor level

The development is to be consistent with any relevant flood evacuation strategy or similar plan

Reliable access for pedestrians or vehicles is required from the building, commencing at a minimum level equal to the lowest habitable floor level to an area of refuge above the PMF level , or a minimum of 40% of the gross floor area of the dwelling to be

Reliable access for pedestrians and vehicles required during a PMF flood

Note: When assessing flood affectation the following must be considered:1. Loss of storage area in the floodplain2. Changes in flood levels & velocities caused by alteration of conveyance of flood waters

Note: 1.Filling of the site, where acceptable to Council, may change the FRP considered to determine the controls applied in the circumstances of individual applications.2. Terms in italics are defined in the glossary of this plan and Schedule 2 specifies development types included in each land use category. These development types are generally as defined within Environmental Planning Instruments applying to the local go

Applicant to demonstrate that any structure can withstand the forces of floodwater, debris & buoyancy up to & including a PMF flood plus freeboard

Applicant to demonstrate that any structure can withstand the forces of floodwater, debris & buoyancy up to & including a 100 year flood plus freeboard, or a PMF plus freeboard if required to satisfy evacuation criteria (see below)


APPENDIX B

PEAK WATER LEVEL PROFILES AND TABULATEDVALUES FOR EXISTING CONDITIONS

TOWRADGI CREEK, WOLLONGONG B-1 BEWSHER CONSULTING PTY LTDFLOODPLAIN RISK MANAGEMENT STUDY June 2003 J829final-Vol1-AppB.doc

APPENDIX B

DESIGN PEAK WATER LEVELS —PROFILES AND TABULATED VALUES FOR EXISTING CONDITIONS

In light of the information provided by the August 1998 flood and inclusion of therequirements of Council’s Conduit Blockage Policy, the MIKE-11 model was updatedand recalibrated as part of the Flood Study Addendum (Bewsher Consulting, 2003).The outcome of this exercise has been a new set of design flood levels, whichincorporates Council’s ‘Conduit Blockage Policy’, that should be used by Council forall future development assessments.

The modelling showed that, in some instances, areas downstream of a blockedstructure (where the floodwaters have been diverted elsewhere) would actually havelower flood levels than if the structure were not blocked. The two reaches where thiswas apparent were on Carr Creek (Branch 6) downstream of the Northern Distributorand Railway Line and on North Corrimal Creek (Branch 5) downstream ofUnderwood Road.

An important part of the MIKE-11 modelling was to determine, for all locations withinthe catchment, which would create the ‘worst flood situation’, a culvert blocked as perthe requirements of Council’s policy or a culvert suffering no blockage at all. Detailsof flood contours for the ‘worst-flood situation’ for various flood sizes for existingconditions (at 0.5m intervals upstream of the Illawarra Railway and at 0.2m intervalsdownstream of the railway) are provided in the following figures in the main body ofthe report:

4 Figure 4.1 — 5 year flood;4 Figure 4.2 — 20 year flood;4 Figure 4.3 — 50 year flood;4 Figure 4.4 — 100 year flood;4 Figure 4.5 — probable maximum flood.

The flood contours depicted on Figures 4.1–4.5 provide the best overview of floodlevels in the Towradgi Creek catchment. However, it should be emphasised thatflood contours are only approximate as flood levels and extents have only beencalculated at MIKE-11 cross-section locations. Between cross-sections, flood levelshave been linearly interpolated. Widths of flood contours have been drawn using theavailable survey information. In some areas, the provision of more accurate groundsurvey may increase or decrease the extent of flooding and the width of the floodcontours. The Flood Study Addendum discusses other approximations and potentialerrors, such as those created by localised obstructions (e.g. fences and sheds) withinthe floodplain.

TOWRADGI CREEK, WOLLONGONG B-2 BEWSHER CONSULTING PTY LTDFLOODPLAIN RISK MANAGEMENT STUDY June 2003 J829final-Vol1-AppB.doc

This Appendix tabulates the design peak water levels from the MIKE-11 modelling forthe 5 year, 20 year, 50 year, 100 year and probable maximum floods (PMF). Floodprofiles for each of these floods are also provided. These flood levels represent theworst flood level scenario derived from the envelope of the unblocked case and theblocked case in accordance with Council’s Conduit Blockage Policy.

Flood levels for individual properties should not be interpolated from the floodcontours provided in Figures 4.1–4.5 or from the tabulated flood levels provided inthis Appendix. To obtain design flood levels for an individual property referenceshould be made to the flood surface layer that has been provided digitally to Council.These flood contours have been derived electronically from the flood surface layer(Bewsher Consulting, 2003).

It should be noted that any changes to the Towradgi Creek catchment as depicted bythe model, could change the flood levels and/or flow velocities in small and/or largefloods. These changes could result from urban development, filling activities orchanges to the amount and type of vegetation within the floodplain.

MIKE 11MIKE 11 MIKE 11MIKE 11 Peak Water level (mAHD)Peak Water level (mAHD) Branch

NameBranch

ChainageProbableMaximum

Flood

100y2h 50y2h 20y2h 5y2h

TOWRADGI 100 43.9 43.6 43.5 43.4 43.2 TOWRADGI 308 38.1 37.6 37.4 37.3 37.1 TOWRADGI 495 33.4 32.8 32.6 32.4 32.1 TOWRADGI 646 29.2 28.4 28.3 28.1 27.6 TOWRADGI 781 27.1 26.3 26.1 25.9 25.6 TOWRADGI 998 24.9 23.7 23.5 23.3 22.8 TOWRADGI 1163 23.7 22.5 22.3 22.0 21.5 TOWRADGI 1453 21.9 20.8 20.7 20.5 20.1 TOWRADGI 1771 21.1 20.4 20.3 20.2 19.9 TOWRADGI 1831 19.0 17.7 17.5 17.2 16.7 TOWRADGI 2102 16.4 15.4 15.2 15.1 14.7 TOWRADGI 2376 15.0 13.8 13.7 13.4 13.1 TOWRADGI 2600 14.3 13.1 13.0 12.9 12.6 TOWRADGI 2625 13.9 12.1 11.7 11.3 10.8 TOWRADGI 2668 13.9 12.1 11.6 11.3 10.7 TOWRADGI 2762 13.9 12.0 11.5 11.1 10.6 TOWRADGI 2781 12.8 10.6 10.4 10.1 9.5 TOWRADGI 3049 10.5 8.1 7.9 7.6 7.2 TOWRADGI 3153 10.4 7.7 7.5 7.2 6.9 TOWRADGI 3190 10.4 7.4 7.1 6.6 5.8 TOWRADGI 3371 10.5 7.4 7.0 6.4 5.6 TOWRADGI 3479 10.5 7.4 7.0 6.4 5.6 TOWRADGI 3515 7.4 5.3 5.1 4.9 4.5 TOWRADGI 3590 7.3 5.3 5.1 4.8 4.5 TOWRADGI 3710 7.1 5.1 5.0 4.7 4.4 TOWRADGI 3740 6.9 5.1 4.9 4.7 4.4 TOWRADGI 3750 6.2 4.6 4.3 3.8 3.2 TOWRADGI 3830 6.5 4.7 4.3 3.9 3.2 TOWRADGI 3991 6.5 4.6 4.3 3.8 3.1 TOWRADGI 4013 5.2 3.8 3.6 3.3 2.9 TOWRADGI 4285 4.7 3.4 3.2 2.9 2.6 TOWRADGI 4521 4.3 2.8 2.7 2.4 2.3 TOWRADGI 4680 4.4 2.9 2.7 2.5 2.3 TOWRADGI 4758 4.4 2.8 2.7 2.5 2.3 TOWRADGI 4986 4.0 2.5 2.5 2.2 2.1 TOWRADGI 4990 3.1 2.3 2.3 2.1 2.0 TOWRADGI 5024 2.8 2.2 2.2 2.0 2.0 TOWRADGI 5117 2.2 2.2 2.2 2.0 2.0

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4600 4800 5000 52000

5

10

15

20

25

30

35

40

45

100 308 495 646 781 998 1163 1453 1771

2102 2376 2600

2781 3049

3190 33713479

3710

38363991

4285 4521 4758 4986

5117

Branch Chainage (m)

Peak

Wat

er le

vel (

mAH

D)

Probable Maximum Flood

100y2h

50y2h

20y2h

5y2h

ADDENDUM TOWRADGI FLOOD STUDYTowradgi Creek (Branch 1) Flood Profiles

Brokers Road

Meadow Street

Northern Distributor

Princes Highway

Pioneer Road

Illawarra Railway

08/05/2003 RESLTFE.WK4

MIKE 11 MIKE 11 Plot Peak Water level (mAHD) Branch

NameBranch

ChainageChainage

(m)ProbableMaximum

Flood

100y2h 50y2h 20y2h 5y2h

BRANCH2 350 350 26.0 25.8 25.7 25.7 25.0 BRANCH2 463 463 26.0 25.8 25.7 25.7 25.0 BRANCH2 480 480 22.9 22.1 21.9 21.8 21.7 BRANCH2 586 586 22.0 21.8 21.7 21.7 21.7 BRANCH2 606 606 20.8 20.2 20.1 20.0 19.9 BRANCH2 676 676 20.1 19.9 19.8 19.8 19.7 WILLIAM-2 100 751 20.1 19.9 19.8 19.8 19.7 WILLIAM-2 175 790 19.4 19.2 19.2 19.2 19.1 BRANCH2 812 812 17.6 17.0 16.9 16.8 16.6 BRANCH2 937 937 15.4 14.9 14.9 14.8 14.6 BRANCH2 1008 1008 15.2 13.8 13.6 13.5 13.3 BRANCH2 1064 1064 15.2 13.6 13.3 13.1 12.9 BRANCH2 1234 1234 15.0 13.4 12.7 12.0 11.2 BRANCH2 1240 1240 14.1 12.3 11.9 11.6 11.1 BRANCH2 1332 1332 13.9 12.2 11.7 11.3 10.8 BRANCH2 1415 1415 13.9 12.2 11.6 11.2 10.8 BRANCH2 1417 1417 13.9 12.0 11.5 11.1 10.6 BRANCH2 1510 1510 13.9 12.0 11.5 11.1 10.6

200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 160010

12

14

16

18

20

22

24

26

Plot Chainage (m)

Peak

Wat

er le

vel (

mAH

D)


100y2h

50y2h

20y2h

5y2h

ADDENDUM TOWRADGI FLOOD STUDYSouth Angels Creek (Branch 2) Flood Profiles

Corrimal Street

Brooker Street

Meadow Street

Williamson Street

Caroline Street Footbridge

Princes Highway


MIKE 11MIKE 11 MIKE 11MIKE 11 PlotPlot Peak Water level (mAHD)Peak Water level (mAHD) Branch Name Branch

ChainageChainage

(m)ProbableMaximum

Flood

100y2h 50y2h 20y2h 5y2h

BRANCH3 100 100 30.3 30.2 30.3 30.3 30.1 BRANCH3 114 114 30.3 30.2 30.3 30.3 30.1 BRANCH3 118 118 29.9 29.5 29.4 29.3 29.2 BRANCH3 186 186 29.8 29.4 29.4 29.3 29.2

BELLAMBI 153 239 28.6 28.4 28.3 28.3 28.2 BELLAMBI 170 256 27.8 27.6 27.5 27.5 27.4 BRANCH3 319 319 26.5 26.3 26.2 26.2 26.1

MEADOW3 130 349 26.1 25.9 25.9 25.9 25.8 MEADOW3 150 369 25.7 25.0 24.9 24.8 24.6

BRANCH3 374 374 25.7 25.0 24.8 24.7 24.4 BRANCH3 399 399 23.8 23.3 23.2 23.1 22.8 BRANCH3 400 400 23.8 23.3 23.2 23.1 22.8 BRANCH3 418 418 22.9 22.5 22.5 22.5 22.2 BRANCH3 437 437 22.8 22.6 22.5 22.5 22.2 BRANCH3 470 470 22.8 22.6 22.5 22.5 22.2 BRANCH3 491 491 22.7 22.2 22.1 22.0 21.9 BRANCH3 543 543 21.7 21.0 21.0 20.8 20.6 BRANCH3 657 657 18.8 18.2 18.1 17.9 17.7 BRANCH3 789 789 17.1 16.5 16.5 16.3 16.2 BRANCH3 794 794 15.9 15.1 15.0 14.9 14.7 BRANCH3 941 941 15.2 13.6 13.3 13.1 12.9

0 200 400 600 800 100012

14

16

18

20

22

24

26

28

30

32

Plot Chainage (m)

Peak

Wat

er le

vel (

mAH

D)


100y2h

50y2h

20y2h

5y2h

ADDENDUM TOWRADGI FLOOD STUDYNorth Angels Creek (Branch 3) Flood Profiles

Bellambi Street

Meadow Street

Tarrawanna Road

Driveway Off AngelStreet


MIKE 11 MIKE 11 Plot Peak Water level (mAHD) Branch Name Branch

ChainageChainage

(m)ProbableMaximum

Flood

100y2h 50y2h 20y2h 5y2h

BRANCH4 100 100 29.7 29.5 29.4 29.3 29.1 BRANCH4 257 257 28.8 28.7 28.6 28.6 28.4

BOWLING-4 150 307 26.9 26.9 26.9 26.9 26.9 BRANCH4 327 327 24.9 24.5 24.4 24.2 23.9 BRANCH4 455 455 23.4 22.6 22.4 22.3 22.0 BRANCH4 574 574 23.4 22.6 22.4 22.3 22.0

AVENUE-4 130 604 23.3 22.5 22.3 22.1 21.9 AVENUE-4 135 609 23.3 22.4 22.3 22.1 21.9 AVENUE-4 146 620 23.3 22.4 22.3 22.1 21.9 AVENUE-4 162 636 23.3 22.4 22.3 22.1 21.9 BRANCH4 700 700 19.5 19.0 18.9 18.8 18.6 BRANCH4 759 759 19.5 18.9 18.8 18.7 18.6 TARRA-4 210 869 18.1 17.9 17.8 17.8 17.7 TARRA-4 255 914 17.0 16.7 16.6 16.6 16.5 TARRA-4 285 944 17.0 16.6 16.5 16.5 16.3 BRANCH4 1069 1069 12.5 11.8 11.6 11.5 11.3 BRANCH4 1273 1273 10.6 9.6 9.5 9.4 9.3 BRANCH4 1424 1424 10.5 8.1 7.9 7.6 7.2 BRANCH4 1494 1494 10.5 8.1 7.9 7.6 7.2

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 16006

8

10

12

14

16

18

20

22

24

26

28

30

Plot Chainage (m)

Peak

Wat

er le

vel (

mAH

D)


100y2h

50y2h

20y2h

5y2h

ADDENDUM TOWRADGI FLOOD STUDYSouth Corrimal Creek (Branch 4) Flood Profiles

Upstream end ofJames Road

Bowling Club

The Avenue

Tarrawanna Road

Princes Highway


MIKE 11MIKE 11 MIKE 11MIKE 11 PlotPlot Peak Water level (mAHD) Branch Name Branch

ChainageChainage

(m)ProbableMaximum

Flood

100y2h 50y2h 20y2h 5y2h

BRANCH5A 0 0 46.0 45.5 45.4 45.3 44.8 BRANCH5A 66 66 43.2 42.8 42.7 42.6 42.4 BRANCH5A 118 118 41.6 41.0 40.9 40.7 40.4 BRANCH5A 245 245 36.6 35.7 35.7 35.5 35.0 BRANCH5A 295 295 34.2 33.3 33.2 33.0 32.5 BRANCH5 139 334 33.8 32.9 32.8 32.6 32.3 BRANCH5 165 360 33.9 33.0 32.8 32.7 32.3 LEMRAC-5 112 372 31.9 31.6 31.5 31.4 31.3 LEMRAC-5 146 406 31.4 31.0 30.9 30.8 30.6 LEMRAC-5 169 429 31.2 30.8 30.7 30.5 30.3 LEMRAC-5 183 443 31.2 30.9 30.7 30.5 30.2 LEMRAC-5 197 457 31.1 30.8 30.6 30.4 30.0 LEMRAC5A 209 469 31.1 30.9 30.7 30.5 30.0 BRANCH5 268 463 31.1 30.9 30.7 30.5 29.9 BRANCH5 303 498 30.6 30.7 30.5 30.3 29.7 BRANCH5 326 521 29.8 29.7 29.5 29.3 28.8 BRANCH5 337 532 29.4 29.4 29.2 29.0 28.5 BRANCH5 361 556 28.6 28.3 28.1 28.0 27.6 BRANCH5 400 595 28.0 27.4 27.3 27.2 27.0 BRANCH5 440 635 27.9 27.3 27.3 27.2 26.8 BRANCH5 457 652 27.8 27.3 27.2 27.1 26.7 BRANCH5 497 692 27.8 27.1 27.0 26.9 26.7 TARRA-5 127 719 27.3 26.6 26.5 26.4 26.2 TARRA-5 135 727 26.7 26.3 26.2 26.2 26.1 TARRA-5 164 756 26.8 26.4 26.3 26.2 26.1 TARRA-5 193 785 26.7 26.3 26.2 26.2 26.1 TARRA-5 234 826 26.6 26.3 26.2 26.2 26.1 TARRA-5 255 847 25.6 25.5 25.5 25.4 25.4 TARRA-5 280 872 24.1 23.5 23.4 23.3 23.1 TARRA-5 312 904 24.0 23.5 23.4 23.3 23.1 TARRA-5 319 911 22.6 22.2 22.1 21.9 21.7 PRINCES-5 407 999 22.6 22.2 22.0 21.9 21.7 PRINCES-5 443 1035 21.1 20.9 20.9 20.9 20.8 BRANCH5 854 1049 19.4 18.5 18.3 18.2 18.1 BRANCH5 962 1157 18.1 17.2 17.0 16.9 16.8 BRANCH5 1044 1239 16.7 15.9 15.8 15.7 15.7 BRANCH5 1050 1245 16.0 15.4 15.4 15.3 15.3 BRANCH5 1110 1305 16.0 15.4 15.4 15.3 15.2 BRANCH5 1187 1382 15.9 15.4 15.4 15.3 15.2 BRANCH5 1238 1433 14.9 13.9 13.8 13.7 13.6 RAIL ST-5 157 1490 14.8 13.8 13.8 13.7 13.6 RAIL ST-5 197 1530 14.8 13.8 13.7 13.7 13.6 RAIL ST-5 201 1534 14.6 13.7 13.6 13.5 13.3

BRANCH5 1350 1545 14.6 13.7 13.6 13.5 13.3 BRANCH5 1516 1711 14.6 13.6 13.5 13.4 13.3 BRANCH5 1527 1722 12.0 11.0 10.8 10.7 10.4 BRANCH5 1662 1857 11.7 10.7 10.6 10.4 10.1 BRANCH5 1784 1979 10.8 10.1 10.0 9.9 9.7 BRANCH5 1845 2040 10.5 7.4 7.0 6.4 5.6 BRANCH5 2012 2207 10.5 7.4 7.0 6.4 5.6

0 200 400 600 800 1000 1200 1400 1600 1800 2000 22005

10

15

20

25

30

35

40

45

50

66 118 245 295 165 146 268 361400 497135 193 280 407 854 962 1050 1110 11871238 157 1238 1516 1662 1784 1845 2012

Plot Chainage (m)

Pea

k W

ater

lev

el (

mA

HD

)


50y2h

100y2h

20y2h

5y2h

ADDENDUM TOWRADGI FLOOD STUDYNorth Corrimal Creek (Branch 5) Flood Profiles

Upstream end of CoxsAvenue

Lemrac Avenue

Collins Street

Underwood Street

Princes Highway


Bridge in Coke Site



NameBranch


Flood

100y2h 50y2h 20y2h 5y2h

BRANCH6 100 11.5 10.9 10.8 10.7 10.5 BRANCH6 119 11.4 10.9 10.8 10.7 10.4 BRANCH6 171 11.4 10.9 10.8 10.7 10.4 BRANCH6 207 10.5 9.6 9.6 9.5 9.5 BRANCH6 254 10.5 9.6 9.6 9.5 9.5 BRANCH6 264 10.5 9.5 9.4 9.4 9.3 BRANCH6 304 10.5 9.5 9.4 9.4 9.3 BRANCH6 346 10.5 9.5 9.4 9.4 9.3 BRANCH6 379 9.1 8.2 8.1 8.0 7.9 BRANCH6 423.8 8.6 8.0 8.0 7.9 7.7 BRANCH6 439 7.1 6.7 6.6 6.6 6.5 BRANCH6 534 6.5 5.0 5.0 5.0 4.9 BRANCH6 590 6.5 4.6 4.3 3.9 3.5 BRANCH6 637 6.5 4.6 4.3 3.9 3.2 BRANCH6 724 6.5 4.7 4.3 3.9 3.2

0 200 400 600 8002

3

4

5

6

7

8

9

10

11

12

Branch Chainage (m)

Peak

Wat

er le

vel (

mAH

D)


100y2h

50y2h

20y2h

5y2h

ADDENDUM TOWRADGI FLOOD STUDYCarr Creek (Branch 6) Flood Profiles

Dalton Street


Illawarra Railway

Colgong Crescent



NameBranch


Flood

100y2h 50y2h 20y2h 5y2h

BRANCH7 75 4.4 2.9 2.7 2.6 2.6 BRANCH7 80 4.4 2.9 2.7 2.6 2.6 BRANCH7 100 4.4 2.8 2.7 2.5 2.3 BRANCH7 189 4.4 2.8 2.7 2.5 2.3 BRANCH7 206 4.4 2.8 2.7 2.6 2.5 BRANCH7 301 4.4 2.8 2.7 2.6 2.5 BRANCH7 396 4.4 2.8 2.7 2.6 2.5 BRANCH7 442 4.4 2.8 2.7 2.5 2.5 BRANCH7 446 4.4 2.8 2.7 2.5 2.5 BRANCH7 509 4.4 2.8 2.7 2.5 2.5 BRANCH7 525 4.4 2.8 2.7 2.5 2.3 BRANCH7 631 4.4 2.8 2.7 2.5 2.3

0 200 400 6000

1

2

3

4

5

75 100 189 301 396 446 509

Branch Chainage (m)

Peak

Wat

er le

vel (

mAH

D)


100y2h

50y2h

20y2h

5y2h

ADDENDUM TOWRADGI FLOOD STUDYParker Creek (Branch 7) Flood Profiles

Carroll Road Parker Road Cawley Street Lake Parade



APPENDIX C

FLOOD DAMAGE ASSESSMENT

TOWRADGI CREEK, WOLLONGONG BEWSHER CONSULTING PTY LTDFLOODPLAIN RISK MANAGEMENT STUDY June 2003 J829final-Vol1-AppC.doc

i

TABLE OF CONTENTS

Page

APPENDIX C — FLOOD DAMAGE ASSESSMENT....................................................C-1

C.1 TYPES OF FLOOD DAMAGE ......................................................................C-1C.2 DIRECT HOUSE DAMAGE...........................................................................C-1C.3 DIRECT RESIDENTIAL PROPERTY DAMAGES......................................C-4C.4 DIRECT DAMAGE TO COMMERCIAL PREMISES..................................C-4C.5 DIRECT DAMAGE TO INDUSTRIAL PREMISES......................................C-5C.6 INDIRECT FLOOD DAMAGE .......................................................................C-6

C.6.1 Indirect Residential Damage ..................................................................C-7C.6.2 Indirect Commercial and Industrial Damage.........................................C-7

C.7 INFRASTRUCTURE AND SERVICES DAMAGE......................................C-7C.8 INTANGIBLE OR SOCIAL DAMAGES ........................................................C-8C.9 DIRECTIVE FROM THE DEPARTMENT OF INFRASTRUCTURE,

PLANNING AND NATURAL RESOURCES..............................................C-10C.10 POTENTIAL AND ACTUAL FLOOD DAMAGE........................................C-10C.11 REFERENCES.............................................................................................C-11

LIST OF FIGURESPage

FIGURE C.1 ADOPTED DEPTH VERSUS DAMAGE RELATIONSHIPS..............C-3

LIST OF TABLESPage

TABLE C.1: TYPICAL PROPERTIES IN COMMERCIAL CATEGORIES ..............C-5TABLE C.2: TYPICAL PROPERTIES IN INDUSTRIAL CATEGORIES ..................C-6TABLE C.3: ADOPTED SOCIAL DAMAGES ...........................................................C-9TABLE C.4: ACTUAL AND POTENTIAL FLOOD DAMAGES..............................C-11

TOWRADGI CREEK, WOLLONGONG BEWSHER CONSULTING PTY LTDFLOODPLAIN RISK MANAGEMENT STUDY June 2003 J829final-Vol1-AppC.docC-1

APPENDIX C — FLOOD DAMAGE ASSESSMENT

This appendix describes the methodology used in this study for the calculation of flooddamages. Each type of flood damage is described in the subsequent sections.

C.1 TYPES OF FLOOD DAMAGE

The definitions and methodology used in estimating flood damage have been establishedby a number of previous investigations. The two main categories are ‘tangible’ and‘intangible’ damages. Tangible flood damages are those that can be more readilyevaluated in monetary terms, while intangible damages relate to the social cost of floodingand hence are much more difficult to quantify.

C.2 DIRECT HOUSE DAMAGE

Direct house damage relates to the tangible damage caused to the residential structureand its contents from the direct action of floodwaters. This type of damage can also resultfrom sediment and debris entering the premises. In this study, the following componentsof damage have been included in this category:

4 replacement of internal items such as white goods, floor coverings, cupboards,clothes, manchester, etc.;

4 structural damage relating to the repair of floors, walls, windows, doors, decorations,fittings, electrical wiring, etc.;

4 clean-up of the inside of the house and the house itself.

Previous studies and investigations have recommended the ‘stage–damage curve’ as themost reliable method of estimating direct residential damage (both ‘house’ and ‘property’).‘Stage–damage curves’ are relationships that relate the amount of potential flood damagefrom different depths of floodwaters. These relationships can be developed in two ways:

4 from actual data collected from residents after a flood;4 synthetically, by utilising actual data collected for other localities.

There are no actual stage-damage data available for the Towradgi study area. Whilstsignificant amounts of flood loss data were collected in Towradgi and wider areas ofWollongong following the August 1998 flood, this data was not available in a suitable formfor use in the current study. Therefore, the stage–damage relationships for potentialdamages used in this study were based on a collation of information from previousinvestigations.


The previous investigations included:

4 Losses and Lessons from the Sydney Floods of August 1986 — Volumes 1 & 2(Smith et al., 1990). Stage–damage relationships were developed from surveys ofresidences and businesses flooded in the Sydney floods of August 1986. A numberof these properties suffered flooding from the Georges River;

4 Lithgow Floodplain Management Study (Kinhill Engineers Pty Ltd, 1991). Stage–damage curves for this study were based on a variety of past studies, particularlyutilising actual data from the 1986 flood in Bathurst (an 80 year flood event) (KinhillEngineers Pty Ltd, 1988). As part of these two studies, actual interviews wereundertaken of about forty properties;

4 Kemps Creek Flood Management Study (Kinhill Engineers Pty Ltd, 1994). Stage–damage curves for this study were derived from results from residentialquestionnaires. Most of the dwellings were located on large rural-residentialproperties;

4 Proposed Warragamba Flood Mitigation Dam: Environmental Impact Statement (ERM Mitchell McCotter Pty Ltd, 1995). A detailed estimate of flood damages forthe Hawkesbury–Nepean floodplain downstream of Warragamba Dam was carriedout for this study;

4 Cabramatta Creek Floodplain Management Study (Bewsher Consulting, 1999).This report contained a review of information from previous flood damage studies;

4 data collected from flood damage surveys from recent large floods in:

– Inverell in February 1991 (Water Studies Pty Ltd, 1991, Marker & Joy, 1994)– Forbes in August 1990 (Water Studies Pty Ltd, 1992a)– Nyngan in April 1990 (Department of Water Resources, 1990)– Coffs Harbour in November 1996 (Withnall & Tye, 1997 and Hegerty, 1997);

4 Stage–damage relationships used in the ANUFLOOD program (Taylor et al., 1987).

4 Stage–damage relationships used in the FLDAMAGE program (Water Studies,1992b).

All stage–damage data collated were updated to reflect year 2000 dollar values usingBuilding Price Indices and Consumer Price Indices provided in Rawlinsons AustralianConstruction Handbook (Rawlhouse Publishing, 1999 and quarterly update of October1999). An allowance of 8% for the Goods and Services Tax (GST) was also applied toresidential flood damages. No GST increase was applied to business sector damages,since this sector is able to claim input tax credit on business related costs.

The adopted stage-damage data was also factored in accordance with the DIPNR directive(see Section C.9). The stage–damage curves or depth versus damage relationships areshown in Figure C.1.

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Stage–Damage Curve for Direct Residential (House) Damage

$0

$10,000

$20,000

$30,000

$40,000

$50,000

$60,000

$70,000

0.00 0.50 1.00 1.50 2.00 2.50 3.00

depth of flooding above floor (metres)

estim

ated

floo

d da

mag

e(2

000

dolla

rs in

clud

ing

GST

)

Stage–Damage Curve for Direct Residential (Property) Damage

$2,400

$7,100

$0$1,000$2,000$3,000$4,000$5,000$6,000$7,000$8,000

0.0m–0.3m >0.3mdepth of flooding above ground (metres)

estim

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GST

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Stage–Damage Curve for Direct Commercial Damage

$0$20,000$40,000$60,000$80,000

$100,000$120,000$140,000$160,000$180,000

0.00 0.50 1.00 1.50 2.00 2.50 3.00

depth of flooding above work area (metres)

estim

ated

floo

d da

mag

e(2

000

dolla

rs in

clud

ing

GST

)

FIGURE C.1ADOPTED DEPTH VERSUS DAMAGE RELATIONSHIPS

TOWRADGI CREEK, WOLLONGONGFLOODPLAIN RISK MANAGEMENT STUDY C-3

BEWSHER CONSULTING PTY LTD June 2003 J829final-Vol1-FigC1.xls


C.3 DIRECT RESIDENTIAL PROPERTY DAMAGES

This type of tangible damage relates to the damage caused from floodwaters entering theresidential property, without necessarily inundating the floor of the house. In this studyresidential property damage includes:

4 damage external to the house, such as, lawns, driveways, landscaping, gardens,sheds, tennis courts, etc.;

4 damage to vehicles — when considering potential damage, it has been assumedthat no cars are moved out of the path of the floodwaters;

4 clean-up costs for outside the house.

From research from previous studies and technical papers, particularly Joy and Porter(1988) and Handmer et al. (1988), direct residential property damage has been previouslyestimated to be in the following typical ranges (in year 2000 dollar values) for average sizedresidential blocks:

4 $1,200–$2,400 for external property damage;4 $1,800–$2,400 for vehicle damage if the depth of flooding is about 0.3m–0.6m;4 about $3,500 for vehicle damage if depth of flooding is more than about 0.6m;4 $600–$2,400 for clean-up costs, depending on the depth of flooding.

The stage–damage curve, or depth versus damage relationship, for direct residentialproperty damage used in this study, is shown on Figure C.1. This data includes for thefactoring specified in the directive provided by the Department of Infrastructure, Planningand Natural Resources (DIPNR) (formerly the Department of Land and Water Conservation(DLWC)) (Section C.9).

C.4 DIRECT DAMAGE TO COMMERCIAL PREMISES

Commercial premises generally include all shops, offices and small retailers. Key stage–damage information from other studies was used, including flood damage surveys of acake shop, butcher, bank, clothing store, takeaway food shop, newsagent, general storeand an electrical repairer in Nyngan, together with a small general store in Lithgow.

The damage categories for commercial properties have been divided into the followingdamage codes although most properties were classified into the “CM” category:

4 CL: commercial property with comparatively low potential flood damages;4 CM: commercial property with medium potential flood damages;4 CH: commercial property with comparatively high potential flood damages;4 CZ: motels and caravan parks.


Table C.1 provides a list of the types of properties that would typically fall within one of theabove four damage categories.

TABLE C.1: TYPICAL PROPERTIES IN COMMERCIAL CATEGORIES

CODE:CL

Low ValueCM

Medium ValueCH

High ValueCZ

Small Cafes Food shops Electrical shops MotelsFlorists Grocers Chemists Caravan ParksOffices Corner stores Shoe ShopsConsulting rooms Take-away food Clothing StoresPost Office Cake shops Bottle ShopsPet Shops Hairdressers BookshopsChurches Banks NewsagentsLaundrettes Dry Cleaners Sporting goodsPublic Halls Professions Furniture Stores

Small hardware Video HireSmall retail Kitchenware

Restaurants

Types ofBusinessIncluded

InEach

Category

Schools

Figure C.1 shows the adopted stage–damage curve or depth versus damage relationshipused to estimate flood damages in the ‘CM’ category. These damages include externaldamage, internal damage and clean-up, and include for the factoring specified in theDIPNR directive (Section C.9).

C.5 DIRECT DAMAGE TO INDUSTRIAL PREMISES

Industrial properties typically include all industrial type establishments, generally with floorareas between about 200m2 and 1,000m2, such as:

4 automotive repairs, sales and smash repairs;4 garages and service stations;4 timber yards4 kitchen manufacturers and woodworking enterprises;4 hardware stores including those selling paint, plastic products, pool products,

handyman requirements, etc.;4 food/grocery storage, warehouse and distribution centres.

Key stage–damage information was adopted from previous studies and included flooddamage surveys of a car repair garage, hardware store and a small car yard in Nyngan,together with an electrical wholesaler, equipment hire shop, a smash repairer, automotiverepairer, engineering/manufacturer and a car yard in Lithgow. Many business owners inBathurst and Lithgow suggested that they would be “out of business” should 1.5m-2.0m ofwater flood their business.


Industrial properties have been divided into the following damage codes:

4 IL: industrial property with comparatively low potential flood damage;4 IM: industrial property with medium potential flood damage;4 IH: industrial property with comparatively high potential flood damage.

Table C.2 provides a list of the types of properties included in these categories in thisstudy. Data for industrial damages obtained from previous studies was factored accordingto the DIPNR directive (Section C.9).

TABLE C.2: TYPICAL PROPERTIES IN INDUSTRIAL CATEGORIES

CODE:IL

Low ValueIM

Medium ValueIH

High Value

Paints & signs Equipment hire Smash repairsAutomotive repairs Food distribution Panel BeatingSand, gravel & cement Leather & upholstery Car yard salesStorage Carpet warehouses Vehicle ShowroomsTransport & Couriers Agricultural Equipment Service StationsPaving & Landscaping Truck yardsFuel depots Vacant factoriesCouncil & Govt depotsChemical storagePool productsSale yards

Types ofIndustryIncluded

InEach

Category

Plumbing supplies

C.6 INDIRECT FLOOD DAMAGE

Indirect flood damages incurred by the community include:

4 costs for alternative accommodation while houses are inundated, being cleaned ordrying out;

4 loss of trading profit for commercial and industrial enterprises;

4 additional transport and time costs resulting from disruption caused by floodedroadways.

Indirect flood damage is difficult to assess and the amount of calculated damage varieswidely between different studies and technical references. Some references also includeall clean-up costs as indirect damages. In this study clean-up costs have been included inthe direct damages, rather than the indirect damages. It is generally accepted, however,that indirect damages can be assumed to a proportion of the total direct damages.


C.6.1 Indirect Residential Damage

From The Sydney Floods of August 1986 (Water Studies, 1986) indirect residentialdamages were estimated to be about 5% of the total direct residential damages.Conversely, the Nyngan April 1990 Flood Investigation (Department of Water Resources,1990) estimated that indirect residential damages were about 25% of the total directresidential damages. It can be concluded that the Nyngan value would be much higher thanfor the Sydney situation because:

4 in Nyngan, residents were away from home for much longer than in Sydney;

4 most people in Nyngan stayed away from home at public expense rather thanstaying with friends and relatives.

In the absence of any additional information, the ‘Sydney’ value would appear more realisticfor Towradgi — a value of indirect residential damage of 5% of ‘actual’ direct residential(house plus property) damage has therefore been adopted for this study. (The term ‘actualdamage is described in Section C.10).

C.6.2 Indirect Commercial and Industrial Damage

Water Studies (1992) suggests an approximate method, based on actual flood survey data,for calculating indirect commercial and industrial damages:

4 the indirect cost to business is about 5% of the actual direct damage for every daythat trading could be lost.

For example, in Nyngan when about 50 days (i.e. 10 weeks) of trading were lost, theindirect damage to business was in the order of 250% of the direct damages. In Inverell,however, the average number of days of lost trading was only 6 days and the indirectdamage to business was only about 30% of the direct damages.

In the absence of such details for Towradgi, it has been conservatively estimated that theaverage time that trading would be lost could be about 2 weeks. Hence indirectcommercial and industrial damage has been adopted as 55% of the actual directcommercial/industrial damage. This value is also consistent with other references such asTaylor et al. (1987).

C.7 INFRASTRUCTURE AND SERVICES DAMAGE

Infrastructure damage relates to the flood damage caused to public and communityfacilities, such as roads, bridges, water, sewerage, telephone, gas, schools and playingfields. The damage to infrastructure varies significantly from one event to another, and issite specific.


Often, a major component of infrastructure damage is the damage caused by thesubmerging of roads. Water that seeps under the pavement can cause weakening of theroad sub-base, and can ultimately lead to failure of the road, indicated by the formation ofpot-holes. Ideally, roads should be closed until they have dried out. However, where themajority of the inundated roads are suburban roads such as in Towradgi, this is often notpractical.

Actual values of infrastructure damage have been compared with total residential andbusiness flood damage (direct and indirect) for recent floods in Lithgow, Bathurst,Hawkesbury-Nepean, Inverell, Nyngan and Narrabri. These results have showed a trendwhere infrastructure damage tended to be a smaller proportion of the total damage, thelarger the size of the flood. This is understandable, as most damage is likely to occur inrelatively low floods, particularly where infrastructure assets are located below Council’snormal flood planning level.

The following infrastructure damage has been adopted for Towradgi:

4 floods up to the 100 year event — 30% of the total direct and indirect residential andbusiness damage;

4 floods larger than the 100 year event — 20% of the total direct and indirectresidential and business damage.

C.8 INTANGIBLE OR SOCIAL DAMAGES

Intangible flood damages are the most difficult to quantify and there are limited studies thathave attempted to quantify them.

In two surveys of the social impacts of flooding (Lustig and Haeusler, 1989), it was foundthat residents suffered both physical (30% of households) and mental (50% of households)effects because of flooding.

Some of the physical problems that people have suggested included:

4 stress and stress related ailments;4 influenza;4 viral infections;4 heart problems;4 back problems (from lifting and cleaning).

Some of the psychological or sociological problems that people suffered included:

4 irritability;4 nervousness;4 alienation;4 obsessive behaviour;4 strain on family relationships;4 stress from the knowledge that there is no insurance cover for damage caused by

floods.


From the studies of residents whose houses were flooded in Sydney in 1986 and 1988, itappears that residents were much more severely affected when floodwaters entered thehouse, rather than when the flood only covered the ground outside, even where damage toitems outside the house was substantial. This is apparently because the entry of water inthe house is felt to be an invasion of privacy, and because personal items such as familyphotographs are lost. Such losses are frequently regarded by residents as worse thanmonetary losses. Thus the number of flooded households has been used as an indicatorfor quantifying the intangible or social impacts of flooding.

Flooding in urban areas can also have social impacts through disruption to daily routine. The temporary closure of roads, for example, will disrupt traffic flow and may createsignificant problems for many people who become temporarily stranded. Social damagesinvolve both the residential sector and the commercial sector, especially in the case of smallbusinesses. Both suffer from anxiety caused by lack of insurance covering flood damage.

Based on a survey of residents after the August 1986 floods in Sydney, Handmer et al.,(1988) attempted to quantify social damages in terms of the percentage of householdsaffected and the lost time associated with:

4 disruption;4 ill-health;4 hospitalisation.

Based on this reference, and in the absence of more recent information, Table C.3quantifies some of the items suggested by Handmer et al., (1988) to provide the values ofsocial damages that have been adopted in this study for Towradgi.

TABLE C.3: ADOPTED SOCIAL DAMAGES

BELOW FLOOR FLOODING ABOVE FLOOR FLOODING

COMPONENT OFSOCIALDAMAGE

Percentageof flood-affected

households(%)

Averagetime lostper flood-affected

household(days)

Averagecost* for

every flood-affected

household($)

Percentageof flood-affected

households(%)

Averagetime lostper flood-affected

household(days)

Averagecost* for

every flood-affected

household($)

Disruption 100% 25 $3,250 100% 75 $9,750Ill-health 13% 3.4 $60 13% 3.4 $240

Hospitalisation** 5% 7.5 $460 5% 7.5 $460

Total adoptedfor this study

Below floor floodingsay

$3,700Above floor flooding

say$10,000

Note: Costs in year 2000 dollar values.Factoring in accordance with DIPNR directive has not been included (see Section C.9).

Source: Derived from Handmer et al. (1988).* Based on $130 per day.** Additional cost of $1,100 per day added for hospitalisation.


C.9 DIRECTIVE FROM THE DEPARTMENT OF INFRASTRUCTURE,PLANNING AND NATURAL RESOURCES

The calculation of flood damages in this study has also included a recent directive from theformer Department of Land and Water Conservation (DLWC) (now the Department ofInfrastructure, Planning and Natural Resources (DIPNR)) instructing that the amount of flooddamage calculated by all stage–damage relationships that have been based on data fromeither ANUFLOOD (Taylor et al., 1987) and FLDamage (Water Studies, 1992) should bedoubled, pending more detailed analysis of recent actual flood damage data.

It has recently been recognised that the current industry method for the calculation of flooddamages using stage–damage curves appears to underestimate the true damage cost. It is understood that the reason for these anomalies are primarily due to the way originalflood damage data was collected at the time. In particular, the insurance valuation ofdamage was often adopted as approximately one half of the replacement value, asopposed to the ‘new for old’ procedure which is currently used.

It is understood that the Specialist Flood Unit of the DIPNR is currently liaising with relevantindustry groups on this issue. It is expected that a detailed assessment of the anomalieswill be available in the near future and that the Specialist Flood Unit will be recommendingrevised stage–damage curves to be used by industry.

As these new curves were not available for use in the current study, the DIPNR haveadvised Council that all stage–damage curves utilised in the study be factored by amultiplier of 2.0.

C.10 POTENTIAL AND ACTUAL FLOOD DAMAGE

All the calculation techniques for estimating flood damages described above relate to the‘potential’ flood damage, as they represent a situation where damages are not mitigatedin any way. ‘Actual’ damages make allowances for mitigating effects, such as:

4 the flood awareness of the community;

4 the available and effective warning time;

4 the ability of residents to relocate goods and possessions away from flood waters.

From inferred relationships by Water Studies Pty Ltd (1992b), between available warningtime, level of flood awareness and ratios of actual to potential damage for four historicalflood damage surveys, actual damages are likely to be significantly less than potentialdamages in a community experienced in dealing with floods where effective warning timesare greater than about 12S24 hours. The studies have shown that even with minimaleffective warning time, direct residential property damage can be reduced by about 50%- this relates directly to people saving their cars first, by moving them to locations above thelevel of the floodwaters.


In the Towradgi catchment however, effective warning times are much less than twelvehours, and may only be minutes in some cases. Therefore, smaller savings in flooddamages could be expected. Table C.4 summarises the adopted relationships betweenactual and potential flood damages used in this study.

TABLE C.4: ACTUAL AND POTENTIAL FLOOD DAMAGES

TYPE OF FLOOD DAMAGE RATIO OF ACTUAL TO POTENTIAL FLOOD DAMAGE

Direct house damage 90%Direct residential property damage 90%Direct commercial and industrial damage 90%Infrastructure damage 100%Social/Intangible damage 90%

C.11 REFERENCES

Bewsher Consulting Pty Ltd. 1999. Cabramatta Creek Floodplain management Study. Report prepared for Liverpool City Council

Department of Water Resources (NSW). 1990. Nyngan April 1990 Flood Investigation.Department of Water Resources.

ERM Mitchell McCotter Pty Ltd. 1995. Proposed Warragamba Flood Mitigation Dam:Environmental Impact Statement. Volumes 1, 2 and 3. Report prepared for Sydney Water.

Handmer, J.W., D.I. Smith and T.L. Lustig. 1988. The Sydney Floods of 1986: Warnings,Damages, Policy and the Future. In Proceedings of Hydrology and Water ResourcesSymposium, 1988. Sydney: Institution of Engineers, Australia.

Hegerty, K.L., 1997. Northern Tributaries of Coffs Creek — November 1996 Storm Event. In proceeding of Clear Water, A Technical Response — Stormwater Industry Conference.Coffs Harbour. 26B29 April 1997.

Joy, C.S. and M.F. Porter. 1988. A Residential Flood Damage Survey after the SydneyFloods of August 1986. In Proceedings of Hydrology and Water Resources Symposium,1988. Sydney: Institution of Engineers, Australia.

Kinhill Engineers Pty. Ltd. 1988. Bathurst Floodplain Management Study. Report preparedfor Bathurst City Council.

Kinhill Engineers Pty. Ltd. 1991. Lithgow Floodplain Management Study. Report preparedfor Council of the City of Greater Lithgow.

Kinhill Engineers Pty Ltd. 1994. Kemps Creek Flood Management Study. Reportprepared for Liverpool City Council.


Lustig, T.L. and T. Haeusler. 1989. Social and Economic Effects of Floods. In proceedingsof 29th Annual Conference of Flood Mitigation Authorities of NSW. (Eurobodalla) 1989.

Marker, M.S. and C.S. Joy. 1994. The Cost of February 1991 Flood Damage in Inverell. In proceedings of 34th Annual Flood Mitigation Conference. Inverell NSW. May 1994.

Rawlhouse Publishing Pty Ltd. 1999. Rawlinsons Australian Construction Handbook(including quarterly update of October 1999). Rawlhouse Publishing Pty Ltd, Perth.

Smith, D.I., J.W. Handmer, M.A. Greenaway, T.L. Lustig. 1990. Losses and Lessons fromthe Sydney Floods of August 1986 — Volumes 1 and 2. Report prepared for Public WorksDepartment (NSW) and Department of Water Resources (NSW). Centre for Resource andEnvironmental Studies.

Taylor, J.A., M.A. Greenaway and D.I. Smith. 1987. ANUFLOOD — Programmer's Guideand User's Manual. Centre for Resource and Environmental Studies.

Water Studies Pty Ltd. 1986. The Sydney Floods of August 1986, Volume 1: ResidentialFlood Survey. Report prepared for Public Works Department (NSW). Centre for Resourceand Environmental Studies.

Water Studies Pty Ltd. 1991. Inverell Flood Damage Study. Report prepared forDepartment of Water Resources (NSW).

Water Studies Pty Ltd. 1992a. Forbes Flood Damage Study. Report prepared forDepartment of Water Resources (NSW).

Water Studies Pty Ltd. 1992b. User Manual ‘FLDAMAGE’. Water Studies Pty. Ltd.

Withnall, B.A. and I.J. Tye. 1997. Coffs Creek Flood of 23 November 1996 — DataCollection, Compilation and Assessment. In proceeding of Clear Water, A TechnicalResponse — Stormwater Industry Conference. Coffs Harbour. 26B29 April 1997.


APPENDIX D

FLOOD DAMAGE ESTIMATESFOR

INDIVIDUAL CREEKS

SUMMARY OF INUNDATED PROPERTIES AND FLOOD DAMAGESExisting Flood Conditions

Residential, Industrial, Commercial and Public Sector Properties Total TotalArea No. of houses and properties 'predicted' 'predicted'

PMF 100 Year 50 Year 20 Year 5 Year Flood Risk Precinct actual actualWithin Above Within Above Within Above Within Above Within Above damages damagesProp Floor Prop Floor Prop Floor Prop Floor Prop Floor High+R Med Low None (AAD) (NPV)

($) ($)

TOTAL 648 474 353 131 299 101 251 82 182 46 418 458 141 21 1,200,000 14,280,000

Branch 1 - Towradgi Creek 257 199 87 34 66 27 46 20 27 4 136 120 96 8 310,000 3,560,000Branch 2 - South Angels Creek 27 9 9 1 7 1 6 1 4 1 55 9 2 0 20,000 220,000Branch 3 - North Angels Creek 26 12 13 8 12 7 5 6 4 3 24 26 2 2 40,000 480,000Branch 4 - South Corrimal Creek 36 15 21 9 20 7 18 7 18 4 61 36 5 1 100,000 1,240,000Branch 5 - North Corrimal Creek 99 70 73 30 61 27 55 25 43 21 101 89 5 5 380,000 4,550,000

Branch 6 - Carr Creek 83 56 60 22 59 17 57 17 38 11 25 76 10 3 170,000 2,120,000Branch 7 - Parker Creek 120 113 90 27 74 15 64 6 48 2 16 102 21 2 190,000 2,130,000Unknown 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Unknown 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Unknown 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Unknown 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Unknown 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Unknown 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Residential PropertiesArea No. of houses and properties AAD - Actual

PMF 100 Year 50 Year 20 Year 5 Year Flood Risk Precinct Direct Direct Total Indirect SocialWithin Above Within Above Within Above Within Above Within Above property house direct residential damagesProp Floor Prop Floor Prop Floor Prop Floor Prop Floor High+R Med Low None damage damage residential

($) ($) ($) ($) ($)

TOTAL 626 451 339 115 285 86 238 67 171 34 343 392 136 15 323,000 402,000 724,000 36,000 83,000

Branch 1 - Towradgi Creek 250 194 85 33 64 27 45 20 27 4 110 117 94 7 81,000 132,000 212,000 11,000 21,000Branch 2 - South Angels Creek 27 9 9 1 7 1 6 1 4 1 49 9 2 0 9,000 3,000 12,000 1,000 2,000Branch 3 - North Angels Creek 26 11 13 7 12 6 5 5 4 3 19 19 2 1 8,000 17,000 25,000 1,000 3,000Branch 4 - South Corrimal Creek 31 13 17 7 16 5 14 5 14 3 54 18 5 1 25,000 40,000 65,000 3,000 6,000Branch 5 - North Corrimal Creek 91 57 67 20 55 17 49 15 38 12 72 53 3 1 77,000 94,000 171,000 9,000 19,000

Branch 6 - Carr Creek 81 54 58 20 57 15 55 15 36 9 24 74 9 3 58,000 51,000 109,000 5,000 16,000Branch 7 - Parker Creek 120 113 90 27 74 15 64 6 48 2 15 102 21 2 65,000 65,000 129,000 6,000 17,000Unknown 0 0 0 0 0Unknown 0 0 0 0 0Unknown 0 0 0 0 0Unknown 0 0 0 0 0Unknown 0 0 0 0 0Unknown 0 0 0 0 0

Industrial, Commercial and Public Sector PropertiesArea No. of buildings and properties AAD - Actual

PMF 100 Year 50 Year 20 Year 5 Year Flood Risk Precinct Direct Indirect Infrastructure TotalWithin Above Within Above Within Above Within Above Within Above industrial & industrial & & public sector Prop Floor Prop Floor Prop Floor Prop Floor Prop Floor High+R Med Low None commercial commercial damage damage

($) ($) ($) ($)

TOTAL 22 23 14 16 14 15 13 15 11 12 75 66 5 6 82,000 45,000 234,000 361,000

Branch 1 - Towradgi Creek 7 5 2 1 2 0 1 0 0 0 26 3 2 1 5,000 3,000 60,000 68,000Branch 2 - South Angels Creek 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 3,000 3,000Branch 3 - North Angels Creek 0 1 0 1 0 1 0 1 0 0 5 7 0 1 1,000 1,000 8,000 10,000Branch 4 - South Corrimal Creek 5 2 4 2 4 2 4 2 4 1 7 18 0 0 3,000 2,000 21,000 26,000Branch 5 - North Corrimal Creek 8 13 6 10 6 10 6 10 5 9 29 36 2 4 67,000 37,000 72,000 176,000

Branch 6 - Carr Creek 2 2 2 2 2 2 2 2 2 2 1 2 1 0 6,000 3,000 35,000 44,000Branch 7 - Parker Creek 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 35,000 35,000Unknown 0 0 0 0Unknown 0 0 0 0Unknown 0 0 0 0Unknown 0 0 0 0Unknown 0 0 0 0Unknown 0 0 0 0

SUMMARY OF POTENTIALLY FLOOD-AFFECTED PROPERTIES D-1 BEWSHER CONSULTING PTY LTD (J829DAM9.WK4; 23/05/2003)

POTENTIAL FLOOD DAMAGESExisting Flood Conditions

TOTAL

Residential properties Industrial, commercial & public sector propertiesFlood size* No. properties Flood damages No. properties** Flood damages Social Total

Property Max House Max Flood Risk Precinct Direct Direct Total Indirect Property Max Work Max Flood Risk Precinct Direct Indirect Infrastructure damages potentialARI AEP flood depth flood depth property house direct residential flood depth area depth industrial & industrial & & public sector damages

liable liable High+R Med Low None damage damage residential liable flood High+R Med Low None commercial commercial damage (years) (%) (m) (m) ($) ($) ($) ($) (m) liable (m) ($) ($) ($) ($) ($)

343 392 136 15 75 66 5 6PMF 0% 626 4.56 451 3.20 11,428,400 31,796,000 43,224,000 1,945,000 22 2.43 23 1.93 2,757,300 1,365,000 9,196,000 2,766,000 61,250,000100 1% 339 2.70 115 1.99 4,787,600 5,034,000 9,822,000 442,000 14 1.37 16 1.05 1,056,300 523,000 3,263,000 1,148,000 16,250,00050 2% 285 2.53 86 1.83 3,737,800 3,804,000 7,542,000 339,000 14 1.29 15 0.97 898,100 444,000 2,532,000 934,000 12,690,00020 5% 238 2.50 67 1.69 2,895,000 2,678,000 5,573,000 251,000 13 1.20 15 0.88 786,300 389,000 1,908,000 794,000 9,700,00010 10% 216 2.48 56 1.60 2,522,000 2,147,000 4,670,000 210,000 12 1.12 14 0.82 707,000 350,000 1,613,000 678,000 8,230,0005 20% 171 2.45 34 1.40 1,776,800 1,086,000 2,863,000 129,000 11 0.97 12 0.70 549,100 272,000 1,024,000 447,000 5,280,000

Average annual damage (AAD): 574,000 608,000 1,182,000 53,000 154,000 76,000 378,000 149,000 1,990,000

Present value of potential damages

Discount No.rate years4% 20 7,801,000 8,263,000 16,064,000 720,000 2,093,000 1,033,000 5,137,000 2,025,000 27,070,0007% 20 6,081,000 6,441,000 12,522,000 561,000 1,631,000 805,000 4,005,000 1,579,000 21,100,00010% 20 4,887,000 5,176,000 10,063,000 451,000 1,311,000 647,000 3,218,000 1,269,000 16,960,000

sum of house 5% 55% 20% : PMFand property of total direct of total direct 30% : 50yr, 100yr

damage actual actual 30% : 20yr, 10yrdamage damage and 5yr

"PREDICTED" ACTUAL FLOOD DAMAGESExisting Flood Conditions

TOTAL

Residential properties Industrial, commercial & public sector properties Flood size* No. properties Flood damages No. properties** Flood damages Social Total

Property Max House Max Flood Risk Precinct Direct Direct Total Indirect Property Max Work Max Flood Risk Precinct Direct Indirect Infrastructure damages 'predicted'ARI AEP flood depth flood depth property house direct residential flood depth area depth industrial & industrial & & public sector actual

liable liable High+R Med Low None damage damage residential liable flood High+R Med Low None commercial commercial damage damages(years) (%) (m) (m) ($) ($) ($) ($) (m) liable (m) ($) ($) ($) ($)

Actual damage as a percentage ofpotential damages: 90% 90% 90% 95% 90%

343 392 136 15 75 66 5 6PMF 0% 626 4.56 451 3.20 10,286,000 28,616,000 38,902,000 1,945,000 22 2.43 23 1.93 2,482,000 1,365,000 8,736,000 2,489,000 55,920,000100 1% 339 2.70 115 1.99 4,309,000 4,531,000 8,840,000 442,000 14 1.37 16 1.05 951,000 523,000 3,100,000 1,033,000 14,890,00050 2% 285 2.53 86 1.83 3,364,000 3,424,000 6,788,000 339,000 14 1.29 15 0.97 808,000 444,000 2,405,000 841,000 11,630,00020 5% 238 2.50 67 1.69 2,606,000 2,410,000 5,016,000 251,000 13 1.20 15 0.88 708,000 389,000 1,813,000 715,000 8,890,00010 10% 216 2.48 56 1.60 2,270,000 1,932,000 4,202,000 210,000 12 1.12 14 0.82 636,000 350,000 1,532,000 610,000 7,540,0005 20% 171 2.45 34 1.40 1,599,000 977,000 2,576,000 129,000 11 0.97 12 0.70 494,000 272,000 973,000 402,000 4,850,000

Average annual damage (AAD) 323,000 402,000 724,000 36,000 82,000 45,000 234,000 83,000 1,200,000

Present value of actual damages

Discount No.rate years4% 20 4,390,000 5,463,000 9,839,000 489,000 1,114,000 612,000 5,137,000 1,128,000 18,320,0007% 20 3,422,000 4,259,000 7,670,000 381,000 869,000 477,000 4,005,000 879,000 14,280,00010% 20 2,750,000 3,422,000 6,164,000 306,000 698,000 383,000 3,218,000 707,000 11,480,000



Notes: * AEP = annual exceedance probability (chance of flood occurring in any one year)ARI = average recurrence interval

** No. of properties includes all industrial, commercial and public sector properties.*** Infrastructure damage = a percentage of total direct + indirect residential + business damage (as shown)

**** Damage in the less than the 5 year flood has assumed to be nil.



Branch 1 - Towradgi Creek




110 117 94 7 26 3 2 1PMF 0% 250 4.56 194 3.20 4,574,400 13,248,000 17,822,000 802,000 7 2.43 5 1.93 1,141,400 565,000 3,793,000 1,119,000 25,240,000100 1% 85 2.70 33 1.34 1,142,000 1,708,000 2,850,000 128,000 2 0.53 1 0.03 24,000 12,000 862,000 286,000 4,160,00050 2% 64 2.44 27 1.03 863,800 1,224,000 2,088,000 94,000 2 0.32 0 0.00 0 0 626,000 228,000 3,040,00020 5% 45 2.21 20 0.57 624,200 666,000 1,290,000 58,000 1 0.09 0 0.00 0 0 387,000 167,000 1,900,00010 10% 39 2.10 15 0.45 522,000 469,000 990,000 45,000 1 0.06 0 0.00 0 0 297,000 133,000 1,470,0005 20% 27 1.87 4 0.21 316,600 74,000 391,000 18,000 0 0.00 0 0.00 0 0 117,000 66,000 590,000

Average annual damage (AAD): 132,000 173,000 305,000 14,000 6,000 3,000 84,000 33,000 450,000


Discount No.rate years4% 20 1,794,000 2,351,000 4,145,000 190,000 82,000 41,000 1,142,000 448,000 6,050,0007% 20 1,398,000 1,833,000 3,231,000 148,000 64,000 32,000 890,000 350,000 4,720,00010% 20 1,124,000 1,473,000 2,597,000 119,000 51,000 26,000 715,000 281,000 3,790,000




Branch 1 - Towradgi Creek





110 117 94 7 26 3 2 1PMF 0% 250 4.56 194 3.20 4,117,000 11,923,000 16,040,000 802,000 7 2.43 5 1.93 1,027,000 565,000 3,603,000 1,007,000 23,040,000100 1% 85 2.70 33 1.34 1,028,000 1,537,000 2,565,000 128,000 2 0.53 1 0.03 22,000 12,000 819,000 257,000 3,800,00050 2% 64 2.44 27 1.03 777,000 1,102,000 1,879,000 94,000 2 0.32 0 0.00 0 0 595,000 205,000 2,770,00020 5% 45 2.21 20 0.57 562,000 599,000 1,161,000 58,000 1 0.09 0 0.00 0 0 368,000 150,000 1,740,00010 10% 39 2.10 15 0.45 470,000 422,000 892,000 45,000 1 0.06 0 0.00 0 0 282,000 120,000 1,340,0005 20% 27 1.87 4 0.21 285,000 67,000 352,000 18,000 0 0.00 0 0.00 0 0 111,000 59,000 540,000

Average annual damage (AAD) 81,000 132,000 212,000 11,000 5,000 3,000 60,000 21,000 310,000


Discount No.rate years4% 20 1,101,000 1,794,000 2,881,000 149,000 68,000 41,000 1,142,000 285,000 4,570,0007% 20 858,000 1,398,000 2,246,000 117,000 53,000 32,000 890,000 222,000 3,560,00010% 20 690,000 1,124,000 1,805,000 94,000 43,000 26,000 715,000 179,000 2,860,000




** No. of properties includes all industrial, commercial and public sector properties.*** Infrastructure damage = a percentage of total direct + indirect residential + business damage (as shown)**** Damage in the less than the 5 year flood has assumed to be nil.



Branch 2 - South Angels Creek




49 9 2 0 6 0 0 0PMF 0% 27 1.96 9 0.73 367,400 274,000 641,000 29,000 0 0.00 0 0.00 0 0 128,000 81,000 880,000100 1% 9 1.26 1 0.16 115,800 26,000 142,000 6,000 0 0.00 0 0.00 0 0 43,000 21,000 210,00050 2% 7 1.16 1 0.11 97,200 26,000 123,000 6,000 0 0.00 0 0.00 0 0 37,000 17,000 180,00020 5% 6 1.06 1 0.08 81,200 16,000 97,000 4,000 0 0.00 0 0.00 0 0 29,000 15,000 150,00010 10% 5 1.04 1 0.06 75,000 16,000 91,000 4,000 0 0.00 0 0.00 0 0 27,000 14,000 140,0005 20% 4 1.00 1 0.03 62,600 16,000 79,000 4,000 0 0.00 0 0.00 0 0 24,000 11,000 120,000

Average annual damage (AAD): 17,000 5,000 22,000 1,000 0 0 6,000 3,000 30,000


Discount No.rate years4% 20 231,000 68,000 299,000 14,000 0 0 82,000 41,000 440,0007% 20 180,000 53,000 233,000 11,000 0 0 64,000 32,000 340,00010% 20 145,000 43,000 187,000 9,000 0 0 51,000 26,000 270,000




Branch 2 - South Angels Creek





49 9 2 0 6 0 0 0PMF 0% 27 1.96 9 0.73 331,000 247,000 578,000 29,000 0 0.00 0 0.00 0 0 122,000 73,000 800,000100 1% 9 1.26 1 0.16 104,000 23,000 127,000 6,000 0 0.00 0 0.00 0 0 41,000 19,000 190,00050 2% 7 1.16 1 0.11 87,000 23,000 110,000 6,000 0 0.00 0 0.00 0 0 35,000 15,000 170,00020 5% 6 1.06 1 0.08 73,000 14,000 87,000 4,000 0 0.00 0 0.00 0 0 28,000 14,000 130,00010 10% 5 1.04 1 0.06 68,000 14,000 82,000 4,000 0 0.00 0 0.00 0 0 26,000 13,000 130,0005 20% 4 1.00 1 0.03 56,000 14,000 70,000 4,000 0 0.00 0 0.00 0 0 23,000 10,000 110,000

Average annual damage (AAD) 9,000 3,000 12,000 1,000 0 0 3,000 2,000 20,000


Discount No.rate years4% 20 122,000 41,000 163,000 14,000 0 0 82,000 27,000 290,0007% 20 95,000 32,000 127,000 11,000 0 0 64,000 21,000 220,00010% 20 77,000 26,000 102,000 9,000 0 0 51,000 17,000 180,000







Branch 3 - North Angels Creek




19 19 2 1 5 7 0 1PMF 0% 26 2.25 11 1.26 318,000 514,000 832,000 37,000 0 0.00 1 0.42 38,000 19,000 174,000 87,000 1,190,000100 1% 13 2.01 7 0.95 99,400 248,000 347,000 16,000 0 0.00 1 0.17 10,400 5,000 107,000 49,000 530,00050 2% 12 1.98 6 0.93 92,800 206,000 299,000 13,000 0 0.00 1 0.18 10,400 5,000 93,000 40,000 460,00020 5% 5 1.94 5 0.88 74,600 156,000 231,000 10,000 0 0.00 1 0.11 10,400 5,000 72,000 31,000 360,00010 10% 5 1.85 4 0.79 65,000 138,000 203,000 9,000 0 0.00 1 0.08 7,000 3,000 63,000 28,000 310,0005 20% 4 1.68 3 0.62 45,200 102,000 147,000 7,000 0 0.00 0 0.00 0 0 44,000 21,000 220,000



Discount No.rate years4% 20 204,000 421,000 612,000 27,000 14,000 14,000 190,000 82,000 940,0007% 20 159,000 328,000 477,000 21,000 11,000 11,000 148,000 64,000 730,00010% 20 128,000 264,000 383,000 17,000 9,000 9,000 119,000 51,000 590,000




Branch 3 - North Angels Creek





19 19 2 1 5 7 0 1PMF 0% 26 2.25 11 1.26 286,000 463,000 749,000 37,000 0 0.00 1 0.42 34,000 19,000 165,000 78,000 1,080,000100 1% 13 2.01 7 0.95 89,000 223,000 312,000 16,000 0 0.00 1 0.17 9,000 5,000 102,000 44,000 490,00050 2% 12 1.98 6 0.93 84,000 185,000 269,000 13,000 0 0.00 1 0.18 9,000 5,000 88,000 36,000 420,00020 5% 5 1.94 5 0.88 67,000 140,000 207,000 10,000 0 0.00 1 0.11 9,000 5,000 68,000 28,000 330,00010 10% 5 1.85 4 0.79 59,000 124,000 183,000 9,000 0 0.00 1 0.08 6,000 3,000 60,000 25,000 290,0005 20% 4 1.68 3 0.62 41,000 92,000 133,000 7,000 0 0.00 0 0.00 0 0 42,000 19,000 200,000



Discount No.rate years4% 20 109,000 231,000 340,000 14,000 14,000 14,000 190,000 41,000 610,0007% 20 85,000 180,000 265,000 11,000 11,000 11,000 148,000 32,000 480,00010% 20 68,000 145,000 213,000 9,000 9,000 9,000 119,000 26,000 390,000







Branch 4 - South Corrimal Creek




54 18 5 1 7 18 0 0PMF 0% 31 2.49 13 2.75 516,800 1,006,000 1,523,000 69,000 5 1.28 2 0.77 116,000 57,000 328,000 116,000 2,210,000100 1% 17 1.76 7 1.99 305,000 510,000 815,000 37,000 4 1.15 2 0.36 40,400 20,000 257,000 70,000 1,240,00050 2% 16 1.61 5 1.83 281,000 460,000 741,000 33,000 4 1.10 2 0.28 36,400 18,000 233,000 62,000 1,120,00020 5% 14 1.46 5 1.69 262,400 404,000 666,000 30,000 4 1.04 2 0.21 26,000 13,000 208,000 58,000 1,000,00010 10% 14 1.36 4 1.60 240,000 349,000 589,000 27,000 4 0.99 2 0.18 21,000 10,000 183,000 51,000 880,0005 20% 14 1.17 3 1.40 194,400 240,000 434,000 20,000 4 0.89 1 0.11 10,400 5,000 133,000 37,000 640,000



Discount No.rate years4% 20 666,000 1,006,000 1,672,000 82,000 68,000 27,000 516,000 149,000 2,510,0007% 20 519,000 784,000 1,303,000 64,000 53,000 21,000 403,000 117,000 1,960,00010% 20 417,000 630,000 1,047,000 51,000 43,000 17,000 324,000 94,000 1,580,000




Branch 4 - South Corrimal Creek





54 18 5 1 7 18 0 0PMF 0% 31 2.49 13 2.75 465,000 905,000 1,370,000 69,000 5 1.28 2 0.77 104,000 57,000 312,000 104,000 2,020,000100 1% 17 1.76 7 1.99 275,000 459,000 734,000 37,000 4 1.15 2 0.36 36,000 20,000 244,000 63,000 1,130,00050 2% 16 1.61 5 1.83 253,000 414,000 667,000 33,000 4 1.10 2 0.28 33,000 18,000 221,000 56,000 1,030,00020 5% 14 1.46 5 1.69 236,000 364,000 600,000 30,000 4 1.04 2 0.21 23,000 13,000 198,000 52,000 920,00010 10% 14 1.36 4 1.60 216,000 314,000 530,000 27,000 4 0.99 2 0.18 19,000 10,000 174,000 46,000 810,0005 20% 14 1.17 3 1.40 175,000 216,000 391,000 20,000 4 0.89 1 0.11 9,000 5,000 126,000 33,000 580,000



Discount No.rate years4% 20 340,000 544,000 883,000 41,000 41,000 27,000 516,000 82,000 1,590,0007% 20 265,000 424,000 689,000 32,000 32,000 21,000 403,000 64,000 1,240,00010% 20 213,000 341,000 553,000 26,000 26,000 17,000 324,000 51,000 1,000,000







Branch 5 - North Corrimal Creek




72 53 3 1 29 36 2 4PMF 0% 91 2.20 57 2.04 1,866,000 3,678,000 5,544,000 249,000 8 1.68 13 1.42 1,322,400 655,000 1,373,000 410,000 9,550,000100 1% 67 2.12 20 1.56 1,102,400 1,240,000 2,342,000 105,000 6 1.14 10 1.05 890,400 441,000 970,000 251,000 5,000,00050 2% 55 1.94 17 1.38 894,600 1,046,000 1,941,000 87,000 6 1.10 10 0.97 773,800 383,000 814,000 210,000 4,210,00020 5% 49 1.72 15 1.16 769,200 884,000 1,653,000 74,000 6 1.05 10 0.88 686,000 339,000 702,000 194,000 3,650,00010 10% 45 1.60 14 1.06 663,000 714,000 1,377,000 62,000 6 1.02 10 0.82 629,000 311,000 602,000 167,000 3,150,0005 20% 38 1.37 12 0.87 451,000 374,000 825,000 37,000 5 0.97 9 0.70 513,800 254,000 402,000 112,000 2,140,000



Discount No.rate years4% 20 1,916,000 2,161,000 4,091,000 177,000 1,780,000 883,000 1,712,000 476,000 9,120,0007% 20 1,494,000 1,684,000 3,189,000 138,000 1,388,000 689,000 1,335,000 371,000 7,110,00010% 20 1,200,000 1,354,000 2,563,000 111,000 1,115,000 553,000 1,073,000 298,000 5,710,000




Branch 5 - North Corrimal Creek





72 53 3 1 29 36 2 4PMF 0% 91 2.20 57 2.04 1,679,000 3,310,000 4,989,000 249,000 8 1.68 13 1.42 1,190,000 655,000 1,304,000 369,000 8,760,000100 1% 67 2.12 20 1.56 992,000 1,116,000 2,108,000 105,000 6 1.14 10 1.05 801,000 441,000 922,000 226,000 4,600,00050 2% 55 1.94 17 1.38 805,000 941,000 1,746,000 87,000 6 1.10 10 0.97 696,000 383,000 773,000 189,000 3,870,00020 5% 49 1.72 15 1.16 692,000 796,000 1,488,000 74,000 6 1.05 10 0.88 617,000 339,000 667,000 175,000 3,360,00010 10% 45 1.60 14 1.06 597,000 643,000 1,240,000 62,000 6 1.02 10 0.82 566,000 311,000 572,000 150,000 2,900,0005 20% 38 1.37 12 0.87 406,000 337,000 743,000 37,000 5 0.97 9 0.70 462,000 254,000 382,000 101,000 1,980,000



Discount No.rate years4% 20 1,046,000 1,277,000 2,324,000 122,000 911,000 503,000 1,712,000 258,000 5,830,0007% 20 816,000 996,000 1,812,000 95,000 710,000 392,000 1,335,000 201,000 4,550,00010% 20 656,000 800,000 1,456,000 77,000 570,000 315,000 1,073,000 162,000 3,650,000







Branch 6 - Carr Creek




24 74 9 3 1 2 1 0PMF 0% 81 4.04 54 2.08 1,386,000 2,708,000 4,094,000 184,000 2 1.90 2 1.20 139,500 69,000 847,000 354,000 5,690,000100 1% 58 2.56 20 0.97 814,200 654,000 1,468,000 66,000 2 1.37 2 0.67 91,100 45,000 468,000 199,000 2,340,00050 2% 57 2.53 15 0.89 661,200 496,000 1,157,000 52,000 2 1.29 2 0.59 77,500 39,000 370,000 179,000 1,870,00020 5% 55 2.50 15 0.80 581,000 436,000 1,017,000 46,000 2 1.20 2 0.50 63,900 32,000 324,000 175,000 1,660,00010 10% 49 2.48 13 0.71 532,000 373,000 906,000 41,000 2 1.11 2 0.41 51,000 25,000 287,000 149,000 1,460,0005 20% 36 2.45 9 0.54 434,800 248,000 683,000 31,000 2 0.94 2 0.24 24,900 12,000 212,000 98,000 1,060,000



Discount No.rate years4% 20 1,536,000 1,196,000 2,732,000 122,000 149,000 68,000 829,000 408,000 4,310,0007% 20 1,197,000 932,000 2,129,000 95,000 117,000 53,000 646,000 318,000 3,360,00010% 20 962,000 749,000 1,711,000 77,000 94,000 43,000 519,000 255,000 2,700,000




Branch 6 - Carr Creek





24 74 9 3 1 2 1 0PMF 0% 81 4.04 54 2.08 1,247,000 2,437,000 3,684,000 184,000 2 1.90 2 1.20 126,000 69,000 805,000 319,000 5,190,000100 1% 58 2.56 20 0.97 733,000 589,000 1,322,000 66,000 2 1.37 2 0.67 82,000 45,000 445,000 179,000 2,140,00050 2% 57 2.53 15 0.89 595,000 446,000 1,041,000 52,000 2 1.29 2 0.59 70,000 39,000 352,000 161,000 1,720,00020 5% 55 2.50 15 0.80 523,000 392,000 915,000 46,000 2 1.20 2 0.50 58,000 32,000 308,000 158,000 1,520,00010 10% 49 2.48 13 0.71 479,000 336,000 815,000 41,000 2 1.11 2 0.41 46,000 25,000 273,000 134,000 1,330,0005 20% 36 2.45 9 0.54 391,000 223,000 614,000 31,000 2 0.94 2 0.24 22,000 12,000 201,000 88,000 970,000



Discount No.rate years4% 20 788,000 693,000 1,481,000 68,000 82,000 41,000 829,000 217,000 2,720,0007% 20 614,000 540,000 1,155,000 53,000 64,000 32,000 646,000 170,000 2,120,00010% 20 494,000 434,000 928,000 43,000 51,000 26,000 519,000 136,000 1,700,000






POTENTIAL FLOOD DAMAGESExisting Flood ConditionsBranch 7 - Parker Creek




15 102 21 2 1 0 0 0PMF 0% 120 2.48 113 2.03 2,399,800 10,368,000 12,768,000 575,000 0 0.00 0 0.00 0 0 2,554,000 599,000 16,500,000100 1% 90 0.89 27 0.44 1,208,800 648,000 1,857,000 84,000 0 0.00 0 0.00 0 0 557,000 272,000 2,770,00050 2% 74 0.77 15 0.32 847,200 346,000 1,193,000 54,000 0 0.00 0 0.00 0 0 358,000 198,000 1,800,00020 5% 64 0.64 6 0.19 502,400 116,000 618,000 28,000 0 0.00 0 0.00 0 0 185,000 154,000 990,00010 10% 59 0.61 5 0.15 426,000 88,000 513,000 23,000 0 0.00 0 0.00 0 0 154,000 137,000 830,0005 20% 48 0.54 2 0.09 272,200 32,000 304,000 14,000 0 0.00 0 0.00 0 0 91,000 102,000 510,000

Average annual damage (AAD): 107,000 78,000 185,000 8,000 0 0 49,000 31,000 270,000


Discount No.rate years4% 20 1,454,000 1,060,000 2,514,000 109,000 0 0 666,000 421,000 3,710,0007% 20 1,134,000 826,000 1,960,000 85,000 0 0 519,000 328,000 2,890,00010% 20 911,000 664,000 1,575,000 68,000 0 0 417,000 264,000 2,320,000



"PREDICTED" ACTUAL FLOOD DAMAGESExisting Flood ConditionsBranch 7 - Parker Creek





15 102 21 2 1 0 0 0PMF 0% 120 2.48 113 2.03 2,160,000 9,331,000 11,491,000 575,000 0 0.00 0 0.00 0 0 2,426,000 539,000 15,030,000100 1% 90 0.89 27 0.44 1,088,000 583,000 1,671,000 84,000 0 0.00 0 0.00 0 0 529,000 245,000 2,530,00050 2% 74 0.77 15 0.32 762,000 311,000 1,073,000 54,000 0 0.00 0 0.00 0 0 340,000 178,000 1,650,00020 5% 64 0.64 6 0.19 452,000 104,000 556,000 28,000 0 0.00 0 0.00 0 0 176,000 139,000 900,00010 10% 59 0.61 5 0.15 383,000 79,000 462,000 23,000 0 0.00 0 0.00 0 0 146,000 123,000 750,0005 20% 48 0.54 2 0.09 245,000 29,000 274,000 14,000 0 0.00 0 0.00 0 0 86,000 92,000 470,000

Average annual damage (AAD) 65,000 65,000 129,000 6,000 0 0 35,000 17,000 190,000


Discount No.rate years4% 20 883,000 883,000 1,753,000 82,000 0 0 666,000 231,000 2,730,0007% 20 689,000 689,000 1,367,000 64,000 0 0 519,000 180,000 2,130,00010% 20 553,000 553,000 1,098,000 51,000 0 0 417,000 145,000 1,710,000







APPENDIX E

COMMUNITY QUESTIONNAIREAND

RESPONSE SUMMARY

1TOWRADGI CREEK FLOODPLAIN MANAGEMENT STUDY J829-1.Q#

TOWRADGI CREEK FLOODPLAIN MANAGEMENT STUDY

IMPORTANT COMMUNITY QUESTIONNAIRE

Please complete this questionnaire for the property in which you have an interest. Please placeyour completed questionnaire in the postage paid envelope provided and return it within ten (10)days.

Your House No Street Name Suburb ____________

Name of Business/Organisation (if applicable)

PART A—GENERAL INFORMATION

1. What is your property?(Tick one or more boxes)

a. House Gb. Flat, villa or townhouse Gc. Business (type ) Gd. Vacant land Ge. Other (type ) G

2. What is the residential status of yourproperty ?

a. Owner residing or conductingbusiness at property G

b. Tenant only Gc. Owner not residing nor

conducting business at property Gd. Other (please specify ) G

3. How long have you owned, lived at orconducted business at this property?

a. Less than 1 year Gb. 1 year to 5 years Gc. 5 years to 20 years Gd. More than 20 years ( years) G

4. If you are a resident, how many peoplenormally reside in your house?

a. 1 Gb. 2 Gc. 3 Gd. 4 Ge. More than 4 ( people) G

5. If there is a business at this property howmany people work here?

a. 1 to 3 Gb. 4 to 6 Gc. 7 to 10 Gd. 11 to 20 Ge. More than 20 ( people) G

6. Do you expect to undertake any furtherdevelopment on your land in the future ?

a. None Gb. Minor extensions Gc. New dwelling Gd. Dual occupancy (granny flat) Ge. Subdivision Gf. Other (please specify ) G

7. Have you undertaken any steps to obtainapprovals for further development on yourland ?

a. No Gb. Made preliminary enquiries with Council Gc. Engaged someone to prepare plans Gd. Lodged plans with Council Ge. Have approved plans but not proceeded G

8. If you expect to undertake furtherdevelopment are you considering any of thefollowing measures to reduce flooddamage?

a. Raising floor levels to satisfyCouncil’s minimum requirements G

b. Raising floor levels aboveCouncil’s minimum requirements G

c. Use of flood compatible buildingmaterials G

d. Preparing a plan of action of whatto do in case of flooding G


PART B—ATTITUDES TO FLOOD-PLAIN MANAGEMENT

9. Please rank the following developmenttypes according to which you think are themost important to protect from floods(1=greatest priority to 7=least priority)

a. Commercial or industrial Gb. Residential Gc. Essential community facilities Gd. Critical utilities Ge. Minor development and additions Gf. Recreation or agricultural land Gg. New residential subdivisions G

10. What level of control do you considerCouncil should place on new developmentto minimise flood related risks ?(Tick more than one box if required)

a. Prohibit all development on landwith any potential to flood G

b. Prohibit all development only inthose locations that would beextremely hazardous to personsor property due to the depth orvelocity of floodwaters, orevacuation difficulties G

c. Place restrictions on developmentwhich reduce the potential forflood damage (e.g. minimum floorlevel controls or the use offlood compatible building materials) G

d. Advise of the flood risks, but allow theindividual a choice as to whether theydevelop or not, provided steps are takento minimise potential flood risks G

e. Provide no advice regarding thepotential to flooding or measuresthat could minimise potentialflood risks G

11. What notifications do you consider Councilshould give about the potential floodaffectation of individual properties?(Tick more than one box if required)

a. Advise every resident and propertyowner on a regular basis of the

known potential flood threat Gb. Advise every resident and property

owner on a regular basis ofCouncil’s policies on the control ofland potentially affected by flooding G

c. Advise prospective purchasers ofproperty or those who enquire ofCouncil’s policies on the control

of development on land potentially affected by flooding G

d. Provide no notifications G

12. Below is a list of possible options thatmay be looked at to try to minimise theeffects of flooding in the study area.

This list is not exhaustive and is in no specificorder of importance. Please indicate (Yes orNo) which options you favour or think shouldbe investigated in detail.

Leave the boxes blank if undecided.Y N

a. Construction of permanent levees G Gb. Widening and/or dredging of the

watercourses G Gc. Removal of floodplain

obstructions G Gd. Council purchase of the most

severely affected flood-liableproperties G G

e. Raising of houses above the 100 year flood level G G

f. Flood proofing of individual properties by waterproofing walls, putting shutters acrossdoors, etc G G

g. Controls on future development inflood-liable areas (e.g. minimumfloor levels, controls on extent offilling allowed on property etc.) G G

h. Improvements to flood warning before a flood G G

I. Better evacuation and emergency assistance plans G G

j. Public education, community participation and flood awareness programs G G

k. Making sure all informationabout the potential risks offlooding is available to allresidents and business owners G G

l. Providing a certificate to allresidents stating whether theirproperty is flood affected G G

m. Making sure residents andbusiness owners have Flood ActionPlans — these outline WHATpeople should do, WHERE theyshould go and WHO they shouldcontact in a flood G G

n. Installing some flood markers(for example, on telegraph poles) toact as constant reminders of theheights of previous floods G G


If you have any other information which you think would be relevant, please provide your telephone numberso that we may contact you.

Work Phone: . . . . . . . . . . . . . . . . (Ask for . . . . . . . . . . . . . . . . )Best time to call is . . . . . . . . . . . . . . . . . . . . . . . Home Phone: . . . . . . . . . . . . . . . . (Ask for . . . . . . . . . . . . . . . . )Best time to call is . . . . . . . . . . . . . . . . . . . . . . .

What are the most important flooding issues you think should be addressed in this study?

Please place your completed questionnaire in the postage paid envelope provided and return it within ten days.

No postage stamp is required. If you have misplaced the supplied envelope or wish to send an additionalsubmission the address is:

Reply paid Permit Number 32TOWRADGI CREEK FLOODPLAIN QUESTIONNAIRE

Bewsher Consulting Pty LtdPO Box 352,Epping NSW 1710

For additional questionnaires or further information about the Towradgi Creek Floodplain Management Study andPlan, please contact either:

Mr Rolyn Sario Mr Don StillProject Engineer Bewsher Consulting Pty LtdWollongong City Council PO Box 352Locked Bag 8821 EPPING NSW 1710SOUTH COAST MAIL CENTRE NSW 2521 Phone: (02) 9868 1966Phone: (02) 4227 7111 Facsimile: (02) 9868 5759.Facsimile: (02) 4227 7277 E-mail: [email protected]: [email protected]

Thank you again for being part of this study

3 TABLE E.1

QUESTIONNAIRE COLOUR: PINKPINK QUESTIONNAIRE RESULTSNO. DISTRIBUTED = 800 NO. RESPONSES = 252RESPONSE RATE = 32%

~ PART A — GENERAL INFORMATIONQUESTION 1 QUESTION 2 QUESTION 3 QUESTION 4 QUESTION 5 QUESTION 6 QUESTION 7 QUESTION 8

No. Type of development Residential status Time at property No. of residents No. of workers at business Future Development Development Approval Reduce Flood Damage

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patib

le M

ater

ial

Plan

of A

ctio

n

a b c d e a b c d a b c d a b c d e a b c d e a b c d e f a b c d e a b c d

TOTALS: 167 50 12 4 1 197 25 6 4 22 62 54 90 37 100 27 39 14 7 6 2 1 1 158 42 5 1 1 8 203 2 1 5 6 19 6 7 19

No. responses:

252 PERCENTAGE ALL RESPONSES 66% 20% 5% 2% 0% 78% 10% 2% 2% 9% 25% 21% 36% 15% 40% 11% 15% 6% 3% 2% 1% 0% 0% 63% 17% 2% 0% 0% 3% 81% 1% 0% 2% 2% 8% 2% 3% 8%

TOWRADGI FLOODPLAIN RISK MANAGEMENT STUDY — QUESTIONNAIRE RESULTS E-5 BEWSHER CONSULTING PTY LTD (J829BCQR.WK4; 27/05/2003)

3 TABLE E.1 (continued)

QUESTIONNAIRE RESULTSQUESTIONNAIRE COLOUR: PINK

NO. DISTRIBUTED = 800NO. RESPONSES = 252RESPONSE RATE = 32%

PART B: ATTITUDES TO FLOOD PLAIN MANAGEMENT OPTIONSQUESTION 9 QUESTION 10 QUESTION 11 QUESTION 12

No. Requires greatest protection (1=greatest) Level of Council Control Flood Notification Options to Minimise Flooding in the Towradgi Creek Catchment

Que

stio

nnai

re

Uni

t num

ber

Stre

et n

umbe

r

Stre

et n

ame

Loca

lity

Com

mer

cial

/Indu

stria

l

Res

iden

tial

Esse

ntia

l Com

mun

ity F

acilit

ies

Crit

ical

Util

ities

Min

or D

evel

opm

ent a

nd A

dditi

ons

Rec

reat

ion

or a

gric

ultu

ral L

and

New

Res

iden

tial S

ubdi

visi

ons

Proh

ibit

all D

evel

opm

ent o

n flo

odpl

ain

Proh

ibit

all D

evel

opm

ent i

n Ex

trem

e Fl

ood

Haz

ard

Area

s

Red

uce

Pote

ntia

l Dam

age

Advi

se o

n Fl

ood

Ris

k, b

ut A

llow

Indi

vidu

al C

hoic

e

No

Advi

ce

Ever

y R

esid

ent/O

wne

r of P

oten

tial F

lood

Thr

eat

Ever

y R

esid

ent/O

wne

r of C

ounc

il's C

ontro

ls

Pros

pect

ive

Purc

hase

rs/e

nqui

rers

on

Cou

ncil

Con

trols

No

Not

ifica

tion

a. P

erm

anen

t lev

ees

b. W

iden

ing/

Dre

dgin

g R

iver

c. R

emov

e O

bstru

ctio

ns

d. C

ounc

il Pu

rcha

se

Land

e. R

aise

Hou

ses

f. Fl

ood

Proo

f

Prop

ertie

s

g. D

evel

opm

ent

Con

trols

h. Im

prov

e Fl

ood

War

ning

i. Im

prov

e Em

erge

ncy

Plan

j. Pu

blic

Edu

catio

n

k. P

rovi

de F

lood

Info

rmat

ion

l. Fl

ood

Affe

ctat

ion

Cer

tific

ates

m. K

now

Flo

od

Actio

n Pl

an

n. In

stal

l Flo

od

Mar

kers

Phon

e fo

r add

ition

al in

form

atio

n

a b c d e f g a b c d e a b c d Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y N

TOTALS: 2.8 1.4 2.2 1.9 3.7 3.8 3.0 122 112 92 68 6 129 113 138 2 98 34 180 12 149 12 114 32 54 59 45 74 171 9 146 8 125 15 134 17 176 6 133 24 151 12 138 26 40

No. responses:

252 PERCENTAGE ALL RESPONSES 48% 44% 37% 27% 2% 51% 45% 55% 1% 39% 13% 71% 5% 59% 5% 45% 13% 21% 23% 18% 29% 68% 4% 58% 3% 50% 6% 53% 7% 70% 2% 53% 10% 60% 5% 55% 10% 16%

TOWRADGI FLOODPLAIN RISK MANAGEMENT STUDY — QUESTIONNAIRE RESULTS E-5 BEWSHER CONSULTING PTY LTD (J829BCQR.WK4; 27/05/2003)


APPENDIX F

COMMUNITY NEWSLETTERFOR NOTIFICATION OF PUBLIC EXHIBITION

OF DRAFT STUDY AND PLAN

F-1 J829Q_1.doc

Frequently Asked QuestionsWhat is a Floodplain? The area of land subject to inundation by floods up to the probable maximum flood event. (ie. Flood-proneland).

What are rare and extreme design flood events? Rare and extreme design flood events are referred to in terms of their chance ofoccurrence. For example, the 1% Annual Exceedence Probability (AEP) flood has a 1% chance (ie. a chance of 1 in 100) of occurringin any one year whilst the Probable Maximum Flood (PMF) is the largest flood that could conceivably occur at a particular location.

What will the Draft Floodplain Risk Management Study show? The Study (currently being exhibited) identifies the floodplainmanagement committee’s preferred floodplain management scheme for reducing the risk of flooding. The scheme was assessedagainst a number of performance objectives including social, economic and ecological.

What are Floodplain Management Options? The feasible measures to manage or reduce the risk of flooding for a particular area of thefloodplain. Options include flood modification, property modification or emergency response modification measures.

Why does Flooding Occur? Flooding is a natural process that occurs periodically as a result of rainfall events in a catchment. Theeffects of flooding in Wollongong (and many other urban areas in New South Wales) are magnified by the proximity of urbandevelopment to natural and modified creeks and channels. The banks of creeks and channels are exceeded in flood events with flowbeing conveyed through properties, via streets or ponding.

What is Flash Flooding? Flash flooding occurs following intense rainfall with resulting flood levels rising to their peak within a veryshort duration, ie 30min – 2hrs. This tends to occur in steep urbanised catchments such as Towradgi Creek and gives residents verylittle warning time.

How will mitigation works be prioritised? The identified mitigation works are funded jointly by Council and the State & FederalGovernment. The floodplain management committee will prioritise the works proposed according to economic, social and ecologicalobjectives. Each option will compete for funding against other mitigation works in the state.

More Details? Contact Mr Michael Nelson at Wollongong City Council on 4227 7111

PUBLIC INFORMATION SESSIONManned public displays will be held in the Myrtle Room of the Corrimal Community Centre on

Saturday 9 November and Saturday 16 November 2002 between 9am – 1.45pm.

PUBLIC DISPLAYUnmanned public displays will be held at the Corrimal Public Library and the Wollongong City

Library (Council Administration Building) from October 21st through to November 15th

All interested persons are welcome to view the display and discuss issues with the team.

Newsletter for Residents of theTowradgi Creek Floodplain October 2002

As part of the Towradgi Creek Floodplain Risk Management Process, Wollongong City Council has engagedBewsher Consulting Pty Ltd to conduct a Floodplain Risk Management Study and prepare a FloodplainRisk Management Plan for the Towradgi Creek catchment area (see over for a map of the study catchment).

These studies are being prepared under the guidance of the Towradgi Creek Floodplain ManagementCommittee which is convened by Wollongong City Council and consists of community representatives,Councillors and Council technical staff as well as the Department of Land and Water Conservation, the StateEmergency Service and other state agencies concerned with flood-related matters.

The Floodplain Risk Management Study aims to identify options for reducing the risk of flooding. However,flooding cannot be eliminated altogether. For more information about flooding refer to the “Facts aboutFlooding” brochure available from Wollongong City Council.

The Floodplain Risk Management Plan will determine preferred management options to reduce floodingbased on an assessment of social, economic, and ecological impacts. This fits into the overall floodplainmanagement process, under the State Government's Flood Prone Land Policy, which follows the stages:

A Draft Floodplain Risk Management Plan for the Towradgi Creek catchment area has been prepared andsome of the options, which make up the Plan are listed over the page. Options include flood modificationoptions, property modification options and emergency response modification options.

Flood modification options can include structural works such as detention basins, creek rehabilitation, leveebanks, culvert amplification, debris control structures.

Planning Control & Property modification options involve the adoption of planning and developmentcontrols, that help to ensure future development is flood compatible and does not increase flooding forexisting residents. Property modifications can also be carried out to existing properties e.g. house raising,flood proofing, voluntary purchase (applying only to residents subject to high hazard flooding).

Emergency response modification options can include modifications to the way in which emergencyresponse is currently handled (by emergency management organisations such as the State EmergencyService, Police, Fire and Ambulance).

Your feedback on the Draft Floodplain Management Plan is invited. Public information displays will be heldfor you to obtain further information (see back page for times and locations). A feedback form is also providedwith this newsletter. Comments received from the feedback forms will be considered in the Floodplain RiskManagement Study review process.

TO THE RESIDENTS OF THE TOWRADGI CREEKCATCHMENT

Towradgi Creek Floodplain Risk Management Study and Plan

ImplementationOf Plan

Data Collection

Completed

Flood Study

Completed

Floodplain RiskManagement Study

Draft UnderExhibition

Floodplain RiskManagement Plan

Draft UnderExhibition

Documents

9. DRAFT FLOODPLAIN RISK MANAGEMENT PLAN · 9. DRAFT FLOODPLAIN RISK MANAGEMENT PLAN ... of design flood levels from current conditions. ... 4 installation of ‘flood proof’ doors