Design Event Approach Report - Publications · Figure 3-22 Brisbane River at Brisbane City 2013 IFD Zone 3 design event hydrographs 24 Figure 3-23 Peak flow rates 2013 IFD design

Brisbane River Catchment Flood Study: Comprehensive Hydrologic Assessment

Design Event Approach Report Prepared for the State of Queensland (acting through): Department of State Development Infrastructure and Planning/Department of Natural Resources and Mines

15 May 2015

Revision: 1

Reference: 238021

Project 238021 File 238021-0000-REP-KT-0006_Design Event Approach Report.docx

15 May 2015 Revision 1

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Aurecon Australasia Pty Ltd ABN 54 005 139 873 Level 14, 32 Turbot Street Brisbane QLD 4000 Locked Bag 331 Brisbane QLD 4001 Australia T F E W

+61 7 3173 8000 +61 7 3173 8001 [email protected] aurecongroup.com

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Document control

Report title Design Event Approach Report

Document ID 238021-0000-REP-KT-0006 Project number 238021

File path 238021-0000-REP-KT-0006_Design Event Approach Report.docx

Client Prepared for the State of Queensland (acting through): Department of State Development Infrastructure and Planning/Department of Natural Resources and Mines

Client contact

Pushpa Onta

Rev Date Revision details/status Prepared by

Author Verifier Approver

A 9 May 2014 Client Review C Smyth T Campbell R Ayre C Russell

B 22 July 2014 Client Review with Comments C Smyth U Baeumer P Vienot C Berry

C 8 December 2014 Final Draft C Smyth U Baeumer R Ayre C Berry

0 15 December 2014 Final Draft C Smyth U Baeumer R Ayre C Berry

1 15 May 2015 Final C Smyth L Toombes R Ayre C Berry

Current revision 1

Approval

Author signature

Approver signature

Name Rob Ayre (RPEQ 4887)

Name Craig Berry (RPEQ 8153)

Title Project Leader Title Project Director

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Brisbane River Catchment Flood Study: Comprehensive Hydrologic Assessment Date 15 May 2015

Reference 238021 Revision 1

Aurecon Australasia Pty Ltd ABN 54 005 139 873 Level 14, 32 Turbot Street Brisbane QLD 4000 Locked Bag 331 Brisbane QLD 4001 Australia T F E W

+61 7 3173 8000 +61 7 3173 8001 [email protected] aurecongroup.com

Important things you should know about this report

Report subject to change This draft final report is subject to change as the assessments undertaken have been based solely upon hydrological modelling and are subject to continuous improvement. Aspects of these assessments that are affected by hydraulics will need to be verified during the hydraulic modelling phase. Therefore the estimates presented in this report should be regarded as interim and possibly subject to change as further iteration occurs in conjunction with the hydraulic modelling phase of the Brisbane River Catchment Flood Study.

Exclusive use This report and hydrologic model data has been prepared by Aurecon at the request of the State of Queensland acting through the Department of State Development, Infrastructure and Planning (“Client”).

The basis of Aurecon’s engagement by the Client is that Aurecon’s liability, whether under the law of contract, tort, statute, equity or otherwise, is limited as set out in the Conditions of Contract schedules: DSDIP-2077-13 and agreed variations to the scope of the contract (terms of the engagement).

Third parties It is not possible to make a proper assessment of this report without a clear understanding of the terms of engagement under which the report has been prepared, including the scope of the instructions and directions given to and the assumptions made by the consultant who has prepared the report.

The report is scoped in accordance with instructions given by or on behalf of the Client. The report may not address issues which would need to be addressed by a third party if that party’s particular circumstances, requirements and experience with such reports were known; and the report may make assumptions about matters of which a third party is not aware.

Aurecon therefore does not assume responsibility for the use of, or reliance on, the report by any third party and the use of, or reliance on, the report by any third party is at the risk of that party.

Limits on scope and information Where the report is based on information provided to Aurecon by other parties including state agencies, local governments authorised to act on behalf of the client, and the Independent Panel of Experts appointed by the client, the report is provided strictly on the basis that such information that has been provided is accurate, complete and adequate. Aurecon takes no responsibility and disclaims all liability whatsoever for any loss or damage that the Client or any other party may suffer resulting from any conclusions based on information provided to Aurecon, except to the extent that Aurecon expressly indicates in the report or related and supporting documentation, including the hydrologic models, analytical tools and associated datasets and metadata, that it has accepted or verified the information to its satisfaction.


15 May 2015 Revision 1 Page I

Legal documents The report may contain various remarks about and observations on legal documents and arrangements such as contracts, supply arrangements, leases, licences, permits and authorities. A consulting engineer can make remarks and observations about the technical aspects and implications of those documents and general remarks and observations of a non-legal nature about the contents of those documents. However, as a Consulting Engineer, Aurecon is not qualified, cannot express and should not be taken as in any way expressing any opinion or conclusion about the legal status, validity, enforceability, effect, completeness or effectiveness of those arrangements or documents or whether what is provided for is effectively provided for. They are matters for legal advice.

Aurecon team The Aurecon Team consists of Aurecon as lead consultant, supported by Deltares, Royal HaskoningDHV, and Don Carroll Project Management and Hydrobiology.


15 May 2015 Revision 1 Page II

Contents 1 Introduction 1 2 Methodology 3

2.1 Models 3 2.2 Intensity-frequency-duration data 3 2.3 Temporal patterns 9 2.4 Rainfall losses 11 2.5 Baseflow 12

3 Design event results 13 3.1 Design event modelling 13 3.2 Design hydrographs 13 3.3 Discussion 33

4 Design event flow volume 38 4.1 Assessment methodology 38 4.2 Design Event duration dependent volume 38 4.3 Discussion 48

5 Sensitivity testing 50 5.1 Purpose of sensitivity testing 50 5.2 Comparison between 1987 and 2013 IFD results 50 5.3 Influence of rainfall losses 53 5.4 Influence of temporal pattern 57 5.5 Influence of base flow 60

6 Dam influence 61 6.1 Modelling of dam operations 61 6.2 Dam influence 61 6.3 Discussion 71

7 Conclusion 74 7.1 Methodology 74 7.2 Design flows 74 7.3 Volume analysis 75 7.4 Sensitivity testing 75 7.5 Dam influence on design flows and volumes 76 7.6 Assumptions and limitations 76

8 References 78 9 Glossary 79

9.1 Hydrologic terms 79 9.2 Study related terms 81


15 May 2015 Revision 1 Page i

Appendices Appendix A

GSDM ellipse locations Appendix B

PMP estimates Appendix C

Comparison of temporal patterns Appendix D

Sensitivity assessment frequency curves Appendix E

Dam influence frequency curves

Figures Figure 3-1 Stanley River at Peachester 2013 IFD Zone 3 design event hydrographs 14 Figure 3-2 Stanley River at Woodford 2013 IFD Zone 3 design event hydrographs 14 Figure 3-3 Stanley River at Somerset 2013 IFD Zone 3 design event hydrographs 15 Figure 3-4 Brisbane River at Linville 2013 IFD Zone 3 design event hydrographs 15 Figure 3-5 Brisbane River at Gregors Creek 2013 IFD Zone 3 design event hydrographs 16 Figure 3-6 Brisbane River at Fulham Vale 2013 IFD Zone 3 design event hydrographs 16 Figure 3-7 Cressbrook Creek at Tinton 2013 IFD Zone 3 design event hydrographs 17 Figure 3-8 Brisbane River at Middle Creek 2013 IFD Zone 3 design event hydrographs 17 Figure 3-9 Brisbane River at Wivenhoe 2013 IFD Zone 3 design event hydrographs 18 Figure 3-10 Lockyer Creek at Helidon 2013 IFD Zone 3 design event hydrographs 18 Figure 3-11 Lockyer Creek at Gatton 2013 IFD Zone 3 design event hydrographs 19 Figure 3-12 Lockyer Creek at Glenore Grove 2013 IFD Zone 3 design event hydrographs 19 Figure 3-13 Bremer River at Walloon 2013 IFD Zone 3 design event hydrographs 20 Figure 3-14 Warrill Creek at Kalbar 2013 IFD Zone 3 design event hydrographs 20 Figure 3-15 Warrill Creek at Amberley 2013 IFD Zone 3 design event hydrographs 21 Figure 3-16 Purga Creek at Loamside 2013 IFD Zone 3 design event hydrographs 21 Figure 3-17 Bremer River at Ipswich 2013 IFD Zone 3 design event hydrographs 22 Figure 3-18 Brisbane River at Savages Crossing 2013 IFD Zone 3 design event hydrographs 22 Figure 3-19 Brisbane River at Mt Crosby Weir 2013 IFD Zone 3 design event hydrographs 23 Figure 3-20 Brisbane River at Moggill 2013 IFD Zone 3 design event hydrographs 23 Figure 3-21 Brisbane River at Centenary Bridge 2013 IFD Zone 3 design event hydrographs 24 Figure 3-22 Brisbane River at Brisbane City 2013 IFD Zone 3 design event hydrographs 24 Figure 3-23 Peak flow rates 2013 IFD design events – Brisbane River catchment sites 31 Figure 3-24 Peak flow rates 2013 IFD design events – tributary catchment sites 32 Figure 3-25 Hydrographs around Brisbane River and Bremer River confluence 33 Figure 3-26 Relationship between peak flow and catchment area 34 Figure 3-27 Relationship between critical duration and catchment area 35 Figure 3-28 Ipswich 1 in 100 AEP Design Event hydrographs 36 Figure 4-1 Peak 24h volume 2013 IFD design events – Brisbane River catchment sites 41 Figure 4-2 Peak 24h volume 2013 IFD design events – tributary catchment sites 41 Figure 4-3 Peak 48h volume 2013 IFD design events – Brisbane River catchment sites 44 Figure 4-4 Peak 48h volume 2013 IFD design events – tributary catchment sites 44 Figure 4-5 Peak 72h volume 2013 IFD design events – Brisbane River catchment sites 47 Figure 4-6 Peak 72h volume 2013 IFD design events – tributary catchment sites 47


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Figure 4-7 Ratio of maximum average 24 hour flow to maximum peak flow 48 Figure 4-8 Ratio of maximum average 48 hour flow to maximum peak flow 48 Figure 4-9 Ratio of maximum average 72 hour flow to maximum peak flow 49 Figure 5-1 Relationship between 2013 IFD and 1987 IFD Design Event Peak Flows 52 Figure 5-2 Influence of IFD data on design event flow as a function of frequency 52 Figure 5-3 Influence of IFD data on design event critical duration as a function of frequency 53 Figure 5-4 Relationship between factored and typical loss Design Event Peak Flows 56 Figure 5-5 Influence of losses on design event flow as a function of frequency 56 Figure 5-6 Zones for temporal patterns (from AR&R 2003) 57 Figure 5-7 Relationship between Zone 3 and Zone 2 design event peak flows 59 Figure 5-8 Influence of temporal pattern on design event flow as a function of frequency 59 Figure 5-9 Influence of temporal pattern on design event flow as a function of catchment area 60 Figure 6-1 Peak ‘with-dams conditions’ flow assuming all dams at FSV 65 Figure 6-2 Peak ‘with-dams conditions’ 24h volume assuming all dams at FSV 65 Figure 6-3 Peak ‘with-dams conditions’ 48h volume assuming all dams at FSV 66 Figure 6-4 Peak ‘with-dams conditions’ 72h volume assuming all dams at FSV 66 Figure 6-5 Peak ‘with-dams conditions’ flow assuming no release from Wivenhoe 69 Figure 6-6 Peak ‘with-dams conditions’ 24h volume assuming no release from Wivenhoe 69 Figure 6-7 Peak ‘with-dams conditions’ 48h volume assuming no release from Wivenhoe 70 Figure 6-8 Peak ‘with-dams conditions’ 72h volume assuming no release from Wivenhoe 70 Figure 6-9 Peak flow attenuation assuming all dams at FSV 71 Figure 6-10 Peak 24h volume attenuation assuming all dams at FSV 72 Figure 6-11 Peak 72h volume attenuation assuming all dams at FSV 73

Tables Table 2-1 IFD locations 4 Table 2-2 Adopted IFD calculation methods 4 Table 2-3 PMP temporal patterns 10 Table 2-4 Initial and continuing loss values 12 Table 2-5 Adopted baseflow volume factors 12 Table 3-1 Peak flow rates 2013 IFD design events (m3/s) 25 Table 3-2 Critical duration 2013 IFD design events 27 Table 3-3 Peak volume of critical duration 2013 IFD design events (GL) 29 Table 3-4 Critical temporal pattern 37 Table 4-1 Peak 24h volume 2013 IFD design events (GL) 39 Table 4-2 Peak 48h volume 2013 IFD design events (GL) 42 Table 4-3 Peak 72h volume 2013 IFD design events (GL) 45 Table 5-1 Peak flow rates 1987 IFD design events (m3/s) 51 Table 5-2 Difference between 1987 and 2013 peak 1 in 100 AEP values (relative to 2013) 53 Table 5-3 Peak flow rates with losses increased by 20% (m3/s) 54 Table 5-4 Peak flow rates with losses decreased by 20% (m3/s) 55 Table 5-5 Peak flow rates Zone 2 temporal pattern design events (m3/s) 58 Table 5-6 Relative difference between Zone 3 and Zone 2 peak 1 in 100 AEP values 60 Table 6-1 Dams influencing Brisbane River gauge locations 61 Table 6-2 Peak ‘with-dams conditions’ flow assuming all dams at FSV (m³/s) 63 Table 6-3 Peak ‘with-dams conditions’ 24h volume assuming all dams at FSV (GL) 63 Table 6-4 Peak ‘with-dams conditions’ 48h volume assuming all dams at FSV (GL) 64 Table 6-5 Peak ‘with-dams conditions’ 72h volume assuming all dams at FSV (GL) 64 Table 6-6 Peak ‘with-dams conditions’ flow assuming no release from Wivenhoe (m³/s) 67 Table 6-7 Peak ‘with-dams conditions’ 24h volume assuming no release from Wivenhoe (GL) 67 Table 6-8 Peak ‘with-dams conditions’ 48h volume assuming no release from Wivenhoe (GL) 68 Table 6-9 Peak ‘with-dams conditions’ 72h volume assuming no release from Wivenhoe (GL) 68


15 May 2015 Revision 1 Page iii

The purpose of the Comprehensive Hydrologic Assessment (CHA) is to develop and apply state of the art methods that produce consistent and robust hydrologic models and analytical techniques that will enable the CHA to provide best estimates of a range of flood flows and flood volumes for annual exceedance probabilities (AEP) across the entire Brisbane River system.

In the CHA, three approaches are used to estimate peak discharges and flow volumes for a range of Annual Exceedance Probabilities (AEP):

1. Flood Frequency Analysis (FFA) 2. Design Event Approach (DEA) 3. Monte Carlo Simulation (MCS) The DEA and MCS methods are both referred to as ‘rainfall based methods’, as they both rely on rainfall statistics in combination with a rainfall-runoff model to compute peak flows and flow volumes at locations of interest. With the FFA method, peak flows and flow volumes for given AEPs are derived directly from observed flows. This current report concerns the application of the Design Event Approach methodology and the estimates that this method produces.

Section 3.6.6.4 of the Brisbane River Catchment Flood Study (BRCFS) brief (dated 1 July 2013) provides details of the design event hydrologic modelling requirements. The brief indicates that hydrologic modelling is required for:

“design flood events with Annual Exceedance Probabilities (AEP) of 50%,20%, 10%, 5%, 2%, 1%, 0.5%, 0.2%, 0.1%, 0.05%, 0.01%, 0.001% as well as the Probable Maximum Flood (PMF). Hydrographs are to be produced for the full range of standard AR&R storm durations”

The brief also requires that design flood estimates be derived for two conditions at each nominated location, ‘No-dams’ and ‘With-dams’. The ‘No-dams’ condition represents the condition of the catchment without the presence of the six major dams:

Wivenhoe

Somerset

Perseverence

Cressbrook Creek

Lake Manchester

Moogerah Dam The level of urban development in the ‘No-dams’ condition was not changed to reflect a ‘pre-development’ scenario, so it should be recognised that this scenario represents the behaviour of the catchment response simply without the presence of the dams.

1 Introduction


15 May 2015 Revision 1 Page 1

This report provides the preliminary results of the ‘With-dams’ condition. The ‘With-dams’ condition results rely on a dam operations module to simulate the performance of the gated flood mitigation dams (Somerset and Wivenhoe Dams), so reference should be made to the report entitled, ’Dam operations module implementation report’. (Aurecon, 2015).

This report presents the design event methodology, and first pass design event estimates for the ‘No-dams’ condition and ‘With-dams’ condition for the nominated locations within the catchment. These estimates are yet to be reconciled with the Flood Frequency Analysis and Monte Carlo Analysis estimates.



2.1 Models The models developed during the recalibration process and discussed in the Aurecon Team’s Hydrologic Model Recalibration Report (dated 10 July 2014) have been used as the basis for the design event modelling. Two scenarios have been investigated by the BRCFS, referred to as ‘with-dams condition’ and ‘no-dams condition’, being the catchment condition with the influence of the dams and reservoirs represented in their current (2013) configuration and without the influence of the dams and reservoirs respectively. The dams referred to are the major water storages that exist within the catchment (Perseverance, Cressbrook, Somerset, Wivenhoe and Moogerah Dams).

The ‘no-dams conditions’ models have been modified to remove all reference to the dams, including storage details and reduced reach length factors for drowned reaches. The catchment data has also been adjusted to remove the effect of impervious area associated with the reservoirs. The design event modelling for the ‘no-dams condition’ is not considered a pre-development scenario; it represents the current catchment conditions with the dams removed. Similarly, it does not represent a future development scenario.

The analysis has been conducted using the URBS model version 5.70 beta. This analysis has been undertaken using the URBS model in a standalone manner, outside of the Delft-FEWS platform.

2.2 Intensity-frequency-duration data The process adopted in developing design event Intensity-frequency-duration (IFD) values is presented in Sections 2.2.1 to 2.2.11. The key steps in this process are identified as follows:

Determine location of interest

Determine events and durations for IFD calcs

Calculate AR&R IFD values (1987 & 2013)

Calculate CRC-Forge IFD values

Calculate PMP IFD values (GSDM/GTSMR)

Calculate 1 in 10,000 & 1 in 100,000 AEP IFD

values

2.2.1 Locations The IFD process has been carried out for each location at which Flood Frequency Analysis is being undertaken. For the “no-dams” assessment, rainfall in all subareas downstream of each location of interest has been set to zero (0). The adopted locations, as well as the catchment area at that location, are presented in Table 2-1.

2 Methodology



Table 2-1 IFD locations

Location Subcatchment Catchment area (km2)

Peachester Stanley 103.0

Woodford Stanley 245.8

Somerset Dam Stanley 1327

Linville Upper Brisbane 2000

Gregors Creek Upper Brisbane 3858

Fulham Vale Upper Brisbane 3950

Tinton Upper Brisbane 424

Middle Ck Upper Brisbane 6686

Wivenhoe Upper Brisbane 7001

Helidon Lockyer 351.5

Gatton Lockyer 1531

Glenore Grove Lockyer 2154

Walloon Bremer 635.1

Kalbar Weir Warrill 459.1

Amberley Warrill 903.3

Loamside Purga 209.5

Savages Xing Lower Brisbane 10160

Mt Crosby Weir Lower Brisbane 10540

Ipswich Lower Brisbane 1861

Moggill Lower Brisbane 12620

Centenary Bridge Lower Brisbane 12940

Brisbane Lower Brisbane 13240

2.2.2 Events and durations Spatially varying IFD values have been calculated for each of the 534 URBS subareas. A summary of the adopted methods is presented in Table 2-2. This methodology has been applied twice at each location, once for 1987 AR&R IFD values and once for 2013 AR&R IFD values.

Location specific Probable Maximum Precipitation (PMP) and Area Reduction Factor (ARF) values have been calculated. For catchments with an area of less than 1000 km2 both the GSDM and GTSMR PMP methods were applied.

Table 2-2 Adopted IFD calculation methods

Event duration (hrs)

1987 AR&R (1 in 2 to 1 in 100 AEP)

2013 AR&R (1 in 2 to 1 in 100 AEP)

CRC-Forge (1 in 200 to 1 in 2000 AEP)

Extreme events (1 in 10,000 and 1 in 100,000 AEP)

PMP

1 Y Y Factored AR&R Book VI Section 3.6.3

GSDM


GSDM


GSDM


GSDM



Event duration (hrs)

1987 AR&R (1 in 2 to 1 in 100 AEP)

2013 AR&R (1 in 2 to 1 in 100 AEP)

CRC-Forge (1 in 200 to 1 in 2000 AEP)

Extreme events (1 in 10,000 and 1 in 100,000 AEP)

PMP


Interpolated

18 Interpolated Interpolated Interpolated AR&R Book VI Section 3.6.3

Interpolated

24 Y Y Y AR&R Book VI Section 3.6.3

GTSMR

36 Interpolated Interpolated Interpolated AR&R Book VI Section 3.6.3

GTSMR


GTSMR


GTSMR

96 Extrapolated Y Y AR&R Book VI Section 3.6.3

GTSMR

120 Extrapolated Y Y AR&R Book VI Section 3.6.3

GTSMR

144 Extrapolated Y Extrapolated AR&R Book VI Section 3.6.3

Extrapolated

168 Extrapolated Y Extrapolated AR&R Book VI Section 3.6.3

Extrapolated

2.2.3 1 in 2, 5, 10, 20, 50 & 100 AEP events – 1987 AR&R IFDs

Source IFD values from 1987 AR&R grids

Extrapolate long duration IFD values

Apply Areal Reduction Factors

Interpolate additional durations

IFD values for the 1, 2, 3, 6, 12, 24, 48 & 72 hour events were sourced from the 1987 AR&R grids.

These were sourced as point values at the subarea centroids

IFD values for the 96, 120, 144 & 168 hour events were log-linearly extrapolated based upon the relationship between the 2013 IFD values for the 72 hour and the respective 96/120/144/168 hour events for each subarea

ARF values were applied according to the processes described in AR&R Project 2 (Engineers Australia, 2013) and outlined in Section 2.2.11

IFD values for the 18 & 36 hour events were log-linearly interpolated between the 12 & 24 and 24 & 48 hour events respectively



2.2.4 1 in 2, 5, 10, 20, 50 & 100 AEP events – 2013 AR&R IFDs

Source IFD values from 2013 AR&R grids



IFD values for the 1, 2, 3, 6, 12, 24, 48, 72, 96, 120, 144 & 168 hour events were sourced from the

2013 AR&R grids. These were sourced as point values at the subarea centroids



2.2.5 1 in 200, 500, 1000 & 2000 AEP events – CRC-Forge IFDs

Source IFD values from CRC-Forge grids

Determine depth factors for short duration events

Calculate short duration IFD values



Extrapolate long duration IFD values

IFD values for the 24, 48, 72, 96 & 120 hour events were sourced from the CRC-Forge grids. These

were sourced as point values at the subarea centroids

Depth factors were derived for the 1, 2, 3, 6 and 12 hour events, based on the 1 in 100 AEP (100 year ARI) rainfall depths, as per Section 3.7.4 of Book VI of AR&R (Engineers Australia, 2003)

𝑋𝑋ℎ𝑟𝑟 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑ℎ 𝑓𝑓𝑓𝑓𝑓𝑓𝑑𝑑𝑓𝑓𝑟𝑟 = 1 in 100 𝐴𝐴𝐴𝐴𝐴𝐴,𝑋𝑋ℎ𝑟𝑟 𝑟𝑟𝑓𝑓𝑟𝑟𝑟𝑟𝑓𝑓𝑓𝑓𝑟𝑟𝑟𝑟 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑ℎ

1 in 100 𝐴𝐴𝐴𝐴𝐴𝐴, 24ℎ𝑟𝑟 𝑟𝑟𝑓𝑓𝑟𝑟𝑟𝑟𝑓𝑓𝑓𝑓𝑟𝑟𝑟𝑟 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑ℎ

IFD values for the 1, 2,3, 6 & 12 hour events were calculated as per Section 3.7.4 of Book VI of AR&R (Engineers Australia, 2003)

1𝑟𝑟𝑟𝑟𝑖𝑖 𝐴𝐴𝐴𝐴𝐴𝐴,𝑋𝑋ℎ𝑟𝑟 𝐼𝐼𝐼𝐼𝐼𝐼 𝑣𝑣𝑓𝑓𝑟𝑟𝑣𝑣𝑑𝑑 = 𝑋𝑋ℎ𝑟𝑟 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑ℎ 𝑓𝑓𝑓𝑓𝑓𝑓𝑑𝑑𝑓𝑓𝑟𝑟 × 1𝑟𝑟𝑟𝑟𝑖𝑖 𝐴𝐴𝐴𝐴𝐴𝐴, 24ℎ𝑟𝑟 𝐼𝐼𝐼𝐼𝐼𝐼 𝑣𝑣𝑓𝑓𝑟𝑟𝑣𝑣𝑑𝑑

IFD values for the 144 & 168 hour events were log-linearly extrapolated based upon the relationship between the 2013 IFD values for the 120 hour and the respective 144/168 hour events for each subarea



2.2.6 PMP – GSDM events (1 to 6hr) This process was only carried out for catchments smaller than 1000 km2



Calculate catchment MAF Determine catchment EAF

Determine terrain factors (R and/or S)

Apply spatial ellipses Determine rainfall depths between ellipses

Determine IFD value for each subarea

Determine subcatchment IFD values

Moisture Adjustment Factor (MAF) values were determined using the process described in Section

2.6 of the GTSMR Guidebook (BoM, 2003a). A catchment average EPW was determined using GIS, then the MAF was calculated

𝐺𝐺𝐺𝐺𝐼𝐼𝐺𝐺 𝐺𝐺𝐴𝐴𝐼𝐼 =𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 𝐴𝐴𝐴𝐴𝐸𝐸

104.5

The Elevation Adjustment Factor (EAF) was set to 1. The highest point within the Brisbane River catchment is below 1500 m AHD, therefore the catchment average elevation is well below the 1500 m limit defined in Section 4.3 of the GSDM documentation (BoM, 2003b)

Catchment terrain categories (Rough and Smooth) were determined as per Section 4.2 of the GSDM documentation (BoM, 2003b). A slope analysis was performed on the Brisbane River catchment DEM. In all areas where the elevation changed more than 50 m over 400 m (slope >7.125º) the catchment was classified as Rough. All areas within 20 km of these Rough areas were also classified as Rough. This resulted in the entire catchment being classified as Rough

The GSDM ellipses (Figure 6 of the GSDM documentation (BoM, 2003b)) were applied to each catchment. The location for the ellipses was selected such that the area within the smaller ellipses was maximised and the ellipses were typically (but not always) concentrated towards the lower end of the catchment. In the case of some of the large elongated catchments (eg Amberley) the ellipses may not cover the entire catchment. The adopted ellipse locations are presented in Appendix A

The rainfall depths between ellipses were determined using the process described in Section 6 of the GSDM documentation (BoM, 2003b): − The area of the catchment falling between each ellipse was determined using GIS − The total area enclosed by each ellipse was calculated as the sum of all smaller ellipse areas − The initial mean rainfall depth (IMRD) was determined from Figure 4 of the GSDM documentation − The adjusted mean rainfall depth was calculated

𝐴𝐴𝐺𝐺𝐺𝐺𝐼𝐼𝑖𝑖 = 𝐼𝐼𝐺𝐺𝐺𝐺𝐼𝐼𝑖𝑖 × 𝐺𝐺𝐴𝐴𝐼𝐼 × 𝐴𝐴𝐴𝐴𝐼𝐼

− The volume of rainfall within each ellipse was calculated 𝑉𝑉𝐴𝐴𝑟𝑟𝑓𝑓𝑖𝑖 = 𝐴𝐴𝐺𝐺𝐺𝐺𝐼𝐼𝑖𝑖 × 𝐶𝐶𝐴𝐴𝑟𝑟𝑓𝑓𝑖𝑖

− The volume of rainfall between ellipses was calculated 𝑉𝑉𝑉𝑉𝑑𝑑𝑟𝑟𝑖𝑖 = 𝑉𝑉𝐴𝐴𝑟𝑟𝑓𝑓𝑖𝑖 − 𝑉𝑉𝐴𝐴𝑟𝑟𝑓𝑓𝑖𝑖−1

− The mean rainfall depth between each was calculated

𝐺𝐺𝐺𝐺𝐼𝐼𝑖𝑖 = 𝑉𝑉𝑉𝑉𝑑𝑑𝑟𝑟𝑖𝑖𝐶𝐶𝑉𝑉𝑑𝑑𝑟𝑟𝑖𝑖



An areally weighted rainfall depth for each subarea was determined according to the portion of each subarea covered by each ellipse

Subcatchment based IFD values were also calculated. These were calculated in accordance with Section 4.5 of the GSDM documentation (BoM, 2003b)

𝐺𝐺𝑓𝑓𝑟𝑟𝑟𝑟𝑓𝑓𝑓𝑓𝑟𝑟𝑟𝑟 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑ℎ = (𝐺𝐺 × 𝐼𝐼𝑆𝑆 + 𝐺𝐺 × 𝐼𝐼𝑅𝑅) × 𝐺𝐺𝐴𝐴𝐼𝐼 × 𝐴𝐴𝐴𝐴𝐼𝐼

2.2.7 PMP – GTSMR events (24 to 120hr) This process was carried out for all catchments

Calculate catchment TAF, DAF, EPW & MAF

Determine initial rainfall depth Calculate rainfall depth

Calculate subarea TAF Determine subarea rainfall depth Calculate AEP of PMP

The catchment average Topographic Adjustment Factor (TAF), Decay Amplitude Factor (DAF) and

Extreme Precipitable Water (EPW) were determined using GIS as per Section 2.3 of the GTSMR Guidebook (BoM, 2003a). The MAF was calculated

𝐺𝐺𝐴𝐴𝐼𝐼 =𝐴𝐴𝐴𝐴𝐸𝐸120

The initial rainfall depth was determined through linear interpolation between the Coastal Summer Depths of the GTSMR (BoM, 2003a)

The rainfall depth was then calculated as per below, and rounded to the nearest 10mm as per Section 2.4 of the GTSMR Guidebook (BoM, 2003a)

𝐺𝐺𝑓𝑓𝑟𝑟𝑟𝑟𝑓𝑓𝑓𝑓𝑟𝑟𝑟𝑟 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑ℎ = 𝐼𝐼𝑟𝑟𝑟𝑟𝑑𝑑𝑟𝑟𝑓𝑓𝑟𝑟 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑ℎ × 𝐺𝐺𝐴𝐴𝐼𝐼 × 𝐼𝐼𝐴𝐴𝐼𝐼 × 𝐺𝐺𝐴𝐴𝐼𝐼

The subarea average TAF values were determined using GIS

The subarea rainfall depths were calculated using the process described in Section 3 of the GTSMR Guidebook (BoM, 2003a)

𝐴𝐴𝐺𝐺𝐴𝐴𝑖𝑖 = 𝐴𝐴𝐺𝐺𝐴𝐴𝑐𝑐 ×𝐴𝐴𝑣𝑣𝑑𝑑𝑟𝑟𝑓𝑓𝐴𝐴𝑑𝑑 𝐺𝐺𝐴𝐴𝐼𝐼𝑖𝑖𝐴𝐴𝑣𝑣𝑑𝑑𝑟𝑟𝑓𝑓𝐴𝐴𝑑𝑑 𝐺𝐺𝐴𝐴𝐼𝐼𝑐𝑐

The AEP of the PMP was determined for use in the extreme event calculations, as per Section 3.5 of Book VI of AR&R (Engineers Australia, 2003)

2.2.8 PMP – 12 and 18hr events The 12 and 18hr IFD values were log-linearly interpolated between the subcatchment-based 6hr IFD values and the 24hr values. The spatially varying subarea based GSDM values were not used for this calculation as some of these values are zero and some are less than the 1 in 2000 AEP values.

2.2.9 PMP – 144 and 168hr events The 144 and 168hr IFD values were log-linearly extrapolated based upon the relationship between the 2013 IFD values for the 120 hour and the respective 144/168 hour events for each subarea.



2.2.10 1 in 10,000 & 1 in 100,000 AEP events The process defined in Section 3.6.3 of Book VI of AR&R (Engineers Australia, 2003) was followed to calculate the 1 in 10,000 and 1 in 100,000 AEP rainfall depths. The subcatchment based GSDM values were used for this calculation in preference to the spatially varying GSDM values for each subarea as some of these values are zero and some are less than the 1 in 2000 AEP values. For catchments where only the GTSMR was applied, this process was only carried out for the 24-72hr events.

𝑋𝑋𝑌𝑌 = 10𝑅𝑅𝑌𝑌log (𝑋𝑋𝑌𝑌2) For the Brisbane City, Centenary Bridge, Moggill, Mt Crosby and Savages Crossing locations with large catchment sizes, only the 1 in 10,000 AEP was calculated as the AEP of the PMP is greater than 1 in 100,000.

2.2.11 Areal Reduction Factors Areal Reduction Factors (ARF) were calculated as per AR&R Project 2 (Engineers Australia, 2013)

Long duration factors were calculated for the 24 to 168hr events 𝐴𝐴𝐺𝐺𝐼𝐼 = 𝐺𝐺𝑟𝑟𝑟𝑟{1,1 + 𝑓𝑓(𝐴𝐴𝑟𝑟𝑑𝑑𝑓𝑓𝑏𝑏 + 𝑓𝑓 log10 𝐼𝐼𝑣𝑣𝑟𝑟𝑓𝑓𝑑𝑑𝑟𝑟𝑓𝑓𝑟𝑟)𝐼𝐼𝑣𝑣𝑟𝑟𝑓𝑓𝑑𝑑𝑟𝑟𝑓𝑓𝑟𝑟𝑑𝑑}

Where: a = -0.2257 b = 0.1685 c = -0.8306 d = -0.3994

Short duration factors were calculated for the 1 to 18hr events 𝐴𝐴𝐺𝐺𝐼𝐼 = 𝐺𝐺𝑟𝑟𝑟𝑟{1,1 + 𝑓𝑓(𝐴𝐴𝑟𝑟𝑑𝑑𝑓𝑓𝑏𝑏 + 𝑓𝑓) + 𝑑𝑑(𝐴𝐴𝑟𝑟𝑑𝑑𝑓𝑓𝑒𝑒)(𝑓𝑓 − log10 𝐼𝐼𝑣𝑣𝑟𝑟𝑓𝑓𝑑𝑑𝑟𝑟𝑓𝑓𝑟𝑟)}

Where a = -0.0539 b = 0.205 c = -0.925 d = -0.0246 e = 0.313 f = 1.16

2.3 Temporal patterns

2.3.1 1 in 2, 5, 10, 20, 50 & 100 AEP events – 1 to 72 hour durations In accordance with Section 2.1 of AR&R (Engineers Australia, 2003), a single temporal pattern has been applied across the entire catchment for each event and for each duration. 1987 AR&R temporal patterns for Zone 3 have been applied for events up to and including the 1 in 100 AEP event. The <30 year ARI temporal patterns have been applied for the 1 in 2, 5, 10 and 20 AEP events and the >30 year ARI temporal patterns have been applied for the 1 in 50 and 1 in 100 AEP events. The 1, 2, 3, 6, 12, 18, 24, 36, 48 and 72 hour patterns have been applied as per the event duration.

2.3.2 1 in 2, 5, 10, 20, 50 & 100 AEP events – 96 to 168 hour durations The GTSMR Coastal AVM temporal pattern for the relevant standard area at each location of interest has been applied.



2.3.3 1 in 200, 500, 1,000, 2,000, 10,000 & 100,000 AEP events Temporal patterns for the intermediate range of flood magnitudes between the 1 in 100 AEP and the PMP event have been interpolated. The interpolation has been conducted using normalised curves of the cumulative temporal patterns. Linear interpolation has been used to estimate the incremental values for each of the respective flood magnitudes. This approach has the advantage of avoiding anomalies between flood magnitudes in the large to rare range (especially the 1 in 100, 200 and 500 AEP events).

2.3.4 PMP events For GSDM events (1, 2, 3 and 6 hour durations) the temporal pattern has been applied as per Section 5 of the GTSMR Guidebook (BoM, 2003a). This has only been applied in catchments smaller than 1000 km2.

For GTSMR events the Coastal AVM temporal pattern for the relevant standard area at each location of interest has been applied as per Section 4 of the GTSMR Guidebook (BoM, 2003a).

For the 12 hour event, both the GSDM temporal pattern and the 24 hour GTSMR temporal pattern, with the time increments halved, have been applied. The worst case results have been adopted. This process has only been applied in catchments smaller than 1000 km2.

A summary of the temporal patterns applied at each location is provided in Table 2-3.

Table 2-3 PMP temporal patterns

Location GSDM temporal pattern (1, 2, 3 & 6hr)

12hr temporal pattern GTSMR temporal pattern (24, 36, 48 & 72hr)

Peachester Y GSDM + Standard Area 100 Standard Area 100

Somerset Dam N/A N/A Standard Area 1,000

Woodford Y GSDM + Standard Area 100 Standard Area 100

Linville N/A N/A Standard Area 2,500

Gregors Creek N/A N/A Standard Area 5,000

Fulham Vale N/A N/A Standard Area 5,000

Tinton Y GSDM + Standard Area 500 Standard Area 500

Middle Ck N/A N/A Standard Area 5,000

Wivenhoe N/A N/A Standard Area 5,000

Helidon Y GSDM + Standard Area 500 Standard Area 500

Gatton N/A N/A Standard Area 1,000

Glenore Grove N/A N/A Standard Area 2,500

Walloon Y GSDM + Standard Area 500 Standard Area 500

Kalbar Weir Y GSDM + Standard Area 500 Standard Area 500

Amberley Y GSDM + Standard Area 1000 Standard Area 1,000

Loamside Y GSDM + Standard Area 100 Standard Area 100

Savages Crossing N/A N/A Standard Area 10,000

Mt Crosby Weir N/A N/A Standard Area 10,000

Ipswich N/A N/A Standard Area 2,500

Moggill N/A N/A Standard Area 10,000



Location GSDM temporal pattern (1, 2, 3 & 6hr)

12hr temporal pattern GTSMR temporal pattern (24, 36, 48 & 72hr)

Centenary Bridge N/A N/A Standard Area 10,000

Brisbane N/A N/A Standard Area 10,000

A graphical comparison between the temporal patterns that have been utilised is presented in Appendix C.

2.4 Rainfall losses AR&R discusses a number of different methods for estimating rainfall losses, including:

An (optional) initial loss, with no runoff until a given capacity has been satisfied regardless of the rainfall rate, followed by an ongoing continuing loss equal to a constant fraction of rainfall in each time period

An (optional) initial loss followed by an ongoing continuing loss equal to a constant fraction of rainfall in each time period

An infiltration curve or equation representing decreasing capacity rates of loss with time

A standard rainfall-runoff relation, such as the U.S. Soil Conservation Service relation The first method is commonly adopted for Queensland catchments and has been used for calibration of the URBS model to historical events with acceptable results. Selection of losses can have significant influence on flood peaks and volumes, particularly for short-duration and/or high AEP events as these have lower overall volume. Review of loss parameters obtained for the calibration events produced mean initial and continuing losses of around 60 mm and 2.3 mm/h respectively, however significant variation is observed. Assessment of historical events does not necessarily produce loss values that are suitable for design application as:

The calibration events are rainfall events that produced significant runoff, however there are likely to be events of similar rainfall on dry catchments where much lower flows occurred. The events will therefore be biased towards wet catchment conditions

Design rainfalls and temporal patterns using AR&R methods are not complete storms, and do not include any lower intensity antecedent rainfall occurring before the main design ‘burst’

Therefore, although these provide some indication of typical catchment losses, they cannot be directly correlated to design event losses. Review of the calibration event losses identified that losses in the Lockyer Creek catchment are typically higher than the mean value while the Stanley and Bremer River catchments are typically lower. These observations are consistent with known characteristics. Consequently Design Event losses applied to these catchments have been scaled up and down by a similar amount.

Design event modelling commonly uses higher losses for frequent events. This is often an effect of calibration to match design event flows to other data (eg flood frequency analysis), however there is some theoretical justification as large rainfall events have a higher probability of occurring in wet periods when the higher frequency and intensity of antecedent rainfall are likely to reduce the infiltration capacity of the catchment.

Typical losses listed in Table 2-1 have been selected for the design events based on experience and comparison with other methods including flood frequency analysis and Monte-Carlo simulation.



Table 2-4 Initial and continuing loss values

Event AEP

(1 in N)

Stanley & Bremer Upper & Lower Brisbane Lockyer

IL (mm) CL (mm/h) IL (mm) CL (mm/h) IL (mm) CL (mm/h)

2 40 2.0 50 2.5 60 3.0

5 32 1.6 40 2.0 48 2.4

10 24 1.2 30 1.5 36 1.8

20 16 0.8 20 1.0 24 1.2

50 8 0.4 10 0.5 12 0.6

≥ 100 0 0.4 0 0.5 0 0.6

2.5 Baseflow In accordance with the URBS model review presented in Aurecon’s Hydrologic Model Calibration and Validation Review Report, a Baseflow Volume Factor is applied according to the magnitude of the design rainfall event. The adopted Baseflow Volume Factors in Table 2-5 have been sourced from AR&R Revision Project 7.

Table 2-5 Adopted baseflow volume factors

Event AEP (1 in N) Factor for Baseflow Volume Factor

2 1.6

5 1.2

10 1.0

20 0.8

50 0.7

100 0.6

>100 extrapolated

The base flow volume factor will be applied to design events to limit the base flow contribution, especially for the rare to extreme flood magnitude range.

The Base Flow Volume Factor (BFVF) as per ARR project 7 was included in the ARR Design Event Approach (DEA). During the calibration phase baseflow parameters were calibrated for each location under investigation. These parameters are based on the URBS baseflow model:

BFi = BR × BFi-1 + BC QRBM

where BR is a daily recession constant and BC is a baseflow constant. URBS makes internal adjustments to account for the model time step. The baseflow exponent BM determines whether linear or non-linear baseflow routing is to be adopted. For the Brisbane River catchment, BM was assumed to be 1, ie a linear model.

It can be shown that BFVF (the ratio of baseflow to quick runoff) = BC/(1 – BR), when BM = 1.

The URBS’ RAINURBS module was modified to include the BFVF parameter for the 1 in 10 AEP event as provided in Table 1 of the AR&R Project 7 report. For the Brisbane catchment this was set to 0.15. Adjustment was made to this value based on the design AEP under investigation using the factors in Table 2-5 as provided in the AR&R Project 7 report. A power curve was fitted to these adjustment factors to extrapolate these factors for AEP’s smaller than 1 in 100.



3.1 Design event modelling The URBS model has been run to calculate design flows at each location of interest. Design flood estimates for each location were determined by running the complete range of storm durations and flood magnitudes, assuming specific rainfall loss rates. The critical storm duration for each flood magnitude (events that produce the highest peak flow estimate for that location) were identified. The flood volume associated with each critical flood event was also identified. Result hydrographs are provided in Sections 3.2.1 to 3.2.5. The peak instantaneous flow, its associated storm duration and flood volume are included in Table 3-1 to Table 3-3 respectively in Section 3.2.6.

Current advice from the Bureau of Meteorology and Engineers Australia is that “In most cases it would be prudent to use the AR&R87 design parameters and conduct sensitivity testing with revised AR&R design parameters (including the 2013 IFD design rainfalls) as they become available”. Nevertheless, the 2013 AR&R IFD intensities were adopted for base case modelling on the basis of:

The regional and ongoing importance of the study

The 2013 AR&R intensities are based on data from 2300 extra rainfall stations and nearly 30 years’ additional rainfall data, including recent events that have had significant impact on many areas of the Brisbane River catchment

Consistency with other components of the study such as the Monte-Carlo simulation, which are not based on AR&R87 and would ideally be performed using best available information

Sensitivity testing has been performed using the 1987 IFD data to quantify the impact on design flows, which is in keeping with BoM and Engineers Australia recommendations in regard to the use of the 2013 IFD. The results of this testing are discussed in Section 5.

3.2 Design hydrographs Result hydrographs are shown for each location in the following sub-sections 3.2.1 to 3.2.5. Peak instantaneous flow, its associated storm duration and flood volume are tabulated in Section 3.2.6. The results are discussed in Section 3.3.

Note that the reported Bremer River flows at Ipswich do not account for potentially significant floodplain storage attenuation that can occur in the areas upstream of the confluence with the Brisbane River. This attenuation is a complex function of Bremer and Brisbane River flows and cannot be fully represented in the hydrologic model.

3 Design event results



3.2.1 Stanley River

Figure 3-1 Stanley River at Peachester 2013 IFD Zone 3 design event hydrographs

Figure 3-2 Stanley River at Woodford 2013 IFD Zone 3 design event hydrographs



Figure 3-3 Stanley River at Somerset 2013 IFD Zone 3 design event hydrographs

3.2.2 Upper Brisbane River

Figure 3-4 Brisbane River at Linville 2013 IFD Zone 3 design event hydrographs



Figure 3-5 Brisbane River at Gregors Creek 2013 IFD Zone 3 design event hydrographs

Figure 3-6 Brisbane River at Fulham Vale 2013 IFD Zone 3 design event hydrographs



Figure 3-7 Cressbrook Creek at Tinton 2013 IFD Zone 3 design event hydrographs

Figure 3-8 Brisbane River at Middle Creek 2013 IFD Zone 3 design event hydrographs



Figure 3-9 Brisbane River at Wivenhoe 2013 IFD Zone 3 design event hydrographs

3.2.3 Lockyer Creek

Figure 3-10 Lockyer Creek at Helidon 2013 IFD Zone 3 design event hydrographs



Figure 3-11 Lockyer Creek at Gatton 2013 IFD Zone 3 design event hydrographs

Figure 3-12 Lockyer Creek at Glenore Grove 2013 IFD Zone 3 design event hydrographs



3.2.4 Bremer River

Figure 3-13 Bremer River at Walloon 2013 IFD Zone 3 design event hydrographs

Figure 3-14 Warrill Creek at Kalbar 2013 IFD Zone 3 design event hydrographs



Figure 3-15 Warrill Creek at Amberley 2013 IFD Zone 3 design event hydrographs

Figure 3-16 Purga Creek at Loamside 2013 IFD Zone 3 design event hydrographs



Figure 3-17 Bremer River at Ipswich 2013 IFD Zone 3 design event hydrographs

3.2.5 Lower Brisbane River

Figure 3-18 Brisbane River at Savages Crossing 2013 IFD Zone 3 design event hydrographs



Figure 3-19 Brisbane River at Mt Crosby Weir 2013 IFD Zone 3 design event hydrographs

Figure 3-20 Brisbane River at Moggill 2013 IFD Zone 3 design event hydrographs



Figure 3-21 Brisbane River at Centenary Bridge 2013 IFD Zone 3 design event hydrographs

Figure 3-22 Brisbane River at Brisbane City 2013 IFD Zone 3 design event hydrographs



3.2.6 2013 IFD design events summary Table 3-1 to Table 3-3 summarise peak flows, critical durations and total volumes for the 2013 IFD Design Events. Flow frequency curves at each site are provided in Figure 3-23 and Figure 3-24.

Table 3-1 Peak flow rates 2013 IFD design events (m3/s)

Location AEP Event (1 in N)

2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley-GSDM 208 419 606 890 1,360 1,710 1,970 2,300 2,570 2,850 3,680 5,820 10,000

Amberley-GTSMR 208 419 606 890 1,360 1,710 1,970 2,300 2,570 2,850 3,680 5,820 10,000

Brisbane 885 3,380 5,610 8,160 11,700 13,900 16,000 18,600 20,800 23,300 30,400 N/A 62,400

Centenary 889 3,390 5,650 8,250 11,600 14,000 16,200 18,800 21,100 23,600 31,200 N/A 64,400

Fulham Vale 482 1,510 2,530 3,650 5,260 6,440 7,330 8,490 9,400 10,400 13,000 25,300 35,700

Gatton 120 789 1,340 1,940 2,680 3,270 3,800 4,470 5,010 5,600 6,110 12,000 23,700

Glenore Grove 163 1,020 1,760 2,580 3,620 4,430 5,120 5,980 6,690 7,440 8,450 16,900 29,900

Gregors Ck 485 1,520 2,550 3,690 5,270 6,440 7,330 8,480 9,400 10,300 12,900 25,400 36,300

Helidon-GSDM 51 222 362 514 728 914 1,060 1,260 1,410 1,580 2,110 3,300 7,240

Helidon-GTSMR 51 222 362 514 728 914 1,060 1,260 1,410 1,580 2,110 3,300 7,520

Ipswich 387 930 1,340 1,850 2,700 3,270 3,790 4,470 5,020 5,610 7,480 12,500 18,900

Kalbar-GSDM 182 392 571 769 1,080 1,330 1,530 1,780 1,980 2,180 2,820 4,190 7,650

Kalbar-GTSMR 182 392 571 769 1,080 1,330 1,520 1,770 1,970 2,180 2,820 4,210 7,810

Linville 270 845 1,420 2,060 2,980 3,600 4,100 4,750 5,270 5,820 6,970 13,000 22,700

Loamside-GSDM 65 150 225 313 438 536 623 730 820 914 1,110 1,650 3,240

Loamside-GTSMR 65 150 225 313 438 536 623 729 818 912 1,110 1,650 3,240

Middle Ck 957 2,660 4,350 6,280 8,820 10,500 12,000 13,900 15,600 17,500 23,300 48,400 57,400

Moggill 897 3,470 5,840 8,540 12,200 14,600 16,700 19,300 21,800 24,200 31,500 N/A 64,100

Project 238021 File 238021-0000-REP-KT-0006_Design Event Approach Report.docx 15 May 2015 Revision 1 Page 25


2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Mt Crosby 842 3,160 5,390 7,900 11,500 13,700 15,800 18,300 20,200 22,300 29,500 N/A 63,600

Peachester-GSDM 113 223 310 403 525 620 733 871 984 1,110 1,390 1,840 2,410

Peachester-GTSMR 113 223 310 403 525 620 733 871 984 1,110 1,390 1,840 2,410

Rifle Range Rd 149 Flow exceeds main channel capacity of ~ 850 to 1000 m³/s

Savages 861 3,220 5,510 8,010 11,700 13,900 15,900 18,200 20,100 22,000 29,800 N/A 64,200

Somerset 666 1,480 2,160 2,900 3,910 4,640 5,340 6,160 6,820 7,510 8,770 12,900 19,900

Tinton-GSDM 140 312 475 652 879 1,060 1,220 1,420 1,580 1,750 2,260 3,430 6,480

Tinton-GTSMR 140 312 475 652 879 1,060 1,220 1,420 1,580 1,760 2,280 3,480 6,660

Walloon-GSDM 209 463 686 930 1,320 1,640 1,880 2,190 2,440 2,700 3,480 5,270 9,480

Walloon-GTSMR 209 463 686 930 1,320 1,640 1,880 2,180 2,430 2,690 3,470 5,260 9,610

Wivenhoe 947 2,620 4,440 6,440 9,110 10,800 12,400 14,300 15,900 17,600 23,100 N/A 48,100

Woodford-GSDM 212 435 614 803 1,060 1,260 1,480 1,760 1,980 2,230 2,760 3,710 4,980

Woodford-GTSMR 212 435 614 803 1,060 1,260 1,480 1,760 1,980 2,230 2,760 3,710 4,980


Table 3-2 Critical duration 2013 IFD design events


2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley-GSDM 36h 72h 72h 24h 24h 24h 24h 24h 24h 24h 24h 24h 24h

Amberley-GTSMR 36h 72h 72h 24h 24h 24h 24h 24h 24h 24h 24h 24h 24h

Brisbane 36h 72h 72h 72h 96h 96h 96h 96h 96h 96h 72h N/A 96h

Centenary 36h 72h 72h 72h 96h 96h 96h 96h 72h 72h 72h N/A 96h

Fulham Vale 36h 36h 36h 36h 18h 18h 18h 18h 18h 18h 24h 24h 24h

Gatton 36h 36h 36h 36h 36h 12h 12h 12h 12h 12h 24h 24h 24h

Glenore Grove 36h 36h 36h 36h 36h 12h 12h 12h 12h 12h 24h 24h 24h

Gregors Ck 36h 36h 36h 36h 18h 18h 18h 18h 18h 18h 36h 24h 24h

Helidon-GSDM 36h 36h 36h 36h 18h 6h 6h 6h 6h 6h 6h 6h 6h

Helidon-GTSMR 36h 36h 36h 36h 18h 6h 6h 6h 6h 6h 6h 6h 12h

Ipswich 36h 36h 36h 36h 120h 120h 18h 18h 18h 24h 24h 24h 24h

Kalbar-GSDM 36h 36h 36h 36h 12h 12h 12h 12h 12h 12h 12h 12h 12h

Kalbar-GTSMR 36h 36h 36h 36h 12h 12h 12h 12h 12h 12h 12h 12h 12h

Linville 36h 36h 36h 36h 18h 18h 18h 18h 18h 18h 24h 24h 24h

Loamside-GSDM 36h 36h 36h 18h 18h 12h 12h 12h 12h 12h 12h 12h 6h

Loamside-GTSMR 36h 36h 36h 18h 18h 12h 12h 12h 12h 12h 12h 12h 6h

Middle Ck 36h 36h 72h 72h 48h 24h 72h 72h 36h 36h 36h 36h 24h

Moggill 36h 72h 72h 72h 72h 72h 72h 72h 72h 72h 72h N/A 96h

Mt Crosby 36h 72h 72h 72h 72h 72h 72h 72h 72h 72h 36h N/A 36h

Peachester-GSDM 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h

Peachester-GTSMR 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h



2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Rifle Range Rd 36h Flow exceeds main channel capacity of ~ 850 to 1000 m³/s

Savages 36h 72h 72h 72h 72h 72h 72h 72h 72h 72h 36h N/A 36h

Somerset 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 24h 24h

Tinton-GSDM 36h 36h 36h 36h 36h 12h 12h 12h 12h 12h 12h 12h 12h

Tinton-GTSMR 36h 36h 36h 36h 36h 12h 12h 12h 12h 12h 12h 12h 12h

Walloon-GSDM 36h 36h 36h 36h 12h 12h 12h 12h 12h 12h 12h 12h 12h

Walloon-GTSMR 36h 36h 36h 36h 12h 12h 12h 12h 12h 12h 12h 12h 12h

Wivenhoe 36h 36h 72h 72h 72h 72h 72h 72h 72h 72h 36h N/A 36h

Woodford-GSDM 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h

Woodford-GTSMR 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h 36h


Table 3-3 Peak volume of critical duration 2013 IFD design events (GL)


2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley-GSDM 25 77 130 119 165 197 220 250 273 296 364 526 808

Amberley-GTSMR 25 77 130 119 165 197 220 250 273 296 364 526 808

Brisbane 221 805 1,510 2,360 3,770 4,600 5,270 6,090 6,750 7,450 8,610 N/A 18,600

Centenary 209 773 1,460 2,290 3,660 4,470 5,110 5,900 5,930 6,530 8,340 N/A 18,500

Fulham Vale 43 125 245 409 448 551 621 708 777 848 1,270 2,270 3,080

Gatton 8 43 82 146 231 176 201 232 257 283 513 851 1,440

Glenore Grove 13 62 120 213 336 250 285 329 363 399 733 1,240 1,950

Gregors Ck 51 141 269 441 463 568 632 718 783 850 1,490 2,280 3,130

Helidon-GSDM 3 11 21 37 43 35 40 46 51 57 73 107 212

Helidon-GTSMR 3 11 21 37 43 35 40 46 51 57 73 107 289

Ipswich 48 114 193 281 599 721 374 426 467 590 736 1,100 1,550

Kalbar-GSDM 14 34 56 79 63 76 85 96 105 115 143 202 343

Kalbar-GTSMR 14 34 56 79 63 76 85 96 105 114 143 202 343

Linville 26 73 139 229 247 302 337 382 416 452 658 1,100 1,780

Loamside-GSDM 6 15 25 26 36 35 40 45 50 55 65 91 138

Loamside-GTSMR 6 15 25 26 36 35 40 45 50 55 65 91 138

Middle Ck 139 365 857 1,310 1,610 1,350 2,580 2,950 2,340 2,540 3,200 6,030 5,970

Moggill 199 746 1,420 2,220 3,300 4,010 4,530 5,210 5,750 6,320 8,060 N/A 17,900

Mt Crosby 157 610 1,180 1,860 2,770 3,370 3,800 4,370 4,820 5,300 4,880 N/A 9,760

Peachester-GSDM 11 24 33 43 56 66 76 89 98 109 132 169 207

Peachester-GTSMR 11 24 33 43 56 66 76 89 98 109 132 169 207



2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Rifle Range Rd 15 Flow exceeds main channel capacity of ~ 850 to 1000 m³/s

Savages 150 585 1,130 1,780 2,660 3,240 3,640 4,180 4,610 5,060 4,670 N/A 9,470

Somerset 62 153 235 324 445 532 610 705 782 863 1,020 1,110 1,550

Tinton-GSDM 9 20 37 57 84 61 70 80 88 97 122 178 317

Tinton-GTSMR 9 20 37 57 84 61 70 80 88 97 122 178 317

Walloon-GSDM 17 41 69 99 81 98 110 125 137 149 186 268 445

Walloon-GTSMR 17 41 69 99 81 98 110 125 137 149 186 268 445

Wivenhoe 145 381 900 1,370 2,000 2,420 2,720 3,120 3,430 3,750 3,370 N/A 6,310

Woodford-GSDM 23 50 72 94 123 146 167 193 213 235 281 362 454

Woodford-GTSMR 23 50 72 94 123 146 167 193 213 235 281 362 454


Figure 3-23 Peak flow rates 2013 IFD design events – Brisbane River catchment sites



Figure 3-24 Peak flow rates 2013 IFD design events – tributary catchment sites



3.3 Discussion

3.3.1 Peak flow rates Peak flow rates have been analysed at each of the specified location within the Brisbane River catchments and are summarised in Section 3.2.6.

Design frequency curves for the Brisbane River catchments, shown in Figure 3-24 above, generally show a similar trend with flow magnitude increasing with distance downstream

Predictably there is a noticeable increase in flow at each of the major tributaries (Stanley River, Lockyer Creek and Bremer River). Due to relative timing of flows in the tributaries, this increase is not simply the sum of the peak flows of the upstream catchments, as illustrated by the 1 in 100 AEP 72 hour design event (critical duration at Moggill) shown in Figure 3-25 where the increase in peak flow from Mt Crosby Weir to Moggill is nearly 3 times smaller than the peak flow in the Bremer River

Floodplain storage attenuation effects are evident in the Brisbane River downstream of Wivenhoe. With the exception of the minor events (1 in 2 to 1 in 5 AEP), the flood peak tends to decrease slightly between intermediate gauges (ie Savages Crossing to Mt Crosby, Moggill to Brisbane City) as the attenuation outweighs the limited additional local catchment inflows

The tributary design frequency curves, shown in Figure 3-24, appear to show significantly different trends for frequencies greater than 1 in 100 AEP, the Lockyer Creek catchments in particular exhibiting a significantly greater slope. This characteristic is related to the adopted catchment losses, which are higher than average in Lockyer Creek and lower than average in the other tributaries. This variation is exacerbated by rainfall intensities, which are generally lower in the Lockyer and higher in the upper Stanley, meaning the losses represent a greater or lower proportion of the total rainfall respectively

All these characteristics are generally consistent with known behaviour of the Brisbane River catchment.

Figure 3-25 Hydrographs around Brisbane River and Bremer River confluence



Figure 3-26 shows the relationship between peak flow and catchment area for the 1 in 2 and 1 in 100 AEP design events. These show a consistent trend (slope). For the 1 in 2 AEP events there is noticeable difference between the magnitude of flows in the different sub-catchments, with higher flows at the Stanley River catchments where the rainfall intensities are much higher and lower flows in the Lockyer Creek catchment where the rainfall losses are higher. By 1 in 100 AEP the difference between the Lockyer Creek catchment and the Brisbane and Bremer catchments has been largely reconciled, however flows in the Stanley River catchment remain higher. These observations are consistent with rainfall intensity trends.

Figure 3-26 Relationship between peak flow and catchment area



3.3.2 Critical durations Critical storm durations identify the duration of the rainfall event and temporal pattern that cause the highest peak flows at a given site. Critical duration is a function of numerous properties, including catchment area, shape and slope, rainfall intensity, temporal pattern and losses. The application of areal reduction factors has a large influence on the critical storm duration, especially for higher frequency design events, as higher reduction factors are applied to short and high frequency storm events.

Critical duration is shown in Figure 3-27 as a function of catchment area. Two distinct trends can be observed:

For large to extreme events (≤ 1 in 50 AEP) there is generally a trend of increasing critical duration with increasing catchment area, consistent with longer time for runoff to concentrate from the catchment. Critical duration sin the lower Brisbane River are typically of the order of 36 to 96 hours, which is consistent with known characteristics of Brisbane River floods

For minor events (≥ 1 in 5 AEP) the critical duration is at least 36 hours at all sites. This is indicative of initial rainfall losses removing a significant proportion of the volume of short-duration rainfall events

Figure 3-27 Relationship between critical duration and catchment area

A number of outliers can also be identified, including:

For the Stanley River sites (Peachester, Woodford and Somerset), all frequencies have a critical duration of 36 hours (see Section 3.2.1). This may be a characteristic of the high rainfall intensities of the catchment, which reduce the relative magnitude of losses and hence their influence on changing the shape of the effective rainfall hyetograph, combined with the strong double-peak shape of the 36 hour Zone 3 temporal pattern

Critical duration at Middle Creek changes significantly, varying between 24 and 72 hours with no obvious trend (see Figure 3-8). This may reflect the site being affected by timing of Brisbane and



Stanley River catchments, but also that several duration temporal patterns may produce similar peak flows

At Ipswich the 1 in 50 and 1 in 100 AEP critical duration is 120 hours, compared to 36 hours for more frequent events and 18 to 24 hours for rarer events. This may reflect a characteristic of this particular temporal pattern matching with timing of contributions from various parts of the catchment. As shown in Figure 3-28, the 120 hour event peak is only 18 m³/s (0.6%) higher than the 18 hour event peak

Figure 3-28 Ipswich 1 in 100 AEP Design Event hydrographs

3.3.3 Total volume The relationship between total event volume and event AEP has been reviewed between the different stations. The volumes reported in Table 3-3 are the flow volume related to the critical storm duration. These have not been plotted as the relationships show many inconsistencies as the critical duration changes with both catchment and AEP, and direct comparison is not meaningful. Some valid information can be gained where the critical storm durations are identical. For example, total volumes increase slightly (~3%) between Centenary Bridge and Brisbane despite the peak flow actually reducing slightly (~1%).

The design event approach simulates a full range of events with the relationship between rainfall depth and duration taken from standard IFD tables. The total event volume is related to balance between the rainfall volume (depth × catchment area) and losses, and therefore increases with event duration up until the continuing loss outweighs the additional rainfall. The total event volume is therefore largely independent of the peak flow and temporal pattern, except for the tail of the pattern where the loss exceeds the rainfall depth in a given time interval. Maximum volume therefore typically occurs for design events in excess of 6 to 7 days, even for small catchments with a short critical storm duration. Even analysing this long duration volume has limited meaning as the IFD tables are based on rainfall bursts and therefore omit possible antecedent and subsequent rainfall.

An assessment of duration-specific flow volume is presented in Section 4.

3.3.4 Comparison between GSDM and GTSMR GSDM is applicable to critical durations ≤6 hours, while GTSMR is applicable to durations ≥24 hours. Intermediate durations (12 and 18 hours) have been interpolated for both methods. In addition to calculation of PMP, temporal patterns for events between 1 in 200 AEP and the PMP were interpolated from the GSDM and GTSMR temporal patterns.



Both the GSDM and GTSMR PMP methods were applied at 8 sites with a catchment area less than 1,000 km². Table 3-4 summarises the method producing the highest peak flow. Unless otherwise noted, the storm critical duration is 12 hours and thus lies between the two methodologies.

At the largest site (Amberley) and the two Stanley River sites (Peachester and Woodford) the critical duration is consistently at or above 24 hours and only the GTSMR method is applicable

At Helidon the critical duration is consistently 6 hours and only the GSDM method is applicable, with the exception of the PMF where the 12 hour GTSMR storm is larger than the 6 hour GSDM

At Loamside the critical duration is consistently 12 hours with the GSDM storm giving larger flows, with the exception of the PMF where the critical duration is the 6 hour GSDM

For the remaining three sites (Tinton, Kalbar and Walloon), the time of concentration is consistently 12 hours with the GSDM pattern typically producing higher flows for the more frequent events (1 in 200 to 1 in 1000) and the GTSMR pattern producing higher flows for the rarest events (1 in 100,000 to PMF)

Realistically, both methods give similar results. The GTSMR PMF is typically up to 4% higher than the GSDM method, while for the smaller events the difference is less than ±1%. It could be argued that, within the uncertainty of the interpolation, either method could be used with reasonable confidence.

Table 3-4 Critical temporal pattern

Location AEP (1 in N)

PMF 200 500 1,000 2,000 10,000 100,000

Peachester 36h (GTSMR) 36h (GTSMR) 36h (GTSMR) 36h (GTSMR) 36h (GTSMR) 36h (GTSMR) 36h (GTSMR)

Loamside GSDM GSDM GSDM GSDM GSDM GSDM 6h (GSDM)

Woodford 36h (GTSMR) 36h (GTSMR) 36h (GTSMR) 36h (GTSMR) 36h (GTSMR) 36h (GTSMR) 36h (GTSMR)

Helidon 6h (GSDM) 6h (GSDM) 6h (GSDM) 6h (GSDM) 6h (GSDM) 6h (GSDM) GTSMR

Tinton GSDM GTSMR GSDM GTSMR GTSMR GTSMR GTSMR

Kalbar GSDM GSDM GSDM GSDM GSDM GTSMR GTSMR

Walloon GSDM GSDM GSDM GSDM GSDM GSDM GTSMR

Amberley 24h (GTSMR) 24h (GTSMR) 24h (GTSMR) 24h (GTSMR) 24h (GTSMR) 24h (GTSMR) 24h (GTSMR)



4.1 Assessment methodology Two fundamentally different approaches may be adopted for the assessment of flood volume. The first is to assess the volume of the complete flood event. As discussed in Section 3.3.3, this assessment is difficult to apply to Design Event modelling. The volume of the event causing maximum flow can vary significantly depending on the critical duration. Total rainfall volume continues to increase with duration, however average rainfall intensity decreases while continuing loss is assumed to remain constant, hence the critical volume duration could be considered to be the point where increased total volume no longer outweighs the loss. However this approach is of limited use and reliability as:

The design event approach and IFD tables are based on rainfall bursts rather than complete rainfall events and therefore do not include possible antecedent and subsequent rainfall

The approximation of constant continuing loss may be flawed as infiltration rates could be expected to decrease as the catchment becomes increasingly saturated

Event volume of real events may be difficult to determine due to baseflow, difficulty of identifying independent flood volume if sequential events occur, and other issues

The alternative approach is to assess the maximum flow volume that occurs in a given time interval. This procedure is straightforward to implement. For each AEP, the flow hydrograph for each storm duration is assessed to calculate the maximum volume within the time interval of interest. The critical volume for that interval is then taken as the maximum of all events. This approach is also more consistent with flood frequency analysis and Monte-Carlo simulation assessments which are based on simulation of rainfall bursts rather than complete flood events. The volume frequency analysis has therefore focussed on volume over a fixed duration.

4.2 Design Event duration dependent volume Peak design event volumes have been calculated for 24, 48 and 72 hour time intervals and are provided for each location in Sections 4.2.1 to 4.2.3. The results are discussed in Section 4.3.

4 Design event flow volume



4.2.1 2013 IFD 24 hour design event volume Table 4-1 summarises peak 24 hour flow volume for the 2013 IFD Design Events. Volume frequency curves at each site are provided in Figure 4-1 and Figure 4-2.

Table 4-1 Peak 24h volume 2013 IFD design events (GL)

AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley-GSDM 14 32.2 47.2 67.7 100 120 137 159 178 199 255 405 676

Amberley-GTSMR 14 32.2 47.2 67.7 100 120 137 159 178 199 255 405 676

Brisbane 70.5 269 465 685 987 1180 1350 1570 1750 1960 2550 N/A 5260

Centenary 70.7 268 465 687 985 1180 1360 1580 1770 1980 2590 N/A 5430

Fulham Vale 30.3 91.2 153 234 365 452 511 587 647 711 937 1760 2450

Gatton 6.19 35.6 59.9 99.3 155 190 219 256 285 316 428 732 1280

Glenore Grove 9.28 49.9 85 136 214 267 307 358 398 441 598 1050 1730

Gregors Ck 30.5 91.6 154 234 363 451 508 583 643 706 931 1770 2480

Helidon-GSDM 2.3 9.28 15.3 25.5 39.2 49 56.5 65.7 73.1 80.9 106 162 359

Helidon-GTSMR 2.3 9.28 15.3 25.5 39.2 49 56.5 65.7 73.1 80.9 106 162 359

Ipswich 27.4 63.6 95.3 137 203 244 280 325 363 403 533 872 1270

Kalbar-GSDM 9.92 21 32.7 46.6 65.9 79.7 90.7 105 116 128 163 234 413

Kalbar-GTSMR 9.92 21 32.7 46.6 65.9 79.7 90.7 105 116 128 163 234 413

Linville 16 48.2 81 126 196 243 275 316 348 382 496 875 1500

Loamside-GSDM 3.96 8.88 13.6 20.1 28.5 34.5 39.7 46.2 51.4 57.1 68.6 99.1 164

Loamside-GTSMR 3.96 8.88 13.6 20.1 28.5 34.5 39.7 46.2 51.4 57.1 68.6 99.1 164

Middle Ck 69.6 190 322 471 688 814 932 1080 1200 1330 1770 3650 4310

Moggill 71.1 270 470 697 1010 1210 1390 1610 1790 2000 2610 N/A 5400


AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Mt Crosby 65.2 240 417 622 914 1100 1270 1480 1640 1820 2350 N/A 5070

Peachester-GSDM 6.05 12.2 18.1 24.2 32.3 38.6 44.6 52.3 59.6 67.6 85.9 117 150

Peachester-GTSMR 6.05 12.2 18.1 24.2 32.3 38.6 44.6 52.3 59.6 67.6 85.9 117 150

Rifle Range Rd 9.32 52.2 72.5 73.4 73.4 73.4 73.4 73.4 73.4 73.4 73.4 73.4 73.4

Savages 66.1 238 414 616 907 1090 1250 1450 1610 1780 2350 N/A 5120

Somerset 39.3 85.5 130 182 254 304 358 421 474 532 646 922 1270

Tinton-GSDM 6.93 15.1 24.3 36.4 53.6 65.6 75.2 87.2 96.7 107 137 201 370

Tinton-GTSMR 6.93 15.1 24.3 36.4 53.6 65.6 75.2 87.2 96.7 107 137 201 370

Walloon-GSDM 11.3 25 38.5 57.4 82 99 113 131 146 161 205 299 518

Walloon-GTSMR 11.3 25 38.5 57.4 82 99 113 131 146 161 205 299 518

Wivenhoe 69.5 194 330 484 701 833 959 1110 1240 1380 1780 N/A 3660

Woodford-GSDM 12.2 25.2 37.3 50.5 68.1 81.6 94.8 113 128 145 181 247 326

Woodford-GTSMR 12.2 25.2 37.3 50.5 68.1 81.6 94.8 113 128 145 181 247 326


Figure 4-1 Peak 24h volume 2013 IFD design events – Brisbane River catchment sites Figure 4-2 Peak 24h volume 2013 IFD design events – tributary catchment sites




AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley-GSDM 20 53.4 84.8 121 172 207 236 273 303 335 416 625 985

Amberley-GTSMR 20 53.4 84.8 121 172 207 236 273 303 335 416 625 985

Brisbane 126 460 849 1290 1870 2240 2560 2960 3290 3660 4740 5880 9760

Centenary 123 453 838 1280 1860 2240 2560 2970 3300 3670 4770 5880 10000

Fulham Vale 39.1 123 232 377 599 739 830 946 1040 1130 1420 2620 3600

Gatton 7.67 43.1 85.9 147 241 292 336 391 435 480 622 1050 1790

Glenore Grove 11.7 62.8 125 206 339 419 481 558 620 685 882 1520 2390

Gregors Ck 39.9 125 235 377 598 737 826 939 1030 1120 1410 2640 3670

Helidon-GSDM 2.71 11.2 21.6 36.9 59.8 74.1 85.2 98.5 109 121 153 236 515

Helidon-GTSMR 2.71 11.2 21.6 36.9 59.8 74.1 85.2 98.5 109 121 153 236 515

Ipswich 38.6 104 166 238 346 419 481 558 621 688 857 1300 1800

Kalbar-GSDM 12.4 31.1 50 73.7 105 126 143 164 180 197 245 350 593

Kalbar-GTSMR 12.4 31.1 50 73.7 105 126 143 164 180 197 245 350 593

Linville 20.7 62.5 119 196 312 385 434 496 545 596 735 1280 2120

Loamside-GSDM 5.14 13.1 21.3 31.7 45.7 55.1 63.9 74.4 82.9 92.4 110 153 241

Loamside-GTSMR 5.14 13.1 21.3 31.7 45.7 55.1 63.9 74.4 82.9 92.4 110 153 241

Middle Ck 101 307 536 806 1210 1470 1670 1920 2130 2350 2960 5690 6650

Moggill 121 447 833 1290 1890 2270 2610 3010 3340 3700 4770 N/A 9990


AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Mt Crosby 102 386 713 1110 1670 2020 2330 2700 3010 3330 4210 N/A 8880

Peachester-GSDM 9.73 20.5 29.9 40.2 53.7 63.9 75.6 89.4 101 113 142 188 225

Peachester-GTSMR 9.73 20.5 29.9 40.2 53.7 63.9 75.6 89.4 101 113 142 188 225

Rifle Range Rd 12.5 70.2 131 147 147 147 147 147 147 147 147 147 147

Savages 102 380 700 1090 1630 1980 2280 2650 2940 3260 4140 8810 8810

Somerset 60.3 138 218 310 433 522 609 710 795 886 1050 1460 1860

Tinton-GSDM 8.22 20.9 35.6 56.1 84.8 103 117 135 149 163 204 298 537

Tinton-GTSMR 8.22 20.9 35.6 56.1 84.8 103 117 135 149 163 204 298 537

Walloon-GSDM 14.2 36.5 59.9 90 131 158 180 208 230 254 314 456 740

Walloon-GTSMR 14.2 36.5 59.9 90 131 158 180 208 230 254 314 456 740

Wivenhoe 102 314 552 839 1240 1510 1730 1990 2220 2450 3060 N/A 5880

Woodford-GSDM 19.7 42.5 62.7 85.3 115 138 162 191 216 244 299 398 485

Woodford-GTSMR 19.7 42.5 62.7 85.3 115 138 162 191 216 244 299 398 485






AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley-GSDM 22.1 65 109 160 233 276 312 357 393 431 508 774 1260

Amberley-GTSMR 22.1 65 109 160 233 276 312 357 393 431 508 774 1260

Brisbane 166 593 1130 1770 2590 3110 3550 4090 4530 5010 6420 N/A 13100

Centenary 160 579 1110 1740 2560 3080 3520 4060 4500 4980 6400 N/A 13300

Fulham Vale 41.7 134 289 490 765 943 1060 1200 1320 1440 1740 3260 4520

Gatton 8.11 45.6 103 186 307 372 424 490 542 597 749 1280 2230

Glenore Grove 12.5 67.2 151 270 435 538 612 705 779 857 1070 1860 2960

Gregors Ck 43.3 138 292 493 766 943 1050 1200 1310 1420 1730 3270 4580

Helidon-GSDM 2.82 11.8 26.5 47 75.2 93.3 106 122 136 149 184 288 653

Helidon-GTSMR 2.82 11.8 26.5 47 75.2 93.3 106 122 136 149 184 288 653

Ipswich 42.7 125 215 319 458 553 629 724 800 880 1070 1620 2300

Kalbar-GSDM 13.7 38.9 64.8 94.5 134 161 180 205 225 245 296 429 752

Kalbar-GTSMR 13.7 38.9 64.8 94.5 134 161 180 205 225 245 296 429 752

Linville 22.4 68.7 148 251 393 484 543 617 677 738 888 1580 2680

Loamside-GSDM 5.57 16.1 27.3 40.4 57.9 69.8 80.6 93.1 103 115 133 188 307

Loamside-GTSMR 5.57 16.1 27.3 40.4 57.9 69.8 80.6 93.1 103 115 133 188 307

Middle Ck 113 367 686 1070 1600 1950 2230 2560 2830 3110 3850 7420 8700

Moggill 156 569 1090 1730 2560 3100 3540 4080 4530 5000 6380 N/A 13200


AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Mt Crosby 124 469 925 1480 2220 2720 3100 3580 3960 4380 5530 N/A 11700

Peachester-GSDM 12.1 26.4 38.2 51.1 68.1 81 96.4 114 129 145 182 237 286

Peachester-GTSMR 12.1 26.4 38.2 51.1 68.1 81 96.4 114 129 145 182 237 286

Rifle Range Rd 13.8 77.7 165 219 220 220 220 220 220 220 220 220 220

Savages 121 458 900 1440 2170 2660 3030 3490 3860 4260 5400 N/A 11500

Somerset 69.4 181 283 400 559 675 791 923 1030 1150 1370 1900 2390

Tinton-GSDM 8.54 23.7 45.7 71.9 107 130 147 169 186 204 250 370 682

Tinton-GTSMR 8.54 23.7 45.7 71.9 107 130 147 169 186 204 250 370 682

Walloon-GSDM 15.3 44.6 77.2 115 167 202 229 262 288 316 382 559 935

Walloon-GTSMR 15.3 44.6 77.2 115 167 202 229 262 288 316 382 559 935

Wivenhoe 117 384 714 1110 1660 2030 2310 2660 2950 3250 4010 N/A 7720

Woodford-GSDM 24 54.7 80.9 110 148 177 209 246 277 310 381 501 617

Woodford-GTSMR 24 54.7 80.9 110 148 177 209 246 277 310 381 501 617




4.3 Discussion The volume frequency curves shown in Figure 4-1 to Figure 4-6 tend to show similar trends to peak flow rates. Figure 4-7 shows the ratio between the peak 24 hour volume, presented in the form of an average flow over that period, and the design event peak flow. Note that these are the maximum values across the full range of durations and do not necessarily come from the same duration event. The ratio approaches unity as the catchment area increases. This is consistent with the flow hydrograph becoming more drawn out and uniform. The relatively lower ratio observed in the Lockyer Creek catchment suggests that hydrographs at these sites tend to have a sharper peak, which may be a function of the catchment shape, rainfall intensity and losses. The patterns for the 48 and 72 hour volumes, shown in Figure 4-8 and Figure 4-9 respectively, are similar however the ratio tends to decrease as the duration increases.

Figure 4-7 Ratio of maximum average 24 hour flow to maximum peak flow







5.1 Purpose of sensitivity testing Design Event analysis is conducted in accordance with standard procedures outlined in AR&R (1987). Although these procedures allow a consistent and accepted design approach to be undertaken, there are still limitations on the reliability of the method as many of the parameters are based on:

Data that is currently in the process of being updated/superseded (eg rainfall IFD)

Variables that in absence of calibration data are based on typical values and engineering judgement (eg rainfall losses)

Normalised and/or regionalised characteristics that do not necessarily reflect either the characteristic or worst-case conditions for a specific catchment (eg temporal patterns)

Sensitivity testing has been conducted to investigate the influence that a number of these adopted parameters have on the peak flow predictions. Results of these analyses are presented and discussed in the sections below. Design event frequency curves comparing the different alternatives are provided in Appendix D.

5.2 Comparison between 1987 and 2013 IFD results The 1987 IFD data has been updated by new IFD data released in 2013, but has not been officially superseded as other components of the update, including temporal patterns, have not yet been released. Current advice from the BoM at the time that the BRCFS analysis was undertaken recommended conducting analysis using the 1987 IFD data and temporal patterns, and to perform sensitivity testing using the 2013 data. As one of the focusses of the BRCFS is the development of new Monte-Carlo simulation techniques, the 2013 IFD data has been adopted as the standard for this study to provide consistency between the techniques.

Peak flows calculated using the 1987 IFD tables are listed in Table 5-1. Figure 5-1 shows the relationship between design event peak flows calculated using the 2013 IFD and 1987 IFD data. The ratio between the peak flows based on 1987 and 2013 data is presented in Figure 5-2 as a function of event AEP. Although these figures appear to show significantly higher flows for high frequency flows when using the 1987 data, particularly for the Lockyer Creek catchment, it is cautioned that 2013 IFD data is provided as a function of AEP whereas the 1987 data is provided as a function of ARI, making direct comparison at high AEP/low ARI difficult.

Although there is a known theoretical relationship between AEP and ARI, the relationship between AEP/ARI and flow varies with catchment and the flow ratio is therefore not consistent. An ARI of 2 years theoretically correlates to an AEP of approximately 1 in 2.5. Figure 3-24 shows that the Lockyer Creek catchment flood frequency curves are significantly steeper than other catchments for high AEP

5 Sensitivity testing



and the difference between a 1 in 2 and 1 in 2.5 AEP flow will therefore be greater. Any conclusions regarding the magnitude of the ratio for high AEP events should be treated with caution. A better comparison may be obtained at each site from the frequency curves in Appendix D where the rainfall ARI has been plotted as an equivalent AEP. These indicate that the trend in high AEP flows is typically in the same direction as low AEP flows (ie Lockyer decreases, Stanley and Bremer increase).

Table 5-1 Peak flow rates 1987 IFD design events (m3/s)

ARI Event (Years)

Location 2 5 10 20 50 100

Amberley-GSDM 268 435 569 866 1300 1610

Amberley-GTSMR 268 435 569 866 1300 1610

Brisbane 1520 3480 5380 7820 11100 13100

Centenary 1530 3490 5410 7900 11100 13200

Fulham Vale 853 1780 2710 3910 5560 6830

Gatton 407 986 1500 2160 2970 3630

Glenore Grove 491 1230 1910 2780 3890 4790

Gregors Ck 861 1800 2740 3950 5570 6840

Helidon-GSDM 147 298 433 615 862 1030

Helidon-GTSMR 147 298 433 615 862 1030

Ipswich 493 978 1300 1780 2540 3030

Kalbar-GSDM 235 423 565 757 1050 1270

Kalbar-GTSMR 235 423 565 757 1050 1270

Linville 506 1070 1630 2340 3310 4010

Loamside-GSDM 73.3 144 201 285 394 475

Loamside-GTSMR 73.3 144 201 285 394 475

Middle Ck 1430 2890 4260 6040 8670 10600

Moggill 1560 3580 5580 8170 11600 13800

Mt Crosby 1520 3380 5190 7610 11000 13000

Peachester-GSDM 137 230 297 383 494 579

Peachester-GTSMR 137 230 297 383 494 579

Rifle Range Rd 448 850 850 850 850 850

Savages 1580 3510 5300 7710 11200 13200

Somerset 795 1450 1940 2580 3430 4070

Tinton-GSDM 175 336 470 643 883 1090

Tinton-GTSMR 175 336 470 643 883 1090

Walloon-GSDM 265 496 673 915 1280 1560

Walloon-GTSMR 265 496 673 915 1280 1560

Wivenhoe 1410 2850 4260 6180 8730 10500

Woodford-GSDM 268 451 582 749 969 1130

Woodford-GTSMR 268 451 582 749 969 1130



Figure 5-1 Relationship between 2013 IFD and 1987 IFD Design Event Peak Flows

Figure 5-2 Influence of IFD data on design event flow as a function of frequency



Table 5-2 lists the average difference between the peak 1 in 100 AEP flow calculated using the 1987 IFD data relative to the 2013 IFD data. Flows in the Lockyer Creek catchment have typically decreased from 1987 to 2013, while flows in the Bremer and Stanley River catchments have increased. Brisbane River flows are relatively unchanged. Flow volumes show similar trends to the peak flows. These changes represent additional years of rainfall record, but also increased number of gauges and different spatial interpolation techniques.

Table 5-2 Difference between 1987 and 2013 peak 1 in 100 AEP values (relative to 2013)

Catchment Peak Flow 24h Volume 48h Volume 72h Volume

Brisbane -0.2% -0.1% -0.1% -2.2%

Bremer -6.8% -7.1% -6.5% -10.1%

Lockyer 10.6% 13.8% 9.9% 2.8%

Stanley -9.7% -7.6% -11.3% -11.1% Figure 5-3 shows the relationship between design event critical duration calculated using the 2013 IFD and 1987 IFD data. For many sites the critical duration remains unchanged, although at a number of sites, particularly in the Bremer River catchment, the critical duration decreases. This may indicate a shift in the intensity-duration relationship (eg a greater increase in long-duration rainfall intensities), although it should be noted that often several durations will produce similar peak flows, as shown in Figure 3-28.

Figure 5-3 Influence of IFD data on design event critical duration as a function of frequency

5.3 Influence of rainfall losses Rainfall losses are subtracted from the incident rainfall before runoff occurs. In the absence of specific calibration data these are selected based on typical values and engineering judgement. Sensitivity testing of the influence of rainfall losses was performed by increasing and decreasing the typical losses listed in Table 2-4 by 20%. Peak flows calculated using the factored losses are listed in Table 5-3 and Table 5-4, and are compared with the original typical losses in Figure 5-4.

The influence of losses on peak flow is dependent on the magnitude of the losses relative to rainfall intensity. The losses have significant impact on high AEP flows, particularly 1 in 2 AEP as illustrated in Figure 5-6. The greatest impact for high AEP events occur for the Lockyer catchment, which has both



the lowest rainfall intensity and highest losses (and hence a higher absolute change in loss when adopting a constant factor). The influence of losses decreases significantly with decreasing AEP as rainfall intensity increases and the adopted losses decrease. The impact of modifying the losses by ±20% is less than ±2% of the 1 in 100 AEP flow.

Table 5-3 Peak flow rates with losses increased by 20% (m3/s)

AEP Event (1 in N)

Location 2 5 10 20 50 100

Amberley-GSDM 179 378 570 826 1330 1690

Amberley-GTSMR 179 378 570 826 1330 1690

Brisbane 554 2860 5160 7740 11300 13600

Centenary 553 2870 5190 7810 11300 13700

Fulham Vale 169 1300 2300 3480 5100 6350

Gatton 22.4 682 1200 1850 2620 3240

Glenore Grove 35.9 876 1570 2450 3540 4380

Gregors Ck 169 1310 2310 3510 5110 6350

Helidon-GSDM 13.8 193 331 492 712 908

Helidon-GTSMR 13.8 193 331 492 712 908

Ipswich 330 829 1260 1770 2650 3220

Kalbar-GSDM 157 359 544 747 1050 1320

Kalbar-GTSMR 157 359 544 747 1050 1320

Linville 89.4 727 1290 1970 2900 3550

Loamside-GSDM 56.1 135 212 299 431 533

Loamside-GTSMR 56.1 135 212 299 431 533

Middle Ck 587 2350 3990 6010 8640 10400

Moggill 557 2930 5330 8080 11900 14300

Mt Crosby 480 2710 4910 7510 11200 13400

Peachester-GSDM 102 213 303 397 523 618


Rifle Range Rd 32.1 820 850 850 851 850

Savages 490 2810 5030 7610 11400 13600

Somerset 580 1380 2080 2840 3880 4610

Tinton-GSDM 91.8 274 444 629 866 1050

Tinton-GTSMR 91.8 274 444 629 866 1050

Walloon-GSDM 180 420 651 902 1300 1630

Walloon-GTSMR 180 420 651 902 1300 1630

Wivenhoe 580 2320 4060 6150 8920 10600

Woodford-GSDM 189 413 596 790 1050 1250

Woodford-GTSMR 189 413 596 790 1050 1250



Table 5-4 Peak flow rates with losses decreased by 20% (m3/s)

AEP Event (1 in N)

Location 2 5 10 20 50 100

Amberley-GSDM 253 461 650 956 1400 1730

Amberley-GTSMR 253 461 650 956 1400 1730

Brisbane 1520 4040 6140 8640 12000 14200

Centenary 1530 4050 6190 8730 12000 14300

Fulham Vale 789 1790 2770 3840 5420 6520

Gatton 376 941 1470 2040 2740 3310

Glenore Grove 479 1220 1940 2720 3710 4480

Gregors Ck 795 1800 2800 3870 5420 6520

Helidon-GSDM 115 260 394 543 744 921

Helidon-GTSMR 115 260 394 543 744 921

Ipswich 482 1020 1430 1920 2760 3320

Kalbar-GSDM 219 428 601 795 1100 1340

Kalbar-GTSMR 219 428 601 795 1100 1340

Linville 438 1000 1560 2170 3060 3650

Loamside-GSDM 79.5 166 239 326 445 540

Loamside-GTSMR 79.5 166 239 326 445 540

Middle Ck 1370 3060 4720 6580 9010 10700

Moggill 1560 4150 6410 9020 12500 14900

Mt Crosby 1510 3770 5900 8330 11800 14000

Peachester-GSDM 124 233 318 408 528 623


Rifle Range Rd 452 850 850 850 850 850

Savages 1570 3840 6000 8470 12000 14200

Somerset 774 1580 2250 2960 3940 4670

Tinton-GSDM 166 350 507 676 893 1070

Tinton-GTSMR 166 350 507 676 893 1070

Walloon-GSDM 252 510 724 977 1350 1650

Walloon-GTSMR 252 510 724 977 1350 1650

Wivenhoe 1350 3080 4830 6750 9290 11000

Woodford-GSDM 237 458 631 816 1070 1260

Woodford-GTSMR 237 458 631 816 1070 1260



Figure 5-4 Relationship between factored and typical loss Design Event Peak Flows

Figure 5-5 Influence of losses on design event flow as a function of frequency



5.4 Influence of temporal pattern The AR&R Design Event methodology adopts standard temporal pattern that are dependent on AEP and duration (event specific) and catchment location (region specific). The Brisbane River catchment is located within the region defined as Zone 3. This zone covers the entire coast region west of the Great Dividing Range from south of the New South Wales border all the way north to the tip of Cape York. All the catchments in this region are assumed to have identical characteristic rainfall patterns.

As shown in Figure 5-7, the western side of the Brisbane River catchment shares a border with Zone 2, while the southern corner of the catchment adjoins Zone 1. Sensitivity testing to the influence of temporal pattern was performed using the Zone 2 temporal patterns. Peak flows calculated using the Zone 2 temporal patterns and 2013 IFD tables are listed in Table 5-5. Figure 5-7 shows the relationship between design event peak flows calculated using the Zone 2 and Zone 3 patterns while the ratio between the peak flows based on is presented in Figure 5-8 as a function of event AEP.

Figure 5-6 Zones for temporal patterns (from AR&R 2003)

Brisbane River



Table 5-5 Peak flow rates Zone 2 temporal pattern design events (m3/s)

AEP Event (1 in N)

Location 2 5 10 20 50 100

Amberley-GSDM 195 569 1030 1560 2110 2610

Amberley-GTSMR 195 569 1030 1560 2110 2610

Brisbane 719 3960 6990 9870 13400 16300

Centenary 708 3980 7090 10100 13800 16900

Fulham Vale 117 1700 3560 5570 7630 9500

Gatton 1.93 776 1910 3130 4270 5350

Glenore Grove 20.8 1020 2520 4170 5770 7260

Gregors Ck 117 1700 3570 5570 7620 9480

Helidon-GSDM 11.2 239 539 855 1150 1450

Helidon-GTSMR 11.2 239 539 855 1150 1450

Ipswich 315 1250 2010 2900 3950 4940

Kalbar-GSDM 183 591 936 1310 1670 2040

Kalbar-GTSMR 183 591 936 1310 1670 2040

Linville 53.3 897 1890 2970 4070 5110

Loamside-GSDM 56.7 207 341 487 635 783

Loamside-GTSMR 56.7 207 341 487 635 783

Middle Ck 745 3570 6480 9520 12900 16000

Moggill 705 4110 7490 10800 15000 18100

Mt Crosby 627 3920 7410 11100 15600 19300

Peachester-GSDM 155 322 459 606 750 912


Rifle Range Rd 19.3 850 850 850 850 850

Savages 635 4080 7660 11600 16100 19700

Somerset 829 2060 3120 4280 5490 6770

Tinton-GSDM 71.8 403 705 1020 1330 1630

Tinton-GTSMR 71.8 403 705 1020 1330 1630

Walloon-GSDM 178 672 1110 1590 2060 2520

Walloon-GTSMR 178 672 1110 1590 2060 2520

Wivenhoe 737 3540 6440 9500 12900 15900

Woodford-GSDM 287 620 895 1190 1490 1820

Woodford-GTSMR 287 620 895 1190 1490 1820



Figure 5-7 Relationship between Zone 3 and Zone 2 design event peak flows

Figure 5-8 Influence of temporal pattern on design event flow as a function of frequency



Figure 5-8 shows that, with the exception of the 1 in 2 AEP, using the Zone 2 temporal pattern results in significant increases in peak flow. Above 1 in 100 AEP the difference decreases as the temporal patterns approach the same PMP pattern. Comparison between the Zone 2 and Zone 3 frequency curves are provided in Appendix D. Table 5-6 lists the average difference between the peak 1 in 100 AEP flows and volumes calculated using the Zone 2 temporal pattern relative to the Zone 2. Figure 5-9 shows the ratio of peak flows as a function of AEP and catchment area. For most sites, flows are increased by between 35% and 80%. The increase is most pronounced for AEP of 1 in 10 to 1 in 20 and catchments of 300 to 1,000 km². For the lower Brisbane sites (Moggill to Brisbane City) the increase is only around 15% to 25%. Maximum 24 hour flow volumes are also increased. The increase in volume decreases with volume duration, and the overall effect on the 72 hour flow volume is negligible.

Table 5-6 Relative difference between Zone 3 and Zone 2 peak 1 in 100 AEP values

Catchment Peak Flow 24h Volume 48h Volume 72h Volume

Brisbane 40% 34% 16% 2%

Bremer 51% 40% 17% 2%

Lockyer 62% 42% 17% -1%

Stanley 46% 40% 15% 2%

Figure 5-9 Influence of temporal pattern on design event flow as a function of catchment area

5.5 Influence of base flow Sensitivity of model results to base flow was undertaken and reported in the ‘Hydrologic Model Calibration and Verification Review Report’ and was found to have relatively minor influence on flood flows. The influence of base flow on design events is therefore considered to be small and well within the variability of the other factors considered above. No additional sensitivity testing on base flow has been conducted.



6.1 Modelling of dam operations The results discussed in Sections 3 to 5 are for ‘no-dams conditions’. Six main reservoirs are considered in the ‘with-dams conditions’. Moogerah, Lake Manchester, Perseverance and Cressbrook Dams are modelled in the URBS hydrological model as level pool storages with fixed crest spillway relationships. Somerset and Wivenhoe Dams are regulated dams with controlled release dependent on upstream and downstream river conditions. A Dam Operations Module was developed within the real-time control software RTC tools as a component of the Delft-FEWS framework for use in assessing the ‘with-dam conditions’ design flood estimates associated with the Monte Carlo Simulation techniques of flood estimation. The Dam Operations Module is based upon the Loss of Communications (LOC) emergency flood operation procedure described in the Flood Manual. Further discussion is provided in the ‘Dam Operations Module Implementation Report’.

Most of the dams represented in the URBS model do not have PMF capacity. In the simulations, flows in excess of the dam capacity are assumed to overtop the dam wall using a weir flow formula. Consequences of overtopping (eg dam failure) are not considered. Further discussion is provided in the ‘Dam Operations Module Implementation Report’, (Aurecon, 2015).

6.2 Dam influence Dam influence has been assessed at the eight sites listed in Table 6-1. The Dam Operations Module operates Somerset Dam releases in response/conjunction to Wivenhoe Dam reservoir levels. Somerset Dam releases have therefore not been independently assessed.

Table 6-1 Dams influencing Brisbane River gauge locations

Dam

Affected Location

Am

berle

y

Ipsw

ich

Wiv

enho

e

Sava

ges

Mt C

rosb

y

Mog

gill

Cen

tena

ry

Bris

bane

Cressbrook Creek

Perseverance

Somerset

Wivenhoe

Lake Manchester

Moogerah

6 Dam influence



A fundamental variable and hence uncertainty in the modelling of catchments with-dams influence is the starting water level in the dams. Monte-Carlo simulation overcomes this uncertainty by starting water levels to be varied in response to a pre-determined probability distribution, however the Design Event methodology requires a starting water level to be assumed.

Dam influence has been assessed for two conditions:

Assuming all dams start at full supply levels

Assuming no release from Wivenhoe (Lake Manchester and Moogerah still start at FSV) The first condition is a conservative upper limit (in terms of the influence of starting water level), and it could be expected that the average starting water level would be less than full supply. As with catchment losses, there may potentially also be some theoretical correlation between starting water level and design event AEP, although investigation of the relationship between initial reservoir volume and cumulative event rainfall presented in the ‘Monte Carlo Simulation Framework and Enhanced MCS Methodology Report’ identified only a weak correlation.

It is acknowledged that this second condition of no Wivenhoe release is not a realistic scenario, particularly for larger floods, and was undertaken solely to identify the relative influence of upper Brisbane River flows/Wivenhoe Dam Release in the lower Brisbane River and as an absolute best-case scenario for any future changes to Wivenhoe capacity or release procedures.

Results of these analyses are presented and discussed in the sections below. Design event frequency curves comparing the different alternatives are provided in Appendix E.

6.2.1 Dam influence – all dams starting at full supply level Table 6-2 to Table 6-5 summarise peak flow and 24, 48 and 72 hour flow volume for the ‘with-dams scenario’ 2013 IFD Design Events assuming all dams start at full supply volume. Flow and volume frequency curves at each site are provided in Figure 6-1 to Figure 6-4.

6.2.2 Dam influence – no Wivenhoe Dam Release Table 6-6 to Table 6-9 summarise peak flow and 24, 48 and 72 hour flow volume for the ‘with-dams scenario’ 2013 IFD Design Events assuming no release from Wivenhoe Dam. Flow and volume frequency curves at each site are provided in Figure 6-5 to Figure 6-8.



Table 6-2 Peak ‘with-dams conditions’ flow assuming all dams at FSV (m³/s)

AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley 147 355 490 690 1100 1350 1560 1830 2050 2280 2860 4510 8280

Brisbane 466 1490 3070 4950 7720 9830 12100 14900 17200 19400 26500 N/A 57700

Centenary 430 1480 3040 4900 7740 9780 12000 15000 17300 19500 27400 N/A 59900

Ipswich 385 909 1310 1780 2540 3110 3570 4190 4680 5200 6690 11300 17300

Moggill 421 1480 3060 4920 7930 10100 12500 15700 17700 20100 28200 N/A 61800

Mt Crosby 135 1120 2360 3840 6610 8810 11600 14800 17300 19000 27100 N/A 63300

Savages 128 1090 2270 3690 6420 8700 11700 15000 17700 18800 29000 N/A 64900

Wivenhoe (Outflow) 135 731 1300 2230 4240 6790 8690 10200 12400 12900 21600 N/A 39000 Table 6-3 Peak ‘with-dams conditions’ 24h volume assuming all dams at FSV (GL)

AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley 10.8 26.2 40.7 56.9 84.8 104 120 141 158 176 223 351 604

Brisbane 36.9 122 255 415 657 838 1020 1260 1450 1640 2220 N/A 4820

Centenary 33 120 251 408 650 832 1010 1260 1450 1640 2250 N/A 4990

Ipswich 24.7 58.3 90.3 126 186 225 259 303 339 377 491 809 1200

Moggill 30.7 119 249 405 657 852 1050 1310 1480 1670 2290 N/A 4960

Mt Crosby 10.7 91.4 194 320 543 747 957 1200 1370 1540 2100 N/A 4670

Savages 10.8 88.6 187 310 528 737 952 1190 1370 1520 2090 N/A 4730

Wivenhoe (Outflow) 11.3 62 110 189 350 521 689 862 968 1090 1460 N/A 2860


Table 6-4 Peak ‘with-dams conditions’ 48h volume assuming all dams at FSV (GL)

AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley 16 45.1 73.9 105 154 186 211 244 270 297 364 565 923

Brisbane 61 230 474 788 1270 1620 1950 2380 2720 3080 4090 N/A 8980

Centenary 53.7 222 461 770 1240 1600 1930 2360 2710 3080 4110 N/A 9210

Ipswich 34.9 95.4 155 221 322 390 449 522 582 645 806 1240 1730

Moggill 48.5 215 451 758 1220 1590 1930 2380 2730 3100 4110 N/A 9170

Mt Crosby 20.9 171 356 599 1010 1350 1680 2090 2400 2730 3610 N/A 8010

Savages 21 166 344 580 988 1320 1640 2040 2350 2680 3530 N/A 7920

Wivenhoe (Outflow) 22 118 211 361 667 920 1160 1480 1720 1980 2540 N/A 5040 Table 6-5 Peak ‘with-dams conditions’ 72h volume assuming all dams at FSV (GL)

AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Amberley 18.8 56.1 95.7 144 213 254 288 332 366 403 477 737 1230

Brisbane 77.2 325 651 1090 1810 2310 2760 3330 3790 4280 5630 N/A 12300

Centenary 67.5 311 629 1060 1780 2280 2730 3290 3750 4240 5610 N/A 12500

Ipswich 39.5 116 202 301 434 526 599 691 764 842 1020 1570 2240

Moggill 61.5 302 614 1040 1760 2260 2710 3280 3750 4250 5580 N/A 12400

Mt Crosby 30.3 233 473 818 1450 1870 2280 2780 3200 3660 4780 N/A 10900

Savages 30.5 227 459 787 1410 1810 2200 2690 3100 3540 4630 N/A 10800

Wivenhoe (Outflow) 31.9 166 299 517 969 1270 1580 1970 2300 2640 3380 N/A 7050


Figure 6-1 Peak ‘with-dams conditions’ flow assuming all dams at FSV Figure 6-2 Peak ‘with-dams conditions’ 24h volume assuming all dams at FSV


Figure 6-3 Peak ‘with-dams conditions’ 48h volume assuming all dams at FSV Figure 6-4 Peak ‘with-dams conditions’ 72h volume assuming all dams at FSV


Table 6-6 Peak ‘with-dams conditions’ flow assuming no release from Wivenhoe (m³/s)

AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Brisbane 466 1260 2270 3720 5420 6570 7580 8760 9680 10600 13700 N/A 28800

Centenary 430 1140 2090 3470 5170 6260 7290 8440 9350 10200 13400 N/A 29800

Moggill 421 1130 2040 3410 5060 6210 7240 8390 9300 10300 14100 N/A 30600

Mt Crosby 135 716 1290 2080 3420 4180 4840 5640 6250 6890 9330 N/A 23400

Savages 84.3 662 1180 1860 3130 3840 4460 5160 5710 6430 9530 N/A 25000 Table 6-7 Peak ‘with-dams conditions’ 24h volume assuming no release from Wivenhoe (GL)

AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Brisbane 36.9 104 192 308 459 554 640 743 824 904 1160 N/A 2420

Centenary 32.9 95.9 179 291 436 527 610 711 791 868 1130 N/A 2490

Moggill 30.5 90.2 169 277 416 510 593 694 773 854 1150 N/A 2450

Mt Crosby 8.55 53.7 101 160 255 317 372 439 493 551 744 N/A 1750

Savages 6.47 48.7 90.7 142 227 283 330 389 436 485 705 N/A 1770


Table 6-8 Peak ‘with-dams conditions’ 48h volume assuming no release from Wivenhoe (GL)

AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Brisbane 60.4 198 361 574 855 1050 1200 1400 1560 1730 2220 N/A 4480

Centenary 52.3 183 337 543 812 997 1150 1330 1480 1640 2130 N/A 4510

Moggill 46.5 172 320 517 779 959 1110 1290 1430 1580 2080 N/A 4380

Mt Crosby 13.8 84.1 176 299 467 583 676 795 892 994 1310 N/A 2860

Savages 10.3 74.5 158 261 404 505 589 692 775 862 1160 N/A 2710 Table 6-9 Peak ‘with-dams conditions’ 72h volume assuming no release from Wivenhoe (GL)

AEP Event (1 in N)

Location 2 5 10 20 50 100 200 500 1,000 2,000 10,000 100,000 PMP

Brisbane 74 258 477 758 1150 1410 1650 1920 2150 2390 3090 N/A 6060

Centenary 63.3 236 443 710 1080 1330 1540 1800 2010 2240 2940 N/A 6050

Moggill 55.5 218 414 665 1020 1250 1450 1700 1900 2110 2780 N/A 5840

Mt Crosby 18.6 108 233 395 625 767 887 1030 1160 1290 1690 N/A 3710

Savages 13.2 88.2 202 346 546 667 765 893 997 1110 1470 N/A 3470


Figure 6-5 Peak ‘with-dams conditions’ flow assuming no release from Wivenhoe Figure 6-6 Peak ‘with-dams conditions’ 24h volume assuming no release from Wivenhoe


Figure 6-7 Peak ‘with-dams conditions’ 48h volume assuming no release from Wivenhoe Figure 6-8 Peak ‘with-dams conditions’ 72h volume assuming no release from Wivenhoe


6.3 Discussion The ‘no-dams conditions’ and ‘with-dams conditions’ design event frequency curves is provided in Appendix E. Figure 6-9 shows the reduction in peak discharge attributable to the dams (assuming starting at FSV). Several general trends are evident:

The main Brisbane River dams provide significant attenuation in the mid-Brisbane River (Wivenhoe to Mt Crosby) for minor events, but become less effective as the magnitude of the flood increases. The attenuation relationship at Wivenhoe release tends to be somewhat erratic, particularly above 1 in 500 AEP when breaching of the fuse plug spillways and then overtopping of the dam crest cause abrupt change in the storage-discharge relationship

Despite the Wivenhoe release showing a reduction in peak flow of around 19% at PMF, the Savages Crossing PMF actually shows a very slight increase. This may be attributable to changes in the timing of the upper Brisbane River and Lockyer Creek flow hydrographs

Attenuation in the lower Brisbane River (Moggill to Brisbane) follows a similar trend to the mid-river sites, but with a smaller attenuation amount due to the additional inflows from the Bremer River

Moogerah Dam tends reduce peak flows at Amberley by around 20% across the full range of events

The dam influence on Bremer River flows at Ipswich is unusual in that it appears to increase with increasing AEP. Moogerah Dam is located in the upper end of an elongated catchment, so this is possibly due to the shape of the rainfall hyetographs and the timing of inflows from Bremer River, Warrill and Purga Creeks. Section 3.3.2 identifies that the Ipswich site displays some unusual variation in the critical duration as different parts of the catchment appear to contribute at different times. Note that as discussed in Section 3.2, the reported flows at Ipswich do not account for storage attenuation due to combined Bremer and Brisbane River flows around the confluence

Figure 6-9 Peak flow attenuation assuming all dams at FSV



Dam influence on 24 and 72 hour flow volumes are shown in Figure 6-10 and Figure 6-11 respectively.

The trends the Brisbane River sites are similar very similar to peak flow (Figure 6-9), which is consistent with the long critical duration of the mid and lower Brisbane River sites. The attenuation of the 72 hour volume tends to be similar but lower. The attenuation would be expected to decrease as the examined duration increases as water is only temporarily stored above the full supply volume

The trend displayed by the 24 hour volumes at Amberley is similar to but slightly lower than the attenuation of peak flow

The 24 hour volume trend at Ipswich is notably different to the peak flow trend, showing attenuation of peak volume for minor events where negligible impact on peak flow is evident. This is consistent with the conclusion that the peak flow is dependent on the timing of inflows from Bremer River, Warrill and Purga Creeks

The 72 hour volume attenuation at Amberley and Ipswich are lower than the 24 hour volume, and decrease as the magnitude of the event increases

Figure 6-10 Peak 24h volume attenuation assuming all dams at FSV



Figure 6-11 Peak 72h volume attenuation assuming all dams at FSV



7.1 Methodology In accordance with Section 3.6.6.4 of the Brisbane River Catchment Flood Study (BRCFS) brief, hydrologic modelling was undertaken to predict design flows, volumes and critical storm durations for design events in the Brisbane River Catchment.

The models developed during the recalibration process and discussed in the Aurecon Team’s Hydrologic Model Recalibration Report have been used as the basis for the design event modelling. These models have been modified to remove all reference to the dams, including storage details and reduced reach length factors for drowned reaches.

The Design Event analysis was performed using standard design procedures outlined in AR&R. This report presents how the calibration models were modified with design specific parameters and assumptions regarding the IFD input, the temporal patterns, the rainfall losses and the baseflow, all depending on the exceedance probability of the design events. Specific variations or amendments to the AR&R methodology are:

The original 1987 IFD data was updated in 2013 with 2300 extra rainfall stations and nearly 30 years’ additional rainfall data, but has not been officially superseded as other components of the update, including temporal patterns, have not yet been released. Current Bureau of Meteorology advice is that “in most cases it would be prudent to use the AR&R87 design parameters and conduct sensitivity testing with revised AR&R design parameters (including the 2013 IFD design rainfalls) as they become available”. For the BRCFS the 2013 IFD data was adopted as the base-case for the Design Event assessment to provide consistency with other components of the study

Temporal patterns for the intermediate range of flood magnitudes between the 1 in 100 AEP and the PMP event have been interpolated using normalised curves of the cumulative temporal patterns to avoid anomalies between flood magnitudes in the large to rare range

PMP rainfall depths were calculated using the GSDM (1 to 6 hour) and GTSMR (24 to 120 hour) methods. Rainfall depths for durations outside this range were long-linearly interpolated and extrapolated. For the 12 hour event, both the GSDM temporal pattern and the 24 hour GTSMR temporal pattern, with the time increments halved, were applied and the worst case results adopted

7.2 Design flows Design flood estimates for each location were determined by running the complete range of storm durations and flood magnitudes. The peak instantaneous flow for each AEP, its associated storm duration and flood volume were included in the summary tables and associated hydrograph plots.

7 Conclusion



Design event flood frequency curves for the Brisbane River catchments generally show similar a trend with flow magnitude generally increasing with distance downstream. The tributary design frequency curves tend to show different trends for frequencies greater than 1 in 100 AEP with the Lockyer Creek catchments in particular exhibiting a significantly greater slope (ie the relative flow magnitude increases more rapidly with event rarity). This characteristic can be related to rainfall intensities and adopted catchment losses. Floodplain storage attenuation effects are evident in the Brisbane River downstream of Wivenhoe with the flood peak of larger floods tending to decrease slightly between Savages Crossing and Mt Crosby and from Moggill to Brisbane City. These characteristics are generally consistent with known behaviour of the Brisbane River catchment.

For minor events (≤ 1 in 5 AEP) the critical duration is at least 36 hours at all sites as rainfall losses removing a significant proportion of the volume of short-duration rainfall events. For large to extreme events (≥ 1 in 50 AEP) the critical duration typically increases with catchment area, consistent with longer time for runoff to concentrate from the catchment.

7.3 Volume analysis Flow volume can be assessed either on an event or burst basis. The former, which requires calculating the total volume of an independent flood event, has limited meaning for design event analysis, which is based on rainfall bursts rather than complete events, and is difficult to apply to independent verification methods such as stream gauge assessment. Total volumes of the critical storm events (the event causing highest peak flow) are presented in Table 3-3 but have limited practical purpose as the volume is dependent on the critical storm duration, which is often not consistent between locations or AEPs.

The volume frequency analysis presented in Section 4 has assessed burst volume, which measures the highest recorded flow volume that occurs over a fixed duration. This does not necessarily occur in the same event that causes maximum flow. There is likely to be some correlation for short duration volumes, particularly for large catchments, but the correlation could be expected to decrease as the duration increases.

The assessment has considered flood runoff volumes over 24, 48, and 72 hour periods. The ratio between the flow volume, presented as an average flowrate over the time interval, and the peak flowrate is dependent on sharpness of hydrograph peak, which is dependent on the catchment shape, response and size. For sites in the lower Brisbane River, which experience relatively prolonged flood events, this ratio can be nearly unity for the 24 hour volume.

7.4 Sensitivity testing Design Event analysis is dependent on parameters that are based on normalised and/or regionalised characteristics, such as IFD and temporal patterns, or on values that must be estimated using knowledge of the catchment behaviour or else assumed from typical values. The currency of and appropriateness of a number of these parameters are currently being assessed as part of the review of AR&R. At the time of the BRCFS assessment some of the updates had been released (eg IFD) however other components were not available (eg temporal patterns).

Testing was performed to investigate the sensitivity of the flow and volume predictions to several of the main parameters, and identified that:

Adopting 1987 or 2013 IFD data results in a difference in peak flow of around ±10% across the full range of frequencies covered by the AR&R IFD tables (1 in 2 to 1 in 100 AEP). The 2013 IFD data typically increases flows in the Stanley and Bremer River systems, but decreases flows in Lockyer Creek. Brisbane River flows are relatively unchanged



Rainfall losses have significant influence on high AEP flows due to the lower intensity/depth. There is relatively little influence on low AEP flows due to the higher intensity rainfall and typically lower losses adopted

Temporal patterns have significant impact across the full range of flood frequencies. Using Zone 2 temporal patterns instead of Zone 3 results in flow increases of 20% to 80%

High AEP flows are strongly affected by assumed losses and temporal patterns. Flow estimates therefore have low reliability unless confirmed against other sources. Low AEP flows are not as sensitive to losses but are still affected by IFD and temporal pattern. Due to this uncertainty, confirmation using independent assessment methods (flood frequency analysis and Monte-Carlo simulation) is recommended.

7.5 Dam influence on design flows and volumes Sites in the Warrill Creek, mid- and lower Brisbane River are affected by the presence of dams. Dam influence on peak flow and flood volume has been assessed at the Amberley, Ipswich, and the six Brisbane River sites from Wivenhoe to Brisbane City.

The major flood mitigation dams of Somerset and Wivenhoe have a strong influence on downstream flows in the Brisbane River. The dam attenuation is particularly significant for minor events (in excess of 80% upstream and 50% downstream of Moggill) but decreases as the event magnitude increases. The dams have minor impact for extreme events (typically <10 to 15% above 1 in 5000 AEP).

Moogerah Dam on Warrill Creek has a consistent but minor influence on peak flows at Amberley; typically around 20% for the full range of design event AEP. The dam has negligible effect on peak flows at Ipswich for minor events, most likely due to the relative magnitude and timing of flows from other parts of the catchment (Bremer River and Purga Creek), but attenuation appears to increase to around 10% of peak flow for extreme events.

It is cautioned that the representation of the dam overflow characteristics does not address the possibility and consequences of dam failure and events/flows that exceed the dam capacity should be used with caution.

7.6 Assumptions and limitations Design event analysis adopts standard procedures and parameters outlined in AR&R to form a consistent and accepted design approach. This is not a simulation of ‘real’ storm events and may not identify the variability or even necessarily the worst-case conditions identify the area or catchment specific. Many of the limitations of this methodology are identified and discussed in AR&R. Specific limitations encountered or identified by this study include:

Design Event assessment has been conducted using hydrologic models. A number of areas of the Brisbane River catchment, such as the perched channel in the lower Lockyer floodplain, backwater effects from the Brisbane River in the lower reaches of Lockyer Creek and the Bremer River, and dynamic response of the lower Brisbane River, display complex hydraulic effects that cannot be completely replicated by a hydrologic model

The hydrologic models have been calibrated against historical flood events. These models have been assumed to be appropriate up to PMF, well in excess of the calibration events. The reliability of the models, in particular the conceptual storages used in the mid- and lower Brisbane River, has not been validated for extreme events



The Design Event methodology has adopted a fixed initial loss and constant continuing loss. This is a commonly adopted procedure that performed acceptably for the model calibration. Early calibration work conducted by Seqwater found a better match could be obtained at some locations and for some long duration events using a continuing loss that reduced with time such as an infiltration curve. Discussions with the IPE considered that this would be too difficult to implement and validate for limited overall benefit

Initial and continuing losses have been adopted based on typical values with some influence from trends observed in calibration events. These losses produce design flow frequencies that show reasonable match with stream gauge flood frequency analysis, however the losses have not specifically been adjusted to reconcile with other methods (eg flood frequency analysis, Monte-Carlo simulation) at any particular site

The most up-to-date design (2013) IFD estimates have been used, in conjunction with earlier (1987) storm temporal pattern information, as appropriate temporal patterns for use with the 2013 IFD information are not yet available. The 2013 IFD information has been used in this design event approach so as to be consistent with the catchment rainfall depth information used in the Monte Carlo approach

Modelling of dam influence has assessed two scenarios – all dams at full supply level and no release from Wivenhoe Dam. The former scenario does not address average/likely starting level in the dams, which is assessed in the Monte Carlo simulations. These results have not been reconciled to produce an equivalent starting level for the Design Event. The latter scenario is not considered a realistic condition, particularly for major events, but has been assessed for information purposes

Dam operations have been modelled using a Dam Operations Module based upon the Loss of Communications (LOC) emergency flood operation procedure described in the Flood Manual. Flows in excess of the dam capacities have been assumed to overtop the dam wall without causing failure. These issues are discussed further in the ‘Dam Operations Module Implementation Report’



Aurecon. (2015). Hydrologic Model Recalibration Report

Aurecon. (2015). Hydrologic Model Calibration and Validation Review Report

Aurecon, (2015), Dam operations module implementation Report

Australian Government Bureau of Meteorology, (2003a). Guidebook to the Estimation of Probable Maximum Precipitation: GENERALISED TROPICAL STORM METHOD

Australian Government Bureau of Meteorology, (2003b). The Estimation of Probable Maximum Precipitation in Australia: Generalised Short Duration Method

Engineers Australia Water Engineering, (2013). Australian Rainfall & Runoff Revision Projects. PROJECT 2 – SPATIAL PATTERNS OF DESIGN RAINFALL: Collation and Review of Areal Reduction Factors from Applications of the CRC-Forge Method in Australia FINAL REPORT (P2/S2/012)

Engineers Australia Water Engineering, (2011). Australian Rainfall & Runoff Revision Projects. REVISON PROJECT 7: BASEFLOW FOR CATCHMENT SIMULATION STAGE 2 REPORT (P7/S2/017)

Engineers Australia, (2003). Australian Rainfall and Runoff Volume One – A guide to flood estimation

Engineers Australia, (1987). Australian Rainfall and Runoff Volume 2

8 References



9.1 Hydrologic terms AEP: Annual Exceedance Probability – is a measure of the likelihood (expressed as a probability) of a flood event reaching or exceeding a particular magnitude in any one year. A 1% (AEP) flood has a 1% (or 1 in 100) chance of occurring or being exceeded at a location in any year

AHD: Australian Height Datum (m), the standard reference level in Australia

AR&R: Australian Rainfall and Runoff (AR&R) is a national guideline document for the estimation of design flood characteristics in Australia. It is published by Engineers Australia. The current 2003 edition is now being revised. The revision process includes 21 research projects, which have been designed to fill knowledge gaps that have arisen since the 1987 edition

CHA: Comprehensive Hydrologic Assessment

CL: Continuing Loss (mm/hour). The amount of rainfall during the later stages of the event that infiltrates into the soil and is not converted to surface runoff in the hydrologic model

CRC-CH: Cooperative Research Centre – Catchment Hydrology. In this report, CRCH-CH usually refers to a Monte Carlo sampling method that was developed by the CRC-CH

CSS: Complete Storm Simulation. This is one of the proposed Monte Carlo sampling methods

Cumulative probability: The probability of an event occurring over a period of time, any time in that period. This probability increases over time

DEA: Design Event Approach. A semi-probabilistic approach to establish flood levels, which only accounts for the variability of the rainfall intensity

Design flood event: Hypothetical flood events based on a design rainfall event of a given probability of occurrence (ie AEP). The probability of occurrence for a design flood event is assumed to be the same as the probability of rainfall event upon which it is based (EA, 2003)

DMT: Disaster Management Tool. Work completed by BCC in 2014 for Queensland Government as part of the development of an interim disaster management tool until the completion of the BRCFS.

DTM: Digital Terrain Model

EL (m AHD): Elevation (in metres) above the Australian Height Datum

FFA: Flood Frequency Analysis – a direct statistical assessment of flood characteristics

Flood mitigation manual (Flood Manual): A flood mitigation manual approved under section 371E(1)(a) or 372(3) of the Water Supply (Safety and Reliability) Act 2008 (QLD)

FOSM: Flood Operations Simulation Model (refer Seqwater 2014)

9 Glossary



Floodplain: Area of land adjacent to a creek, river, estuary, lake, dam or artificial channel, which is subject to inundation by the PMF (CSIRO, 2000)

FSL: Full Supply Level - maximum normal water supply storage level of a reservoir behind a dam

FSV: Full Supply Volume – volume of the reservoir at FSL

GEV: Generalised Extreme Value statistical distribution

GIS: Geographic Information System

GL: Gigalitres This is a unit of volume used in reservoir studies. A Gigalitre = 1,000,000,000 litres or equivalently 1,000,000 m3

GSDM: Generalised Short Duration Method of extreme precipitation estimation for storms of less than 6 hour duration and catchments of less than 1,000 km2. Refer BoM, 2003

GTSMR: Revised Generalised Tropical Storm Method of extreme precipitation estimation for storms of tropical origin. Applicable to storm durations of up to 168 hours and catchments up to 150,000km2. Refer BoM, 2003

IFD-curves: Intensity-Frequency-Duration curves, describing the point- or area-rainfall statistics. In the current report rainfall depth is generally used as an alternative to rainfall intensity. Rainfall depth is the product of duration and intensity. It was decided to maintain the term “IFD” as this is the terminology that the reader is most likely to be familiar with

IL: Initial Loss (mm). The amount of rainfall that is intercepted by vegetation or absorbed by the ground and is therefore not converted to runoff during the initial stages of the rainfall event

LOC: Loss of Communications dam operating procedure, refer Flood Manual (Seqwater 2013)

LPIII: Log-Pearson Type III statistical distribution

IQQM: Integrated Quantity and Quality Model for water resources planning

JPA: Joint Probability Approach. A general term for probabilistic methods to establish design flood levels

MCS: Monte Carlo Simulation

MHWS: Mean High Water Spring Tide level

ML: Megalitre. This is a unit of volume used in reservoir studies. A megalitre is equal to 1,000,000 litres or, equivalently, 1,000 m3

m3/s: Cubic metre per second – unit of measurement for instantaneous flow or discharge

PMF: Probable Maximum Flood – the largest flood that could conceivably occur at a particular location, resulting from the PMP (CSIRO, 2000) and Australia Rainfall and Runoff, 2003 (EA, 2003)

PMP: Probable Maximum Precipitation – 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 year, with no allowance made for long-term climatic trends (CSIRO, 2000; EA 2003)

PMP DF: Probable Maximum Precipitation Design Flood – the flood event that results from the PMP event

Quantiles: Values taken at regular intervals from the inverse of the cumulative distribution function (CDF) of a random variable.

Stochastic flood event: Statistically generated synthetic flood event. Stochastic flood events include variability in flood input parameters (eg temporal and spatial rainfall patterns) compared to design flood events. Stochastic flood events by their method of generation exhibit a greater degree of variability and randomness compared to design flood events (See also Design flood event)



Synthetic flood event: See Stochastic flood event

TPT: Total Probability Theorem. This is one of the fundamental theorems in statistics. In this report, TPT refers to a Monte Carlo sampling method that is based on stratified sampling and, hence, makes use of the total probability theorem

URBS: Unified River Basin Simulator. A rainfall runoff routing hydrologic model (Carroll, 2012)

9.2 Study related terms BCC: Brisbane City Council

BoM: Australian Bureau of Meteorology

BRCFS: Brisbane River Catchment Flood Study

BRCFM: Brisbane River Catchment Floodplain Management Study

BRCFMP: Brisbane River Catchment Floodplain Management Plan

Delft-FEWS: Flood Early Warning Systems, a software package developed by Deltares, initially for the purpose of real-time flood forecasting. Delft-FEWS is used all over the world, including by the Environment Agency (UK) and the National Weather Service (US). Currently, it is also being implemented by Deltares and BoM for flood forecasting in Australia. The Monte Carlo framework for the BRCFS-Hydrology Phase will be implemented in Delft-FEWS

DEWS: Department of Energy and Water Supply

DIG: Dams Implementation Group

DNRM: Department of Natural Resources and Mines

DSITIA: Department of Science Information Technology, Innovation and the Arts

DSDIP: Department of State Development and Infrastructure Planning

EA: Engineers Australia formally known as The Institute of Engineers, Australia

GA: General Adapter, an interface between the Delft-FEWS environment and an external module

IC: Implementation Committee of the BRCFS

ICC: Ipswich City Council

IPE: Independent panel of experts to the BRCFS

LVRC: Lockyer Valley Regional Council

ND: No-dams condition. This scenario represents the catchment condition without the influence of the dams and reservoirs. The reservoir reaches have effectively been returned to their natural condition

NPDOS: North Pine Dam Optimisation Study conducted in response to the QFCOI Final Report

PIG: Planning Implementation Group

QFCOI: Queensland Floods Commission of Inquiry

RTC: Real-Time Control. A software package for simulations of reservoir operation. RTC tools is used for the simulation of Wivenhoe and Somerset reservoirs

SC: Steering Committee of the BRCFS

SRC: Somerset Regional Council

TWG: Technical Working Group



WD: With-dams condition. This scenario represents the catchment condition with the influence of the dams and reservoirs represented in their current (2013) configuration

WSDOS: Wivenhoe and Somerset Dam Optimisation Study conducted in response to the QFCOI Final report



Appendices

Appendix A GSDM ellipse locations

Figure A1 Peachester

Figure A2 Woodford

Figure A3 Tinton

Figure A4 Helidon

Figure A5 Walloon

Figure A6 Kalbar Weir

Figure A7 Amberley

Figure A8 Loamside

Appendix B PMP estimates

PMP depth estimates (mm)

Location Storm Duration (Hours)

1 1.5 2 2.5 3 4 5 6 24 36 48 72 96 120

Amberley 200 270 320 360 390 440 470 500 920 1100 1260 1540 1740 1840 Brisbane 670 800 910 1120 1270 1320 Centenary 680 800 920 1120 1280 1330 Fulham Vale 810 940 1060 1280 1460 1540 Gatton 960 1130 1280 1560 1780 1870 Glenore Grove 920 1080 1220 1480 1690 1780 Gregors Ck 820 950 1080 1300 1480 1570 Helidon 250 330 380 430 470 530 570 610 1130 1370 1590 1970 2210 2330 Ipswich 870 1020 1150 1400 1590 1680 Kalbar 240 310 360 410 440 500 540 570 1020 1220 1420 1760 1970 2080 Linville 900 1050 1190 1450 1650 1740 Loamside 280 360 410 470 510 570 620 660 890 1080 1260 1580 1770 1860 Middle Ck 800 940 1060 1290 1470 1540 Moggill 680 810 920 1130 1290 1340 Mt Crosby 720 850 970 1180 1340 1410 Peachester 320 410 470 530 580 650 720 760 1660 2030 2370 2980 3350 3500 Rifle Range Rd 890 1040 1180 1420 1620 1720 Savages Xing 720 850 980 1190 1350 1420 Somerset 1180 1390 1590 1940 2200 2320 Tinton 240 320 370 420 450 510 550 590 1030 1240 1440 1780 2000 2110 Walloon 220 300 340 390 420 470 510 540 920 1100 1270 1570 1770 1860 Wivenhoe 800 930 1060 1280 1460 1530 Woodford 280 370 420 480 510 580 630 670 1540 1870 2180 2720 3050 3210

Appendix C Comparison of temporal patterns

Zone 3 Area=100 km²








Zone 3 Area = 5000 km²




Appendix D Sensitivity assessment frequency curves

Stanley River

Stanley River at Peachester sensitivity assessment peak flow rate frequency curves

Stanley River at Woodford sensitivity assessment peak flow rate frequency curves

Stanley River at Somerset sensitivity assessment peak flow rate frequency curves

Upper Brisbane River

Brisbane River at Linville sensitivity assessment peak flow rate frequency curves

Brisbane River at Gregors Creek sensitivity assessment peak flow rate frequency curves

Brisbane River at Fulham Vale sensitivity assessment peak flow rate frequency curves

Cressbrook Creek at Tinton sensitivity assessment peak flow rate frequency curves

Brisbane River at Middle Creek sensitivity assessment peak flow rate frequency curves

Brisbane River at Wivenhoe sensitivity assessment peak flow rate frequency curves

Lockyer Creek

Lockyer Creek at Helidon sensitivity assessment peak flow rate frequency curves

Lockyer Creek at Gatton sensitivity assessment peak flow rate frequency curves

Lockyer Creek at Glenore Grove sensitivity assessment peak flow rate frequency curves

Bremer River

Bremer River at Walloon sensitivity assessment peak flow rate frequency curves

Warrill Creek at Kalbar sensitivity assessment peak flow rate frequency curves

Warrill Creek at Amberley sensitivity assessment peak flow rate frequency curves

Purga Creek at Loamside sensitivity assessment peak flow rate frequency curves

Bremer River at Ipswich sensitivity assessment peak flow rate frequency curves

Lower Brisbane River

Brisbane River at Savages Crossing sensitivity assessment peak flow rate frequency curves

Brisbane River at Mt Crosby Weir sensitivity assessment peak flow rate frequency curves

Brisbane River at Moggill sensitivity assessment peak flow rate frequency curves

Brisbane River at Centenary Bridge sensitivity assessment peak flow rate frequency curves

Brisbane River at Brisbane City sensitivity assessment peak flow rate frequency curves

Appendix E Dam influence frequency curves

Upper Brisbane River

Brisbane River at Wivenhoe sensitivity assessment peak flow rate frequency curves

Bremer River

Warrill Creek at Amberley dam influence peak flow rate frequency curves

Bremer River at Ipswich dam influence peak flow rate frequency curves

Lower Brisbane River

Brisbane River at Savages Crossing dam influence peak flow rate frequency curves

Brisbane River at Mt Crosby Weir dam influence peak flow rate frequency curves

Brisbane River at Moggill dam influence peak flow rate frequency curves

Brisbane River at Centenary Bridge dam influence peak flow rate frequency curves

Brisbane River at Brisbane City dam influence peak flow rate frequency curves

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Documents

Design Event Approach Report - Publications · Figure 3-22 Brisbane River at Brisbane City 2013 IFD Zone 3 design event hydrographs 24 Figure 3-23 Peak flow rates 2013 IFD design