STORM WATER MANAGEMENT PLAN 43-59 Bruce Street, Colac

Proposed 7 lot Residential Development

Heil Engineering Consultants— Suite C, Level , The Parade Ocean Grove, Vic

T: W: heconsult.com.au E: info@heconsult.com.au

STORM WATER MANAGEMENT PLAN 43-59 Bruce Street, Colac

Proposed 7 lot Residential Development

HEC No: 20015

Date: 22nd April 2020

Version Status Author Approved By Release Date

1 FOR SUBMISSION MQ JH 21.04.20

2 FOR SUBMISSION MQ JH 22.04.20

3 FOR SUBMISSION MQ JH 06.07.20

This report has been prepared for Rosie Genua. Heil Engineering Consultants P/L cannot accept any responsibility for any use of or reliance on the continents of this report by any third party.

CONTENTS

Introduction 4

Minor & Major Flow Systems 5

Minor Flow System 5

Lot no. 1 5

Lots 2-7 (lot areas approximately 1000m2) 5

Major Flow System 6

Onsite Detention Capacities 6

Lot no. 1 6

Lots 2-7 6

Water Quality Improvement 7

Attachment 1 – Storm Water Management Plan 8

Attachment 2 – Detention Computation 9

STORM WATER MANAGEMENT PLAN 43-59 Bruce Street, Colac

Proposed 7 lot Residential Development | 4

Introduction Heil Engineering Consultants P/L have been engaged by Rosie Genua to prepare this storm water management plan in support of a proposed 7 lot residential subdivision of land located at 43-59 Bruce Street, Colac in accordance with the infrastructure design manual (IDM). This will be hereby referred to as the subject site.

The parcel of land in question has an area of approximately 0.8 hectares and is located approximately 1.5 kilometers east of the commercial center of Colac, Victoria. The subject site is located on the western side of Bruce Street and is bordered by residential properties. The subject site is within close proximity to the Colac Showgrounds, Bruce Street Reserve and the Bird Sanctuary.

The key document referred to in this report is: - Drawing No 20015_SWMP_P1 named Stormwater Management Plan (hereafter referred to as the “SWMP”) – Refer to Attachment 1.

The following stormwater management plan has been proposed to ultimately convey stormwater runoff from the site to potential points of discharge available at the site. The potential nominated legal point of discharge is the existing Council underground drainage infrastructure located within Bruce Street. The existing Council drainage infrastructure consists of 1200mm dia. concrete underground storm water pipes that are directed north approximately 140m to the existing bird sanctuary reserve in which it discharges into a natural wetland. Refer SMWP for a conceptual layout of the subject site.

STORM WATER MANAGEMENT PLAN 43-59 Bruce Street, Colac

Proposed 7 lot Residential Development | 5

Minor & Major Flow Systems

Minor Flow System

The existing site consists of surface gradients of approximately 1.25% (1 in 80) directed from the southern boundary corner to the northern boundary corner. The conveyance of stormwater from the overall development has been assessed as three separate catchment scenarios as summarised below and outlined on the SWMP in Attachment 1; Its proposed that the existing dwelling located on the existing lot 1 maintain the existing drainage discharge point.

Lot no. 1

Lot 1 contains the existing dwelling onsite. As outlined previously, it is proposed that lot 1 maintain the existing drainage and discharge arrangement.

Lots 2-7 (lot areas approximately 1000m2)

It is proposed that Lots 2- 7 utilize the existing drainage infrastructure located immediately east of the site within the Bruce Street road reserve which includes drainage infrastructure consisting of 1200mm dia. pipes that discharge into a natural water course downstream.

Based on our preliminary calculations it is estimated that the peak minor flow from each lot will be as follows;

Minor Flow (5yr ARI):

Approximate Catchment Area (per lot): 0.1Ha

C: 0.50 (Refer SWMP in Attachment 1)

I5YR,6MIN:71.4 mm/hr

Q = 0.010 m3/sec or 10 l/s

It is noted that as per Council guidelines, discharge rates from the site will be restricted to match pre-developed discharge rates for a 5yr ARI event. Preliminary calculations indicate that the predeveloped and allowable discharge rate from the overall site is approximately 46l/s/ha. Therefore, the discharge rate from Lots2- 7 will be restricted to the below;

Q = 46 l/s/ha

Q = 4.6l/s ( 1,000m² or 0.1ha Lot)

Refer to Onsite Detention Capacities section and drainage calculations in Attachment 2 for additional information.

STORM WATER MANAGEMENT PLAN 43-59 Bruce Street, Colac

Proposed 7 lot Residential Development | 6

Major Flow System

Major event flows from all lots shall be directed away from the development based on the finished surface level gradients falling away from the proposed lots. The adjacent road reserve shall act as an open channel to safely convey the 1 in 100-year ARI storm event flows towards a natural water course located within Colac Bird Sanctuary and Lake Colac to the north. Refer SWMP in Attachment 1

Based on our preliminary calculations it is estimated that the peak major flows will be as follows;

Major Flow (100yr ARI) – Development Site:

Area: 0.80 Ha

C: 0.50

I100yr,6min: 164 mm/hr

Q = 182.2 L/sec

Onsite Detention Capacities In order to satisfy runoff conditions as per the IDM and Council requirements, a preliminary analysis has been undertaken to ensure onsite detention volumes satisfy peak flows for all events up to and including a 1 in 10yr ARI assuming that development discharge rates are restricted to predeveloped rates. The predeveloped rates for a 5yr ARI have been estimated to be approximately 46l/s/ha. (See Attachment 2 – Detention Computations)

It’s noted that given the nature of the development being essentially an “infill” residential development it is difficult to include systems to accommodate required onsite detention. It is proposed that onsite detention be achieved by a combination a above ground and below ground methods. Above ground methods can include shallow detention ponds/ basins strategically located onsite. Below ground methods may include an oversized pit with outflows restricted to nominated discharge rates using an orifice plate. Both options are to be explored in more detail during the detailed design phase.

Preliminary calculations have been prepared for the catchment areas and can be found in Attachment 2. A summary of the calculation is outlined below;

Lot no. 1

Lot 1 contains the existing dwelling onsite. As outlined previously, it is proposed that lot 1 maintain the existing drainage and discharge arrangement.

Lots 2-7

Preliminary calculations suggest that during a 1 in 10yr ARI 24hr storm event, the proposed Lots will require approximately 3.11 m3 of onsite detention storage assuming a discharge rate of 46L/sec/ha. (See Attachment 2 – Detention Computations).

STORM WATER MANAGEMENT PLAN 43-59 Bruce Street, Colac

Proposed 7 lot Residential Development | 7

Water Quality Improvement The IDM stipulates that the development drainage system must be consistent with the “Best Practice Environmental Management Guidelines for Urban Stormwater”.

The subject development proposes to utilize existing underground drainage infrastructure currently servicing Bruce Street as the nominated legal point of discharge. It is noted that the drainage system discharges into the existing bird sanctuary wetland reserve located approximately 140m downstream of the site.

As the proposed development is essentially an “infill” residential development it is extremely difficult to include stormwater treatment methods as part of the proposed drainage system. Potential storm water treatment methods suitable for an infill development of this nature potentially include onsite bio-retention raingardens and rainwater harvesting from tanks. As the proposal is for a subdivision only it is difficult to allow for onsite treatment systems in this early phase.

In discussions with the Engineering Department at the Colac Otway Shire, it has been proposed that a contribution be paid in lieu of water sensitive urban design to go towards end op pipe treatment. It is proposed that the contribution amount be based on the estimated construction costs for treatment solutions for the site.

The Water Sensitive Urban Design quality outcomes will be investigated further and modelled using “MUSIC” software as part of the stormwater detailed design. It is proposed construction cost estimates be determined in the detailed design phase and once Council planning permit conditions have been confirmed.

Attachment 1 – Storm Water Management Plan

1

2002m²

2

983m²

3

989m²

4

990m²

5

990m²

6

1051m²

7

992m²

54

.5

1

36.70

36.70

54

.5

9

54

.5

9

54

.6

3

18.1018.10

19.2018.10

54

.6

3

54

.6

7

54

.6

7

54

.7

0

54

.7

0

54

.7

4

54

.7

4

54

.7

7

54

.7

7

54

.8

1

36-52

41

43

45

47

49

51

18.00 18.1018.10

18.1019.20 18.10

18.1018.00

EX.1200mm DIA. RCP

EX.1200mm DIA. RCP

APP.

SHEET NO.

DRAWING NO.

A1

DESCRIPTIONDATE

DRAWN

DESIGNED

0

Scale

C

Heil Engineering Consultants P/L

THIS DOCUMENT IS COPYRIGHT AND MAY ONLY BE USED FOR THE PURPOSE FOR WHICH IT WAS

COMMISSIONED. UNAUTHORISED USE PROHIBITED. ALL DIMENSIONS AND LEVELS TO BE

CHECKED ON THE PROJECT BEFORE COMMENCING ANY WORKS OR SHOP DRAWINGS. DRAWINGS

NOT TO BE SCALED.

REVISION NO.

HEIL

ENGINEERING

CONSULTANTS

PTY LTD

Urban Development Project Management

Infrastructure Design Construction Administration

SWAN HILL, VIC 3585

OCEAN GROVE, VIC 3226www.heconsult.com.au

NO.

RELEASE DETAILS

DOCUMENT STATUS

CAD:

P. 03 50332189

P. 03 52552220

MRS ROSIE GENUA

STORMWATER MANAGEMENT PLAN

43-59 BRUCE STREET

COLAC, VIC

DRAINAGE CATCHMENT AREA PLAN

20015_SD01

P2

01 of 01

20015_SD.dwg

1:400 @ A1

4 8 16

JH FEB 20

MQ FEB 20

BEWARE OF EXISTING

OVERHEAD POWER CABLES.

NOTE !

given that all existing services are shown.

given that all existing services are shown.

should be proven on site. No guarantee is

The locations of underground services are

BEWARE OF UNDERGROUND SERVICES

approximate only and their exact position

WARNING

THE EXISTING SERVICE INFORMATION CONTAINED WITHIN THIS PLAN HAS

BEEN DERIVED FROM A DESKTOP STUDY ONLY. THE EXISTING SERVICES

SHOWN ON THIS PLAN HAVE BEEN INDICATIVELY INCLUDED FROM A DIAL

BEFORE YOU DIG INQUIRY AND HAVE NOT BEEN VERIFIED ON SITE.

WARNING

CONCEPTUAL ONLY

FOR DISCUSSION PURPOSES

DRAINAGE CATCHMENT AREA PLAN

B R U C E S T R E E T

²

SITE RUNOFF COEFFICIENTS: (Table 10, IDM)

ALLOWABLE DISCHARGE RATE: 46 L/s (Pre-developed rate for a 5yr ARI)

DRAINAGE CALCULATIONS:

STORAGE METHODS:

REFER TO DRAINAGE CALCULATIONS FOR ADDITIONAL INFORMATION

LEGEND

Attachment 2 – Detention Computation

DRAINAGE DESIGN CALCULATIONS

Concept Only

Client: Rosie Genua Date:Project: 43-59 Bruce Street, Colac

Design By: Matthew Quinn Sheet No: 1Project No.: 20016

Rev: 0

ASSUMPTIONS

Maximum Total Area of Allotment (Lot 6) = 1050 m2

Runoff Coefficient, Refer Infrastructure design manual (IDM) Table 10 = 0.5

Therefore Adopt C = 0.50

Allowable Discharge Rate to be predevloped rate for 5yr ARI

Total Development Area = 7900 m2

Total Existing Impervious Area (Estimated) = 1100 m2 Impervious C = 0.9

Total Existing Pervious Area (Estimated) = 6800 m2 Pervious C = 0.25

Estimated Weighted Coefficient Cw = (1100/7900) x 0.9 + (6800/7900) x 0.25 = 0.341

Allowable Discharge Rate Q= CIA/360 Q = 36.5 l/s

= 46l/s/ha

Therefore, Allowable Discharge Rate, Q = 46l/s/ha

From Retention Calculations Required Storage = 3.11 m3 (refer following pages)

Assume above and below ground storage within a shallow basin area and pit :-Shallow landscape basin and pit with orifice = 3200 L (minimum)

Conceptual only and subject to detailed design

6/07/2020

RETENTION CALCULATIONS (.25 to 2 Hour Duration)Client : Rosie Genua

Project : 43-59 Bruce Street, ColacRef. No. : 20016

Temporal Rainfall Pattern data for A.R.I. <30 years. Allowable discharge from site:- Orifice Plate Calculations:-Catchment area (A) 0.105 ha Q = 46 l/sec/ha (refer IDM TBL 13) Ao = Q/Co√2gHVolumetric runoff coefficient. 0.50 A = 0.105 ha = 0.002570 m2Design A.R.I.Total Area of Allotment = 10 YearsMinimum Head (H) 0.50 m Q = 0.1051x 37 Orifice Diameter :Orifice Discharge Coefficient (Co) 0.6 Q = 4.83 litres per second Do = √Aox4/π mm2Orifice Cross Sectional Area (Ao) 0.002570 m2 = 0.057 mOrifice Diameter (Do) 51 mm = 57 mmDischarge rate. 4.83 l/sec

Duration 15min 30min 60min 90min 120min *Adopted CumulativeIntensity 53.8 mm/hr 38.4 mm/hr 24.9 mm/hr 20.1 mm/hr 15.6 mm/hr Cumulative Runoff Outflow

Interval min. %

Equivalent Intensity mm/hr.

Cumulative Equivalent Intensity mm/hr.

%Equivalent Intensity mm/hr.

Cumulative Equivalent Intensity mm/hr.

%Equivalent Intensity mm/hr.

Cumulative Equivalent Intensity mm/hr.

%Equivalent Intensity mm/hr.

Cumulative Equivalent Intensity mm/hr.

%Equivalent Intensity mm/hr.

Cumulative Equivalent Intensity mm/hr.

Equivalent Intensity mm/hr

CIA*(dt) /360

m3

4.8 l/s

Excess

m3

0 05 32.0 51.65 51.65 16.0 36.86 36.86 3.9 11.65 11.65 4.1 14.83 14.83 2.1 7.86 7.86 51.65 2.26 1.45 0.8110 50.0 80.70 132.35 25.0 57.60 94.46 7.0 20.92 32.57 13.0 47.03 61.87 6.1 22.84 30.70 132.35 5.79 2.90 2.8915 18.0 29.05 161.40 33.0 76.03 170.50 16.8 50.20 82.77 21.2 76.70 138.57 12.9 48.30 79.00 170.50 7.46 4.35 3.1120 9.0 20.74 191.23 12.0 35.86 118.62 7.8 28.22 166.79 6.8 25.46 104.46 191.23 8.37 5.80 2.5725 11.0 25.34 216.58 23.2 69.32 187.95 10.5 37.99 204.78 17.9 67.02 171.48 216.58 9.48 7.25 2.2330 6.0 13.82 230.40 10.1 30.18 218.12 5.8 20.98 225.76 9.4 35.19 206.67 230.40 10.08 8.69 1.3935 8.9 26.59 244.72 7.4 26.77 252.54 5.3 19.84 226.51 252.54 11.05 10.14 0.9140 5.7 17.03 261.75 5.5 19.90 272.44 5.0 18.72 245.23 272.44 11.92 11.59 0.3345 4.8 14.34 276.09 4.7 17.00 289.44 4.2 15.72 260.96 289.44 12.66 13.04 -0.3850 3.1 9.26 285.35 3.5 12.66 302.10 3.2 11.98 272.94 302.10 13.22 14.49 -1.2755 2.6 7.77 293.12 3.0 10.85 312.96 4.1 15.35 288.29 312.96 13.69 15.94 -2.2560 1.9 5.68 298.80 2.7 9.77 322.73 3.6 13.48 301.77 322.73 14.12 17.39 -3.2765 2.5 9.05 331.77 2.9 10.86 312.62 331.77 14.51 18.84 -4.3270 2.2 7.96 339.73 2.6 9.73 322.36 339.73 14.86 20.29 -5.4275 1.9 6.87 346.60 2.3 8.61 330.97 346.60 15.16 21.74 -6.5780 1.7 6.15 352.76 1.9 7.11 338.08 352.76 15.43 23.18 -7.7585 1.4 5.07 357.82 1.8 6.74 344.82 357.82 15.65 24.63 -8.9890 1.1 3.98 361.80 1.6 5.99 350.81 361.80 15.83 26.08 -10.2595 1.5 5.62 356.43 356.43 15.59 27.53 -11.94

100 1.3 4.87 361.30 361.30 15.81 28.98 -13.17105 1.2 4.49 365.79 365.79 16.00 30.43 -14.43110 1.0 3.74 369.53 369.53 16.17 31.88 -15.71115 0.8 3.00 372.53 372.53 16.30 33.33 -17.03120 0.5 1.87 374.40 374.40 16.38 34.78 -18.40

For 10 Year ARI

Maximum Retardation for no outflow condition = 16.38 m3

Maximum Retardation for given outflow = 3.11 m3

Tem

pora

l

R

ainf

all

Pat

tern

Note: Retardation calculations have been calculated for a 1 in 10 year ARI storm event. Maximum retardation volumes have been calculated for a critical storm determined by routing various duration scenarios for a 1 in 10 year storm event until peak flows are determined assuming a discharge rate of 46L/S/HA. The scenarios included routing a stormwater duration of;- 15min - 2hr duration- 3hr duration- 6hr-12hr duration- 24hr duration

It was determined that a stormwater duration between 15min and 2 hours incurred the highest values of rainfall intensity and as such is the "critical storm duration" requiring the highest amount of stormwater retention. The above data suggests that for a given outflow of 46L/S/HA the maximum required storage is approximately 3.11m³.