drainage strategy - kingston.vic.gov.au · figure 2-3 shows the draft masterplan for the site...

Drainage Strategy

Kingswood Golf Course Redevelopment CG150599

Prepared for AS Residential Property No.01 Pty Ltd

3 August 2017

Drainage Strategy

Kingswood Golf Course Redevelopment CG150599

Drainage Strategy Kingswood Golf Course Redevelopment

3 August 2017 Cardno ii

Document Information

Prepared for AS Residential Property No.01 Pty Ltd

Project Name Kingswood Golf Course Redevelopment

File Reference CG150599_V03_Kingswood_GC_Drainage_Strategy_310717.docx

Job Reference CG150599

Date 3 August 2017

Contact Information

Cardno Victoria Pty Ltd

Trading as Cardno

ABN 47 106 610 913

Level 4

501 Swanston Street

Melbourne

Victoria 3000 Australia

Telephone: (03) 8415 7777

Facsimile: (03) 8415 7788

International: +61 3 8415 7777

[email protected]

www.cardno.com

Document Control

Version Date Author Author Initials

Reviewer Reviewer Initials

D01 33/08/17 Daniel Wood DW Ed Henty EH

D02 23/12/15 Daniel Wood DW Ed Henty EH

V01 11/01/16 Daniel Wood DW Ed Henty EH



© Cardno. Copyright in the whole and every part of this document belongs to Cardno and may not be used, sold, transferred, copied or reproduced in whole or in part in any manner or form or in or on any media to any person other than by agreement with Cardno.

This document is produced by Cardno solely for the benefit and use by the client in accordance with the terms of the engagement. Cardno does not and shall not assume any responsibility or liability whatsoever to any third party arising out of any use or reliance by any third party on the content of this document.


3 August 2017 Cardno iii

Table of Contents

1 Executive Summary 5

2 Introduction 6

2.1 Background 6

2.2 Changes from Previous Report 6

2.3 Existing Conditions Flood Impacts 8

2.4 Proposed Development 9

3 Scope of Works 10

3.1 Introduction 10

3.2 Existing Conditions Model Update 10

4 Model Development 11

4.1 Existing Conditions Model Setup 11

4.2 Existing Conditions Model Review and Update 12

4.3 Post Development Hydrological Modelling 13

4.4 Post Development Hydraulic Modelling 14

4.4.1 Development Conditions with No Basins 14

4.4.2 Development Conditions with Basins 15

5 Results 17

5.1 Existing Conditions Hydraulic Model Results 17

5.2 Post Development Hydraulic Model Results 17

6 Water Quality 21

6.1 Water Quality Objectives 21

6.1.1 Best Practice Management Targets 21

6.2 Water Sensitive Urban Design 21

6.2.1 Available Stormwater Management Options 21

6.2.2 MUSIC Model setup 21

6.2.3 Catchments 22

6.2.4 Treatment Node Parameters 22

6.2.5 Stormwater Treatment Measures and Results 23

7 Recommendations 24

7.1 Outcomes 24

Figures

Existing Site Conditions 7

Reported Flood Extent for Kingswood Golf Course and Surrounds 8

Kingswood Golf Course Draft Masterplan 9

Existing Conditions model – flood extent comparison of cut down against original model extent 11

Revised Existing Conditions Flood Extent onsite 12

Updated Sub catchments – FI revised to 0.65 13

Post Development Flood Impact – 1% AEP with no storage. 14


3 August 2017 Cardno iv

Diversion System at Downstream of Melbourne Water Storage 15

Proposed Drainage System 16

1% AEP – Existing Conditions Results 18

1% AEP Results – Proposed Drainage Network 19

10% AEP Results – Proposed Drainage Network 20

MUSIC model layout 22

Location of Wetlands in the Southern Retarding Basins 23


3 August 2017 Cardno 5

1 Executive Summary

The Drainage Strategy has been prepared to address the relevant requirements of the Kingston City Council

and Melbourne Water in relation to the proposed rezoning and redevelopment of the previous Kingswood Golf

Club in Dingley Village. The strategy has also contributed to the master planning of the site.

The site is currently partially inundated from overflow from an existing Melbourne Water detention basin in

events greater than the 2% AEP. At the downstream end of the site and external to the site, significant property

flooding is experienced along Golfwood Close, Lee Andy Court, Campbell Grove and Timms Crescent. In the

1% AEP event a peak flow of 5.43 m3/s is recorded as discharging off the site with Melbourne Water flood

mapping showing that this affects approximately 70 properties downstream of the site.

As part of the conditions set by Melbourne Water in consenting to the rezoning and redevelopment of the site,

the future development must contain all discharge offsite to less than 3.3 m3/s. This discharge rate is the

estimated capacity of the downstream drainage network and will provide 1% AEP protection for properties

downstream of the site.

In order to meet the conditions set by Melbourne Water, the redeveloped site will require 62,000m3 of storage,

in addition to the existing basin, to be provided onsite. This will take the following form:

Increasing the existing Melbourne Water Retarding Basin to 20,000m3

An 18,000m3 retarding basin incorporating a water quality wetland

A 2,800m3 retarding basin incorporating a water quality wetland

A 22,000m3 “dry” retarding basin which activates in events greater than the 10% AEP

If the site was only required to detain for increases in impervious areas as part of its redevelopment, then

approximately 10,000m3 would be required. However, the 62,800m3 of storage required to address Melbourne

Water’s site conditions has been provided for and will benefit approximately 70 properties downstream of the

site.

We anticipate that Melbourne Water will revisit the appropriateness of the extent of the current Special Building

Overlay in the near future following the completion of the proposed redevelopment of the site.



2 Introduction

2.1 Background

Kingswood Golf Course is a 53.35 Ha site located in Dingley Village. The site is bounded on the north by

Spring Road and McClure Road, the south by Centre Dandenong Road and residential properties on the west

and east. In the North West corner, adjacent to the site, is a Melbourne Water reservoir and detention storage

basin. In the western portion of the site, an existing Melbourne Water 1200mm drain runs in a south east

direction through the site, discharging through a vacant lot on Golfwood Close. In the eastern portion a 450

mm diameter pipe runs through the site, providing a point of discharge for properties in the vicinity of Mungari

Street. Figure 2-1 shows the site in its current development condition.

As part of the condition set by Melbourne Water to allow for the redevelopment of the site, the future

development must contain all discharge offsite to less than 3.3 m3/s. This discharge rate is the estimated

capacity of the downstream drainage network and will provide 1% AEP protection for properties downstream

of the site.

2.2 Changes from Previous Report

Based on minor design changes within the site there have been adjustments to the flood analysis which

have been documented in this report.

Since the previous reporting the following has been modified:

Minor pipe network adjustments to ensure minimal flooding of the middle basin in the 10% AEP while

ensuring flows are controlled to less than 3.30 m3/s (Section 4.4.2, Figure 4-5 and Figure 4-6)

Update of all relevant figures to incorporate the updated masterplan

Update of flood mapping results to the current basin shape and arrangement (Figure 5-2 and

Figure 5-3)

Provision of a 10% AEP flood map to confirm flood impacts within the middle basin (Figure 5-3)



Existing Site Conditions



2.3 Existing Conditions Flood Impacts

The site is currently inundated from overflow from the Melbourne Water detention basin in events greater than

the 2% AEP. At the downstream end of the site significant property flooding is experienced along Golfwood

Close and Lee Andy Court. In the 1% AEP event a peak flow of 5.43 m3/s is recorded as discharging off the

western region of the golf course. Melbourne Water flood mapping shows that this affects approximately 70

properties downstream of the site. No flow is recorded entering the downstream properties from the eastern

section of the golf course.

Reported Flood Extent for Kingswood Golf Course and Surrounds



2.4 Proposed Development

Figure 2-3 shows the draft masterplan for the site (FS038). The proposed development will provide a mix of

residential housing lots, superlots, green spaces made up of constructed wetlands, parks, and remnant

vegetation, and a mix of constructed roadways and paths designed throughout as per the included masterplan

layout. The total approximate site area is 533,500 m2.

Kingswood Golf Course Draft Masterplan



3 Scope of Works

3.1 Introduction

The purpose of this analysis was to determine appropriate basin sizing for the proposed redevelopment of

Kingswood Golf Course. In order to achieve this outcome the following works were required.

Development of an existing conditions hydraulic model that matches the existing Melbourne Water

flood extent of the site;

Revision of the existing hydrological model to incorporate the increased fraction impervious associated

with the design;

Development of a suitable basin scenario to ensure the offsite flow meets the Melbourne Water

discharge requirements of 3.3 m3/s offsite; and

Confirmation of the basin design within the previously validated hydraulic model.

3.2 Existing Conditions Model Update

For the purposes of the existing conditions assessment, Melbourne Water provided to Cardno a Tuflow model

of the area. This model was developed as part of the Mordialloc Settlement Drain Flood Mapping (GHD 2013).

This model has been utilised in order to determine the existing conditions flood impacts for the site.

As this model was developed with the intention of flood mapping the entire catchment, it was identified that for

the local assessment the model would have to be updated to ensure that the resolution of the model was

sufficient to assess the site. This task consisted of the following processes:

Rerun the existing Tuflow Model of the site in the most up to date version of Tuflow

(Build_2013_12_AD_64);

Cut down the model to only include the area relevant to the study and confirm results against the

previous modelling;

Update the confirmed model to ensure the most up to date topographic information; and

Confirm all relevant assumptions within the model are still relevant and acceptable for the detailed

assessment of the golf course.



4 Model Development

4.1 Existing Conditions Model Setup

The existing model, provided by Melbourne Water, was rerun in the newest version of the Tuflow system to

develop a baseline model. The Mordialloc Settlement Drain Flood Mapping (GHD, 2013) project determined

that the 1% AEP flood level for the site and surrounds was dominated primarily by the 9 hour rainfall event.

For the purposes of the preliminary review this event was utilised.

Upon completion of the model rerun, the model was cut down to only contain the area of interest. The entire

catchment area upstream of the site was maintained within the model to ensure the same hydraulic

performance as the previous modelling.

The models downstream boundary was set to 16.9 mAHD, this value matches the peak recorded water level

within the larger existing conditions hydraulic model. The water level at the downstream was set in both the

1D and 2D boundaries to ensure the hydraulic system acted in the same manner as the existing model. Figure

4-1 shows a comparison of the flood extents achieved through the site in both models. The results onsite and

immediately downstream are virtually identical.

Based on the outcomes of this assessment it was deemed that the cut down model was acting in a manner

identical to the full size model provided by Melbourne Water.

Existing Conditions model – flood extent comparison of cut down against original model extent



4.2 Existing Conditions Model Review and Update

Upon verification that the model was replicating the existing hydraulic model, the surface inside the model was

updated to incorporate the most recent LiDAR and ground survey for the region. The model surface was

updated with the following datasets:

Ground Survey of the Kingswood Golf Course, undertaken by Hellier McFarland on 22/07/2015

(9940S_1A.dwg); and

LiDAR survey for the area flown in October 2008

(e336n5794_vmmultires_2008oct28_dem1m_v10cm_mga55.asc)

Where ground survey was available this was used in preference to the LiDAR information.

Once the model surface was updated a general review of the model setup was undertaken to confirm its

suitability for use within the detailed study area.

It was found in general that for the purposes of determining the extent of flooding in the existing conditions

scenario for the site the model was suitable, however it was noted that the model was utilising an initial water

level of 22.3 mAHD in the existing Melbourne Water storage basin. This level was not consistent with the final

storage level (FSL) shown within DVA drawings (111108006 Kingswood Golf Club- Storage Lake and

Retarding Basin Cross Sections Ch.tif) for the basin.

Based on site survey and the DVA drawings it was concluded that the correct FSL was as per the drawing and

should be updated to 22.5 mAHD. Figure 4-2 shows the extent of flooding using the revised surface and basin

water level. The revised existing conditions model results in approximately 30,000 m3 of volume spilling out of

the existing Melbourne Water storage basin and on to the site in the 1% AEP 9 hour rainfall event.

Revised Existing Conditions Flood Extent onsite



4.3 Post Development Hydrological Modelling

In order to represent the increased runoff that will be generated by the site once it has been fully developed

the existing RORB model, provided by Melbourne Water (1102_Base_Case_RB.cat) was updated to

incorporate a fraction impervious (FI) of 65% for all sub catchments within the site. Figure 4-3 shows the sub

catchments updated to have an FI of 0.65 and the associated existing FI.

This assumption was considered to be conservative given the current development plan, however due to the

uncertainties around the masterplan design it is suitable at this stage. Upon finalisation of the masterplan this

assumption should be confirmed and revised if necessary.

Updated Sub catchments – FI revised to 0.65



4.4 Post Development Hydraulic Modelling

4.4.1 Development Conditions with No Basins

In order to determine the impact of the post development conditions upon the volume of water discharging

from the site in the 1% AEP event a post development hydraulic model utilising the current drainage network

and post development flows was undertaken. This model was utilised to inform the preliminary basin sizing.

In the 1% AEP 9 hour rainfall event, an additional 8800 m3 of runoff is generated due to the increased

development.

Post Development Flood Impact – 1% AEP with no storage.



4.4.2 Development Conditions with Basins

In order to mitigate the impact of the development and also ensure the peak flow rate off the site is reduced to

less than 3.3 m3/s, a concept drainage and basin design was established. This system improves the utilisation

of the existing Melbourne Water basin as well as incorporating three additional basins within the site. Note that

all pipe and drainage dimensions at this stage are conceptual only and are subject to revision once detailed

design occurs.

In order to cater for flows on the west of the site the following concept is proposed. The existing Melbourne

Water basin is to be increased in capacity by approximately 20,000 m3. A 1500 mm Dia pipe will run from the

downstream end of the basin through the site. This pipe has the capacity to carry approximately the 10% AEP.

Once this flow rate is exceeded a secondary flow diversion will transfer excess flow from the Melbourne Water

basin to an additional storage area immediately east of the downstream end of the Melbourne Water basin.

This basin has a storage capacity of 22,000 m3 and only activates in low frequency rainfall events. Figure 4-5

shows the concept design for this bypass.

At the downstream end of the site another large capacity basin is present. Discharge from the site, along with

the flow from the Melbourne Water basin is captured within this basin. A volume of 18,000 m3 is present, which

limits the peak flow rate back to 2.80 m3/s offsite in the 1% AEP.

On the east of the site, a small basin which caters for the local catchment is proposed. This basin has

approximately 2,800m3 of storage capacity and limits flows back to the carry capacity of the downstream

450 mm dia RCP of 0.4 m3/s. The capacity of this pipe has been derived from the existing conditions hydraulic

model provided by Melbourne Water. Due to the presence of a trapped low point at the End of Mungari Street

the catchment upstream of the golf course is disconnected from the onsite detention basin and cannot be

captured.

Figure 4-6 shows the concept drainage system. A total of approximately 62,000 m3 of storage is proposed

under this arrangement. It should be noted that included within this calculation is some compensation for the

removal of storage at the south eastern end of the existing Melbourne Water storage. In addition to the storage

upgrades it is proposed to move the discharge point from the eastern region of the site to discharge along

Centre Dandenong Road.

Diversion System at Downstream of Melbourne Water Storage



Proposed Drainage System



5 Results

5.1 Existing Conditions Hydraulic Model Results

Figure 5-1 shows the impacts of the 1% AEP event for the Kingswood Golf Club site. Significant inundation is

present on both the site itself and the surrounding properties. At the downstream end of the site overland flow

inundates properties along Golfwood Close. This overland flow path then continues south and over Centre

Dandenong Road. This overland flow path is attributed to a Melbourne Water asset which has insufficient

capacity to handle flows discharging from the existing storage basin.

5.2 Post Development Hydraulic Model Results

Figure 5-2 shows the 1% AEP results of the post development with the concept drainage network incorporated.

Various durations were run (1.5, 2, 9 and 12 hour rainfall events) as part of this assessment to ensure the

critical duration was captured for the entire site.

The proposed design limits the total flow to less than 3.3 m3/s from the site. Significant reductions to flooding

in the 1% AEP are seen along Greenwoods Close and Golfwood Close –this is due to improved capacity in

the Melbourne Water drain as well as significantly less catchment now being directed to this location.

A slight depression is still present in the design surface to the west of Mungari Street which results in minor

ponding onsite. Minor adjustments to the design surface in this area in during functional design will

accommodate this. A total of 250 m3 of additional storage has been considered within the basin to cater for

this additional runoff.

Figure 5-3 presents the 10% AEP results for the post development concept drainage. The middle basin in this

event only partially fills, with less than 200 mm of depth present in the lower area.

At the point where the two pipe networks converge (downstream of Centre Dandenong Road) the peak

recorded flow rate is 2.21 m3/s. The downstream boundary within the hydraulic model is set to 16.9 mAHD

which is influencing the capacity of all pipes downstream of Centre Dandenong Road). Because of this the

flood extents shown at these locations are considered conservative.



1% AEP – Existing Conditions Results



1% AEP Results – Proposed Drainage Network



10% AEP Results – Proposed Drainage Network



6 Water Quality

6.1 Water Quality Objectives

6.1.1 Best Practice Management Targets

To achieve the requirements of the City of Kingston, water quality treatment measures will be incorporated into the layout to meet the best practice management targets outlined in Table 1. Table 1: Best Practice Water Quality Targets

Pollutant Target Reduction

Total Suspended Solids 80%

Total Nitrogen 45%

Total Phosphorus 45%

Gross Pollutants 100%

6.2 Water Sensitive Urban Design

6.2.1 Available Stormwater Management Options

Options were investigated and sized in the MUSIC water quality model to meet the targets in Table 1. The following options have been proposed following consideration of the detention requirements for the site. 2 wetlands with 2 sedimentation basins (located in the retarding basin footprints) have been proposed to treat the site.

o Wetland 1 (South West RB) – 6,900m2 wetland and 1,300m2 sedimentation basin in South West corner near the existing club house.

o Wetland 2 (South East RB) – 3,500m2 wetland and 600m2 sedimentation basin in South East Corner

Gross pollutant traps will be implemented prior to entry into sedimentation basins.

6.2.2 MUSIC Model setup

The MUSIC model requires the user to specify, among other things, meteorological data (rainfall and evaporation), soil properties and pollutant generation parameters. The appropriate parameters for the MUSIC model were adopted in accordance with Melbourne Water MUSIC Modelling Guidelines. The main parameters used in the MUSIC model are described below:

Rainfall and Evaporation – Rainfall and evaporation data for Melbourne City with a range of 01/01/1966 to 31/12/1966 was used in the model

Rainfall Runoff Parameters - The appropriate rainfall-runoff parameters associated with urban residential nodes as per the Melbourne Water MUSIC guidelines are listed in Table 2.

Table 2: Rainfall-Runoff Parameters (Melbourne Water MUSIC Guidelines) Parameter Source Node

Rainfall threshold (mm) 1

Soil storage capacity (mm) 30

Initial Storage (%) 25

Field Capacity (mm) 20

Infiltration Capacity Coefficient - a 200

Infiltration Capacity Exponent - b 1

Initial Depth (mm) 10

Daily Recharge rate (%) 25

Daily Baseflow Rate (%) 5

Daily deep Seepage Rate (%) 0



6.2.3 Catchments

The catchments are as per the hydraulic modelling with the exception of Catchment C which is a small

catchment of which most will drain to the existing drainage in Greenwood Close. The South East wetland

has been over sized to treat the same area of land, i.e. Catchments B & C.

The catchment sizes are:

Catchment A (West) – 34.6ha

Catchment B (East) – 12.82ha

Catchment C (North East) – 4.71ha

6.2.4 Treatment Node Parameters

An extended detention depth (EDD) (m) of 0.35m has been used for the wetlands as Melbourne Water

guidelines recommend an EDD of 350mm or less. 0.5m EDD has been used to model the Sedimentation

Basin

The wetlands have been modelled with notional detention times of 72hours.

Figure 6-1 shows the MUSIC model layout

MUSIC model layout



6.2.5 Stormwater Treatment Measures and Results

The proposed stormwater treatment measures for the site include 2 wetlands with 2 sedimentations basins. The results of the MUSIC modelling show that the proposed treatment measures will meet the water quality objectives for the site. Table 6-1 shows the MUSIC model results.

Table 6-1 MUSIC model results for Kingswood Golf Club

Location of Wetlands in the Southern Retarding Basins

Wetland / Retarding Basins



7 Recommendations

7.1 Outcomes

Kingswood Golf Course is a 53.35 Ha lot located in Dingley Village. A proposal to convert the existing golf

course into a residential precinct is currently underway.

In order to gain approval from Melbourne Water to proceed with this conversion, the proposed development

must be designed to ensure the peak flow rate discharging from the site is less than 3.3 m3/s.

Based on this requirement a concept drainage system has been developed which incorporates several

detention basins spread throughout the site. The basins are designed in a manner to ensure the peak flow rate

offsite never exceeds the Melbourne Water requirements. The proposed design takes into account the

proposed landform as well as the proposed increased level of development. Based on the outcomes of the

hydraulic modelling the basin design proposed successfully mitigates the impacts of both the increased

development in the area as well as catering for the existing 1% AEP flood impacts.

In order to achieve the criteria set by Melbourne Water, the design proposed requires 62,800 m3 of storage, in

addition to the existing basin, to be provided onsite.

In addition to the retarding basins, two wetlands are proposed to be located in the south eastern and south

western basins to treat stormwater from the development to best practice targets.

drainage strategy - kingston.vic.gov.au · figure 2-3 shows the draft masterplan for the site...

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