WATER SENSITIVE URBAN DESIGN PLAN

Geostar Australia Pty Ltd T/A BMB Engineers; ABN 72 154 094 041; Phone 02 9836 1373; www.bmbengineers.com.au; [email protected]

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WATER SENSITIVE URBAN

DESIGN PLAN

for

PROPOSED RESIDENTIAL FLAT

BUILDING

73-75 ROOTY HILL ROAD

NORTH, ROOTY HILL,

NSW 2766

June 2018


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Report Description

Report Name Water Sensitive Urban Design Plan for Proposed Residential Flat Building

Address 73-75 Rooty Hill Road North, Rooty Hill, NSW 2766

Client Mr. Amir Entezami

Prepared By Muna Pradhan Flood and Drainage Engineer MIEAust CPEng NER


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Contents

1 INTRODUCTION 4

1.1 Site Description 4

1.2 Objective 4

2 PROPOSED DEVELOPMENT 5

3 STORM WATER MANAGEMENT STRATEGY 6

4 WATER SENSITIVE URBAN DESIGN 6

4.1 Treatment Devices 6

4.2 Water Quality Modelling 8

4.3 Results and Discussion 11

List of figures

Figure 1: Location of Site (Source: Department of Lands - Six Maps) 4 Figure 2: Site Plan of Proposed Development 5 Figure 3: EnviroPod 7 Figure 4: Jellyfish filter 8 Figure 5: Schematic Layout of MUSIC Model for Pre-development analysis 11 Figure 6: Schematic Layout of MUSIC Model for Post-development analysis with Treatment 11

List of tables

Table 1: Water Quality Objectives 4 Table 2: Monthly Potential Evapotranspiration 9 Table 3: MUSIC Rainfall-Runoff Parameters for Blacktown area 10 Table 4: Stormwater Quality parameters for MUSIC Source Nodes 10 Table 5: Music Results for mean annual loads 12


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1 INTRODUCTION

Mr. Amir Entezami commissioned BMB Engineers in May 2018 to prepare water sensitive urban

design plan for the proposed residential flat building at 73-75 Rooty Hill Road, Rooty Hill, NSW 2766.

This report has been prepared to ensure that the proposed development can be carried out while

meeting the requirements for water sensitive urban design management.

The location of proposed development is shown in Figure 1. The outline of the site given in Figure 1

is the outline of the proposed development site. The land is identified as Lot A in- DP 331481. The

site has an overall area of approximately 1,937.68 m2.

Figure 1: Location of Site (Source: Department of Lands - Six Maps)

1.1 Site Description

The site is currently vacant and located at south-west of the road. The proposed development

comprises mixed use 4 storey apartment with two underground basement car park.

1.2 Objective The Blacktown City Council Development Control Plan (DCP) sets objectives for the reduction of

pollutants in runoff from new developments. These targets are shown in Table 1.

Table 1: Water Quality Objectives

Pollutant Reduction Target

Total Suspended Solids (TSS) 85%

Total Phosphorous (TP) 60%

Total Nitrogen (TN) 45%

Gross Pollutants 90%


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2 PROPOSED DEVELOPMENT

The proposed development of residential flat building in the site is shown in Figure 2.

Figure 2: Site Plan of Proposed Development


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3 STORM WATER MANAGEMENT STRATEGY

Stormwater drainage for the proposed development will be provided by means of a pit and pipe

system which caters up to the 100yr ARI flows. The above ground On Site Detention (OSD) basin has

provided to match pre and post development flows from the site as per council requirement.

Please refer to the stormwater concept plan designed by SDS Engineering for the proposed for the

development. The features of the concept plan are as follows:

Pit and pipe drainage system to be provided with the 100yr ARI capacity. Pits within the

proposed landscape area range from 600x600 to 900x900 grated pits.

Pits in back landscape and front landscape area i.e. Pits 1 and 3 are to be fitted with

EnviroPod to remove gross pollutants and coarse sediments.

The Jellyfish filters are to be provided on the back landscape area to remove pollutants such

as TSS, TP, TN.

The above ground OSD basin drains dry and will only fill during significant rainfall events. The

above ground OSD basin will collect overflow from the roof of residential flat building. The

flow from the OSD basin is controlled by orifice. The outlet of this basin is to be connected to

street inlet pit system at road. In case of extreme rainfall event, OSD basin overflows from

the weir and overflows to the front landscape then to the road.

4 WATER SENSITIVE URBAN DESIGN

To meet the water quality requirements of the Blacktown City Council DCP stormwater treatment is

required on the site. The proposed stormwater treatment system includes gross pollutant trap with

EnviroPods and Jellyfish filters.

4.1 Treatment Devices

The stormwater design for the proposed development will use a combination of at source and

conveyance controls to treat the stormwater runoff from the site. The following are the treatment

trains proposed for this development.

4.1.1 Gross Pollutant Traps (GPT)

The stormwater inlet pits in the back landscape area (i.e. Pit 1) and front landscape area (i.e. Pit 3)

are to be fitted with the Enviropod. The EnviroPod is an effective, easily maintained catch pit

insert that captures and retains litter, debris and other pollutants as runoff enters the storm drain

system. It removes 90 percent of gross pollutants and coarse sediments over 100 micron size

(Source: http:\\www.stormwater360.com.au). Figure 3 shows the commercially available EnviroPod.

In this site, EnviroPod Type A with length 600 mm and width 600 mm is recommended for 600 mm x

600 mm grated pit and length 900 mm and width 750 mm is recommended for 900 mm x 900mm

grated pit. The detail guide for operation and maintenance of Enviropod is attached in Appendix B.


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Figure 3: EnviroPod

4.1.2 Jellyfish Filter

This device is one of the latest in filtration technology and uses gravity, flow rotation, and up-flow

membrane filtration to provide stormwater treatment in an underground compact stand-alone

system. Using unique filtration cartridges, each Jellyfish filter has a large membrane surface area,

resulting in high flow rates and pollutant removal capacity. The filter has a number of ‘tentacles’ that

catch and remove floatables, litter, oil, debris, TSS, silt-sized particles (as small as 2 microns), and a

high percentage of particulate-bound pollutants; including phosphorus, nitrogen, metals and

hydrocarbons. This filter has a much smaller footprint than other best-management practices

(BMPs), greater design flexibility and no replaceable media. (Source:

http:\\www.stormwater360.com.au). In this site, two Jellyfish filters will be used to remove the

pollutants. Figure 4 shows the commercially available Jellyfish filter. The detail guide for operation

and maintenance of Jellyfish filer is attached in Appendix B.


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Figure 4: Jellyfish filter

4.2 Water Quality Modelling

The software used for the water quality modelling is MUSIC version 6.2. This program is well

regarded as industry best practice for analysis of the effectiveness of treatment mechanisms on the

quality of stormwater runoff from a development site of this size.

MUSIC simulates the performance of stormwater management systems in removing nutrients and

sediments from a catchment by evaluating the average annual pollutant load delivered to the

receiving waters.

It uses both source nodes (produce pollutants) and treatment nodes (remove pollutants) to analyse

the stormwater system.

4.2.1 Rainfall Data

MUSIC requires the user to input both rainfall and evaporation data. Rainfall data is required in the

form of six (6) minute rainfall data, over a minimum period of 20 years that closely matches the

historical average annual rainfall for the area.

Rainfall data for the 1967 to 1976 period from Station 067035 Liverpool (Whitlam Centre) shall be

utilised for MUSIC modelling in the Blacktown LGA. The data over this period is relatively complete

with a mean annual rainfall of 857 mm.


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4.2.2 Evaporation Data

When considering potential evapotranspiration (PET) data in MUSIC, following points should be

taken into consideration:

Local PET information is preferred (where available).

In most cases, local data will not be available in which case average monthly data from

Sydney (available within the MUSIC model) can be used in the Greater Sydney region.

Average Sydney PET data is suitable for use in modelling water quality and hydrology.

The monthly PET values for the Sydney region, including Blacktown area, are shown in Table 2.

Table 2: Monthly Potential Evapotranspiration

Month Potential Evapotranspiration (mm)

January 180

February 135

March 128

April 85

May 58

June 43

July 43

August 58

September 88

October 127

November 152

December 163

4.2.3 Model Inputs

MUSIC requires the input of both rainfall-runoff data and pollutant concentrations for each node.

Both of these data sets were sourced from the Developer Handbook of Water Sensitive Urban

Design of Blacktown City Council, NSW. The MUSIC rainfall-runoff parameters for Blacktown area are

presented in Table 3 and storm water quality parameters for MUSIC source nodes are presented in

Table 4.


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Table 3: MUSIC Rainfall-Runoff Parameters for Blacktown area

Impervious Area Parameters

Rainfall threshold (mm) 1.4

Pervious area parameters

Soil Storage Capacity (mm) 170

Initial Storage (% of capacity) 30

Field Capacity (mm) 70

Infiltration Capacity Coefficient -a 210

Infiltration Capacity Exponent - b 4.7

Groundwater properties

Initial Depth (mm) 10

Daily Recharge Rate (%) 50

Daily Base Flow Rate (%) 4

Daily Seepage Rate (%) 0

Table 4: Stormwater Quality parameters for MUSIC Source Nodes

Land-use Category Log10 TSS (mg/L) Log10 TP (mg/L) Log10 TN (mg/L)

Storm Flow

Base Flow

Storm Flow

Base Flow

Storm Flow

Base Flow

Road Areas Mean

Std Dev 2.43 0.32

---* ---*

-0.30 0.25

---* ---*

0.34 0.19

---* ---*

Roof Areas Mean

Std Dev 1.30 0.32

---* ---*

-0.89 0.25

---* ---*

0.30 0.19

---* ---*

Other impervious area Mean

Std Dev 2.15 0.32

---* ---*

-0.60 0.25

---* ---*

0.30 0.19

---* ---*

Pervious area Mean

Std Dev 2.15 0.32

1.20 0.17

-0.60 0.25

-0.85 0.19

0.30 0.19

0.11 0.12

*Base flows are only generated from pervious areas, therefore these parameters are not relevant to

impervious areas

4.2.4 Catchment

The area of the site is 1,937.68 m2. For the pre-development analysis, the catchment is considered

as landscape. The area of catchment is as follows:

Landscape area = 1,937.68 m2

For the post-development, the catchment is broken into five types of sub-catchments in order to

adequately model the use of the treatment devices. These sub-catchments are roof, driveway,

pedestrian pathway, landscape and front landscape. The areas of sub-catchments are as follows:

Roof = 1,406.88 m2


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Driveway = 46.49 m2

Pedestrian pathway = 92.14 m2

Landscape = 256.14 m2

Front landscape = 136.03 m2

4.3 Results and Discussion

The development of site for pre-development and post-development in MUSIC models are shown in

Figures 5 and 6 respectively. The results for annual pollutant loads are presented in Table 5 with the

reduction percentage.

Figure 5: Schematic Layout of MUSIC Model for Pre-development analysis

Figure 6: Schematic Layout of MUSIC Model for Post-development analysis with Treatment


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Table 5: Music Results for mean annual loads

Flow Pre Development

(Without

Treatment)

Post Development % Reduction

Sources Residual load

Flow (ML/yr) 0.405 1.22 1.22 0

Pollutants:

TSS (kg/yr) 31.9 69.8 7.22 89.7

TP (kg/yr) 0.0829 0.235 0.0817 65.2

TN (kg/yr) 0.673 2.64 1.08 58.9

Gross Pollutants

(kg/yr)

0 29.5 0.0337 99.9

It can be seen from Table 5 that the Total Suspended Solids (TSS), Total Phosphorous (TP), Total

Nitrogen (TN) and Gross Pollutants loads with the proposed stormwater management measures are

lower than in the post-development scenario without treatment. The MUSIC model results show

that reduction targets would be achieved using the proposed treatment measures which consist of

two EnviroPods of Type C and two Jellyfish filters. Hence, these treatment trains significantly reduce

the pollutants.

The Storm Erosion Index (SEI) has been applied as a stormwater flow target for protecting streams

from increased erosion following new development. The SEI is most commonly used to identify an

appropriate level of change in erosion from pre to post development. The SEI is defined as the ratio

of the volume of post development stormwater flows exceeding the ‘stream forming flow’ to the

volume of stormwater flows exceeding the ‘stream forming flow’ under natural catchment

conditions (Brookes and Wong, 2009). This target therefore takes account of both the magnitude

and duration of flows potentially impacting on the stream. The detail of calculation of SEI is given in

Draft NSW MUSIC Modelling Guidelines. The SEI is calculated as follows:

SEI = ∑(𝑄𝑝𝑜𝑠𝑡 −𝑄2.𝑥%)

∑(𝑄𝑝𝑟𝑒 −𝑄2.𝑥%)

Where Q2 being the 2-year ARI event

X% varies from 10% to 50% depending upon the substrate in the waterway at the location

Typical stream forming flows for typical soils found in streams within NSW catchments include:

Sand and silts: 10% of 2 year ARI flow


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Silty clays: 25% of 2 year ARI flow

Stiff clays: 50% of 2 year ARI flow

Typically 25% of the 2 year ARI flow is adopted as an appropriate critical or stream forming flow in

Blacktown Council.

In this case, the Stream Erosion Index is calculated as follows:

SEI= -0.00593/-0.00595 =0.99566 =1

In this site, the post-development duration of stream forming flows is not greater than 3.5 times the

pre-development duration of stream forming flows because of using Jellyfish filters for infiltration

purposes.

Sources:

1. ewater (2014) music by ewater User Manual.

2. Blacktown City Council (2013) Developer Handbook for Water Sensitive Urban Design.

3. Weber, T. and Fletcher, T. (2010) Draft NSW MUSIC Modelling Guidelines.

4. Brookes, K. and Wong, T.H.F. (2009) The adequacy of the Stream Erosion Index as an alternative

indicator of geomorphic stability in urban waterways. WSUD09 proceedings.

5. Stormwater 360, Australia (2012) EnviroPod – Operations and Maintenance Manual.

6. Stormwater 360, Australia (2017) Jellyfish filter Membrane Filtration.

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WATER SENSITIVE URBAN DESIGN PLAN