APPENDIX 6 STORMWATER MANAGEMENT …...Serling Consulting (Australia) Pty Ltd Bellevue Lot 3 and Lot...

$: APPENDIX 6 STORMWATER MANAGEMENT …...Serling Consulting (Australia) Pty Ltd Bellevue Lot 3 and Lot 15597 Our Ref: SC00182.010 6 S:\Projects\SC00182.010 - Bellvue Primary School Site\Report\140910$
APPENDIX 6

STORMWATER MANAGEMENT (SERLING CONSULTING)

Bellevue Primary School

Redevelopment

City of Swan, Western Australia

Stormwater Drainage Strategy

Report

Lot 3 and Lot 15597

Our Ref: SC00182.010

September 2014

Serling Consulting (Australia) Pty Ltd Bellevue Lot 3 and Lot 15597 Our Ref: SC00182.010

S:\Projects\SC00182.010 - Bellvue Primary School Site\Report\140910 Bellevue Primary School Redevelopment Drainage Strategy Rev 2.docx

Bellevue Primary School Redevelopment

City of Swan, Western Australia

Our Ref: SC00182.010

Serling Consulting (Australia) Pty Ltd

ABN 15 162 648 222

Unit 1, 61 Guthrie Street

Osborne Park WA 6017

Tel: +61 8 6500 8802

Web: www.serlingconsulting.com.au

COPYRIGHT: The concepts and information contained in this document are the property of Serling Consulting (Australia) Pty Ltd. Use or copying of this document in whole

or in part without the written permission of Serling Consulting (Australia) Pty Ltd constitutes an infringement of copyright.

Stormwater Drainage Strategy Report

Lot 3 and Lot 15597

REV 2

September 2014



PAGE i

Contents

1. Introduction 5

1.1 Background 5

1.2 Previous Reports and Assessments 5

2. Proposed Development 6

3. Design Criteria 7

3.1 Water Quantity Management 7

3.2 Water Quality Management 7

3.3 Disease Vector and Nuisance Insect Management 7

4. Pre-development Environment 8

4.1 Surface Water Hydrology 8

4.2 Surface Water Quality 8

5. Stormwater Management Strategy 10

5.1 Catchment Area 10

5.2 Lot and Road Drainage 10

5.3 Detention Storage Requirements 11

5.4 Stormwater Quality 12

6. Groundwater Management Strategy 13

6.1 Clearance to Groundwater 13

6.2 Subsurface Drainage 13

7. Implementation 14

Appendix A Locality Plan 15

Appendix B Concept Plan 16

Appendix C Bellevue Drain 17

Appendix D Catchment Areas 18

Appendix E Site Plan and Proposed Basin Location 19

Appendix F Living Stream Concept 20



PAGE ii

Document history and status

Revision Date issued Reviewed

by

Approved

by

Date

approved Revision type

A 16/06/14 G Alexander G Alexander 16/06/14 Draft

0 26/6/14 G Alexander G Alexander 26/6/14 Final

1 28/8/14 G Alexander G Alexander 28/8/14 Final

Distribution of copies

Revision Copy no Quantity Issued to

A 1 1 Gil Alexander

A 1 1 Taliska Securities Pty Ltd

0 1 1 City of Swan, Shire of Mundaring,

Taliska Securities

1 1 1 City of Swan, Shire of Mundaring,

Taliska Securities

2 1 1 City of Swan, Taliska Securities

Printed: 10 September 2014

Last saved: 10 September 2014

File name: 140910 Bellevue Primary School Redevelopment Drainage Strategy Rev 2.docx

Author: Willem du Toit

Project Manager: Willem du Toit

Name of Organisation: Serling Consulting (Australia) Pty Ltd

Name of project: Bellevue Primary School Redevelopment

Name of document: 140910 Bellevue Primary School Redevelopment Drainage Strategy

Document version: Rev 2

Project number: SC00182.010


5


1. Introduction

1.1 Background

This Stormwater Drainage Strategy Report has been prepared in support of a redevelopment and

amalgamation application for Lot 3 and Lot 15597. The subject land includes the previous Bellevue

Primary School, a section of Wilkins Street, a City of Swan drainage easement and vacant land next

to the Roe Highway / Clayton Street road reserves.

The site is situated approximately 16km north-east of the Perth CBD and approximately 3km south-

east of the Midland town centre. The lots are within the boundaries of City of Swan, with the southern

boundary of the Wilkins Street road reserve, the border with Shire of Mundaring.

The primary school buildings have not been used in recent years and part of the site is currently used

as a nursery. The subject site, as well as the properties Lots 800 and 239 to the south, have a single

owner.

A site locality plan is included in Appendix A.

1.2 Previous Reports and Assessments

A District Water Management Strategy (DWMS) for Lots 800 and 239 Wilkins Street Bellevue has

been completed by RPS. (Report No D12146, Rev 1, March 2013) and has been submitted to the

City of Swan Planning Department before.

This previously submitted DWMS has included review and comments on Lots 3 and 15597 and this

Stormwater Drainage Strategy should be read in conjunction with the DWMS.

This Stormwater Drainage Strategy will include information on Stormwater Management and will not

repeat information on Geology, Acid Sulfate Soils, Flora and Fauna, Heritage, Environmental issues,

Groundwater Hydrology, Water Supply Planning or monitoring requirements. These issues are

covered in the DWMS.


6


2. Proposed Development

Following amalgamation, it is proposed to develop the site as one Group Housing site with a

combination of Grouped dwellings and Multiple dwellings, as shown in the concept design layout

attached in Appendix B.

The Grouped dwellings will be developed on a 5,690 square metre area with a yield of 19 dwellings.

The Multiple dwellings will be developed on 7,100 square metre area with a yield of 53 dwellings.

It is proposed to incorporate the fronting section of Wilkins Street as part of the private development.

Pascoe Street will be widened to a boulevard cross section, which will also be the main entry of the

future development of Lots 800 and 236 to the south.

The land has a very gentle slope from north-east to south-west and these natural grades will be

incorporated in the proposed drainage designs.


7


3. Design Criteria

3.1 Water Quantity Management

The objective is to have the post-development annual discharge volume and peak flows maintained

relative to pre-development conditions. The intention is to implement water sensitive urban design

(WSUD) measures that provide the best outcome in relation to water management for the site. The

following would be specific design criteria:

• Calculate pre-development and post-development flows to confirm they are maintained.

• Confirm that 1 year ARI event is maintained, as this may impact on desirable environmental

flows.

• Confirm the 1:100 year ARI post-development flows are contained on site similar to the pre-

development flows as part of flood management.

3.2 Water Quality Management

The objective is to maintain surface water and ground water quality at pre-development levels and, if

possible, improve the quality of water leaving the development area.

The design criteria is for the development to meet relevant water quality guidelines stipulated in the

“National water quality management strategy, 1994”

All runoff contained within the drainage infrastructure network will receive treatment prior to discharge

to a receiving environment. This includes outflows from subsoils.

3.3 Disease Vector and Nuisance Insect Management

Retention and detention treatments would be designed to ensure that between the months of

November and May, detained immobile stormwater is fully infiltrated within a time period not

exceeding 96 hours.


8


4. Pre-development Environment

Details of the existing environment with regard to landform, topography and soils, Phosphorus

Retention Index (PRI), Acid Sulphate Soils (ASS), Flora and Fauna, Conservation Areas, Cultural

Heritage, Floodways and Surface water hydrology, Surface water quality, Groundwater hydrology,

Groundwater quality and information on monitoring sites are all covered in the DWMS prepared by

RPS and this information is also relevant to the Bellevue Primary School site.

A number of specific issues related to the pre-development environment will be discussed in this

report.

4.1 Surface Water Hydrology

An existing drain, the Bellevue drain, passes through the property. It is located in an easement in

favour of the City of Swan and conveys stormwater from external catchments to the north and north-

west of the site. It consists of a number of larger diameter pipes. Although no stormwater from Lots 3

and 15597 would be added to the closed section of the Bellevue drain in the pre-development

environment, site runoff would reach the downstream open section of the drain. Photos of the pipe

culvert outlet and open drain are included in Appendix C.

The Bellevue drain currently carries significant flows from upstream catchments (quoted as in the

order of 4 – 6 m3 /sec for the critical 1:5 year ARI event in the DWMS). Flows from Lots 3 and 15597

would only be a very small percentage of these values, as shown in the table below.

Table 4.1: Pre-development and post-development flows:

Although the site has been split up into two catchments for the pre-development scenario, all pre-

development runoff from the site will eventually discharge towards the southern side and the open

section of the Bellevue drain, either as overland flow or via existing underground stormwater systems

in Wilkins Street.

The insitu material is mostly clay and most of the catchment can be classified as impervious.

4.2 Surface Water Quality

A sample of the Bellevue drain was taken on 3 September 2012 to provide a preliminary qualitative

assessment of stormwater flows discharging through this drainage network.

Sub-Catchment

A1

A20.039 0.076

Post-development flow

(m3/sec)

0.0230.007

1 in 1 year 1 in 5 year

Pre-development flow

(m3/sec)

Post-development flow

(m3/sec)

0.071


(m3/sec)

0.031

Sub-Catchment

A1

A20.235

0.083

1 in 100 year


(m3/sec)

Post-development

flow (m3/sec)

0.195


9


The DWMS includes details of the results, showing Total Nitrogen (TN) exceeding the ANZECC

guidelines for lowland rivers. The other water quality parameters are generally within the guidelines. It

can be assumed that the water quality results are related to flows from the upstream catchment and

not the very small percentage of flows from the Bellevue Primary School site.


10


5. Stormwater Management Strategy

5.1 Catchment Area

The proposed development includes a combination of grouped dwellings (19 dwellings) and multiple

dwellings (53 dwellings). It is a medium density development in a clay environment so it was

assumed that all dwelling roof runoff will be connected to an underground street stormwater drainage

system. Assuming some planting and vegetation, the overall catchment was assumed to be 80%

impervious (paved) and 20% pervious. A clay / silt soil type was selected for the “pervious” vegetation

areas.

No upstream catchments feeds into the site, as these are all discharging to existing road systems

and then into the Bellevue drain. Major overland flow paths follow roads around the proposed

development site and not through the site.

The development site was divided into 7 sub-catchments as shown in Appendix D. Wilkins Street

and the proposed Pascoe Street Boulevard were included. The 7 sub-catchments were modelled

assuming all of the catchment area contributing to the discharge from the catchment. Several of the

sub-catchments actually feed into downstream sub-catchments of the proposed development and

eventually discharge into a proposed drainage basin directly south of the development. A preliminary

layout of pits and stormwater pipes for each sub-catchment are shown in Appendix D as well.

A breakdown of the catchment areas are shown in the table below:

Table 5.1: Sub-catchments

Sub-Catchment

Number (Post-

development)

Catchment

Area Minor

Storms (ha)

Catchment

Area Major

Storms (ha)

Impervious

Catchment

Area Minor

Storms (ha)

Impervious

Catchment

Area Major

Storms (ha)

Receiving

Basins

Infiltration

Rate

(m/day)

1 0.4300 0.4300 0.3440 0.3440 Basin 1 0.1

2 0.2500 0.2500 0.2000 0.2000 Basin 1 0.1

3 0.2550 0.2550 0.2040 0.2040 Basin 1 0.1

4 0.0700 0.0700 0.0560 0.0560 Basin 1 0.1

5 0.2750 0.2750 0.2200 0.2200 Basin 1 0.1

6 0.1600 0.1600 0.1280 0.1280 Basin 1 0.1

7 0.2600 0.2600 0.2080 0.2080 Basin 1 0.1

5.2 Lot and Road Drainage

The proposed development will be a group housing development of medium density. In the clay

environment, it is proposed that all lots will have direct connection to the piped road drainage network

and all flows will be directed towards a discharge point on the south-western side of the site.

The piped road drainage network shall be sized to convey up to the 5 year ARI rainfall event. Rainfall

events larger than the 5 year ARI event, will be contained within the road reserve and discharge to

the lower areas on the south-western side of the proposed development site.


11


5.3 Detention Storage Requirements

The long term drainage strategy for the area downstream of Lots 3 and 15597 is described in the

DWMS prepared by RPS. A key part of the long term strategy is the conversion of the existing

Bellevue open drain section into a natural living stream. It will become a central urban design feature.

The aesthetic and biological functioning of the proposed living stream will have to be maintained and

in addition to that, consistent flows through the system will have to be provided to reduce water

stratification in the downstream wetlands and increase dissolved oxygen levels in the water bodies.

It is therefore important to maintain first flush and larger event runoffs from the primary school

development site into the Bellevue drain. As the proposed development will be medium density and

impervious areas will be increased significantly, total runoff from pre-development to post-

development will be increased. Detention storage will have to be provided to reduce the peak runoff

for both minor and major rainfall events.

The proposed Lot 3 and Lot 15597 development will be in the upper catchment of the future

development of Lots 800 and 239 Wilkins Street and it is proposed to combine the drainage

strategies for the two developments. As no detail calculations for Lots 800 and 236 are available, a

temporary solution is proposed, which may also become part of the future longer term drainage

strategy.

It is proposed to excavate a temporary drainage basin directly south-west of Lots 3 and 15597 and

next to the open section of the Bellevue drain, as shown in Appendix E. The proposed basin will

have a small diameter (150mm diameter in the current model) low flow outlet to make sure pre-

development flows are maintained and at the same time prevent water from ponding in the basin for

extended periods of time. Details of the basin storage parameters are included in the tables below.

Table 5.2: Basin Size and Storage Details

Basin / Storage

Parameters Basin 1

Invert Level (m

AHD) 14.8

Side Slopes (V:H) 1:6

Depth (m) 1.2

Basin Area at base

(m²) 100

Total Volume (m³) 417

Basin Area at top

(m²) 595

MGLs (m AHD) -

Base separation

from MGL (m) -

*AAMGLs (m AHD) 11.0

Base separation

from AAMGL (m) 3.8

* AAMGL assumed to be 0.5m above the 03/09/12 measurements by RPS


12


The basin and detention calculations can then be incorporated into the future living stream

calculations and designs once the future development goes ahead. Refer Appendix F for concepts

of the future development.

5.4 Stormwater Quality

Prior to discharging to the proposed drainage basin, stormwater will be treated by passing through a

pollutant trap. As the stormwater drainage system will be designed to convey the 5 year ARI rainfall

event, all first flush runoff will pass through the pollutant trap prior to discharging into the temporary

drainage basin and the Bellevue drain.

Area

Inundated

(m²)

Storage

Volume (m³)

Water Depth

(m)

Area

Inundated

(m²)

Storage

Volume

(m³)

Water

Depth (m)

Area

Inundated

(m²)

Storage

Volume

(m³)

Water

Depth

(m)

484 285 1.0 452 241 0.9 338 148 0.7

1:100 yr ARI 1:5 yr ARI 1:1 yr ARI

Basin Number

Max

Infiltration

Time (hrs)

1: 100 yr

overflow /

outflow

(m³/sec)

Basin 1 25 0.235


13


6. Groundwater Management Strategy

6.1 Clearance to Groundwater

Preliminary groundwater monitoring results are included in Table 7 in the DWMS prepared by RPS.

Bore ID C01 is the only one close to Lots 3 and 15597 and this shows groundwater elevations of

9.99m AHD on 28 June 2012 and 10.5m AHD on 3 September 2012 respectively. The existing

surface level at this point is 16.49m AHD.

Perth Groundwater Atlas shows groundwater levels below these values for Lots 3 and 15597 and in

the absence of more detail information, it was assumed that maximum groundwater levels will be in

the order of 11.0m AHD.

Existing site levels are generally over 16.0m AHD, resulting in groundwater clearances of

approximately 5.0m. As a result of structural design clearance requirements for building footings

above clay layers, it is expected that final lot levels will generally be the same or higher than existing

levels.

6.2 Subsurface Drainage

As there may be a risk of localised perched groundwater in the clay environment, it is proposed to

install a subsurface drainage system along one side of all of the internal roads to improve the flow of

groundwater away from both buildings and lots in the clay environment. The design shall be in

accordance with the City of Swan design standards.

The subsurface drainage system will be connected to the upstream side of drainage pits and

discharge to the last drainage manhole directly upstream of the pollutant trap.


14


7. Implementation

Applications for the amalgamation of the subject lots have been submitted to the local authorities and

this drainage strategy will be submitted in support of those applications.

Following approvals to proceed with the development, a detail design development stage will

commence. It is during this stage that the following more detail work will be completed:

- Earthworks design and final lot levels;

- More detail drainage designs based on final building and road layout;

- Testing of soil to confirm clay content and impact on drainage design;

- Details of WSUD applications;

- Details of pollutant traps and other possible stormwater treatment methods;

- Cover over existing underground section of the Bellevue Drain and invert level requirements

for the stormwater drainage system;

- Subsurface drainage design requirements, levels and discharge;

- Landscaping and vegetation that may form part of the stormwater drainage system eg

planting in the temporary basin; and

- Interaction between the road reserve and lot drainage systems.


15


Appendix A Locality Plan


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Appendix B Concept Plan

Clayton Street

Pas

coe

Stre

et

Wilkins Street

Concept plan – Density compliance mackay urbandesign

Belle View Estate: Bellevue Primary School concept design: March 2014

Grouped dwellings

Grouped Dwellings Grouped dwelling site area: 5,690sqm Residential yield:19 dwellings Average site area per dwelling: 299sqm R-code minimum average: 220sqm COMPLIANT

Multiple Dwellings Multiple dwelling site area: 7,100sqm Residential yield: 53 dwellings

11x 1-bed apts @ 55sqm: 605sqm 42x 2-bed apts @ 74sqm: 3,108sqm

Total Plot Ratio floorspace: 3,713sqm Plot Ratio: 0.52 R-Code maximum PR: 0.6 COMPLIANT

Multiple dwellings


17


Appendix C Bellevue Drain


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Appendix D Catchment Areas

Concept plan mackay urbandesign

Belle View Estate: Bellevue Primary School concept design: March 2014

Clayton Street

Pas

coe

Stre

et

Wilkins Street

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Area 1

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Discharge

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Basin 1

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Catchment Plan

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Subsurface Drainage

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Stormwater Drainage


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Appendix E Site Plan and Proposed Basin Location


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Proposed temporary basin

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Discharge

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Site Plan showing Proposed Drainage Basin

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LOT 3

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LOT 15597


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Appendix F Living Stream Concept


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Location of proposed temporary basin. In future the basin will be removed and become part of the site drainage management and Living Stream Concept

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APPENDIX 6 STORMWATER MANAGEMENT …...Serling Consulting (Australia) Pty Ltd Bellevue Lot 3 and Lot...

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