1 sustainable arch water sensitive urban design guidelines-2

Water Sensitive Urban Design Guidelines

1 July 2002

Hobsons Bay City Council, Brimbank City Council & Wyndham City Council

A Partnership between PPK E&I Pty Ltd and Parsons Brinckerhoff International (Australia) Pty Ltd Parsons Brinckerhoff Companies

76P051A - R01bP051A Rev B M01378

PPK Environment & Infrastructure [2002]

This document is the property of PPK Environment & Infrastructure ("PPK"). This document and the information contained in it are solely for the use of the authorised recipient and this document may not be used, copied or reproduced in whole or part for any purpose other than that for which it was supplied by PPK. PPK makes no representation, undertakes no duty and accepts no responsibility to any third party who may use or rely upon this document or the information contained in it. Author: John Downs

Reviewer: Robert Davies

Approved by: Robert Davies

Signed: ...............................................................

Date: 1 July 2002

Distribution: Hobsons Bay City Council, Brimbank City Council, Wyndham City Council, J Downs, PPK Library

1234 Water Sensitive Urban Design Guidelines

Contents

Page Number

1. Introduction 1

2. Public Open Space 4 2.1 Constructed Wetlands 4 2.2 Detention Basins 5 2.3 Infiltration Basins 7

3. Housing Layout 8

4. Water Reuse 10 4.1 Rainwater Tanks 10 4.2 Greywater Reuse 10

5. Road Layout and Streetscape 11 5.1 Porous Pavements 11 5.2 Modular Pavements 12 5.3 Grass Swales 13 5.4 Filter Strips 13 5.5 Infiltration Trenches 14 5.6 Sand Filters 15

6. Conclusion 16

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Contents (continued) Page Number

List of Figures

Figure 1.1: Runoff Changes with Increasing Urbanisation 1 Figure 1.2: Changes in Runoff Characteristics with Urbanisation 2 Figure 2.1: Waterways and Public Open Space 4 Figure 2.2: Constructed Wetland 5 Figure 2.3: Detention Basin 6 Figure 2.4: Use of Detention Basins 6 Figure 2.5: Infiltration Basin 7 Figure 3.1: Preferred Housing Layout 8 Figure 3.2: Alternative Housing Layouts 9 Figure 5.1: Alternative Streetscape Designs 11 Figure 5.2: Porous Pavements 12 Figure 5.3: Modular Pavements 12 Figure 5.4: Grass Swale 13 Figure 5.5: Filter Strip 13 Figure 5.6: Infiltration Trench 14 Figure 5.7: Sand Filter 15

Appendices

Appendix A Further Reading and Resources

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1. Introduction

The degradation of stormwater receiving environments, such as lakes, waterways and Port Phillip Bay from polluted urban stormwater is becoming an increasingly important consideration in both the management of existing urban areas and in the design and construction of new urban development. One of the emerging trends in best practice urban stormwater management is the implementation of water sensitive urban design (WSUD) principles. They aim to improve the quality of stormwater flowing into receiving waters, such as waterways, lakes and dams, through a range of measures to reduce the volume of stormwater runoff and remove pollutants before they are deposited into those receiving environments.

These WSUD Guidelines are intended as a resource for Council officers, developers, landowners and permit applicants. They provide specific techniques which can be incorporated in subdivision and development designs to address issues of stormwater quality.

Stormwater is rainfall and runoff from activities such as street cleansing, irrigation and other sources, which enters our drainage systems and, ultimately, our rivers and bays. Traditional urban development dramatically increases the area of impervious surfaces which decreases infiltration into the soil and increases runoff into constructed stormwater drains as shown in Figure 1.1.

Figure 1.1: Runoff Changes with Increasing Urbanisation

The increase in impervious surfaces not only increases the volume of stormwater runoff after a rainfall event but also dramatically alters the flow characteristics associated with the catchment. Heavily urbanised catchments experience greater peak stormwater flows after rainfall than more natural catchments and these peaks occur

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over shorter timeframes than those of natural catchments. This is illustrated in Figure 1.2 below.

Figure 1.2: Changes in Runoff Characteristics with Urbanisation

Traditional urban developments have treated stormwater as a waste product which needed to be disposed of quickly and efficiently. The solutions to improving water quality have focused on engineered solutions that are largely end of pipe and can be visually unattractive, obtrusive and take up valuable public open space.

Water Sensitive Urban Design (WSUD) offers an alternative approach to our traditional drainage network techniques in the management and treatment of stormwater. It recognises that water is a valuable resource and aims to integrate a range of water management techniques within urban areas. WSUD aims to facilitate the conveyance of stormwater runoff and protect receiving environments while minimising water use and maximising water recycling in urban areas. This is achieved by managing the water balance of the catchment, maintaining and enhancing the quality of stormwater, encouraging water conservation and maintaining environmental, recreational, cultural and aesthetic values.

The Goals and Principles of WSUD

The overall goals of water sensitive urban design are to:

preserve existing topographic and natural features, including watercourses and wetlands;

protect surface water and groundwater resources; and

integrate public open space with stormwater drainage corridors, maximising public access, passive recreational activities and visual amenity.

The broad principles of water sensitive urban design include:

minimising impervious areas;

minimising use of formal drainage systems (eg. pipes);

encouraging infiltration (where appropriate);

protecting existing vegetation, particularly riparian vegetation; and



encouraging the reuse of stormwater.

These principles can be adopted at a range of development scales, including:

the overall extent of proposed development areas;

the road and block layout with a development; and

the specific development forms on individual blocks.

This document provides guidelines on the range of water sensitive urban design principles that may be incorporated when planning and designing new developments or when redeveloping existing urban areas. It aims to provide developers, consultants and managers with tools to enable them to meet water sensitive urban design objectives.

The document does not address engineered structures such as sediment or gross pollutant traps (litter traps), or chemical treatment measures which can be used in conjunction with the techniques described in these guidelines. WSUD techniques focus on minimising the volume and improving the quality of stormwater runoff that is ending up in the stormwater drainage system. Engineered solutions attempt to improve the quality of the water, without reducing volumes, once the water is in the stormwater drainage system. There are a variety of information resources available on the various types on engineered solutions available to complement the WSUD techniques described in these guidelines, including A Manual for Managing Urban Stormwater Quality in Western Australia produced by the Waters and Rivers Commission (1998).



2. Public Open Space

The use of public open space for treating urban stormwater can be achieved using a number of techniques that not only perform their primary role in treating stormwater but can also create an attractive water feature and fauna habitat that can also increase recreational amenity and adjacent real estate values. Some of the treatments that can be used include wetlands and various types of detention basins. These can either be permanently or seasonally wet depending on the sources of runoff and the types of stormwater flows. Other considerations include the secondary role of the water feature in the function of the public open space. Using a variety of WSUD techniques in the design and development of public open space can encourage a greater use of these areas and increase their value to the community. The options for the management of stormwater drainage are illustrated in Figure 2.1 below.

Figure 2.1: Waterways and Public Open Space

2.1 Constructed Wetlands

Constructed wetlands are generally landscape features that incorporate both ponded water and aquatic vegetation. Wetlands are a highly desirable option where multiple benefits are the desirable outcome as they can provide both stormwater treatment and good quality habitat as well as a highly visually attractive landscape feature. They can also be used for community education programs or community stormwater reuse programs if properly designed.



Wetlands are most effective at removing sediment and nutrients from the stormwater but are also able to remove a range of other pollutants such as oxygen depleting materials, oils and grease and other pathogens. Wetlands are also highly effective at removing litter from stormwater but this is not a desirable function as it can adversely impact on the visual attractiveness of the wetland and reduce its effectiveness in treating other types of pollutants in the stormwater.

Wetlands do need a reliable and regular source of water and are suited to larger catchments. They may also require a large amount of land area depending on the size of the catchment and are unsuitable for steep sites.

Figure 2.2: Constructed Wetland

2.2 Detention Basins

The purpose of detention basins is to store stormwater for a number of days and allow some of the attached sediment to settle out and be deposited in the basin. It can also be used as a flood retardation measure and also provide an attractive landscape feature when constructed as an ornamental lake. With the addition of some fringing vegetation, detention basins can also remove nutrients from the stormwater and can also provide a habitat to some waterbirds such as ducks and swans.

Detention basins can require a large area of land such as that found in public open spaces and are generally unsuitable for steep sites and unstable slopes but are applicable on steeper sites than constructed wetlands. They have potential for integration into stormwater reuse schemes.



Figure 2.3: Detention Basin

Detention Basin

Detention basins can be incorporated into appropriate locations within conventional subdivisions as shown below in Figure 2.4 and can be included in existing developments where a suitable location of adequate size is available.

Figure 2.4: Use of Detention Basins



2.3 Infiltration Basins

Infiltration basins are generally grassed depressions along seasonal drainage lines that receive and store stormwater during storm events. The stormwater captured in the infiltration basin is allowed to slowly infiltrate through the soil profile. This reduces runoff rates and volumes downstream and removes sediments and nutrients from the stormwater system.

This method of stormwater treatment is most appropriate in areas with highly permeable soils such as sands where the infiltration rates are high or in areas with high evaporation rates.

During dry periods, the grassed area that forms the base of the basin can be used for general recreational purposes, creating a valuable community asset.

Figure 2.5: Infiltration Basin

Infiltration Basin



3. Housing Layout

The layout of housing in residential areas and of buildings in general can create a range of potential options for improving the quality of stormwater flowing into the receiving environments as well as improving the recreational and visual amenity of the area.

The primary focus of designing housing layouts to facilitate water sensitive urban design is to work with the natural landscape where possible and design the housing layout, including streets and walkways around it. The layout of the development should be sympathetic to the natural environment and use landscape features such as existing drainage lines, depressions and waterways as landscape features that will also provide opportunities for stormwater treatment. These features should be reserved as part of the public open space network for the development and can be developed using a variety of techniques, particularly those listed in Section 2 above. An example of a desirable housing layout is illustrated in Figure 3.1 below.

Figure 3.1: Preferred Housing Layout

With good design and a greater focus on community open space, it may be possible to reduce the size of residential blocks or to develop houses in clusters which focus on central water features located in public open space. This water feature should be designed to not only improve the quality of the stormwater flowing from the development but also to provide a visual and recreational focus to the area and to provide a valuable wildlife habitat. Ideally, houses should face the community open space to create an improved sense of community ownership and to potentially reduce the occurrence of illegal activities such as dumping and vandalism. An example of this is illustrated in Figures 3.2 below.



Figure 3.2: Alternative Housing Layouts



4. Water Reuse

One of the key objectives of WSUD is to encourage water conservation and to facilitate the best use of the available water therefore reducing the demand for outside supply. There are a number of ways to conserve water and reduce the amount of water from urban areas that needs to be disposed of including simple measures such as the installation of dual flush toilet systems and water saving shower roses. There are also a two measures that can be implemented to make the best use of water on the site.

4.1 Rainwater Tanks

Stormwater from the rooftops of buildings makes up a high proportion of the volume of runoff water from urban areas. The installation of on site rainwater tanks for all properties will dramatically reduce runoff volumes and decrease the frequency of flooding in urban areas. The water collected in rainwater tanks can later be used for garden watering and other non-potable uses.

4.2 Greywater Reuse

Greywater is all waste water draining from a house except for toilet wastes. The reuse of domestic greywater for garden watering one method to reduce the volume of waste water entering sewerage systems and reduce the demand for treated water for garden watering purposes. The reuse of greywater does have a number of limiting factors, particularly in an urban context given that it contains a variety of bacteria and other contaminants.

If it is intended to use untreated greywater for garden watering, it should be used promptly, preferably within 24 hours. There are a number of other precautions that need to be taken when watering plants, particularly fruit and vegetables, and it is important that the water be applied directly to the soil rather than through sprinkler systems.

Treated greywater can be stored for longer periods once the bacteria have been killed. This will require the installation of additional equipment to physically and chemically treat the greywater and associated maintenance and expense. It should also consider how much greywater will be treated and what it will be used for making it less desirable within urban areas than the reuse of rainwater flowing from rooftops of buildings.



5. Road Layout and Streetscape

There are a number of methods available when designing and constructing road networks, particularly in residential areas, which reduces the volume and improves the quality of runoff. These methods can include:

Porous pavements;

Modular pavements;

Grass swales and filter strips; and

Infiltration trenches and sand filters.

These techniques can be used in combination with small local retarding basins to gain a streetscape such as that illustrated in Figure 5.1 below and can either be used in isolation or in combination with other engineered techniques such as oil and grit separators or gross pollutant traps.

Figure 5.1: Alternative Streetscape Designs

5.1 Porous Pavements

Porous paving is most useful on reasonably flat areas that are not subjected to heavy traffic loads such as car parks, driveways and lightly used roads. They decrease the volume of stormwater runoff by allowing water to infiltrate through the soil profile and decrease runoff velocities. This can be achieved through a variety of methods illustrated in Figure 5.2 below.



Figure 5.2: Porous Pavements

Geotextile or Impermeable MembraneAccording to Soil Conditions

ConcreteBlocks

Sand

Geotextile

CleanStone

Concrete Block Asphalt Porous Concrete

From: Waters and Rivers Commission, (1998)

5.2 Modular Pavements

Modular pavements consist of a network of pavers that are regularly interspersed with voids that are filled with highly porous materials such as gravel, sand or grass. The benefits and limitation of modular pavers is similar to porous pavement described in Section 5.1 above. They can be in a number of forms such as those illustrated in Figure 5.3 below.

Figure 5.3: Modular Pavements

Poured in Place Slab Castellated Unit

Lattice Unit


While the installation of modular pavements is more expensive than traditional bitumen surfacing, by increasing the amount of water infiltration and reducing the volume of stormwater runoff, the infrastructure costs associated with stormwater



drainage systems may be reduced due to the decreased volumes that need to be carried.

5.3 Grass Swales

Grass swales provide an alternative to concrete kerb and channel for conveying runoff from roads and other impervious areas. Grass swales are open grass lined channels that may also have small mounds or barriers at regular intervals to reduce runoff velocities to prevent erosion. Swales can reduce runoff velocities and increase infiltration rates and remove sediments from stormwater runoff. While swales require more area than concrete kerb and channel, they have a greater visual appeal,

Figure 5.4: Grass Swale

particularly if they are properly landscaped. They can also act as an important pre treatment mechanism before the stormwater flow into one of the larger treatment mechanisms detailed in Section 2. An example of the application of a grass swale in a residential area is illustrated in Figure 5.4.

5.4 Filter Strips

Filter strips or buffer strips are vegetated areas that treat overland flow before flowing into a receiving environment such as a creek or river. The stormwater runoff velocity is reduced and the level of infiltration is increased which removes a range of attached and dissolved pollutants. Filter strips are most commonly used as part of the riparian environments of natural waterways with a mix of understorey and overstorey vegetation as illustrated in Figure 5.5 below. Council can provide advice on appropriate planting schemes for your area.

Figure 5.5: Filter Strip



5.5 Infiltration Trenches

Infiltration trenches are shallow trenches filled with highly permeable materials such as gravel or sand which collect runoff from hard surfaces such as roads or carparks. In areas with soils with low infiltration rates such as heavy clay soils, a porous drainage pipe can be installed in the bottom of the trench and connected to the stormwater drainage system if required.

Infiltration trenches can be used instead of grass swales where higher levels of infiltration are required and if properly landscaped, can be an attractive streetscape element.

Figure 5.6 illustrates an example of the application of an infiltration trench.

Figure 5.6: Infiltration Trench

Filter StripDirectly Abuts

Pavement

Dripline of TreeShould not

Extend over Trench

Berm (Grassed)

Slotted Curbs actas Level Spreader

Protective FilterCloth Filter

Sand Filter

Trench

Slotted Curb Spacers

Plan Cross Section

Storm Drain(if Partial Exfiltration)

Slope ofParking Lot



5.6 Sand Filters

Sand filters are a variation of the infiltration trench principle and can be used to treat runoff from hard surfaces such as car parks. An example of the structure of a sand filter is illustrated in Figure 5.7 below. The filter consists of a grassed top layer overlying a sand layer that filters the pollutants from the stormwater. The base layer is a highly permeable material such as coarse gravel with porous pipe that is connected to the stormwater system. Filter fabric is used to prevent the filtering down of fine sediments that may cause clogging or blocking of the filtering system separates the various layers.

Providing proper maintenance and mowing, the area containing the sand filter can be used as public open space or be an attractive streetscape element.

Figure 5.7: Sand Filter

Sand

Topsoil

Subsoil Pipe

Grass Cover Storage Depth

Gravel

Filter Fabric

Impermeable Liner




6. Conclusion

By implementing a combination of the treatments discussed above, it is possible to improve the quality of stormwater flowing from urban areas into our waterways and Port Phillip Bay and also help create a living environment that is more visually attractive with greater recreational amenity and which can also provide an improved habitat for native wildlife.

While individual measures can be implemented and have a positive impact on stormwater quality, combining the treatment measures in a series is the most effective way of having a positive impact in reducing the volume of stormwater runoff and improving the quality of the runoff but can also have additional benefits such as reducing the cost of the construction and maintenance of infrastructure and the demands on reticulated water supply within the area.


Appendix A

Further Reading and Resources

1. Australian Water Association, We All Use Water: A users guide to water and wastewater management, brochure series, NSW.

2. CSIRO, (1999), Urban Stormwater Best Practice Environmental Management Guidelines, Chapter 5: Water Sensitive Urban Design, CSIRO Publishing, Victoria.

3. EPA Victoria, http://www.epa.vic.gov.au/Programs/Stormwater/, 19/12/01.

4. Melbourne Water, http://www.conservewater.melbournewater.com.au/, 19/12/01.

5. NSW EPA, (1998), Managing Urban Stormwater: Source Control Water Sensitive Urban Design (Part E) Draft, NSW EPA Stormwater Trust, NSW, http://www.epa.nsw.gov.au/stormwater/docs.htm, 14/12/01.

6. Warrington, P. D., (2000, March), Best Management Practices to Protect Water Quality: Urban, http://www.nalms.org/bclss/urban.html, 13/12/01.

7. Waters and Rivers Commission, (1998), A Manual for Managing Urban Stormwater Quality in Western Australia, The Information Centre: Waters and Rivers Commission, Western Australia, http://www.wrc.wa.gov.au/public/WSUD_manual, 09/01/02.

IntroductionPublic Open SpaceConstructed WetlandsDetention BasinsInfiltration Basins

Housing LayoutWater ReuseRainwater TanksGreywater Reuse

Road Layout and StreetscapePorous PavementsModular PavementsGrass SwalesFilter StripsInfiltration TrenchesSand Filters

Conclusion

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