2 Australian. Water Conservation and Reuse Research Program. A Review of Stormwater Sensitive Urban Design in Australia

Transcription

1 1 2 Australian Water Conservation and Reuse Research Program A Review of Stormwater Sensitive Urban Design in Australia Tim D. Fletcher, Ana B. Deletic & Belinda E. Hatt Department of Civil Engineering & Institute for Sustainable Water Resources, Monash University January 2004 ISBN

2 This is a report of the Australian Water Conservation and Reuse Research Program, a joint initiative of CSIRO and AWA. Stakeholders of the Program, who supported this research are: Victorian Smart Water Fund United Water International Australian Water Association Water Corporation WA Queensland Department of Natural Resources and Mines Northern Adelaide Barossa Catchment Water Management Board Patawalonga Catchment Water Management Board City of Albury NSW Brighton City Council Tas City of Mount Gambier SA City of Mitcham SA Queensland EPA Albury City Council Western Water Beaudesert Shire Council Wide Bay Water Corporation Ipswich Water Narrandera Shire Council

3 Table of Contents 1 INTRODUCTION AND SCOPE NATIONAL GUIDELINES STATE GUIDELINES AND LITERATURE PERFORMANCE OF STORMWATER SENSITIVE URBAN DESIGN STRUCTURAL BEST MANAGEMENT PRACTICES Gross Pollutant Traps Vegetated Swales and Filter Strips Infiltration and Bioretention Systems Ponds, Wetlands and Sediment Basins Porous Pavements STORMWATER RE-USE LITERATURE AND GUIDELINES GAPS IN CURRENT GUIDANCE DOCUMENTS OVERSEAS BEST PRACTICES CASE-STUDIES OF STORMWATER SENSITIVE URBAN DESIGN Case Study 1: Lynbrook Estate (Source: Lloyd et al., 2002) Cast Study 2: Second Ponds Creek (Source: Ecological Eng, 2002; Landcom, 2002) Case Study 3: Byford Village (Source: Ecological Engineering, 2003a) Case Study 4: Inner Urban Streetscape: Melbourne St, Brisbane (Source: Ecological Eng, 2003b) Case Study 5: Oaklands Park Case Study 6: Manly Stormwater Treatment and Re-use (STAR) Project POLICY, ECONOMIC AND INSTITUTIONAL ISSUES AFFECTING ADOPTION OF STORMWATER SENSITIVE URBAN DESIGN IN AUSTRALIA Policy and Institutional Issues Economic Issues CONCLUSIONS APPENDIX I CASE STUDIES OF INTEGRATED STORMWATER TREATMENT AND RE-USE REFERENCES... 38

4 1 Introduction and Scope As part of the Australian Water Conservation and Reuse Research Program, the CRC for Catchment Hydrology were invited to provide an inventory of Australian water sensitive urban design. It was to include: successes, issues, barriers, models of good practice, lessons, knowledge gaps, policy issues, community interactions, economics, special /unique features, water quality characteristics, and site characteristics. The ensuing report provides a review of the application of Water Sensitive Urban Design (WSUD) in Australia, with the main emphasis being on treatment and use of stormwater. Therefore, the term stormwater sensitive urban design is commonly used throughout this report. Relevant literature are summarised and reviewed, including national and state guidelines. Many of the documents referred to are important sources of original information, and should be read for further information. The expected water quality performance of a range of stormwater sensitive urban design technologies is summarised, and the potential for application of technologies from overseas is assessed. Key gaps in literature and guidelines are outlined, along with a brief assessment of the most important factors affecting adoption of stormwater sensitive urban design, and stormwater reuse, in Australia. The report includes a comprehensive selection of up-to-date case studies, firstly dealing with stormwater sensitive urban design, and secondly focussing on stormwater re-use. The increasing adoption of stormwater sensitive urban design in Australia has been supported by the publication of a number of influential documents, which have outlined its principles, objectives and in some cases, design methods. Whilst the inventory provided here is not meant to be extensive (and does not cover the large number of documents which provide guidance on a narrow range of technologies suitable for WSUD, such as rainwater tanks, or constructed wetlands), it does provide a summary of the key documents and their scope. 2 National Guidelines There are a number of national guidance documents related to stormwater sensitive urban design. For example, Austroads recently released guidelines for the treatment of road runoff (Wong et al., 2003), updating earlier water sensitive road design guidelines (Wong et al., 2000). Whilst focussed on roads, the document provides useful guidance on design of WSUD technologies (particularly swales, bioretention systems, infiltration systems and wetlands), and includes a number of case studies, from different regions of Australia. Relatively detailed information is given on design processes, although the document stops short of being a design manual. The Stormwater Industry Association and Urban Water Resources Centre at the University of South Australia released a handbook of source control stormwater detention and retention systems (Argue, 2002). Dealing with both stormwater quantity and quality, the handbook provides design procedures, including particular detail for infiltration and ASR (Aquifer Storage and Recovery systems). A useful and very reader-friendly introduction to stormwater sensitive urban design by Lloyd et al. (2002) was published by the CRC for Catchment Hydrology (and is available from their website at The report outlines the key considerations in the planning, design and assessment of a stormwater sensitive urban design. It stresses the Australian Water Conservation and Reuse Research Program, January 2004 Page 1

5 importance of using a multidisciplinary team, and of stakeholder consultation. It outlines both non-structural and structural measures, and stresses the need for modelling techniques to assess the performance of the proposed scheme. The report also emphasises the importance of the application of both methods, to achieve sustainable urban water management. Planning &Design Technology Best Planning Practices Best Management Practices (Technology) Water Sensitive Urban Design Efficient Sustainable Attractive Figure 1. Relationship between structural and non-structural practices, to achieve stormwater sensitive urban design (Source: Lloyd et al., 2002). Non-structural measures identified include: - environmental and urban development policy (at local, state & federal level) - construction management practices - education and training (local government, industry, business) - community education programs - enforcement program. Lloyd et al. (2002) also identify a range of structural best management practices (BMPs) with potential application for stormwater sensitive urban design, and identify the appropriate scale of application. Lynbrook Estate an early example of the application of stormwater sensitive urban design, is used as an effective case study by Lloyd et al. (2002). Further details are provided later on in this document. Australian Water Conservation and Reuse Research Program, January 2004 Page 2

6 Table 1. Application of structural best management practices for stormwater sensitive urban design (Source: Lloyd et al., 2002). Unfortunately, national documents relating to stormwater management have evolved in parallel with the particular needs of their target audience, and as such, implementation has been somewhat hindered by gaps, inconsistencies and duplication between the different documents; all of this has created confusion in implementation. The recently-released (draft) Australian Runoff Quality (edited by Wong, 2003) attempts to overcome this, by providing a standard Australian reference on stormwater management. The overall purpose of Australian Runoff Quality is to provide: - Procedures for the estimation of a range of urban stormwater contaminants; - Design guidelines for commonly applied stormwater quantity and quality management practices; - Procedures for the estimation of the performance of these practices; and - Advice with respect to the development of integrated water cycle management practices. Australian Runoff Quality is not a technical manual, and needs to be used in conjunction with design manual and standard design specifications from State and/or Local Government Authorities, based on local terrain, geological and climatic conditions. There are 13 chapters in Australian Runoff Quality, which cover: Australian Water Conservation and Reuse Research Program, January 2004 Page 3

7 1. An introduction describing the purpose and scope of water sensitive urban design, and its context within ecologically sustainable development (Figure 2). 2. A summary of stormwater pollutants, their pathways and processes, 3. Expected stormwater pollutant concentrations and loads, for a range of land uses, 4. Principles and implementation of water sensitive urban design (with a strong emphasis on stormwater management), 5. Use of roofwater, stormwater and wastewater as alternative water supplies, 6. Water quality criteria for design of stormwater management strategies, 7. Design and selection of gross pollutant traps and sediment traps, 8. Hydrocarbon management, 9. Design of buffer strips, vegetated swales and bioretention systems, 10. Design of stormwater infiltration systems, 11. Design of constructed stormwater wetlands and ponds, 12. Management of urban waterways 13. Modelling of urban stormwater management systems. Figure 2. Components of water sensitive urban design, and its relationship to ecologically sustainable development (Source: Wong, 2003). Whilst Australian Runoff Quality provides an important benchmark in setting a consistent framework for stormwater management in Australia, the document does not provide adequate design details to facilitate implementation, without reference to design standards. Australian Runoff Quality also fails to encompass guidance on application of non-structural management techniques, and on the institutional issues affecting stormwater management. These are important if such a document is to provide substantial improvements in current practice. Australian Water Conservation and Reuse Research Program, January 2004 Page 4

8 3 State Guidelines and Literature Documents on stormwater sensitive urban design at a State level take two forms (a) guidelines prepared by relevant State or other agencies, and (b) compiled information on stormwater sensitive urban design principles and design. The former are summarised briefly below. The latter are made available by relevant agencies (e.g. New South Wales Environment Protection Authority, Brisbane City Council, Victorian EPA, Melbourne Water Corporation), usually at websites (Table 2). These websites have a great range of information, although they require quite a bit of searching, since there is no consistent layout or indexing on each site. Table 2. Agency and other websites providing information on stormwater sensitive urban design. Organization Dept of Environment & Heritage Melbourne Water Corp. Brisbane City Council NSW EPA Victorian EPA Stormwater Industry Association Municipal Association of Victoria Water Sensitive Urban Design in the Sydney Region WA Waters and Rivers Commission Web URL The earliest guidelines for stormwater sensitive urban design were released in 1994 (Department of Planning and Urban Development et al., 1994), for the Perth urban region. They provide a summary of stormwater management measures, detailing their application, limitations, cost effectiveness and maintenance. Conceptual drawings are provided for each treatment measure, but there is inadequate information to allow detailed design. The scope of measures and management practices is impressive, covering everything from wetlands and infiltration systems, to mulching, xeriscaping, local-site water harvesting, and soil improvement measures. Regarded as a pioneering document in Australia, a number of the concepts have been incorporated into subsequent documents. More recently, the WA Waters and Rivers Commission released a manual for urban stormwater quality ( Guidelines for stormwater management were developed by Victoria (Victoria Stormwater Committee, 1999) and NSW at the same time, with significant collaboration, resulting in documents with a high degree of commonality. The NSW EPA document was released only in draft form, but a document entitled Managing Urban Stormwater: Treatment Techniques was released (Environment Protection Authority of New South Wales, 1997), which provided guidance on selection of stormwater treatment measures, and then detailed the design and application of a number of measures. The list of techniques examined was quite extensive, including primary (litter and sediment removal devices), secondary (swales, filter strips, basins, sand filters and infiltration systems, and porous pavements) and tertiary (constructed wetlands) treatment devices. The Victorian Urban Stormwater Best Practice Environmental Management Guidelines (Victoria Stormwater Committee, 1999) are very comprehensive, and focus not only on design guidance, but on the principles and objectives of stormwater management and stormwater sensitive urban design, along with the role of stormwater management and planning controls. This is one of the first documents to place such a strong emphasis on the non-structural elements of stormwater sensitive urban design, rather than having a sole focus on technology. Australian Water Conservation and Reuse Research Program, January 2004 Page 5

9 Chapter 5 of the Victorian guidelines specifically outlines the principles and approaches of water sensitive urban design, and Chapter 6 then lists a selection of non-structural source controls. Queensland has Stormwater Quality Control Guidelines for Local Government (Department of Natural Resources and Department of Environment, 1998), which outlines the issues relating to stormwater quality, and outlines the legal and planning framework for stormwater management. The focus on planning both stormwater management planning, and strategic/ land use planning is useful (although will need regular updating). There is some information provided on stormwater quality management practices, but not in great detail. 4 Performance of Stormwater Sensitive Urban Design Structural Best Management Practices Being able to predict the likely water quality performance of a given treatment measure is important in facilitating its adoption. Whilst this document cannot provide a detailed review of all the literature in this area, a recent review of the performance of a wide range of stormwater sensitive urban design structural best management practices was undertaken by the NSW Environment Protection Authority (Fletcher et al., 2003a), and a summary of its main findings is provided here. 4.1 Gross Pollutant Traps Most of the studies of non-proprietary GPTs focus on the load captured over a certain storm, or duration. Unfortunately, these data do not allow removal efficiency to be calculated. In particular, there is a distinct lack of field studies that quantify removal efficiency. This deficiency, noted previously by Allison et al., (1998), is not easy to overcome, however, because field efficiency sampling is very expensive, and logistically difficult, due to safety concerns and risks of increasing flooding due to installation of monitoring equipment. Nonproprietary GPTs are generally large scale, increasing these difficulties. For example, the newly released Australian Runoff Quality guidelines include a chapter on gross pollutant and sediment traps, but do not quote typical performance data (Allison and Pezzaniti, 2003). There are very little reliable data on which to base summaries of expected performance. However, Table 1 provides a summary of expected performance, derived from a review of literature by Fletcher et al. (2003), along with rationale for these estimates, and caveats to be considered in their adoption. Table 1. Pollutant Removal Estimates for Gross Pollutant Traps (Source: Fletcher et al., 2003) Pollutant Litter and organic matter Expected removal (mean annual load) Comments 10%-30% Depends on effective maintenance, specific design (hydraulic characteristics, etc). 10% where trap width is equal to channel width, 30% where width is 3 or more times channel width. TSS 0-10% Depends on hydraulic characteristics; will be higher during low flow. TN 0% (negligible) Transformation processes make prediction difficult TP 0% (negligible) TP trapped during stormflows may be re-released during interevent periods, due to anoxic conditions. Coarse sediment 10-25% Depends on hydraulic characteristics; will be higher during low flow. Oil and grease 0-10% Majority of trapped material will be that attached to organic matter and coarse sediment. Faecal coliforms unknown Heavy metals 0% (negligible) Australian Water Conservation and Reuse Research Program, January 2004 Page 6

10 4.2 Vegetated Swales and Filter Strips Swales are open vegetated (generally grass) drains, which provide some stormwater filtration prior to discharge to downstream drainage systems or receiving waters (Wong et al., 2000). Whilst a traditional feature in rural environments (due to lower infrastructure cost, and available space), swales are increasingly being used to reduce impacts of urban stormwater. A buffer or filter strip is aligned perpendicular to the direction of flow, and is used to filter particulate matter and associated pollutants prior to entry to the (usually adjacent) receiving water. With a relatively short flow path length through the buffer, treatment performance relies on having well-dispersed flows (i.e. low hydraulic loading). Effectiveness will therefore be reduced in situations where flow channelisation occurs. Table 1 provides a broad estimate of overall performance for a range of pollutants, where available. The values should NOT be regarded as prescriptive, and should be used as indicative only; performance at any particular time will depend on operating conditions at that time. It is also important to recognise that a swale or filter strip that promotes significant infiltration will remove a large proportion of pollutant mass through this mechanism. This has not been taken into account by the estimates provided in Table 1. Table 1 Pollutant Removal Estimates for Vegetated Swales and Filter Strips (Source: Fletcher et al., 2003) Pollutant Litter & organic matter Expected removal (mean annual load) Very high (>90%) Comments Should be almost 100% removal, provided there is adequate vegetation cover, and flow velocities are controlled (below 0.5m/s). TSS 60-80% Assumes low level of infiltration. Will vary with varying particle size distribution. TN 25-40% Dependent on speciation and detention time. TP 30-50% Dependent on speciation and particle size distribution. Coarse sediment Very high (>90%) Assumes re-suspension and scouring is prevented, by controlling inflow velocities to <0.8m/s, and maintaining dense vegetation. Oil and grease n/a No reliable data available. Faecal coliforms n/a No reliable data available. Heavy metals 20-60% Highly variable: dependent on particle size distribution, ionic charge, detention time, etc. 4.3 Infiltration and Bioretention Systems This category of treatment measure is unified by the use of a filtration medium (e.g. loam, sand, gravel) to treat urban stormwater. Filtration systems may include sand filters, rain gardens, bioretention basins, etc. Similarly, infiltration systems may take many forms, including trenches, or basins (dry or wet). The distinction between the two systems is the destination of the treated water: Infiltration systems remove water from surface flow, allowing it to infiltrate below ground, and ultimately to groundwater Filtration and biofiltration (also called bioretention) systems detain water, and discharge it back to receiving surface waters. A detailed description of the principles and design of biofiltration and infiltration systems is given in Chapter 9 and 10 of Australian Runoff Quality (Argue and Pezzaniti, 2003; Fletcher et Australian Water Conservation and Reuse Research Program, January 2004 Page 7

11 al., 2003b), and in Auckland s stormwater technical guidelines (Auckland Regional Council, 2002). The role of vegetation in biofiltration systems is critical, contributing to biological uptake, maintaining porosity of the soil media, facilitating microbial growth, and enhancing sedimentation in above-ground treatment (whilst ponded). Data on the performance of infiltration and biofiltration systems are still quite rare, both in Australia and internationally. Typical performance data are summarised in Table 2. Table 2. Pollutant removal estiamtes of infiltration and bioretention systems (Source: Fletcher et al., 2003) Pollutant Expected removal Comments (mean, range) (%)* Litter & organic matter 100 Expected to trap all gross pollutants, except during high-flow bypass. TSS Pre-treatment required to reduce clogging risk. TN 50-70** Dependent on speciation and state (soluble or particulate). TP Dependent on speciation and state (soluble or particulate). Coarse sediment May pose a clogging risk. These systems should have pre-treatment to remove coarse sediment prior to entry into the filter media. Oil and grease n/a Inadequate data to provide reliable estimate, but expected to be >75% Faecal n/a Inadequate data coliforms Heavy metals Dependent on form (soluble or particulate). * For infiltration systems, the total performance will include the proportion of mean annual runoff that is infiltrated, and therefore not discharged to downstream receiving waters. Figures presented do not take into account this flow loss, but instead reflect changes as a result of in-situ pollutant reduction. ** Occasional instances of negative removal have been reported in the literature, but are not expected to represent typical performance. 4.4 Ponds, Wetlands and Sediment Basins Although apparently different, ponds, wetlands and sediment basins operate using similar mechanisms (flow attenuation, sedimentation, and in some cases, filtration), to remove contaminants from urban stormwater. The variation observed in wetland performance can be explained in part by relationships between key factors (e.g. hydraulic loading and input concentration), which vary greatly in the highly dynamic processes influencing stormwater flow and quality. Table 1 provides a summary of the typical range of performance for stormwater wetlands, ponds and sedimentation basins, with comments as appropriate. The range represents an approximate standard deviation of the studies reviewed, whilst the centre of the range can be used as an approximate estimate of typical performance. Australian Water Conservation and Reuse Research Program, January 2004 Page 8

12 Table 1 Pollutant Litter and Organic matter TSS TN TP Summary of Expected Pollutant Removal by Ponds (p), Wetlands (w) and Sedimentation Basins (Source: Fletcher et al., 2003) Expected removal (mean annual load, %) Very high (>95%) (s,p,w) (p) (w) (s) (p) (w) (s) (p) (w) (s) Very high (>95%) Comments Subject to appropriate hydrologic control Litter and coarse organic matter should ideally be removed in an aerobic environment PRIOR to a pond or wetland, to reduce potential impacts on BOD. Depends on particle size distribution. Dependent on speciation and detention time. Dependent on speciation and particle size distribution. Will be greater where a high proportion of P is particulate. Subject to appropriate hydrologic control. Coarse Sediment Oil and Grease n/a Inadequate data to provide reliable estimate, but expected to be >75% Faecal n/a Inconsistent data. Coliforms Heavy Metals (p) Quite variable: dependent on particle size distribution, (w) ionic charge, attachment to sediment (vs. % soluble), (s) detention time, etc. 4.5 Porous Pavements Porous pavements, as their name implies, are a pavement type that promote infiltration, either to the underlying soil, or to a dedicated storage reservoir below it. Porous pavements come in several forms (Figure 1), and are either monolithic or modular. Monolithic structures include porous concrete and porous pavement. Modular structures include porous pavers (which may be either made of porous material, or constructed so that there is a gap in between each paver) and modular lattice structures (made either of concrete or plastic). Porous pavements are usually laid on sand or fine gravel, underlain by a layer of geotextile, with a layer of coarse aggregate below. Porous pavement has two main advantages over impervious pavement, in terms of stormwater management: (a) improvement to water quality, through filtering, interception and biological treatment and (b) flow attenuation, through infiltration and storage. However, they may also be expensive, and prone to clogging. The pollutant removal by porous pavement appears to be relatively consistent (Table 1). However, this finding should be viewed with some caution, because it may reflect at least in part the lack of studies which have specifically reported on performance relative to input variables, such as inflow concentration, hydraulic loading, and properties of the pavement. Australian Water Conservation and Reuse Research Program, January 2004 Page 9

13 Porous pavers (Photo: Porous carpark, road gutter, Manly (Photo: Tim Fletcher) Porous pavers in Manly residential street (Photo: Tim Fletcher) Porous carpark, Washington DC (Photo: Ecological Engineering) Grasspave (Photo: Ecological Engineering) Figure 1. Examples of Porous Pavement Table 1. Summary of expected porous pavement performance (Source: Fletcher et al., 2003) Pollutant Expected concentration Comments reduction (+ range) Total Suspended Solids 80 (70-100) Total Nitrogen 65 (60-80) Will decrease with proportion dissolved Total Phosphorus 60 (40-80) Will decrease with proportion dissolved Hydrocarbons/Oils/Grease 85 (80-99) Depends on level of microbial activity. BOD - Inadequate data Pb, Cu, Cd, Zn, Ni 75 (40-90) Will decrease with proportion dissolved Litter - Litter will simply wash off Pathogens - Inadequate data 5 Stormwater Re-use Literature and Guidelines Stormwater re-use, as defined for the purposes of this section, does not include rainwater harvesting. In 1999 the Queensland Water Recycling Strategy released a Stormwater Recycling Background Study, prepared by WMB Oceanics Australia (WBM, 1999). This study Australian Water Conservation and Reuse Research Program, January 2004 Page 10

14 investigated the status of stormwater recycling in Queensland, interstate and overseas, as well as identifying advantages, disadvantages and potential benefits of such practices. However, it did not go so far as to provide definitive guidance, and as such, adoption of stormwater re-use is still hampered by a lack of guidelines (and necessary research to back the development of such guidelines). The Institute for Sustainable Resources at Monash University recently compiled an inventory of integrated stormwater treatment and re-use practices in Australia with the aim being to develop an inventory of technologies for collection, treatment, storage and distribution of general stormwater runoff (Hatt et al., 2004). Regulation, performance, construction, operation and maintenance, implementation issues, and costs and benefits were also assessed. Current knowledge gaps were identified and future research needs to overcome these gaps are discussed. Again, since this document was a review of current practice, it provides little guidance for future practice in industry: instead this document makes recommendations for research to form the basis of guidelines (and cautions about developing guidelines without having first conducted research to identify and overcome key risks). There are a limited number of journal and conference papers, and technical and industry reports that address integrated stormwater treatment and re-use from a broad viewpoints (e.g. Mitchell et al., 2002; Radcliffe, 2003). However, accessible literature is generally specific to particular systems, much of which can be found on the websites of various Australian research institutions, local councils and water associations. In terms of stormwater re-use there are currently no specific guidelines. However, there are specific statutory obligations under health, environmental, agricultural or food legislation for reuse of wastewater (this varies from state to state). The suite of documents that comprise the National Water Quality Management Strategy (NWQMS) includes guidelines for use of reclaimed water, specific to effluent arising from municipal wastewater plants (ARMCANZ et al., 2000), and most States either refer to this (or their own guidelines which appear to have been based on the NWQMS) as a guide to evaluate and operate stormwater re-use schemes. The NWQMS provides guidance for specific reclaimed water applications in terms of type of re-use, level of treatment, reclaimed water quality, reclaimed water monitoring, and controls. However, the characteristics of stormwater and wastewater are very different, therefore these guidelines are only adequate to a certain extent. New National Water Recycling Guidelines are currently being developed as part of the federal government s National Water Initiative and will address stormwater recycling but not as a first priority (G. Jackson, personal communication). 6 Gaps in Current Guidance Documents There are perhaps three principal weaknesses in the various guidance documents produced to date: 1. Despite the potential importance of non-structural measures to achieve the objectives of water sensitive urban design, this area has generally received little focus or resources in Australian guidelines. This has been addressed in part by recent publication by the CRC for Catchment Hydrology of a series of reports on application of non-structural measures (e.g. Taylor and Wong, 2002). What is now needed is the translation of these into agency guidelines. 2. No guidelines have yet provided the detailed design guidance necessary to simplify the design process, so that it can be conducted by non-specialists. Melbourne Water is currently attempting to overcome this, by developing a Water Sensitive Urban Design Technical Manual (in preparation), which will include details such as standard drawings of commonly applied stormwater sensitive urban design techniques. Australian Water Conservation and Reuse Research Program, January 2004 Page 11

15 3. There has been a tendency for stormwater sensitive urban design to evolve somewhat in isolation from developments in other areas of urban water cycle management (e.g. water re-use), and guidelines have reflected (or contributed to) this separation. 7 Overseas Best Practices Stormwater treatment systems are known under different names in different parts of the World. Even in English speaking countries there are different terms used in practice. In the UK, the stormwater systems are referred to as Sustainable Urban Drainage Systems (SUDS). The SUDS Database (Duffy, 2001) and regularly updated since, documents the adoption of SUDS systems across Scotland. Although limited to Scotland, this documentation is considered typical of general SUD practice. Most SUD systems in Scotland have been incorporated into residential sites, followed by commercial i.e. at the allotment and/or neighbourhood scale (Figure 2). Interestingly, there is a much wider uptake of SUD systems in redevelopment of brownfield sites compared with greenfield sites. This is probably because space is of a much higher premium in Europe and therefore there is a much higher proportion of brownfield sites than in Australia. As is also the case in Australia, different councils in Scotland have adopted SUD systems to different extents. Figure 2. Application of WSUD by land use type (Source: Duffy, 2001) Infiltration trenches are the most common type of SUD system to be adopted in Scotland followed by pervious paving, ponds, swales and filter drains (Figure 3). It is logical that infiltration systems are the most widely used given that they are cheaper and more space efficient than surface systems such as wetlands. This is also true for some other European countries, and also for Japan. Australian Water Conservation and Reuse Research Program, January 2004 Page 12

16 Figure 3. WSUD techniques used in Scotland (Source: Duffy, 2001)) In the US, WSUD has been referred to in the past as structural Best Management Practices and more recently Low Impact Design. A survey of SUD practice was conducted in Prince George s county in the state of Maryland. Although the results are only for one county, they are indicative of general US practices. It can be seen that infiltration trenches are again the most widely used WSUD system followed by oil/grit separators (Figure 4). Swales, ponds and filter basins, which have been widely adopted in Europe are not extensively used in the US. Figure 4. Number and type of SUD systems in operation in Prince George s County (Source: (Galli, 1992)) Although trends in adoption of WSUD systems across Australia has not been well documented, it is known that infiltration systems are favoured in SA and WA, while the eastern States tend to utilise swales and wetlands (surface systems). The wide use of infiltration systems in SA and WA is due to underlying pervious soils rather than the space constraints that promote the use of such systems in the UK. Australian Water Conservation and Reuse Research Program, January 2004 Page 13

17 It seems that wetlands are more popular systems in Australia than in Europe. This may be due to the space availability, or perhaps due to the presence of a number of key advocates of wetland research and technology in Australia. In the similar way, bio-filters are of slightly different design here than in the UK. However, when compared to the overseas practice it appears that one of main differences is in the use of porous pavement. In Australia, porous pavements are still a highly neglected form of WSUD (Newton et al., 2003), mainly due to false impressions by practitioners that they are prone to clogging. However, from a worldwide literature survey (Fletcher, et al., 2003), it was concluded that particularly modular systems with underdrains are performing to high standards, being one of the better WSUD measures available (Newton et al., 2003). They are highly effective in reducing peak flows, volumes, and pollutant concentrations of stormwater (by filtration and biological treatment). They are inexpensive systems suitable for densely populated areas (where other SUDs are usually not applicable), and do not require substantial maintenance (Fletcher, et al., 2003). Therefore, it could be concluded that these systems should be promoted in Australia Apart from this, there are no major gaps in the adoption of the wide variety of Stormwater Sensitive Urban Design practices in Australia. 8 Case-studies of Stormwater Sensitive Urban Design The following case studies are provided as a diverse cross-section of applications of stormwater sensitive urban design in Australia. Since opportunities and constraints at each site will be unique, these case-studies should be read as examples only, and not viewed as templates for implementation. Case Study 1: Lynbrook Estate (Source: Lloyd et al., 2002). Introduction Scale Opportunities & Constraints Objectives Design process Lynbrook Estate is a greenfield residential development south-east of Melbourne. Full details of the case study are available at (search for Lynbrook ). 32 Ha (271 medium density (average size = 600m 2 ) allotments Initial hesitancy by local government was overcome by Melbourne Water, who provided an underwriting of the project, committing to retrofit to traditional drainage design, if the system failed within 5 years. Being a greenfields site made the design process easier than retrofitting. The design sought to appear conventional, with traditional kerb and gutter on much of the estate, being used to convey water intro treatment swales and bioretention systems, placed within the nature strip. Design ensured that ponding was minimised (meaning a compromise on treatment effectiveness). Hydraulic standards are same as conventional systems (ie. 5 year ARI event conveyed within system, designated flow path for 100 year ARI event). Stakeholders involved in design process. Site management practices during construction included sediment fences, protective use of geotextile, etc. Australian Water Conservation and Reuse Research Program, January 2004 Page 14

18 Treatment techniques Flow & water quality benefits Economic benefits Other benefits Maintenance Loads of TSS, TP and TN reduced by at least 73, 77 and 70% respectively. Lower peak concentrations. Runoff volume reduced by between 51% and 100% for monitored storms. Increased time of concentration. Overall development cost was 0.5% higher than conventional, attributed to contingency charges by contractors, who had not previously worked on such systems. Subsequent stages at Lynbrook, utilising WSUD, had no additional cost over traditional. Very strong (>90%) community support, with majority of those surveyed citing benefits in terms of water quality and aesthetics. Developer has adopted stormwater sensitive urban design on all future stages at Lynbrook, and is now incorporating broader WSUD into a number of other developments. Developer extended their maintenance contract by 12 months (to 2 years). Cast Study 2: Second Ponds Creek (Source: Ecological Eng, 2002; Landcom, 2002) Introduction Scale Opportunities & Constraints Objectives Design process Treatment techniques Second Ponds Creek is a large development site north-west of Sydney, amongst a rapidly developing area. 320 ha, including open space, trunk drainage land, and a public school site. The site was affected by a number of constraints, which the design consultants had to overcome in their design: 1. Salinity: shallow groundwater tables of highly saline water have caused gullying and scalding since the earl 1900s. 2. Dispersive sodic clays. Protect the health of receiving aquatic ecosystem, and maintain channel stability. Meet EPA pollutant load reduction targets (80, 45 & 45% reduction in TSS, TP and TN respectively). Minimize salinity hazard. Rehabilitate existing waterways. Minimise infiltration by ensuring that treatment systems such as bioretention systems are lined, with all water ultimately conveyed to surface waters. Restore Second Ponds Creek, morphology and riparian zone, with appropriate flow management to maintain rehabilitated systems (maintain peak flows to pre-development levels). Combination of bioretention systems (incorporating vegetated swales) and constructed wetlands. Bioretention systems incorporated into median strips and nature strips. Design includes rain-gardens within boulevards, both as a treatment system, and as an Australian Water Conservation and Reuse Research Program, January 2004 Page 15

19 ornamental feature. Flow & water TSS, TP and TN mean annual load reduced by >80, 45 and 45% respectively, in quality benefits comparison to traditional design. Peak flows up to 1.5 year ARI maintained at predevelopment levels. Economic benefits - Other benefits WSUD objectives integrated with urban design and aesthetic objectives, along with protection of important remnant flora Maintenance - Case Study 3: Byford Village (Source: Ecological Engineering, 2003a) Introduction Scale Opportunities & Constraints Objectives Design process Treatment techniques Flow & water quality benefits Located in Perth, within the catchments of the Serpentine River and Peel-Harvey Estuary (which is subject to blue-green algal blooms), Byford Village is constructed on an old munitions site. 800 lot subdivision The site had a number of pre-existing and potential flooding issues, and the design needed to achieve both environmental and flood protection. The prevalence of long dry periods meant that the stormwater treatment techniques used had to be able to remain sustainable, with extended periods of low or zero inflow. For this reason, ephemeral wetlands were chosen, rather than the more commonly-used wetlands with some permanent water. To maintain pre-development water quality. In particular, the aim is to reduce sediment and nutrient loads in the Peel-Harvey estuary. Mitigate flooding threats. A site constraints and opportunities workshop was used by the design consultants, along with detailed site and data investigations, to select a range of potential stormwater management scenarios. Each scenario was then modelled using MUSIC (Wong et al., 2002), to identify the optimal solution. The approach involved trying to reduce pollutant loads discharged to downstream receiving waters not only by treatment techniques, but by facilitating opportunities for re-use (for local irrigation on-site). Integrating public open-space, through the use of linear corridors, was adopted as a principle, to integrate stormwater management and urban design objectives. Includes a multi-function drainage corridor, incorporating a number of stormwater treatment wetlands, with vegetated swale pre-treatment and flow conveyance. Bioretention systems are used within the streetscape. Wetlands are contained within a number of retarding basins, which attenuate flows to downstream receiving waters. Mean annual loads of TSS, TP and TN were reduced by 77, 82 and 41% respectively, based on MUSIC modelling: 100% 100% 100% 100% Percentage of "Conventional Drainage" Pollutant Load 90% 80% 70% 60% 50% 40% 30% 20% 10% 81% 85% 63% 91% 93% 87% 87% 90% 90% 64% 70% 73% 70% 75% 81% TSS TP TN 56% 63% 62% 58% 65% 65% 0% Existing Conditions Conventional Drainage - No WSUD Permanent Pool Wetlands Only Ephemeral Wetlands Only Ephemeral Wetlands and Bioretention in POS Bioretention in POS Only Ephemeral Wetlands, Bioretention in POS and Bioretention in Roads Bioretention in POS And Bioretention in Roads Economic benefits - Australian Water Conservation and Reuse Research Program, January 2004 Page 16

20 Other benefits The multiple use drainage corridor also provides for a number of passive recreational opportunities, and is a key part of the landscape design of the development. Maintenance - Case Study 4: Inner Urban Streetscape: Melbourne St, Brisbane (Source: Ecological Eng, 2003b) Introduction Scale Opportunities & Constraints Objectives Design process Treatment techniques Not all stormwater sensitive urban design is done at the large-scale greenfields-type site. Brisbane City Council, as part of its Suburban Centre Improvement Program (SCIP), attempts to integrate water sensitive urban design into suburban and inner-city precincts and streetscapes. A recent example was that applied to Melbourne St, where landscape elements were incorporated into the streetscape, to treat stormwater, and provide passive watering of the landscape by stormwater runoff. Streetscape scale, within constrained inner-urban or suburban sites. Constrained sites offer limited opportunity (hence need innovative approach) Stormwater sensitive urban design is part of a broader retrofit/renovation (increases feasibility) Disconnect impervious surfaces from underground pipe network as much as practicable. Collect and treat as much stormwater as practicable, as close to its source as possible. Treat stormwater to a standard that allows it to be re-used or discharged to receiving waters. Collect, store and re-use as much treated stormwater as is practicable. Integrate stormwater collection and treatment functions with landscape elements. Design consultants identified opportunities to intercept the conventional drainage system. The innovative approach they adopted was to create a number of bioretention planter cells, supporting street trees, with treated flow then discharged to the traditional drainage network below. To ensure no adverse hydraulic impacts, the existing density of Side Entry Pits within the street was maintained, with the bioretention cells installed in additional side entry pits. Bioretention system planter cells, containing street trees. Flow is conveyed by gutters to the cells, which act under low flows like Side Entry Pits, but allowing the flow to percolate through the soil/root filter medium, before discharge to the pipe network. Under high flows, the systems surcharge, with bypassed flow being conveyed to the next traditional Side Entry Pit on the street. Depressed garden beds were also used as bioretention systems within the street median. Tanks were also used for the collection and storage of stormwater for re-use. Australian Water Conservation and Reuse Research Program, January 2004 Page 17

21 Flow & water quality benefits Economic benefits Other benefits Maintenance - Modelling undertaken using MUSIC showed a reduction in the mean annual load of TSS, TP and TN from the Melbourne St case study site of 55, 60 and 53% respectively. The MUSIC model was also used to size a number of stormwater storages, which were shown to support between 45 and 95% of the average annual irrigation demand, depending on their size. Cost of implementing the street-scale approach was compared with the alternative of using regional scale stormwater quality treatment measures (e.g. large constructed wetlands), showing a total implementation cost of approximately $5/m 2 of catchment area, compared to $1.30/m 2 for regional measures. However, in constrained urban sites, space for regional treatments is unlikely to be available. Aesthetic and landscape benefits, as part of an entire local area improvement. Australian Water Conservation and Reuse Research Program, January 2004 Page 18

22 There are a number of stormwater treatment and re-use projects in operation around Australia (most of which are in New South Wales and South Australia) and numerous schemes at design or construction stage (Hatt et al., 2004). These systems harvest rainwater (roof runoff only) and/or general storm runoff (runoff from all surfaces) for largely non-potable re-use, and they may also incorporate re-use of greywater and/or wastewater. The following two case studies are presented as a sample of applications of stormwater re-use in Australia. Further detail on these and three other case-studies are presented in Appendix I. Case Study 5: Oaklands Park Introduction Scale Opportunities & Constraints Objectives Design process Treatment techniques Oaklands Park is a greenfield semi-rural residential development north-west of Melbourne. 174 ha (80 allotments plus 121 ha open space) Mains water supply not available to estate. Reported little support or involvement from relevant institutions. Some buyer reluctance experienced initially however persistence on the part of developer persuaded prospective purchasers that their ideas were economically viable. To pioneer a number of best practice approaches to ecologically sustainable design Collection designed to typical standards (to safely convey 5 year ARI flow). Storage modelling based on projected demand for summer peak (3 months during Nov-Mar) and remaining period; 100 year ARI spillways installed on storages, provision to move water from one store to another to minimise evaporation. Roof runoff collects in storage tanks fitted with first flush diversion devices. Runoff from roads and open spaces (general runoff) conveyed through open swale drains to a system of three lakes. Flow & water quality benefits Economic benefits Other benefits Maintenance Swales slow water flows, minimise erosion and increase point of contact groundwater infiltration. General runoff distributed via mains pressure reticulation system and re-used for non-potable purposes (mostly outdoor uses but some houses also use general runoff for toilet flushing), including fire-fighting. Roof runoff provides drinking water for household consumption. No water and sewage usage fees and rates for residents (although there is an initial extra cost in the home design to allow provision of rainwater tanks and wastewater treatment systems). Collection, treatment and re-use of wastewater, as well as planting of locally native trees, shrubs and grasses further integrate system into total urban water cycle. Little maintenance required apart from pumping water between storages. Weed management and removal program for open space areas. Pumps have self-cleaning filters but require manual pressure wash quarterly. Maintenance of grass cover surrounding lakes, rock lining, monitoring for leakage. Australian Water Conservation and Reuse Research Program, January 2004 Page 19

23 Case Study 6: Manly Stormwater Treatment and Re-use (STAR) Project Introduction Scale Opportunities & Constraints Objectives Design process Treatment techniques The Manly STAR Project is a pilot stormwater management project retrofitted into the Manly Ocean Beach/Pine Street catchment in Sydney s north-east. 3 ha catchment Retrofit fully developed ultra-urban suburb with a high population density and large numbers of tourists (urban runoff contains relatively high levels of pollutant loading). Opportunity to provide stormwater quality improvement as well as improve visual amenity. Protect and improve surface water quality by developing sub-catchment programs that pursue the following objectives: Reduce the pollution load and concentration in stormwater Attenuate flow to reduce flooding Infiltrate stormwater to groundwater Treat, collect and re-use stormwater Reduce the transportation of pollutants Find a cost effective and ecologically sustainable way to achieve these outcomes Develop a prototype model for use elsewhere Initial risk assessment suggested the health risk associated with stormwater re-use was below the generally accepted limits for re-use of water. Roadbase is similar to normal transport authority standards except for the lower percentage of material that is less than 1mm in size. Treatment train consists of permeable pavement, coarse and fine screens, and filtration through ecosoils to underground storage tanks where final sedimentation occurs. Flow & water quality benefits Economic benefits Other benefits Maintenance System capable of infiltrating high flows (excess stormwater bypasses to conventional drainage system). Improved stormwater quality discharging onto Ocean Beach. Treated stormwater re-used for irrigation. Cheaper alternative to removal of stormwater drains from beachfront (project initially prompted by a call from the community to relocate the drains). Reduced potential health risk to beach users. Preventing pollution through use of information boards. According to manufacturer specifications ecosoils should be harvested every ten years and accumulated pollutants extracted (although there is currently no defined feedback mechanism to determine whether this maintenance frequency is adequate). No other maintenance program devised. Australian Water Conservation and Reuse Research Program, January 2004 Page 20

24 9 Policy, Economic and Institutional Issues Affecting Adoption of Stormwater Sensitive Urban Design in Australia The major barriers to implementation of Stormwater Sensitive Urban Design include: regulatory framework; assessment and costing; marketing and acceptance; and technology and design (Lloyd et al., 2002). Lloyd et al. (2002) conducted surveys of industry practitioners to rank potential barriers to implementation of WSUD (Table 2). Table 2. Potential barriers to implementation of WSUD (Source: Lloyd et al., 2002) Hatt et al. (2004) found similar results, identifying the lack of regulation, clear design criteria, and a method to adequately assess costs and benefits of WSUD against conventional practices as the major obstacles to widespread adoption of WSUD. Public acceptance of WSUD has reportedly increased as knowledge has become more extensive, however interest on the part of the development industry appears to still be somewhat subdued, and this is most likely due to lack of progress in overcoming the other three identified impediments. 9.1 Policy and Institutional Issues The development industry has reported lengthy and resource intensive negotiation, assessment and approval processes for implementing WSUD, particularly if stormwater re-use is Australian Water Conservation and Reuse Research Program, January 2004 Page 21