chapter 1 introduction - brisbane · introduction august 2005 1-1 chapter 1 introduction ... 1-6...

Draft Water Sensitive Urban DesignEngineering Guidelines

Introduction August 2005 1-1

Chapter 1 Introduction

CHAPTER 1 INTRODUCTION .....................................................................................1-11.1 Background ................................................................................................................................ 1-2

1.2 Purpose of the Guidelines.......................................................................................................... 1-2

1.3 Target Audience......................................................................................................................... 1-2

1.4 How to use the Guidelines ......................................................................................................... 1-2

1.4.1 How Council will use the Guidelines ............................................................................. 1-3

1.4.2 How Applicants (Designers) use the Guidelines........................................................... 1-3

1.5 Structure of the Guidelines......................................................................................................... 1-4

1.5.1 Chapters 2 to 11 - WSUD Elements ............................................................................. 1-4

1.5.2 Plant Selection for WSUD Systems (Chapter 12 ) ........................................................ 1-5

1.6 Summary of WSUD Elements Covered ..................................................................................... 1-6

1.6.1 Swales (incorporating Buffer Strips) (Chapter 2) .......................................................... 1-6

1.6.2 Bioretention Swales (Chapter 3) ................................................................................... 1-7

1.6.3 Sedimentation Basins (Chapter 4) ................................................................................ 1-8

1.6.4 Bioretention Basins (Chapter 5) .................................................................................... 1-9

1.6.5 Constructed Wetlands (Chapter 6).............................................................................. 1-10

1.6.6 Infiltration Measures (Chapter 7)................................................................................. 1-10

1.6.7 Sand Filters (Chapter 8) .............................................................................................. 1-11

1.6.8 Other Measures (Chapter 9) (NOT INCLUDED IN DRAFT)....................................... 1-12

1.6.9 Aquifer Storage and Recovery (Chapter 10)............................................................... 1-12

1.6.10 Ponds and Lakes (Chapter 11) (NOT INCLUDED IN DRAFT)................................... 1-12

References ......................................................................................................................................... 1-14



1.1 Background

Note: The Water Sensitive Urban Design Engineering Guidelines (the Guidelines) are being releasedas a draft document and will remain so for a period of twelve (12) months. A review of the draft willcommence in mid 2006.

Over the last five years, there have been an increasing number of initiatives to manage the urban watercycle in a more sustainable way. These initiatives are underpinned by sustainability principles of waterconservation, waste minimisation and environmental protection. Integration of urban water cyclemanagement with urban planning and design is known as Water Sensitive Urban Design (WSUD). Managingurban stormwater as a resource and for the protection of receiving ecosystems is a key element of WSUD.

WSUD promotes innovative integration of urban water management technologies into an urban environment.It requires strategic planning and concept designs, underpinned by sound engineering practices in designand construction.

While there are a number of documents providing guidance for planning and strategy development ofWSUD, guidance on the next level of design detail (i.e. from concept plans to detailed plans suitable forconstruction) is not well documented, and is the focus of these Guidelines.

1.2 Purpose of the Guidelines

These guidelines provide advice on the detailed design of WSUD stormwater systems and complimentexisting Brisbane City Council (BCC) resources that promote WSUD. The guidelines provide a consistentapproach to the design of WSUD elements for urban developments in the BCC local government area byoutlining design procedures, simplified design tools and checklists for individual WSUD elements that can beused by designers and Council development assessment officers when checking detailed designs.

The guidelines are NOT intended to be a decision making guide for selecting, integrating and locating WSUDelements (i.e. site feasibility). BCC’s Subdivision and Development Guidelines (BCC 2000), specifically PartC (Water Quality Management Guidelines) should be consulted as the primary reference for developingconcept designs. Further guidance on the selection, location and combination of WSUD elements into a‘treatment train’ is provided in Australian Runoff Quality (Engineers Australia 2003) and Urban Stormwater:Best Practice Environmental Management Guidelines (Victorian Stormwater Committee 1999).

1.3 Target Audience

The Guidelines are intended to support design engineers and BCC development assessment officers inpreparing and assessing detailed designs of WSUD elements. They are intended for professionals withappropriate experience in urban hydrology and hydraulics, and assume a basic knowledge in these fields.

While primarily directed at design engineers, it is recognised that all WSUD applications require theinvolvement of a range of urban design professionals to ensure a sustainable solution is found. Typically, thiswould involve planners, urban designers, architects, landscape architects and environmental scientists/ecologists. Sections of these Guidelines provide initial advice in this regard.

1.4 How to use the Guidelines

The Guidelines provide a consistent approach to the detailed engineering design of WSUD elements inBrisbane. They will help to ensure that treatment objectives and conveyance requirements of a stormwater



system are achieved. Figure 1.1 illustrates how the Guidelines fit into BCC’s assessment process(highlighted).

Figure 1.1: Development Process

1.4.1 How Council will use the Guidelines

Council will use the Guidelines to:

• provide better practice guidelines to actively promote WSUD in Brisbane• assist designers in preparing construction plans for proposed developments• provide a clear and transparent development assessment process for construction plans for WSUD

elements and promoting the achievement of catchment-based water management objectives.

Specifically:

• Design Assessment Checklists provide a template for checking development submissions, ensuring asufficient level of detail is presented for assessment.

• Inspection Forms, Maintenance Schedules and Asset Transfer Checklists can be used to help ensureWSUD elements are built as designed, are maintained and are in good operating condition prior to assethandover to Council.

1.4.2 How Applicants (Designers) use the Guidelines

The purpose of the Guidelines for applicants is to:

• Provide a tool for developing design responses that incorporate better water management practices andwhich meet defined performance standards.

• Help in preparing detailed designs for WSUD systems as part of a development proposal.

City Plan

• Proposal complies with WSUD objectives

Subdivision and Development Guidelines

• establish possible WSUD approaches

WSUD incorporated in development

Asset Transfer to Council

Construction

Performance Criteria and WQOGuidelines

• Establish performance targets

Detailed design of WSUD elements

Ongoing Maintenance

• Maintains WQOs



Specifically, once a WSUD strategy has been selected (typically informed by modelling using Guidelines forPollutant Export Modelling in Brisbane Version 7 (BCC 2003)), the Guidelines are to be used to provideadvice on detailed engineering calculations required to:

• confirm the size of the treatment measures to achieve the required performance outcomes• determine the physical dimensions to suit site characteristics and Council standards• ensure the conveyance requirements of the drainage system are maintained• size inlet and outlet hydraulic structures• provide suitable landscape characteristics to conform with treatment performance and aesthetic

objectives• compile calculation summary sheets where basic information from the design process can be recorded

and submitted as part of a development application.

1.5 Structure of the Guidelines

Chapters 2 to 11 of the Guidelines contain engineering design procedures for ten types of WSUD elements.The format in each of these chapters follows a standard layout, as shown in Figure 1.2, to provide forconsistency in the design process for each WSUD element and to assist checking of designs. Each of thesechapters also includes a worked example to illustrate application of each design procedure. Checklists fordesign, construction and maintenance are provided to summarise key information related to the WSUDelement to facilitate the design approval process.

Figure 1.2: Structure of the Guidelines

1.5.1 Chapters 2 to 11 - WSUD Elements

Following is a brief description of the sub-sections in Chapters 2 to 11.

Design considerations: This section provides detailed discussion on key considerations that will informdesign decisions made during application of the design process presented in each chapter.

Chapters 2 to 11 WSUD Elements

Design considerations

Design procedure

Landscape design notes

Maintenance requirements

Checking tools

Worked example

• Design assessment checklist• Construction checklist• Asset transfer checklist• Construction advice

Chapter 12 Planting Notes for WSUDElements

For example:• Verifying size for treatment• Estimating design flows• Determining physical dimensions• Design inflow systems• Vegetation scour velocity check• Velocity and depth check• Design outlets• Vegetation specifications• Maintenance plan• Design calculation summary

• Functions of groundcover vegetation• Required plant characteristics• Plant species selection• Recommended plant species tables

Chapters 2 to 11 WSUD Elements

Design considerations

Design procedure

Landscape design notes

Maintenance requirements

Checking tools

Worked example

• Design assessment checklist• Construction checklist• Asset transfer checklist• Construction advice

Chapter 12 Planting Notes for WSUDElements

For example:• Verifying size for treatment• Estimating design flows• Determining physical dimensions• Design inflow systems• Vegetation scour velocity check• Velocity and depth check• Design outlets• Vegetation specifications• Maintenance plan• Design calculation summary

• Functions of groundcover vegetation• Required plant characteristics• Plant species selection• Recommended plant species tables



Design procedures: A step by step process to perform detailed design calculations is presented. The firststep in the design process is to verify the size of the WSUD element to achieve its required treatmentperformance. For each WSUD element, typical configurations have been modelled with the CooperativeResearch Centre for Catchment Hydrology’s (CRCCH) Model for Urban Stormwater ImprovementConceptualisation (MUSIC). Expected pollutant reductions for total suspended solids (TSS), totalphosphorus (TP) and total nitrogen (TN) are represented by performance curves for varying sizes of eachWSUD element. Performance curves can be used during the design process and for checking a design.

The subsequent steps in the design process outline the equations that are to be used as well as providinggeneral commentary on the approach to design, while emphasising important components that are critical totreatment performance and should not be compromised.

Calculation summary sheets are provided to help ensure that designers follow each step in the designprocess. Advice on the construction and establishment of WSUD elements is also provided and is based onrecent industry experiences around Australia.

Landscape design notes: Landscape design and installation considerations are discussed and illustrationsof the WSUD elements showing possible landscape forms are provided. These illustrations help to show howthe elements can fit into an urban landscape.

Maintenance requirements: Maintenance requirements are discussed and a maintenance inspection formis provided for each element to highlight the important components of a system that should be routinelychecked. These can be used as templates to develop more site specific maintenance inspection forms.

Checking tools: A series of checking tools, comprising design, construction, asset transfer andmaintenance checklists, are provided in each chapter, to assist Council development assessment officers aswell as designers in checking the integrity of designs pre- and post-construction. The Construction InspectionChecklist is provided to allow verification of key elements on–site both during and after construction. TheAsset Transfer Checklist is provided to ensure the WSUD element is functioning as designed following anon-maintenance period and prior to being handed over to BCC.

Worked example: A worked example is provided to illustrate application of the design procedure. Theworked example completes a detailed design based on an initial concept design layout and discusses designdecisions that are required as well as performing the calculations outlined in the design procedure. Workingdrawings that detail the key elements of the system are also presented to illustrate the level of detail requiredin the documentation to facilitate successful construction.

1.5.2 Plant Selection for WSUD Systems (Chapter 12 )

Advice on plant species selection and lists of recommended plant species is provided for different WSUDelements as well as for different functional zones within WSUD elements. The lists are of species that havethe required characteristics to perform water quality treatment and erosion protection functions.



1.6 Summary of WSUD Elements Covered

This section introduces the WSUD elements covered in the Guidelines, being:

• Swales (incorporating Buffer Strips) - Chapter 2• Bioretention Swales - Chapter 3• Sedimentation Basins - Chapter 4• Bioretention Basins - Chapter 5• Constructed Wetlands - Chapter 6• Infiltration Measures - Chapter 7• Sand Filters - Chapter 8• Other Measures - Chapter 9• Aquifer Storage and Recovery - Chapter 10• Treatment Ponds and Lakes - Chapter 11

Combinations of these WSUD elements can be used in a ‘treatment train’ to effectively manage stormwaterfrom a range of different land uses. The design procedures presented in Chapters 2-11 allow each of theseWSUD elements to be sized to target particular pollutant reductions (depending on their position in atreatment train).

Following is a brief description of the WSUD elements covered in these Guidelines.

1.6.1 Swales (incorporating Buffer Strips) (Chapter 2)

Vegetated swales are used to convey stormwater in lieu of, or in concert with, underground pipe drainagesystems and to remove coarse and medium sediment. Swales alone cannot provide sufficient treatment tomeet current BCC stormwater treatment/ water quality objectives. As such, they are commonly used as partof an overall stormwater ‘treatment train’ to deliver acceptable stormwater quality for discharge to aquaticecosystems or for potential reuse applications.

Swales also disconnect impervious areas from hydraulically efficient pipe drainage systems, which isimportant for protecting aquatic ecosystems in receiving waterways by managing the frequency of damage toaquatic habitats by storm flows. This is achieved by slower travel times for flows along swale systemscompared with efficient pipe drainage systems. This reduces the flashy response from impervious areas,particularly for frequent storm events, and resultant impact on natural receiving waterways.

The longitudinal slope of a swale is the most important consideration. They generally operate best withslopes of 1 % to 4 %. Milder sloped swales can tend to become waterlogged and may have stagnantponding, although the use of subsoil drains can alleviate this problem. For slopes steeper than 4 %, checkdams can help to distribute flows evenly across the width of the swale as well as reducing velocities to avoidscour and resuspension of retained sediments. Dense vegetation and drop structures can be used to servethe same function as check dams but care needs to be exercised to ensure that velocities in the vicinity ofthe drop structures are appropriately managed.

Vegetation is an integral component of swales as it promotes even distribution and retardation of flows, thuspromoting settlement of coarse to medium sized sediments. Vegetation is required to cover the full width of aswale, be capable of withstanding design flows, and be of sufficient density to provide significant contactbetween flows and vegetation.



If runoff enters the swale as distributed flow (i.e. perpendicular to the main flow direction), the swale batterreceiving the inflows acts as a vegetated buffer and can provide an important pretreatment function for theswale by removing coarse sediment prior to flows concentrating along the invert of the swale.

Swales can be incorporated into urban designs along streets (within the median strip or footpaths), inparklands and between allotments where maintenance access can be preserved. In addition to theirtreatment function, these systems can add to the aesthetic character of an area.

Plates 1 – 4: Swale vegetation is selected based on required treatment performance and appearance

1.6.2 Bioretention Swales (Chapter 3)

Bioretention swales (or biofiltration trenches) are treatment systems that are located at the downstream endof a swale cell (i.e. immediately upstream of the swale overflow pit). Bioretention swales provide efficienttreatment of stormwater through fine filtration, extended detention treatment and some biological uptake, andare particularly efficient at removing nitrogen and other soluble or fine particulate contaminants. They alsoprovide a conveyance function (i.e. along the swale).

Bioretention swales can form attractive streetscapes and provide landscape features in an urbandevelopment. They are commonly located in the median strip of divided roads, in carparks and in parklandareas.

Runoff is ‘filtered’ through a prescribed filter media as it percolates downwards under gravity. The ‘filtered’runoff is then collected at the base of the filter media via perforated pipes and flows to downstreamwaterways or to storages for potential reuse. Unlike infiltration systems (discussed in Section 1.5.6),bioretention systems are well suited to a wide range of soil conditions, including low hydraulic conductivity‘clay’ soils and areas affected by soil salinity and saline groundwater, as their operation is designed tominimise or eliminate exfiltration from the filter media to surrounding in-situ soils.

Any reductions in runoff volumes are primarily attributed to maintaining soil moisture of the filter media(which is also the growing media for the vegetation) and evapotranspiration losses. Should in-situ soilconditions be favourable, infiltration can be encouraged from the base of a bioretention system to rechargelocal groundwater and to reduce surface runoff volumes (refer section 3.9).



Vegetation that grows in the filter media of bioretention swales is an integral component of these treatmentelements. Both the vegetation and the filter media have functional roles in stormwater treatment and it is theintrinsic relationship between the two that ensures the long term functional performance of the system.

Plates 5 – 7: Bioretention swales are commonly located in median strips of roads and carparks

1.6.3 Sedimentation Basins (Chapter 4)

Sediment basins are used to retain coarse sediments from runoff, are typically the first element in a‘treatment train’, and are frequently used for trapping sediment in runoff from construction sites. Within a‘treatment train’ they play an important role by protecting downstream elements from becoming overloadedor smothered with sediments, thus optimising treatment performance and minimising ongoing maintenancecosts.

Sediment basins operate by reducing flow velocities and encouraging sediments to settle out of the watercolumn. They rely on the creation of quiescent flow conditions and the prevention of ‘short circuit’ flow pathsbetween the inlet and outlet. Sediment basins are typically constructed with sufficient depth (usually 1.5 m to2.0 m) to allow for sediment accumulation and to prevent colonisation by fringing aquatic macrophytes(which is undesirable due to the requirement for regular desilting of sediment basins). They can also bedesigned as ephemeral systems, allowing them to drain during periods without rainfall and refill during runoffevents.

Sediment basins can have various configurations including hard edges and base (e.g. concrete), or a morenatural form with edge vegetation creating an attractive urban element. They are, however, typically turbidand maintenance usually requires significant disturbance of the system. Further guidance on designing andconstructing sediment basins is offered in Sediment Basin Design, Construction and Maintenance Guidelines(BCC 2001).

Maintenance of sediment basins involves dewatering and dredging/ excavating accumulated sediments. Thisis required approximately every five years, but depends on the nature of the catchment. For constructionsites that can produce very large loads of sediment, desilting may be required more frequently.

Plates 8 – 10: Sedimentation basins can be installed into hard or soft landscapes



1.6.4 Bioretention Basins (Chapter 5)

Bioretention basins operate with the same treatment processes as bioretention swales except do not have aconveyance function. High flows are either diverted (bypassed) away from the basin or are discharged intoan overflow structure.

Like bioretention swales, bioretention basins can provide efficient treatment of stormwater through finefiltration, extended detention treatment and some biological uptake, particularly for nitrogen and other solubleor fine particulate contaminants.

Bioretention basins have an advantage of being applicable at a range of scales and shapes and thereforehave flexibility for locations within a development. They are equally applicable to redevelopment sites andgreenfield sites. Smaller systems may take the form of ‘planters’ that can be located within allotments (e.g.gardens) and along roadways at regular intervals (e.g. in traffic calming devices) to create a boulevardaesthetic. All of these systems treat runoff near to its source and prior to entry into an underground drainagesystem.

Larger bioretention basins may be located at outfalls of a drainage system (e.g. in the base of retardingbasins) to provide ‘end-of-pipe’ treatment to runoff from larger subcatchments where ‘at source’ applicationsmay not be feasible. Large size bioretention basins need to consider the delivery of runoff into the basin toavoid scour and to ensure even distribution over the full surface area of the filter media.

Plates 11 – 19: Bioretention basins are applicable at a range of scales and can be integrated into an urban landscape

A wide range of vegetation can be used within bioretention basins, allowing them to be easily integrated intothe landscape theme of an area. Vegetation that grows in the filter media of bioretention basins is an integralcomponent of these treatment devices. Both the vegetation and the filter media have functional roles in



stormwater treatment and it is the intrinsic relationship between the two that ensures the long term functionalperformance of the system. They are however, sensitive to any materials that may clog the filter medium ordamage the vegetation and therefore vehicles, building materials and construction washdown wastes shouldbe kept away from bioretention basins.

1.6.5 Constructed Wetlands (Chapter 6)

Constructed wetland systems are shallow, extensively vegetated water bodies that use vegetation enhancedsedimentation, fine filtration and biological pollutant uptake processes to improve stormwater quality. Waterlevels rise during rainfall events and outlets are configured to slowly release flows, typically over two to threedays, back to a permanent pool level.

Wetlands generally consist of an inlet zone (sediment basin to remove coarse sediments), a macrophytezone (a shallow heavily vegetated area to remove fine particulates and uptake of soluble pollutants) and ahigh flow bypass channel (to protect the macrophyte zone from high velocity flood flows).

Wetland processes are engaged by slowly passing runoff through heavily vegetated areas. Plants filtersediments and pollutants from the water and biofilms that grow on the plants can absorb nutrients and otherassociated contaminants. In addition to playing an important role in stormwater treatment, wetlands can alsohave significant community benefits. They provide habitat for wildlife and a focus for recreation, such aswalking paths and other passive recreational pursuits. They can also improve the aesthetics of adevelopment and be a central feature in a landscape.

Plates 20 – 25: Wetlands can be constructed on many scales

Wetlands can be constructed on many scales, from house block scale to large regional systems. In highlyurban areas they can have a hard edge form and be part of a streetscape or used in the forecourts ofbuildings. In regional settings, they can be over 10 ha in size and provide significant habitat for wildlife.

1.6.6 Infiltration Measures (Chapter 7)

Infiltration measures encourage appropriately pretreated stormwater runoff to infiltrate into surrounding soilsand underlying groundwater. Their purpose in a stormwater treatment train is as a conveyance measure tofacilitate infiltration of surface waters to groundwater and NOT as a treatment device. They are highlydependant on local soil characteristics and are best suited to sandy soils with deep groundwater. All



infiltration measures require significant pre-treatment of stormwater before infiltration to avoid clogging of thesurrounding soils and to protect groundwater quality.

Infiltration measures generally consist of a shallow excavated trench or ‘tank’, designed to detain a certainvolume of runoff and subsequently infiltrate to the surrounding soils. They reduce surface runoff volumes byproviding a pathway for treated stormwater runoff to recharge local groundwater aquifers. Generally, thesemeasures are well suited to highly permeable soils, so that water can infiltrate at a sufficient rate. Areas withlower permeability soils may still be applicable, but larger areas for infiltration and detention storage volumesare required to allow for the slow rate of exfiltration from the base of the system. In addition, infiltrationmeasures are required to have sufficient setback distances from structures to avoid any structural damagefrom the wetting and drying of soils (e.g. from soil shrinkage). These setback distances depend on local soilconditions.

Plates 26 – 27: Infiltration systems are best suited to sandy soils with deep groundwater

Depending on the saturated hydraulic conductivity of the infiltration measure, they may also be vegetatedand provide some landscape amenity to an area.

1.6.7 Sand Filters (Chapter 8)

Sand filters operate in a similar manner to bioretention systems with the exception that they have novegetation growing on their surface. Therefore, they have a reduced stormwater treatment performance dueto the absence of a biologically active soil layer typically created around the root zone of vegetation plantedin bioretention systems. Sand filters lack vegetation because the filter media does not retain sufficientmoisture to support vegetation growth or they are installed underground (therefore light limits vegetationgrowth).

Prior to entering a sand filter, flows are generally subjected to pretreatment to remove litter, debris andcoarse sediments (typically via a sedimentation chamber). Following pretreatment, flows are spread over thesand filtration media and water percolates downwards to perforated pipes located at the base of the sandmedia. The perforated pipes collect treated water for conveyance downstream. During higher flows, watercan pond on the surface of the sand filter increasing the volume of water that can be treated. Very high flowsare diverted around sand filters to protect the sand media from scour.

Sand filters are particularly useful in areas where space is a premium and treatment is best achievedunderground, such as in high density developments with little to no landscape areas. Due to the absence ofvegetation, they require regular maintenance to ensure the surface of the sand filter media remains porousand does not become clogged with accumulated sediments. This typically involves regular routineinspections and tilling or removing any fine sediments that have formed a ‘crust’ on the surface.



Plates 28 – 30: Sand filters can be installed above or below ground

1.6.8 Other Measures (Chapter 9) (NOT INCLUDED IN DRAFT)

This chapter will be developed following the selection of appropriate alternative WSUD elements by BCC.

1.6.9 Aquifer Storage and Recovery (Chapter 10)

Aquifer storage and recovery (ASR) is a means of enhancing water recharge to underground aquifersthrough either pumping or gravity feed of appropriately treated stormwater runoff (or other water sources). Itcan be a low cost alternative to store water compared to surface storages and can minimise loss of waterfrom evaporation. During wet periods, excess treated stormwater runoff from urbanised catchments can bestored in natural or constructed aquifers and subsequently extracted during dry periods to reduce reliance onmains water supply.

Any water source injected into a natural aquifer system must be of sufficient quality to protect the beneficialuses of the ground water. The level of treatment required is dependant on the quality of the groundwaterresource and the current uses of the groundwater. In most instances, the treatment elements described inthese Guidelines configured into an appropriate ‘treatment train’ will provide sufficient treatment prior toinjection.

The viability of an ASR scheme is highly dependant on the underlying geology of an area and the presenceand nature of aquifers. There are a range of aquifer types that can accommodate an ASR scheme, includingfractured unconfined rock, confined sand and gravel aquifers. It is also possible to construct an aquifer if theeconomics of this allows. Detailed geological investigations are required to establish the feasibility of anyASR scheme. These Guidelines provide an overview of the main elements of the system and direct readersto more specific guidance documents.

1.6.10 Ponds and Lakes (Chapter 11) (NOT INCLUDED IN DRAFT)

Ponds and lakes are common features within the urban landscape and can provide a healthy, aestheticallypleasing environment. However, they are often prone to water quality problems such as toxic algal bloomsand exotic aquatic weed infestations such as Salvinia and Water Hyacinth. Whilst ponds and lakes can formpart of a stormwater ‘treatment train’ they typically require significant pretreatment to minimise the loading oforganic carbon and particulate bound nutrients. Therefore, ponds must always be the last element in a‘treatment train’.

Irrespective of the level of pretreatment provided to flows entering ponds and lakes, careful attention mustalso be given to the size and depth of these systems to ensure there is sufficient ‘turn-over’ (i.e. flushing) ofthe water body. This is to prevent long detention times (preferably less than 20 days) and provide sufficientmixing of the water column to prevent thermal stratification. In situations where the urban layout requires alarge pond or lake that cannot be adequately ‘turned-over’ by stormwater inflows, the design must allow for



an artificial recirculation system to physically displace the water stored in the pond or lake and pass itthrough an appropriately sized treatment wetland before being allowed to re-enter the pond/ lake. Theseimportant design considerations are frequently overlooked and are the principle cause of most water qualityproblems experienced by urban ponds and lakes.

Plates 31 – 33: Ponds are popular landscape features in urban areas



References

BCC 2000, Subdivision and Development Guidelines, BCC, Brisbane,http://www.brisbane.qld.gov.au/BCC:STANDARD::pc=PC_1388

BCC 2001, Sediment Basin Design, Construction and Maintenance Guidelines, BCC, Brisbane

BCC 2003, Guidelines for Pollutant Export Modelling in Brisbane Version 7, BCC, Brisbane

Engineers Australia 2003, Australian Runoff Quality, Engineers Australia, ACT,http://www.arq.org.au/

Victorian Stormwater Committee 1999, Urban Stormwater: Best Practice Environmental ManagementGuidelines, CSIRO Publishing, Victoria

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