Water Sensitive Urban Guidelines

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Water Sensitive Urban Design

Murphy Design GroupKLM Development Consultants

April 2002

Guidelinesfor theCity of Knox

Category: Water SensitiveUrban Design Project


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Water Sensitive Urban Design Knox City Council

MDG Landscape Architects n KLM Development Consultants

1 INTRODUCTION 1

1.1 What is WSUD? 1

2 IMPETUS FOR AND BENEFITS OF WATER SENSITIVE URBAN DESIGN 3

2.1 Water in Cities 3

2.2 Traditional Approaches to water in Cities 3

2.3 Urban Storm Water 5

2.4 Urban Storm Water Quality 5

2.5 Urban Stormwater Quantity 7

3 CURRENT SITUATION AT THE CITY OF KNOX 9

3.1 Policy Context 9

3.2 Physical Context 12

3.3 Infrastructure Context 15

4 WSUD PRINCIPLES AND ELEMENTS 16

4.1 Water Sensitive Urban Design Principles 16

4.2 Water Sensitive Urban Design Elements 17

4.3 Connecting the Pieces 22

5 IMPLEMENTATION ISSUES AND CHALLENGES 24

5.1 Policy Issues 24

5.2 Physical & Management Issues 26

5.3 Construction Costs 29

5.4 Opportunities in the existing storm water / drainage system 30


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MDG Landscape Architects n KLM Development Consultants

Acknowledgements

Murphy Design Group and KLM Development Consultants wish to acknowledge thecontribution of the Urban and Regional Land Corporation in allowing the details ofresearch, design, construction and trialing of WSUD measures at the Lynbrook Estate tobe used in these Guidelines.


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Chapter 1 Introduction

MDG Landscape Architects n KLM Development Consultants Page 1

1 I n t r od uct i onThe City of Knox has committed itself through the Knox 2001/2010 Sustainable CityPlan to a vision that sees the City as a leading example of a sustainable city by conserving, enhancing and managing our natural and built environment through innovation, co-operation and education for present and future generations.

The Mission Statement embodied in the Sustainable City Plan is:To actively engage and provide leadership to the community in becoming a sustainable city through a commitment to best practice, innovation, co-operation and education.

It is in this context of providing leadership in the area of sustainability that the Citycommissioned the preparation of these Guidelines for Water Sensitive Urban Design(WSUD) by Murphy Design Group and KLM Development Consultants.

The main aims of the project are to: summarise the environmental issues around urban stormwater management; outline the benefits of incorporation of WSUD principles; provide guidance for the implementation and maintenance of WSUD principles in new

and existing environments; and provide indicative details for adoption by Council in order to include WSUD principles

in new and existing developments.

1.1 What is WSUD?

At the outset, it is important to realise that Water Sensitive Urban Design is a componentof Environmentally Sustainable Design, along with other things such as energyconservation, pollution reduction, protection of productive lands and a myriad of otherconcerns.

To understand what WSUD is about, we need to remind ourselves about how cities work.Slightly over-simplifying, but nevertheless accurate, cities draw on resources fromsubstantially beyond their geographic extent and then discharge their wastes to areasagain substantially beyond that extent. They have an ecological footprint far in excessof the actual area they occupy. Figure 1 over shows diagrammatically how these inputsand outputs are related.

This impact outside the citys geographic area applies to water as much as it does to anyother resources.

WSUD is therefore concerned with the urban water cycle component of designing oururban environments being more sustainable by limiting the negative impacts of urbandevelopment on the total water cycle. Contrary to the common misconception however, itis about more than swales and wetlands. It is about designing our urban environments tomore closely match the original water cycle that occurred prior to development. It istherefore about: reducing the amount of water we transport between catchments, both in water supply

import and wastewater export; optimising the use of rainwater that falls on our urban areas; trying to more closely match the pre-development stormwater runoff regime, in both

quality and quantity.

The integration of water supply, wastewater and stormwater is a fundamental principleunderpinning water sensitive urban design. It includes a range of within-catchmenttechniques applied in the management of the impacts of urban developments, in addition

to the traditional end of pipe solutions frequently applied.


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Chapter 1 Introduction

Page 2 MDG Landscape Architects n KLM Development Consultants

While to some extent touching on the issues of water use and to a lesser extentwastewater, this report focuses on the stormwater aspects of Water Sensitive UrbanDesign.

Figure 1 Model of Urban dependence on external environments (Source: Barton 1996)


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Chapter 2 Impetus for and Benefits of WSUD


2 I mp et u s f o r an d Ben ef i t s o fWa t er Se ns i t i v e Ur b a n Des i g n

2.1 Water in CitiesThe impetus for WSUD is environmental sustainability.

The way our cities have developed has led us to a system that imports much of our waterfrom beyond the citys geographic area, uses that water for a range of purposes and thendisposes of the used water to areas again outside its geographic extent. Additionally, therain that falls on the citys surfaces is generally disposed of in ways that avoid potential forflooding or property damage. Therefore, we essentially capture natural resources from avery wide area (much larger than the city itself) to make our cities habitable, and thendispose of wastes over a much larger area also. Our ecological footprint then issignificantly larger than the city in which we live and consequently threatens thesustainability of our environment.

The impetus for Water Sensitive Urban Design is therefore just one part of ourcommunitys need to address sustainability in a pro-active manner.

2.1.1 Water Supply

Of the overall water demand of Australian cities, approximately 60% is used for domesticpurposes. Of that usage in Melbourne, some 35% is used outdoors for garden watering,car washing, and the like, while between 1% and 4% is used for human consumption.Consequently, well in excess of 95% of our potable (or drinking quality) water suppliesare used for non-potable needs, even though all mains water is treated to this potablestandard. Opportunities clearly exist for reducing this demand on our communitys watersupplies.

2.1.2 Stormwater

The rainwater that falls on the city collects a range of pollutants along its course. (ReferSection 2.3) Coupled with the greatly increased runoff created by the large amount ofimpervious surfaces in the city, the impacts on the natural waterways in cities areenormous. Dealing with the impacts of stormwater therefore needs to address issues ofboth quality and quantity.

2.1.3 Wastewater

Water that has been used for various residential and commercial purposes (such askitchens, bathrooms and toilets) becomes wastewater and is disposed of to sewersystems for eventual treatment and disposal to some receiving waters (in Melbournescase, Port Phillip Bay.) While this waste water is treated prior to discharge, it still containssubstantial nitrogen and other nutrient loads which accumulate in the Bay.

2.2 Traditional Approaches to Water in Cities

Traditional urban water management is underpinned by a highly efficient and centralisedapproach to both imports and exports of water and wastewater. Newman describes this

as follows:


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Water supply Stormwater Sewage

Large scale water supplyfrom few sources

Collect it all and discharge toreceiving waters

Traditional design watercourses and drains

Collect it all and dischargeit after some treatment toreceiving waters, ie.

based on dilution

i.e. big pipes in big pipesout

Table 2.1 - 19 th Century solutions to urban water management (Source: Newman and Mouritz 1994)

This traditional approach to urban water management brings with it a significant numberof problems however, including:

Traditional Practice ImpactsWater supply:

Large scale water supplyfrom relatively few sourcesoutside the city. As the citygrows and its water usagegrows, the need for damsincreases.

Catchment erosion.Catchment deforestation.

Habitat destruction in drowning of land area.

Reduced downstream flows causing habitatdegradation.

Stormwater:

Collect quickly

Discharge to receivingwaters quickly engineered channels lots of pipes

Increased peak flow volumes with: flooding impacts increased erosion of bed and banks increased habitat disturbance, within stream and

through increased bankfull discharges higher sediment (and pollutant) transfer rates.

Decreased base flows in urban waterways.

Concentration of collected pollutants in receivingwaterways affects flora and fauna.

Eventual delivery of pollutants to Port Phillip Bay.

Increased water temperatures affecting habitat

Transfer of urban litter into waterways.

Sewage:

Collect, treat and dischargeto receiving waters

Unsustainable organic and nutrient loads to receivingwaters.

Heavy metal discharge to receiving waters.

Dilution at source increases treatment costs.

Table 2.2 - Impacts of Traditional water infrastructure practice.

Our environment cannot survive the degradation that flows from these traditionalpractices and their effects. We therefore need new ways of dealing with our water needsand uses in the city. Water Sensitive Urban Design provides a range of measures to helpaddress these issues.


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2.3 Urban Storm Water

With the focus of this project being urban stormwater in Knox, it is clear that currentstormwater practices must be changed.

Stormwater must be managed as a valuable resource, protecting the water quality andecological health of receiving waterways and water bodies, and managing the risk topublic safety from flooding. Conventional stormwater management has traditionallyfocused on only the flood risk management objective.

Giving cause for optimism, we have in recent years seen substantial new innovations inconstructed wetlands, which together with the treatment of receiving waters, have begunto improve the urban situation.

Additionally, and importantly, the communitys view of the environment and their urbanexpectations have changed. The community has begun to value urban waterways,creeks, rivers, wetlands and lakes for their inherent value, environmentally, recreationallyand aesthetically, rather than just their ability to dilute wastes.

As noted earlier, addressing the impacts of urbanisation on storm water requiresmeasures to deal with storm water quality and storm water quantity. However, incontemplating the relative size of various WSUD elements, it is important to understandone of the key characteristics of stormwater runoff. The vast majority of stormwater runoffvolume is generated in relatively frequent (and less intense) rainfall events. In fact, 99%of flows would be captured by a treatment device sized to accommodate an AnnualRecurrence Interval (ARI) flow of 0.7 years, while an ARI of 0.5 years corresponds to over98.5% of mean annual flow. (Note that ARI can be seen as a probability of occurrenceof a particular intensity rainfall event. For example, 0.5 ARI equates to the intensity ofrainfall that occurs statistically twice a year.) It is clear therefore that water qualityimprovement devices and measures that deal only with these frequent flows (rather thanlarge high intensity events) can have substantial beneficial impact on the overall water

quality over a year.

2.4 Urban Storm Water Quality

Urban development brings with it a range of pollutants from a variety of sources, the mostcommon being: vehicles; construction activity and silt creation; spills; leachates; and atmospheric deposits.

These combine with the naturally occurring atmospheric pollutants and the loads causedby erosion and silt deposition to detrimentally affect natural waterways.

Wong, Breen & Lloyd, (2000) identify that these pollutants can be grouped according totheir impact on water quality and include: Gross pollutants and litter Sediment and suspended solids Nutrients (primarily phosphorous and nitrogen) BOD and COD (biochemical- and chemical-oxygen demand) Micro-organisms Metals Toxic organics, oils and surfactants.


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2.4.1 Gross pollutants

Storm events flush large amounts of debris into the waterways, including litter, vegetationand coarse sediments. These create not only a visual problem but also have detrimentalimpacts on aquatic habitats, with physical damage to habitats as well as contaminationwith toxic materials and increases in oxygen demanding matter.

2.4.2 Suspended Solids

This includes inorganic solids such as soil particles and airborne particles, as well asorganic particles such as vegetative matter, bacteria and micro-organisms. Inorganicsuspended solids carry with them a wide variety of sediment-bound contaminants andconsequently form a major transport mechanism of pollutants to receiving waterways.

Urban development generates high levels of inorganic solids, particularly during theconstruction phase of development and infrastructure projects, when sediment loads canbe at least two to six times, and up to several hundred times, pre-development levels(Wong, Breen & Lloyd, 2000) and a somewhat smaller multiplier beyond pre-development

levels once an urban area is established.

2.4.3 Metals

Metals such as copper, nickel, chromium, cadmium, lead and zinc are common in urbanstormwater and are transported by being attached to sediments. Damage to habitats andorganisms occurs when their concentrations build up beyond certain threshold levels.The impacts are complex but when they occur, are detrimental to the environment inwhich they are accumulated.

2.4.4 Toxic Organics, Oils and Surfactants

These products are largely transport related, occurring from roadway deposits fromvehicles, as well as being contributed to by poor industrial practices. They increase thechemical oxygen demand in receiving waters and are highly associated with organicsolids. (Colwill et al, in Wong, Breen & Lloyd, 2000)

2.4.5 Nutrients

Higher than natural levels of nutrients cause environmental degradation throughincreased growth of aquatic vegetation, eutrophication and algal blooms. Our rivers andstreams carry significantly elevated levels of nutrients into Port Phillip Bay where they cancause substantial environmental degradation.

2.4.6 Micro-organisms

Urban stormwater generally contains micro-organisms at levels between 3 to 4 orders ofmagnitude higher than recommended for human contact. Faecal coliforms andSalmonella are common, with the primary sources being domestic pet and bird faeces.

2.4.7 Oxygen Demanding Chemicals

The process of decomposition of the organic material carried and deposited in waterwaysleads to a reduction in the levels of dissolved oxygen in the water. Where thisbiochemical oxygen demand gets too high, oxygen levels are substantially reduced,

stressing or killing the aquatic life in the system.


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2.5 Urban Stormwater Quantity

In an undeveloped state, natural bushland or even pastureland creates less than 30%runoff in average rainfall events. It is not hard to understand that urbanised areas, withtheir roads, footpaths, roofs and other paved areas create substantially greater runoff,usually between 60 and 70% for a suburb such as Knox, and up to 90% or more forhigher density and commercial industrial development. This radical increase in runoffcauses substantial detrimental environmental impacts, as well as the potential forproperty and asset damage through flood damage.

2.5.1 Runoff Frequency

The increase in runoff created by urbanisation increases stream bank erosion and causesa substantial increase in bankfull discharge (ie. the flow that fills the channel up to thetop of banks, prior to flooding,) typically from 5 years ARI to 0.5 years ARI. (Wong,Breen & Lloyd, 2000) While traditionally this has been only of concern in relation to theobvious flooding it may bring with it, the environmental impacts are significant andinclude: more frequent disturbance of the stream bed (benthic) habitat; potential for changes in the stream bed characteristics by changes in particle size that

affect the range of organisms that can survive in that environment; increased erosion of the stream bed and its banks; increased transportation of sediment (due to higher volumes and velocities), further

concentrating sediment bound pollutants in the final receiving waters of the Bay; changes to the riparian habitat even beyond the bed and banks to a more limited

range of species that can withstand more frequent inundation, mechanical abrasionand water forces of flooding events. This often translates into massive weedinvasions of the riparian zone.

2.5.2 Runoff Reduction

With the impacts of increased runoff established above, it is clear that reducing overallvolumes of runoff would create environmental improvements. Water sensitive urbandesign incorporates a range of measures that address this issue of volume, and in someinstances, provide stormwater quality improvements simultaneously. Rainwater storagetanks, ponds, pervious storage areas and many other measures described in thefollowing sections provide tools to reduce the overall runoff of urbanised areas andrestore the water balance more toward the original regime.

2.5.3 Stormwater harvestingCapturing roof runoff for reuse within the home can achieve substantial environmentalbenefits in relation to the provision of water supply infrastructure. Research by Coombeset al (cited in Coombes, 2001) indicates that the introduction of rainwater tanks to supplydomestic toilet, hot water and outdoor uses will significantly defer (38 100 years) theneed to construct new dams in the Sydney, Lower Hunter and Central Coast regions ofNSW. Additionally, it was found that installation of trickle top-up to rainwater tanks canreduce annual maximum daily peak demands by up to 40% for residential development,thus creating the opportunity for reduced costs in water supply distribution infrastructure.While this project and guidelines are focussed on stormwater issues, the inextricable linkbetween rainwater harvesting and stormwater runoff cannot be ignored.


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A study by Mitchell et al (1998) evaluated two Melbourne housing sites, one in Knox, forthe impact of the installation of a rainwater storage tank (13 kilolitre) on water use anddemand in the sites. The developments were as follows:Allotment area 750 m2Roof area 203 m2Paved areas 113 m2

Garden areas 435 m2Occupancy 3 persons

The individual site details are as follows:

Parameter Essendon ScoresbyAverage Rainfall 591 mm/yr 887 mm/yrRain days 196 days 215 daysSoil type Clay Silty clay

Table 2.1 - Comparative Site parameters

While the extent of the evaluation is somewhat affected by the fact that bathroom and

laundry greywater were used for garden watering, the effects of the rainwater tankinstallation was substantial, as shown below:

Essendon ScoresbyAnnual water demand 278 kilolitres 265 kilolitresDemand for mains water -41% -51%Stormwater runoff -56% -49%Wastewater discharge -11% -8%Supply from rainwater tank 84 kilolitres 107 kilolitresGreywater demand 28 kilolitres 24 kilolitres

Table 2.2 - Impact of Rainwater Storage Tank installation on Stormwater and water supply.

It is clear from the table above that there are major benefits to be gained by use ofrainwater tanks, including: substantial reduction (41% - 51%) in mains water used by a household; and significant diminution (49% 56%) of stormwater runoff from a site.


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Chapter 3 Current Situation at the City of Knox


3 Cur r en t Si t uat i on at t h e Ci t y ofKnox

3.1 Policy Context

3.1.1 State based Policies

A number of state based policies are relevant to the need to encourage WSUD in the Cityof Knox. These policies include: encouragement of urban consolidation and the provision of efficient, affordable and

sustainable housing; protection of natural processes, in line with State Environmental Protection Policies

(SEPP) for the waters, air and land; protection of areas of natural significance, particularly waterways.

Additionally, the State Environmental Protection Policies set standards for reduced stormflows and water quality improvements in relation to Port Phillip Bay. These are alsoincluded in the Urban Stormwater Best Practice Environmental Management Guidelines (1999).

The Department of Infrastructure is (at time of writing) reviewing the MetropolitanStrategy. Part of that task is a review of planning policies and practices in relation to theirimpact on sustainability. Water sensitive urban design is being reviewed in this contextfor its ability to contribute to sustainability and in relation to opportunities for including it inthe State Planning Policies.

3.1.2 ResCode of Victoria

The recent release of the new residential code, ResCode, brings with it some additionalimpetus for WSUD.

Clauses 54.03 (One dwelling on a Lot) and 55.03 (Two or more Dwellings on a Lot andResidential Buildings) state a Permeability Objective that at least 20 per cent of the siteshould not be covered by impervious surfaces.

Clause 56 sets out the requirements for residential subdivision, with Cl 56.09 DrainageSystems identifying the following objectives: to minimise increases in stormwater run-off and protect the environmental values

and physical characteristics of receiving watercourses from degradation by urban runoff.

to protect the environmental values and physical characteristics of receiving watercourses.

A number of Standards are articulated also and provide further direction toward WaterSensitive Urban Design. Standard C25 states that:Verge widths should be increased where necessary to allow space for..swale drains.

Standard C31 includes: The minor drainage system should be designed to ensure that existing downstream

flows are restricted to pre-development levels unless otherwise agreed to by the responsible drainage authority.

The drainage network should be accessible and designed for easy maintenance. Drainage networks should minimise the potential for accumulation of silt and debris,

and provide for collection and removal at accessible locations.


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These new planning provisions mean that most new subdivisions within the City of Knoxare required to meet these standards. Water Sensitive Urban Design principles willprovide the tools to achieve them.

3.1.3 Melbourne WaterAs the regional drainage authority, Melbourne Water (MW) plays a critical role in urbanstormwater management beyond the local drainage system. MWs Urban Stormwater Best Practice Environmental Management Guidelines (1999) set out a range ofperformance objectives in relation to urban stormwater systems. These are based on theexpected improvements required to meet SEPP objectives and the improvements able tobe met by current best practices.

Pollutant Receiving water objective Current best practice

Performance objective:

Post construction phase:Suspended solids (SS) comply with SEPP (eg. Not exceed

the 90 th percentile of 80 mg/L) (1)80% retention of the typicalurban annual load

Total phosphorus (TP) comply with SEPP (eg. base flowconcentration not exceed0.08mg/L (2)

45% retention of the typicalurban annual load

Litter comply with SEPP (eg. No litter inwaterways) (1)

70% reduction of typical urbanannual load (3)

Flows Maintain flows at pre-urbanisationlevels

Maintain discharges for the1.5 year ARI at pre-development levels

Construction phase:

Suspended solids comply with SEPP Effective treatment of 90% ofdaily run-off events (eg


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While Knoxs MSS is not explicit in its direction on WSUD, it is clear on its commitment tosustainable development in the City. The Strategic Vision and Framework encouragessustainable development which brings continuing prosperity and identifies a land usevision that develops and supports the community of Knox by: maintaining, enhancing and protecting the key natural, cultural and lifestyle features

of the City, both economically and environmentally; capitalising on opportunities for sustainable development which add to the economic

prosperity of the City.

These elements clearly point to the need to increase the level of sustainability in anydevelopment in the City. From a water resources viewpoint, WSUD is the only way toachieve this.

Reinforcing this need is the commitment in the Planning Scheme to ensure that newdevelopment be adequately serviced so as not to have detrimental effects upon theenvironment.

Additionally, the implementation strategies within the section Recognising and ProtectingSignificant Natural Features and Cultural Heritage (Cl 21.08) identify the need to ensure: best practice environmental management be used in the design, construction and

operation of drainage systems to reduce impacts on surface waters and ground water;

development is designed and managed to minimise the impact of urban stormwater runoff on waterways, in accordance with any best practice environmental management guidelines approved by relevant state authorities.

Finally, the MSS acknowledges the need for and benefits of urban consolidation toaccommodate the changing needs of the community. With the probability that thisconsolidation will result in increased impermeable surface areas, then the resultantimpact on receiving waters can be minimised or reduced to zero by the adoption ofWSUD principles in both new development and redevelopment.

3.1.5 Stormwater Quality Management Plan, Vol 1

A Stormwater Quality Management Plan (SWMP) has been prepared for the City of Knox.Melbourne Water encourages the preparation of these plans for all municipalities.Generally, SWMPs must identify strategies to put best-practice structural and non-structural techniques into place. Techniques are grouped as follows: Land use planning - the strategic and statutory planning system Urban design - the design of the public realm and its infrastructure Land management - Council operations and development of sites Education and awareness - business and community education programs Stormwater treatment and flow management - structural measures

Some key proposals are contained in the Plan that would work in tandem with theseWSUD Guidelines to achieve improvements in stormwater quality in Knox. Theseinclude: Develop simple Environmental Management Plan Guidelines for building sites,

covering sediment, erosion control and waste management; Establish links with developers to educate them regarding obligations to maintain

clean building sites; Distribute Building Site Waste Management Guidelines; Signage to be placed on building sites, providing contact details to report sites

exporting pollutants;

Enforce infringement notices and fines; Audit and inspect building sites for compliance with regulations; Media and community education;


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Work with Community and Special Interest Groups to raise awareness of threats andresponses to them;

Demonstration Project of WSUD principles; Guidelines / educational literature for residential areas

These opportunities are discussed further in Chapter 5, Implementation Issues andChallenges.

3.2 Physical Context

The key variables affecting the detail design and implementation of WSUD systems inany location include: local climate; terrain; and soil type & geology.

3.2.1 ClimateThe Knox climate is not radically different to much of the eastern portion of Melbourne. Itexists within a relatively stable and evenly distributed rainfall precinct that does varysomewhat across the municipality, with higher rainfall experienced to the east. Table 1and Figure 2 below show the distribution across the year and between the higher andlower rainfall areas.

J a n

F e

b M a r

A p r

M a y

J u n

J u

l A u g

S e p

O c

t N o v

D e c

T o

t a l

Scoresby 55.9 51.5 56.1 69.8 96.0 70.5 77.5 85.5 88.8 89.6 81.4 76.8 899.4Mt Dandenong 69.7 53.8 81.4 108.4 139.2 103 97.4 120.9 110.3 114.2 107.7 96.1 1202

Table 3.2 - Rainfall in the City of Knox

Figure 3.1 - Annual rainfall distribution in Knox.

Knox Rainfall

0

20

40

60

80

100

120

140

160

J a n

F e b

M a r

A p r

M a y

J u n

J u l

A u g

S e p

O c t

N o v

D e c

M e a n

M o n

t h l y R a i n

f a l l ( m m

)

Scoresby

Mt Dandenong


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It can be seen from the graph that while there is some variation in distribution from monthto month across the year, the statistical average indicates a relatively stable supply ofrainwater suitable for collection and re-use.

3.2.2 Terrain

Terrain can have a substantial impact on the design detail of water sensitive elements.The use of different swale designs for example is determined by the overall grade atwhich they are to be installed.

While the City of Knox encompasses many hilly areas, over 50% of the municipalityexhibits terrain that slopes less than 5% or 1 in 20 (V:H). Figure 3.2 over shows theextent of areas of differing terrain slopes throughout the municipality.

Additionally, even on steeper slopes, opportunities exist to install WSUD measuresparallel to the contours, thus negating the limiting effects of the cross slope. Thisindicates that the implementation of WSUD principles in the municipality is not highlyconstrained by terrain.

3.2.3 Geology and soil types

Geology and soil types can have a significant impact on some of the measuresincorporated in Water Sensitive Urban Design. They do not however necessarily preventthe implementation of the principles but rather, limit the applicability of some of thespecific measures.

The City of Knox district spans a number of geological divisions. The geology of the areais predominantly sedimentary in origin. Some areas of contact metamorphism and acidvolcanic rock exist towards the Dandenong Ranges.

The geological divisions found in Knox are as follows:1. Silurian & Devonian aged Siltstone rock & Clays central and northern regions2. Quaternary Alluvium Clay & Silt Sediments from creeks & lowlands3. Tertiary Sediment Sand & Sandy Clays Southern regions4. Devonian aged Rhyodacite Volcanics Dandenong Ranges / uplands

Typically, a soil cover of Clayey Silt is common overlying the Clay horizon or subsoil.

In areas of Rhyodacite geology however (ie around the Dandenong Ranges and uplands,4 above), the soil cover is usually quite thin and rock is encountered at shallow depth.

Most of the weathered clays have a low hydraulic permeability. In areas of Rhyodacite

rock however, water can percolate away quite quickly through rock fractures, where theseare not cut off from infiltration by clays.

Some of the Clays in Knox are moderately dispersive, these generally being Silurian &Devonian (1 & 4). The dispersion of the clay is, in simple terms, the tendency of the clayto cloud and disintegrate (i.e. pipe, erode, etc) when in contact with water. Laboratorytesting (Emersion Class) and visual inspection (drilling) can readily measure this soilcharacteristic of the insitu Clay.

In summary then, while much of the municipality is comprised of clay soils that have lowinfiltration rates, Section 4.2.3 of this report outlines research that shows many WSUDmeasures to still be appropriate to such clay soils.


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Figure 3.2: Slope categories across Knox


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3.3 Infrastructure Context

3.3.1 Existing engineering design standards

The City of Knox engineering standards for stormwater are very similar to otherMelbourne municipal standards with the exception of some minor Knox-specificvariations. The design standards are based on Australian Rainfall and Runoff Data, thisis independent of any control method . The current standards therefore adopt thetraditional highly efficient and centralised approach to stormwater collection, transferand discharge, with its associated negative environmental impacts.

Storm water volumes are calculated using industry adopted methods and again areindependent of any control methods. Collection, transmission and discharge styles aretypically pit, pipe, pit/free outlet, or the efficient traditional practices. This situationmakes the City of Knox no more difficult or easy to implement WSUD for than any otherregion.

3.3.2 Maintenance regimes and issues

The existing drainage infrastructure of Knox requires high level maintenance as it isdesigned to operate as if in new condition i.e. clean and unrestricted. Stormwater systemmaintenance requires periodic removal of silt and litter that would otherwise reduce thecapacity of the system. Maintaining this as new level of operation is as impractical as itis impossible. As with most municipalities, maintenance is more reactive than proactive,with attention being given to drainage systems once failure has occurred. All non-naturalcontrol devices require maintenance, and generally the higher the level of traditionaldesign, the higher the maintenance.

Because of the existing systems efficiency, storm water quality improvement elements

such as constructed wetlands are dealt with remote from the source, often outside themunicipality and by other authorities, such as Melbourne Water. Therefore, this cost tothe community for services provided by Melbourne Water is in large part due to thetraditional efficient form of the drainage infrastructure under Councils control.


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Chapter 4 WSUD Principles and Elements


4 WSUD Pr i n ci p l es an d El emen t s

4.1 Water Sensitive Urban Design Principles

The following table shows how WSUD can address the negative impacts resulting fromtraditional urban and infrastructure design:

Impacts Design Principle

Water supply:

Catchment erosion

Catchment deforestation

Habitat destruction

Reduced downstream flows

Reduce dependency on remote watersupply by: using local rainwater as a resource; using stormwater for non-potable uses; adopting greywater usage. (This can

bring health related issues however and must be referred to Knox Health Services for approval.)

Stormwater:

Increased peak flow volumes with: flooding impacts habitat disturbance

Concentration of collected pollutants inreceiving waterways affects flora andfauna

Eventual delivery of pollutants to PortPhillip Bay

Increased water temperatures affectinghabitat

Transfer of urban litter into waterways

Flow detention and retardation

Reduction and removal of stormwater bornepollutants

Reduction and removal of pollutants

Reduced impervious surfaces

Removal of gross pollutants

Table 4.1 - Design principles to mitigate the impacts of traditional water infrastructure design.

In adopting these principles, it is important also to understand the connection betweenquantity and quality of stormwater. Over 98% of the total annual rainfall occurs in rainfallevents at or below 0.5 years ARI. While these relatively small but frequent rainfall eventscarry the bulk of sediment bound pollutants, their size makes them easier to design forthan might be anticipated. Additionally, the nature of urban stormwater means that evenif rainfall events are greater than this level, most of the pollutants are taken into a WSUDin the first flush of rainfall through the stormwater system . Rainfall that continues afterthis time is substantially cleaner and consequently any runoff that bypasses WSUDmeasures due to them being at capacity has a greatly reduced detrimental impact on theenvironment.

In designing stormwater systems to be water sensitive then, the key design principlescould be described as follows: retain as much water on site as possible; transport as little water as possible to receiving waters and lose as much along the

transport chain as possible; slow down the transport to receiving waters as much as possible; and prevent the transportation of gross and sediment-borne pollutants as far as is

possible.


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4.2 Water Sensitive Urban Design Elements

The elements and measures available to achieve Water Sensitive Urban Design performa wide variety of functions, depending on where they are located in the treatment trainor arrangement of water quality treatment initiatives. The following diagram showsbroadly how these elements can combine to form a suite of treatments for stormwaterquality improvement.

Figure 4.1 - Relationship between WSUD Elements (Adapted from Coomes et al, 2000)

In more detail, the elements noted in the diagram above are described further in thefollowing sections.

4.2.1 Gross Pollutant Traps

Gross pollutant traps are constructed devices designed to remove solids greater than5mm diameter from the stormwater system. They remove the large debris washed into

Carparks &Commercial /Industrial Areapavements

HouseLots &Parks

Roads Roofs

Gross

PollutantTrap

S o u r c e s

Source

Controls

Swales & Grass Buffers

Infiltration measures:Filtration Ponds, Underground Storage Tanks,

Pervious Storage Areas

Conveyance Measures:Swales, Filtration & Conveyance Trenches

ConveyanceControls

Gross Pollutant Trap DischargeControls

DetentionBasins

Vegetated FilterStrips

ConstructedWetlands

Rehabilitated orNatural Stream

Receiving waters

Gross

PollutantTrap

Gross

PollutantTrap

Water ConservationReuse roof water fortoilet flushing &external uses


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the stormwater system before the stormwater enters the receiving waters. They canrange from simple to complex constructions including: simple grated entry pits, suited to preventing large litter items from entering the

drainage system; side entry pit trash racks, formed by simple baskets or screens placed at, or close

after, the throat entry. They typically have screen sizes between 5mm and 20mm; proprietary manufactured traps are available and fall into three broad types:

. boom diversion systems (eg CSR Humes);

. return flow litter baskets (eg Ecosol);

. continuous deflection separation (eg CDS Technologies).

4.2.2 Swales

Swales are linear depressions that are used for the conveyance of stormwater runoff.They can be grassed or more densely vegetated with a variety of species. They providea number of functions, including: reduce total runoff through infiltration (and even more so when coupled with a

Filtration Trench); reduce the speed of runoff; catch sediments and attached pollutants; when grassed, accommodate pedestrian movement across and along them.

4.2.3 Filt ration Trenches

Sometimes called bioretention trenches, filtration trenches are a sub-surface waterfiltration system capable of holding stormwater run-off to allow it to infiltrate the groundand/or be temporarily detained to achieve some water quality improvement. They arecomprised of perforated pipes combined with a gravel trench. In some circumstances

they can be used to convey stormwater run-off while losing some of the quantity toinfiltration.

Filtration trenches can provide the following functions: provide infiltration of stormwater run-off into the ground; provision of on-site detention and retention capacity; improvement in water quality emerging from the trench; reduce the peak flow of a storm event in the system.

Concerns are often raised in relation to such devices in clay or rocky soils. Research byvan der Werf et al (cited in Lloyd & Wong, 1999) indicates that infiltration into clay soilswith shallow bedrock was completely successful. Argue (cited in Lloyd & Wong, 1999)asserts that it is a myth that infiltration into clays and/or shallow soils is not feasible.

Even with the limited opportunities for new development in Knox, filtration andconveyance trenches offer opportunities in both new construction and retrofit situations.

4.2.4 On site Detention and Retention

On-site Stormwater Detention (OSD) and On-site Stormwater Retention (OSR) provideopportunities to reduce the outflow of stormwater runoff to reduce peak flows and/or tocapture or harvest runoff for re-use.

OSD involves the temporary storage and controlled release of stormwater generatedwithin a site. Without adversely affecting the property, it relies on thoughtful design andpassive engineering during site development to achieve significant reductionsdownstream flooding. (UPRCT, 1999)


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Scott (1999) defines detention and retention as follows:Detention refers to the holding of runoff for short periods to reduce peak flow rates andlater releasing into natural or artificial watercourses to continue in the hydrological cycle.The volume of surface runoff involved in this process is relatively unchanged;Retention refers to procedures and schemes whereby stormwater is held for

considerable periods causing water to continue in the hydrological cycle via infiltration,percolation, evapotranspiration and not via direct discharge to watercourses.

On site detention and retention measures included in these guidelines include:OSD: underground storage tanks; ponds;OSR: porous pavements; pervious storage areas; rainwater storage tanks.

OSD is one way of overcoming the limitations of existing stormwater systems in thecontext of urban consolidation or increase in urban densities. By its ability to ensure thatthere is no increase in runoff, OSD and OSR are a key opportunities to foster moresustainable development in the City of Knox.

While OSDs primary function is to control runoff, the positive impacts on receiving watersare twofold: gross pollutants are trapped on site and prevented from being transferred to

watercourses; organic matter in the form of leaves, grass clippings and the like, are prevented from

entering watercourses where they would otherwise decompose and decreaseavailable oxygen, threatening aquatic life.

OSR has similar benefits, but with the addition of an absolute reduction in the total runoff,as well as reducing the demand on remote water storage supplies.

a) Rainwater Storage Tanks Rainwater tanks have been in use in various forms for millennia. Most cultures survivingin locations with a less than abundant water supply adopted some variation of collectingrainwater for future use.

In Melbourne, rainwater tanks provide an excellent opportunity to gain environmentalbenefits on a number of fronts, including: reduction in peak discharges and the consequent negative environmental impacts

these cause; reduction in importation of water from distant catchments.

Research in Newcastle (Coombes & Kuczera, 2001) has indicated that rainwater tankscan provide up to 50% mains water reduction and up to 24% annual maximum daily peakwater demand reduction when used for hot water, toilet and outdoor uses. Additionally,they note that the effectiveness of rainwater tanks as a stormwater managementmeasure increases with housing density due to greater proportions of the site area(roofs)) contributing to rainwater tanks. This finding is particularly important for the City ofKnox where increasing residential densities are often seen (erroneously) as anti-environment.

With Rainwater Storage Tanks (RST) connected for re-use in toilets and laundries, theconstant draw-down on the tank means that there is usually spare volume available withinthe tank to achieve the reduction in peak discharges. Coombes and Kuczera (2001)found that such tanks have storage volume available for retention in 92% of annual


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maximum storm events. Importantly the rainwater tank provides retention volumes in98% of annual maximum storm events greater than the 10 year ARI.

Rainwater storage tanks are best installed with a first flush bypass device, though this isnot mandatory if the intended use is purely for external purposes such as gardenwatering. The device prevents the first flush of rain, which washes particles and

pollutants form the roof surface, from being carried into the RST

Rainwater tanks can also be designed to provide a retardation (or OSD) function if theyincorporate an air space above the normal captured volume. This area is provided witha low volume outlet that allows slow release of water in higher rainfall events.

b) Porous Pavements Porous pavements are pavements that allow the ingress of water and flow through to thepaving substrate and eventually into the underlying subsoil.

The purpose of porous pavements is to: provide for on-site retention of stormwater run-off, therefore reducing peak flows; reduce the overall volume of stormwater run-off from a site; minimise the export of sediments and pollutants from the site.

When coupled with the use of such pavements for temporary storage, or on-sitedetention, their effectiveness can be significant. They are most appropriately used inresidential situations where vehicle use is low and there are low sediment loads that couldreduce the porosity over time.

c) Ponds Ponds are simply open bodies of water that may be used to: provide on-site detention to reduce peak flows; store water for re-use in the landscape; provide ornamental purposes; provide infiltration and consequent reduction in stormwater run-off.

As with other types of above ground storage, safety is a key issue and consequently thedesign must be carefully considered to ensure safety benches are included. (ReferSection f) below.)

d) Underground Storage Pits These are below ground storage devices that retain stormwater run-off. Their mainWSUD functions are to:

provide on-site detention thereby reducing peak flows; provide potential for stormwater re-use for non-potable uses (such as irrigation, wash-down water etc.)

Underground storage pits also provide a small water quality improvement functionthrough the settling of sediments and their attached pollutants.

e) Pervious Storage Areas Pervious storage areas take the form of vegetated depression areas, providing surface ordepression storage as well as soil moisture storage in the effective root zone. Their mainpurpose is to provide stormwater retention and infiltration. They can be vegetated withgrass or a range of other species that can survive periodic inundation.


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f) Safety, amenity and functionality Safety is a key issue with a number of OSD, retention basins, wetlands and similar openwater bodies.

Surface storages must be constructed so that they are easily accessible. Unless aswimming pool level of fencing is envisaged, the sides of any storage that could exceed600mm depth storage must be graded at 1 in 8 (V:H) to provide a safety bench aroundthe full perimeter of the area.

In the design of storage, creation of above-ground storage is preferred over below-grounddue to both reduced costs of implementation as well as potentially greater flexibility in thesiting of the area. Additionally, where possible, the creation of larger common storages inmulti-owner developments offers construction cost savings as well as simplifiedmaintenance arrangements and costs.

The following table shows the acceptable depth and frequency of occurrence of waterbeing held in above ground stormwater storage areas:

Storage Area Suggested Depth Frequency of InundationPedestrian areas 50mm

beginning to pondonce in 100 yearsonce in 20 years

Parking and driveways 200mm100mmbeginning to pond

once in 100 yearsonce in 20 yearsonce in 10 years

Gardens 600mm400mm200mmbeginning to pond

once in 100 yearsonce in 10 yearsonce in 2 yearsonce a year

Private courtyards (where thearea is between 25 and 60 m 2) 200mm100mmbeginning to pond

once in 100 yearsonce in 20 yearsonce in 10 years

Paved recreation common areas beginning to pond 6 times per year

Table 4.2 - Suggested Flood Frequencies for Storage Areas (from UPRCT, 1999)

4.2.5 Grass Buffers

Grass buffers are broad sloped areas of grass or other dense vegetation, capable of

withstanding shallow sheet flow stormwater run-off. They provide the functions of: sediment and pollutant removal from run-off prior to entering a drainage system some reduction in run-off volume through infiltration; and slightly reducing peak volumes through delay in run-off.

The vegetation used in buffers is important in that grass density and length affectsperformance. It is worth noting that while it may appear attractive to use bushland areasfor a similar buffer role, the impacts on the bushland can be quite detrimental. Thenutrient loads often carried by stormwater can create substantial weed invasion ofbushland areas, which when combined with the increased moisture levels can decreasethe diversity and abundance of indigenous species.


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4.2.6 Constructed Wetlands

Constructed wetlands are human constructed copies of a natural wetland system,containing: a sediment trap in the form of a deep open pond at the stormwater entry point; and a range of shallow (but variable depth) water areas containing dense macrophytic

planting.

Wetlands function to improve stormwater quality by: removing sediments and suspended solids, together with their attached pollutants; removing a range of dissolved nutrients and contaminants.

The detailed design and construction of these wetlands is a relatively complex task.Melbourne Waters Urban Stormwater Best Practice Environmental Management Guidelines (1999) provides detailed design and construction guidelines for these facilitiesand is available through Melbourne Water.

4.3 Connecting the PiecesWSUD is best incorporated in the initial development of land, in that it is an approach thatachieves its best outcomes by being incorporated at the earliest points in the land designand development process. Therefore, given that the majority of the City of Knox isalready developed to some level, the primary areas of opportunity for inclusion of WSUDwill come as part of redevelopment and retro-fitting existing urban areas. Theopportunities are not as limited as they might at first seem however.

The following table identifies the main WSUD tools described in this report andhighlights their relative applicability to the various situations in Knox.


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Chapter 5 Implementation Issues and Challenges


5 I mp l emen t a t i on I ssues an dC h a l l e n g e sBecause WSUD is a new and evolving technology, it brings with it some particularissues and challenges. This section discusses some of those issues.

5.1 Policy Issues

5.1.1 Drainage Benchmarks and Planning Controls

ResCode requires that existing downstream flows are restricted to pre-developmentlevels unless otherwise agreed to by the responsible drainage authority. It is thereforeimportant that Council clearly adopts a standard of any development achieving run-offequivalent to present development (ie. no net increase).

Environment and Land Management suggest that all site development should betargeted if the proposal results in more than 20% of the site being covered withimpermeable surfaces. This is the point at which adverse environmental effects areexperienced in the system. (ELM & EE, 2001)

Council should therefore review the levels at which WSUD measures might becomecompulsory in any development within the Municipality. It is only through the PlanningScheme that any such measures will become statutory requirements. Incorporation couldbe effected by inclusion as a local planning policy, subject to meeting VPP requirements.

A recent draft report prepared for the Association of Bayside Municipalities (Environment& Land Planning, Ecological Engineering, 2001) proposes the concept of equivalentpercentage impervious area as a trading mechanism that allows proponents to achievebenchmark requirements through on site measures, contributions to off-site measures, ora combination of both. The model provisions proposed are being assessed by the ABMand could form a useful basis for a similar approach in the City of Knox, albeit adapted tothe specifics of local conditions.

5.1.2 Private expenditure and Community Benefit

One of the fundamental consequences of adopting water sensitive urban design is that ittransfers the community cost (through rates and taxes) for environmental management,(eg. Melbourne Water sponsored wetlands and the like,) to the private individual or

developer. These individuals then pay for something that has a community benefit, viz, acleaner environment.

Despite the rapidly growing community awareness, interest in and concern forenvironmental issues, the private sponsorship of community benefit is unlikely to bewarmly received in the community.

In the context of new development, the community concerns raised can be adequatelyargued where the requirements of WSUD become part of Councils policy through theplanning scheme. In the case of Knox however, with its substantially built out character,significant improvements in storm water quality and reduction in water supply used willrequire a reasonable proportion of the existing population to adopt WSUD measures incurrently developed areas. Rainwater tanks are the simplest opportunities to make

environmental gains in a municipality such as Knox. Yet because of the long pay backperiods involved, the incentive is low. Recent NSW research (Coombes et al, 1999) showthat pay back periods can range from 27 to 45 years, depending on tank size and


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available roof area. (This period is obviously affected by water supply costs also whichdiffer in Victoria.)

5.1.3 Incentives

It may therefore require some incentives for the community to adopt source controls attheir cost and on their land. One model for such incentives is found in the StateGovernments Solar Hot Water Heater rebate which provides homeowners who installsuch a system a substantial rebate to reduce the cost of the unit and installation. Toachieve substantial uptake of WSUD measures, Council would need to investigate (withthe State Government) the possibility of sponsoring a similar rebate scheme for watertanks above a certain size that can be determined to positively affect the run-off from anygiven property.

Economic incentives often require both the carrot and the stick to be applied. Historyhas shown that simply adding costs to a development results in the cost being passed onto consumers in the supply (or construction phase) and easily borne by many consumers

in the ongoing life of the development. Coombes et al (1999) suggests that a balancedapproach would require the implementation of a polluter pays model with economicdisincentives for property owners in the form of a load-based fee calculated on theaverage volume of runoff from the site, coupled with compensatory payments fortreatment facilities (eg. wetlands,) or rate rebates for source control, or developmentbonuses for WSUD incorporation. For example, if a WSUD element rating system couldbe implemented, then any development that exceeded the minimum level determined forthat development could receive a rate rebate for the additional contribution to stormwatermanagement.

Clearly the difficulty with any such system is the issue of one authoritys costs becomeanother departments gain. This challenge can only be addressed between State andLocal Government.

5.1.4 Design of Developments

The implementation of WSUD measures in any development is highly dependant onparticular site conditions. This puts particular onus on designers (architects, engineers,landscape architects etc.) to take great care in the site planning to accommodate thevarious elements with their space or offset distance requirements. WSUD does not lenditself easily to off the shelf design solutions.

As many project designers and Council officers charged with approving the designs willnot be highly familiar with WSUD elements, further training will be required for these

individuals.

5.1.5 Education and Demonstration

As noted above, education will be critical to the successful implementation of WSUDpolicies in any municipality. Such education must work at a number of levels, including: the broad community; the developer community; the design community; and Council officers.


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The broad Community The broad community needs to be brought along with the push for sustainability. Aprogram of media campaigns aimed at raising awareness and targeted at householderswould be a start. Demonstrations of how WSUD can be incorporated without detriment toa home or development would be useful in negating latent concerns with potentialretrofitters or new home-owners.

The developer community The developer community, like the broader community, is not an homogeneous group.Some development groups are already showing a growing interest in WSUD, whetherspurred on by environmental concern or by the opportunity to gain a marketing edge.This level of interest is most likely to be seen at the large end of the industry however,which is of limited value to Knox, as most redevelopment is more likely to occurpiecemeal and by smaller building and/or development organisations. For these groups,the carrot and stick approach will again be required. The stick will need to take the formof clear Council requirements in relation to WSUD incorporation in all developments. Thecarrot could be some of the incentives outlined in 5.1.3 above, together with:

easy to use guidelines for the incorporation of WSUD (as this project aims to provide);and demonstration projects that allay fears about how difficult it is, how it might look and

other concerns of small and medium sized developers/builders.

The design community As this group is the one that has to deliver on the requirements, education is critical.Awareness raising of sustainability issues, and WSUD in particular, could be run inparallel, but more directly targeted, with the broader community awareness raising. Moredetailed design education can be achieved through professional journals and publicationssuch as the Building Design Professionals Environmental Design Guide.

At a higher level, training through universities and TAFEs will be required to ensure thatfuture generations of designers have a fundamental understanding of the issues.

Council Officers This group is responsible for the review and approval of projects that incorporate WSUDmeasures. Their understanding of the principles and practices is critical to gettingsuccessful developments built. Specific officers may need to parallel the training of thedesign professions in order to have sufficient understanding to critically assessdevelopment proposals.

5.2 Physical & Management Issues

5.2.1 Sediment Control

The threat of sedimentation reducing or negating the effects of a WSUD system is a keyconcern. There are many anecdotes of some level of failure of elements such asporous paving, leaky wells and the like.

Sediment comes from three main sources: atmospheric sediment; sediment from the construction phase of a suburb; sediment from fully established suburbs.

Sedimentation during the construction or establishment phase of a suburb is a majorchallenge. Even in the redevelopment of infill sites, sediment control is a crucial issue.


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Sediment control involving silt barriers, sediment collection, storage and regular removalare critical to the long term health of the WSUD system. In the adoption of WSUDmeasures in the municipality, Council will need to ensure that development proponentsprovide a clear and comprehensive Environmental Management Plan (EMP) for theconstruction site. In relation to sediment control, a wide range of measures will berequired, including hydroseeding, straw mulching, sediment barrier fences, pit and inlet

protection fences, hay bales and other devices. Additionally, education will be critical forthe consultants, contractors and sub-contractors involved in any project.

Equally important obviously, will be the need to monitor and ensure compliance with suchEMPs to achieve the desired protection of the WSUD systems being installed.

5.2.2 Gross Pollutant Control

During the construction phase of new development, building waste (including off-cuts,breakages, product wrapping and a variety of other debris) is a major source of grosspollutant influx into the drainage system.

Due to the nature of the housing construction industry in particular, with its high relianceon sub-contractors, control of this debris can be difficult. Some municipalities haveintroduced requirements for builders to provide a rubbish container on each allotment forthe sub-contractors, and to empty it regularly. In the City of Casey, failure to install themeasures incurs a penalty notice and fine, with failure to pay or re-offending resulting inprosecution in the Magistrates Court and fines of up to $2,000.

As part of the resource materials for its General Works Local Law, which protects publicassets, Knox Council is introducing a number of guidelines to reduce water pollution fromconstruction activities. Sediment control devices such as sediment fences and hay balesare illustrated in Council publications which are a reference guide for those in the buildingindustry. The issue of litter leaving sites and polluting waterways is also addressed by the

mandatory requirement of bins on-site. The publications emphasise not only theenvironmental benefits which come from following these practices, but also the economicgains from losing less soils etc. from building sites and from less clean up costs.Infringement notices carry fines of $1000 or court fines of up to $2000 for failing to complywith the Local Law.

5.2.3 Construction Co-ordination

In a development setting, the introduction of WSUD elements such as swales andfiltration trenches brings the need to carefully co-ordinate the construction sequence ofthe WSUD elements with the other services on site. Consequently, the installation of

services such as gas, electricity, water supply and telecoms needs to be carefullycontrolled in the process so that their installation does not damage underground WSUDelements.

Additionally, construction sequencing and access has an impact and needs to be plannedcarefully for the particular project. In a subdivision setting for example, constructionaccess should be from the rear of lots wherever possible to allow swale grass toconsolidate and reduce potential for access across the swales (with resultant compactionand/or contamination.)

5.2.4 Construction Supervision & Verification

While many elements of WSUD are conceptually simple in their approach, someelements demand a higher level of construction supervision than traditional drainagesystems do. Elements that depend on careful levelling and grading, for example swales


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or on-site stormwater detention systems, require very close attention to set-out andlevels. Adequate time and budget must be allowed for experience supervision in theconstruction phase to avoid the need for expensive rectification works later on.

Bewsher (1995) identifies a number of problems specifically with OSD, including: deficient storage volumes; uncertain discharge control; incorrect or absent screening; decomposing organic matter causing odours; inappropriate and unnecessarily costly layout; access and structural design deficiencies; and ongoing maintenance.

A number of municipalities that have adopted On Site Detention have introducedreasonably stringent certification requirements, including design and certification ofconstruction by a regulated range of professionals. In situations where the failure ofWSUD elements in a development would not result in flooding and property damage,certification would not necessarily be required. Where failure or lack of maintenancemight result in downstream flooding, then the legal implications for Council demand atightly controlled regulatory system, more so than for conventional drainage systems.

Many municipalities currently require bonds for civil and landscape subdivisional works,returned to the developer upon satisfactory completion of the works. In situations ofcritical importance, it would be worthwhile Council requiring a bond for on-site stormwaterdetention works for all developments that would be released upon provision ofindependent verification of the works.

5.2.5 Maintenance

Because WSUD is predicated on source control of water cycle elements, it necessarilycreates infrastructure at the individual lot level where home owners are new to the sorts ofmaintenance requirements that such a system might demand. It also fundamentallyredistributes maintenance requirements from the current situation where many of theproblems of urban stormwater are shifted to the Bay.

The WSUD system leaves both home owners and Councils with a higher level ofmaintenance than they have currently. This shifting of cost is a key political issue to bedealt with, as what is now a community cost, borne through taxes and levies of varioussorts, will become an individual cost with a community (and environmental) benefit.(Refer 5.1.2)

Additionally, the perception of extra costs for the maintenance and upkeep of WSUDsystems, together with the potential for inappropriate maintenance by property owners areissues that suggest a need for a centralised, local authority based maintenance system.Offsets in the cost of this maintenance regime need to be studied however, as the currentassessment of WSUD maintenance costs being extra ignores the substantial costs ofenvironmental harm or rehabilitation created by traditional stormwater systems.

A combination of upfront integration of WSUD in the site planning and design phases,together with high quality implementation, and particularly protection during theconstruction phase, will reduce ongoing maintenance costs. However, carefulconsideration will need to be given to WSUD measures in relation to titling arrangements(eg body corporate responsibilities, easement creation) and provision of ongoing fundingof shared WSUD installations.

In the light of VCAT decisions requiring Council to grant a permit on condition of theproponent not increasing the site runoff, Council will need to establish clear and legallyenforceable parameters for the design, implementation and maintenance of OSD andOSR systems for example. The enforcement of the required maintenance then becomes


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and additional problem to be overcome. With the reality that future occupiers of such adevelopment will have little or no knowledge of, or interest in, maintaining an OSD/OSRsystem, Council may need to review the potential for a differential rate on dwellings withOSD/OSR to cover the cost of Council taking on the maintenance role.

Coombes (2000) suggests in contrast however, that where residents show acceptable

maintenance of their source controls that they might be granted a rate reduction, whilethose that do not contribute to stormwater management should pay an additionalstormwater management levy.

5.3 Construction Costs

Construction cost comparison data is limited in relation to WSUD. The Lynbrook Estate(by the URLC) in the City of Casey has incorporated a range of WSUD elements in aportion of the development and its costs have been analysed against traditional drainagesystems.

CONVENTIONAL DESIGN1. 5 x side entry pits @ $929.46/pit = $ 4,647.302. 76 x 1m: 300 diameter drainage pipe @ $45.87/1m = $ 3,486.123. 60 x 1m: 375 diameter drainage pipe @ $61.21/1m = $ 3,672.604. 24 x 1m: 450 diameter drainage pipe @ $71.39/1m = $ 1,713.365. 7x standard house drain to pipe @ $227.11/hd = $ 1,589.776. 160 x 1m kerb and channel @ $26.74/1m = $ 4,278.407. 7 x driveway lay backs @ $141.94/lay back = $ 993.58

TOTAL AUS$20,381.13WATER S ENSITIVE URBAN DESIGN

1. 1 x swale side entry pit @ $1400.00/pit = $ 1,400.002. 24 x 1m: 300 diameter drainage pipe @ $45.87/1m = $ 1,100.883. 7 x swale house drain and pit @ $766.50/hd&pit = $ 5,365.504. 160 x 1m swale trench and turf @ $26.09/1m = $ 4,174.405. 160 x 1m kerb @ $21.71/1m = $ 3,473.606. 7 x swale lay back @ $159.25/lay back = $ 1,114.757. 64 m 2 pavement @ $18.21/m 2 = $ 1,165.448. 738 m 3 earthworks cut @ $4.90/m 3 = $ 3,616.20

TOTAL AUS$21,410.77

Table 5.1 - Comparison between WSUD and Conventionally designed Drainage works at Lynbrook Estate (based on typical 160m length of road covering 7 lots) Source: Lloyd, Wong & Porter, 2000

It is important in relation to the above costs to note that the comparison is based on theLynbrook system being capable of carrying the same amount of water as a conventionalsystem.

However, Coombes (2001) states that stormwater or roofwater reuse can providesubstantial cost savings for the construction of stormwater infrastructure in newdevelopments. A 1% saving ($960 per dwelling) was achieved in a medium density unitdevelopment at Figtree Place, Newcastle (Coombes et al, 2000). Additionally, Kuczeraand Coombes (2001) suggest that roofwater reuse in new developments would return a3% cost saving (including the cost to install the rainwater tanks) through reducedstormwater pipes and sizes, as well as reduced need for end-of-pipe water qualitytreatment.


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The cost of installation of different size rainwater tanks was also studied by Coombes etal (2000) and reported as follows:

Item Cost to install each tank size ($)5 kL 10 kL 15 kL

Aquaplate rainwater tank 540 870 1200Pump and pressure controller 200 + 160 200 + 160 200 + 160Plumber and fittings 500 500 500Float system 100 100 100Concrete base 200 200 200GST 170 200 240Total 1910 2230 2600

Table 5.2 - Cost to install a rainwater tank system (from Coomes et al, 2000).

This research shows that while there is only marginal additional cost involved in largeincreases in storage capacity, the basic cost remains relatively high and does not providea cost saving incentive to home owners to install such devices. As noted earlier,incentive schemes will be required to enhance the take-up of this measure.

5.4 Opportunities in the existing storm water / drainage system

The broadscale replacement of existing stormwater infrastructure (ie. underground pipes)with environmentally sensitive systems is technically and economically difficult. With thedrainage system designed to work for 50 to 100 years without replacement, opportunitiesfor the implementation of WSUD in the public realm of existing urbanised areas wouldseem limited. There are however a number of opportunities, including: the removal of gross pollutants from the system through the relatively straight

forward installation of gross pollutant traps, trash baskets in existing side entry pitsand retrofitting of side entry pits to grated pits;

small scale retrofitting of filtration and conveyance trenches where ever opportunitiesarise in the reconstruction of damaged areas or road reconstruction projects;

installation of a suite of WSUD measures in large road reconstruction projects androad duplication projects;

installation of rainwater storage tanks in existing dwellings, connected for toiletflushing and external uses.

The other key opportunity is presented by the Public Open Space system in the scope itcreates to provide effective water quality improvement (via constructed wetlands) andpotentially the retardation of runoff in certain rainfall events (retarding basins). Thisreduction of peak flows in frequent rainfall events has the important consequence ofreducing riparian and aquatic habitat disturbance, a key detrimental impact of urbanisedcatchments. It is acknowledged however that the opportunities for these installations maybe somewhat limited and that the Public Open Space systems primary function is to caterfor the leisure and recreation needs of the community.

Another area of retrofitting opportunity lies in the performance improvement of retardingbasins to improve water quality, as well as retardation of discharge. Wetland treatmentscan be constructed within retarding basins with no reduction of their effective volume, butto provide improved water quality outflows, as well as improving the aesthetics andlandscape amenity of some of these structures.


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WSUD Gui de l i nes and M easu r e s

Introduction

These Guidelines are intended to provide information for those proposing developmentwithin the City of Knox as to how Water Sensitive Urban Design can be incorporated intotheir projects.

Apart from the Council requirement that all new development match pre-developmentstormwater run-off levels, the guidelines are not meant to be prescriptive. They areintended to provide a range of opportunities and techniques that can be employed toachieve that primary objective.

How to use these Guidelines

The guidelines are organised into the following sections:1. Overall applicability of WSUD Measures to various situations;2. Examples of incorporation of Measures into different development types;3. WSUD Measures and Guidelines, together indicative construction details.

The Guideline construction details are coded as follows:Guideline Guideline CodeExamples of WSUD incorporation EXGross Pollutant Traps GPTOil / Grit Separators OGSGrass Swales GSVegetated Swales VS

Filtration Trenches FTFiltration & Conveyance Trench FCTRainwater Storage Tank RSTPorous Pavement PPPond POUnderground Storage Pit USPPervious storage area PSAGrass Buffer GBConstructed Wetland WLSundry Construction Details SCD


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WSUD Guidelines and Measures


Applicability of WSUD Measures

The table below gives a guide to the most appropriate WSUD Measures for differenttypes of development situations in the City of Knox.

Applicability of measures

Situation / Location G r o s s p o

l l u t a n t

t r a p

O i l / G r i t

S e p a r a t o r s

G r a s s e d

S w a l e

V e g e t a t e d

S w a l e

F i l t r a

t i o n

T r e n c

h

F i l t r a t

i o n

& C o n v e y a n c e

T r e n c h

R a i n w a t e r

S t o r a g e

T a n k

P o r o u s

P a v e m e n

t

P o n

d

U n d e r g r o u n d

S t o r a g e

T a n k

P e r v i o u s

S t o r a g e

A r e a

G r a s s

B u f

f e r

W e t

l a n d

New Streetsin large or small development areas

- on slopes less than 4% l l l l l m m l

- on slopes greater than 4% l m l l l m m l

Existing Streets & Roadways

where drainage or pavements to be substantiallyupgraded or roadway duplicated

- on slopes less than 4% l l l l m m

- on slopes greater than 4% l m l l l m m

Publicly owned land (incl. POS)

where land area and land-use allow additional l l l l l m l m l l l

facilities to be incorporated

New Residential Development

New detached housing (on lots >500 m2) m m l l m l l l

New medium density or integrated housing (lots < 300 m2) l m l l l l m l m m

Existing Residential Development

Existing dwellings on lots > 650 m2 m m l l l l m l m m

Existing dwellings on lots < 650 m2 m m l l l l m l m m

Commercial Development

Commercial / Industrial properties l l m l l l l l m l m m m

Carparks - Public or Private Property

New carpark construction l l m l l l l l m l m m m

Legend l Highly applicable m Moderately applicable depending on detailed design (Additional

site assessment may be required.)


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Role and Function of WSUD measures

While the previous table shows where the various WSUD measures can be applied, it isimportant to understand the primary role and function of each so that proponents canassemble a stormwater treatment train that addresses the key issues for their site.

The following table shows the role and focus of each measure:

Focus of WSUD MeasureWater Quality Water Quantity

Gross pollutant trap l mOil / Grit Separator l mGrassed Swale l mVegetated Swale l m

Filtration Trench l wFiltration & Conveyance Trench l wRainwater Storage Tank m l

Porous Pavement w wPond m lUnderground Storage Tank m l

Pervious Storage Area w lGrass Buffer l mConstructed Wetland l m

Legendl Highw Mediumm Low


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WSUD Guidelines and Measures


Examples of WSUD Incorporation(Refer Guidelines EX 1, EX 2, EX 3, EX 4, EX 5)

The following diagrams show how the various measures described in the next section canbe put together to form a suite of elements that provide stormwater quality and quantityimprovements. They can be described as follows:

EX1 Typical Single Detached Residential Development

EX2 New subdivision, with standard lot sizes (450 m2 750 m2)

EX3 Typical Detached Unit or Integrated Housing Development (Lot size between 350m2 and 450 m2)

EX4 Typical Unit Development (Lot size between 250 m2 and 300 m2)

EX5 Typical Urban Park Retrofit

EX6 Roadway Installation


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LEGEND1. RAIN STORAGE WATER TANK2. FILTRATION TRENCH

3. OVERFLOW DEVICE4. POROUS PAVING5. FILTRATION & CONVEYANCE TRENCH6. HOUSE DRAIN7. CONNECTION PIT8. ON-SITE DETENTION TANK9. KERB "BREAK"

11

2

2

6

433 7

9

20

19.5

19

18.5

4

9

9

5

5

5

5

4

4

4

4

4

4

4

4

4

4

4

7

7

1

1

8

8

5

5

5

5

Level 2, 45 Victoria Avenue, Albert Park, Vic, 3206 Australia

E-Mail: [email protected] Design Group Pty.Ltd.

Tel: 96964957Fax: 96963594

WATER SENSITIVE URBAN DESIGN GUIDELINES

KNOX

NEW SUBDIVISIONSTANDARD LOT SIZES (450m2 - 750m2)

0124

03

31-10-01

1:500

GUIDELINE EX 2

NOTE: DEVELOPMENT IS DIAGRAMMATIC FOR WSUDDEMONSTRATION PURPOSES ONLY. NO ASSESSMENTHAS BEEN MADE OF COMPLIANCE WITH RES CODE.


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C R

OWN E D R

OA D

LEGEND1. RAINWATER STORAGE TANK

2. POROUS PAVING3. DRIVEWAY ENTRY PIT4. GRASS SWALE WITH

CONVEYANCE TRENCH BELOW5. UNDERGOUND STORAGE PIT6. GRATED INLET PIT

5 66

5

4 4

4

4

1

1

1

1

1

2

2

3

2

2

2

2

2

2

2

2

5

TO STREET DRAIN

2

3

3

3

2

Level 2, 45 Victoria Avenue, Albert Park, Vic, 3206 Australia

E-Mail: [email protected] Design Group Pty.Ltd.

Tel: 96964957Fax: 96963594

WATER SENSITIVE URBAN DESIGN GUIDELINES

KNOX

TYPICAL UNIT OR INTEGRATEDHOUSING DEVELOPMENT

0124

03

31-10-01

1:500

GUIDELINE

Documents

Water Sensitive Urban Guidelines