Water sensitive urban design and laneways: the 210 million litre question

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Water sensitive urban design and laneways: the 210 million litre question R.Catchlove. Environmental Scientist. BSc (Adv Env), M Env Mgm (UNSW).

January 2013

One of the environmental benefits of a traditionally laid bluestone laneway (i.e. with a sandy base) is its ability to infiltrate water and prevent runoff (and associated pollution) from going into local creeks and bays. This is a short overview of this issue.

The 210 million litres in the title refers to the volume of water each year (based on Essendon Airport rainfall station) that falls on the approximately 109 kilometres of laneways within the City of Moreland (bluestone, concrete, unmade) that are approximately 3.3 metres wide.

The question is How do we best manage and use this 210 million litres of water each year?

What is water sensitive urban design (WSUD)? The National Water Commission defines water sensitive urban design as ensuring that urban water management is sensitive to natural hydrological and ecological cycles. It integrates urban planning with the management, protection and conservation of the urban water cycle. This includes the capture, treatment and harvesting of stormwater. WSUD is a wide ranging definition of managing water in urban environments, but in Melbourne it is often a short hand for one type of WSUD, raingardens that allow stormwater from roads (and laneways) to be naturally captured, filtered and infiltrated.

The diagram below illustrates how urbanisation affects the natural water cycle and how WSUD can mitigate that impact.

What are the objectives? The objectives of WSUD are (again from the National Water Commission):

Minimise impacts on existing natural features and ecological processes

WSUD and Laneways. Overview by Rob Catchlove January 2013.

Minimise impacts on natural hydrologic behaviour of catchments

Protect water quality of surface and ground waters

Minimise demand on the reticulated water supply system

Improve the quality of and minimise polluted water discharges to the natural environment

Incorporate collection treatment and/or reuse of runoff, including roofwater and other stormwater

Reduce run-off and peak flows from urban development

Re-use treated effluent and minimise wastewater generation

Increase social amenity in urban areas through multi-purpose greenspace, landscaping and integrating water into the landscape to enhance visual, social, cultural and ecological values

Add value while minimising development costs (e.g. drainage infrastructure costs)

Account for the nexus between water use and wider social and resource issues

Harmonise water cycle practices across and within the institutions responsible for waterway health, flood management, pollution prevention and protection of social amenity.

Professor Tony Wong and Professor Rebecca Brown from University of Monash are leaders in this area. Chris Davis, Commissioner at the National Water Commission is also a respected leader in the industry.

Is the design of the 'original bluestone pitcher laneways' considered WSUD? Yes. By laying a sand base and laying bluestone pitchers that have small gaps in between the stones, this allows water to infiltrate.

This type of WSUD is called permeable paving.

Are the traditionally laid bluestone laneways still infiltrating and retaining water even today? Yes and No. The hundred plus years have reduced the effectiveness of the laneways in retaining small rainfall events. Council staff indicate that sand layer has basically disappeared (washed away or degraded and transported into the sub surface over years and years). The gaps between the pitchers have also clogged and reduced the ability of water to infiltrate. But as long as the pitchers don't have a concrete base and some kind of impervious grouting then they will still allow some water to infiltrate. The nature of the uneven surface is also allowing water to get trapped in tiny little cracks that will then evaporate in time.

The only way to determine if they are still allowing water to infiltrate is to do some site specific monitoring (beyond just an observation that some are flooding). Nonetheless no asset performs at its deign standard some 150 years after it was constructed.

Does WSUD work in clay areas? Yes. The constraint that clay puts on WSUD is that the rate of infiltration is reduced and therefore the soil is more likely to become saturated at a quicker rate. A typical infiltration rate would be 1 mm / hr. That doesnt mean that 5 millimetres in a day would take 5 hours to infiltrate, as the surface that runs into the laneway is usually greater than the laneway area itself. Basically it works, but wont be able to capture and infiltrate as much water as a sandy area would.

Clay soils are common across Melbourne (the Yarra Rivers colour is attributed to clay soils and silt runoff), and WSUD in these areas is also common.


Clay soils probably mean that more water will travel overland and go into stormwater pits and drains downstream, than would in a sandy area.

And lastly the existence of bluestone laneways for over 100 years in the City of Moreland is proof that is works in clay areas

Professor Tim Fletcher from University of Melbourne is an expert in this area.

Does WSUD work in trafficable areas? Yes. Typically a WSUD asset doesnt have any transport or access. I.e. its a garden bed or wetland that doesnt need to be able to cater for cars, bikes, trucks or whatever. The traditional method of bluestone laneways is a type of permeable paving. Permeable paving is a normal practice in car parks and even on some roads. Porous asphalt is another form of this. The fact that it needs to be able to handle cars and trucks etc just means that it should be designed to be compacted with heavy vehicles.

Examples of this type of WSUD are common in South Australia, Queensland and of course in Europe.

Professor John Argue from University of South Australia is an expert in this area.

What are the costs? Costs vary considerably. The cost of laying a sand layer beneath a bluestone pitcher layer would be less than the cost of including a concrete base and may or may not be less than the straight concrete version. Its too hard to put a dollar figure on the works, when they are part of road works / drainage works anyway. The Queensland Water by Design centre did a study on the business case for WSUD, led by Sarah Jones and Shaun Leicester.

How important is it to include laneways in a whole of Moreland WSUD program? This question relates to the strategic approach to WSUD in Moreland. This is debatable. Reconstructing laneways in a WSUD approach may not be the most cost effective way of capturing and infiltrating stormwater (when compared to using road reserves and local parks that have existing drains through them). But there is an opportunity cost, i.e. every time a laneway is made impervious, it adds to the need to do WSUD somewhere else. The total area of all laneways is approximately 35 hectares (109 km by 3.3 metre average width). This is slightly less than the area of the Coburg Initiative, of 40 hectares, so it is like a policy of concreting over the whole Coburg Initiative area.

The other reason is that all capital works are an opportunity to include WSUD and any policy that doesnt promote this is a lost opportunity.

Does a concrete base affect the effectiveness of WSUD in laneways? Yes. There is no point in allowing permeable paving or gaps between bluestone pitchers if there is a concrete layer beneath. It would probably reduce the life of the concrete base anyway.

Is the industry changing and exploring new options for WSUD. The industry is in a state of rapid change due to: new policy, new appreciation of water resources in urban areas, and new science.

The new state government policy is Living Melbourne Living Victoria policy that promotes a generational change to the use of rainwater, stormwater and recycled water.

The new appreciation of water resources is the need to consider alternative water supplies after a decade of drought and water restrictions. The industry has experienced billion dollar investments and is now looking to prevent a future shock to the urban water system as occurred in 2000s.


The new science is the appreciation that the frequency of stormwater runoff days is equally or more important than the pollution that the stormwater carries to the bay.

The science of constructing WSUD is continuing to change as more monitoring and research is conducted. The latest research is focused on how WSUD contributes to a liveable city, which is part of a $120 million dollar Cooperative Research Centre grant.

Associate Prof Chris Walsh is an expert in this area.

What are the state and local government policies that support WSUD generally? Living Melbourne Living Victoria policy.

Victorian Planning Provisions, which require WSUD in residential subdivisions (Clause 56.047)

State Environmental Protection Policy

6 star Building code requires a solar hot water or rainwater tank

Moreland Integrated Water Management Plan

Morelands Brunswick Structure Plan

Professor Rob Skinner (ex Managing Director of Melbourne Water and now at Monash University) and Mike Waller, acting CEO of the Office of Living Victoria are experts in this area.

Other types of WSUD that might help or even be more effective than permeable paving in laneways. Rainwater tanks and raingardens on private property to reduce the small rainfall events that flow into a laneway could be a positive complementary measure or an alternative to permeable paving.

As many of the laneway issues are related to flooding or drainage problems, the use of rainwater tanks (that are drawn down through toilet flushing or leaking in a garden) to prevent the small rainfall events constantly flowing into laneways could be a reasonable and cost effective strategy.

Professor Tim Fletcher (University of Melbourne) and Associate Professor Peter Coombes (University of Newcastle) are experts in this area.

Examples of permeable paving Courtesy of Dr Lucke from University of Sunshine Coast.


Many more case studies can be found on: http://wsud.melbournewater.com.au/content/case_studies/case_studies.asp and http://waterbydesign.com.au/case-studies/

The impact of impervious surfaces The two main creeks in the region, Merri Creek and Moonee Ponds Creek would be affected by excess stormwater runoff and pollution. The runoff would contribute to poor water quality and a loss of macroinvertebrates, but of course laneways are not the only source of that impact on water quality. Litter has the potential to affect the habitat that platypus and fish live in.

It is difficult to isolate the impact of laneways on creeks and bays, but it is safe to say that it contributes to poorer environmental outcomes. Each time a square metre of concrete (or asphalt) is laid, the opportunity to revisit that place and provide a water sensitive approach is lost for another 100 years.

So what about the 210 million litres The impact of laneways becoming impervious is that close to all of the 210 million litres is going straight into the two local creeks.

Often stormwater harvesting is proposed as a solution to increased stormwater runoff problems. In this context that is unlikely to be practical due to the distributed nature of the laneway network.

Any strategy that is concerned about liveability, green spaces, walkable streets, urban design and character, water conservation and healthy waterways would benefit from the retention and infiltration of the as much as possible of the 210 million litres of water. Not only would it be beneficial, but to achieve greener suburbs without water sensitive urban design, there would be a need to import other water sources.

In a natural setting only 15% of that water would flow to the creek, and most of that would be filtered through the soil and arrive as baseflow to the creek.


References Burns, M. J., Fletcher, T. D., Walsh, C. J., Ladson, A. R., and Hatt, B. E. (2012). Hydrological

shortcomings of conventional urban stormwater management and opportunities for reform. Landscape and Urban Planning, 105 230240.

http://waterbydesign.com.au/whatiswsud/

http://watersensitivecities.org.au/

http://wsud.melbournewater.com.au

http://www.bom.gov.au/climate/averages/tables/cw_086038.shtml

http://www.buildingcommission.com.au/www/html/2565-faq---about-6-star.asp?intLocationID=2565

http://www.knox.vic.gov.au/Files/Lucke_-_Permeable_Pavement_Presentation_-_Knox_City_Council_15-3-2011_-_Slides.pdf

http://www.water.vic.gov.au/livingvictoria/implementation-plan

Shackel, B, Beecham, S, Pezzaniti,D, Myers,B, 2008. Design of permeable pavements for Australian conditions. ARRB conference, 23rd, 2008, Adelaide, South Australia.

Walsh, C. J., Roy, A. H., Feminella, J. W., Cottingham, P. D., Groffman, P. M., and Morgan, R. P. (2005). The urban stream syndrome: current knowledge and the search for a cure. Journal of the North American Benthological Society 24, 706723. Full text (2005 North American Benthological Society)

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Water sensitive urban design and laneways: the 210 million litre question