Publication (Media): RESTORING THE URBAN WATER BALANCE

Publication Type:	Media Release
Publication Name:	RESTORING THE URBAN WATER BALANCE

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Lawrence, Ian (2001) RESTORING THE URBAN WATER BALANCE - Apr 11 2001, CRCFE, Canberra - Media Release.

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Acres April 01

RESTORING THE URBAN WATER BALANCE

Integrated urban water based management

Taking a more natural approach to designing urban environments is the way of the future according to Ian Lawrence, a scientist with the Cooperative Research Centre for Freshwater Ecology.

That ‘natural’ approach involves using vegetated waterways instead of concrete drains and pipes and incorporating design features to increase infiltration of water into soils on residential blocks.

“While such systems can be designed into new developments, elements of them are also relatively simple to ‘retro-fit’ in established urban and suburban areas and in many instances far more cost-effective than renewing existing infrastructure,” Mr Lawrence said.

“The over-riding aim is to reduce the urban footprint on the environment by reducing the area of hard surfaces in urban environments to benefit the urban living environment, reduce the amount of water used for irrigation and reduce peak and total run-off into the storm-water drainage system.”

The more natural approach being advocated by Mr Lawrence and his team is a holistic one that addresses the integrated management and use of roof rainwater, storm water, grey water, wastewater effluent and town water supply.

“One of the major negative impacts of frequent urban stormwater discharges on local streams is the washout of small aquatic animals in the waterways. By reducing the frequency of ‘wash-out’ conditions in downstream urban waterways, the smaller aquatic animals are able to substantially recover their populations.”

“If we can reduce peak flows by holding water on the block instead of running it directly into the stormwater drains, the flow regime in the local streams will revert to something nearer normal, enabling restoration of the ‘health’ of the local streams,” Mr Lawrence said.

One of the most obvious signs of more sustainable urban water management is the use of constructed wetlands and vegetated waterways, or retention of natural waterways, instead of the construction of concrete channels.

“We have recently come to understand that vegetated waterways not only look more attractive than concrete drains but are more effective because they hold more water, slow the rate of flow and in the process facilitate ‘treatment’ of the water by natural physical, chemical and biological processes.” Mr Lawrence said.

Other characteristics of sustainable urban water design are tanks to collect rainwater from the roofs, which help break the connection between the roofs and the storm water infrastructure; swales and other devices to enhance local infiltration of rainfall into the soil to achieve nearer to a natural water balance; and dual reticulation systems, one for drinking water and one for second-class water for irrigation and other non-potable uses.

“Applying these principles requires thinking more in terms of lifestyle and natural landscape than in terms of separate engineering infrastructure solutions.”

“Concrete drains are designed to remove water quickly whereas constructed wetlands in urban areas are designed to delay the flow of storm water down the system, which results in the reduction of the peak discharge.”

“At the same time, wetlands offer valuable landscape facilities capable of sustaining a diverse range of plants and animals, although not the full biodiversity existing pre-development.”

“The over-riding aim is more sustainable urban development,” Mr Lawrence said.

“By reducing the frequency of high-discharge events, it is possible to reduce urban pollution of streams by up to 80 per cent as well as reducing physical and environmental damage through erosion caused by the high velocity of such large volumes of water.”

”The underlying objectives of the ‘integrated’ approach are to get pollutants loads and discharge rates in local streams back to levels approaching pre-urban conditions and allow a more natural flow pattern to prevail in the streams.” Mr Lawrence said.

However, swales and such structures needed to be used with caution in some situations.

A swale is a grassed bank or ditch which temporarily holds water and allows time for it to permeate into the soil, reducing the amount of water running off to the storm-water system.

According to Mr Lawrence, “there can be potential risks from the use of swales; including the impact of changing groundwater levels on building foundations in locations with reactive clay soils like those found in some parts of Canberra, Adelaide and Melbourne.”

“Swales need to be located so they do not impact on building foundations. They also need to be used with caution on long hill slopes where there is potential for impact of elevated water tables on properties lower down the slope from cumulative infiltration water.”

“One way of managing this potential risk is the incorporation of agricultural (porous) drains to limit the potential rise in groundwater. Another way is to designate areas suitable for the application of swales.”

“A possible location for accommodating swales is within road-side nature strips.”

“One of the practical design challenges of this approach is the exclusion of vehicles from the swale area, where because of the wetter soil conditions, vehicle movement would cause damage to the surface and loss of streetscape amenity and values.”

“There is a need to think through all the design elements in the context of uses and amenity in residential areas.”

“What we are talking about is a move away from the old approach of separate consideration of water supply, storm water, sewage, groundwater, to an approach which considers these elements as integral and interrelated components,” he said.

“The average household block exports the same volume of stormwater that it imports in town water supply at other times to water the garden.”

“We need to achieve much better water balance in the soils if urban areas are to be anywhere near sustainable.”

“The problem is the drainage system is so efficient that only limited amounts of rainfall infiltrate into the soil, seriously depleting the moisture levels in the soil.”

“We need to get water back into the soil to maintain the health of landscaping such as trees and shrubs without having to irrigate. This can be achieved relatively easily by the use of swales.”

“In less permeable clay soils the rate of infiltration to the soil can be enhanced by creating an infiltration trench, backfilled with gravel,” Mr Lawrence said.

“The key is to reduce the volume and rate of stormwater discharge from residential blocks, and to break the connection between impervious run-off areas such as roofs and paved areas and piped drains. This is achieved by running stormwater over the surface of the block and into swales to maximise the opportunity for infiltration, and extending the time taken to reach public stormwater drains in the street.”

In fact Mr Lawrence believes the future could lie in a distributed or decentralised system of small local treatment plants, designed to occupy an area no larger than the average urban house block, which would greatly reduce the cost of pumping the effluent to the point of treatment and returning the treated water back for use in the community.

“There are enormous costs involved in pumping water 20 kilometres to and from a treatment plant, so moving effluent out of the local area limits its opportunity for re-use.”

“The greatest efficiency would be achieved by locating local treatment plants adjacent to sports grounds or golf courses which use large volumes of irrigation water, with treated water also being reticulated back into the town as ‘second-class water’ for domestic irrigation and other applications such as flushing toilets.”

“The level of treatment would be such that, if there was a surplus of water not needed for irrigation or other “second-class” uses, it can be diverted to a creek or storm water system.”

“By significantly reducing the need for trunk sewers, a decentralised approach would produce significant cost savings,” Mr Lawrence said.

BOXED PIECE

Benefits of an Integrated Approach

Social benefits

§ Enhanced open space
§ Recreational opportunities
§ Enhanced landscape values, eg. wetlands

Economic Benefits

§ Savings in infrastructure and service costs (up to 70%)
§ Urban blocks that front on to a water feature can increase in value by up to 100%
§ Urban blocks that offer a view of a water feature can increase in value by up to 70%

Environmental Benefits

§ Reduced stormwater pollutants (by 50-80%)
§ Less frequent and lower peak flows
§ Second-class water supply opportunities
§ Opportunities for re-use of grey water
Application of a more natural approach to urban water management

The principles of integrated urban design advocated by Mr Lawrence have been applied in Golden Grove, Adelaide, Homebush Bay and the Rouse Hill development in Sydney.

Golden Grove is a large sub-division established about 15 years ago which was in the lower cost bracket when it was released but its later stages are attracting buyers in the middle to upper price bracket because of the environmental properties of the development, which has been designed to integrate many of the elements advocated by the Urban Water team.

The Homebush Bay Olympic Village, now a public residential area, has been designed with a storm-water management system incorporating wetlands to slow and treat run-off water. The runoff water is stored in a disused quarry, then re-used for irrigation in the residential, Olympic and Showground areas from which it was collected in the first place, at an estimated saving of $600,000 to $700,000 a year in water supply costs.

“The Rouse Hill development incorporates a series of wetlands, which are used for final treatment of sewage, from which water will be reticulated back to the households in the development as second-class water for irrigation, use in toilets, and so on.”

“At Rouse Hill the designers have focused on protecting the Hawkesbury-Nepean system downstream of the sub-division. It represents a more engineered approach than the ‘on-block’ use of swales and wetlands,” Mr Lawrence said.

If you can’t get to Golden Grove, Homebush Bay or Rouse Hill, think in terms of a lot more natural plant growth (as a result of near-natural infiltration rates), creeks instead of concrete drains, and ponds.

“In Canberra, improvements in treatment of sewage in the late 1970s and early ’80s successfully reduced the discharge of organic material and nutrients to streams. The next major source of pollution was stormwater discharges from urban areas.”

“That prompted the development of a system of ponds and wetlands on the major urban drains; an approach which has proved so successful that the quality of water in the Murrumbidgee River leaving the ACT to the north is very close to the quality of water entering the ACT in the south,” Mr Lawrence said.

In the ACT, while urban areas comprise just 2% of the upper Murrumbidgee River catchment area, they contribute some 10% of the catchment mean annual pollutant exports, or 4 times the rural land (low intensity grazing) export per square km.

Implementation issues

Retro-fitting the natural measures within established urban areas is more complicated than their application to new sub-divisions, where the measures are as an integral part of the design.

“Replacing the pipes or concrete lined drains with a vegetated waterway involves removing the pipes or breaking out the concrete channel and establishing a “softer”, more natural vegetated waterway which will detain water and slow flow rates, reducing the peak discharges further down the drainage system,” Mr Lawrence said.

“Opportunities for the reticulation of treated stormwater or grey water, for example, require the reticulation of a second class water supply distribution pipe system, separate from the potable supply. Dual reticulation is feasible provided it is built into the initial development, with the two pipes put in the same trench at the same time.”

“Labour costs are the problem. A dual reticulation system costs only 20 to 30 per cent more than a single system if the pipes are laid at the same time. The cost of having to open up a second trench makes a dual system prohibitively expensive,” he said.

“One area where attitudes are changing significantly is the approach to on-site re-use of ‘grey water’ - household waste water mainly from the laundry and bathroom - with a variety of technologies for re-use of grey water becoming readily available.”

“If the water is applied to the garden through a sprinkler system there could be potential for an aerosol effect to spread any bacteria present but if it is applied through an underground watering system or drip irrigators for example, any bacteria present will be immediately taken up in the soil,” Mr Lawrence said.

While few local government bodies were likely to immediately start removing stormwater pipes or concrete lined drains and replacing them with urban streams and wetlands, he believes that could well occur when the time comes for the existing infrastructure to be replaced; particularly since the cost of constructing and maintaining a wetland system is about a third that of the traditional engineering solutions.

“ The more natural approach not only reduces construction costs but also enhances property values by anything from 70 to 100 per cent by providing water views and valued open space systems.”

“I see windows of opportunity when an urban area is re-developed or when the trunk drainage system needs replacing and believe councils need to start developing relationships with local residents and planning for replacement with more natural water management measures.”

“The realisation that natural stormwater and effluent management design has the potential to enhance real estate values has seen developers adopt ponds and swales as part of their sub-division designs to present a softer landscape as well as enhanced landscape values,” he said.

And while some local government bodies are keeping pace with the trends and concepts and developing regulations to accommodate these and other innovations in sub-division design; others are finding it harder to come to terms with.

“These new concepts, despite the fact that they too need to be carefully designed, challenge the previous principles and approaches and are not always well received by the engineering fraternity.”

“It partly relates to Council’s need to be confident that the new approaches will work effectively and meet community expectations for safety and amenity.”

“One of the challenges for Councils and the wider community in the context of some of the approaches being proposed is how to ensure cooperation and compliance of individuals in the community.”

“One of the challenges confronting wide acceptance of the more natural approach is the acceptance by the community of responsibilities for maintaining the measures on residential blocks.”

“We need to raise awareness of residents regarding the range of measures to reduce water and pollutant discharge to the public stormwater system. It will take time to change both government agency and community perceptions regarding their partnership in managing the environment,” Mr Lawrence said.

“Many local government authorities are now developing the skills and knowledge necessary to implementing the new approaches. We are seeing an interesting social shift in values as well as a change in engineering and technology.”

“Many of the systems now being tried or proposed involve joint responsibility requiring partnerships of residents and service agencies.”

“Until very recently State and Local Government authorities and agencies accepted full responsibility for and had total control of water supply and the public drainage system.”

“However, if they accept that the community should play an active role in meeting flood, health and amenity expectations, one of the issues is the commitment of individual residents to maintain those elements of the system for which they are responsible,” Mr Lawrence said.

“How should a system be set up to protect and maintain the public interest?”

“There is, for example, no legislative or administrative power for Local Government employees to go onto private property to check that swales and other elements of the sort of system we are proposing are working properly.”

‘The sort of problems that could be encountered in such areas was illustrated by the experience of some Local Government authorities recently, in the application of on-site rainwater detention tanks as a means of alleviating downstream flooding. The tanks are designed to hold runoff from the roofs and other impervious areas and release it slowly, over an extended period of time, into the storm water system,” Mr Lawrence said.

“While the tanks were duly designed and built, some residents failed to maintain the systems, with continued downstream flooding as a result.”

“The system was good in theory but socially it is failing, so councils and water managers are looking at other ways to achieve the outcomes the tanks were designed to achieve that are more acceptable to the community,” he said.

“At this stage, some Councils are looking at constructing neighbourhood wetlands in place of the tanks.”

“The difference between the wetlands and the tanks is that the wetlands are more likely to be valued by the community and will have amenity values in addition to their water retention roles,” Mr Lawrence said. “And if resident interest does flag, the fact that they are on public land means local government or other relevant agencies can step in to maintain and manage them in the wider public interest.”

“That is just one of the policy areas requiring development to make this sort of approach work.”

Application to the rural sector

Many of the innovative concepts in urban water management design also have application in the rural context.

“In fact the CSIRO is exploring similar concepts in work at Griffith where researchers are looking at the use of wetlands in treatment of agricultural waste water such as “tail” water draining off irrigated plantings,” Mr Lawrence said.

“Wetlands also offer an effective option for treatment of effluent,” Mr Lawrence said, “and while the potential for wetland effluent treatment in urban areas is limited by land values because of the area of land needed; effluent wetlands are relatively common in rural areas where land values are relatively low so land is readily available for such uses.”

“Where land is available, running treated effluent through a well-designed wetland system may be a very cost-effective way of ‘polishing’ effluent before it is returned to local streams or used for irrigation of landscaping or sporting ground in the town.”

“The concept of wetland treatment of wastewater is far from new,” he said, "with the Werribee sewage farm, a wetland system, established about 120 years ago. Melbourne depended on the Werribee sewage farm for many years and it is still used to treat some 40 per cent of Melbourne’s sewage,”

“The designers of the system were visionaries but the large area of land it occupies means it would not be constructed today because the land it occupies would be considered too valuable,” Mr Lawrence said.

Ongoing urban water research

The Cooperative Research Centre for Freshwater Ecology urban water research is now focussed on a major project to protect and restore Melbourne’s Yarra River.

The multi-disciplinary team involved in the Yarra project is examining flow regimes and pollutant loads, water quality, river ecology and habitat, land use and river health with the aim of identifying how best to restore impaired reaches of the Yarra.

Information from that research will provide residents, planners and Councils with “a better understanding of urban water management needs and policies”, Mr Lawrence said.

While the project is only in its preliminary stages, the team is already beginning to develop an understanding of the physical, chemical and biological aspects and the movement of water pollutants in the system.

The Cooperative Research Centre for Freshwater Ecology is a national research centre specialising in river and wetland ecology. The CRC for Freshwater Ecology provides the ecological knowledge needed to help manage the rivers in a sustainable way. The CRC was established in 1993 under the Australian Government’s Cooperative Research Centre Program.

For further information: Ian Lawrence: lawrence@lake.canberra.edu.au

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