Human Settlements Theme Report

Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Professor Peter W. Newton, CSIRO Building, Construction and Engineering, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06747 7

Waste, recycling and reuse (continued)

Urban stormwater (continued)

Utilising stormwater as a resource

Stormwater is being seen increasingly as a resource that has been undervalued. Future stormwater use is likely to be of significant environmental benefit by minimising the need to augment traditional water supply (WBM Oceanics Australia 1999). The COAG Water Reform Agenda recommended that stormwater be considered a resource and greater use of it be made (WSAA 1997, Thomas et al. 1997). In comparison to wastewater, stormwater may initially appear to be a more suitable resource for urban use because of its perceived higher quality. However, due to the intermittent nature of rainfall and the variable quality of stormwater runoff, there are substantial difficulties associated with the use of this resource. Options for stormwater use include: on-site rainwater tanks, community collection and storage for irrigation, aquifer storage and recovery, and habitat restoration such as wetlands or streams. The benefits and costs of stormwater use in comparison to alternative sources of water depends on the specific location and the options for demand-side management.

Roof runoff collected in domestic tanks is an important source of water throughout Australia. Nationally in 1998, 17% of households used stormwater from rainwater tanks (ABS 2000f). On a state and territory basis, the Australia Capital Territory has the lowest use of rainwater tanks, being in the order of 1% of households (ABS 1998l). South Australia has the highest percentage of households with rainwater tanks, with 54% in 1998, a rise from the 1982 level of 52% and the 1994 level of 48%, indicating that there has been a relatively recent turnaround in attitude and action among Adelaide residents in relation to on-site rainwater usage (ABS 1983, 1998e, 1999a). The earlier decline had been attributed to the esteem value attached to reticulated supply, convenience and freedom from maintenance offered by reticulated supply, shortage of space for aboveground tanks with reducing lot size and higher density housing, and lack of innovation in roof runoff capture (van der Wel 1999). An explanation for the turnaround could be that South Australia has the highest rate of dissatisfaction with the quality of mains water for drinking (42%) in Australia, with one in 10 households stating that they do not drink the mains water connected to their household. It is also the state with the highest proportion of households indicating that their water usage is influenced by cost (54%). These factors will partially explain the significantly higher utilisation of rainwater tanks in that state.

There are no comprehensive data available on the extent of stormwater use in Australia, although anecdotal evidence would suggest that only a small proportion of stormwater generated from urban areas is utilised. Even in South Australia, where stormwater use is more advanced and the trend is for more such activity, the portion of total water use supplied by stormwater is still small (WBM Oceanics Australia 1999). Exceptions to this trend are the cities of Perth and Canberra. In Perth there is extensive indirect stormwater use due to the prevalence of on-site disposal of roof runoff through spoon drains and extensive use of shallow groundwater bores for non-potable water supply. The city of Canberra uses stormwater from detention basins for non-potable uses, reported as providing 6% of its total water needs in the mid-1990s (Anderson 1996a). Overall, there appears to be no serious impediments to achieving significantly greater use of stormwater than presently occurs in Australia (WBM Oceanics Australia 1999). However, it is essential that any stormwater use scheme addresses both the reliability of supply (if there is an intermittent pattern of rainfall) and the assurance of appropriate water quality for the intended use.

The requirement for stormwater storage is determined by the relationship between the temporal pattern of runoff and that of the water demand. In areas of winter-dominant rainfall and summer-dominant water demands, a large storage capacity may be required to maximise the potential for stormwater use. An example of this situation is the city of Adelaide, where methods such as aquifer storage and recovery are used to provide the storage capacity required (see Table 62). Storage requirements can be substantially smaller where rainfall patterns are more constant throughout the year.

Table 62: Stormwater reuse schemes. [HS Indicator 2.9]
Scheme Description
Fig Tree Place, Newcastle (Coombes et al. 1999) A 0.6 ha urban site has been redeveloped, containing 27 housing units. The stormwater system involves underground rainwater tanks which have been fitted with first-flush devices to collect roof runoff. In-house hot water and toilet flushing is supplied from the rainwater tanks, and overflow is disposed of on site through gravel trenches, providing groundwater recharge. Runoff from paved areas flows into a detention basin and groundwater recharge area. Groundwater is drawn for irrigation and bus washing at the adjacent bus station.
Andrews Farm, Adelaide (Dillon et al. 1997) In April 1993, an aquifer storage and recovery facility was established on the northern fringe of Adelaide. Ephemeral stormwater runoff from a semi-urban catchment is collected, passively treated, and injected into an underlying confined aquifer. The water is later recovered for landscape and crop irrigation. Water quality testing has shown that the facility provides water suitable for irrigation, and may with time meet drinking water guidelines.
Homebush, Sydney (Phillips et al. 1998, WBM Oceanics Australia 1999) Development of the Sydney Olympics site at Homebush Bay has included a major drainage and stormwater recycling system. Site runoff is collected and treated using gross pollutant traps and water quality control ponds/wetlands. The runoff is then directed into the Brickpit Storage, which also receives treated wastewater. Water from the Brickpit Storage is used on site for irrigation, toilet flushing and other purposes. Maximum demand for recycled water is estimated to be approximately 14 ML/day.
Kogarah Town Square, Sydney (Mouritz 2000) The Kogarah Town Square redevelopment covers 1 ha, comprising retail and commercial space, along with 190 apartments, a public library and underground parking. Stormwater is used for landscape irrigation, toilet flushing and car washing. Some 17% of the water used in the redevelopment will be stormwater, in the order of 5700 kL/year. Solar power is also generated. The project commenced in early 2001, with completion in 2002.

The main problem with reliance on urban stormwater as the sole water source is the reliability of supply through extended dry periods. As a result, the best option is to use stormwater in conjunction with other water resources such as wastewater, to overcome the need for large carry-over storage.

As already noted, the quality of stormwater in urban areas is highly variable. The level of treatment necessary is determined by the quality of the particular stormwater source and the intended water use. Market research carried out in the ACT found that, from a health perspective, the community was less concerned about the use of stormwater than of wastewater (ACTEW 1994). A survey of the 26 tenants of Fig Tree Place in Newcastle (see Table 62) found that 95% of respondents accepted the use of rainwater tanks to supply their irrigation, toilet flushing, hot water, clothes washing and cooking water demands (Coombes et al. in press). Some 70% of respondents accepted the possible use of rainwater for drinking purposes.

There are a number of guidelines that deal with the use of stormwater, but guidelines are not enforceable standards, and any scheme still requires the approval of local health authorities and local government. Because of the wide range of possible circumstances and implications, the guidelines are interpreted case by case. In the absence of definite criteria, many potential users have been deterred, and cautious about the practical and legal implications (McIntosh and Pugh 1991). It is desirable that more specific criteria be developed, aiding the adoption of reuse practices in urban areas. Despite the low level of stormwater use in Australia, there are a number of urban developments that have incorporated stormwater use, a selection of which are described in Table 62.

Like Australia, most countries throughout the world utilise very little urban stormwater. However, water is a scarce resource in Singapore due to limited land area and competing uses for land to sustain the economy. As a result, Singapore is one of the few countries to utilise urban stormwater on a large scale to augment its limited supplies and provide a source of potable water (Lim and Lim 1998). Since 1986 the Lower Seletar/Bedok Water Scheme has been collecting up to 70% of the runoff. The stormwater resource is generally of good quality due to pollution control measures, although it is also treated to ensure World Health Organization standards are meet.

Implications

Many professionals, including stormwater planners, managers and technical specialists, have embraced the idea of sustainable development, but are finding it a challenge bringing it to realisation. It is difficult to determine the 'sustainability' of a particular stormwater management strategy. There is a realisation that problems are complex and that stormwater management can only be efficient, in terms of human needs and environmental constraints, if it is integrated with the management of all other water resources and human activities (Niemczynowicz 1992). But to date, the relationship between water and land use planning has received little attention from researchers and policy-makers.

The use of a water-sensitive urban design approach to integrate stormwater management into urban development is an outcome of the movement towards creating urban developments that have a lower impact on the environment. Water supply and wastewater also need to be added to the traditional equation, which includes such components as transport, housing and employment, to provide a holistic approach to urban planning and sustainable development (see Whelans and Halpern Glick Maansell 1994).

Currently there is little use of urban stormwater runoff as a water resource, despite the community being more accepting of using it in comparison to treated wastewater (ARCWS 1999). Because of concern about the effects of stormwater contaminants on receiving environments, there is increasing effort (and money) going into improving stormwater quality. As stormwater quality improves, it will be an even more attractive source of water in urban environments and may well result in a sharp increase in stormwater use.