Engineering design is largely founded on hard engineering science including a comprehensive knowledge of the behaviour of materials and systems under various loading conditions. According to Beder (l993), engineers see themselves as the interface between science, technology and business allowing industry to create wealth from scientific and technological developments. More recently, engineering design has relied on ecological science and the interrelationships between their products and various ecosystems. In urban hydrology, this has manifested itself through the development of Water Sensitive Urban Design (WSUD). Lloyd (2001) maintains that the term WSUD was first referred to in various publications exploring concepts and possible structural and non-structural practices in relation to urban water resource management during the early 1990s. Parallel movements, such as Sustainable Urban Drainage Systems (SUDS), were also developing in Europe and the United States. SUDS is now generally referred to as SuDS to reflect the wider application of Sustainable Drainage Systems. Both WSUD and SUDS embrace the concept of integrated land and water management and in particular integrated urban water cycle management. This includes the harvesting and/or treatment of stormwater and wastewater to supplement (normally non-potable) water supplies. Lloyd quotes Whelans et al. (1994) and CSIRO (1999) who defined the objectives or desirable outcomes of WSUD. Whelans er al.s objectives are: i) To manage a water balance • to maintain appropriate aquifer levels, recharge and stream-flow characteristics in accordance with assigned beneficial uses • to prevent flood damage in developed areas • to prevent excessive erosion of waterways. slopes and banks ii) To maintain and. where possible, enhance water quality • to minimise waterborne sediment loading • to protect existing riparian or fringing vegetation • to minimise the export of pollutants to surface or ground waters • to minimise the export and impact of pollutants from sewage iii) To encourage water conservation • to minimise the import and use of potable water supply • to promote the reuse of stormwater • to promote the reuse and recycling of effluent • to reduce irrigation requirements • to promote regulated self-supply iv) To maintain water-related environmental values v) To maintain water-related recreational values The more recent publication Urban Stormwater: Best Practice Environmental Management Guidelines (CSIRO, 1999) lists five key objectives of WSUD for application to urban srormwater planning and design: WATERFALL JOURNAL SUMMER 2003 i) Protect natural systems; protect and enhance natural water systems within urban developments ii) Integrate storrnwater treatment into the landscape; use storm water in the landscape hy incorporating multiple use corridors that maximise the visual and recreational amenity of developments iii) Protect water quality; protect the water quality draining from urban development LV) Reduce run-off and peak flows; reduce peak flows from urban developments by local detention measures and minimising impervious areas v) Add value while minimising development costs; minimise the drainage infrastructure cost of development Being located in the driest inhabited continent, most Australian towns and cities rely on importing and storing enormous volumes of fresh water from rivers, groundwater and dams. At the same time. large volumes of stormwater and wastewater are discharged. unused, from the same urban areas. For the two largest cities in Australia. the combined volumes of discharged stormwater and wastewater greatly exceed the amount of water imported into the area for water supply (Figure 1).