Cost of incorporating WSUD into greenfield site development and application of an offset trading scheme

Future directions in urban planning will be strongly influenced by financial procedures capable of encapsulating enhanced environmental outcomes. Even after achieving the Victorian water quality targets for an urban catchment, development still results in a considerable increase in annual flow volume and nitrogen load from the typical pre-development farmland or pre-European condition. These increases in flow volume and pollutant loads impact on downstream water quality, waterway hydrology and aquatic ecosystem health. Future growth in urban populations will exacerbate these impacts and even if greenfield sites achieve the current water quality targets, annual nitrogen loads will increase by 34% and flow volume by 37% by the year 2030. Water Sensitive Urban Design (WSUD) offers enhanced environmental, economic and social outcomes over traditional drainage design. Melbourne Water is considering introducing an offsets scheme that would provide support for developers implementing WSUD and ensure best practice water quality targets are achieved for all developments. In addition to presenting how various offset options may be applied to greenfield site development, the findings presented in this paper demonstrate that adopting a distributed treatment approach using bio-filtration systems to meet downstream environmental targets will have savings to the community of 17% when compared to constructing a large, downstream wetland.