Institutionalising water sensitive road design
Government has introduced requirements for stormwater quality to protect receiving waters from the impacts of urban development. These requirements are contained in the document titled “Urban Stormwater: Best Practice Environmental Management Guidelines” prepared by the Victorian Stormwater Committee (1999).
In principle, all development must meet these new environmental standards, however mechanisms to ensure that these requirements can be consistently and equitably implemented are still evolving. Greenfield development in Melbourne is served by a system of drainage schemes (sub-catchment based plans), which incorporate stormwater quality treatment measures consistent with the Guidelines’ requirements. Redevelopment, industrial development within the existing urban area and other development such as roads however are rarely required to meet these objectives. When the objectives are enforced it is usually through the implementation of large downstream wetland systems. Water Sensitive Urban Design (WSUD) however has been shown to offer better environmental outcomes than “end of pipe” treatment at a lower overall cost to the community. Kingston City Council and Melbourne Water have been encouraging the adoption of this integrated approach including the use of on-site and streetscape measures.
Roads generally make up 20-25% of urban areas consisting mainly of impervious surfaces, almost all of which are directly connected to the stormwater system. Recent studies by the CRC for Freshwater Ecology have demonstrated the link between these directly connected impervious areas and stream health. A Brisbane study by WBM Oceanics found that up to 40% of heavy metals and petroleum hydrocarbons catchment loads originate from roads. Therefore treatment of road runoff is an integral component of catchment based stormwater quality treatment. With the use of Water Sensitive Road Design (WSRD) the impact of road runoff on receiving waters can be minimised by disconnection and treatment. However, the majority of these systems are owned and maintained by local government and it is currently at the discretion of council to implement such systems.
Kingston council has a program of reconstructing roads using WSRD with a number of reconstruction projects of different scales already completed. VicRoads have also implemented WSRD on several of their major freeway projects.
This paper will give several case studies of WSRD at variety of scales. These case studies will focus on design issues, on-going maintenance of the systems, performance and costs associated with road reconstruction using WSRD. It will concentrate on the implementation of an ongoing road upgrade program rather than isolated “pilot project” examples. Lessons learnt in terms of the increased planning time required, consultation with residents and changed maintenance regimes will be presented.
The paper will also discuss how a road reconstruction program could be built into a larger stormwater quality program, and will consider other mechanisms currently underway such as DSE’s “Sustainable Neighbourhoods Code” for residential subdivisions and Melbourne Water’s offsets program.