Alison Duffy

A cost comparison of traditional drainage and SUDS in Scotland.

The Dunfermline Eastern Expansion (DEX) is a 350 ha mixed development which commenced in 1996. Downstream water quality and flooding issues necessitated a holistic approach to drainage planning and the site has become a European showcase for the application of Sustainable Urban Drainage Systems (SUDS). However, there is minimal data available regarding the real costs of operating and maintaining SUDS to ensure they continue to perform as per their design function. This remains one of the primary barriers to the uptake and adoption of SUDS. This paper reports on what is understood to be the only study in the UK where actual costs of constructing and maintaining SUDS have been compared to an equivalent traditional drainage solution. To compare SUDS costs with traditional drainage, capital and maintenance costs of underground storage chambers of analogous storage volumes were estimated. A whole life costing methodology was then applied to data gathered. The main objective was to produce a reliable and robust cost comparison between SUDS and traditional drainage. The cost analysis is supportive of SUDS and indicates that well designed and maintained SUDS are more cost effective to construct, and cost less to maintain than traditional drainage solutions which are unable to meet the environmental requirements of current legislation.

Sustainable Urban Drainage Systems (SUDS) treatment train assessment tool.

This paper outlines a rationale and scoring system for the stormwater treatment train assessment tool (STTAT) which is a proposed regulatory tool for Sustainable Urban Drainage Systems (SUDS). STTAT provides guidance and regulatory consistency for developers about the requirements of planners and the Scottish Environment Protection Agency (SEPA). The tool balances the risks of pollution to the receiving water body with the treatment provided in a treatment train. It encourages developers to take SUDS into account early, avoiding any misunderstanding of SUDS requirements at the planning stage of a development. A pessimistic view on pollution risks has been adopted since there may be a change of land use on the development in the future. A realistic view has also been taken of maintenance issues and the survivability of a SUDS component. The development of STTAT as a response to the requirements of the Water Framework Directive is explored, the individual scores being given in tabular format for receiving water and catchment risks. Treatment scores are proposed for single SUDS components as well as multiple components within treatment trains. STTAT has been tested on a range of sites, predominantly in Scotland where both development and receiving water information was known. The operational tool in use by SEPA is presented.

Whole life costs and benefits of sustainable urban drainage systems in Dunfermline, Scotland

Sustainable urban drainage systems (SUDS) are increasingly prominent as a solution to many of the performance and environmental problems associated with traditional drainage systems. Questions remain regarding the values of maintenance costs and environmental benefits delivered throughout the useful lives of SUDS. Using the Dunfermline East Expansion area in Scotland as a case study, this study represents a novel approach in that it collects actual maintenance data, assesses ecosystem services, and carries out whole life cost analyses. Findings suggest that SUDS may be accounted as a net asset, although assumptions inherent to ecosystem services assessment methodologies produce a wide range of uncertainty.