Abstract
Urban water management via Sustainable Urban Drainage Systems (SuDS) has been successfully applied in cities worldwide. This infrastructure has proven to be a cost efficient solution to manage flood risks whilst also delivering wider benefits. Despite their technical performance, large-scale SuDS uptake in many places has been slow, mostly due to reasons beyond the engineering realm. This is the case of England and Wales, where the implementation of SuDS has not reached its full potential. This paper investigates the strategic role of SuDS retrofit in managing environmental risks to urban infrastructure at a catchment level, through an economic appraisal of all benefits (i.e. flood reduction and wider benefits). The Decoy Brook catchment in London, UK, was used as a case study. Average Annual Benefits were used to monetise the value of SuDS in reducing surface flood risk, whilst a Value Transfer approach was used to appraise wider benefits. It was found that by including the latter, their economic feasibility improves considerably. This paper also shows how to split the investment amongst multiple stakeholders, by highlighting the benefits each one derives. Finally, recommendations regarding incentives and policies to enhance the uptake of SuDS are given. The proposed methodology for SuDS mapping and economic appraisal in the planning phase can be used in cities worldwide, as long as general principles are adapted to local contexts.
Highlights
The increased frequency of extreme weather events associated with climate change poses a significant threat to the integrity and function of critical urban infrastructure – rail, road, and power and water supply/sewerage networks (Bell et al, 2012; Zevenbergen & Gersonius, 2007)
This study found that the feasibility of Sustainable Urban Drainage Systems (SuDS) implementation considerably improves when wider benefits are taken into account, as all Net Present Values were increased when the latter were included
The degree of change and the overall performance depended on the type of SuDS used
Summary
The increased frequency of extreme weather events associated with climate change poses a significant threat to the integrity and function of critical urban infrastructure – rail, road, and power and water supply/sewerage networks (Bell et al, 2012; Zevenbergen & Gersonius, 2007). In England and Wales, flood management is currently seen as a separate issue to water supply and water quality management (Richard Ashley, Blanksby, Cashman, et al, 2007; Richard Ashley, Blanksby, Chapman, et al, 2007; Thames Tunnel Commission, 2011) This hinders the possibility of merging efforts and budget across these domains to maximise outputs, through solutions such as SuDS, which simultaneously address several challenges in a cost-efficient way. Several tools have been developed to appraise/quantify these wider benefits (Richard Ashley et al, 2012; MWH, 2015; Natural Economy Northwest et al, 2010; Technology & Rivers, 2010). They are yet to be widely accepted and used. It would be desirable that a methodology merging flood risk reduction and wider benefits appraisal was consolidated as general practice within the industry and government
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