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The Welsh Government (WG) commissioned Environmental Policy Consulting to assess the performance of SuDS on new developments, including costs and benefits, compared with conventional drainage approaches. The purpose of this assessment is to inform potential policy changes that could be made to accelerate the use of SuDS on new developments in Wales.

The key findings from the collated information are:

• SuDS are already used extensively on new developments in Wales. However, these are variable in quality and performance, and there is currently a preponderance of ‘hard’ SuDS (largely comprising underground measures and attenuation ponds), with fewer ‘landscaped’ (vegetated) SuDS that can potentially deliver multiple benefits.

• At present, the key barrier to greater uptake of good quality, landscaped SuDS is uncertainty around adoption and ongoing operation and maintenance. A variety of adoption and funding arrangements are currently used, and these are arrived at by different means.

• Different SuDS schemes in different places have very different costs and benefits. However, based on the evidence obtained, the capital costs of SuDS solutions are lower than the capital costs of comparable conventional solutions. This differential can be very significant and depends primarily on the size of the scheme and the SuDS components used. SuDS on new developments: Analysis of Evidence Executive Summary Environmental Policy Consulting 3 January 2017

• Operational and maintenance costs also tend to be lower for SuDS. However, there is more variability here and some important caveats to this, primarily related to the type of measures and management regime used.