Comparisons of costs and benefits

Although there is a lot of guidance available on carrying out cost benefit appraisals and a growing body of evidence that can help to quantify intangible benefits, there is still a lack of information available on the costs and benefits of sustainable drainage and even less on comparisons between SuDS and traditional drainage.

The Lamb Drove example in Cambridge has been evaluated. The exercise, primarily based on evaluating the tangible costs and benefits, suggested around a 10% saving on capital costs with the SuDS scheme. It’s been suggested that the savings could have been greater if the SuDS layout had been considered earlier in the development process.

Defra, as part of the work on the Flood and Water Management Act, has also undertaken a number of comparative studies on the costs and benefits of traditional drainage and SuDS. Clients, designers, engineers and quantity surveyors compared the capital (and sometimes the maintenance) costs for draining sites using sustainable drainage and more traditional approaches. The sites they looked at included:

• Mixed housing development, Daniels Cross, Shropshire

• Rail freight terminal, Telford, Shropshire

• School, Redhill, Worcester

• Housing, Islington, London

• Mixed housing development, Hadley, Shropshire

All of the sites in these studies showed that the inclusion of SuDS was cheaper than a traditional drainage system.

Read more on:

• Guidance on cost benefits analysis