PROSuDs: Providing Real-world Opportunities for Sustainable Drainage Systems

Developments, such as housing estates, generally mean that more rain "runs off" the surface compared to green fields. This increased "urban runoff" often causes more river or surface water flooding downstream and also contains pollutants washed off from surfaces, such as metals and oil from cars. Sustainable Drainage Systems (SuDS) are a drainage concept that aims to mimic the pre-development hydrology by constructing systems to pass rain water back into the ground or store it, and then release it slowly back into rivers. Often this involves creating grass channels and wetlands, which can create attractive urban areas, habitat for animals and plants and also trap and remove pollutants. SuDS are one of the components of the Green Infrastructure ideal.

Research has shown that SuDS can deliver these "ecosystem services" and design guidance has been developed. However the SuDS often have a higher land take than traditional piped drainage, a concern to housing developers. They also have very different, often poorly understood, maintenance requirements. There is also uncertainty about their longevity and how to manage any long term accumulation of pollutants. Water Companies "adopt" piped drainage, but in England the long term adoption and payment for SuDS is uncertain. Planning guidance and legislation requiring SuDS to be included in schemes and adopted by local authorities has also been watered down as part of the Government's lighter touch planning policy. This means that achieving the additional benefits of lower pollution in rivers, improved urban environment and increased biodiversity are dependent on SuDS being able to be economically attractive to developers. However there are no standard guidelines for this economic evaluation and different schemes use different methods and boundaries for calculations. Therefore valuation of SuDS needs be standardised so that schemes can be compared, the appropriate amount of land allocated for high quality designs and to give confidence to property professionals in project appraisal.

This project will work with stakeholders, including developers, regulators and SuDS designers to arrive at best practice guidance for calculating the capital costs of SuDS, quantifying the economic values to developments (e.g. house prices, willingness to pay for upkeep by residents) and to explore what other contributions can be sought for off-site benefits. Key partners will be the Royal Institution of Chartered Surveyors (RICS) who provide professional guidance to quantity surveyors and valuation surveyors. We will work with RICS to create a professional Guidance Note and test this against case study projects. In addition to this valuation toolkit, training materials will be developed and delivered to surveying professionals.

The overall aim is to increase the uptake of high quality SuDS designs through synthesising and translating the environmental, social and engineering benefits in a way that allows their inclusion in decision-making processes. The University of Portsmouth team is made up of engineers who have studied the technical aspects of SuDS for over 20 years and valuation surveyors who have experience of valuing social and environmental services. This multidisciplinary team are therefore well placed to deliver this innovative project.

The main outcome of the project will be to increase the uptake of high quality SuDS designs as part of Green Infrastructure strategies that will deliver multiple benefits to the UK - through improved flood protection; higher quality surface water; improved urban landscape; improved urban habitat and biodiversity; health improvements due to increased access to public open space; and more resilient urban infrastructure. Moreover, high quality SuDS can directly affect the habitus of residents and also have benefits for those living off site, particularly those living hydrologically downstream.

These broad and cross cutting benefits are to be delivered by facilitation of the economic case for including SuDS in developments by engaging with a range of stakeholders to develop standardised valuation guidance, endorsed by RICS, the professional body that accredits valuation surveying professionals. A lack of standardised valuation guidance, especially relating to ecosystem services and property values, has been identified as a limitation to the full exploitation of the research and case based evidence concerning the benefits of SuDS. Standardisation will enable professions such as Quantity Surveyors to engage with SuDS in a confident and efficient manner, facilitating the mainstream acceptance of Green Infrastructure as assets to be valued and also to enable the relationship between property values and SuDS amenity to be assessed in a standard framework.

The benefits to developers are that the economic case can be estimated with confidence using standard methods. This will mean that masterplans can be presented to planners and regulators with reference points to accepted practice and, it is hoped, that the broad value of SuDS will be apparent and demonstrated. Public planning authorities and regulators are potentially major beneficiaries, as a standardised economic case that can consider social and environmental externalities, will mean that officers will have a standard framework for assessing projects, improving efficiency in times of reduced capacity and allowing the quality of design to be considered more fully in planning decisions. This compares to current situations where unscrupulous rogue developers are able to select the economic analysis that best fits their goals and present extended legal arguments.

Although proposing an intervention based on economic standardisation, the project team believe that this is a leverage point for realising the potential of SuDS research to deliver multiple environmental benefits.