Sustainable Drainage Systems (SuDS) retrofit planning: a scalar approach to site prioritisation

SuDS provide a means of controlling urban diffuse pollution, reducing flood risk, incidence of combined sewer overflow, and may also have amenity value. They are most commonly implemented with respect to new build however, even if SuDS for new build result in no net change to the diffuse load and discharge regime of the site in question, the legacy of extant urban development means that flood risk and diffuse pollution problems will not be addressed. The bulk of all development we will have in 2050 has already been built, and there is a clear need for SuDS retrofit into the existing built environment.
Retrofit SuDS offer a greater challenge than new build SuDS for two reasons. First, there is significant uncertainty over where in the built environment SuDS are needed most. This is important as, compared to new build, there are fewer regulatory drivers for retrofit SuDS and so it is important to be confident that any investment is made in the right places. Second, retrofit SuDS face greater physical, economic and social challenges. In general, we can assume that areas of high SuDS need occur in areas where the implementation constraints are also greatest. There is therefore likely to be a series of sites within any built environment which are optimal for SuDS retrofit, considering need and feasibility.
The purpose of this research is to determine how best to identify where, in a given urbanised catchment, the optimal sites for SuDS retrofit are through consideration of need and feasibility.