The first piece of research to introduce the concept of 'retrofit SUDS' was Andy Swan's PhD. The Leeds feasibility studies led to the development of a decision-support framework for the identification and evaluation of retrofit SUDS-based candidate solutions for sewer rehabilitation (Swan and Stovin, 2002). The framework is aimed at efficiently identifying those retrofit SUDS options that will deliver hydraulically effective solutions that are straightforward and cost-effective to implement. Flowcharts have been prepared to direct the engineer to consider the range of options in a logical and efficient manner [download]. The flowcharts embody four hierarchies constructed around urban surface type, the surface water management train concept, the mode of operation of the device and cost. The flowcharts direct the user to consider institutional roofs before residential roofs, source controls before off-site controls, infiltration systems in preference to storage based systems and the cheapest options within each category are highlighted.
This research developed approaches for the hydraulic modelling and costing of retrofit SUDS. Feasibility studies undertaken for two catchments in Leeds suggested that retrofit SUDS could represent a viable and cost-effective alternative to more conventional underground storage based sewer rehabilitation measures.
The study was biased towards CSO spill reduction and sewer flooding problems, and so could not fully consider the wide range of other drivers that might lead to retrofit SUDS being considered feasible for implementation, such as urban water quality particularly diffuse sources of pollution may be the most significant contributing factor or restrictions to new development or inner city redevelopment arising from a lack of capacity within the existing sewer system.