A decision-support system for the design of retrofit sustainable urban drainage systems (SUDS)

Sustainable Urban Drainage Systems (SUDS) is a generic term that refers to various measures aimed at minimising surface runoff (and consequent flooding and pollution problems) from urban catchments. SUDS technologies include local infiltration, storage and storm-water re-use devices. Although there is considerable international evidence of the successful incorporation of SUDS technologies in new developments, there is very little indication of the extent to which they represent a viable rehabilitation option for retrofit applications to problem urban catchments in the UK. It is believed that uncertainties about the design, hydraulic performance and cost of retrofit SUDS schemes, as well as some regulatory issues, have prevented UK engineers from exploiting the full potential of this approach. This thesis presents two case studies in which retrofit SUDS have been evaluated against 'conventional' (i. e. in-sewer) drainage rehabilitation schemes. The case studies relate to the City of Leeds in Northern England, UK. In both cases it was found that SUDS technologies were viable, both in terms of hydraulic performance criteria (number and volume of CSO spills or flooding events) and in terms of comparative construction costs. Novel procedures were developed for evaluating hydraulic performance and SUDS scheme costings. The identification of the most cost-effective from all feasible SUDS technologies for a given location is not straightforward. This thesis, therefore, proposes a design methodology for retrofit SUDS. The methodology comprises a decision making model (flow chart) that indicates whether SUDS-based approaches are likely to be viable, and cost-effective for a particular application. The flow charts make reference to SUDS design criteria (such as land-take, slope and infiltration capacity) and regulatory constraints (such as Building Regulations and local groundwater protection policies). Fundamental to the flow charts arc hierarchies that characterise urban surface type, the treatment train concept, the disposal mechanism, and cost.