Engineering infrastructure is provided at high cost and is expected to have a useful operational life of decades. However, it is clear that the future is uncertain. Traditional approaches to designing and operating urban storm drainage assets have relied on past performance of natural systems and the ability to extrapolate this performance, together with that of the assets across the usable lifetime. Whether or not climate change is going to significantly alter future weather patterns in Europe, it is clear that it is now incumbent on designers and operators of storm drainage systems to prepare for greater uncertainty in the effectiveness of storm drainage systems. A recent U.K. Government study considered the potential effects of climate and socio-economic change in the U.K. in terms of four future scenarios and what the implications are for the performance of existing storm drainage facilities. In this paper the modelling that was undertaken to try to quantify the changes in risk, together with the effectiveness of responses in managing that risk, are described. It shows that flood risks may increase by a factor of almost 30 times and that traditional engineering measures alone are unlikely to be able to provide protection.

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Combined sewer overflows are a known source of aesthetic pollution in urban watercourses, and screens have traditionally been used as a means of preventing such pollution. The authors have established the effectiveness of combined-sewer overflow bar screens in preventing the visual pollution of rivers and have determined the factors which influence screen efficiency so that guidance can be given on improving the performance of future installations. A field study has been undertaken to monitor existing bar screens with different bar spacings. The hydraulic performance of the overflow chambers has been established, and the sources and type of visual pollutants have been identified. Analysis of the field data has established that screen performance (for the main polluting solids) depends on (a) screen bar spacing, (b) mean rate of flow through the screens, and (c) frequency of raking. Overall, mechanically raked bar screens are likely to achieve retention efficiencies of less than 50%.

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