Guiding the development of urban drainage systems by sustainability criteria

The development of urban drainage towards sustainability is discussed, primarily on the basis of case studies of mature urban drainage systems. Typical problems and a series of possible measures to enhance the systems performance are evaluated. We consider CSOs, receiving water quality, and decreasing ground water levels as actual problems. We distinguish between improvement strategies which focus on the technical system itself (e.g. storm water retention tanks, real time control) and strategies which may be described either as source control or as improving the resilience of the receiving water. Their efficiency is evaluated on the basis of short term ‘conventional’ criteria and by means of the following sustainability criteria: systems definition (time and space constants), resource efficiency and degrees of freedom. Surprisingly, the rating of the different strategies according to the two sets of criteria are quite close: In both cases, the measures which do not narrowly focus on the technical system obtain the better score.