Quantifying effects of interacting optimisation measures in urban drainage systems

Abstract

A vast amount of resources is being spent on system development for Water Framework Directive compliance. Owing to the increased numbers of possibilities given for system optimisation the available budget maybe split and a package of single measures are applied in parallel. This paper discusses the application of single optimisation measures compared to the parallel application of several single measures in one scenario with regard to existing synergistic (or antagonistic) effects using a multi-criteria evaluation system that includes emission based, operational and water quality based aspects. The question to be answered is to which extent and why does the global effect differ from the sum of single effects and what are the prerequisites for a sustainable system development. Theoretical analysis is supported by real-life investigations on a case study for which a model-based scenario assessment has been carried out to quantify the effect of different management scenarios. Different effects have been evaluated by means of a summary index and criteria-specific indices. The results show that two measures which solely applied give a positive effect do not necessarily give the same positive effect if they are applied in parallel. In case of one scenario combination the (still positive) effect is even lower than the effect of a single measure. Furthermore, the role of ‘index design’ is discussed by means of a simple example as the selection of evaluation criteria can obviously influence the decision to be made considerably.