Uncertainties, performance indicators and decision aid applied to stormwater facilities

Performance indicators play an increasing role in the design and the operation of urban drainage systems. However, uncertainties linked to both calculation of performance indicators and their use in decision-aid tools and methods have been rarely accounted for. Two case studies concerning stormwater facilities are presented in this paper. The first one concerns the effect of sampling and analytical uncertainties on the evaluation of a single performance indicator defined as the annual interception efficiency of a stormwater storage and settling tank. The second one is related to the effect of modelling uncertainties on the evaluation of several performance indicators and on their impact as regards the choice of maintenance strategy of a stormwater infiltration tank. Both cases show that uncertainties are very significant and shall be accounted for in the calculation and the use of performance indicators.