Risk-based analysis of a detention basin for urban runoff control

Various uncertainties exist in detention basin design which contribute to the potential failure or unsatisfactory performance of the system. Risk-based analysis provides a systematic framework to explicitly consider the trade-off among the cost of facility, its failure probability, and failure consequences. Conventional risk-based analysis requires the information of failure damage function. Such information is often unavailable and this hinders the implementation of risk-based analysis. Under this circumstance, a viable procedure is presented according to marginal cost analysis for risk-based design of a detention basin. The procedure utilizes the physical characteristics of system failure (overflow volume) which generally can be straightforwardly obtained from flow simulations. In addition to using the mean value of annual overflow volume, the suggested procedure further incorporates variability of overflow volume in decision-making. For illustration, this study applies the modified rational method in the risk-based framework for sizing the detention basin.