Analysis of storage facilities for urban stormwater quantity control

Storage facilities for urban drainage systems are frequently planned and implemented to mitigate the negative impacts of stormwater discharges on receiving waters. For screening level analysis of various runoff control alternatives, cost-effective planning and design of the storage facilities could significantly benefit from analytical tools with explicit solutions to the determination of the relative magnitudes of the storage capacity and the controlled outflow capacity in conjunction with the desired level of system performance. This paper presents methodologies for the development of closed-form mathematical expressions of system performance measures, with which existing drainage system performance and a wider range of alternative designs can be evaluated. As an alternative to continuous simulation for urban stormwater runoff control analysis at the planning stage, these analytical models for stormwater control analysis are developed with the derived probability distribution approach whereby the probability density functions (PDFs) of rainfall characteristics of the catchment are mathematically transformed by rainfall–runoff transformation to create the PDFs of system outputs, such as spill volumes from the storage facility, runoff capture efficiency, etc. This study demonstrates that analytical models, with consideration of the entire spectrum of meteorological conditions, are capable of providing comparable results to continuous simulation models and can be employed as effective tools in urban stormwater management planning.