Urban Storm Water Control Evaluation with Analytical Probabilistic Models

In urban storm water management planning, a common problem associated with the widespread implementation of storage/treatment facilities, is the determination of the relative magnitudes of the storage capacity and the controlled outflow capacity in conjunction with the desired levels of system performance. For this purpose, cost-effective designs in the configuration of storage/treatment facilities can benefit from analytical tools that are able to provide explicit analytical solutions to system control measures in terms of the catchment meteorological characteristics and the drainage system control elements (e.g., storage capacity and controlled release rate). This paper presents methodologies and necessary procedures for the development of system performance measures (such as average annual volume of spills and number of spills from storage facilities) for storm water runoff quantity control based on derived probability distribution theory. Essentially, these runoff control measures with closed-form mathematical expressions are derived from transformations of the probability density functions (PDFs) of the rainfall characteristics into the PDF of runoff volume in terms of a modified version of the rainfallrunoff transformation, which explicitly considers the infiltration process. Results from a case study indicate that these analytical models can be employed as effective tools for storm water runoff quantity control analysis. In contrast to continuous simulation, these analytical tools (models) are especially useful at the planning stage in the evaluation of a wide range of alternative designs.