Reliability-Based Design of Urban Stormwater Detention Facilities with Random Carryover Storage

Abstract

Evaluation of the operational efficiency of a stormwater detention facility may involve deterministic simulation or application of probabilistic models derived from runoff statistics. Using a probabilistic approach, a model for runoff capture efficiency at a facility is derived that is functionally related to storage capacity and release rate. The runoff storage/release cycle considers carryover storage capacity from a preceding storm, an ensuing interevent dry period, and probable overflow from the following storm occurrence. Hydrologic variables are assumed independent, identically distributed exponential variates. The model allows for the adoption of different release rates for the interevent time and subsequent intraevent duration. A novel feature of the probabilistic model consists in treating the carryover storage capacity as a random variable. The model is validated with published results from various studies, including bioretention applications. It allows construction of attainable capture efficiency envelope curves, as a measure of reliability, and estimation of controlled release rates that would increase the runoff capture efficiency of a facility.