Stochastic water balance dynamics of passive and controlled stormwater basins

Abstract

Abstract Urbanization and changing rainfall intensities affect the performance of urban stormwater infrastructure, creating the necessity to design resilient stormwater systems. One proposed method to increase the resilience of stormwater infrastructure is the active control of system flows. To improve the understanding of actively-controlled urban water infrastructure function under variable hydro-climate, we develop a stochastic water balance model for stormwater retention and detention basins with both passive and actively-controlled outflow structures. Under active outflow control, the outflow valve is closed until the water level in the basin reaches a specified maximum at which point the valve opens and the basin empties. Using the stochastic water balance model, we develop analytical expressions for the steady-state probability density functions (PDFs) of water level and valve closure time, as well as the joint PDF of water level and valve closure time. These PDFs then are used to define water level and flow duration curves that provide a probabilistic description of the full range of basin performance. The model accurately predicts the water level PDF estimated from data collected at a retention basin with a passive outflow structure. The model provides a basis for evaluating how changes in the rainfall-runoff process, affected by land use and climate change, will impact the variability of stormwater basin water storage and pollutant removal function. We find that this variability can be managed through the adaptive updating of the active control rule for the outflow structure.