Dynamic water balance of infiltration-based stormwater best management practices

Infiltration-based urban stormwater best management practices (BMPs) are widely used for the reduction of runoff volumes and improvement of runoff quality. In this paper, closed-form analytical equations, collectively referred to as the analytical stormwater models (ASMs), are derived for analyzing the dynamic water balance of infiltration-based BMPs. For simplicity, previously developed ASMs only considered vertical infiltrations through the bottoms of infiltration-based BMPs although lateral infiltrations are not negligible and can even be the predominant ones in some real cases. To overcome this limitation, the ASMs developed in this study take into account infiltrations through the sides and the bottoms of BMPs. The concept of effective storage capacity is also proposed and used in this study to reduce the discrepancies caused by representing rainfall inputs as instantaneous pulses. Using infiltration trench as an example, the acceptability of the simplifying assumptions based on which the ASMs are derived is demonstrated by comparing ASMs’ results with those from numerical simulations which do not require the same simplifying assumptions. The effects of many influencing factors on the hydrologic performance of infiltrations trenches are also illustrated. The ASMs are recommended as a computationally efficient alternative for use in the planning, design, and analysis of infiltration-based BMPs.