Title: Modeling stormwater runoff: The strengths and weaknesses of current software

Abstract

With climate change and urbanization, the world is faced with frequent flash floods, depletion of groundwater, and water pollution simultaneously. Stormwater Best Management Practices (BMPs) is an effective method to mitigate flash floods, purify stormwater, and recharge groundwater. To design successful BMPs, it is crucial to predict the BMPs’ effectiveness in terms of both stormwater volume reduction and pollutant removal under current and future weather conditions. However, such a modeling tool is not yet available. In this work, we reviewed 14 currently available modeling tools designed for either agricultural fields or urban areas in the perspective of assisting stormwater simulations. Two publicly available models were applied to simulate two experimental bioretention systems. The results verify that no current models are successful in stormwater quality modeling. The current urban stormwater models are advanced at hydraulic calculations, but describe removal of all dissolved pollutants with first-order reaction kinetics, not influenced by environmental factors like temperature or soil moisture. This description is not accurate for nutrients which degrade through biochemical processes. On the contrary, agricultural models simulate nitrogen transformations in detail, while important hydraulic processes of surface run-on and drainage discharge are overlooked. Based on the review and case study, a process-based nitrogen module is developed as an extension of current urban stormwater models.