Evaluation of SuDS Device-scale Simplified Modelling Methods in SWMM

Abstract

As Sustainable Drainage Systems (SuDS)/Low Impact Development (LID) methods are increasingly utilised to manage stormwater in urban areas, it becomes crucial for drainage engineers to accurately represent their hydrological and hydraulic impacts within drainage modelling tools. However, not all tools include explicit SuDS modelling capabilities, or their utilisation may be considered too computationally expensive in some practical contexts. This research examines the potential for representing two common SuDS devices – a green roof and a bioretention cell – using generic hydrological/hydraulic model components. Approaches including initial losses, storage, catchment area disconnection, and reassignment to permeable surfaces were compared against outputs from the SWMM LID module. The findings indicate that all approximation approaches have limitations. Methods involving complete disconnection or transferring catchment areas to pervious surfaces failed to accurately simulate the hydrological dynamics at the device scale. In contrast, approaches based on initial losses and storage showed greater potential, with continuous losses based on evapotranspiration (ET) providing more realistic responses than those using a daily fixed recharge depth. However, neither model performed acceptably in scenarios where detention effects were dominated by substrate percolation.