A spatially distributed hydrodynamic model framework for urban flood hydrological and hydraulic processes involving drainage flow quantification

Two-dimensional hydrodynamic models are increasingly used to predict overland surface water flooding in urban catchments. The complexity of urban surfaces and subsurface drainage systems poses great challenges to modelling urban rainfall-runoff and flood hydraulics. This work develops a spatially distributed hydrodynamic model framework incorporating both hydrological and hydraulic processes of surface and subsurface drainage processes during urban flooding. The model is built upon 2D full shallow water equations solved by a Godunovtype finite volume method with robust treatments of the bed source term. To properly involve drainage flow effects, we present three methods to quantify the drainage flow discharge and its delay time which affect both urban hydrology and surface inundation. Besides, a simple OpenMPI-based parallel algorithm is applied to accelerate the model and ensure computational efficiency when applied to real-world events. The model framework is justified through the validations with five benchmark cases. Benchmark results indicate that the well-balanced treatment of bed source term ensures the model applicability in irregular urban surfaces, the model can predict both urban surface inundation and flood hydrograph, and the proposed drainage flow treatments can well reproduce drainage flow hydrograph. The model framework is successfully applied to simulate rainstorm-induced flood events in a rural-urban catchment, the upper Shenzhen River catchment. Results further demonstrate the robust capability of the model in the quantification of flow exchange between surface and subsurface systems to some extent even in the absence of drainage information. Our framework provides a practical solution for urban flood simulation even when pipe data are scarce.