Integrated mathematical modeling of hydrological and hydrodynamic response to rainfall events in rural lowland catchments

In rural lowland catchments, negligible topographic gradients and possible interactions between overland and channel flows complicate efforts to predict flood formation, propagation, and inundation. In this study, we demonstrate that an approach in which a two-dimensional shallow water model is coupled with a two-dimensional model for the saturated flow in the topsoil layer can accurately reproduce floods in such a lowland catchment. The topsoil porous layer is treated as a confined aquifer where water ponds on the ground surface and as an unconfined aquifer elsewhere. The model includes infiltration from the ground surface into the topsoil layer and downward percolation out of the topsoil layer. The equations of both surface and subsurface models are suitably averaged over a representative elementary area to yield a subgrid model for the coupled surface-subsurface flow. Field data collected in two rural lowland catchments in the North-East of Italy are used to evaluate the model performance. The good agreement between computed and measured discharge at the catchments' outlet and the agreement between predicted and surveyed spatial pattern of inundated areas indicate that the model effectively reproduces overland flow and efficiently accounts for the surface-subsurface flow interaction and the relevant subsurface processes. Key Points A process-based, coupled surface-subsurface, 2-D mathematical model is presented The model effectively integrates the main hydrologic and hydraulic processes The model can be applied to storm events in rural lowland catchments.