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.
It is widely recognized that the complex relationship between humans, soil, and water has become increasingly complicated due to anthropogenic activities, and is further expected to worsen in the future as a result of population dynamics and climate change. The present study aims at shedding light on the multifaceted links between floods, landscape modifications, and population dynamics in anthropogenic coastal lowlands, using a large flood-prone area (the Polesine Region, northeastern Italy) as a significant case study. Based on the analysis of historical events and the results of hydraulic modeling, it is shown that human interventions on both the landscape and the subsoil have substantially altered the flooding dynamics, exacerbating hydraulic hazard. Furthermore, the combined analysis of people and assets exposure to inundation reveals that flood risk is not properly taken into account in land-use planning, nor it is properly understood by people living in areas subject to low-probability, high-impact flooding events.
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