Subgrid local inertial model (1D-2D)

[verseve]

For the local inertial model (1D river routing and 2D overland /floodplain routing) water depths and fluxes between cells, especially for cells with large subgrid elevation differences, may not be accurate enough. The use of a subgrid approach would improve accuracy of simulated water depths and fluxes between cells. A simple approach could be to build on the already implemented 1D floodplain schematization for local inertial river flow and to use a minimal water depth threshold for each 2D link (activation), or to build on approaches in literature like for example Volp et al. (2013) and Casulli (2019).