Comparison of Three Methodologies for Quasi-2D River Flood Modeling with SWMM5

Three methods for quasi-2D model setup of a SWMM5 project are explored with the PCSWMM 5.6 software using real project data from a hydraulic study of the Birse River in the town of Court in Switzerland. The first method is the standard method for constructing a 1D-2D model with PCSWMM (quasi-2D mesh with direct connections towards the 1D conveyance network). Care needs to be taken in the model construction to avoid double accounting of the channel conveyance and overestimation of the channel roughness. The second method uses the technique of representing the river channel with a 1D approach and making orifice side connections with the quasi-2D floodplain mesh. Side connections can be tedious to construct, so a routine using FME software was developed to automatically create the orifice side connections. The third method uses a complete quasi-2D model to represent the river and floodplain conveyance. In this method, care needs to be taken in representing the bridges.