Regional flood dynamics in a bifurcating mega delta simulated in a global river model

In this paper we show the importance of bifurcation channels for flow in river mega deltas through the use of a new computational scheme implemented in the global hydrodynamic model, CaMa-Flood (Catchment-based Macro-scale Floodplain model). First, we developed a new river network map based on SRTM3 DEM (Shuttle Radar Topography Mission 3 arc-second Digital Elevation Model) and HydroSHEDS (hydrological data and maps based on shuttle elevation derivatives at multiple scales) which includes bifurcation channels. Next, we implemented a new bifurcation scheme in CaMa-Flood capable of routing flow along this network and used the model to simulate the Mekong River. We show that in the Mekong delta such channels route about 50% of total flow and that their representation is essential for realistic hydrodynamic simulations. A simulation without bifurcation channels was obviously unrealistic because no flow occurred between the mainstem and adjacent channels even when their water level difference was >6m. The bifurcation channels are extracted from globally available data sets; thus, it is straightforward to expand the proposed scheme to global-scale studies. Key Points Automatic delineation of bifurcation channels in a global river network map A new channel bifurcation flow scheme in a global hydrodynamic model Simulation with bifurcation flow shows reasonable agreement to observations