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 >6 m. 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