The development of scour holes in a tidal area with heterogeneous subsoil under anthropogenic influence

Variable flows and fast morphological changes characterize the river system of Bangladesh, which includes the downstream reaches and delta of the Ganges and Brahmaputra rivers, two of the largest rivers in the world. In contrast, fresh water supply around the country largely depends on much smaller distributaries that take off from those large rivers. With the arrival of the dry season and the drop of water levels in the rivers, some of the distributaries become disconnected during several months from their parent rivers because of aggradation at the offtake during the monsoon season. Analysing the evolution of such offtakes from a morphodynamic perspective is fundamental for the definition of effective measures to prevent their closure. However, bed elevation data required to perform such analyses are rarely available, and bathymetric surveys of large rivers are costly and quickly outdated by fast morphological changes. Physics-based numerical models provide a way to fill the gap of unavailable data, while also allowing to explore river morphodynamics beyond the setting of existing rivers.