In the densely populated Rhine-Meuse Delta in the Netherlands, deep scour holes develop very suddenly. The holes may form a potential risk for the stability of surrounding riverbanks, dikes, bridges, tunnels and buildings, risking flooding of the hinterland. Approximately 40% of the scour holes in the delta are found to be (partially) caused by the composition of the subsoil@en

River delta degradation has been caused by extraction of natural resources, sediment retention by reservoirs, and sea-level rise. Despite global concerns about these issues, human activity in the world’s largest deltas intensifies. Harbour development, construction of flood defences, sand mining and land reclamation emerge as key contemporary factors that exert an impact on delta morphology. Tides interacting with river discharge can play a crucial role in the morphodynamic development of deltas under pressure. Emerging insights into tidal controls on river delta morphology suggest that—despite the active morphodynamics in tidal channels and mouth bar regions—tidal motion acts to stabilize delta morphology at the landscape scale under the condition that sediment import during low flows largely balances sediment export during high flows. Distributary channels subject to tides show lower migration rates and are less easily flooded by the river because of opposing non-linear interactions between river discharge and the tide. These interactions lead to flow changes within channels, and a more uniform distribution of discharge across channels. Sediment depletion and rigorous human interventions in deltas, including storm surge defence works, disrupt the dynamic morphological equilibrium and can lead to erosion and severe scour at the channel bed, even decades after an intervention.@en

An estuary forms the transition between the  ocean/sea and a river and within its boundaries  fresh and salt water mix. Fresh water intake  points may be located within the reach of salt  intrusion. In order to justify political and  managerial decisions it is thus necessary to  understand and be able to predict the process  of salt intrusion in estuaries.  For one-dimensional dynamic simulation of  the hydrodynamics and salinity intrusion the  modelling suite SOBEK is available. In the  Netherlands this software is used to evaluate  the impact of for example measures and  climate change on salinity intrusion in the  Dutch Rhine Meuse Delta (RMD). Recent  validations of SOBEK have mainly focused on  water levels and discharges, while less  attention was payed to its capability to describe  salt transport. Therefore the objective of this  research is to obtain a better understanding of  dynamic one-dimensional modelling of salt  transport and improve the governing  formulations with the newest scientific insights 

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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. @en

Scale model tests show that the natural tendency of scour holes in heterogeneous subsoil and unidirectional flow is to grow in downstream direction, with a stable upstream slope and undermining of the downstream edge. The initial depth development is fast, gradually decreasing towards an equilibrium depth. Field data of two recently developed scour holes show for one case a similar development. For the other case, scour hole growth mainly proceeds in the dominant upstream direction. Differences may be linked to the presence of tide, horizontal heterogeneity of the poorly erodible layer, the influence of a nearby confluence or scaling effects. This will be further investigated@en