Climate change and human influences on sediment fluxes and the sediment budget of an urban delta: the example of the lower Rhine—Meuse delta distributary network

Abstract

Deltas require sufficient sediment to maintain their land area and elevation in the face of relative sea-level rise. Understanding sediment budgets can help in managing and assessing delta resilience under future conditions. Here, we make a sediment budget for the distributary channel network of the Rhine—Meuse delta (RMD), the Netherlands, home to the Port of Rotterdam. We predict the future budget and distribution of suspended sediment to indicate the possible future state of the delta in 2050 and 2085. The influence of climate and anthropogenic effects on the fluvial and coastal boundaries was calculated for climate change scenarios, and the effects of future dredging on the budget were related to port development and accommodation of larger ships in inland ports. Suspended sediment rating curves and a 1D flow model were used to estimate the distribution of suspended sediment and projected erosion and sedimentation trends for branches. We forecast a negative sediment budget (net annual loss of sediment) for the delta as a whole, varying from −8 to −16 Mt/year in 2050 and −11 to −25 Mt/year by 2085, depending on the climate scenario and accumulated error. This sediment is unfavourably distributed: most will accrete in the northern part of the system and must consequently be removed by dredging for navigation. Meanwhile, vulnerable intertidal ecosystems will receive insufficient sediment to keep up with sea-level rise, and some channels will erode, endangering bank protection. Despite increased coastal import of sediment by estuarine processes and increased river sediment supply, extensive dredging for port development will cause a sediment deficit in the future.