Half a century of morphological change in the Haringvliet and Grevelingen ebb-tidal deltas (SW Netherlands) - Impacts of large-scale engineering 1964–2015.

The damming of the estuaries Brielse Maas, Haringvliet and Grevelingen in the SW Netherlands, distributaries of the rivers Rhine and Meuse, caused large-scale morphodynamic changes in their respective ebb-tidal deltas that continue until today. The strong reduction of the cross-shore tidal flow triggered erosion of the ebb-delta front, the building of a coast-parallel, linear intertidal sand bar at the seaward edge of the delta platform, levelling of bars and infilling of the tidal channels. The stepwise extension of the port of Rotterdam north of the Haringvliet ebb-tidal delta increasingly sheltered this area from the impact of waves and caused a large supply of sand. This finally led to breaching and erosion of the shore-parallel bar. Moreover, large-scale sedimentation reduced the average depth in this area. The Grevelingen ebb-tidal delta has a more exposed position and a smaller sediment supply and has not reached the stage of bar breaching yet. The observed development of the ebb-tidal deltas caused by blocking of the tidal flow in the associated estuary or tidal inlet is summarized in a three-stage conceptual model. This model can help to assess the impact of interventions in estuaries and tidal inlets, for instance to mitigate the impacts of sea-level rise. • Fife decades of data show changes in ebb-tidal deltas caused by damming of inlets. • The ebb-tidal deltas have been strongly reduced in extent and average water depth. • The observed morphodynamic evolution can be summarised in a conceptual model. • This model can assess impact of engineering, e.g. anticipating future sea-level rise. [ABSTRACT FROM AUTHOR]