Half a century of morphological change in the Haringvliet and Grevelingen ebb-tidal deltas (SW Netherlands) - Impacts of large-scale engineering 1964-2015 Ad J.F. van der Spek1,2; Edwin P.L. Elias3 1Deltares, P.O. Box 177, 2600 MH Delft, The Netherlands;
[email protected] 2Faculty of Geosciences, Utrecht University, P.O. Box 80115, 3508 TC Utrecht 3Deltares USA, 8070 Georgia Ave, Silver Spring, MD 20910, U.S.A.;
[email protected] Abstract The estuaries in the SW Netherlands, a series of distributaries of the rivers Rhine, Meuse and Scheldt known as the Dutch Delta, have been engineered to a large extent. The complete or partial damming of these estuaries in the nineteensixties had an enormous impact on their ebb-tidal deltas. The strong reduction of the cross-shore tidal flow triggered a series of morphological changes that includes erosion of the ebb delta front, the building of a coast-parallel, linear intertidal sand bar at the seaward edge of the delta platform and infilling of the tidal channels. The continuous extension of the port of Rotterdam in the northern part of the Haringvliet ebb-tidal delta increasingly sheltered the latter from the impact of waves from the northwest and north. This led to breaching and erosion of the shore-parallel bar. Moreover, large-scale sedimentation diminished the average depth in this area. The Grevelingen ebb-tidal delta has a more exposed position and has not reached this stage of bar breaching yet. The observed development of the ebb-tidal deltas caused by restriction or even blocking of the tidal flow in the associated estuary or tidal inlet is summarized in a conceptual model.