Netherlands Journal of Geosciences — Geologie en Mijnbouw |96 – 3 | 233–259 | 2017 doi:10.1017/njg.2016.37 The ‘Voordelta’, the contiguous ebb-tidal deltas in the SW Netherlands: large-scale morphological changes and sediment budget 1965–2013; impacts of large-scale engineering Edwin P.L. Elias1,∗, Ad J.F. van der Spek2 & Marian Lazar3 1 Deltares USA, 8601 Georgia Ave., Suite 508, Silver Spring, MD 20910, USA 2 Deltares, AMO, P.O. Box 177, 2600 MH Delft, The Netherlands 3 Rijkswaterstaat, Sea and Delta, P.O. Box 556, 3000 AN Rotterdam, The Netherlands ∗ Corresponding author. Email:
[email protected] Manuscript received: 20 December 2015, accepted: 9 September 2016 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 as part of the Delta Project. The Voordelta, a coalescing system of the ebb-tidal deltas of these estuaries, extends c.10 km offshore and covers c.90 km of the coast. The complete or partial damming of the estuaries had an enormous impact on the ebb-tidal deltas. The strong reduction of the cross-shore directed tidal flow triggered a series of morphological changes that continue until today. This paper aims to give a concise overview of half a century of morphological changes and a sediment budget, both for the individual ebb-tidal deltas and the Voordelta as a whole, based on the analysis of a unique series of frequent bathymetric surveys. The well-monitored changes in the Voordelta, showing the differences in responses of the ebb-tidal deltas, provide clear insight into the underlying processes.