The state of the coast – Toestand van de kust - : case study: The South-Westerly Delta

The South-Westerly Delta is the area within the Netherlands which has been subject to the larger and longest anthropogenic interventions during the history. The construction of polders started already in the 12th century. From the 17th century, hard structures have been built against coastal erosion, and then accompanied by sand nourishments during the last decades. Next to it, other major interventions were built: the Delta Works, the construction with subsequent extension of the Maasvlakte harbour, and the Sulfter. Due to the strong anthropogenic impact, the assessment of the morphological evolution of the region is a complex task. Next to it, a number of natural morphological features along the coastline (i.e. sand waves and tidal channels) have a very large impact on the coastline development. Moreover, those natural features also interact with the different human interventions. It is therefore very important for coastal managers to account for their effect on the coastline morphology, while planning further interventions along the coast. In this study ,the morphodynamic development of the coastline of the South-Westerly Delta has been assessed using an indicator approach. In particular, the following indicators were used in the analysis: MKL, mean low and mean high water line, dune foot position, and probability of breaching. As part of this analysis, the impact of different natural morphological features has been analysed: the sand wave development along the entire coastline and the morphological development of a number of tidal channels. The impact of those features on the indicators has been assessed, in combination with the effects of sand nourishments and other antropogenic interventions. By looking at the past morphological changes and the effects of past nourishments, useful information is derived as a basis for planning of the future nourishments works.