The state of the coast (Toestand van de kust). Case study: North Holland

Over more than a thousand years, the Dutch coast has been eroding for large stretches. Coastal retreat puts coastal functions (e.g. safety against flooding) under pressure. Since 1990, the Dutch policy aims at preventing further retreat of the coastline, but in the meantime taking the valuable dynamical behaviour of the coast into account. Therefore, sand nourishments have been preferred over hard structures to counteract the systematic erosion. The Dutch Government is responsible for the planning and realization of the nourishments. Deltares has been commissioned to develop the knowledge needed to carry out an effective nourishment strategy. Due to its strategic importance, the Dutch coastal area is also one of the most extensive studied areas in the world. However, most of the morphological research so far has focussed into the understanding of just part of the Dutch coastal system (e.g. dune area, foreshore). Hardly any attempt has been made to describe in a quantitative way the complete morphodynamic development of the system from the dunes to deep water and the cumulative effect of the past nourishment strategy at various time- and spatial scales. The aim of this study is the assessment of the functioning of the complete coastal system through a number of indicators describing the morphological system at different time scales. In particular, the relations between anthropogenic intervention (e.g. sediment management over the past 40 years, construction of hard structures), natural yearly variation in storminess and time variation of the indicators are assessed. As a case study, the North Holland coast has been analyzed. The study shows that the current nourishment strategy has lead to a clear shift in indicators related to safety, nature and recreation towards a "safer" coastline, with larger space suitable for nature and tourism . Hard structures also play a primary role into the morphological development of the coastline. The effect of the yearly variation in storminess appears to be correlated to a number of indicators (e.g. dune foot position). However, nourishments have contributed to damp the effect of these natural forcings. The results of different nourishment strategies applied in different areas have been intercom pared with the aim of assessing the most cost-effective management strategy. The present study is part of the project (KPP - Beheer en Onderhoud van de kust; Coastal Management and Maintenance). We would like to acknowledge comments and remarks from Gemma Ramaekers (Waterdienst) which have resulted into an improved manuscript. We would also like to thank the photo raph Jurriaan Brobbel for the picture on the cover.TAW/EN