Shoreline evolution of the Holland coast on a decadal scale

The decadal evolution of the dunefoot position along 120 km of the Holland coast is analysed. Firstly, a new definition of dunefoot is introduced based on hydrodynamic and morphologic considerations, which is not affected by local and instantaneous processes occurring immediately before the bathymetric survey. The dunefoot evolution over decadal scales indicates the existence of spatial and temporal oscillations in the shoreline position with magnitudes of 2–3 km length and a periodicity of 4–15 years. Two main controlling factors of this behaviour are identified: (1) influence of sub-aqueous bar systems, and (2) changes in the storm-wave conditions reaching the coast. Although the precise controlling processes of the relation between the dunefoot and the subaqueous profile still remain unclarified, we introduce the concept that the development of a morphological bar cycle requires a fixed amount of time-integrated forcing that is proportional to the cumulative effect of storm waves. Beach mobility along the Holland coast on decadal scales (10–20 m) is similar or lower than mobility introduced by storms or by seasonal cycles. However, it is important to consider these changes for the possible implications on the local vulnerability of the coast to extreme events. Copyright © 1999 John Wiley & Sons, Ltd.