Understanding sediment bypassing processes through analysis of high-frequency observations of Ameland Inlet, the Netherlands

Abstract

Ameland inlet is centrally located in the chain of West Frisian Islands (the Netherlands). A globally unique dataset of detailed bathymetric charts starting in the early 19th century, and high-resolution digital data since 1986 allows for detailed investigations of the ebb-tidal delta morphodynamics and sediment bypassing over a wide range of scales. The ebb-tidal delta exerts a large influence on the updrift and downdrift shorelines, leading to periodic growth and decay (net erosion) of the updrift (Terschelling) island tip, while sequences of sediment bypassing result in shoal attachment to the downdrift coastline of Ameland. Distinct differences in location, shape and volume of the attachment shoals result from differences in sediment bypassing, which can be driven by morphodynamic interactions at the large scale of the inlet system (O(10 km)), and through interactions that originate at the smallest scale of individual shoal instabilities (O(0.1 km)). Such shoal instabilities would not be considered to affect the ebb-tidal delta and inlet dynamics as a whole, but as we have shown in this paper, they can trigger a new sediment bypassing cycle and result in complete relocation of channels and shoals. These subtle dynamics are difficult, if not impossible, to capture in existing general conceptual models and empirical relationships. These differences are, however, essential for understanding tidal inlet and channel morphodynamics and hence coastal management.