Bedforms and their effect on sediment transport on ebb-tidal deltas

Abstract

In order to manage the Wadden coast and protect it against sea level rise, it is important to understand the natural behaviour of the system. Seaward of the inlets between the Wadden Islands are relatively shallow sand bodies: the ebb-tidal deltas. In between the ebb-tidal deltas are deeper channels. Both on the ebb-tidal deltas and in the channels the sea bed is not flat; rhythmic patterns are formed in the sand, which are called bedforms. Bedforms occur on various spatial scales, with heights and lengths ranging from centimeters to meters and hundreds of meters. These bedforms affect the water flow and the transport of sand, and in turn they are affected by the waves and currents on the ebb-tidal delta. In this thesis, bedforms and their behaviour are described on three spatial scales. After that, the bedform characteristics are compared to those predicted by existing bedform predictors. Such predictors are often incorporated in numerical models that are used to predict the behaviour of the coast. One of these models was also tested in this thesis, and it was studied how the way in which bedforms are parameterized in the model affects the predicted sand transport. The results of this thesis improve our understanding of the sediment transport pathways on ebb-tidal deltas, and will thus give a solid knowledge base for future coastal management and protection measures.