Long-term morphodynamic evolution of Texel Inlet and its ebb-tidal delta (The Netherlands)

Abstract

A series of regular bathymetric surveys of Texel Inlet and its ebb-tidal delta spanning a period of over 400 years forms a unique long-term morphodynamic dataset of this largest inlet of the Wadden Sea. The substantial changes in ebb-tidal delta evolution provide a clear example of the response of the inlet system to the cumulative effects of human intervention. Analysis of the evolution of the ebb-tidal delta morphology shows different stages, each characterized by specific orientations of the main channels and shoals. Prior to construction of extensive coastal defense works on the southern shore of the inlet in 1750 A.D., the ebb-tidal delta showed a downdrift asymmetry. Periodic shoal breaching and downdrift channel relocation were the dominant mechanisms for sediment by-passing (major shoal bypassing). After construction of the coastal defence works, a stable ebb-tidal delta with a westward stretching main ebb-channel developed over a period of ca. 60 years. Damming of the Zuiderzee, the major part of the back-barrier basin in 1932 A.D., distorted this stable state and over a period of about 40 years the main channel switched to a southward course, remaining stable ever since. During the pre- and post-damming stable states the sediment bypassing took place as minor shoal by-passing; the main channel remained in position and smaller parts of the swash platform (periodically) migrated landward over the ebb-tidal delta. The well-monitored large-scale changes on the ebb-tidal delta which were initiated by the construction of the coastal defence works and closure of the Zuiderzee show that incorporation of inlet modifications and back-barrier processes is vital for a correct description of the ebb-tidal delta dynamics and processes of Texel Inlet. A conceptual model is introduced to describe the process–response relation between intervention and ebb-tidal delta change.