Short Term Morphological Impact of the Eierlandsedam

After decades of coastal erosion in the north-west area of the Island of Texel, the shore-normal `Eierlandse Dam` had been built in 1995. The dam, situated in the outer delta of the Eierlandse Gat tidal inlet, resulted in a remarkable short-term morphological development of the adjacent coast. Four years following completion of the dam, large sedimentation rates were measured on both sides of the dam. On the updrift (south) side, sedimentation was predicted as a result of the blocked alongshore sediment transport. However, on the downdrift (north) side of the dam, no sedimentation was predicted. Today, almost two decades later, it remains unclear which processes contributed to the sediment accumulation on the north side of the dam. The increased functionalities and capabilities of the present-day modelling software enable a re-evaluation of the morphological processes around the dam in particular, and gain insights in the complex short-term morphodynamics in this area. To capture the driving mechanism(s) of the net sediment transport towards the northern area of the Eierlandse dam, the state-of-the-art process-based computational model Delft3D is applied. To investigate the influence of various conditions and processes on the morphological development around the dam, simulations are performed with various boundary conditions, model processes and formulations. After calibration of the model, one-year morphological predictions show large similarities with the observed bed level development at both sides of the dam. The ebb tidal currents seem responsible for the large amounts of sedimentation at the north side of the dam, predominantly during spring tides when flow velocities and tidal excursion increase. The ebb tidal channel `Robbengat` is located along the northern tip of the Island of Texel and curves from the inlet around the Eierlandse dam. The Robbengat channel has been eroding by strong ebb tidal currents since 1985. The eroded sediments of the channel are transported by the flow towards the outer delta. Before the channel curves, the flow is partly deflected towards the northern area of the Eierlandse dam. The flow enters a shallow area and decelerates, resulting in deposition of sediment. This conclusion rejects the conclusions drawn by previous studies regarding the same area, where complex hydrodynamics such as eddy forming and spiral flow in the channel bend were drawn as possible causes of the sedimentation.Hydraulic EngineeringCivil Engineering and Geoscience