CYCLIC BEHAVIOR OF A SHOAL-CHANNEL SYSTEM IN THE WESTERN SCHELDT ESTUARY

Many tidal embayments feature shoals that cyclically form and migrate in a specific direction. The period between successive formations of shoals varies among the tidal embayments. This cyclic behavior characterizes many ebb-tidal deltas seaward of tidal inlets. However in tidal estuaries such as the Western Scheldt, cyclic behavior occurs as well. This is shown in Figure 1, which presents the morphological evolution of the seaward area of Western Scheldt near Vlissingen between 1974 and 2012. Initially, a shoal detaches from the northern part of the shoal “Hooge Platen”, which starts to migrate towards north until it merges with the northern shoal (“Spijkerplaat”). Subsequently, a new shoal detaches again and start to move north. The period between the successive shoal detachments is approximately 30 years. Beside shoal migration, the adjacent northern channel (“Schaar van Spijkerplaat”) also migrates in the northern direction (indicated by the circles). The northern migration of the shoal-channel system is also visible in Figure 2, which shows the evolution of the bedlevel along a cross-channel transect (red dashed line in Figure 1) between 1964 and 2014. While previous research has mainly focused on understanding the cyclic behavior of shoals in tidal inlet systems, little is known about the mechanisms underlying the cyclic behavior of shoals and channels in estuaries. The overall aim of this study is to quantify the physical mechanisms that are responsible for the observed migration of the shoal-channel system in the Western Scheld

CYCLIC BEHAVIOR OF A SHOAL-CHANNEL SYSTEM IN THE WESTERN SCHELDT ESTUARY

Many tidal embayments feature shoals that cyclically form and migrate in a specific direction. The period between successive formations of shoals varies among the tidal embayments. This cyclic behavior characterizes many ebb-tidal deltas seaward of tidal inlets. However in tidal estuaries such as the Western Scheldt, cyclic behavior occurs as well. This is shown in Figure 1, which presents the morphological evolution of the seaward area of Western Scheldt near Vlissingen between 1974 and 2012. Initially, a shoal detaches from the northern part of the shoal “Hooge Platen”, which starts to migrate towards north until it merges with the northern shoal (“Spijkerplaat”). Subsequently, a new shoal detaches again and start to move north. The period between the successive shoal detachments is approximately 30 years. Beside shoal migration, the adjacent northern channel (“Schaar van Spijkerplaat”) also migrates in the northern direction (indicated by the circles). The northern migration of the shoal-channel system is also visible in Figure 2, which shows the evolution of the bedlevel along a cross-channel transect (red dashed line in Figure 1) between 1964 and 2014. While previous research has mainly focused on understanding the cyclic behavior of shoals in tidal inlet systems, little is known about the mechanisms underlying the cyclic behavior of shoals and channels in estuaries. The overall aim of this study is to quantify the physical mechanisms that are responsible for the observed migration of the shoal-channel system in the Western Scheld

A Rational Method for the Design of Sand Dike/Dune Systems at Sheltered Sites; Wadden Sea Coast of Texel, The Netherlands

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A Rational Method for the Design of Sand Dike/Dune Systems at Sheltered Sites; Wadden Sea Coast of Texel, The Netherlands

A rational method for the design of sand dike/dune systems at sheltered sites is presented, focussing on the cross-shore dimensions of the sand dike in relation to the local wave climate, tidal regime and available sandy materials. The example case is the new sand dike/dune system along the south-east coast of Texel, The Netherlands. The old dike protecting the island was not sufficiently strong to withstand an extreme storm event and has been strengthened by a new sand dune/dike. Various empirical and numerical models have been used, compared and validated to determine the erosion volumes during annual conditions and extreme storm events. Potential wind-induced (aeolian) sediment transport and erosion is also studied using the modified Bagnold-equation including the effects of grain size, moisture content and vegetation. The overall design method resulted into an innovative design solution, guarantying a naturally integrated and resilient sand protection as well as optimal coastal safety

Modelling the past and future evolution of tidal sand waves

This study focuses on the hindcasting and forecasting of observed offshore tidal sand waves by using a state-of-the-art numerical morphodynamic model. The sand waves, having heights of several meters, evolve on timescales of years. Following earlier work, the model has a 2DV configuration (one horizontal and one vertical direction). First, the skill of the model is assessed by performing hindcasts at four transects in the North Sea where sand wave data are available of multiple surveys that are at least 10 years apart. The first transect is used for calibration and this calibrated model is applied to the other three transects. It is found that the calibrated model performs well: the Brier Skill Score is ’excellent’ at the first two transects and ’good’ at the last two. The root mean square error of calculated bed levels is smaller than the uncertainty in the measurements, except at the last transect, where the M2 is more elliptical than at the other three transects. The calibrated model is subsequently used to make forecasts of the sand waves along the two transects with the best skill scores

Modelling the past and future evolution of tidal sand waves

This study focuses on the hindcasting and forecasting of observed offshore tidal sand waves by using a state-of-the-art numerical morphodynamic model. The sand waves, having heights of several meters, evolve on timescales of years. Following earlier work, the model has a 2DV configuration (one horizontal and one vertical direction). First, the skill of the model is assessed by performing hindcasts at four transects in the North Sea where sand wave data are available of multiple surveys that are at least 10 years apart. The first transect is used for calibration and this calibrated model is applied to the other three transects. It is found that the calibrated model performs well: the Brier Skill Score is ’excellent’ at the first two transects and ’good’ at the last two. The root mean square error of calculated bed levels is smaller than the uncertainty in the measurements, except at the last transect, where the M2 is more elliptical than at the other three transects. The calibrated model is subsequently used to make forecasts of the sand waves along the two transects with the best skill scores