Dunefoot dynamics along the Dutch coast

Abstract

The dynamics of the dunefoot along a 160 km portion of the Dutch coast has been investigated based on a data set of annual surveys dating back to as early as 1850. The linearly detrended (or residual) dunefoot positions comprise an alongshore uniform and an alongshore non-uniform component. The former is expressed as 10 to 15 m of landward retreat along extensive (>10 km) stretches of coast during years with severe storm surges and as up to 5 m of seaward advance during years without significant storm activity. The latter, alongshore non-uniform component is organized in sandwave-like patterns, which may have a longevity of decades to up to the duration of the entire data set (150 years). Their wavelengths vary along the coast, from 3Ð5 to 10 km; migration rates are 0-200 m a 1 . Dunefoot sandwaves are shown to be the shoreward extensions of similar sandwave patterns in the beach position. The non-uniform dunefoot behaviour constitutes at least 80 per cent of the total residual dunefoot dynamics, implying that along the Dutch coast residual dunefoot variability is controlled by temporal and spatial variability in beach characteristics, and not by storminduced uniform erosion. Various potential mechanisms causing beach sandwaves are discussed.

The effect of climate change on extreme waves in front of the Dutch coast

“…The February 1953 storm, during which the dune foot retreated by 10-20 m along large parts of the Dutch coast (e.g. Ruessink and Jeuken 2002), resulted in a coastal policy in which the safety of the dunes to withstand an event with a 1:10,000 probability is assessed every 4-6 years (Kabat et al 2009). Laboratory experiments (e.g.…”

“…The aforementioned 99th percentile, for example, implies wave conditions that happen on 3-4 days each year. For dune erosion, we should look at events with 1:1-to 1:10-year return value (Ruessink and Jeuken 2002;Quartel et al 2008) or even smaller, such as the 1:10,000-year value prescribed in Dutch coastal policy.…”

Modeling shoreline sand waves on the coasts of Namibia and Angola

“…Further north, there are some long stretches of sandy coasts downdrift of river deltas. Whilst on other coasts around the world shoreline undulations can only be observed after analysis of detailed measurements of the shoreline position (Verhagen, 1989;Ruessink and Jeuken, 2002), the undulations on this African coast can be clearly observed from a quick survey of satellite images. Most striking are the large spits of Walvis Bay and Sandwich Bay and a large scale shoreline sand wave located in the north of the coast of the Namib Sand Sea (Fig.…”

“…The undulations do not only occur in the shoreline position but the bathymetric contours also undulate with decreasing amplitude up to a certain depth. Shoreline sand waves are episodically or persistently found along various sandy coasts around the world (Bruun, 1954, Verhagen, 1989Inman et al, 1992;Thevenot and Kraus, 1995;Gravens, 1999;Guillén et al, 1999;Stive et al, 2002;Ruessink and Jeuken, 2002;Davidson-Arnott and van Heyningen, 2003; Medellin et al, 2008; Alves, 2009).…”

“…The undulations do not only occur in the shoreline position but the bathymetric contours also undulate with decreasing amplitude up to a certain depth. Shoreline sand waves are episodically or persistently found along various sandy coasts around the world (Bruun, 1954, Verhagen, 1989Inman et al, 1992;Thevenot and Kraus, 1995;Gravens, 1999;Guillén et al, 1999;Stive et al, 2002;Ruessink and Jeuken, 2002;Davidson-Arnott and van Heyningen, 2003; Medellin et al, 2008; Alves, 2009).Shoreline sand waves can be triggered by different physical mechanisms, including forcing by offshore bathymetric anomalies (Gravens, 1999) or periodic input of large quantities of sand due to inlets and rivers (Thevenot and Kraus, 1995). However, sand waves can also emerge from small irregularities of an otherwise rectilinear coast in absence of any forcing at its wavelength.…”