| dc.description.abstract | The Dutch Holland Coast is an important protection to the sea. Along the Dutch Holland Coast, high and steep dunes act as a primary defense against flooding the hinterland. Dunes are accretionary landforms and show much variation as a result of wind, waves, fetch length and nearshore bathymetry. In order to get a better understanding alongshore variations in foredune development, the present study aims to identify the factors that control alongshore variations in foredune development.
The alongshore variations in foredune development along the Dutch North Holland Coast (DNHC) are studied between 2007 and 2016, using the coastal LiDAR dataset. The dataset consists of 3-D point clouds which are processed and computed into 1x1 m Digital Elevation Models (DEM’s). These DEMs are used to calculate for each cross shore transect the foredune volume(V), foredune volume change(∆V) and dune elevation(Z). The data is used to calculate volumetric changes in m3/m. As a first step we focus on landscape scale along-shore variations (20-100 km). Next, we investigate regional (1 km – 10 km) variations from the landscape scale. Finally, we investigate local (100 -500 m) differences from the regional trends and investigate possible causes.
The following research question is answered: What causes the alongshore variation in foredune (volume) development along the Dutch Holland Coast?
The study shows high variability in alongshore foredune development of (∆V) on all scale-levels (landscape, regional and local). On landscape scale the overall ∆V is +9,4 m3/m/year, on regional scale +10,5 m3/m/year and ranging from around -1 m3/m/year (blowouts) to +11,2 m3/m/year (constructions on the beach). The most pronounced variation at landscape scale is found between the regions of Castricum aan Zee-Camperduin, the Hondsbossche Dunes and the Kop van Noord-Holland, with ∆V raging from approximately +8 m3/m/year to +10 m3/m/year. On regional scale the most pronounced variation on foredune development is caused by the presence of coastal towns and more natural areas. The differences in coastal zone management contribute here to an average development of ∆V at coastal towns and developed sections of +11,3 m3/m/year and +10,1 m3/m/year at more natural sections. Features that cause variations in the present study on local scale are blowouts and constructions on the beach. Blowouts show a clear effect on volume development prior to and after the blowout, with an averaged value of +8.1 m3/m/year and +4.2 m3/m/year after the blowout. At the blowout itself, negative values are observed (-0,9 m3/m/year). Volumetric development at constructions on the beach roughly coincides with the general alongshore trend.
When linking foredune volume development to metrological conditions, major storms such as the Sinterklaasstorm (2013-2014) do have a considerable effect on foredune volume development, but the safety boundary level is always maintained. Following these storms, more natural areas show a much quicker recovery rate although being also the most affected by erosion. Blowouts respond to storms, especially high-water levels. The present study gives a confirmation of the usability of the LiDAR dataset (part of the JARKUS dataset) and the possibilities of mapping alongshore erosion and accretion in foredune behavior along the Dutch Holland Coast on landscape-scale and on regional-scale. At local-scale the time interval of measurements is too long to analyze small and very local variation. The study highlights and acknowledges the general consensus on dynamic foredune management strategies and their effects. Furthermore, insights are gained in the alongshore development of blowouts and how they affect alongshore foredune volume development, but only crude regularities are estimated. Not many studies have been conducted addressing the alongshore development of blowouts, instead studies have focused on all the dynamics inside blowouts. The insights that are gained are rudimental but could be used to learn more lessons about natural forcing properties on foredune volumes. | |
