Worldwide along several sandy beaches coastal erosion is a serious threat when the hinterland is densely populated or cultivated. The hinterland can be protected by taking hard engineering measures (e.g. groins or piers), but also by co-called soft engineering solutions like nourishing the near-shore or the beach with sand. Normally such nourishments protect against coastal retreat for several years, but are no long term solution.
Recently a new concept was introduced, named mega-nourishment. Such a mega- nourishment should feed adjacent beaches for decades. Besides efficiency a mega-nourishment should also be more attractive from an economic, environmental and recreational point of view. A pilot study is the Sand Motor, a hooked-shape peninsula in front of the Holland coast (map). To prove the functioning of a mega-nourishment as coastal defense the morphologic evolution needs to be studied. When successfully proven, the concept of a mega-nourishment can be applied at threatened coasts worldwide.
The aim of the PhD project is to understand predictively the morphological evolution in the sub- and intertidal zone of a mega nourishment on timescales of days to years. Morphologic change will be traced by traditional measurement techniques, but also by video, radar and laser observations. The several data sources combined in bathymetric maps will be used in numerical modeling.
The Sand Motor nourishment (www.dezandmotor.nl) is a pilot study testing the concept of a mega-nourishment as coastal defense. The Sand Motor is located in between Hoek van Holland and Scheveningen, along the Holland coast.
Morphologic change at timescales of years can be studied by traditional techniques like jetski measurements of bottom elevation. Hourly video and radar observations will help to understand the sediment distribution on timescales of days to months. Sandbar and shoreline position can be extracted from video and radar images and used as indicator for morphologic change. Recent development on a bottom estimation algorithm using video observations offers the possibility to also quantify the morphologic change on day-month timescales. Bottom estimates from video and radar observations will be combined in a single bathymetric map, every few hours.
Next to a field experiment in autumn 2014, a morpho-dynamic numerical model will be used to test which processes are driving the sediment redistribution around a mega-nourishment. The bathymetric maps derived from video and radar observations will be used iteratively to steer the numerical model.
The PhD project started in April 2013. A first publication will be on the accuracies of the morphological dataset, collected by traditional and remote sensing techniques. The publication can be expected in 2014.
The PhD research is part of the Nature Coast project, in which 12 PhD students and 3 postdocs look to different aspects (coastal safety, dune formation, marine ecology, terrestrial ecology, hydrology & geochemistry and governance) of the Sand Motor and its functioning.