J.S. Reedijk

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Master thesis (1)

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The influence of an Ecobeach PEM on beach development

Master thesis (2009) - J.J. Pieterse (author) , S. De Vries (mentor) , V.E.A. Post (mentor) , J.S. Reedijk (mentor) , M.J.F. Stive (mentor) , T.N. Olsthoorn (mentor)

Since the end of 2006 in the Netherlands a test is going on with a passive beach drainage system called Ecobeach. The system consists of vertical draining tubes with a length of 2.0 m called PEMs (Pressure Equalizing Modules). Under the surface level, every 100 m a row of PEMs is installed between the high and low waterline. Ecobeach is a Danish invention and the inventor claims that at beaches at different places around the world the volume of sand is increased thanks to the PEMs. This “drainage system” differs from other beach drainage systems in the way that normally horizontal drains are being placed under the beach, connected by a pump. When the Dutch test started very little was known about the functioning of the PEM system. For this reason scientific research to the PEMs was being started in September 2008. First the situation in the test area is examined. The beach, and especially the swash zone, is a complex area, influenced by tides, waves, sediment transport and groundwater flows. Five hypotheses are formulated of the influence PEMs can have on their environment. If a PEM can influence the groundwater behaviour in its direct vicinity, a process can be initiated which has an effect on the total beach. The initial events, caused directly by the PEMs, have to be studied in the field to make clear if the different hypothesised processes are realistic. Moreover consequences of the possible processes initiated by the PEMs should be recognized if anything happens. For this reason a fieldwork is executed in August-September 2009. Measurement results of the groundwater behaviour in the vicinity of PEMs show that some hypotheses are unlikely, and some are still questionable. An analysis of the sediment in and around the test area makes clear that possibly a process is going on in the Ecobeach test area, which could be a result of the PEMs. Because this study will be continued, this report shows an initial study to a very complex system. It shows the setup of a large study, interesting analysis methods and surprising results. Nevertheless it will lead sometimes to new questions.