Sand exchange between groyne‐field beaches and the navigation channel of the Dutch Rhine: the impact of navigation versus river flow

Abstract

AbstractThe morphodynamics of groyne‐field beaches along the Dutch Rhine was studied from in situ measurements of hydrodynamics and sand transport, aerial photographs, and bed‐level time series. From the analyses, it appeared that groyne‐field beaches experience an alternation of periods of erosion and deposition. The erosion is due to navigation at low to moderate discharge; the deposition is due to floods. On a time scale of a few decades, periods of erosion and deposition are in equilibrium. Navigation‐induced erosion is mainly due to vessels >60 m. The impact of passing vessels on the currents near the banks and the erosion of the beaches increases as underwater volume increases. Individually, loaded barge‐tows have the greatest influence on groyne‐field hydrodynamics and sand transport. On a yearly basis, however, the relatively strong influence of push towing is superseded by the higher frequency of passing motorized vessels. The erosion on a yearly basis, therefore, is driven by the effects of the large motorized vessels. The effects of push towing are negligible.Underwater volume and passing distance from the bank are the most important parameters of passages, insofar as their effect on groyne‐field beaches is concerned. The effect of underwater volume is clearly reflected in the different behaviour of groyne‐field beaches on the north and south banks. Loaded vessels sailing along the south bank from Rotterdam to Germany have a much greater effect on the beaches on the south bank than do returning vessels, often empty or partly loaded, on the beaches of the north bank. As a result, beach erosion on the south bank is twice as pronounced as the erosion on the north bank. Remarkably, the greater erosion of the beaches observed on the south bank was compensated by a similarly larger deposition during the flood of 1998.The impact of navigation on groyne‐field beach erosion increased strongly from 1970 to 2001, and probably will have doubled from 1970 to 2010. Copyright © 2004 John Wiley & Sons, Ltd.