Quantified and applied sea-bed dynamics of the Netherlands Continental Shelf and the Wadden Sea

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Sedimentary coasts and shallow-sea beds may be dynamic. The large-scaled spatial variation in these dynamics and the smaller-scaled behaviour of individual marine bedforms are largely unknown. Sea-bed dynamics are relevant for the safety of shipping, and therefore for monitoring strategies, and for offshore engineering projects and archaeological investigations. To date, sea-bed dynamic studies in the North Sea that are based on high-resolution echo soundings are mostly local. Recently, sufficient time series of modern, digital echo sounder surveys have become available to allow for a Netherlands Continental Shelf-wide quantification of vertical dynamic trends as well as for the detailed analysis of the morphodynamics of marine bedforms. Results show that (i) tidal channels, estuaries and longshore bars are particularly dynamic, (ii) the shelf offshore is less dynamic in general, and (iii) the most dynamic zones offshore are the zones where marine bedforms occur. The occurrence of superimposed sand banks, long bed waves, sand waves and megaripples is limited to the sandy shelf and sand wave migration rates vary spatially between 0 to 20 m/year. This spatial knowledge of morphodynamics is used in combination with environmental conditions and sea traffic to validate and to optimise re-survey policies.