" SAND ENGINE " : BACKGROUND AND DESIGN OF A MEGA-NOURISHMENT PILOT IN THE NETHERLANDS

Abstract

Coastal policy in the Netherlands is characterised by three scale levels. The smallest scale is aimed at the preservation of safety agaisnt flooding by maintaining a minimum dune strength; the middle- and large scales at preservation of sustainable safety and of functions in the coastal zone by maintaining the coast line, respectively the sand volume in the coastal foundation. The definition of three scales basically implies a pro-active approach, based on the idea that the larger scale sets boundary conditions for the smaller scale. This pro-active approach appears to be succesful: nourishments since 1990 not only have resulted in maintaining the coast line, but also in an extension of the dunes, contributing to an increased safety against flooding. The succes has been achieved by a yearly nourishment volume of 12 Mm3. Recent studies have indicated the need to upscale the yearly averaged nourishment volume. A recent update of the sediment balance of the coastal foundation shows a negative total of ca. 20 Mm3 per year; so apparently 12 Mm3 nourishments per year is insufficient to maintain the total active sand volume of the system. Besides, in a study on future adaptation options to climate change in the Netherlands, the authoritive Deltacommissie (2008) even recommends a raise of nourishment budgets up to 85 Mm3/year until the year 2050, taking into account an ultimate worst case scenario of a sea level rise of 13 cm in 2100. To investigate innovative ways of nourishing larger volumes of sand, a Pilot project Sand Engine has been developed. The pilot implies a mega-nourishment of approximately 20 Mm3 (~ 10000 m3/m) on the coast of Holland, between Hook of Holland and The Hague. In the design phase of the pilot, a morphodynamic Delft3d model has been used to calculate morphological effects of several alternatives. The Environmental Impact Assessment EIA has decided on a shore attached cross shore bar with a length of ca. 1.5 km, as the preferent alternative. Implementation is planned for 2011, starting december 2010.