Mud dynamics on the shoreface and upper shelf, Noordwijk, The Netherlands

Abstract

Mud dynamics on the shoreface were studied with measured mud concentrations in the water related to hydrodynamics and measured mud concentrations in the sandy bed. In addition, mud infiltration into the bed was modelled and mud inmixing into the bed by macro-benthos was assessed. The mud concentrations and the near-bed flow were measured for 2800 hours in the spring and autumn of 2003. The mud content of the top layer of the bed was studied from boxcores along a 20 km transect from upper shoreface (12 m depth) to upper shelf (20 m depth) and at various times over the year. Infiltration of mud into the sandy bed by pressure differences over bedforms is negligible. Mud inmixing into the bed is mostly coupled to macrobenthic activity, while re-entrainment is again coupled to the sand mobilisation during storms. Mud settling is modelled for a scenario sand extraction pit. The findings suggest that obliteration of the suspension feeding benthos within a sand pit will cause the mud to deposit on top of the sand bed rather than be mixed into the sand