Progress made during a preliminary multidisciplinary study of the circulation and sediment transport on sand banks in the North Sea is described. The long term aims of the work are to quantify the role of linear sand banks in affecting nearshore processes and in providing protection to adjacent coastlines. The project has concentrated on evaluating technologies for the direct measurement of boundary layer processes with a view to mounting a future coordinated field measurement campaign on a typical nearshore bank system. 2 particular technologies have been studied in the laboratory and in the North Sea. Firstly, a special boundary layer rig, STABLE, has been used to measure nearbed processes, and secondly, a bed shear stress meter (SSM) has been developed for the direct field measurement of shear stresses in combined waves and tidal currents. The work shows that both technologies are capable of producing useful field data and that experience gained from the research will lead to improved design of future instruments. In addition, the new field data and associated work on the analytical description of wind, sea and swell spectra together with the computer modelling of bed form characteristics and nearbed hydrodynamics and suspended sediment movements has also extended knowlege of coastal processes near nearshore banks.
The work involves the deployment of an instrumented rig at the Brown Ridge Sand Wave site off the Dutch coastline and will enable the measurement of turbulence, wind waves, suspended sediment concentrations and the passage of bedforms using electromagnetic current meters, a pressure recorder, an acoustic backscatter probe and a time lapse camera, respectively. Separate to this, an acoustic Doppler current profiler, a bottom pressure recorder and a meteorological buoy will be installed close by, along with a vertical array of drogue net traps and current meters to measure the variations in the vertical current profile and suspended sediment flux. Further development of an existing bed shear stress meter is also proposed for use in wave-current boundary layers. Finally, using data collected from the test site and from a complementary MAST project (MAST-0025), existing flow and sediment transport models will be validated and updated. These models will, in turn, be used to assist with a better understanding of coastal morphology changes and their prediction being undertaken in the parallel MAST project MAST-0035.
Funding SchemeCSC - Cost-sharing contracts
L43 7RA Birkenhead
OX11 0RA Didcot - Oxfordshire