Measurements and Computation of Wave Spectral Transformation at Island of Sylt, North Sea.

摘要

Wave spectra were measured in the nearshore region extending approximately 900 m from the shore at the Island of Sylt (North Germany) in the North Sea. Seven gage stations were in operation for a period of two weeks in May, 1976 for data collection. The field results were presented and compared with numerical computations for energy transformation in shallow water, based on a method developed earlier for the same project. The numerical computation agreed well with the field data in the range of energy-containing wave components and low frequency components but failed in high frequency range. Based upon commonly-used wave instability criteria, an equilibrium energy spectral density function in water of finite depth has been developed. This function provides saturation conditions on spectral density for the complete spectrum. Comparison with field data is encouraging but, nevertheless, inconclusive. Combining field evidence and numerical results, an assessment has been made on the wave climate of the test area. It was demonstrated that the offshore bar located in the test area plays a double role as energy dissipator and trapper. It was also shown that waves from the N-W quadrant are more effective in generating longshore current and thus in longshore material transport. (Author)