SPECTRAL DESCRIPTION OF SMALL SCALE WAVE FORMED RIPPLEDSEDIMENT BEDS

摘要

The formation of rippled sedimentary beds under the action of waves directly affects wave dissipation rates within shallow shelf seas by increasing the hydraulic roughness of the sea floor. Current methods to determine wave energy loss due to rippled beds have largely been based on simple empirical relationships for the roughness height of ripple forms generated under regular waves and have, for the most part, ignored the overall variability in ripple patterns and shapes across the sediment surface being studied. A new method is presented which describes rippled beds in terms of their two dimensional variance spectrum in a direct analogy to methods which describe the water surface in terms of its variance spectrum. The measured ripple spectra are compared with a traditional method to estimate ripple geometry from the water surface record. Differences in ripple spectra formed under different shaped water surface spectra and under different frequencies were investigated. The spectral representation of bed forms leads to a more complete description of the bed with bed-form differences due to the oscillatory wave properties being defined more clearly.