A field investigation of the relationship between oscillation ripple spacinng and the near-bottom water orbital motions

Abstract

Abstract Measurements of oscillation ripples have been obtained in the high-energy wave environment off the Oregon coast, and in the relatively mild summer-wave environment near Fisher's Island, New York. Scuba-equipped divers measured ripple characteristics while the simultaneous causative near-bottom orbital motions were determined from a wave pressure transducer and electromagnetic current meter mounted near the bottom. The data collected in this study, together with previously published field measurements of oscillation ripples, are compared with empirical relationships for ripple geometry based on laboratory data. As expected, the field data are more scattered than the laboratory data. Reasons for this scatter include several wave spectral effects, ocean waves in the study areas having wide spectra in contrast to the simple harmonic motions of the laboratory devices. Any selected trend that relates the ripple spacing to the wave orbital motions must take into consideration this spectrum and the manner in which the orbital parameters are defined. Orbital parameters calculated from a significant wave height were found to give the best comparison with the laboratory results.