Bedform evolution under the combined influences of waves and currents at the inner-shelf MISO site

Abstract

Observations of the temporal evolution of waves, currents, and bed response data collected by an instrumented frame deployed in 12m of water at the Monterey Inner Shelf Observatory (MISO) off the coast of Monterey, California are analyzed in terms of measured wave and current forcing statistics and ripple geometry. During the year 2000, a Broadband Acoustic Doppler Current Profiler (BADCP) collected continuous wave and current measurements. Bed morphology was continually mapped by a Scanning Acoustic Altimeter (SAA) in a 1m alongshore by 1.5m cross-shore area immediately offshore from the MISO frame. Relict ripples were observed to dominate the bedforms throughout much of the year. Ripple growth in the alongshore direction was observed during conditions of marginally critical flow as defined by the critical combined wave and current Shields parameter. As flow conditions increased above the critical level, ripple growth in the alongshore direction ceased, and cross-shore wavelengths began to grow and dominate. Together, these observations and data sets are used to evaluate the applicability of existing ripple prediction algorithms. Altogether, five models are tested, and it was concluded that they could not independently predict the bed's response.