SMALL-SCALE MORPHOLOGY ACROSS THE SURF ZONE

Small-scale (<5 m horizontal length) nearshore morphologic height vari ations were measured by combining CRAB surveys with bed elevations acq uired with a 1 MKz sonic altimeter mounted on the CRAB during the Octo ber Phase of the DUCK94 experiment. Bedform plan views were recorded s imultaneously using a 500 kHz side-scan sonar mounted on the CRAB. Wav es and currents were measured at the same time. Significant temporal a nd spatial variations in the small-scale morphology were measured in r esponse to changing waves and currents during the 2 weeks examined. Th ree cases are examined in detail: (1) mild waves and weak longshore cu rrents resulting in wave ripples throughout the study area; (2) storm waves with strong longshore currents resulting in lunate and straight- crested mega-ripples in the trough of the barred beach; and (3) narrow -band, normally incident waves with a strong rip current resulting in a planar bed except in the throat of the rip where mega-ripples were m easured. Wavenumber spectra of the bed were generally broad, indicatin g newly formed ripples coexisted with residual ripples from the past t o form complex, multi-scaled ripple patterns. (C) 1998 Elsevier Scienc e B.V.