Description
Bedforms and sediment studies were conducted using S.C.U.B.A., during Southern California's winter and summer seasons in the nearshore environment at La Jolla, California. The seasonal variations at the time of this study were limited in that, swells characteristic of the summer season were few if not absent. Observations yielded no significant changes in oscillation ripples from the start to the end of the study. The presence of troughs occurred in the latter half of the study. The deeper location of fresh ripple marks in the beginning of the study was evidence of the larger swells that had previously hit La Jolla Bay in January, 2000. The inactive zone, which roughly extends from about 40 feet of seawater (fsw ), westward to deeper depths of the canyon, was characteristic throughout the summer season. Bedforms found at the head of La Jolla Canyon include symmetrical and asymmetrical oscillation ripples, troughs, sheet-flow structures and backwash ripple marks. The oscillation ripple wavelengths range from 6 to 20 cm with heights from 0.5 to 4 cm Oscillation ripple marks of these wavelengths are consistent with the sediment size as indicated by Inman ( 1957). Sediment analyses indicate that the shelf and nearshore environments consist of well-sorted, near symmetrical, fine sands. The beach foreshore contains well-sorted, positively skewed, fine sands. Extremes are present in both the troughs and crests of the ripple marks found at depths from 10 to 35 feet. Sediment analyses of the troughs found the worst sorting of all environments when shell fragments were included in the distribution parameters. When reanalyzed without the shell fragments, they generally contained the finest particles and were well-sorted. Ripple crests are well sorted and contain the coarsest particles. The best-sorted environments are the swash zone and beach face.
