Rippled scour depressions on the inner continental shelf off central California

Side-scan sonar records taken during the recent Coastal Ocean Dynamics Experiment
(CODE) show elongate, shore-normal tippled depressions of low relief on the inner continental shelf
off central California between Bodega Bay and Point Arena. These features extend up to 2 kin from
the coast into water depths of up to 65 m. The proposed mechanism for their generation is storm-
generated bottom currents associated with coastal downwelling during the late fall and winter which
scour the surficial fine-sand sediment and expose the coarser-sand substrate in the depressions. The
zones of most intense erosion and the irregular spacing of the features may be controlled by submerged
rock ledges and other prominent coastal features. The large straight-crested ripples within the depres-
sions (heights to 40 cm; wavelengths to 1.7 m) are probably formed by large-amplitude, long-period
surface waves generated by winter storms.