Coastal fine-grained sediment plumes from beach nourishment near Santa Barbara, California

Abstract

Terrestrial sediments captured by flood control facilities such as dams, debris basins, and engineered stream channels can reduce sediment fluxes to littoral cells. The beneficial use of these sediments for beach nourishment may induce negative environmental effects from turbidity or sedimentation caused by the source material. Here, we examine the size and extent of turbid coastal plumes produced by beach nourishment with sediment containing significant fine-grained (silt and clay) fractions near Santa Barbara, California, to evaluate the potential effects of beneficial use of fluvial sediment captured in upstream facilities. Using remotely sensed imagery and hydrodynamic and sediment transport model simulations, we find that wave height, wind speed and direction, and sediment settling velocity have strong controls on the direction and extent of the turbid plume produced by beach nourishment. These results are consistent with monitored nourishment projects, suggesting generalizable patterns and processes across the studies. Additionally, we find that sediment placement method (hauling versus dredging) can influence the magnitude and duration of fine-sediment concentrations in the adjacent coastal waters. Combined, these results will inform sediment management strategies that intend to minimize the environmental effects of beach nourishment within the study area and across similar coastal sites.