Fine-grained suspended sediment dynamics in the Eel River flood plume

Abstract

Small rivers (drainage basins <10 4 km 2 ) discharging runoff from mountainous terrain are major contributors of mud to the marine environment. However, little understanding of the dispersal mechanisms and fate of discharged fine-grained sediments to the continental shelf is known due to the episodic and unpredictable nature of discharge from these rivers. This study used a helicopter-based sampling program to capture unprecedented measures of Eel River, northern California, flood plume events during 1997, 1998, and 1999. In situ measures of floc size and estimated floc fraction show no relationship with concentration, turbulent-kinetic-energy, time from river mouth, wind speed, wave height, or discharge. A relationship apparently does exist between effective settling velocity (bulk mean settling velocity) of plume sediments and wind speed/direction, as well as with tides. Results implicate the energetic nearshore as a source of suspended sediment resupply to the offshore region of the plume. Future studies focusing on surf zone suspended fine-grained sediment dynamics are needed in order to understand the fate of flood plume sediments discharged to exposed, energetic shelves, such as the Eel River margin.