Evaluation of sediment trap efficiency in an estuarine environment

Abstract

Trench-traps are utilized where sediment containment is a concern. In this study, trapping efficiency is key concern. A 60 m(L) x 300 m(W) x 2 m(D) trap was incorporated into the Cedar River, near the confluence with the Ortega River. A second trap of same dimensions was also incorporated 420 m upstream. Trap efficiency was calculated as a sediment removal ratio, or the percentage by which influent sediment load to the trap is reduced in the effluent load from the trap. Trap efficiency was carried out for varying Cedar River discharges. A specific discharge (16.4 cu m/s) was found to yield the maximum removal. At discharges above and below this discharge, the removal ratio decreases. This is attributed to the increase in tidal influence at lower discharges and velocities too large to allow settling at higher discharges. Future work includes developing a monitoring scheme to determine actual sedimentation rates in a test trap at the chosen location.