Sediment Tracer Tracking and Numerical Modeling at Coos Bay Inlet, Oregon

An investigation was conducted on transport of dredged material placed in the nearshore area of an ocean dredged material disposal site (ODMDS) adjacent to the Coos Bay inlet, Oregon. A sediment tracer release/sampling and field data collection program was carried out and a numerical hydrodynamic, wave, and sediment transport model, the Coastal Modeling System, was developed to perform the analysis of sediment transport around the inlet system and the ODMDS. The data were used to calibrate and validate model calculations, and the model was set up to calculate sediment fluxes and to simulate the process of sediment tracer release and movement, and determine the pathways of sediment tracer under combined wave, current, and wind conditions within and around the immediate vicinity of the Coos Bay ODMDS. The calculations and the measurements indicate that sediment tracer movement is primarily controlled by tidal current inside Coos Bay and at the inlet entrance, and responding to wave and storm conditions in the open coastal area. A divergence in net sediment transport directions in the adjacent nearshore beach was apparent in the results of the tracer release and numerical simulations. This methodology may be used to determine sediment bypassing pathways and optimal placement of sediment within a nearshore environment adjacent to tidal inlets.