Case Study: Sediment Transport in Proposed Geomorphic Channel for Napa River

A model study evaluates sediment transport in a geomorphic channel proposed for restoration and flood damage reduction of an 11-km tidally influenced reach of the Napa River located in California. The model study employs the unsteady quasi-2D hydrodynamic and sediment transport model MIKE 11, the simplified marsh plain accretion model MARSH 98, and the Rouse equation to predict annual average morphological changes of the geomorphic channel. The adopted modeling approach allows for the simulation of salient sediment transport processes in a river estuary, including lateral and vertical sorting of sediments, and local flushing of fine cohesive and noncohesive sediments during flooding. Accretion rates, particularly within the marsh plain terrace of the multistage channel, are found to be within acceptable limits for project maintenance and ecosystem restoration purposes. This enhanced 1D modeling approach may offer a viable and cost-effective alternative compared to fully 2D and 3D models, with relatively less model set-up and run-time requirements.