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Seminar- Modeling and predicting sediment dynamics in a heavily used estuary for historic, modern, and future bathymetries

Emily Eidam
Emily Eidam
Department of Marine Sciences
University of North Carolina at Chapel Hill
261 Marine Science Bldg.

Estuaries provide critical habitat for eelgrass, oysters, and other species, and also serve as natural sediment traps. The sediment regimes of many modern estuaries are evolving, however, in response to land use changes, shoreline alterations, dredging, and other human impacts. In order to assess hydrodynamics and sediment dynamics in the Coos Bay Estuary (Oregon), we used an unstructured finite-volume model (FVCOM) and multi-year measurements of water velocities, salinities, and turbidities to re-construct patterns of water and sediment flow. Despite relatively low inputs of sediment and strong tidal forcing, a ~10-km-long estuarine turbidity maximum (ETM) persists in the upper estuary, in association with a pool of bottom sediment which requires annual dredging. Rainstorms generate 10-fold increases in the strength of the ETM, but tidal currents flush this new material to the lower reaches of the estuary within 3 weeks. These patterns of sediment transfer have been impacted by channel constriction and deepening projects dating to the late 1800s, and are expected to change in the future pending the approval of a channel deepening project. Together with stakeholder groups including federal reserve managers, tribal resource managers, port managers, and engineering consultants, we are working to use historic and proposed bathymetry to evaluate the evolution of hydrodynamics and sediment dynamics dictated by bathymetric changes, in order to inform management planning for the estuary.

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