The Deschutes Estuary Restoration Feasibility Study: development of a process-based morphological model

Continual sediment accumulation in Capitol Lake since the damming of the Deschutes River in 1951 has altered the initial morphology of the basin. As part of the Deschutes River Estuary Restoration Feasibility Study, the United States Geological Survey (USGS) is modeling how tidal and storm processes will influence the river, lake and lower Budd Inlet should estuary restoration occur. Understanding these mechanisms will assist in developing a scientifically sound assessment on the feasibility of restoring the estuary. We are using a process-based sediment transport model, Delft3D, to simulate conditions prior to dam construction and the accumulation of sediment subsequent to dam construction. Potential changes in hydrodynamics and sediment transport after dam removal will also be modeled. Key components of the model include tidal currents, density-driven circulations, cohesive and non-cohesive sediment transport and bathymetric change. Model results will be compared to historical and recent field data consisting of bathymetric surveys and bottom sediment classification. Future modeling work will incorporate simulation of mud flocculation in the more saline Budd Inlet and integrate model results with expected biological changes due to a shift from a freshwater environment to a more brackish estuarine one if the estuary is restored.