Modeling the Hydrodynamics of Puget Sound Using a Three-Dimensional Unstructured Finite Volume Coastal Ocean Model

Abstract

Puget Sound is a complex fjordal estuarine system located in the Northwest Pacific coast of the state of Washington. It is one of the most pristine estuarine systems in the United States that provide marine habitats for salmon and marine wildlife. Circulation in Puget Sound exhibits fjordal characteristics, dominated by tides propagating from Pacific Ocean through the Strait of Juan de Fuca and freshwater discharges from various rivers and runoff. Local circulation patterns in the major sub-basins within Puget Sound are complex and different from each other due to their distinct features such as complex coastlines, existence of mudflats, freshwater inflows, presence of islands, and man-made shoreline modifications. Over the last century, considerable nearshore tidal marshland habitats have been lost due to historical diking and agricultural land use. A number of habitat restoration projects focused on restoring estuarine functions such as tidal flushing, brackish nearshore environment, supply of nutrients and sediment have been proposed with an overall goal of recovering fish stocks. To better understand the details of circulation characteristics in Puget Sound, and to help assess the feasibility of the proposed restoration actions, a hydrodynamic model for the entire Puget Sound with high resolution in the nearshore regions was needed. In this paper, we present the development of a three-dimensional circulation model of Puget Sound using an unstructured finite volume framework (FVCOM). The model has been constructed with sufficient resolution in the nearshore region to address the complex coastline, multi-tidal channels and tidal flats. To account for the influences of ocean water intrusion from the Strait of Juan de Fuca and the Fraser River plume from the Georgia Strait, model open boundaries are extended to the entrance of the Strait of Juan de Fuca and the north end of the Georgia Strait. The model is driven by tides, meteorological forcing and river inflows. Model results for circulation patterns, freshwater plumes and particle trajectories are presented and discussed. Preliminary results show that the model successfully reproduces general features such as propagation of tides, currents, in the main basin as well as wetting and drying, freshwater plumes, and nearshore salinity distribution. 1 Water Resources Modeling. Pacific Northwest National Laboratory, Battelle Seattle Research Center. 1100 Dexter Avenue North, Suite 400, Seattle, WA 98109