Analysis of Stratified Flow and Separation over Complex Bathymetry in a Field-Scale Estuarine Model

Tidal flows in estuaries produce surface-coherent structures, such as eddies, when the flow interacts with complex topography. These coherent structures, in turn, can be used to infer the properties of the flow, such as speed and direction, turbulent intensity, stratification, suspended sediment concentration, and bathymetry. While simulation of coherent structures is straightforward in smaller domains with idealized geometries, it is extremely difficult to accurately simulate them in real field-scale domains. Accurate simulation of small-scale features requires that the model first accurately simulate the large-scale, tidally-induced flow, which depends to great extent on accurate simulation of salinity and the complex flow features over mudflats that can become exposed during low tides. In this paper, we will analyze the stratified tidal flow over a sill in the Snohomish River estuary and the associated eddies that are produced. We will first discuss model details that are required to simulate the tidal-scale hydrodynamics in the domain that is O(10 km) in extent, followed by the flow physics of the eddies with length scales of O(1 m).