Effect of Local Winds on Circulation and Stratification in a Large Discharge Mesotidal Estuary: the Case of the Columbia River Estuary

In the highly energetic Columbia River estuary river discharge and tides are known dominant control factors of circulation. In this study the 3D hydrodynamic model SELFE is used to investigate the influence of the wind in the estuary with high-enough resolution atmospheric forcing. Numerical simulations are carried out for realistic conditions of the year 2014. The effect of the wind is also investigated by switching it off in the estuary. Controlled experiments are then performed for idealized conditions of wind, tide and river discharge. Analysis of residual currents and salinity metrics are presented for both realistic simulations and controlled numerical experiments. The results show that in particular conditions wind may exert control on stratification and salinity intrusion length. Effects are particularly noticeable during autumn and winter seasons for high wind speed values. In neap tide conditions Easterly winds tend to increase stratification and salinity intrusion length, while Westerly winds tend to do the reverse, but in spring tide conditions the situation changes and stratification seems always to decrease. The results from the idealized simulations also suggest that energetic winds may alter water and salt exchanges between North and South channel of the Columbia River estuary and have some influence on the prevailing estuarine regime, if the original regime is close to transitional. An inertial effect induced by the wind is observed too. The high-enough resolution of the atmospheric forcing is fundamental to meaningfully capture the effect of local winds: indeed circulation shows markedly different features than when using previously available lower resolution forcing. These findings offer motivation for future studies to better understand the processes and the functioning of this coastal ecosystem. Finally comparison with experimental data would be needed for further insight.