Characterization of the vertical structure of tidal currents in the Mouth of the Columbia River and evaluation of the SELFE model

Abstract

Lack of measurements has led to a poor understanding of tidal currents within the Mouth of the Columbia River (MCR). Shipboard ADCP measurements are a technically viable means to measure these currents and their vertical structures. Shipboard ADCP measurements from a three-week long cruise conducted by the R/V Point Sur are used in this study. Transects along the main shipping channel and across the bar were extracted using criteria of constant speed and heading. Vertical sections from each transect were compared with predictions from the SELFE model in order to evaluate the models’ ability to predict these currents. Observed flood currents within the river are bottom intensified with slight river outflow at the surface early in the flood cycle. Complete reversal of the flow throughout the column is experienced later as the flood fully develops. Ebb currents are much stronger and more homogenous throughout the water column due to the combination of river outflow and tidal current. Inside the river mouth, the SELFE model agrees qualitatively well with observations, with only a few discrepancies. Outside the river mouth, the SELFE model does not resolve the observed vertical structure, possibly due to coarse grid resolution and limited observational input.