Mapping of tide and tidal flow fields along a tidal channel with vessel‐based observations

Abstract

We present the results of a study focused on the tidal regime of a shallow channel with a large intertidal area. Data from a vessel‐towed acoustic Doppler current profiler (ADCP) were used to infer tidal constituents for both tidal elevation and tidal current along an upstream portion of the Okatee River, South Carolina. The tidal elevation is estimated from the depth recorded by the moving ADCP. This tidal elevation is then used to correct the vertical coordinates of each depth bin below the ADCP for the velocity profiles. The ability to resolve both tidal elevation and velocity allows us to determine that the tide is a standing wave. A statistical analysis demonstrates that the along‐channel velocity has a stronger tidal signal (larger R2 values) than the across‐channel velocity. When only the M2 and mean components are included in the harmonic analysis, about 75% of the covered area along the ship track has a “good fit,” where at least 70% of the variability can be explained by the tidal and mean components. By adding the M4 component to the harmonic analysis, an additional 2% of the covered area has “good fit” for the elevation, depth‐averaged velocity, and mid‐depth velocity, but 12% for the near‐surface velocity. The observed spatial distribution of the residual flow is in reasonable agreement with that predicted by an unstructured grid, finite‐volume coastal ocean model (FVCOM).