Navigation Channel Effects on Estuarine Mean Water Level

Abstract

The traditional conceptual model of freshwater-dominated estuarine hydrodynamics states that long-term average within-estuary water level is elevated over long-term average sea level at the sea inlet(s) in order to push freshwater inflows seaward. At low freshwater inflows, other factors, including nonlinear tidal propagation, can cause either setup or setdown in the average estuary water level. The Cumberland Sound estuary straddles the Georgia–Florida state line. Deepening and widening of the Cumberland Sound entrance and interior channels from 1984 through 1988 increased channel dimensions by 25%–66%. A weight of evidence approach considering analytic, physical, and numerical models’ results, plus statistical analysis of observed MTL from 1953 through 2019 leads to the conclusion that the channel enlargements reduced a pre-existing Fernandina Beach MTL setdown of up to 0.02–0.05 m.