The Sensitivity of Salt Wedge Estuaries to Channel Geometry

Abstract

he authors develop a two-layer hydraulic model to determine the saline intrusion length in sloped and converging salt wedge estuaries. They find that the nondimensional intrusion length = CiL/hS depends significantly on the channel bottom slope and the rate and magnitude of landward width convergence, in addition to the freshwater Froude number. In the definition of , Ci is a quadratic interfacial drag coefficient, L is the salt wedge intrusion length, and hS is the depth at the mouth of the estuary. Bottom slope is found to limit the saline intrusion length, and this limitation accounts for the deviation of the observed exponent n in a scaling relationship with the river discharge of the form L ~ Q?n from the canonical value of 2 to 2.5 predicted by the theory of Schijf and Schönfeld for a flat, prismatic estuary. The authors find that estuary convergence is important only when the ratio of the slope-limited intrusion length to the convergence length is greater than one, and that the effects of convergence are less significant than those of slope limitation. They compare this model to field and validated numerical data and find that the solution predicts the intrusion length with good accuracy, improving on the flat, prismatic solution by orders of magnitude. While this model has good predictive capability, it is sensitive to Ci and the location of the hydraulic control point, both difficult to determine a priori.