The Sensitivity of Salt Wedge Estuaries to Channel Geometry

Abstract

The 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.

Assessment of sea-level rise impacts on salt-wedge intrusion in idealized and Neretva River Estuary

“…10 show that as Q and F 0 approach zero, the salt-wedge length approaches a theoretical limit of C f /S 0 . This is also in agreement with a theoretical analysis of the salt-wedge sensitivity to channel geometry by Poggioli and Horner-Devine (2015). Three approaches for assessing SLR impact on salt-wedge intrusion are considered here: a) analytical expressions for idealized estuaries derived from the two-layer theory, b) ODE for sloped estuaries, also derived from the two-layer theory, and c) time-dependant two-layer SWE model for irregular channels derived by extending the two-layer theory.…”

The shelf sources of estuarine inflow

“…The mixed water within an estuary is composed of river water and a significant amount of ocean water that originates on the shelf. Much has been written about the path by which mixed water leaves the estuary as a river plume (Horner-Devine et al 2015). Here we focus on the path by which dense ocean water is drawn into the estuary from the shelf, hereafter ''shelf inflow.''…”

Sedimentological and ichnological implications of rapid Holocene flooding of a gently sloping mud‐dominated incised valley – an example from the Red River (Gulf of Tonkin)

“…In particular, far upstream seawater incursion is facilitated during low discharge, when a saltwater wedge may form in deep incised channels (e.g. Poggioli & Horner‐Devine, ). For instance, in the Southwest Pass of the Mississippi River, seawater flows 235 km upstream during low discharge while the tidal range is only 36 cm (Schubel & Meade, ).…”

“…In a gently inclined valley segment seawater can intrude upstream for a longer distance than in a steeply inclined segment, especially at low discharge in a channel having uniform geometry (e.g. Poggioli & Horner‐Devine, ). Seawater incursions in response to strongly fluctuating fluvial discharge lead to recurrent salinity changes induce flocculation and deposition of water‐rich, soft to fluid mud at the interface between river and seawater.…”