Book of Abstracts 2024

Hendrik Jongbloed^1,2, Henk M. Schuttelaars², Yoeri M. Dijkstra_², Antonius J.F. Hoitink¹

¹Hydrology and Environmental Hydraulics, Wageningen University and Research, Wageningen, The Netherlands; ²Delft Institute of Applied Mathematics, Delft University of Technology, Delft, The Netherlands

henk.jongbloed@wur.nl

Introduction

Estuarine channel depth is known to be one of the most important factors controlling salt intrusion. To parametrically understand its influence, idealized width-averaged (2DV) or along-channel (1D) approaches (e.g. Hansen and Rattray (1965)) are often employed. This type of exploratory model necessarily requires a measure of effective water depth as input. However, an estuarine bathymetry often varies considerably throughout the estuary, causing intrinsically three-dimensional transport mechanisms that potentially influence salt dispersion to a large degree. These significant correlations cannot be straightforwardly translated to 2DV and 1D models, instead, they must be parametrized.

Objective and Methods

In this work, we attempt to capture and parametrize the influence of lateral bathymetric variations on longitudinal salt transport processes, suitable for direct application in existing 2DV and 1D frameworks. We present a three-dimensional subtidal model for water motion and salinity in partially stratified estuaries, extending the width-averaged approaches of Hansen & Rattray (1965) and MacCready (2004) to general 3D geometries. This model allows for semi-analytically investigating the net effect of lateral bathymetric variations on salt transport mechanisms and salt intrusion, leading to an effective depth parametrization that follows directly from the analysis of the transport equations.

Results

 As a first result, we demonstrate that in single channel systems, lateral depth variations may directly cause a twofold increase in salt intrusion, keeping other parameters (i.e. cross-sectional area) unchanged. Secondly, we quantify the influence of bed variations at tidal channel junctions on salt fluxes across the junction branches, however, an analysis of salt transport terms at channel junctions is yet to be done.

Cross-sectional view of an estuary with a Gaussian lateral bathymetry. Top to bottom: Salinity [psu], along-channel and cross-channel flow [m/s].

References

Hansen, D. V., & Rattray, M. (1965). Gravitational circulation in straits and estuaries. Journal of Marine Research, 23(2), 104–122.

MacCready, P. (2004). Toward a unified theory of tidally-averaged estuarine salinity structure. Estuaries, 27(4), 561–570. https://doi.org/10.1007/BF02907644