Semester of Graduation

Spring 2026

Degree

Master of Science (MS)

Department

Department of Geography and Anthropology

Document Type

Thesis

Abstract

River deltas are typically composed of networks of bifurcating channels that regulate the distribution of water, sediment, and nutrients from upstream. The routing of these materials plays a key role in shaping the morphological evolution of deltas. Previous studies have provided important insights into the hydrodynamics at channel bifurcations; however, hydrodynamics at bifurcations that exhibit shallow benches and seasonal vegetation remain poorly understood. Within South Pass of the Mississippi River Delta, multiple bifurcations have shallow benches which undergo submergence and seasonally vegetated.

This study investigates how such shallow benches influence the 3D flow structure and discharge partitioning at a deltaic river bifurcation. Field observations of velocity and cross-sectional bathymetry were collected using an acoustic Doppler current profiler (ADCP) during two surveys conducted under emergent bench conditions. These measurements were complemented by a semi-idealized Delft3D-Flexible Mesh (Delft-3D FM) hydrodynamic model representing four scenarios: no bench, emergent bench, submerged bench without vegetation, and submerged bench with vegetation.

Results show that the presence of a shallow bench fundamentally alters flow redistribution at the bifurcation by introducing lateral asymmetry in channel geometry. Benches increase the velocity in the main channel and shift high-momentum flow away from the bench margin toward the opposite bank, enhance secondary circulation, and promote the formation of low-velocity wake regions downstream of the bench. Emergent benches produce the strongest velocity contrasts and secondary flows, while submerged benches continue to exert a measurable influence on the flow. Vegetation on submerged benches further reduces velocities over the bench surface and modifies wake structure but has a limited effect on overall discharge partitioning. However, this vegetation likely plays an important role in trapping and depositing sediment and organic material on the bench surface and adjacent wetlands. Both field measurements and numerical simulations indicate that the presence of a bench increases the fraction of discharge routed into the lateral channel relative to a no-bench configuration.

These findings demonstrate that shallow benches exert strong control on the hydrodynamics at channel bifurcations. Accounting for this is therefore essential for improving predictions of flow redistribution, sediment transport pathways, and morphological evolution in river deltas.

Date

3-27-2026

Committee Chair

Konsoer, Kory M.

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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