Degree

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Document Type

Dissertation

Abstract

Coastal wetlands play a critical role in shoreline protection, biodiversity support, and carbon sequestration. In coastal Louisiana, however, these systems are experiencing rapid loss driven by relative sea-level rise, sediment deprivation, subsidence, and anthropogenic stressors. Their long-term resilience depends on vertical accretion, the accumulation of mineral and organic matter that enables marshes to maintain elevation relative to rising water levels. Yet many existing marsh models use static or time-averaged sediment inputs, overlooking the strong seasonal and event-driven variability characteristic of deltaic environments.

This dissertation addresses this gap through a three-stage research framework. Stage 1 examines how seasonal variations in suspended sediment concentration (SSC) influence vertical accretion across microtidal marshes in the Atchafalaya and Terrebonne basins. Using hourly CRMS water levels combined with monthly SSC inputs derived from USGS monitoring and NASA Delta-X datasets, chronic tidal influences were separated from acute and tropical events. Results demonstrate that frequent, moderate high-water events supply approximately 40–45% of annual mineral loading, while tropical surges contribute only 2–3%.

Stage 2 formulates the Full Mathematical Form (FMF) for stiff-aware eco-morphodynamic coupling, integrating fast hydrodynamic processes (water levels, sediment transport) with slower ecological–soil processes (biomass production, organic accumulation). The FMF framework employs operator splitting to ensure numerical tractability and stability under the disparate time scales governing hydrodynamics and ecological change.

Stage 3 implements a prototype one-year coupled Delft3D–MEM loop. The automated workflow runs an idealized 1-D Delft3D model; extracts water levels through MATLAB; computes tidal datums, inundation metrics, and hydroperiod in Python; executes the MEM-based ecological model; and updates Delft3D bathymetry and roughness files. While the resulting one-year outputs are preliminary and uncalibrated, they confirm the technical feasibility of two-way eco-morphodynamic coupling.

Together, these three stages advance coastal wetland modeling by incorporating process-based SSC seasonality, establishing a mathematically rigorous coupling formulation, and demonstrating a functional prototype for dynamic feedbacks between hydrodynamics and marsh accretion. This framework lays essential groundwork for future long-term simulations and planned validation with CRMS observations under varying sediment and hydrodynamic conditions.

Date

1-10-2026

Committee Chair

Kees, Christopher E.

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Available for download on Sunday, January 10, 2027

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