Quantifying Surface Processes Using Remote Sensing: Accretion in River Deltas and Migration of Barchan Dunes

Detecting and quantifying geomorphic change in sedimentary landscapes is essential for understanding how surface processes respond to environmental forcing and for addressing societal challenges. This thesis investigates how sediment is distributed and stored in river deltas and aeolian dune fields using remote sensing. In river deltas, sediment accretion maintains land elevation relative to sea level, whereas in arid regions, sand mobility controls dune migration, which may overwhelm civil infrastructure. Despite advances in constraining boundary conditions such as sediment supply, sea-level rise, and wind regimes, the internal dynamics that regulate sediment retention and transport remain poorly understood. In Chapter 2, I quantify decadal accretion patterns in the Wax Lake Delta (WLD), Louisiana, using repeat lidar surveys. I show that accretion exhibits strong spatial variability, with higher rates at island edges and within elevations associated with moderate inundation frequency in the high-intertidal zone. Downstream topographic gradients suggest that the delta tends to maintain an equilibrium gradient that is coupled to floodwater surface gradients, while vegetation and island morphology cause local variations. I further demonstrate that large flooding events contribute disproportionately to elevation gain and enhance sediment trapping. In Chapter 3, I show that secondary channels can deliver sediment to sediment-starved island interiors, increasing their accretion rates to levels comparable to those at levees and helping deltaic islands extend accretion beyond their edges. These channels cycle through phases of initiation, progradation, and backfilling, consistent with previous numerical predictions. Because deposition along secondary channel lobes is concentrated in topographic lows, their autogenic cycles may redistribute sediment across island interiors through time, promoting more spatially uniform island accretion through compensational stacking of channel lobes. In Chapter 4, I explore the response of barchan dune fields to changes in environmental conditions. I develop an automated workflow to detect, segment, and track barchan dunes from satellite imagery and apply it to a dune field in Qatar. I show that coastal dunes migrate at rates comparable to those of inland dunes, indicating that reduced interdune spacing near the coast is not due to modern stabilization. Instead, the present morphology likely reflects an inherited dune-field organization that was reworked following an ancient marine transgression. Using migration rates to back-propagate dune positions, I show in Chapter 5 that dune arrival times along the northern coast coincide with the mid-Holocene filling of the Arabo-Persian Gulf, which likely terminated sediment supply. Back-projected dune positions further suggest that sediments were sourced from paleo-river systems linked to the Zagros Orogeny rather than from Arabia. Together, these results demonstrate how remote sensing of geomorphic change can be used to quantify sediment trapping, identify dominant surface processes, and reconstruct ancient environmental conditions. This work highlights the importance of internal dynamics in regulating sediment distribution and provides a framework for linking modern landscape evolution to geological events.