267-1 Quantitative Insights into Sediment Transport in the DeGrey River Delta: Cyclonic Influences and Bedform Persistence

Session: Advances in Fluvial Processes and Sediment Transport (Posters)

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Abstract:

This study characterizes the sediment transport dynamics of the fluvial portion of the DeGrey River delta, a dryland tide/wave-dominated delta along the Pilbara coast of northwestern Australia. Particularly, the study isolates the discrete deposits of yearly floods. The DeGrey operates as an ephemeral river with discharge driven by cyclones and tropical depressions during austral summer.

Methodology involves utilizing water discharge data, sub-centimeter digital elevation models, and field grain size analysis to calculate shear stress on the riverbed and linking it to discrete flood deposits. A time series of DEM datasets consisting of a 1-m aerial survey (2021) and drone photogrammetry surveys (2022, 2023, 2024) were used to generate differential DEM maps to detect yearly morphological change within the channel. Field surveys of selected sites indicating morphological change enabled characterization of grain size, porosity, water flow, and structures of flood deposits. Ground penetrating radar surveys taken on select bars reveal shallow structure in accordance with traditional trenching.

Cyclone floods in the region cause propagation of preexisting dunes, unit bars, and compound bars. This leaves dominantly lower-flow-regime structures in mostly medium grained sand. Unit bars are composed of primarily down-climbing cross-stratified sets. Reactivation surfaces are common among unit bars and point bars. General lower-flow-regime bar and bedform morphology is maintained and propagated between flows despite intense flash flooding which can produce discharge in excess of 100,000 ML/day in prior dry channels that would predict channel excavation or preservation of upper-flow-regime bedforms.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9488

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