Date of Graduation

12-2018

Document Type

Thesis

Degree Name

Master of Science in Geology (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Shaw, John B.

Committee Member

Boss, Stephen K.

Second Committee Member

Cothren, Jackson D.

Third Committee Member

Sharman, Glenn R.

Fourth Committee Member

Wagner, Daniel

Keywords

Bathymetry; Delta Morphology; River Delta; Subaqueous Delta Growth; Subaqueous Distributary Channel

Abstract

I report changes to the subaqueous bathymetry of the Wax Lake Delta (WLD) located in coastal Louisiana with the purpose of quantifying the two- and three-dimensional evolution of the entire delta front. The spatial distribution and volume of erosion and deposition were determined by differencing two Digital Elevation Models (DEMs) collected 16 months apart, including the 2nd largest high flow event (flood) in the WLD’s recorded history. The difference map showed 6.41×10^6 m^3 ± 3.70% of sediment were deposited and 1.19×10^7 m^3 ± 2.71% were eroded yielding 5.46×10^6 m^3 ± 7.32% of net erosion in the survey area (~75.9 km^2). Generally, deposition on the delta front was spatially localized around channels and the delta flanks whereas erosion was spatially uniform. The widespread erosional signature was likely associated with sediment resuspension and export out of the survey area during winter cold fronts, with minor influences from shallow subsidence and tides. Despite the occurrence of a significant flood during the survey period, I conclude that subaqueous delta growth is less influenced by the flood cycle than more proximal subaerial islands. Floods do, however, act to increase channel network asymmetry by aggrading a majority of channels and incising a few. I attempted to test if the distribution of flow between distributary channels scales with the distribution of net deposition in a channel’s respective nourishment area, the space that receives water and sediment from a given channel. A majority of nourishment areas were net-erosional which violated a central assumption about the hypothesis. I conclude that deposition within a nourishment area cannot be predicted from discharge alone. The field data presented here suggests that models of deltaic growth need to account for significant volume export from the delta front. Given that the subaqueous delta was net erosional, delta retrogradation is possible over short timescales in an environment that is progradational overall. Thus, future models should also introduce annual variability in growth rates to better predict the decadal growth of the WLD. Improvement of the predictive models of subaqueous WLD growth have important implications to land building from sediment diversions and stratigraphic analysis of deltas.

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