Analysis Of Long-Term Spatially Varying Vertical Accretion Rates Within Paleo-Environments And Vulnerable Wetlands Of The Mid-Barataria Diversion Receiving Basin, Louisiana, USA

Author

Michael C. Piorkowski, Louisiana State University at Baton RougeFollow

Semester of Graduation

Summer 2024

Degree

Master of Science (MS)

Department

Geology and Geophysics

Document Type

Thesis

Abstract

The Mid-Barataria Diversion basin is an interlobe basin located south of New Orleans, Louisiana, USA. Along with the proximal Mid-Breton Sound, these two basins are proposed locations for river sediment diversion projects to restore Louisiana’s receding wetlands and marshes. Following ratification of the Flood Control Act of 1928, anthropogenic levees were constructed along the banks of the Mississippi River to prevent flooding and to protect the state’s infrastructure. As a result, the floodplains are starved of their natural sediment replenishment and are now subject to the effects of subsidence and relative sea level rise (RSLR; total subsidence + geocentric sea level rise). The river-sediment diversion proposed by the Louisiana Coastal Protection and Restoration Authority has great potential to restore the subsiding wetlands, though it is crucial to be certain that the basin can support such a drastic increase in water and sediment flux. A larger, over-arching study aims to quantify the rates of differential subsidence across the Mid-Barataria Diversion basin, along with how different basin lithologies in the subsurface are affected by RSLR. The research presented here leverages previous work by Hughes (2016) and Bomer et al. (2019) by using ¹³⁷Cs and ²¹⁰Pb geochronology to calculate long-term (~100 year) rates of vertical accretion within targeted shallow subsurface environments (e.g. marsh, paleochannel, bay). The data are then compared to physical sediment properties to estimate marsh surface stability over this time period. It was found that no spatial trends of VARs were observed in Mid-Barataria, though VARs were greater in marsh sites than bay sites. Geochronology results provided by Drs. Liz Chamberlain & Kelly Sanks show that the St. Bernard delta complex is responsible for creating most of the underlying lithology of Mid-Barataria and more recent active delta complexes served to maintain marsh surfaces. Materials deposited since the St. Bernard delta were found to have very low density in surface marsh units and are actively converting to bay environments due to wave action on marsh edges coupled with RSLR. Direct measurements of wet and dry bulk density of surface marshes were found to be 0.54 ± 0.15 g/cm³ and 0.24 ± 0.19 g/cm³, respectively, much lower than wet bulk densities of 1.1 – 1.3 g/cm³ reported in Bomer et al. (2019). Caution should be exercised while operating the diversion as the hydraulic head gradient will be large, regardless of season, and surface marshes were found to be more susceptible to erosion and subsidence than previously thought. However, these marshes were able to survive thousands of years of natural overbank deposition in Mid-Barataria basin.

Date

7-10-2024

Recommended Citation

Piorkowski, Michael C., "Analysis Of Long-Term Spatially Varying Vertical Accretion Rates Within Paleo-Environments And Vulnerable Wetlands Of The Mid-Barataria Diversion Receiving Basin, Louisiana, USA" (2024). LSU Master's Theses. 5999.
https://repository.lsu.edu/gradschool_theses/5999

Committee Chair

Wilson, Carol A.

DOI

https://doi.org/10.31390/gradschool_theses.5999