Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Schmitz, Darrel W.

Committee Member

Barlow, Jeannie R. B.

Committee Member

Rodgers, John C. III

Committee Member

Paul, Varun

Date of Degree

8-10-2018

Document Type

Dissertation - Open Access

Major

Earth and Atmospheric Sciences

Degree Name

Doctor of Philosophy

College

College of Arts and Sciences

Department

Department of Geosciences

Abstract

The Mississippi Alluvial Plain, a robust agricultural region in the South-Central United States, provides commodities across the United States and around the world. Water for irrigation, which is necessary due to irregular rainfall patterns during the growing season, is withdrawn largely from the Mississippi River Valley Alluvial aquifer, one of the most intensely used aquifers in the United States. The groundwater-dependent region has observed recent declines in groundwater and streamflow levels, raising concerns about the availability and use of fresh-water resources. Declining water levels have prompted investigation into the current understanding of groundwater and surface-water interaction. Previous research does not adequately quantify the unobservable exchange of water between surface-water bodies and the underlying aquifer. This research was designed to advance the current understanding of the interaction between groundwater and surface water through the quantification of spatial and temporal trends in streamflow and groundwater level changes and the use of high-resolution spatial estimates of streambed hydraulic conductivity. Changes in streamflow and groundwater levels were quantified with the use of hydrograph-separation techniques and trend analyses. High-resolution estimates of streambed hydraulic conductivity were found through the correlation of waterborne continuous resistivity profiling data to hydraulic conductivity and streambed hydraulic conductivity estimates were incorporated into the existing Mississippi Embayment Regional Aquifer Study (MERAS) groundwaterlow model. Site-specific empirical relationships between resistivity and hydraulic conductivity were developed with near-stream borehole geophysical logs to improve model estimates of streambed hydraulic conductivity. Results of the quantification of changes in streamflow and groundwater levels suggested agricultural groundwater withdrawals for irrigation to be the primary source of groundwater-level declines. Results from the incorporation of high-resolution estimates of streambed hydraulic conductivity showed that the existing groundwaterlow model is sensitive to changes in streambed hydraulic conductivity, which may impact model accuracy. The incorporation of streambed hydraulic conductivity estimates derived from site-specific empirical relationships impacted MERAS model water-budget estimates. Information gained from this research will be used to improve the existing groundwaterlow model, which acts as a decision-support tool for water-resource managers at state and local levels to make informed water-use decisions for the conservation of fresh-water resources for sustainable agricultural irrigation practices.

URI

https://hdl.handle.net/11668/21276

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