Date of Award

2026-05-01

Degree Name

Master of Science

Department

Geophysics

Advisor(s)

Hugo A. Gutiérrez-Jurado

Abstract

Groundwater in arid or semi-arid regions is critical for agricultural production, yet the contribution of irrigation return flow to regional aquifer recharge remains poorly constrained. As is the case beneath flood-irrigated pecan orchards in the Rio Grande floodplain of Far West Texas. This study integrates time-lapse electrical resistivity tomography (ERT) with stable water isotopes (δ¹⁸O, δ²H) in vadose-zone soil-pore water to evaluate how irrigation water infiltrates. This study tracks how irrigation return is stored and may contribute to recharge of the Hueco Bolson aquifer. The objectives are to (1) relate observed resistivity variations to stratigraphic heterogeneity influencing infiltration, (2) characterize recharge pathways using isotope depth profiles from a pecan agroforestry system, and (3) integrate geophysical and isotopic datasets to assess the role of irrigation return flow in aquifer recharge. Two-dimensional ERT surveys collected over an irrigation season in a pecan orchard near Tornillo, Texas, show laterally variable conductive and resistive zones that align with stratigraphic changes. Indicating that soil texture, minerals, and saturation are primary controls on infiltration pathways and subsurface storage. Time-lapse percent-change analyses reveal vertically continuous zones of increased conductivity that extend from the surface to depths exceeding the shallow semi-perched Rio Grande alluvial aquifer. The time-lapse percent change analyses identified preferential flow paths where irrigation-influenced water penetrates more deeply than in surrounding areas. To extend interpretations from seasonal to decadal timescales, δ¹⁸O and δ²H were measured in vadose-zone soil-pore waters from a 50 m core collected at a nearby pecan orchard. The isotope profile defines a soil-water evaporation line with a low slope relative to the local meteoric water line, indicating strong evaporative modification of shallow water. Enriched isotopic values and elevated dissolved solids in the shallow alluvium reflect repeated cycles of irrigation, evaporation, and short-term storage above clay-rich, low-permeability layers. Deeper pore waters become more depleted and converge toward local groundwater compositions. Together, the geophysical and isotopic results show that irrigation water is strongly modified and partially retained in a shallow, evaporated, semi-perched zone. However, irrigation water can bypass low-permeability units along limited preferential pathways, migrating into deeper parts of the vadose zone and mixing with existing groundwater. Irrigation return flow therefore does not translate into uniform or proportional recharge beneath pecan orchards; instead, deep recharge depends on the balance between shallow storage, evaporative losses, stratigraphic controls, and preferential flow connectivity to depth. This integrated framework provides a process-based basis for evaluating irrigation-enhanced recharge in arid agroforestry systems of the U.S. Southwest.

Language

en

Provenance

Received from ProQuest

File Size

81 p.

File Format

application/pdf

Rights Holder

Jose Josue Cabral

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