39-12 Advancing the Conceptualization and Data Inputs to the Groundwater Model of the Devils River – Edwards-Trinity Aquifer System

Session: Understanding Karst Hydrology and Karst Aquifers Using Innovative Tracers and Other Technologies

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The Devils River in west-central Texas has a perennial reach over 100 kilometers that interacts with the Edwards-Trinity (Plateau) Aquifer, supporting possibly the most pristine river ecosystem in the state and contributing significant flows to the Rio Grande/Amistad International Reservoir. Like many water resources in Texas, the groundwater – surface water linked system of the Devils River is threatened by stressors, including extended drought and potential large-scale pumping. The State uses groundwater availability models as a primary tool to project aquifer conditions and inform water policy, and these models rely on accurate conceptualization and robust data inputs to optimize results of model outputs. Recent and ongoing research along the Devils River has advanced our understanding of how the aquifer and river may respond to future conditions.

The Devils River is characterized by losing ephemeral reaches in the Upper and Dry basins and a spring fed Lower basin. Recharge is dominated by rapid infiltration through karst permeability in ephemeral reaches and diffuse recharge plays a limited role as precipitation/evapotranspiration ratios are low in this arid environment. The river is predominantly gaining, with a median flow of 4.39 cms at Pafford Crossing at the downstream extent of the river before entering Amistad Reservoir. Significant baseflow originates in the upper 40 km from the Pecan Springs (PS) and Finnegan Springs (FS) complexes. The PS complex is the headwaters of the river and has a median flow of 1.36 cms. A losing river section between PS and FS recharges the aquifer and the FS complex downstream of the losing reach has a median flow of 1.42 cms, contributing 30% of Pafford Crossing's flow.

The aquifer framework is highly developed through karstification with primary conduits focused within valleys and secondary/tertiary conduits developed distally from modern river location. Relatively high primary porosity in the matrix limestone supports high storativity in the aquifer and provides extended spring flow to the river. Major springs form at the intersection of southwest trending groundwater flow with the southeast trending river incision, often along stratigraphically controlled karst horizons near the top of the Fort Terrett Formation. Future work will expand continuous data in the area and aid in understanding the complex spatio-temporal hydrogeology of the aquifer and springs that sustain the Devils River.

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

doi: 10.1130/abs/2025AM-10847

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