Abstract

ABSTRACT The Devils River in south-central Texas is recognized as one of the remaining pristine rivers in the state. Adding to its importance, the Devils River is a key tributary to the Rio Grande, providing essential freshwater flows to south Texas and the Rio Grande Valley. An efficient conveyance system for groundwater is shown to have formed in the karst carbonate watershed, located in a semiarid environment with modest distributed recharge, oftentimes less than 1–2 cm/yr. This conveyance system comprises preferential flow pathways that developed coincident with river channels. A strong correlation between wells with high well yield and proximity to higher-order river channels (i.e., within 2.5 km) was used as evidence of the presence of preferential flow pathways. An important observation is that groundwater flow in the Devils River watershed appears to be controlled by the morphology of the area more than the bulk hydraulic properties of the rocks. Flow measurements in the Devils River measured under relatively high- and low-flow conditions support the hypothesis that the river is gaining in downstream reaches. This characteristic leads to perennial river flow being restricted to only the lower reach of the river. Last, essentially all of the recharge to Amistad Reservoir that is derived from the Devils River watershed is contributed as surface flow from the river, and there is minimal underflow or cross-formational flow from the watershed at the point where the watershed abuts Amistad Reservoir.

Highlights

  • The Devils River in south-central Texas has been recognized as one of the remaining pristine rivers in the state and is a key tributary to the Rio Grande, providing essential freshwater flows to south Texas and the Rio Grande Valley (Fig. 1)

  • The Devils River watershed is located in a semiarid environment with modest distributed recharge, oftentimes less than 1–2 cm/yr (0.4–0.8 in./yr)

  • The Edwards-Trinity Aquifer of the watershed is characterized as a karstic carbonate aquifer with preferential flow paths that align with major river channels

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Summary

Introduction

The Devils River in south-central Texas has been recognized as one of the remaining pristine rivers in the state and is a key tributary to the Rio Grande, providing essential freshwater flows to south Texas and the Rio Grande Valley (Fig. 1). Factors that control conduit development in the Devils River watershed are: (1) the degree to which rocks are susceptible to dissolution, (2) the exhumation of the Edwards Plateau, leading to increased hydraulic gradients, and (3) the focus of recharge into a defined stable river system (White and White, 2001, 2003). The importance of lineaments and topographic expressions, the principles of carbonate dissolution, and a surrogate estimate of aquifer permeability were used to explain the development of preferential flow paths aligned with the river channels in the Devils River watershed.

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Conclusion

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