Geologic framework, structure, and hydrogeologic characteristics of the Knippa Gap area in eastern Uvalde and western Medina Counties, Texas

Clark, Allen L.; Pedraza, Diana E.; Morris, Robert R.

doi:10.3133/sir20135149

Cited by 4 publications

(4 citation statements)

References 27 publications

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“…The phylogenetic topology is also congruent with the added detail provided by studies of the upper Medina River near the Knippa Gap (Clark & Journey, 2006; Doyle, 2003). The Pleistocene Leona Formation (Stoeser et al., 2006) further reveals ancestral river courses (Clark et al., 2013; Hill & Vaughan, 1898) that correspond to the Pleistocene distribution and phylogenetic diversification of E. lepidum revealed in this study (Figure 2a, d).…”

Section: Discussionsupporting

confidence: 67%

Integrative ichthyological species delimitation in the Greenthroat Darter complex (Percidae: Etheostomatinae)

et al. 2021

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Species delimitation is fundamental to deciphering the mechanisms that generate and maintain biodiversity. Alpha taxonomy historically relied on expert knowledge to describe new species using phenotypic and biogeographic evidence, which has the appearance of investigator subjectivity. In contrast, DNA‐based methods using the multispecies coalescent model (MSC) promise a more objective approach to describing biodiversity. However, recent criticisms suggest that under some conditions the MSC may over‐split lineages, identifying species that do not reflect biological reality. Here, we reconcile these approaches using empirical data for the Greenthroat Darter complex (Etheostoma lepidum), a small freshwater fish species with a disjunct distribution in Texas and New Mexico, USA. We demonstrate that MSC methods recognizes all nine sampled populations as distinct species, sometimes splitting specimens from a single locality into multiple species. However, environmental, phenotypic, and biogeographic evidence do not corroborate the nine species supported by the MSC. Instead, collective evidence indicates that E. lepidum is comprised of just three species that are consistent with the molecular phylogeny: Etheostoma lepidum (Greenthroat Darter) in rivers draining the eastern Edwards Plateau, Etheostoma cf. lepidum (Texas Darter) in the Concho and San Saba rivers, and Etheostoma cf. lepidum (Pecos Darter) in the Pecos River. The Pecos Darter is likely highly imperiled due to its localized distribution and reliance on vanishing spring‐fed stream habitats. The impending biodiversity crisis makes integrative and swift species delimitation more necessary than ever. Our study exemplifies how classic taxonomic expertise combined with molecular phylogenetics can produce a more robust description of threatened biodiversity.

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Section: Discussionsupporting

confidence: 67%

Integrative ichthyological species delimitation in the Greenthroat Darter complex (Percidae: Etheostomatinae)

et al. 2021

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“…However, is it possible that other structures such as relay ramps may also influence groundwater flow? These types of structures have been attributed to control groundwater flow paths in other parts of the Edwards Aquifer, such as the Knippa Gap west of San Antonio (Clark et al, 2013). We know that the fractures associated with faulting can be as significant as the faults themselves in terms of influencing groundwater recharge, flow, and discharge.…”

Section: Approachmentioning

confidence: 99%

Relay Ramp Structures and Their Influence on Groundwater Flow in the Edwards and Trinity Aquifers, Hays and Travis Counties, Central Texas

Hunt¹,

Smith²,

Andrews³

et al. 2015

Sinkholes and the Engineering and Environmental Impacts of Karst: Proceedings of the Fourteenth Multidisciplinary Conference

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The Cretaceous Edwards and Middle Trinity Aquifers of central Texas are critical groundwater resources for human and ecological needs. These two major karst aquifers are stratigraphically stacked (Edwards over Trinity) and structurally juxtaposed (normal faulting) in the Balcones Fault Zone (BFZ). Studies have long recognized the importance of faulting on the development of the karstic Edwards Aquifer. However, the influence of these structures on groundwater flow is unclear as groundwater flow appears to cross some faults, but not others. This study combines structural and hydrological data to help characterize the potential influence of faults and relay ramps on groundwater flow within the karstic Edwards and Middle Trinity Aquifers. Detailed structure contour maps of the top of Walnut Formation in the study area were created from a geologic database (n=380) comprised of primarily geophysical and driller's logs. The data were then contoured in Surfer® (Kriging) with no faults. Structure contour surfaces revealed detailed structural geometries including linear zones of steep gradients (interpreted as faults) with northeast dipping zones of low gradients (interpreted to be ramps) between faults. Hydrologic data (heads, dye trace, geochemistry) were overlaid onto the structure contour maps in GIS. Results for the Middle Trinity Aquifer suggest relay ramps provide a mechanism for lateral continu-ity of geologic units and therefore groundwater flow from the Hill Country (recharge area) eastward into the BFZ. Faults with significant displacement (>100 m) can provide a barrier to groundwater flow by the juxtaposition of contrasting permeabilities, yet flow continues across fault zones where ramps exist, or where permeable units are juxtaposed with other permeable units. In the Barton Springs segment of the Edwards Aquifer the primary flow path defined by dye tracing and heads is coincident with the Onion Creek relay ramp dipping to the northeast. This work addresses the lateral continuity (intra-aquifer flow) of the Edwards and Trinity Aquifer systems, which has importance for conceptual models and ultimately resource management.The purpose of this paper is to describe the influence of faults and related structures called relay ramps on Smith et al., 2015). This paper will explore the mechanism for lateral continuity of flow in a karst setting with complex structures. Implications of this work address the lateral continuity of units and therefore intra-aquifer flow. This has great importance for conceptual models and ultimately, resource management. 14TH SINKHOLE CONFERENCENCKRI SYMPOSIUM 5 itorial review. The authors appreciate the comments and edits of Dr. Daniel Doctor and one anonymous reviewer.

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“…Maclay and Land (1988) correctly identified the Knippa Gap as a constriction to groundwater flow in the Edwards Aquifer. Clark et al (2013) presented a similar conceptualization of the geology in this area; however, they designated the Knippa Gap location as downgradient and to the southeast of the location noted in . This constriction is bordered on the north by an extension of Cooks fault located at the southern extent of the Edwards Aquifer recharge zone (Fig.…”

Section: Characterization Of the Uvalde Poolmentioning

confidence: 92%

Uvalde Pool of the Edwards (Balcones Fault Zone) Aquifer

Green¹,

Bertetti²,

Fratesi³

et al. 2019

The Edwards Aquifer: The Past, Present, and Future of a Vital Water Resource

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The Uvalde Pool comprises the western portion of the San Antonio segment of the Edwards (Balcones Fault Zone) Aquifer. Assessment of available data on the hydro geology of Uvalde County confirms the conceptualization that the Edwards Aquifer in Uvalde County to the west of the city of Knippa acts as a partially separate ground water basin. This portion of the Edwards Aquifer is referred to as the Uvalde Pool. The Edwards Aquifer to the east of the Uvalde Pool is referred to as the San Antonio Pool. A constriction in groundwater flow between the two pools, referred to as the Knippa Gap, and marked differences in groundwater elevations on either side of the Knippa Gap are the motivation to treat the Uvalde and San Antonio Pools as sepa rate hydrogeological features. The Uvalde Pool is unique because it is the only place where the Edwards Aquifer is in hydraulic communication with the overlying and younger Buda Limestone and the Austin Chalk Aquifers. Given the karstic nature of the Edwards Aquifer in the Uvalde Pool and its relatively limited spatial extent, the Uvalde Pool is characterized as a highly transmissive aquifer, but with relatively limited storage capacity.

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Geologic framework, structure, and hydrogeologic characteristics of the Knippa Gap area in eastern Uvalde and western Medina Counties, Texas

Cited by 4 publications

References 27 publications

Integrative ichthyological species delimitation in the Greenthroat Darter complex (Percidae: Etheostomatinae)

Integrative ichthyological species delimitation in the Greenthroat Darter complex (Percidae: Etheostomatinae)

Relay Ramp Structures and Their Influence on Groundwater Flow in the Edwards and Trinity Aquifers, Hays and Travis Counties, Central Texas

Uvalde Pool of the Edwards (Balcones Fault Zone) Aquifer

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