Discharge From the Edwards Aquifer Through the Leona River Floodplain, Uvalde, Texas¹

Abstract

Analysis of results from an electrical resistivity survey, a magnetic survey, and an aquifer test performed on the Leona River floodplain in south-central Texas indicates that ground-water discharge from the Edwards Aquifer through the Leona River floodplain may be as great as 91.7 Mm 3 ⁄ year. When combined with an estimate of 8.8 Mm 3 ⁄ year for surface flow in the Leona River, as much as 100.5 Mm 3 ⁄ year could be discharged from the Edwards Aquifer through the Leona River floodplain. A value of 11,200 acre-ft ⁄ year (13.82 Mm 3 ⁄ year) has been used as the calibration target in existing ground-water models for total discharge from Leona Springs and the Leona River. Including ground water or underflow discharge would significantly increase the calibration target in future models. This refinement would improve the conceptualization of ground-water flow in the western portion of the San Antonio segment of the Edwards Aquifer and would thereby allow for more accurate assessment and management of the ground-water resources provided by the Edwards Aquifer.

Uvalde Pool of the Edwards (Balcones Fault Zone) Aquifer

“…The Uvalde Pool portion of the Edwards Aquifer is classified as confined and is designated as the confined zone; however, since the Edwards Aquifer is in hydraulic communication with the Austin Chalk and Buda Limestone Aquifers, which are unconfined, the Edwards Aquifer in the Uvalde Pool is, in reality, unconfined (Fratesi et al, 2015). Using a similar argument, the Leona Aquifer is apparently hydraulically connected with the Edwards, Buda Limestone, and Austin Chalk Aquifers at the headwaters of the Leona River from Highway 90 in the city of Uvalde south to Fort Inge (Green et al, 2008(Green et al, , 2009. To the south of Fort Inge, a difference in groundwater elevations between the Leona and Edwards Aquifers suggests that the Leona Aquifer is not hydraulically connected with the Edwards Aquifer in this locality.…”

“…The southern boundary of the Edwards Aquifer in the Uvalde Pool is modeled as a no-flow boundary aligned with the transition from fresh to saline water (typically set at 1000 mg/L total dissolved solids; Harden, 1968;Groschen and Buszka, 1997), with the exception of discharge occurring in the Leona River floodplain as underflow via paleo-streambeds and discharge from springs in the Nueces River channel south of the city of Uvalde (Green et al, 2008(Green et al, , 2009. The recharge zone of the Edwards Aquifer forms the northern boundary of the Uvalde Pool.…”

“…In addition to the Edwards Aquifer, there are significant secondary aquifers in the Uvalde Pool, including the Austin Chalk, Buda Limestone, and the Leona Formation (Green et al, 2008(Green et al, , 2009. Similarities in groundwater elevations to the west of the Uvalde salient support the conceptualization that the Edwards, Buda Limestone, and Austin Chalk Aquifers are in hydraulic communication with the Uvalde Pool.…”

Kinney Pool: Defining the western boundary of the Edwards (Balcones Fault Zone) Aquifer, Texas

“…Potential stream floodplains that could provide points of discharge include Las Moras Creek, Pinto Creek, and other smaller tributaries, although the flow capacity of these smaller tributaries is probably limited. Recent assessments of the capacity of subsurface flow through floodplains along the southern boundary of the Edwards Aquifer, however, indicate that these floodplains can have sufficient capacity for subsurface flow to accommodate at least a portion of the discharge from the Kinney County segment to balance the water budget (Green et al, 2008). However, it is likely that total recharge to the Kinney Pool is somewhat less than 86 × 10 6 m 3 /yr.…”

Application of factor analysis and electrical resistivity to understand groundwater contributions to coastal embayments in semi-arid and hypersaline coastal settings

“…Statistical methods such as analysis of variance (ANOVA), multivariate linear regression (MLR) and factor analysis on environmental data have also produced valuable models that aid in identifying variations in water quality and contamination sources in various hydrologic systems (Morehead et al, 2008;Thareja et al, 2011;Hae-Cheol and Montagna, 2012). Recently, subsurface imaging techniques such as direct current electrical resistivity (ER) surveys have been increasingly used to delineate and quantify groundwater flow paths and discharge rates into surface water bodies (White, 1988;Greenwood et al, 2006;Green et al, 2008). Consecutive ER images conducted along the same survey line during different environmental conditions give groundwater discharge estimates over time (Nyquist et al, 2008;Dimova et al, 2012;Johnson et al, 2012).…”