Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer, central Texas

Abstract

The Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer is a prolific karst aquifer system containing the fourth largest spring in Texas, Barton Springs. The Barton Springs segment of the Edwards Aquifer supplies drinking water for ~60,000 people, provides habitat for federally listed endangered salamanders, and sustains the iconic recreational Barton Springs pool. The aquifer is composed of Lower Cretaceous carbonate strata with porosity and permeability controlled by depositional facies, diagenesis, structure, and karstification creating a triple permeability system (matrix, fractures, and conduits). Groundwater flow is rapid within an integrated network of conduits discharging at the springs. Upgradient watersheds provide runoff to the recharge zone, and the majority of recharge occurs in the streams crossing the recharge zone. The remainder is direct recharge from precipitation and other minor sources (inflows from Trinity Group aquifers, the San Antonio segment, the bad-water zone, and anthropogenic sources). The long-term estimated mean water budget is 68 ft 3 /s (1.93 m 3 /s). The Barton Springs/Edwards Aquifer Conservation District developed rules to preserve groundwater supplies and maximize spring flow rates by preserving at least 6.5 ft 3 /s (0.18 m 3 /s) of spring flow during extreme drought. A paradox of the Barton Springs segment of the Edwards Aquifer is that rapid recharge allows the Barton Springs segment of the aquifer to be sustainable long term, but the aquifer is vulnerable and limited in droughts. The karstic nature of the aquifer makes the Barton Springs segment vulnerable to a variety of natural and anthropogenic contaminants. Future challenges will include maintaining the sustainability of the aquifer, considering climate change, population growth, and related land-use changes.

Subterranean movement inferred by temporary emigration in Barton Springs salamanders (Eurycea sosorum)

“…However, more research is required to understand ecological consequences of surface and subterranean habitat for these salamanders. Unfortunately, the subterranean ecology of the Barton Springs segment of the Edwards Aquifer is largely undocumented; even basic research on the diversity and distribution of its fauna is scarce (but see Hutchins, 2018 ; Nissen et al, 2018 ), despite otherwise extensive study of its hydrogeology and geochemistry ( Hunt, Smith & Hauwert, 2019 and references therein).…”

“…Eliza Spring is adjacent to Barton Springs Pool, a popular spring-fed swimming pool. Barton Springs is the primary discharge point for the Barton Springs segment of the Edwards Aquifer, a sole-source karstic aquifer that responds rapidly to changes in precipitation via a system of sinking streams that occur over a 430 km 2 area ( Hunt, Smith & Hauwert, 2019 ). Eliza Spring emerges into a concrete-bottomed pool (74 m 2 ) with a water depth of approximately 0.3 m ( Fig.…”

The Edwards Aquifer

“…In some areas, faulting has juxtaposed overlying and underlying units so that they act as part of the aquifer. These include the underlying Upper Glen Rose Formation (Hunt et al, 2019), which is part of the Trinity Group, and down-dropped sections of the overlying Buda Limestone and Austin Chalk formations that are hydraulically part of the aquifer in the Uvalde pool (Green et al, 2019b). The underlying and up-gradient portions of the Trinity Group contribute water flow to the aquifer in some areas via cross-formational flow Sharp, 1987, 1988;Oetting, 1996;Johnson et al, 2019) or where they are juxtaposed to the Edwards Aquifer by faulting.…”

“…The porosity and, in particular, permeability can vary significantly, both spatially and temporally. As a consequence, the estimated residence times of waters produced from wells or spring discharge reflect mixtures of waters with varying age (Hunt et al, 2019).…”

“…The San Antonio segment is subdivided into two pools: the larger and more significant San Antonio pool (Green et al, 2019b) and the Uvalde pool (Green et al, 2019a) located to the west (Figure 12). The Barton Springs segment contains two pools, the main pool that primarily discharges to Barton Springs, and a smaller pool that discharges to Cold Springs and directly to the Colorado River (Hauwert et al, 2004;Hunt et al, 2019) Hence, the Colorado River watershed is not identified as a contributing zone to the Edwards Aquifer (Figure 2 and Figure 12).…”