Emilie & Albert
Friedrich Wilderness Park
    21395 Milsa Road | San Antonio TX | 78256

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The Waters of Friedrich Park

The balcony effect caused by alternating layers of hard and soft limestone. It inspired the Spanish word "Balcones" as the name for the escarpment and fault zone that extend through the region.

Hydrogeology is the study of water as it moves through the earth. Most of the rural population of the country depends on groundwater, and the baseflow (normal flow) of most streams also depends on groundwater. However, as people in Texas well know, water is something we tend to take for granted until it is contaminated or we start to run out.

The Edwards Aquifer is without a doubt the most controversial and frequently discussed geologic feature in the Bexar County area. A complex hydrologic system within the Edwards Limestone in the Balcones Fault Zone, the Edwards Aquifer is divided into four segments: San Antonio, Barton Springs, Northern Balcones, and Washita Prairie. When most studies refer to the Edwards Aquifer, they refer to the San Antonio Segment that extends from Brackettville about 150 km east to San Antonio, then northeast about 80 km to near the town of Kyle.

The San Antonio Segment of the Edwards Aquifer is divided into four zones: contributing or drainage zone, recharge zone, artesian or confined zone, and saline zone. Friedrich Park is in the contributing zone, the upstream and predominantly non-

Edwards Limestone area from which streams flow onto or cross the recharge zone, the exposure of Edwards Limestone within the fault zone where water enters the aquifer. The artesian zone is that area where the Edwards Limestone is down-faulted into the subsurface, and its groundwater is confined between upper and lower less permeable formations. The aquifer's largest springs occur where groundwater rises up fractures to discharge in stream valleys. The "bad water line" is the downgradient boundary of the artesian zone with the saline zone, where total dissolved solids in the groundwater exceed 1,000 mg/l. Groundwater flow in the aquifer is complicated but generally southward from the recharge to artesian zone, then east and northeastward to discharge from major springs in Uvalde, San Antonio, New Braunfels, and San Marcos.

While the Edwards Aquifer takes center stage in local hydrogeologic discussions and in its geographic position in the county, other important aquifers include the Glen Rose and Cow Creek aquifers to the north (often grouped together with other aquifers and called the Trinity Aquifer), and the Carrizo-Wilcox Aquifer to the south. Water storage, flow rate, recharge and discharge rates, and susceptibility to contamination vary greatly between the county's aquifers, and assumptions should not be made that characteristics of one apply to the others.

The upper member of the Glen Rose is the sole unit of the Upper Trinity Aquifer. Underlying Friedrich Park, this aquifer is unconfined and locally recharged. Although the upper Glen Rose contains enough clay and marl beds to make it the lower barrier for much Edwards Aquifer groundwater, its outcrop exposes enough limestone and dolomite beds to absorb some recharge. Regionally, there is little use or demand for the aquifer's groundwater because of its low yield and its contact with gypsum zones, which results in occasional high sulfate

concentrations. Yet in the north Bexar County area, many privately owned wells tap upper Glen Rose water, especially since some strata in the unit are cavernous and store and yields larger volumes of water. In addition to wells, the Upper Trinity also discharges through seeps and minor springs.

Significant volumes of water also discharge from the upper Glen Rose into the Edwards Aquifer. This hydrologic connection is demonstrated in northern Bexar County by a continuous water table flowing downgradient from the upper Glen Rose into the Edwards, the absence of a lithologic barrier to impede flow, the presence of several recharge caves that cross from one unit into the other, and the lack of an outlet for the considerable recharge entering the upper Glen Rose. This last point is especially evident following storm events when relatively few streams on the upper Glen Rose on and near Freidrich Park discharge water onto the state-designated portion of the Edwards Aquifer recharge zone. Most streamflows are lost down fractures and sinkholes before reaching the Edwards' recharge zone and enter the Edwards underground via the Glen Rose.

For more information:

The Edwards Aquifer Authority contains a wide array of informational and educational materials on the Edwards Aquifer available on the web and in printed form.

More information on the Edwards, as well as on several other Texas aquifers is available from the Bureau of Economic Geology, Texas Water Development Board, and the U.S. Geological Survey

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