1.7       Water Supplies

1.7.1    Groundwater[1]

There are five major and two minor aquifers supplying water to the region.  The five major aquifers are the Edwards, Carrizo, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers (Figure 1-5).  The two minor aquifers are the Sparta and Queen City Aquifers.  Each aquifer is described below, and a summary of water availability is presented in Section 1.7.1.8.

1.7.1.1     Edwards-Balcones Fault Zone Aquifer (Edwards Aquifer)

The Edwards Aquifer underlies parts of five counties (Uvalde, Medina, Bexar, Comal, and Hays) in the South Central Texas Region.  The aquifer forms a narrow belt extending from a groundwater divide in Kinney County through the San Antonio area northeastward to the Leon River in Bell County.  A groundwater divide near Kyle in Hays County hydrologically separates the aquifer into the San Antonio and the Austin regions.  The name Edwards-BFZ distinguishes this aquifer from the Edwards-Trinity (Plateau) and the Edwards-Trinity (High Plains) Aquifers, however, in this study, it will be referred to as the Edwards Aquifer (Figure 1-5).

A “bad water” line generally runs west-east through southern Uvalde and Medina Counties, the northern tip of Atascosa County, Southeastern Bexar, Comal, and Hays Counties, and the western tip of Guadalupe County.[2]  South and southeast of the “bad water” line the aquifer contains water having more than 1,000 milligrams per liter of dissolved solids.  The potential for movement of this poor quality water into the fresh water zone, as fresh water levels are lowered during periods of low recharge and high pumpage, is considered a threat to the quality of water in the fresh water zone of the aquifer, and consequently may be a threat to the water supplies of these who depend upon the aquifer.

The Edwards Aquifer supplied approximately 46 percent of the total water used in the South Central Texas Region in 1990.  Water demands of the area that is now being supplied from the Edwards Aquifer are growing at a rate of approximately 1.7 percent per year.  However, not even the present level of use can be sustained while maintaining adequate levels of flows at Comal and San Marcos Springs to support habitats of endangered species and also to meet downstream water rights.

Water from the aquifer is primarily used for municipal, irrigation, and recreational purposes.  Historically, approximately 54 percent of the total water pumped from the aquifer in the region has been used for municipal supply, with 39 percent used for irrigation purposes.  San Antonio, which presently obtains the vast majority of its municipal water supply from the aquifer, is the largest city in the United States and one of the largest in the world that relies on a single groundwater source.  The Edwards Aquifer also supplies water to industries in the San Antonio area and is the source of flow of Comal, San Marcos, Leona, San Antonio, and San Pedro Springs.  Both the Guadalupe and San Antonio Rivers are supplied with base flows from springs, which, in turn, are used downstream for municipal, industrial, and agricultural purposes.

The aquifer, composed predominantly of limestone formed during the early Cretaceous Period, exists under water-table conditions in the outcrop and under artesian conditions where it is confined below the overlying Del Rio Clay.  The Aquifer consists of the Georgetown Limestone, formations of the Edwards Group (the primary water-bearing unit) and their equivalents, and the Comanche Peak Limestone where it exists.  Saturated thickness ranges from 200 to 600 feet.

Recharge to the aquifer occurs primarily by the downward percolation of surface water from streams draining off the Edwards Plateau to the north and west and by direct infiltration of precipitation on the outcrop.  This recharge reaches the aquifer through crevices, faults, and sinkholes in the unsaturated zone.  Unknown amounts of groundwater enter the aquifer as lateral underflow from the Glen Rose Formation.  Water in the aquifer generally moves from the recharge zone toward natural discharge points such as Comal and San Marcos Springs.  Water is withdrawn through hundreds of wells, particularly municipal and industrial wells in Bexar, Comal, and Hays Counties, and irrigation wells in Bexar, Medina, and Uvalde Counties.

In the updip portion, groundwater moving through the aquifer system has dissolved large volumes of rock to create highly permeable solution zones and channels that facilitate rapid flow and relatively high storage capacity within the aquifer.  Highly fractured strata in fault zones have also been preferentially dissolved to form conduits capable of transmitting large amounts of water.  Due to its extensive honeycombed and cavernous character, the aquifer yields moderate to large quantities of water to wells, with some wells yielding in excess of 16,000 gallons per minute (gpm) (35.6 cfs, 25,810 acft/yr).  One well drilled in Bexar County flowed 24,000 gpm (53.5 cfs, 38,720 acft/yr) from a 30-inch diameter pipe.  The aquifer is significantly less permeable farther downdip where the concentration of dissolved solids in the water exceeds 1,000 mg/L.

Due to its highly permeable nature in the fresh-water zone, the Edwards Aquifer responds quickly to changes and extremes of stress placed on the system.  This is indicated by rapid water-level fluctuations during relatively short periods of time.  During times of high rainfall and recharge, the Edwards Aquifer is able to supply significant quantities of water for municipal, industrial, and irrigation uses, as well as sustain spring flows.  However, under conditions of below-average rainfall or drought, when discharge and withdrawals exceed recharge, springflows may decline to levels that are unacceptable to both environmental and downstream water rights concerns (See Section 1.10.3.1).

Operations of the largest existing surface water supply sources in the South Central Texas Region are linked to the Edwards Aquifer.  Dependable supplies from Canyon Reservoir for municipal and industrial customers are a function of springflows from the Edwards Aquifer, since releases from Canyon Reservoir are necessary to meet downstream water rights when springflows drop below certain levels.  Storage in the Medina Lake System contributes significantly to recharge of the Edwards Aquifer, and reservoirs used for power generation (Coleto Creek, Calaveras, and Braunig) are dependent upon springflows and/or treated municipal effluent, which originated from the Edwards Aquifer.  Surface water supplies available to the region are also a function of recharge to and withdrawal from the Edwards and other aquifers, and the quantities of streamflows permitted for use in counties of the Nueces, San Antonio, and Guadalupe River Basins outside the South Central Texas Region.

An important management issue for the Edwards Aquifer includes establishing a level of groundwater withdrawals to ensure adequate water levels and at least minimum springflows.  In the three river basin area where the Edwards Aquifer is located, growing demands are increasing the competition for scarce water resources.  Aquifer recharge and pumpage affect streamflows and springflows, which in turn affect endangered species, stream flows for downstream water rights holders, and instream supplies for fish and wildlife.

In 1959, after the severe drought from 1950 to 1957 that lowered water levels in the aquifer to record lows and caused Comal Springs in Comal County to go dry for several months, the Texas Legislature created the Edwards Underground Water District.  The district included Bexar, Comal, Hays, Medina, and Uvalde Counties and was charged with conserving, protecting, and recharging the underground water-bearing formations within the district and preventing waste and pollution of such underground water.  In 1989, Medina and Uvalde Counties withdrew from the district and each formed a countywide district.  In 1993, while under threat of federal intervention for alleged failure to protect federally protected species that rely on springflows from the Edwards Aquifer, the Texas Legislature enacted Senate Bill 1477.

Senate Bill 1477 abolished the Edwards Underground Water District and created a new entity, the Edwards Aquifer Authority.  SB1477 directs the Authority to implement a comprehensive management plan for the aquifer that regulates pumpage, while taking into consideration the interests and needs of all the individuals and entities that rely on the aquifer as a water source, and maintains the delicate relationship between springflows and the environment.

1.7.1.2     Carrizo-Wilcox Aquifer (Carrizo Aquifer)

The Wilcox Group, including the Calvert Bluff, Simsboro, and Hooper Formations, and the overlying Carrizo Formation of the Claiborne Group, form a hydrologically connected system known as the Carrizo-Wilcox Aquifer, which is referred to in this study as the Carrizo Aquifer.  This aquifer extends from the Rio Grande in South Texas northeastward into Arkansas and Louisiana, providing water to all or parts of 60 counties in Texas, 13 of which are located in the South Central Texas Region.  The Carrizo Sand and Wilcox Group outcrop along a narrow band that is located about 130 miles inland from the Gulf of Mexico at the eastern edge of the South Central Texas Region and about 200 miles inland at the western edge.  The aquifer dips beneath the land surface toward the coast.

The Carrizo Aquifer is predominantly composed of sand locally interbedded with gravel, silt, clay, and lignite deposited during the Tertiary Period.  Water-bearing thickness of the aquifer ranges from 200 feet in Dimmit County to more than 1,500 feet in the downdip artesian portion in Atascosa County.  In the outcrop area, Carrizo water is hard, but low in total dissolved solids.  Downdip water is softer, higher in temperature, higher in dissolved solids, locally is high in iron, and locally may contain hydrogen surfide and methane gas.[3]  Where it is found at the surface, the aquifer exists under water-table conditions and, in the subsurface, is under artesian conditions.  Yields of wells are commonly 500 gpm (1.1 cfs, 810 acft/yr), and some may reach 3,000 gpm (6.7 cfs, 4,840 acft/yr) downdip where the aquifer is under artesian conditions.  Some of the greatest yields are produced from the Carrizo Sand in the southern, or Winter Garden, area of the aquifer.

Historically, municipal and irrigation pumpage account for about 35 percent and 51 percent, respectively, of total pumpage from the Carrizo Aquifer within the region, with irrigation being the predominant use in the Winter Garden region (Sections 1.10.3.2 and 1.10.3.3).  Significant water-level declines have occurred in the semiarid Winter Garden portion of the Carrizo Aquifer, as the region is heavily dependent on groundwater for irrigation.  Since 1920, water levels have declined 100 feet in much of the area and more than 250 feet in the Crystal City area of Zavala County.

1.7.1.3     Trinity Aquifer

The Trinity Aquifer provides water to all or parts of 55 counties in Texas, including five counties (Hays, Comal, Kendall, Bexar, and Medina) in the South Central Texas Region.  The Trinity Aquifer consists of early Cretaceous Age formations of the Trinity Group that are organized into the lower Trinity Aquifer (Hosston Sand and Sligo Limestone), the middle Trinity Aquifer (lower Glen Rose Limestone, the Hensell Sand, and Cow Creek Limestone), and the upper Trinity Aquifer (upper Glen Rose Limestone).[4]  Because of its depth and poor quality, the lower Trinity has not been extensively developed.  The middle Trinity is the most widely used part of the aquifer in the South Central Texas Region.  The upper Trinity yields are low due to low porosity and permeability, and water quality is poor due to the presence of evaporate beds.

Trinity well yields are rarely more than 100 gpm (0.22 cfs, 160 acft/yr) in the South Central Texas Region.  At the present time the aquifer is being stressed due to rapid growth in the number of wells being drilled to supply new homes and commercial establishments.  Due to the heavy demands being placed upon the aquifer in relation to supplies available, much of the area underlain by the Trinity Aquifer in the Hill Country has been included in a Priority Groundwater Management Area.

1.7.1.4     Gulf Coast Aquifer

The Gulf Coast Aquifer forms a wide belt along the Gulf of Mexico from Florida to Mexico.  In Texas, the aquifer provides water to all or parts of 54 counties, including all or parts of seven coastal counties (Karnes, Gonzales, DeWitt, Goliad, Victoria, Refugio, and Calhoun) in the South Central Texas Region.  Municipal and irrigation uses have historically accounted for 90 percent of the total pumpage for the aquifer in the planning region.

The aquifer consists of complex interbedded clays, silts, sands, and gravels of the Cenozoic Age, which are hydrologically connected to form a large, leaky artesian aquifer system.  This system comprises four major components consisting of the following generally recognized water-producing formations.  The deepest is the Catahoula, which contains groundwater near the outcrop in relatively restricted sand layers.  Above the Catahoula is the Jasper Aquifer, primarily contained within the Oakville Sandstone.  The Burkeville confining layer separates the Jasper from the overlying Evangeline Aquifer, which is contained within the Fleming and Goliad Sands.  The Chicot Aquifer, or upper component of the Gulf Coast Aquifer system, consists of the Lissie, Willis, Bentley, Montgomery, and Beaumont Formations, and overlying alluvial deposits.  Not all formations are present throughout the system, and nomenclature often differs from one end of the system to the other.  In the South Central Texas Region, saturated thickness ranges from 500 feet in Karnes County to about 1,500 feet in Victoria County.  Average well yields are about 1,600 gallons per minute.  Water quality tends to deteriorate from about 500 mg/L of dissolved solids in Karnes County to over 1,000 mg/L near the coast.  Water levels have declined in areas where withdrawals have been made for municipal, industrial, and irrigation purposes.  As water levels decline, the threats of land subsidence and salt-water intrusion increase.

1.7.1.5     Edwards-Trinity (Plateau) Aquifer

The Edwards-Trinity (Plateau) Aquifer provides water to the northern portions of Uvalde and Kendall Counties in the South Central Texas Region.  The aquifer consists of saturated sediments of lower Cretaceous Age Trinity Group, including the Fredericksburg Group and Washita Group.[5]  The Glen Rose Limestone is the primary unit in the Edwards-Trinity (Plateau)

Aquifer in the southern areas of its extent.  This unit is estimated to have a thickness of up to 300 feet in these southern areas of its extent.

The aquifer generally exists under water-table conditions, however, where the Trinity (Plateau) Aquifer is fully saturated and a zone of low permeability occurs near the base of the overlying Edwards, artesian conditions may exist.  Reported well yields commonly range from less than 50 gpm where saturated thickness is thin to more than 1,000 gpm where wells are completed in jointed and cavernous limestone.  Water quality ranges from fresh to slightly saline.  The water is generally hard and varies in concentrations of calcium, magnesium, and bicarbonate.

1.7.1.6     Sparta Aquifer

The Sparta Aquifer extends in a narrow band from the Frio River in South Texas northeastward to the Louisiana border, and underlies parts of five counties (Frio, LaSalle, Atascosa, Wilson, and Gonzales) in the South Central Texas Region.  The southwestern boundary is placed at the Frio River because of a facies change in the formation, which makes it difficult to delineate the boundaries of the Sparta and contiguous formations southwestward.  The facies change results in reduced amounts of water and poorer quality water being produced from the interval.  The Sparta provides water for domestic and livestock supply throughout its extent in the region.

The Sparta Formation, part of the Claiborne Group deposited during the Tertiary, consists of sand and interbedded clay with massive sand beds in the basal section.  These beds gently dip to the south and southeast toward the Gulf Coast and reach a total thickness of up to 300 feet.  Usable quality water is commonly found within the outcrop and for a few miles downdip and in some areas may occur down to depths approaching 2,000 feet.  Yields of individual wells are generally less than 100 gpm, although some wells average 400 to 500 gpm, and a few wells produce as much as 1,200 gpm.  Water occurs under water-table conditions in the outcrop and under artesian conditions downdip where the Sparta is covered by younger, non water-bearing rocks.  Water from the aquifer is low in dissolved solids, however, in some areas is high in iron.

1.7.1.7     Queen City Aquifer

The Queen City Aquifer extends across Texas from the Frio River in South Texas northeastward into Louisiana and underlies five counties (Medina, Frio, Atascosa, Wilson, and Gonzales) in the South Central Texas Region.  The southwestern boundary is placed at the Frio River because of a facies change in the formation.  This facies change results in reduced amounts of poorer quality water produced from this interval southwest of the Frio River.  The aquifer provides water for domestic and livestock purposes throughout most of its extent and water for irrigation in Wilson County.

Sand, loosely cemented sandstone, and interbedded clay units of the Queen City Formation of the Tertiary Claiborne Group make up the aquifer.  These rocks dip gently to the south and southeast toward the Gulf Coast.  Total aquifer thickness is usually less than 500 feet.  In the outcrop area, water occurs under water-table conditions, while in the downdip subsurface, where the Queen City is covered by younger, non water-bearing rocks, the water is under artesian conditions.  Yields of individual wells are commonly low, but a few exceed 400 gpm.  Concentrations of dissolved solids are usually less than 3,000 mg/L, however, locally the water has a low pH and is high in iron.

1.7.1.8     Groundwater Availability in the South Central Texas Region

According to TWDB data, the total quantity of water obtained from aquifers of the South Central Texas Region and used within the Region in 1990 was 967,327 acft (Table 1-11).  Of this total, 53.7 percent was from the Edwards Aquifer, 28.9 percent was from the Carrizo, 9.3 percent was from the Gulf Coast, 4.9 percent was from the Sparta, and the remaining 3.2 percent was from the Queen City, Trinity, and Edwards-Trinity (Plateau) Aquifers
(Table 1-11).

Projected future groundwater supplies available in the South Central Texas Region are 812,868 acft/yr in 2000, 812,868 acft/yr in 2020, and 675,187 acft/yr in 2050 (Table 1-11).[6]  Supplies available from the Sparta, Queen City, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers are projected to hold steady on an annual basis throughout the 2000 through 2050 projection period (Table 1-11).  However, these aquifers are projected to supply only about 25 percent of the total groundwater available to the region in 2050 (Table 1-11).  The supply available from the Carrizo Aquifer is projected to decline from 304,484 acft/yr for the 2000 through 2020 period to 168,159 acft/yr for the period after 2020 (Table 1-11).  The supply for the period 2000 through 2020 includes withdrawals from storage plus estimated annual recharge, whereas the supply after 2020 is only estimated annual recharge.  The quantities available for use are subject to regulations of groundwater districts in counties where such districts exist.

1.7.2    Surface Water

The South Central Texas Region includes parts of the Rio Grande, Nueces, San Antonio, Guadalupe, Colorado, and Lavaca River Basins and parts of the Colorado-Lavaca, Lavaca-Guadalupe, and San Antonio-Nueces Coastal Basins (Figure 1-6).  The existing surface water supplies of the region include storage reservoirs and run-of-river water rights.  The geographical relationship between the river basins and the South Central Texas Region is described below, followed by a description of the existing surface water supplies.

1.7.2.1     Rio Grande Basin

The southwestern corner of Dimmit County, an area of approximately 164 square miles, is located in the Rio Grande Basin and in the South Central Texas Region.  The only surface water presently available to this area is that which can be captured in stock tanks.

1.7.2.2     Nueces River Basin

The Nueces River Basin is bounded on the north and east by the Colorado, San Antonio, and Guadalupe River Basins and the San Antonio-Nueces Coastal Basin, and on the west and south by the Rio Grande Basin and the Nueces-Rio Grande Coastal Basin.  Total drainage area of the basin is about 16,950 square miles, of which 8,973 square miles are located in the planning region.  The Nueces River rises in Edwards County and flows 315 miles to Nueces Bay on the Gulf of Mexico near Corpus Christi.  Principal tributaries of the Nueces River are the Frio and Atascosa Rivers.  Major population centers located in the basin include the cities of Uvalde (Uvalde County), Crystal City (Zavala County), Pearsall (Frio County), Pleasanton (Atascosa County), Hondo (Medina County), and Carrizo Springs (Dimmit County).

1.7.2.3     San Antonio River Basin

The San Antonio River Basin is bounded on the north and east by the Guadalupe River Basin and on the west and south by the Nueces River Basin and the San Antonio-Nueces Coastal Basin.  Total drainage area of the basin is about 4,180 square miles, of which 3,506 square miles are located in the planning region.  The San Antonio River has its source in large springs within and near the city limits of San Antonio.  The river flows more than 230 river miles across the Coastal Plain to a junction with the Guadalupe River near the Gulf of Mexico.  Its principal tributaries are the Medina River and Cibolo Creek, both spring-fed streams.  Major population centers located in the basin include the cities of San Antonio (Bexar County), Universal City (Bexar County), Schertz (Bexar County), Live Oak (Bexar County), Leon Valley (Bexar County), Converse (Bexar County), Kirby (Bexar County), Alamo Heights (Bexar County), and Floresville (Wilson County).

1.7.2.4     Guadalupe River Basin

The Guadalupe River Basin is bounded on the north by the Colorado River Basin, on the east by the Lavaca River Basin and the Lavaca-Guadalupe Coastal Basin, and on the west and south by the Nueces and San Antonio River Basins.  The Guadalupe River rises in the west-central part of Kerr County.  A spring-fed stream, it flows eastward through the Hill Country until it issues from the Balcones Escarpment near New Braunfels.  It then crosses the Coastal Plain to San Antonio Bay.  Its total length is more than 430 river miles, and its drainage area is approximately 6,700 square miles, of which 4,728 square miles are located within the South Central Texas Region.  Its principal tributaries are the San Marcos River, another spring fed stream, which joins the Guadalupe River in Gonzales County; the San Antonio River, which joins it just above its mouth on San Antonio Bay; and the Comal River, which joins it at New Braunfels.  Comal Springs are the source of the Comal River, which flows about 2.5 miles before joining the Guadalupe River.  Major population centers located in the basin include the cities of Victoria (Victoria County), San Marcos (Hays County), New Braunfels (Comal County), Seguin (Guadalupe County), Lockhart (Caldwell County), Cuero (DeWitt County), Gonzales (Gonzales County), and Luling (Caldwell County).

1.7.2.5     Lower Colorado River Basin

Only a small portion of Kendall and Caldwell Counties is located in that part of the Lower Colorado River Basin located inside the planning region.  The total drainage area of the Colorado River Basin is 41,763 square miles, of which only 76 square miles are located in the planning region.  The only surface water presently available to these two areas of the South Central Texas Region is from local stock tanks.

1.7.2.6     Lavaca River Basin

Small portions of DeWitt, Gonzales, and Victoria Counties are located in that part of the Lavaca River Basin inside the planning region.  The total drainage area of the Lavaca River Basin is 2,309 square miles, of which 156 square miles are located in the planning region.  The Lavaca-Navidad River Authority along with the TWDB owns and operates Lake Texana and has contracts to provide 32,000 acft/yr of water to customers in the Colorado-Lavaca Coastal Basin, 41,840 acft/yr to Corpus Christi in the Nueces-Rio Grande Coastal Basin, and 594 acft/yr for use in the Lavaca-Guadalupe Coastal Basin.

1.7.2.7     Coastal Basins

Parts of the Colorado-Lavaca, Lavaca-Guadalupe, and San Antonio-Nueces Coastal Basins are located within the South Central Texas Region.  None of these coastal basins has large surface water projects.  Because of potential subsidence problems and salt-water intrusion, groundwater usage is limited; thus, these basins generally rely on adjoining river basins to provide surface water to meet their needs.  The Colorado-Lavaca Coastal Basin obtains 32,000 acft/yr of surface water from Lake Texana in the Lavaca River Basin.  The Lavaca-Guadalupe Coastal Basin obtains approximately 69,000 acft/yr of imported surface water, the majority of which is supplied from the Guadalupe River.  The San Antonio-Nueces Coastal Basin obtains approximately 26,000 acft/yr of imported surface water supplied from the Nueces River Basin.

1.7.3    Existing Surface Water Resources, Including Major Springs

Development of surface water resources has been limited in the South Central Texas Region because of both the presence of significant quantities of groundwater and a comparatively low quantity of developable surface water in the western part of the region.  Existing reservoirs (Figure 1-6) and run-of-river water rights within the region are described below.

1.7.3.1     Lakes and Reservoirs

Medina Lake is located on the Medina River, of the San Antonio River Basin, at the boundaries of Medina and Bandera Counties, with Diversion Lake on the Medina River downstream of Medina Lake.  These lakes are owned by the Bexar-Medina-Atascosa Counties Water Control and Improvement District No. 1 (BMA) and historically have been used to supply irrigation water to farms along the Medina Canal System (Table 1-12).  In addition to supplying irrigation water, seepage through the lakes and riverbeds recharges the Edwards Aquifer.

Braunig and Calaveras Lakes are located in the San Antonio River Basin in Bexar County to the southeast of San Antonio and are used for electric power plant cooling water (Table 1-12).  Runoff from the watersheds above the lakes, diversion from the San Antonio River, and diversions of San Antonio reclaimed wastewater are used to maintain the necessary lake levels and meet the cooling water demands (24,263 acft in 1990).

Canyon Reservoir in the Guadalupe Basin is located in Comal County on the mainstem of the Guadalupe River.  Uses of the reservoir include water supply for municipal, industrial, steam-electric power generation, irrigation, hydroelectric power generation, flood protection, and recreation (Table 1-12).  The annual authorized diversion from Canyon Reservoir is an average of 50,000 acft/yr. GBRA has applied to TNRCC for an amendment to the Canyon Reservoir Certificate of Adjudication (#18-2074) to increase authorized diversions to approximately 90,000 acft/yr.  Stored water is made available by GBRA to water users within their district and the South Central Texas Region.

Lakes Dunlap, McQueeny, Placid, Nolte, H-4, and Wood, on the Guadalupe River, form hydroelectric power generation pools and are the sites of hydroelectric power plants on the Guadalupe River in the reach from New Braunfels to about eight miles west of Gonzales.  The lakes and the water rights are owned by GBRA, and since hydroelectric power generation is a non-consumptive use of water, water availability to these rights is not included in the tabulation of water rights for the Guadalupe Basin.

Coleto Creek Reservoir, owned by Central Power and Light Company, is located at the border of Victoria and Goliad Counties in the lower Guadalupe River Basin and is a cooling reservoir for steam-electric power generation.  The source of water is drainage from the Coleto Creek watershed, with diversions from the Guadalupe River, backed by storage in Canyon Reservoir, when needed.  The reservoir supplies water for steam-electric power generation at a power plant located in Goliad County (12,165 acft in 1990).

1.7.3.2     Run-of-River Water Rights

In addition to surface water from reservoirs, rights have been issued by the TNRCC and predecessor agencies to individuals, cities, industries, and water districts and authorities for diversion from flowing streams of the South Central Texas Region.  Each right bears a priority date, diversion location, maximum diversion rate, and annual quantity of diversion.  Some rights may include off-channel storage authorization, instream flow requirements, and various special conditions.  The principle of prior appropriation or “first-in-time-first-in-right” is applied, which means that the senior or oldest right (earliest priority date) has first call on flows, with the second, third, and more recent rights having second, third, and later standings for diversions.  This procedure gives senior right holders priority when stream flows are low, as in periods of drought, and renders junior rights less reliable during droughts (i.e., the most junior right holders may not be able to divert any water during severe droughts).

It is important to note that many run-of-river rights are for irrigation purposes, where chances are taken at planting time upon whether or not water will be available for crop production during the growing season.  In fact, TNRCC staff has historically considered whether 75 percent of the proposed diversion would be available in 75 percent of the years when reviewing applications for irrigation rights.  Most of the municipal, industrial, and steam-electric power demands, however, are for more reliable supplies than are available from run-of-river flows.  Thus, reservoirs having firm yields have been permitted by TNRCC and constructed by water suppliers.

Run-of-river permits have been summarized for the streams of the South Central Texas Region (Table 1-13).  For the Nueces River Basin part of the Regional Planning Area, run-of-river water rights total 120,097 acft, most of which are for irrigation purposes (Table 1-13).

In the San Antonio River Basin on the Medina River, downstream of the Medina Lake System to San Antonio, there are 31,794 acft of run-of-river rights (Table 1-13).  On the San Antonio River from San Antonio to the confluence with the Guadalupe River, 28,866 acft of run-of-river rights have been awarded (Table 1-13).  Most of the rights are for irrigation and livestock water with some limited municipal and industrial use and can be viewed as supply available to meet those needs in areas along the Medina and San Antonio Rivers.

Consumptive run-of-river rights in the South Central Texas Region in the Guadalupe River Basin upstream of Canyon Reservoir total 4,674 acft/yr, and downstream of Canyon to Victoria total 46,468 acft/yr.  These rights are primarily for irrigation, municipal, and industrial purposes.

In the Guadalupe River Basin downstream of Victoria, total run-of-river rights are 223,884 acft/yr considering only consumptive rights for municipal, irrigation and industrial process water (Table 1-13).

In the South Central Texas Region, the sum of the major consumptive run-of-river permitted water rights is 455,783 acft/yr (Table 1-13).  New computer models for estimating the quantity of dependable supply from run-of-river rights and reservoirs has been developed by the TNRCC through its Water Availability Modeling effort.  Results from the application of these new models subject to assumptions adopted by the SCTRWPG are included in Section 4.

1.7.3.3     Major Springs

According to selected references,[7],[8] there are six major springs located within the planning area (Comal, San Marcos, Hueco, Leona, San Antonio, and San Pedro Springs).

Comal Springs: Comal Springs is located in Landa Park, New Braunfels in Comal County.  Comal Springs discharges water from the Edwards and associated limestones of the Edwards Aquifer and issues through the Comal Springs Fault.  SB1477, Section 1.14, limits the quantity of water that can be withdrawn from the Edwards Aquifer in each calendar year for the period ending December 31, 2007 to no more than 450,000 acft, and for the period beginning January 1, 2008 to no more than 400,000 acft.  Section 1.14, Subsection h, specifies that the Edwards Aquifer Authority shall implement and enforce water management practices, procedures, and methods to ensure that not later than December 31, 2012, the continuous minimum spring flows of Comal and San Marcos Springs are maintained to protect endangered and threatened species to the extent required by federal law.  Section 1.15 of SB1477 provides that the Edwards Aquifer Authority (Authority) shall manage withdrawals and points of withdrawal from the aquifer by granting permits.  Long-term average discharge from Comal Springs is about 280 cfs.

San Marcos Springs: San Marcos Springs is located 2 miles northeast of San Marcos, in Hays County.  San Marcos Springs discharges water from the Edwards and associated limestones of the Edwards Aquifer and issues through the San Marcos Springs Fault.  SB1477, as described in the Comal Springs text above, also applies to San Marcos Springs.  Long-term average discharge from San Marcos Springs is about 150 cfs.

Hueco Springs: Hueco Springs is located about 3 miles north of New Braunfels near the confluence of Elm Creek and the Guadalupe River in Comal County.  There are two main springs issuing from a fault in the Edwards limestone at this location.  Sources of water for these springs include the Edwards Aquifer and, possibly, underflow from the Guadalupe River.  Long-term average discharge from Hueco Springs is about 40 cfs.

Leona Springs: Leona Springs consists of three groups of springs located from 1 to 6 miles southeast of Uvalde, in Uvalde County.  These springs discharge water from the Edwards Aquifer.  Long-term average discharge from Leona Springs is about 25 cfs.

San Antonio Springs: San Antonio Springs is located just above East Hildebrand Street in San Antonio, in Bexar County.  San Antonio Springs discharge water from the Edwards Aquifer.  Long-term average discharge from San Antonio Springs is about 20 cfs.

San Pedro Springs: San Pedro Springs is located in San Pedro Park, San Antonio in Bexar County.  San Pedro Springs discharges water from the Edwards Aquifer.  Long-term average discharge from San Pedro Springs is about 5 cfs.

Since present levels of withdrawals from the Edwards Aquifer are greater than the withdrawal rates specified in SB1477, it will be necessary to either limit future withdrawals to those specified in SB1477, or to increase recharge to the Aquifer in sufficient quantities to meet the future needs of those who depend upon it for their water supplies.  Therefore, actions specified by SB1477 to limit withdrawals from the Edwards Aquifer and/or to supplement supplies from the aquifer directly affect water supplies of the South Central Region.  To the extent that pumping limits are imposed to limit withdrawals to those specified by SB1477 in order to maintain flows at Comal and San Marcos Springs at levels sufficient to protect endangered and threatened species to the extent required by federal law, then the SCTRWPG will be required to obtain water from other sources to meet a part of the present needs, and for growth of needs of users that now obtain water from the Edwards Aquifer.  In any event, protection of flows at Comal and San Marcos Springs, as specified in SB1477, limits the supply of water available to the SCTRWPG to meet needs within the region, and thereby necessitates that supplies for parts of the region be obtained from other sources.

1.8       Water Quality

1.8.1    Groundwater Quality[9]

1.8.1.1     Edwards Aquifer Water Quality

The chemical quality of water in the Edwards Aquifer is typically fresh, although hard, with dissolved solids concentrations averaging less than 500 mg/L.  The downdip interface between fresh and slightly saline water represents the extent of water containing less than 1,000 mg/L.  Within a short distance down gradient of this “bad water line,” the groundwater becomes increasingly mineralized.

1.8.1.2     Carrizo Aquifer Water Quality

In the South Central Texas Region, water from the Carrizo Aquifer is fresh to slightly saline.  In the outcrop, the water is hard yet usually low in dissolved solids.  Downdip, the water is softer, has a higher temperature, and contains more dissolved solids.  A downdip “bad water” line generally runs northeast-southwest through the southeast portion of La Salle and McMullen Counties, the northeast portion of Live Oak and Karnes Counties, and southeast Gonzales County.  Southeast of the “bad water” line the groundwater has more than 1,000 mg/L of total dissolved solids.  Localized contamination of the aquifer in the Winter Garden region is attributed to direct infiltration of oil field brines on the surface and to downward leakage of saline water from the overlying Bigford Formation.  Some recently sampled wells in Dimmit and Zavala Counties were found to contain high concentrations of dissolved solids, chloride, and/or sulfate.  Downward leakage of more highly-mineralized water from overlying strata through the uncemented annular space between the well casings and boreholes of such wells is considered to be the most likely cause.  Caldwell and Gonzales Counties have areas where water from the aquifer is high in iron and manganese.  The Calvert Bluff, Simsboro, and Hooper formations of the Wilcox group all contain mean iron concentrations greater than the secondary drinking water standard of 0.3 mg/L.  Water from all three formations is hard to very hard.  Mean concentrations of sulfate and chloride are below regulatory standards in all three formations.

1.8.1.3     Trinity Aquifer Water Quality

Water quality from the Trinity Aquifer is acceptable for most municipal and industrial purposes; however, excess concentrations of certain constituents in many places exceed drinking water standards for municipal supplies.  In the southern Hill Country region, the primary contribution to poor quality in wells that have not been adequately cased through the evaporite beds in the upper part of the Glen Rose.  Water quality naturally deteriorates in the downdip direction of all the Trinity water-bearing units.  A downdip “bad water” line for the Trinity Aquifer generally trends east-west through southern Uvalde and Medina Counties, then trends southeast-northwest through central Bexar County and the southeast edge of Comal and Hays Counties.  South and southeast of this “bad water” line, the groundwater contains greater than 1,000 mg/L of total dissolved solids.  Average concentrations of nitrates, fluorides, chlorides, and sulfates are below regulatory standards.  However, localized areas of nitrate pollution due to human or animal waste, and ranching and farming activities has been identified in parts of Kendall and Hays Counties.

1.8.1.4     Gulf Coast Aquifer Water Quality

In the Gulf Coast Aquifer, water quality is generally good in the shallower portion of the aquifer.  Groundwater containing less than 500 mg/L dissolved solids is usually encountered to a maximum depth of 3,200 feet in the aquifer from the San Antonio River basin northeastward to Louisiana.  From the San Antonio River Basin southwestward to Mexico, quality deterioration is evident in the form of increased chloride concentration and salt-water encroachment along the coast.  Little of this groundwater is suitable for prolonged irrigation use due to either high salinity, or alkalinity, or both.  The downdip extent of fresh water in the Gulf Coast Aquifer is approximately equal to the coast line of the Gulf of Mexico.

1.8.1.5     Edwards-Trinity (Plateau) Aquifer Water Quality

Natural chemical quality of Edwards-Trinity (Plateau) water ranges from fresh to slightly saline.  The water is typically hard and may vary widely in concentrations of dissolved solids made up mostly of calcium and bicarbonate.  The lower formations of the Edwards-Trinity Plateau Aquifer are transitionally contiguous with the formations of the Trinity Aquifer, which crops out to the east.  The extent of fresh water in the Trinity Aquifer was discussed in subsection 1.8.1.3.  Average concentrations of nitrate, fluoride, chloride, and sulfates are below regulatory drinking water standards.

1.8.1.6     Sparta Aquifer Water Quality

The Sparta Aquifer produces water of excellent quality throughout most of its extent in the South Central Texas Region; however, water quality deteriorates with depth due to high chlorides and dissolved solids in the downdip direction.  The extent of downdip fresh water in the Sparta Aquifer generally runs along a line trending southwest-northeast from northern La Salle and McMullen Counties through southeast Atascosa and Wilson Counties to central Gonzales County.  In some locations, water within the aquifer may contain iron concentrations in excess of secondary drinking water standards.

1.8.1.7     Queen City Aquifer Water Quality

Water of excellent quality is generally found within the outcrop and for a few miles downdip, but water quality deteriorates with depth in the downdip direction due to high chlorides and dissolved solids.  The extent of downdip fresh water in the Queen City Aquifer is approximately the same as the Sparta Aquifer in the previous subsection.  Queen City Aquifer groundwater contains relatively high iron concentrations in some locations.

1.8.2    Surface Water Quality[10]

1.8.2.1     Nueces River Basin Water Quality

 Water quality in the upper portion of the Nueces River Basin in the less-inhabited reaches is good, except for relatively high nitrate-nitrogen levels occurring naturally in the spring-fed streams.  A substantial part of the flow of the upper Nueces River and its tributaries upstream of the Edwards Aquifer recharge zone enters the fractured and cavernous limestone formation of the Edwards Aquifer.  As a result, stream flows in the Nueces River Basin downstream from the recharge zone consist almost entirely of stormwater.  During low-flow conditions, chloride, sulfate, and total dissolved solids levels increase due to natural and man-made activities.  The Atascosa River has experienced elevated fecal coliform bacteria, inorganic nitrogen, and phosphorus levels downstream of the City of Pleasanton.

1.8.2.2     San Antonio River Basin Water Quality

In the past, water quality in the San Antonio Basin varied from very good in the upper basin to relatively poor in the lower basin, particularly during periods of low flow.  Since 1987, advanced water treatment has been instituted at the three major San Antonio area water recycling plants, Dos Rios, Leon Creek, and Salado Creek.  As a result dissolved oxygen concentrations in the San Antonio River have been maintained well above the State stream standard of 5.0 mg/L and aquatic life has been significantly enhanced.  However, certain water quality concerns remain in the basin.  Nutrient concentrations are elevated in nine segments, all of which occur within the planning region.  The nutrients occur in natural groundwater discharges, but concentrations become elevated with contributions from municipal wastewater discharges and non-point sources.  Elevated fecal coliform bacteria levels occur in five segments preventing

attainment of contact recreation use.  The elevated bacteria levels are primarily attributed to both urban and rural non-point pollution sources.  Although toxic chemicals have been detected in three segments, aquatic life use is only partially supported due to the lack of habitat.  There is only one industrial discharge located in the basin, the primary origin of toxic chemicals are non-point sources introduced by urban stormwater runoff.

1.8.2.3     Guadalupe River Basin Water Quality

The Guadalupe River Basin is characterized by generally high quality throughout.  Low dissolved oxygen concentrations are found sometimes in Plum Creek, possibly associated with rainfall runoff.  Elevated levels of fecal coliform bacteria associated with rainfall runoff occur in several segments, but only Plum Creek does not support contact recreation use.  Elevated levels of nutrients occur in several segments.  Elevated levels of phosphates in the 1.0 to 2.5 mg/L range associated with fairly constant spring flows in the San Marcos and Comal Rivers likely contribute to abundant growths of lush aquatic vegetation in these streams.

1.8.2.4     Lavaca-Guadalupe Coastal Basin Water Quality

The TNRCC routinely monitors the Victoria Barge Canal segment in the Lavaca-Guadalupe Coastal Basin, which has no known water quality problems.  All water quality standards and uses are supported, although phosphorus and chlorophyll-a levels are occasionally elevated.  At certain times during the year, the canal is very biologically productive, but other parameters do not indicate water quality instability.

1.8.2.5     San Antonio-Nueces Coastal Basin Water Quality

According to the TNRCC, water quality in the Mission River, located in the San Antonio-Nueces Coastal Basin, is impaired by elevated levels of fecal coliform, but the river otherwise has good water quality.  The Aransas River exhibits good water quality in the tidal stretch, but elevated levels of fecal coliform, chloride, sulfate, and total dissolved solids are common above tidal levels.

 


[1] “Ground-water Availability in Texas,” Texas Department of Water Resources, Austin, Texas, September 1979.

[2] “Groundwater Resources, and Model Applications for the Edwards (Balcones Fault Zone) Aquifer in the San
    Antonio Region, Texas,” Texas Department of Water Resources, Ulent, William B., Tommy R. Knowles,
    Glenward R. Elder, and Thomas W. Sieb, Report 239, Austin, Texas, October 1979.

[3] Ibid.

[4] “Groundwater Availability of the Lower Cretaceous Formations in the Hill Country of South-Central Texas,”
    Texas Department of Water Resources, Austin, Texas, 1983.

[5] Barker, Rene A., and Ann F. Ardis, Hydrogeologic Framework of the Edwards-Trinity Aquifer System, West Central Texas, USGS Professional Paper 1421-B, 1996.

[6] Note: The quantities available in each county are shown in Section 4.

[7] Texas Water Development Board (TWDB), “Major and Historical Springs of Texas (Report #189),” March 1975.

[8] Brune, Gunnar, “Springs of Texas,” Volume I, Branch-Smith, Inc., Fort Worth, Texas, 1981.

[9]   TWDB, “Water for Texas: A Consensus-Based Update to the State Water Plan,” Austin, Texas, August 1997.

[10] “Texas Water Quality, A Summary of River Basin Assessments,” Texas Clean Rivers Program, TNRCC,
  Austin, TX, 1996.