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The Alamo region is one of distinctly Texan natural beauty, with clear waters bubbling through Hill Country limestone on their way through rolling green hills to the Gulf of Mexico. The region has abundant water resources, but also has an ever-increasing water demand.

San Antonio, the region’s largest city, historically has depended entirely upon water from the Edwards Balcones Fault Zone (BFZ) aquifer, but is seeking other supplies to reduce its draw on that source. (The Edwards BFZ aquifer is commonly called the Edwards aquifer, but is distinct from its neighbor, the Edwards-Trinity aquifer; references in this chapter to the “Edwards aquifer” mean the Edwards BFZ.) Meeting those demands will be among the region’s top concerns in the coming decades.

Exhibit 17

Alamo Region, Major Surface Groundwater Features

See text alternative.

Source: Texas Water Development Board.

View surface groundwater features.

Annual rainfall in the Alamo region averages 25 inches annually in the Hill Country, gradually increasing to 40 inches along the Gulf Coast. Average annual maximum daily temperatures show very little variation from west to east, hovering between 76 and 78 degrees Fahrenheit. Statewide, average annual rainfall amounts range from 10 inches annually in far West Texas to 55 inches in the Beaumont/Port Arthur area, while average annual temperatures range from 70 degrees in the Panhandle to 82 degrees in South Texas.1

Five major rivers and five major aquifers provided the region with some 776,193 acre-feet or about 252.9 billion gallons, in 2006, as estimated by the Texas Water Development Board (TWDB) using the most recent data available. (An acre-foot is the amount of water needed to cover an acre of land to a depth of one foot, or 325,851 gallons, about the annual consumption of two to three Texas households. A regulation Olympic-sized swimming pool holds about two acre-feet.)

The Colorado, Guadalupe, Nueces, San Antonio and Lavaca rivers provide the region with 26 percent of its total supplies, or almost 202,000 acre-feet. Five aquifers – the Gulf Coast, Carrizo-Wilcox, Edwards-Trinity Plateau, Edwards and Trinity – provide more than 574,000 acre-feet for a 74 percent share (Exhibit 17).

Exhibit 18

Alamo Region, Total Water Use, 2006

See text alternative.

Sources: Texas Water Development Board and Texas Comptroller of Public Accounts.

View Total Water Use

Municipalities consumed almost half (48.5 percent) of the region’s water in 2006. Irrigation accounted for 30.8 percent of the remainder; manufacturing, 10.3 percent; steam-electric plants (which convert water to steam to produce electricity), 6 percent; livestock, 2.9 percent; and mining, 1.5 percent (Exhibit 18).

Groundwater – from underground streams, the water table and major and minor aquifers – is the Alamo region’s most important source of water by far, supplying about 74 percent of it. The region’s cities depend overwhelmingly on groundwater, which supplied 86.1 percent or 105.5 billion gallons of all the water they consumed in 2006. Mining and livestock uses also rely heavily on groundwater, at 84.5 percent and 66.7 percent of total usage from all supplies, respectively.

Conversely, manufacturing and steam-electric water consumers depended largely on surface water. The region’s manufacturers received 77.6 percent or 20.3 billion gallons of their water from surface sources in 2006, while steam-electric uses consumed 14.3 billion gallons of surface water, which accounted for 94.5 percent of that industry’s total water intake (Exhibit 19).4

Exhibit 19

Alamo Region, Water Sources by Sector, 2006

see alternative
In acre-feet:MunicipalManufacturing Mining Steam ElectricIrrigationLivestockTotal
Surface Water 52,402 (14%) 62,173 (78%) 1,835 (16%) 43,892 (94%)34,058 (14%)7,586 (14%)201,946 (26%)
Ground Water 323,851 (86%) 17,992 (22%) 9,966 (84%) 2,574 (6%)204,642 (86%)15,222 (86%)574,247 (74%)

Source: Texas Water Develoment Board and Texas Comptroller of Public Accounts.

The Hill Country counties – Bandera, Gillespie, Kendall and Kerr – contain the headwaters for the Guadalupe and Medina rivers, while Bexar County is the source of the San Antonio River.

In 1997, Texas Senate Bill 1 required TWDB to divide the state into 16 regions under the administration of regional water planning groups (RWPGs). The Alamo region contains all or portions of four of those RWPGs. Gillespie County is part of Region K (also known as the Lower Colorado region); Kerr and Bandera counties are in Region J (Plateau); Lavaca and Jackson counties comprise the entire Region P (Lavaca); and the remaining counties are part of Region L (South Central Texas) (Exhibit 20).5

Exhibit 20

Alamo Regional Water Planning Areas

The Alamo region's 19 counties are in 4 water planning :
The Plateau RWPG (or Region J) covers Kerr and Bandera counties. Gillespie County is in the Lower Colorado RWPG, (Region K). The South Central Texas RWPG, (Region L) consists of Atascosa, Bexar, Calhoun, Comal, DeWitt, Frio, Goliad, Gonzales, Guadalupe, Karnes, Kendall, Medina, Victoria and Wilson counties.
Lavaca and Jackson counties comprise the Lavaca RWPG (Region P).

Sources: Texas Water Development Board.

SB 1 requires at least 11 stakeholder groups – such as agriculture, municipal, environmental and business interests, electric generating utilities, water districts and river authorities – to be represented on RWPGs. Each RWPG also may add other representatives at will.6 SB 1 requires RWPGs to evaluate their current water supplies and estimate their supplies and uses over a 50-year period; the current planning horizon extends to 2060. Based on 2000 data, the TWDB projects that the Alamo region’s overall water use will rise by 36.7 percent to 1,185,400 acre-feet in 2060.

Irrigation is the only category of water use expected to decline by 2060, by 22.4 percent to 287,787 acre-feet. Steam-electric use is expected to increase by 168.6 percent to 95,025 acre-feet, followed by large increases in manufacturing (79.4 percent growth in water use, to 179,487 acre-feet), municipal (78.3 percent, to 581,275 acre-feet) and mining uses (61.1 percent, to 17,197 acre-feet), with a minimal increase in livestock use (1.2 percent, to 24,629 acre-feet) (Exhibit 21).7

Exhibit 21

Upper Rio Grande Actual and Projected Water Use by Sector 2000-2060 (in acre feet)

Sector 2000 Actual 2020 Projected 2040 Projected 2060 Projected
Irrigation 370,850 326,852 305,510 287,787
Livestock 24,335 24,629 24,629 24,629
Manufacturing 100,071 132,677 156,493 179,487
Mining 10,672 14,393 15,825 17,197
Municipal 326,062 422,828 505,800 581,275
Steam Electric 35,379 49,161 67,609 95,025
Total 867,369 970,540 1,075,866 1,185,400

Source: Texas Water Development Board.

The expected increase in steam electric use, the largest among the major use categories, is attributable to Atascosa, Bexar, Goliad and Guadalupe counties, with smaller increases expected in Calhoun, Frio and Victoria counties. Many factors could explain the increase, according to TWDB, including the region’s proximity to several fuel sources that lend themselves to electricity production as well as the general increase in the state’s population and electricity needs.8

Surface Water

The Alamo region is blessed with many rivers and streams. The Hill Country counties – Bandera, Gillespie, Kendall and Kerr – contain the headwaters for the Guadalupe and Medina rivers, while Bexar County is the source of the San Antonio River. The Colorado River flows southeast through the region’s eastern counties, while the Lavaca River bisects Lavaca and Jackson counties. Springs from the Edwards aquifer in Comal County feed both the Guadalupe and Comal rivers.

Because of the region’s high-volume river flows and generally gentle topography, it has little need or opportunity to build many reservoirs to store water. The region’s 12 reservoirs were designed to contain 974,524 acre-feet water for industrial, municipal, irrigation, flood control and recreational uses. Over time, the lakes have filled somewhat with sediment, lowering their current conservation storage capacity to 913,510 acre-feet.

Exhibit 22

Alamo Region, Major Lakes and Reservoirs

Reservoir/Lake Name River Basin Year 2010 projected yield (acre-feet) Conservation storage capacity (acre-feet)
Victor Braunig Lake San Antonio 12,000 26,500
Calaveras Lake San Antonio 37,000 63,200
Canyon Lake Guadalupe 88,107 378,781
Coleto Creek Reservoir Guadalupe 20,848 31,040
Lake Dunlap Guadalupe Hydroelectric power only 5,900
Lake Texana Lavaca 74,500 153,246
Medina Lake San Antonio - 254,843
Total 232,455 913,510

Source: Texas Water Development Board.

Freshwater from the state’s rivers flowing into bays and estuaries is critical to maintaining ecosystems that support the state’s coastal fishing, shrimp, oyster and tourism industries.

Exhibit 22 lists the region’s seven major reservoirs. Three smaller lakes – Mud Lake No. 4, Cox Lake and Prudential Reservoir – are owned by corporations and used for industrial purposes only. The remaining two minor reservoirs – Lake McQueeney in Guadalupe County and Lake Gonzales in Gonzales County – have a combined conservation storage capacity of less than 12,000 acre-feet.9

The Alamo region narrows downstream to include only one of the state’s many estuaries, San Antonio Bay. Freshwater from the state’s rivers flowing into bays and estuaries is critical to maintaining ecosystems that support the state’s coastal fishing, shrimp, oyster and tourism industries.


As noted above, the Alamo region’s five major aquifers – the Gulf Coast, Carrizo-Wilcox, Edwards-Trinity Plateau, Edwards and Trinity – provide 74 percent of its water supply. These aquifers are water-bearing layers of permeable rock, sand or gravel. They can be shallow or deep, with waters that are fresh, brackish or saline (Exhibit 23).

Where the upper layers of an aquifer emerge on the surface of the land, in what hydrologists call an outcrop, springs result. Several springs either create or contribute to many of the region’s rivers; these include the San Marcos and Comal along the Balcones Escarpment, a geological formation of porous limestone following a semicircle from Kinney County in the west through Medina, Bexar and Comal counties northeastward to Travis County.

The Alamo region’s dependence on groundwater, however, may be problematic because both TWDB and all regional planning groups anticipate a statewide reduction in groundwater supplies. TWDB projects that Texas’ groundwater supplies, with current permits and infrastructure, will fall by 32 percent between 2010 and 2060. Although no projection data exists specifically for the Alamo region, regional planning groups collectively estimate that the state’s groundwater supplies will fall by 22 percent over the same period.10

Exhibit 23

Alamo Region, Major Aquifers

See text alternative

Source: Texas Water Development Board.

View major aquifers text.

Exhibit 24

Edwards Aquifer

See text alternative

Source: Texas Water Development Board.

View Edwards Aquifer text.

To manage and conserve groundwater resources, to which landowners may have extensive property rights, state law allows for the creation of groundwater conservation districts (GCDs, sometimes abbreviated as GWCDs) to allow for some local control over groundwater pumping and export. GCDs generally follow county boundaries, but of course aquifers do not; every aquifer in Texas underlies multiple counties, which can make groundwater management complex and disjointed.

Exhibit 25

Alamo Region, Groundwater Conservation Districts and Groundwater Management Areas

See text alternative

Source: Texas Water Development Board.

View groundwater conservation districts and management Areas text.

To provide for greater cohesiveness, state law requires TWDB, together with the Texas Commission on Environmental Quality (TCEQ), to create Groundwater Management Areas, or GMAs. Groundwater districts within GMAs must meet at least annually to develop mutually agreeable “desired future conditions” of the aquifers based on TWDB models and other hydrology information. Once an amount is determined, RWPGs within the GMA may use the data for planning, and GCDs may issue groundwater withdrawal permits within the amount of “managed available groundwater” determined by the GMA.11

A unique state entity, the Edwards Aquifer Authority (EAA), manages the Edwards aquifer. EAA was created by the 1993 Texas Legislature to “manage, conserve, preserve and protect the aquifer” and to “increase recharge and prevent waste or pollution of the aquifer.” A 17-member EAA governing board includes 15 members elected from the region and two non-voting members appointed by local entities (Exhibit 24).12

Every county in the Alamo region except Calhoun is within either a GCD’s jurisdiction or that of the EAA (Exhibit 25).

The San Antonio Water System (SAWS) and other municipal water providers in the region are well aware of their dependence on the Edwards aquifer, and have worked hard both to conserve it and to find new supplies. In 1993, SAWS began an intensive conservation program by providing rebates for low-flow toilets, encouraging drought-tolerant landscapes and even restricting charity car washes to designated areas. According to environmental groups, SAWS customers have reduced their average daily water usage from 225 gallons per person in 1982 to 140 today, even though SAWS estimates that the city’s population rose by 50 percent over the same period.13 The city of San Antonio also implemented a drought ordinance in 2005 that could save 1.3 billion gallons of water annually.14

The city is also pursuing new, unconventional water sources. In July 2009, TWDB approved a $35 million loan to San Antonio to help it begin developing a desalination facility that could treat water from a saline aquifer in the area and make it fit for human consumption.15


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