Texas Almanac, 1986-1987 Page: 46
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46 TEXAS ALMANAC 1986-1987
Green River Valley Bolson and the Presidio and Redford
Bolsons. In the Cenozoic Alluvium region, the Pecos-
Coyoiosa area and northeastern Ward County are the
most productive areas of usable quality ground water.
Supplies are produced from the Seymour aquifer in
North Central Texas.
Edwards-Trinity (Plateau) - This aquifer underlies
the Edwards Plateau region of Southwest Texas. It con-
sists of saturated sediments of the Lower Cretaceous Co-
manchean Series made up of sand, sandstone, gravel
and conglomerate of the Trinity Group (Antlers Sand);
and cherty, gypseous, argillaceous, cavernous lime-
stones and dolomites of the Comanche Peak, Edwards
and Georgetown Formations. The ground water gener-
ally flows southeasterly, and near the edge of the Pla-
teau, movement is toward the main streams where the
water issues from springs. The water ranges in quality
from fresh to slightly saline and is hard. Most of the
municipalities on the Plateau depend on this aquifer for
.their water supply. Where the land is arable and yield
from wells is sufficient, irrigated farming is possible.
Problems exiSt in those areas where development has
exceeded the capabilities of the aquifer.
Edwards (Balcones Fault Zone) - Ground water oc-
curs in fractures, honeycomb zones and solution chan-
nels in this aquifer that underlies'an area along the
Balcones Fault Zone from Kinney County on the west
through Bexar County to Bell County on the north. Geo-
logically, it is made up of the Edwards and associated
limestones of Cretaceous age and consists of massive to
thin-bedded, nodular, cherty, gypseous, argillaceous,
white to gray limestone and dolomite of the Comanche
Peak, Edwards and Georgetown Formations, which have
been downset from the Edwards Plateau due to fault-
ing. The aquifer is recharged rapidly by water dis-
charged from springs along the edge of the Edwards
Plateau which then flows in streams that traverse the
many faults along the Balcones. The ground water
moves through the aquifer generally in an easterly,
northeasterly direction to points of discharge, notable
of which are Leona, San Antonio, San Pedro, Comal, San
Marcos, Barton and Salado Springs, plus numerous
smaller springs. In Bexar County, wells pumping from
this aquifer are among the world's largest. The water is
generally of good quality and it is used for public sup-
ply, irrigation, industrial, domestic and livestock wa-
tering purposes. Hydrologically, the aquifer is unique
and is one of the state's most valuable natural re-
sources. In the past, the aquifer was adequate to meet
San Antonio's water needs, but increased growth and
development in this area necessitate additional surface
water supplies.
Trinity Group - These basal Cretaceous-age rocks
extend over a large area of North and Central Texas
and are composed primarily of sand with interbedded
clays, limestone, dolomite, graver and conglomerates.
The Trinity Group is made up of the Twin Mountains,
Glen Rose and Paluxy Formations; however, to the west
and north where the Glen Rose Formation thins or
pinches out, the Twin Mountains and Paluxy Formations
coalesce and are called the Antlers Formation. The wa-
ter quality is acceptable for most municipal and indus-
trial purposes. Extensive irrigation occurs in Coman-
che, Eastland and Erath Counties. The aquifer has been
overdeveloped in the Dallas-Fort Worth metropolitan
area and in the vicinity of Waco where water levels have
declined to as much as 1,200 feet below the land surface.
Carrizo-Wilcox - This aquifer of Eocene age is one
of the most extensive water-bearing formations in Tex-
as geograpically, and it furnishes water to wells in a
wide belt extending from the Rio Grande northeast-
ward into Arkansas and Louisiana. It consists of hydro-
logically connected ferruginous, cross-bedded sand
with clay, sandstone, silt, lignite and gravel of the Wil-
cox Group and overlying Carrizo Formation. Throughout
most of Texas, the Carrizo-Wilcox aquifer yields fresh
to slightly saline water which is acceptable for most
irrigation, public supply and industrial uses. Because
of excessive pumping, the water levels have been sig-
nificantly lowered particularly in the Winter Garden
District of Dimmit and Zavala Counties and in the muhici-
pal and industrial areas located north of Lufkin in Ange-
lina and Nacogdoches Counties.
Gulf Coast Aquifer - Geologically, the Gulf Coast
aquifer ranges in age from Miocene to Holocene, and it
is collectively composed of the Catahoula, Oakville, La'-
garto, Goliad, Willis, Lissie and Beaumont Formations.
Lithologically, it consists of alternating beds of clay,
silt, sand and gravel which are hydrologically connect-
ed. The principal water-bearing units are the Goliad,
Willis and Lissie Formations. It parallels the Texas GulfCoast from Mexico to Louisiana. Normally, fresh to
slightly saline ground water occurs in the aquifer from
the San Antonio River basin northeastward to Louisi-
ana. In this area, large quantities are pumped for mu-
nicipal, industrial and irrigation use. Ground-water
quality tends to deteriorate in the San Antonio River
basin and southwestward to Mexico where there are
areas in which no appreciable amounts of fresh to
slightly saline water can be found. Problems of land-
surface subsidence in the Houston area are well docu-
mented. Additionally, withdrawal of ground water
from the Gulf Coast aquifer can cause increased chlo-
ride content, especially in the southwest portion, and
salt-water encroachment along the coast. Therefore,
management of future withdrawals from the aquifer is
necessary in order to alleviate serious ground-water
problems.
Minor aquifers occur in Texas as shown on the ac-
companying map and, in certain areas, are a signifi-
cant source of water supply.
Water Budget ,
Average annual precipitation in Texas is estimated
at 413,000,000 acre-feet. (One acre-foot is 325,851 gal-
lons.) The Average Yearly Water Budget for Texas
which follows, was compiled by the Texas Department of
Water Resources.
This shows that more water is lost through evapora-
tion, consumption by useless weeds and brush and dis-
charge into the Gulf of Mexico than is used by Texas
municipalities, industries and agriculture. In addition
to these losses, precipitation is very unevenly distrib-
uted in Texas, with abundant supplies in the eastern
half of the state contrasting with scarcities in the west-
ern portion. Also, it shows that the total outgo exceeds
the income, which is the result.of mining ground water.
AVERAGE ANNUAL WATER BUDGET FOR TEXAS
Million Per
Acre-Ft. Cent
INCOME
All precipitatiori 413 100.0
OUTGO
Evaporation 174 42.0
From plant cover 52 12.5
From soil surface 122 29.5
Transpiration 193 47.0
From non-economic plants 154 37.5
Cultivated crops 16 4.0
Range and pasture plants 13 3.0
Commercial forests 10 2.5
Addition to ground-
water storage 5 1.0
Surface Runoff 49 12.0
Industrial, municipal and
irrigation consumption 2 0.5
Evaporation from water surface 8 2.0
Discharged into sea 39 9.5
Total Outgo 421 102.0
Streams and Drainage Basins
Some 3,700 streams are identified in the U.S. Geo-
logical Survey Gazetteer of Texas Streams. Their com-
bined length is about 80,000 miles, and they drain 263,513
square miles within Texas. The following discussion de-
scribes 13 major rivers in its first part, with a later de-
scription of secondary streams.
Rio Grande
The Pueblo Indians called this river Posoge, "river
of great water." In 1582, Antonio de Espejo of Nueva
Vizcaya, Mexico, followed the course of the Rio Con-
chos to its confluence with a great river, which Espejo
named Rio de Norte (River of the North). The name Rio
Grande was first given the stream apparently by the
explorer Juan de Onate, who arrived on its banks near
present day El Paso in 1598.
Thereafter the names were often consolidated, as
Rio Grande del'Norte. (It has its counterpart in the Por-
tuguese Rio Grande do Sul in the state of that name in
Brazil.) It was shown also on early Spanish maps as Rio
Sari Buenaventura and Rio Ganapetuan. tni its lower
course it early acquired the name Rio Bravo, and it is
called by that name today by many Mexicans living in
its valley. At times it has also been known as Rio Turbio,
probably because of its appearance during its frequent
rises.
From source to mouth, the Rio Grande drops 12,000
feet to sea level as a snow-fed mountain torrent, carver
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Texas Almanac, 1986-1987, book, 1985; Dallas, Texas. (https://texashistory.unt.edu/ark:/67531/metapth113818/m1/48/: accessed April 23, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting Texas State Historical Association.