Hydrology of the Texas Gulf Coast aquifer systems
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Geology topics
Paul D. Ryder
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Ground Water Atlas of the United States: Segment 4, Oklahoma, Texas
The two States, Oklahoma and Texas, that compose Segment 4 of this Atlas are located in the south-central part of the Nation. These States are drained by numerous rivers and streams, the largest being the Arkansas, the Canadian, the Red, the Sabine, the Trinity, the Brazos, the Colorado, and the Pecos Rivers and the Rio Grande. Many of these rivers and their tributaries supply large amounts of water for human use, mostly in the eastern parts of the two States. The large perennial streams in the east with their many associated impoundments coincide with areas that have dense populations. Large metropolitan areas such as Oklahoma City and Tulsa, Okla., and Dallas, Fort Worth, Houston, and Austin, Tex., are supplied largely or entirely by surface water. However, in 1985 more than 7.5 million people, or about 42 percent of the population of the two States, depended on ground water as a source of water supply. The metropolitan areas of San Antonio and El Paso, Tex., and numerous smaller communities depend largely or entirely on ground water for their source of supply. The ground water is contained in aquifers that consist of unconsolidated deposits and consolidated sedimentary rocks. This chapter describes the geology and hydrology of each of the principal aquifers throughout the two-State area. Precipitation is the source of all the water in Oklahoma and Texas. Average annual precipitation ranges from about 8 inches per year in southwestern Texas to about 56 inches per year in southeastern Texas (fig. 1). In general, precipitation increases rather uniformly from west to east in the two States. Much of the precipitation either flows directly into rivers and streams as overland runoff or indirectly as base flow that discharges from aquifers where the water has been stored for some time. Accordingly, the areal distribution of average annual runoff from 1951 to 1980 (fig. 2) reflects that of average annual precipitation. Average annual runoff in the two-State area ranges from about 0.2 inch in the western part of the Oklahoma panhandle and parts of west Texas to about 20 inches in southeastern Oklahoma. Comparison of the precipitation and runoff maps shows that runoff is greater where precipitation is greater. However, precipitation is greater than runoff everywhere in the two-State area. Much of the precipitation that falls on the area is returned to the atmosphere by evapotranspiration, which is the combination of evaporation from surface-water bodies, such as lakes and marshes, and transpiration from plants. Part of the precipitation percolates downward through the soil and permeable rocks and is available for aquifer recharge throughout the area. Oklahoma and Texas lie within six major physiographic provinces which are differentiated on the basis of differences in landforms and geology (fig. 3). The physiographic features vary greatly and range from the low, flat Coastal Plain Province through the high, gently rolling High Plains Province to mountain ranges in the Ouachita and the Basin and Range Provinces.
Oklahoma, Texas↗
Hydrology of the Texas Gulf Coast aquifer systems
A complex, multilayered ground-water flow system exists in the Coastal Plain sediments of Texas. The Tertiary and Quaternary clastic deposits have an areal extent of 114,000 square miles onshore and in the Gulf of Mexico. Two distinct aquifer systems are recognized within the sediments, which range in thickness from a few feet to more than 12,000 feet The older system--the Texas coastal uplands aquifer system-consists of four aquifers and two confining units in the Claiborne and Wilcox Groups. It is underlain by the practically impermeable Midway confining unit or by the top of the geopressured zone. It is overlain by the nearly impermeable Vicksburg-Jackson confining unit, which separates it from the younger coastal lowlands aquifer system. The coastal lowlands aquifer system consists of five permeable zones and two confining units that range in age from Oligocene to Holocene. The hydrogeologic units of both systems are exposed in bands that parallel the coastline. The units dip and thicken toward the Gulf. Quality of water in the aquifer systems is highly variable, with dissolved solids ranging from less than 500 to 150,000 milligrams per liter. Substantial withdrawal from the aquifer systems began in the early 1900's and increased nearly continuously into the 1970's. The increase in withdrawal was relatively rapid from about 1940 to 1970. Adverse hydrologic effects, such as saltwater encroachment in coastal areas, land-surface subsidence in the Houston-Galveston area, and long-term dewatering in the Whiter Garden area, were among some of the factors that caused pumping increases to slow or to cease in the 1970's and 1980's. Ground-water withdrawals in the study area in 1980 were about 1.7 billion gallons per day. Nearly all of the withdrawal was from four units: Permeable zones A, B, and C of Miocene age and younger, and the lower Claiborae-upper Wilcox aquifer. Ground-water levels have declined hundreds of feet in the intensively pumped areas of Houston-Galveston, Kingsville, Winter Garden, and Lufkin-Nacogdoches. Water-level declines have caused inelastic compaction of clays which, in turn, has resulted in land-surface subsidence of more than one foot in an area of about 2,000 square miles. Maximum subsidence of nearly 10 feet occurs in the Pasadena area east of Houston. A three-dimensional, variable-density digital model was developed to simulate predevelopment and transient flow in the aquifer systems. The modeled area is larger than the study area, and includes adjacent parts of Louisiana and Mexico. The transient model calibration period was from 1910 (predevelopment) to 1982. Model-generated head distributions, water-level hydrographs, and land-surface subsidence were matched to measured data in selected, intensively pumped areas. For the study area, mean horizontal hydraulic conductivity in the calibrated model ranges from 10 feet per day for the middle Wilcox aquifer to 25 feet per day for permeable zone A. Mean transmissivity ranges from about 4,600 feet squared per day for the middle Claiborne aquifer to about 10,400 feet squared per day for permeable zone D. Mean vertical hydraulic conductivity ranges from 1.1x10 -5 feet per day for the Vicksburg-Jackson confining unit, to 3.8x10 -3 feet per day for permeable zone A. Mean values of calibrated storage coefficient range from 52x10 -4 for the middle Claiborne aquifer to 1.7x10 -3 for the middle Wilcox aquifer and permeable zone C. Calibrated inelastic specific storage values for clay beds in permeable zones A, B, and C in the Houston-Galveston area are 8.5x10 -5 , 8.0x10 -5 , and 8.0x10 -6 feet -1 , respectively. These values are 85, 80, and 8 times greater than the estimated elastic specific storage value for the clays in permeable zones A, B, and C, respectively. Recharge rates were mapped for predevelopment conditions as determined from a steady-state model calibration. A maximum rate of 3 inches per year was simulated in small areas, and the average rate for the study area was 034 inch per year. Total simulated recharge was 85 million cubic feet per day in the outcrop area. Recharge was equal to discharge in outcrop areas (79 million cubic feet per day) plus net lateral flow out of the study area (6 million cubic feet per day). Rates of inflow and outflow to the ground-water system have nearly tripled from predevelopment to 1982 (85 to 276 million cubic feet per day) based on model simulation. Withdrawal of 231 million cubic feet per day was supplied principally by an increase in outcrop recharge and, to a lesser extent, from a decrease in natural discharge and release of water from storage in aquifers and compacting clay beds. The average simulated 1982 recharge rate for the study area was 0.52 inch per year, with a maximum simulated rate of 6 inches per year in Jackson and Wharton Counties. Because withdrawal has caused problems such as saltwater intrusion, land-surface subsidence, and aquifer dewatering, the Texas Department of Water Resources has projected that ground-water use will decline substantially in most of the study area by the year 2030. Some areas remain favorable for development of additional ground-water supplies. Pumping from older units that are farther inland and in areas where potential recharge is greater will minimize adverse hydrologic effects.
Texas↗
Hydrogeology and predevelopment flow in the Texas Gulf Coast aquifer systems
A multilayered ground-water flow system exists in the Coastal Plain sediments of Texas. The Tertiary and Quaternary clastic deposits have an area! extent of 128,000 square miles onshore and in the Gulf of Mexico. Two distinct aquifer systems are recognized for the sediments, which range in thickness from a few feet to more than 12,000 feet. The older system the Texas coastal uplands aquifer system consists of four aquifers and two confining units in the Wilcox and Claiborne Groups. It is bounded from below by the practically impermeable Midway confining unit or by the top of the geopressured zone. It is bounded from above by the poorly permeable Vicksburg-Jackson confining unit, which separates it from the younger coastal lowlands aquifer system. The coastal lowlands aquifer system consists of five permeable zones and two confining units that range in age from Oligocene to Holocene. The hydrogeologic units of both systems are exposed in bands that parallel the coastline. The units dip and thicken toward the Gulf. Quality of water in the aquifer systems varies greatly, with dissolved solids ranging from a few hundred to more than 200,000 milligrams per liter. A three-dimensional, variable-density digital model was developed to simulate predevelopment flow in the aquifer systems, for which steady-state conditions were assumed. Horizontal hydraulic conductivities of the aquifers and permeable zones in the calibrated model range from 15 feet per day for the middle Wilcox aquifer, to 170 feet per day for the Holocene-upper Pleistocene aquifer. Vertical hydraulic conductivities range from 1 x 10 -5 foot per day for the Vicksburg-Jackson confining unit, to 1 x 10 -2 foot per day for four of the aquifers and permeable zones. The simulated values of transmissivity and leakance are functions of the percent of sand that is present in each model grid block. There is a large range in precipitation across the study area, from about 21 inches per year in the west to about 56 inches per year in the east. Eastward from a line through Corpus Christi and San Antonio, average annual precipitation ranges from about 30 to about 56 inches. A few inches per year reaches the saturated zone in topographically high areas and is discharged in low areas as evapotranspiration, seepage, springflow, and stream base flow. A smaller amount of water flows through the aquifers and permeable zones downdip from the outcrop areas. This flow results in upward or downward leakage into adjacent hydrogeologic units, but is generally upward into overlying units. Westward from the line through Corpus Christi and San Antonio, average annual precipitation ranges from about 30 to about 21 inches. The general pattern of flow in the aquifers and permeable zones is similar to that in the east, but rates of flow are somewhat smaller. In contrast to the east, ground-water discharge in the west is generally not visible. Evapotranspiration is the main mechanism for ground-water discharge, with most ground water being discharged through evapotranspiration by phreatophytes. Simulated discharge and recharge rates in the combined outcrop areas of all units do not exceed 6 inches per year. The large rates occur in small, local topographically low and high areas. The average discharge rate simulated in the outcrops of the units is 0.45 inch per year. The recharge area is considerably smaller than the discharge area, and the average recharge rate over this smaller area is 0.74 inch per year. Total simulated recharge in the outcrop areas is 269 million cubic feet per day, which is offset by an equal amount of discharge in the outcrop areas. The smallest rates of leakage are across the Vicksburg-Jackson confining unit, with downward and upward rates of less than one million cubic feet per day. The greatest rate of leakage is 47 million cubic feet per day upward into the Holocene-upper Pleistocene permeable zone.
Texas↗
Digital model of predevelopment flow in the Tertiary limestone (Floridan) aquifer system in west-central Florida
A computer model was calibrated to approximate predevelopment flow conditions in a multilayered aquifer system in 10,600 square miles in west-central Floria. The lowermost aquifer, called the Floridan aquifer, is confined in most of the study area and consists of carbonate rocks ranging up to 1,300 feet thick. The Floridan aquifer is the chief source for large withdrawals and natural springflow in the study area. Daily springflows within the study area have averaged about 2.4 billion gallons. The secondary artesian and the surficial aquifers are much less permeable than the Floridan aquifer. Where they are present and have heads higher than those in the Floridan aquifer, they provide recharge to the Floridan. Initial estimates of recharge to the Floridan aquifer were from water-balance calculations for surface-water basins; initial estimates of transmissivity were from aquifer tests and flow-net analyses. The model was calibrated for the predevelopment era, wherein steady-state flow conditions were assumed. Calibrated transmissivities for the Floridan aquifer range from less than 15,000 to several million feet squared per day. Recharge to the system was about 3,700 cubic feet per second. About 90% was discharged as springflow, and 10% was upward leakage.
Florida↗
Model evaluation of the hydrogeology of the Morris Bridge well field and vicinity in West-Central Florida
The Morris Bridge well field in west-central Florida, which is being developed may have a maximum well-field withdrawal of 40 million gallons per day. The water will be pumped from the Floridan aquifer--a sequence of carbonate rocks about 1,100 feet thick underlying surficial sand and clay deposits. A highly fractured and transmissive zone about 500 feet below National Geodetic Vertical Datum of 1929 will supply a large proportion of the water. Two-dimensional and three-dimensional digital flow models were used to evaluate the hydrogeology of the area. The model-derived leakance distribution (a property of the confining bed) for a 285-square-mile area ranged from 0.00002 to 0.008 per day. Model-derived transmissivity values for the Floridan aquifer ranged from 37,000 to 600,000 feet squared per day. Model-derived specific yield values for the surficial aquifer ranged from 0.05 to 0.30. The three-dimensional model was used to predict drawdowns in both the Floridan and surficial aquifers in response to a 40 million gallon per day stress. Mass-balance data from a 30-day simulation with no recharge from rainfall show percentage of withdrawn water that is derived from: (1) aquifer storage, (2) the Hillsborough River, and (3) reduction of evapotranspiration losses. (USGS)
Florida↗
Water table in the surficial aquifer and potentiometric surface of the Floridan Aquifer in selected well fields, west-central Florida, September 1977
The water table in the surficial aquifer and the potentiometric surface of the Floridan aquifer in a 1,200 square-mile area in west-central Florida are mapped semiannually by the U.S. Geological Survey. Maps are prepared on the basis of water levels measured in wells each May to coincide with seasonal low levels; and in September, when levels are high. The mapped area for this report contains nine producing wells fields which supplied 76.2 million gallons on September 21, 1977, to municipalities in the Tampa Bay area. The effect of localized withdrawal of groundwater from the Floridan aquifer is shown on the maps as cones of depression in both the potentiometric surface and water table. In September, water levels in observation wells in the Floridan aquifer were above those measured in May. These increases ranged from about 1 foot at the Eldridge-Wilde well field to about 25 feet at the Sun City well field. (Woodard-USGS)
Open-File Report↗
Model evaluation of the hydrogeology of the Cypress Creek well field in west-central Florida
The Cypress Creek well field is being developed to help supply a rapidly growing population in west-central Florida. The ground-water system in the Cypress Creek well-field area consists of a surficial sand aquifer, a semiconfining clay layer ranging from 2 to 25 feet in thickness, and a sequence of carbonate rocks, approximately 1,000 feet thick, called the Floridan aquifer. All recharge to the Floridan aquifer in the local area is derived from the overlying surficial sand aquifer by downward percolation through the semiconfining clay bed. The major proportion of water supplied to municipal wells open to the Floridan aquifer comes from a dolomitic section of the Avon Park Limestone containing two major cavernous zones. The hydrogeology of the well-field area was evaluated by digital model simulation. Model runs were made to analyze sensitivity of the model to variations in selected hydrologic parameters. The model was tested further by attempting to simulate the potentiometric surface of the Floridan aquifer under actual pumping stresses during the January 1976 dry period.
Florida↗
Potentiometric surface of Floridan Aquifer, Southwest Florida Water Management District, September 1976
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Open-File Report↗
Water table in the surficial aquifer and potentiometric surface of the Floridan Aquifer in selected well fields, west-central Florida, September 1976
The water table in the surficial aquifer and the potentiometric surface of the Florida aquifer in a 1200 square-mile area in west-central Florida are mapped semiannually by the U. S. Geological Survey. Maps are prepared on the basis of water levels measured in wells each May to coincide with seasonal low levels, and in September, when levels are high. The mapped area contains nine producing well fields which supplied 67.2 million gallons on September 8, 1976, to municipalities along the Gulf Coast. The water is from the Floridan aquifer, the major aquifer in Florida. The effect of localized withdrawal of ground water is shown on the maps as cones of depression in both the potentiometric and water-table surfaces. The September 1976 maps show the seasonal rise in water levels from the low levels of the previous May.
Open-File Report↗
Potentiometric surface of Floridan Aquifer, Southwest Florida Water Management District and adjacent areas, May 1977
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Open-File Report↗
Water table in the surficial aquifer and potentiometric surface of the Floridan Aquifer in selected well fields, west-central Florida, May 1977
The coastal parts of Pasco, Pinellas and Hillsborough are undergoing extensive urban development. The Floridan aquifer is the area 's principal water supply. Potentiometric and water-table maps were prepared in order to determine the effect of groundwater withdrawals in selected well fields in west-central Florida. These maps were prepared in May 1977 to capture the annual low-water-level period. Declines in the potentiometric surface ranged from 3 feet in the Starkey well field to 25 feet in the Sun City well field. (Woodard-USGS)
Open-File Report↗
Saltwater intrusion in the Floridan aquifer, coastal Citrus and Hernando Counties, Florida, 1975
The coastal parts of Citrus and Hernando Counties, Fla., are undergoing extensive urban development along U.S. Highway 19. The Floridan aquifer, a thick sequence of limestone and dolomite , is the principal source of water supply for the coastal parts of these two counties. The construction of canals that penetrate the Floridan aquifer, deficient rainfall during 1964-75, and pumping of ground water, have caused saltwater to intrude the aquifer. A map shows the inland extend of that intrusion as of 1975. The report is based on field data collected in 1964, 1973, and 1975. (Woodard-USGS)
Florida↗
Ground water in the alluvium along the Kentucky River between Carrollton and Frankfort, Kentucky
A study was undertaken to define the potential of the Kentucky River alluvial aquifer between Frankfort and Carrollton, Kentucky. An inventory of existing water wells showed that one well yielded water at a rate exceeding 300 gal/min. However, six out of the ten holes that were augered into the alluvium contained little or no water-bearing sand or gravel. Water-level data were collected from test wells installed in four of the augered holes. These data, collected when the aquifer was stressed by a flood wave in the Kentucky River, were analyzed by computer in an attempt to determine aquifer diffusivity. The method was unsuccessful due to the exceedingly heterogeneous nature of the aquifer. The probability of constructing a water well in the alluvium capable of yielding more than a few gallons per minute seems to be low. Test drilling is an essential step for those users seeking a moderate-to-large water supply from the Kentucky River alluvial aquifer.
Kentucky↗
Ground water in the alluvium along the Levisa Fork of the Big Sandy River between Louisa and Pikeville, Kentucky
A study was undertaken to define the potential of the Levisa Fork alluvial aquifer between Louisa and Pikeville, Kentucky. An inventory of existing water wells disclosed no public or industrial use of water from the alluvium, and very few screened wells drilled in the alluvium for domestic supply use. Ten test holes were augered into the alluvium to the bedrock valley floor. Although all of these holes disclosed a substantial thickness of alluvium, seven holes contained virtually no aquifer material. However, in the other three holes as much as 50 feet of clean, coarse sand and gravel was encountered, much of which would be saturated and probably in good hydraulic connection with the Levisa Fork when it is at higher stages. The probability of constructing a water well in the alluvium that is capable of yielding more than a few gallons per minute seems to be low. Test drilling is an essential step for those users seeking a moderate to large water supply from the Levisa Fork alluvium.
Kentucky↗
Ground water in the alluvium along the Licking River between Covington and Butler, Kentucky
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Open-File Report↗
Ground water in the alluvium along the Green River between its mouth and Woodbury, Kentucky
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Open-File Report↗
Ground water in the alluvium along the Green River between its mouth and Woodbury, Kentucky
The are of investigation is that part of the Green River flood plain which is in the Western Coal Field region of Ken tucky. It extends from the mouth at the Ohio River to river-mile 149 (river-kilometer 240) at Woodbury, Ky. The flood plain varies in width from 0.4 mile (0.6 kilometer) to over 6 miles ( 9 kilo meters). Total surface area is about 345 square miles (89,400 hectares). Navigational pools are maintained on this part of the Green River by a series of locks and dams.
Kentucky↗