The Geological Survey of the United States Department of the Interior has for many years conducted various geologic and geophysical studies, topographic mapping, and water-resource investigations in Texas. The survey's work is organized under three divisions: geologic, national mapping, and water resources.
Geologic Division. In cooperation with the Bureau of Economic Geology of the University of Texas at Austin, the Geologic Division has made important contributions to the knowledge of the mineral composition, rock structure, mineral resources, and geologic history of the state. Regional investigations supplemented by chemical, physical, and paleontological research, in the laboratory and in the field, enable scientists to determine the nature of the rocks and minerals that make up the earth to specify how they were formed and to identify coal, oil, and gas resources as well as to assess their potential for development. Data from assessments for coal resources are entered into the National Coal Resources Data System and are used in the generation of maps and resource reports. Several regional geologic studies have been completed by the USGS in Texas. Included are professional papers on the Sierra Blanca region, and the Sierra Diablo and the Guadalupe Mountains of the Trans-Pecos; on the Pennsylvanian and Permian rocks of north central Texas; and on the rocks of the Del Rio-Indian Wells area. Professional papers, bulletins, and maps have focused on economic mineral deposits such as the mercury in the Terlingua District of the Big Bend region, the oil geology of the Horseshoe Atoll (a buried reef in west central Texas that is the largest limestone reservoir in the United States), the uranium deposits of southern Texas, the oil-bearing Jurassic rocks of northeastern Texas, and the uranium-bearing black shales. Additional reports and maps have been produced regarding the geology of the Franklin Mountains near El Paso and of the eastern Marathon Basin, gravity surveys and petrography of native sulfur deposits of Culberson County, environmental studies of the outer continental shelf of the Gulf of Mexico, seismic activity, geologic hazards on the Gulf floor, geomorphology of the Sierra Madera Cryptoexplosion Structure in Pecos County, stratigraphy of the Glass Mountains in West Texas, mineral-resource potentialities of national forests in East Texas, and linear features in the Panhandle. Monographs have been written on fossils of the Woodbine Formation in Northeast Texas, the conodonts of the Llano Uplift, the fusulinids of north central Texas, the ostracods of the Glass Mountains in western Texas, and aeroradioactivity in South Texas.
Ongoing work by the Geologic Division involves sedimentation in coastal areas. The environmental degradation of Texas estuaries, which are a major fish resource, has prompted a cooperative program of the USGS, the Texas Water Development Board, and the Bureau of Economic Geology. The program began in three Texas estuarine systems in 1993. Its goal is to develop a historical record of the water supplied to the estuaries by determining the rate of delta growth. This information will provide the database needed to develop a water-supply policy. Studies of the Trinity and Lavaca River systems are near completion, and a study of the Nueces River is projected.
National Mapping Division. The USGS has been making topographic maps of Texas since the 1880s. The early maps show roads, towns and settlements, and political boundaries though the physical features are only generalized. Some of these maps are valuable for historical studies, since they portray roads and trails, water holes, river crossings, and other important landmarks used by early travelers and cattle drovers. From the 1940s through the 1980s the National Mapping Division, then known as the Topographic Division, used the most modern techniques for defining in great detail the physical and cultural features of the state. By cooperating with several state agencies, the division was able to accomplish the complete primary map coverage for Texas at 1:24,000-scale (one inch = 2,000 feet) in graphic (paper) format. The National Mapping Division also has completed Texas State coverage in both 1:100,000 (paper and digital) and 1:250,000-scale maps. The cooperative programs between the state and the National Mapping Division support the production of 1:24,000-scale computerized (digital) maps including 1:12,000 Digital Orthophoto coverage. Digital map data are used by the state in its geographic information systems (computer systems capable of assembling, storing, manipulating, and displaying geographically referenced information) to support the applications that were originally accomplished by the use of paper maps.
Water-Resources Division. The initiation of water-resources surveys in Texas is associated with a meeting in fall 1898 between Cyrus C. Babb and Thomas U. Taylor of the University of Texas. Taylor had an interest in the hydrology of Texas rivers and had made miscellaneous measurements at selected sites. As a result of the meeting, he was appointed resident hydrographer for Texas. The state legislature enacted a general irrigation law in 1913, which provided for administration of water resources by a Board of Water Engineers. Given the cost of obtaining streamflow information, the USGS and the board eventually combined funds to form a cooperative program that provided the data requisite to the missions of both agencies. Later activities of the USGS include the groundwater resources of the state as well as the quality of both surface and ground water. The USGS now works in cooperation with the Texas Water Development Board, the Texas Natural Resources Conservation Commission, the Texas Department of Transportation, and the Texas Parks and Wildlife Department, plus more than seventy other state and local agencies, river authorities, and other federal agencies involved in water-related issues. Surface and ground water supplies are studied to provide a better understanding of water-resource problems, including quantity, quality, contaminants, and water use distribution, variability, and flooding. Water-resource work of the USGS in Texas includes collection of hydrologic data, flood-related activities, monitoring of land subsidence, national water-quality-assessment programs, land-use effects on water quality, assessment of water-quality conditions at federal installations, and availability of groundwater. Programmatic areas provide information useful to varied goals of several planning, management, and regulatory agencies.
Water-resources investigations in Texas involve both the collection and interpretation of hydrologic information. Water data are used to facilitate water-resources planning and management decisions. Data are collected for streamflow studies at 374 stream sites, for storage studies at 72 reservoir sites, for water-quality assessments at 308 stream sites and in 221 wells, and for water-level studies in 747 wells. Because of the long-term, continual nature of the data-collection program, the USGS is in a unique position to monitor and assess trends in hydrologic conditions. For example, trends in selected water-quality constituents in the Trinity River downstream from Dallas-Fort Worth since the mid-1970s indicate that improvements in wastewater-treatment facilities have improved the quality of water in the Trinity River.
Meteorologic and physiographic factors in parts of Texas combine to produce some of the most intense rainstorms in the nation: these cause severe, destructive floods somewhere in Texas almost every year. The catastrophic flooding in the Houston area in October 1994, for instance, resulted in at least twenty-two deaths, hundreds of millions of dollars in property damage, and substantial environmental damage. When flooding is imminent, the USGS mobilizes field crews that work around the clock making direct measurements of streamflow and water-surface elevations. The data collected by USGS personnel are provided continuously to the National Weather Service and the Federal Emergency Management Agency, among other agencies. The data collected during a series of floods provide a chronology of historical peak streamflows and water-surface elevations that aid in flood forecasting and the design of structures to convey or withstand floodwater. The USGS also is involved in related statewide flood studies, including a flood-frequency analysis and a study of channel scour at bridges. The flood-frequency analysis, which is done on a cost-sharing basis with the Texas Department of Transportation, uses streamflow data collected at previous and current streamflow-gauging sites to predict such streamflow characteristics as flood magnitude and probability. The information from this study, together with knowledge of low-flow streamflow characteristics at gauging sites, is useful in bridge and highway design, reservoir design and operation, and waste-discharge and pollution-abatement activities. Strong currents, such as those caused by floodwater, can erode the streambed at the foundation of a bridge. If the streambed is eroded (scoured) sufficiently, then the foundation can shift and cause sudden failure of the bridge. Studies of streambed scour in Texas by the USGS, done in cooperation with the Texas Department of Transportation, are identifying the bridges in the state most susceptible to scour-related failure. The work also includes development and testing of instrumentation for monitoring streambed scour at bridges during floods.
Compaction of underground clay layers caused by the withdrawal of large amounts of groundwater, as well as oil and gas, in the Houston area has resulted in land subsidence from one to nearly ten feet in an area of more than 5,000 square miles. Tidal inundation and increased frequency of flooding in subsidence-affected areas have required the expenditure of millions of dollars to reclaim submerged land, construct levees, and elevate structures and roadways. The USGS, in cooperation with the Harris-Galveston Coastal Subsidence District, continually monitors land subsidence in the Houston area. Global Positioning System technology uses satellites to measure land-surface elevations with an accuracy of within one centimeter. The elevation data are electronically transmitted daily to a computer at the subsidence district office. Because of the relation between groundwater withdrawals and land subsidence, the USGS, in cooperation with the Harris-Galveston Coastal Subsidence District, the Fort Bend Subsidence District, and the city of Houston, measures and prepares reports of changes in groundwater levels in the Houston area.
The long-term goals of the National Water-Quality Assessment Program are to describe the status and trends in the quality of a large representative part of the nation's surface and groundwater resources and to identify the natural and human factors that affect their quality. The NAWQA Program is designed to produce a wealth of water-quality information useful to policymakers and water managers at local, state, and national levels. Two NAWQA Program studies are underway in Texas: the Trinity River basin study, which was started in 1991, and the South-Central Texas study, which was started in 1994 and focuses on the Edwards Aquifer in the San Antonio region. Communication and coordination with water-management, environmental-protection, and other water-resource agencies and institutions are key components of the program studies. Results of the studies are presented in a variety of technical and lay reports to local, state, and federal agencies and to the public. One approach being used to address water-quality trends involves examining and doing laboratory analysis of bottom-sediment cores from reservoirs and correlating the ages of sediment layers in the cores with concentrations of various trace elements and organic constituents in those layers. For example, examination of cores of sediment from White Rock Lake in Dallas has shown that concentrations of lead in the bottom sediments were constant from 1910 to the late 1950s, then increased about fivefold between about 1960 and the early 1970s, when rapid urbanization of the watershed began. Concentrations decreased markedly from the early 1970s to the present, coincident with the change to unleaded gasoline.
The USGS is cooperating with local water-resource-management agencies to monitor stormwater runoff in many of the major urban areas in Texas. These data have been collected for several years in the Austin, Dallas-Fort Worth, Houston, and San Antonio metropolitan areas. Information obtained from stormwater monitoring and characterization studies has been used by the cooperating agencies to assess the effectiveness of stormwater-detention structures, to establish basinwide water-quality ordinances, to assess the quality of recharge water entering the Edwards Aquifer, and to serve as the basis for permitting stormwater discharges into streams in Dallas-Fort Worth and San Antonio. The USGS is cooperating with the State Soil and Water Conservation Board in studies designed to help evaluate the effectiveness of agricultural "best management practices." A major study underway in the Seco Creek basin west of San Antonio is to quantify the effects of farming and ranching in order to inaugurate the best management practices for water quality and quantity, sediment discharge to streams, and rates of recharge to the Edwards aquifer.
The USGS is cooperating with the United States Navy, the United States Air Force, the United States Army Corps of Engineers, and Department of Energy in a variety of complex contaminant hydrology, hydrogeology, and lake studies at federal installations. A study is in progress at the Naval Weapons Industrial Reserve Plant and the adjacent Naval Air Station, Dallas to determine whether contaminants from sites on the installations have affected the water quality and aquatic ecology of adjacent Mountain Creek Lake and whether contaminants have migrated into the well casings of deep water-supply wells that pass through contaminated zones in the shallow aquifer. The USGS is assisting Air Force Plant 4 in Fort Worth in studies involving issues similar to those at NAS Dallas. Hazardous substances from the Superfund site at the installation have contaminated parts of the shallow aquifer; the installation is adjacent to residential areas and a reservoir. One of the studies is defining the groundwater-flow system and characterizing groundwater quality in the residential areas adjacent to the plant. At the Superfund site at the Pantex Plant near Amarillo, the USGS, in cooperation with the Department of Energy and the corps of engineers, is conducting a study to determine the potential for contaminants in shallow groundwater to migrate downward into water-yielding zones of the Ogallala Aquifer, which is the major source of water supply in the Panhandle.
Aquifers supply about 60 percent of the freshwater used in Texas. Withdrawal of groundwater from some aquifers at rates exceeding those of natural recharge have reduced supplies and resulted in extensive local water-level declines. The USGS, in cooperation with the El Paso Water Utilities-Public Service Board, the Texas Water Development Board, and the United States Army, has monitored the Hueco Bolson aquifer since the 1930s and is studying the water resources in this border area in an effort to minimize the effects of groundwater use and to prolong the life of the aquifer. Competition for groundwater supplies in the San Antonio region is intense, particularly during droughts. Withdrawals from the Edwards Aquifer to meet increasing water-supply needs are a threat to the continuation of flows at Comal Springs, the largest spring in the Southwest, and at San Marcos Springs. The highly productive Edwards Aquifer is the San Antonio region's major source of water. Both springs supply downstream water requirements, sustain federally listed endangered species, and are tourist attractions. The USGS has monitored the quality and quantity of the Edwards Aquifer for more than sixty years and is involved in studies to provide the information needed by the Edwards Underground Water District, the San Antonio Water System, and other agencies to assess and manage the water resources of the Edwards. See also GEOLOGICAL SURVEYS OF TEXAS, GEOLOGY, MARINE RESOURCES, MINERAL RESOURCES AND MINING, WATER LAW, and other articles beginning with WATER.