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L. F. Land

Publications and source records attributed to L. F. Land.

10 recordsLinked to original sources
USGS1997

Water-quality assessment of the Trinity River Basin, Texas — Nutrients and pesticides in the watersheds of Richland and Chambers Creeks, 1993-95

A study of nutrients and pesticides was conducted during February-August 1995 in the west-central part of the Trinity River Basin, where land commonly is used for growing crops. Water and bed-sediment samples were collected at 8 small reservoir sites in the headwaters (known as Natural Resources Conservation Service reservoirs), at 5 stream sites, and at 3 Richland-Chambers Reservoir sites. The analysis included data from the Chambers Creek near Rice site (08064100), which was sampled repeatedly during March 1993-September 1995. Total nitrogen concentrations in the Natural Resources Conservation Service reservoirs were less than 1.0 milligram per liter, as nitrogen, except in 2 of the 8 reservoirs. For the five stream sites, total nitrogen concentrations at the beginning of the study ranged from 0.5 to 1.8 milligrams per liter. Peaks were noted in all stream sites during either March or April; the greatest peak concentration was 4.8 milligrams per liter, as nitrogen. By the end of the study, concentrations decreased to less than 1.2 milligrams per liter, as nitrogen. In the Richland-Chambers Reservoir, the February-March and June sampling showed total nitrogen concentrations of about 0.6 milligram per liter, as nitrogen. At the beginning of the study, all five of the stream sites had total phosphorus concentrations less than 0.04 milligram per liter, as phosphorus. Peak concentrations in the streams occurred in the May sampling except at one site. Two sites had concentrations greater than 0.2 milligram per liter, as phosphorus. By the end of the study, concentrations decreased to less than 0.04 milligram per liter, as phosphorus, except at one site where the concentrations were about 0.08 milligram per liter. Concentrations in the Richland-Chambers Reservoir were less than 0.04 milligram per liter, as phosphorus. Total nitrogen and total phosphorus concentrations generally increased with streamflow and with the percentage of cropland in the drainage area upstream from the sampling site. Herbicides were detected in the streams much more often than insecticides were. Nineteen herbicides and 9 insecticides were detected at the 08064100 Chambers Creek near Rice site. Atrazine and metolachlor, the most commonly detected herbicides, occurred in all samples at this site. Other herbicides detected in 25 percent or more of the samples were alachlor, fluometuron, prometon, simazine, trifluralin, and 2,4-D. At the beginning of the study, the number of herbicides detected in the five stream sites was 4 or 5. The greatest number of herbicides detected in the streams occurred in May samples, ranging from 7 to 10. The number of herbicides detected in the Richland-Chambers Reservoir ranged from 6 to 8. Generally, more herbicides were detected in high-streamflow samples than in low-streamflow samples. However, a consistent relation between the number of herbicides in samples and the percentage of cropland in a drainage area was not evident. At the beginning of the study, atrazine concentrations at the stream sites were less than 0.4 microgram per liter, except at one site. In the streams, concentrations peaked in March and April; the greatest peak concentration was 20 micrograms per liter. By the end of the study, atrazine concentrations decreased to less than 0.4 microgram per liter at all the stream sites. In the Richland-Chambers Reservoir, the concentrations were about 1 microgram per liter during February-March and about 3 micrograms per liter in June. Atrazine concentrations tended to increase with increasing streamflow. A consistent relation between atrazine concentrations and the percentage of cropland in a drainage area was not evident. The greatest number of insecticides detected in water samples was two. Diazinon, the most frequently detected insecticide, had slightly greater concentrations in May and June - between 0.01 and 0.02 microgram per liter. The only organochlorine insecticides detected in bed-sedime

Texas↗
USGS1988

U.S. Geological Survey ground-water studies in Texas

Ground-water resources supply almost 60 percent of the freshwater used in Texas, excluding withdrawals for thermoelectric-power generation (less than 3 percent). About 73 percent of the ground water withdrawn is used for irrigation, about 17 percent for public supply, and about 7 percent for industrial, rural domestic, and livestock uses. About 8 million people, or 48 percent of the population of Texas, depend on ground water as a public or rural domestic supply. The dependence on ground water is greatest in the arid northwestern part of the State, where most of the water is used for irrigation. This area contains 70 percent of all irrigated land in Texas, and uses about 85 percent of the total ground water withdrawn for irrigation.

Texas↗
USGS1988

Reassessment of the Georgetown limestone as a hydrogeologic unit of the Edwards Aquifer, Georgetown area, Texas

The Edwards aquifer consists of geologic units known as the Comanche Peak (oldest) and Edwards Limestones, Kiamichi Formation, and Georgetown Limestone. The Edwards Limestone is the main water-bearing zone. The shallow geologic units dip to the east-southeast at a slope of 50 to 100 feet per mile in the Georgetown area. The Edwards aquifer extends from the western limits of the outcrop to the transition zone from freshwater to saline water to the east. The downdip continuity of the geologic units is interrupted by several faults in the Balcones fault zone. The aquifer is recharged by the infiltration of precipitation and streamflow in the outcrop and is discharged by springs in the outcrop and by wells, evapotranspiration, and leakage through the overlying confining bed in the confined area. Streams in the area regionally flow from the west to the east. A reassessment of the uppermost geologic unit of the Edwards aquifer, the Georgetown Limestone, was conducted in the Georgetown area, Texas, using: (1) data from six surveys of streamflow gains and losses and ground-water levels, (2) aquifer tests at three clusters of test wells, (3) variation in water-quality characteristics to indicate ground-water circulation, and (4) previous studies. Data from the six surveys did not show a pattern of corresponding streamflow gains and losses with positive (upward) and negative (downward) head differentials, respectively, between the main water-bearing zone of the Edwards aquifer and the streams. A consistent and corresponding pattern was shown only for the subreach containing Berry Springs. The aquifer tests consisted of "slug" test analyses to determine the transmissive characteristics of the Georgetown Limestone and produced 8 9 hydraulic conductivity values ranging from 1.4 X 10 -8 to 2.8 X 10 -9 centimeters per second at four of the six test wells. The other two test wells did not produce data suitable for conventional aquifer-test analysis. An analysis of the water-quality characteristics suggests that the Edwards Limestone and the streams have a significant hydraulic connection but the ground-water circulation between the Edwards Limestone and the Georgetown Limestone is very limited. The only area where a high degree of hydraulic connection between the main water-bearing zone of the Edwards aquifer (Edwards Limestone) and the streams was found is near the updip limits of the Georgetown Limestone, where a nearby major fault occurs and where major springs have developed. These findings suggest that the Georgetown Limestone does not function as a unit of the Edwards aquifer but as a regional confining bed with localized avenues that allow flow to and from the underlying Edwards aquifer.

Water-Resources Investigations Report↗
USGS1987

Simulation of flow in the Edwards Aquifer, San Antonio region, Texas, and refinement of storage and flow concepts

The Edwards aquifer is a complexly faulted, carbonate aquifer lying within the Balcones fault zone of south-central Texas. The aquifer is recharged mainly by streamflow losses in the outcrop area of the Edwards aquifer and is discharged by major springs located at considerable distances, as much as 150 mi, from the areas of recharge, and by wells. Groundwater flow within the Edwards aquifer of the San Antonio region was simulated to investigate concepts relating to the storage and flow characteristics. A general purpose, finite difference model, modified to provide the capability of representing barrier faults, was used to simulate groundwater flow and storage in the aquifer. The simulations investigated the effects of complex geologic structures and significant changes in transmissivity, anisotropy, and storage coefficient, with initial values based on concepts developed in previous studies. Results of the simulations confirmed the original estimates of transmissivity values (> 100 sq ft/sec) in the confined zone of the aquifer between San Antonio and Comal Springs. A storage coefficient of 0.05 in the unconfined zone of the aquifer produced the best simulation of water levels and springflow. A major interpretation resulting from the simulations is that two essentially independent areas of regional flow were identified in the west and central part of the study area. Flow from the two areas converges at Comal Springs. The directions of computed flux vectors reflected the presence of major barrier faults which locally deflect patterns of groundwater movement. The most noticeable deflection is the convergence of flow through the geologic structural opening, the Knippa gap, in eastern Uvalde County. A second significant interpretation is that groundwater flow in northeastern Bexar, Comal, and Hays Counties is diverted by barrier faults toward San Marcos Springs, a regional discharge point. (Lantz-PTT)

Texas↗
USGS1985

Water-resources activities of the U.S. Geological Survey in Texas; fiscal years 1982-84

The U.S. Geological Survey (USGS) was established by an act of Congress on March 3, 1879, to provide a permanent Federal agency to conduct the systematic and scientific classification of the public lands, and examination of the geological structure, mineral resources, and products of national domain. An integral part of that original mission includes publishing and disseminating the earth-science information needed to understand, to plan the use of, and to manage the Nation's energy, land, mineral, and water resources. Since 1879, the research and fact-finding role of the USGS has grown and been modified to meet the changing needs of the Nation it serves. As part of that evolution, the USGS has become the Federal Government's largest earth-science research agency, the Nation's largest civilian mapmaking agency, the primary source of data on the Nation's surface- and ground-water resources, and the employer of the largest number of professional earth scientists. Today's programs serve a diversity of needs and users. Programs include: Conducting detailed assessments of the energy and mineral potential of the Nation's land and offshore areas. Investigating and issuing warnings of earthquakes, volcanic eruptions, landslides, and other geologic and hydrologic hazards. Conducting research on the geologic structure of the Nation. Studying the geologic features, structure, processes, and history of the other planets of our solar system. Conducting topographic surveys of the Nation and preparing topographic and thematic maps and related cartographic products. Developing and producing digital cartographic data bases and products. Collecting data on a routine basis to determine the quantity, quality, and use of surface and ground water. Conducting water-resources appraisals in order to describe the consequences of alternative plans for developing land and water resources. Conducting research in hydraulics and hydrology and coordinating all Federal water-data acquisition. Using remotely sensed data to develop new cartographic, geologic, and hydrologic research techniques for natural resources planning and management. Providing earth-science information through an extensive publications program and a network of public access points. Along with its continuing commitment to meet the growing and changing earthscience information needs of the Nation, the USGS remains dedicated to its original mission to collect, analyze, interpret, publish, and disseminate information about the natural resources of the Nation providing "earth science in the public service."

Open-File Report↗
USGS1985

A preliminary assessment of land-surface subsidence in the El Paso area, Texas

The northeast and southeast parts of the El Paso area are underlain by Hueco bolson deposits as much as 9,000 feet thick. The deposits consist of lenses of gravel, sand, silt, and clay. In the Rio Grande Valley, about 400 to 450 feet of these deposits have been eroded and replaced with as much as 200 feet of alluvium. Ground water in the shallow alluvial aquifer in the Rio Grande Valley and in the Hueco bolson aquifer outside the valley is under water-table conditions, whereas ground water in the bolson aquifer in the valley is under leaky artesian conditions. Maximum water-level declines in the Hueco bolson aquifer are 110 feet east of the Franklin Mountains and 150 feet in the downtown El Paso area. For the shallow aquifer, the maximum declines have been 125 feet in the downtown area. Compressable materials in the freshwater zone of the aquifer range from 50 to 450 feet. Recharge from the Rio Grande to the shallow alluvial aquifer has increased from an estimated 15,000 acre-feet during 1968 to 30,000 acre-feet during 1983, an increase of about 1,000 acre-feet per year. Leakage from the Rio Grande is expected to continually increase in the near future because of a continued decline in ground-water levels. The amount of leakages from the canals is much less than from the river. Releveling of bench marks along lines to the northeast and the southeast of the Rio Grande, and along its channel commonly show land subsidence of about 0.2 foot. The maximum measured subsidence is 0.41 foot along the river in the Chamizal zone. No subsidence was detected at the Riverside Diversion Dam. A comparison of subsidence, water-level declines, and clay thickness along the three survey lines shows the expected correlation of greater subsidence with thicker accumulated clay material for a given decline in water levels. The preconsolidation stress was expected to range from 85 to 115 feet of water-level decline on the basis of subsidence studies in Arizona and California. A study of specific-unit compaction along the three survey lines shows that the values usually range between 1.0 to 2.5 x 10-5 feet per feet squared. These values are comparable to the ones computed in the Tulare-Wasco, California, and Houston-Galveston, Texas, areas following the exceedance of the local preconsolidation stress. Because of this comparability, the specific-unit compaction for future periods in the El Paso area probably will not increase dramatically when the preconsolidation stress is exceeded, if it has not already been exceeded. In addition to regional subsidence, local subsidence is indicated by observable surface fractures but has not been verified by precise leveling. These local areas coincide with areas that historically were swamps along the Rio Grande.

Texas↗
USGS1983

Streamflow losses along the Balcones Fault Zone, Nueces River basin, Texas

An investigation was conducted to quantify and to determine distribution of streamflow losses and gains that occur during sustained flow conditions in the Balcones Fault Zone of the Nueces River basin. The streams studied include the West Nueces, Nueces, Dry Frio, Frio, and Sabinal Rivers, and Seco, Hondo, and Verde Creeks. Streamflow measurements made during the recession of storm flows identified direct recharge to outcrops of the Edwards aquifer and related limestones that ranged from as high as 393 cubic feet per second for the Dry Frio River to as low as 42 cubic feet per second for the Sabinal River. Recharge to outcrops of the Buda Limestone, Eagle Ford Shale, and Austin Group also eventually reaches the Edwards aquifer, and measurements identified losses to these formations ranging from as high as 174 cubic feet per second for the Frio River to near zero for Verde Creek. Statistical evaluations of historical daily flow records for the streams that have gaging stations upstream and downstream from the recharge zone provided mathematical relationships that expressed downstream flow in terms of other significant parameters. For each stream, flow entering the recharge zone is most significant in defining downstream flow; for some streams, antecedent flows at the upstream site and ground-water levels are also significantly related to downstream flow. The analyses also determined the discharges required upstream from the recharge zone to sustain flow downstream from that zone. These discharges ranged from 355 cubic feet per second for the combined Frio and Dry Frio Rivers to 33 cubic feet per second for the Nueces River. The entire flows of lesser magnitude are generally lost to recharge to the aquifer.

Texas↗
USGS1977

Ground-water resources of the Riviera Beach area, Palm Beach County, Florida

The principal source of freshwater that has been developed in the Riviera Beach area is the so-called shallow aquifer, which is composed of sand, shells, sandstone, limestone, marl, and occasionally clay strata. Often a stratum contains mixtures of two or more of these materials and occasionally they are cemented. The aquifer ranges in thickness from approximately 300 feet at Lake Worth to less than 175 feet in the interior. The major water-bearing zone usually consists of cemented layers of sand and shells, about 100 feet thick, in the lower part of the aquifer. The quality of water in the shallow aquifer is generally suitable for municipal use except for an area along C-17 Canal where the dissolved solids concentration exceeds 500 milligrams per liter. The primary source of recharge to the shallow aquifer is rainfall. Discharge is mainly by evapotranspiration. Other discharges include seepage into drainage canals and Lake Worth, and pumpage. The configuration of the water table is greatly influenced by Lake Worth, C-17 Canal, West Palm Beach water catchment area, rainfall, and municipal pumpage. The major threat to development of water supplies, and possibly to the continuation of a current withdrawal rate of over 5 million gallons per day, is seawater intrusion. The municipal supply wells are almost 1 mile inland from the source of the seawater (Lake Worth), but the combined effects of increased pumpage, reduced recharge resulting from increased land development, and below normal rainfall, have caused seawater to advance inland in the aquifer. Additional supplies could be developed to the west, away from the threat of seawater intrusion.

Florida↗