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U.S. Geological Survey Karst Interest Group Proceedings, Fayetteville, Arkansas, April 26-29, 2011

Karst aquifer systems are present throughout parts of the United States and some of its territories and are developed in carbonate rocks (primarily limestone and dolomite) that span the entire geologic time frame. The depositional environments, diagenetic processes, and post-depositional tectonic events that form carbonate rock aquifers are varied and complex, involving both biological and physical processes that can influence the development of permeability. These factors, combined with the diverse climatic regimes under which karst development in these rocks has taken place result in the unique dual or triple porosity nature of karst aquifers. These complex hydrologic systems often present challenges to scientists attempting to study groundwater flow and contaminant transport. The concept for developing a Karst Interest Group evolved from the November 1999 National Groundwater Meeting of the U.S. Geological Survey (USGS), Water Resources Division. As a result, the Karst Interest Group was formed in 2000. The Karst Interest Group is a loose-knit grass-roots organization of USGS employees devoted to fostering better communication among scientists working on, or interested in, karst hydrology studies. The mission of the Karst Interest Group is to encourage and support interdisciplinary collaboration and technology transfer among USGS scientists working in karst areas. Additionally, the Karst Interest Group encourages cooperative studies between the different disciplines of the USGS and other Federal agencies, and university researchers or research institutes. This fifth workshop is a joint workshop of the USGS Karst Interest Group and University of Arkansas HydroDays workshop, sponsored by the USGS, the Department of Geosciences at the University of Arkansas in Fayetteville. Additional sponsors are: the National Cave and Karst Research Institute, the Edwards Aquifer Authority, San Antonio, Texas, and Beaver Water District, northwest Arkansas. The majority of funding for the proceedings preparation and workshop was provided by the USGS Groundwater Resources Program, National Cooperative Mapping Program, and the Regional Executives of the Northeast, Southeast, Midwest, South Central and Rocky Mountain Areas. The University of Arkansas provided the rooms and facilities for the technical and poster presentations of the workshop, vans for the field trips, and sponsored the HydroDays banquet at the Savoy Experimental Watershed on Wednesday after the technical sessions.

Scientific Investigations Report↗

Effects of regulation on L-moments of annual peak streamflow in Texas

Several techniques exist to estimate annual peak-streamflow frequency for streamflows that have recurrence intervals ranging from 2 to 500 years for natural (unregulated) drainage basins in Texas. Unfortunately, such techniques have limited applicability in regulated basins. There are numerous regulated basins throughout Texas, which has more than 7,000 dams that are identified by Texas Natural Resource Conservation Commission permits. The effects on annual peak streamflow from reservoirs created by these dams range from negligible to the complete suppression of the flood hydrograph; also, reservoirs can artificially create flood-like hydrographs. The large number of reservoirs and their widespread distribution in Texas necessitate an assessment of flood characteristics in regulated basins. Therefore, the U.S. Geological Survey, in cooperation with the Texas Department of Transportation, conducted a study of the effects of regulation on L-moments of annual peak streamflow in Texas. For this report, the State was divided into three regions. Four regression equations to estimate the L-moments of natural annual peak-streamflow data for ungaged sites were derived for each region from data for 367 streamflow-gaging stations in natural basins. The explanatory variables in the equations are contributing drainage area, basin shape factor, and stream slope. The effects of regulation on the L-moments of annual peak-streamflow data were determined by analysis of maximum and normal storage-capacity data from reservoirs for 96 streamflow-gaging stations in variously regulated basins. The results indicate that as potential flood storage (defined by the difference between total maximum and normal capacity) in a basin increases, the mean annual peak streamflow decreases nonlinearly. Evidence strongly indicates (despite contrary expectation) that the higher L-moments (coefficient of L-variation, L-skew, and L-kurtosis) are unaffected by regulation.

Texas↗

Areal-reduction factors for the precipitation of the 1-day design storm in Texas

The reduction of the precipitation depth from a design storm for a point to an effective (mean) depth over a watershed often is important for cost-effective design of hydraulic structures by reducing the volume of precipitation. A design storm for a point is the depth of precipitation that has a specified duration and frequency (recurrence interval). The effective depth can be calculated by multiplying the design-storm depth by an areal-reduction factor ( ARF ). ARF ranges from 0 to 1, varies with the recurrence interval of the design storm, and is a function of watershed characteristics such as watershed size and shape, geographic location, and time of year that the design storm occurs. This report documents an investigation of ARF by the U.S. Geological Survey, in cooperation with the Texas Department of Transportation, for the 1-day design storm for Austin, Dallas, and Houston, Texas. The "annual maxima-centered" approach used in this report specifically considers the distribution of concurrent precipitation surrounding an annual precipitation maxima. Unlike previously established approaches, the annual maxima-centered approach does not require the spatial averaging of precipitation nor explicit definition of a representative area of a particular storm in the analysis. Graphs of the relation between ARF and circular watershed area (to about 7,000 square miles) are provided, and a technique to calculate ARF for noncircular watersheds is discussed.

Texas↗

Hydrologic data for North Creek, Trinity River basin, Texas, 1977

The U.S. Soil Conservation Service is actively engaged in the installation of flood- and soil-erosion reducing structures in Texas under the authority of "The Flood Control Act of 1936 and 1944" and "Watershed Protection and Flood Prevention Act" (Public Law 566), as amended. The Soil Conservation Service has found that approximately 3,500 floodwaterretarding structures would be physically and economically feasible in Texas. As of September 30, 1977, 1,695 (corrected figure) of these structures had been built. This watershed-development program will have varying but important effects on surface- and ground-water resources of river basins, especially where a large number of the floodwater-retarding structures are built. Basic hydrologic data under natural and developed conditions are needed to appraise the effects of the structures on the yield and mode of occurrence of runoff. During the period 1951-62, the U.S. Geological Survey began hydrologic investigations in 12 small watersheds (fig. 1). As of Sept. 30, 1977, data collection in eleven of these study areas has been completed and is now in progress in one area. This study is being made in cooperation with the Texas Department of Water Resources, the Soil Conservation Service, the San Antonio River Authority, the city of Dallas, and the Tarrant County Control and Improvement District No. 1. The 12 study areas were chosen to sample watersheds having different rainfall, topography, geology, and soils. In five of the study areas (North, Little Elm, Mukewater, Little Pond-North Elm, and Pin Oak Creeks), streamflow and rainfall records were collected prior to construction of the floodwater-retarding structures, thus affording the opportunity for analyses of the conditions "before and after" development. A summary of the development of the floodwater-retarding structures in each study area as of Sept. 30, 1977, is shown in table 1.

Texas↗

Chemical and physical characteristics of water in estuaries of Texas, October 1976-September 1978

The Texas Water Plan (1968) proposes development and utilization of water resources in Texas and includes provision for the use and preservation of water in the estuaries of the State. Management of estuarine waters requires knowledge of the hydrodynamics and of the continuing changes in the chemical and physical characteristics of water in the estuaries. In September 1967, the U.S. Geological Survey and the Texas Department of Water Resources began a cooperative water-resources investigation of the principal estuaries along the Texas coast (fig. 1) except the Rio Grande estuary, which is under the jurisdiction of the International Boundary and Water Commission, United States and Mexico. The objectives of the investigation are to define: (1) The occurrence, source, and distribution of nutrients; (2) the physical, organic, and inorganic water-quality constituents and their areal distribution and time variations; (3) the chemical and physical characteristics of Gulf water that enters the estuaries; (4) the occurrence, quality, quantity, and dispersion of drainage entering the estuarine systems; and (5) the current patterns, directions, and rates of water movement. The coastal waters of Texas are not classical estuaries, but are similar to them in ecosystems and mixing phenomena. A description of various types of estuaries is presented in "Estuaries" edited by Lauff (1967, p. 3-11). The term estuary as used in this report, refers to concomitant water bodies in which streamflow mixes with seawater.

Open-File Report↗

Use of the STORM model for estimating the quantity and quality of runoff from the metropolitan area of Houston, Texas

The "STORM" model, developed by the U.S. Army Corps of Engineers, was selected from existing models and adapted to use available data to compute runoff from the Houston, Texas, area and to compute the loads and concentrations of biochemicaloxygen demand, dissolved solids, total phosphorus, total organic carbon, total nitrogen, and fecal-coliform bacteria. The water-quality data simulated by the STORM model will be used by the Texas Department of Water Resources to refine and verify a model of the Calveston Bay estuarine system. Discharge and precipitation data for the 1975 water year and all available waterquality analyses were used to calibrate the model for the Buffalo, Whiteoak, Brays, Sims, Hunting, Greens, and Vince Bayous. Data for the 1974 water year were used to verify the model for discharge. After verification, the calibrations were adjusted to balance the difference between the 1974 and 1975 error predictions for discharge. The adjusted model was used with records of precipitation and evaporation to simulate a 20-vear record of the quantity and quality of runoff from the modeled area.

Texas↗

Attributes for MRB_E2RF1 Catchments by Major River Basins in the Conterminous United States: NLCD 2001 Land Use and Land Cover

This tabular data set represents the estimated area of land use and land cover from the National Land Cover Dataset 2001 (LaMotte, 2008), compiled for every MRB_E2RF1 catchment of the Major River Basins (MRBs, Crawford and others, 2006). The source data set represents land use and land cover for the conterminous United States for 2001. The National Land Cover Data Set for 2001 was produced through a cooperative project conducted by the Multi-Resolution Land Characteristics (MRLC) Consortium. The MRLC Consortium is a partnership of Federal agencies (http://www.mrlc.gov), consisting of the U.S. Geological Survey (USGS), the National Oceanic and Atmospheric Administration (NOAA), the U.S. Environmental Protection Agency (USEPA), the U.S. Department of Agriculture (USDA), the U.S. Forest Service (USFS), the National Park Service (NPS), the U.S. Fish and Wildlife Service (USFWS), the Bureau of Land Management (BLM), and the USDA Natural Resources Conservation Service (NRCS). The MRB_E2RF1 catchments are based on a modified version of the U.S. Environmental Protection Agency's (USEPA) ERF1_2 and include enhancements to support national and regional-scale surface-water quality modeling (Nolan and others, 2002; Brakebill and others, 2011). Data were compiled for every MRB_E2RF1 catchment for the conterminous United States covering the South Atlantic-Gulf and Tennessee (MRB2), the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy (MRB3), the Missouri (MRB4), the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf (MRB5) and the Pacific Northwest (MRB7) river basins.

Data Series↗

Hydrologic and water-quality data at Government Canyon State Natural Area, Bexar County, Texas, 2002-10

The U.S. Geological Survey, in cooperation with the U.S. Department of Agriculture Natural Resources Conservation Service, the Edwards Aquifer Authority, and the Texas Parks and Wildlife Department, collected rainfall, streamflow, evapotranspiration, and stormflow water-quality data at the Laurel Canyon Creek watershed, within the Government Canyon State Natural Area, Bexar County, Tex. The purpose of the data collection was to support evaluations of the effects of brush management conservation practices on components of the hydrologic budget and water quality. One component of brush management was to take endangered wildlife into consideration, specifically the golden-cheeked warbler ( Dendroica chrysoparia ). Much of the area that may have been considered for brush management was left intact to protect habitat for the golden-cheeked warbler. The area identified for brush management was approximately 10 percent of the study watershed. The hydrologic data presented here (2002–10) represent pre- and post-treatment periods, with brush management treatment occurring from winter 2006–07 to spring 2008.

Texas↗

Attributes for MRB_E2RF1 Catchments by Major River Basins in the Conterminous United States: NLCD 2001 Tree Canopy

This tabular data set represents the mean percent tree canopy from the Canopy Layer of the National Land Cover Dataset 2001 (LaMotte and Wieczorek, 2010), compiled for every MRB_E2RF1 catchment of Major River Basins (MRBs, Crawford and others, 2006). The source data set represents tree canopy percentage for the conterminous United States for 2001. The Canopy Layer of the National Land Cover Data Set for 2001 was produced through a cooperative project conducted by the Multi-Resolution Land Characteristics (MRLC) Consortium. The MRLC Consortium is a partnership of Federal agencies (http://www.mrlc.gov), consisting of the U.S. Geological Survey (USGS), the National Oceanic and Atmospheric Administration (NOAA), the U.S. Environmental Protection Agency (USEPA), the U.S. Department of Agriculture (USDA), the U.S. Forest Service (USFS), the National Park Service (NPS), the U.S. Fish and Wildlife Service (USFWS), the Bureau of Land Management (BLM), and the USDA Natural Resources Conservation Service (NRCS). The MRB_E2RF1 catchments are based on a modified version of the U.S. Environmental Protection Agency's (USEPA) ERF1_2 and include enhancements to support national and regional-scale surface-water quality modeling (Nolan and others, 2002; Brakebill and others, 2011). Data were compiled for every MRB_E2RF1 catchment for the conterminous United States covering New England and Mid-Atlantic (MRB1), South Atlantic-Gulf and Tennessee (MRB2), the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy (MRB3), the Missouri (MRB4), the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf (MRB5), the Rio Grande, Colorado, and the Great basin (MRB6), the Pacific Northwest (MRB7) river basins, and California (MRB8).

Data Series↗

Attributes for MRB_E2RF1 Catchments by Major River Basins in the Conterminous United States: NLCD 2001 Imperviousness

This tabular data set represents the mean percent impervious surface from the Imperviousness Layer of the National Land Cover Dataset 2001, (LaMotte and Wieczorek, 2010), compiled for every MRB_E2RF1 catchment of selected Major River Basins (MRBs, Crawford and others, 2006). The source data set represents imperviousness for the conterminous United States for 2001. The Imperviousness Layer of the National Land Cover Data Set for 2001 was produced through a cooperative project conducted by the Multi-Resolution Land Characteristics (MRLC) Consortium. The MRLC Consortium is a partnership of Federal agencies (http://www.mrlc.gov), consisting of the U.S. Geological Survey (USGS), the National Oceanic and Atmospheric Administration (NOAA), the U.S. Environmental Protection Agency (USEPA), the U.S. Department of Agriculture (USDA), the U.S. Forest Service (USFS), the National Park Service (NPS), the U.S. Fish and Wildlife Service (USFWS), the Bureau of Land Management (BLM), and the USDA Natural Resources Conservation Service (NRCS). The MRB_E2RF1 catchments are based on a modified version of the U.S. Environmental Protection Agency's (USEPA) ERF1_2 and include enhancements to support national and regional-scale surface-water quality modeling (Nolan and others, 2002;Brakebill and others, 2011). Data were compiled for every MRB_E2RF1 catchment for the conterminous United States covering New England and Mid-Atlantic (MRB1), South Atlantic-Gulf and Tennessee (MRB2), the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy (MRB3), the Missouri (MRB4), the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf (MRB5), the Rio Grande, Colorado, and the Great basin (MRB6), the Pacific Northwest (MRB7) river basins, and California (MRB8).

Data Series↗

Water budget for the Nueces Estuary, Texas, May-October 1998

The Texas Water Development Board (TWDB), Texas Parks and Wildlife Department (TPWD), and Texas Natural Resource Conservation Commission (TNRCC) are charged by the Texas Legislature with determining freshwater inflows required to maintain the ecological health of streams, bays, and estuaries in Texas. To determine required inflows, the three agencies collect data and conduct studies on the needs for freshwater inflows to Texas estuaries. The U.S. Geological Survey (USGS), in cooperation with the TWDB, conducted a study in the Nueces estuary (fig. 1) during May–October 1998 to provide water-budget data for calibration of a TWDB model that will be used to estimate the effects of different freshwater inflow volumes on circulation and salinity in the estuary. The water budget (inflows and outflows) for the Nueces estuary was estimated by using (1) data collected during this study, (2) data collected at two upstream streamflow-gaging stations previous to this study, and (3) evaporation and return-flow data obtained from other agencies. This fact sheet describes the data-collection methods and the results of the water-budget estimates for the Nueces estuary.

Texas↗

Documented and potential extreme peak discharges and relation between potential extreme peak discharges and probable maximum flood peak discharges in Texas

The U.S. Geological Survey, in cooperation with the Texas Department of Transportation, conducted a study of extreme flood potential for Texas. Potential extreme peak discharges, derived from the relation between documented extreme peak discharges and their contributing drainage areas, can provide valuable information concerning the maximum expected peak discharge that could occur at a stream site. Documented extreme peak discharges and associated data were aggregated for 832 sites with and without streamflow-gaging stations in natural basins in Texas. A potential extreme peak discharge curve was developed for each of 11 hydrologic regions in Texas and for the State as a whole, based on documented extreme peak discharges and associated contributing drainage areas. The curve envelops, for a large range of drainage areas, the largest documented extreme peak discharges. Potential extreme peak discharges estimated from the curves were compared to probable maximum flood peak discharges estimated from various simulation models.

Texas↗

U.S. Geological Survey response to flooding in Texas, May–June 2015

As a Federal science agency within the Department of the Interior, the U.S. Geological Survey (USGS) collects and disseminates streamflow stage and discharge information along with other types of water information as a major part of its Water mission area. Data collected at USGS streamflow-gaging stations (hereinafter referred to as “streamgages”) are used for a variety of purposes including flood warning, engineering design, management of water resources, and scientific research. During flood events, the need for timely, accurate, and complete streamflow data is underscored because these data are relied on by local, State, and Federal emergency management personnel for flood response purposes. For example, the National Weather Service uses the data from USGS streamgages to develop flood forecasts for specific locations on a river. Tasks that the USGS performs in response to floods include monitoring the operation of gages and responding to any interruptions in data collection, calibrating and verifying stage-discharge ratings, and documenting extreme events including peak stage and peak discharge. Frequent, severe storms during May and June 2015 caused widespread flooding in Texas. By various measures, the storms that caused the flooding were extreme and persistent. May 2015 was the wettest month on record for Texas, with a statewide average precipitation of 9.06 inches. In comparison, the long-term statewide average monthly precipitation is 3.37 inches, with the previous record average monthly precipitation reported as 6.66 inches during June 2004. The Office of the Texas State Climatologist compiled monthly precipitation amounts for 19 selected cities throughout Texas and for 1 city in Louisiana; the total monthly precipitation amounts exceeded the monthly normal precipitation for 18 of the 19 selected cities in Texas, with 5 of these cities exceeding their previous record for the month of May. The onset of abundant precipitation in May 2015 resulted in the National Weather Service flood stage being exceeded at USGS streamgages on numerous rivers. The widespread and prolonged nature of the flooding was unusual; most flood events in Texas are localized, typically affecting only one or two river basins and generally lasting only a few days. With the exception of the Rio Grande, flooding was widespread in all of the major rivers in Texas during May–June 2015.

Texas↗

Chemical quality of water, sediment, and fish in Mountain Creek Lake, Dallas, Texas, 1994-97

The occurrence, trends, and sources of numerous inorganic and organic contaminants were evaluated in Mountain Creek Lake, a reservoir in Dallas, Texas. The study, done in cooperation with the Southern Division Naval Facilities Engineering Command, was prompted by the Navy’s concern for potential off-site migration of contaminants from two facilities on the shore of Mountain Creek Lake, the Naval Air Station Dallas and the Naval Weapons Industrial Reserve Plant. Sampling of stormwater (including suspended sediment), lake water, bottom sediment (including streambed sediment), and fish was primarily in Mountain Creek Lake but also was in stormwater outfalls from the Navy facilities, nearby urban streams, and small streams draining the Air Station. Volatile organic compounds, predominantly solvents from the Reserve Plant and fuel-related compounds from the Air Station, were detected in stormwater from both Navy facilities. Fuel-related compounds also were detected in Mountain Creek Lake at two locations, one near the Air Station inlet where stormwater from a part of the Air Station enters the lake and one at the center of the lake. Concentrations of volatile organic compounds at the two lake sites were small, all less than 5 micrograms per liter. Elevated concentrations of cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc, from 2 to 4 times concentrations at background sites and urban reference sites, were detected in surficial bottom sediments in Cottonwood Bay, near stormwater outfalls from the Reserve Plant. Elevated concentrations of polycyclic aromatic hydrocarbons and polychlorinated biphenyls, compared to background and urban reference sites, were detected in surficial sediments in Cottonwood Bay. Elevated concentrations of polycyclic aromatic hydrocarbons, indicative of urban sources, also were detected in Cottonwood Creek, which drains an urbanized area apart from the Navy facilities. Elevated concentrations of polychlorinated biphenyls were detected in two inlets near the Air Station shoreline. Polycyclic aromatic hydrocarbon and heavy metal concentrations near the Air Station shoreline were not elevated compared to urban reference sites. Much larger concentrations of selected heavy metals, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls were detected in deeper, older sediments than in surficial sediments in Cottonwood Bay. The decreases in concentrations coincide with changes in wastewater discharge practices at the Reserve Plant. Elevated concentrations of polycyclic aromatic hydrocarbons and polychlorinated biphenyls also were detected in older sediments in the Air Station inlet. On the basis of dated sediment cores and contaminant discharge histories, contaminant accumulation rates in Cottonwood Bay were much greater historically than recently. Most heavy metals, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls that accumulated in the central and eastern parts of Cottonwood Bay appear to have come from the west lagoon on the Reserve Plant. Treated sewage and industrial-process wastewater were discharged to the west lagoon from about 1941 to 1974. Estimated annual contaminant accumulation rates in Cottonwood Bay decreased by from 1 to 2 orders of magnitude after 1974, when most point-source discharges to the west lagoon ceased. Polychlorinated biphenyls were detected in 61 of 62 individual fish-tissue samples. The largest average concentrations were in eviscerated channel catfish and the smallest were in largemouth bass fillets. Polychlorinated biphenyl and selenium concentrations from analyses of this study were large enough to prompt the Texas State Department of Health to issue a fish-possession ban for Mountain Creek Lake in 1996. Suspended sediments in stormwater at the lagoon outfalls and at sites on Cottonwood Creek were sampled and analyzed for major and trace elements, polycyclic aromatic hydrocarbons, organochlorine pesticides, and polychlorinated biphenyls. The suspended sediments from the outfalls contained about the same mixture of heavy metals and organic compounds, in elevated concentrations compared to reference sites, as bottom sediments from the lagoons and surficial bottom sediments in Cottonwood Bay. Diagnostic ratios of polycyclic aromatic hydrocarbons indicate that uncombusted fuel sources contribute to older sediments and that pyrogenic sources of polycyclic aromatic hydrocarbons dominate recently deposited sediments in Cottonwood Bay and along the Air Station shoreline.

Texas↗

Hydrologic and water-quality data, Honey Creek State Natural Area, Comal County, Texas, August 2001-September 2003

The U.S. Geological Survey collected rainfall, streamflow, evapotranspiration, and rainfall and stormflow water-quality data from seven sites in two adjacent watersheds in the Honey Creek State Natural Area, Comal County, Texas, during August 2001–September 2003, in cooperation with the U.S. Department of Agriculture, Natural Resources Conservation Service, and the San Antonio Water System. Data collected during this period represent baseline hydrologic and water-quality conditions before proposed removal of ashe juniper ( Juniperus ashei ) from one of the two watersheds. Juniper removal is intended as a best-management practice to increase water quantity (aquifer recharge and streamflow) and to protect water quality. Continuous (5-minute interval) rainfall data are collected at four sites; continuous (5-minute interval) streamflow data are collected at three sites. Fifteen-minute averages of meteorological and solar-energy-related data recorded at two sites are used to compute moving 30-minute evapotranspiration values on the basis of the energy-balance Bowen ratio method. Periodic rainfall water-quality data are collected at one site and stormflow water-quality data at three sites. Daily rainfall, streamflow, and evapotranspiration totals are presented in tables; detailed data are listed in an appendix. Results of analyses of the periodic rainfall and stormflow water-quality samples collected during runoff events are summarized in the appendix; not all data types were collected at all sites nor were all data types collected during the entire 26-month period.

Texas↗

Extreme precipitation depths for Texas, excluding the Trans-Pecos region

The U.S. Geological Survey, in cooperation with the Texas Department of Transportation, conducted a study of extreme precipitation depths for various durations and storm areas for Texas, excluding the Trans-Pecos region. The extreme precipitation depth is an estimate, from documented storms, of the largest precipitation depth expected to occur over a given area. The extreme precipitation depth exceeds the precipitation depth associated with recurrence intervals greater than 100 years. Storm durations of 1, 2, 3, 4, 5, and 6 days were investigated for this report. The extreme precipitation depth for a particular area is estimated from an “extreme precipitation curve” (an upper limit or envelope curve developed from graphs of extreme precipitation depths for each climatic region). The extreme precipitation curves were determined using precipitation depth-duration information from a subset (24 “extreme” storms) of 213 “notable” storms documented throughout Texas. The extreme precipitation curves can be used to estimate extreme precipitation depth for a particular area. The extreme precipitation depth represents a limiting depth, which can provide useful comparative information for more quantitative analyses.

Texas↗

U.S. Department of the Interior South Central Climate Science Center

On September 14, 2009, the Secretary of the Interior signed a Secretarial Order (No. 3289) entitled, "Addressing the Impacts of Climate Change on America's Water, Land, and Other Natural and Cultural Resources." The Order effectively established the U.S. Department of the Interior (DOI) Climate Science Centers (CSCs) for the purpose of integrating DOI science and management expertise with similar contributions from our partners to provide information to support strategic adaptation and mitigation efforts on public and private lands across the United States and internationally. The South Central Climate Science Center (SC CSC) is supported by a consortium of partners that include The University of Oklahoma, Texas Tech University, Louisiana State University, The Chickasaw Nation, The Choctaw Nation of Oklahoma, Oklahoma State University, and the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory. Additionally, the SC CSC will collaborate with a number of other universities, State and federal agencies, and nongovernmental organizations (NGOs) with interests and expertise in climate science. The primary partners of the SC CSC are the Landscape Conservation Cooperatives (LCCs), which include the Desert, Eastern Tallgrass Prairie and Big Rivers, Great Plains, Gulf Coast Prairie, Gulf Coastal Plains and Ozarks, and Southern Rockies. CSC collaborations are focused on common science priorities that address priority partner needs, eliminate redundancies in science, share scientific information and findings, and expand understanding of climate change impacts in the south-central United States and Mexico.

Arizona;Louisiana;Oklahoma;Texas↗

Gulf of Mexico summary report 3 August 1982: A revision of Outer Continental Shelf oil and gas activities in the Gulf of Mexico and their onshore impacts: Gulf of Mexico summary report 2, August 1981

Now, and for the near future, the Gulf of Mexico will remain the most developed Outer Continental Shelf (OCS) region in the United States and the world. Virtually all production from the U.S. OCS emanates from the Gulf of Mexico. In calendar year 1981, for the two primary categories of hydrocarbons produced from the OCS, oil/condensate and gas, Gulf production accounted for over 94 and 99 percent, respectively. Oil production for 1981 was 0.27 billion barrels, and gas production was 4.84 trillion cubic feet. Although most of the shallow-water areas of the Gulf of Mexico Continental Shelf have been explored, considerable amounts of hydrocarbons may yet be discovered in deepwater locations. Industry has been developing the technology to explore deepwater areas, and interest in these portions of the Gulf is increasing. As of December 1981, the total of all identified oil and gas fields in the Gulf of Mexico OCS increased to 505 from 482 at the end of the previous year; this net increase of 23 fields discovered in 1981 compares to net increases of 50 in 1980, 51 in 1979, and 25 in 1978. The number of active fields increased from 466 in 1981, and fields for which reserve estimates have been made increased from 419 to 445. As of January 1982, 19,736 offshore oil and gas wells had been drilled in the Gulf of Mexico OCS; most of the wells (17,257) are off the coast of Louisiana. Currently, there are 2,027 active oil and gas leases in the Gulf of Mexico; 1,200 of them are producing leases. The Department of the Interior's 5-year OCS oil and gas leasing schedule projects 2 to 3 Gulf of Mexico lease sales per year through 1987, for a total of 12 offerings, and starting in 1983, the Gulf will be divided into three planning areas. Resource estimates issued for the following Gulf of Mexico lease sales are as follows: Lease Sale 67--75.16 million barrels of oil and 1.03 trillion cubic feet of gas; Lease Sale 69--48.24 million barrels of oil and .785 trillion cubic feet of gas; Lease Sale 72--97 million barrels of oil and 1.04 trillion cubic feet of gas; Lease Sale 74--29 million barrels of oil and .525 trillion cubic feet of gas; and Lease Sale 79--123 million barrels of oil and .157 trillion cubic feet of gas. Since 1972, oil production in the Gulf of Mexico has declined each year, and gas production, thought to have reached its peak in 1981, is also expected to begin a noticeable decline. To date, most of the oil and gas discovered in the Gulf has occurred on the Texas-Louisiana Shelf, but in the future, oil and gas exploration is likely to include a number of areas where previous leasing has not been extensive. The West Florida Shelf, especially the area off the coast of southwest Florida and the deepwater areas southeast of the Mississippi River Delta, are potential areas for future exploration. As production begins to decline from mature fields, smaller fields will become economically producible, and implementation of secondary and tertiary recovery techniques will make it possible to extract more oil and gas from reservoirs than was possible previously. Each year, hundreds of miles of pipelines are added to the existing network in the Gulf of Mexico. Recently, there have been a number of proposals for deepwater ports and transshipment terminals as well as projects including the deepening or widening of existing conventional ports. The process of transportation planning in the Gulf of Mexico is done by industry and government through the Intergovernmental Planning Program and its Regional Technical Working Group. The Gulf Coast region is an area of significant onshore oil and gas activity, with many cities and towns offering a wide range of services and supplies to onshore and offshore oil operators and their ancillary industries. While the western and central Gulf oil and gas support infrastructure is quite extensive and complex, the support facilities in the eastern Gulf are still in the early stages of development. In the likely event of a decline in Gulf OCS production, imported oil may be substituted for dwindling domestic stocks at Gulf Coast refineries. Planners must consider impacts generated by changes in oil and gas productivity and focus on finding alternative uses for facilities and alternative employment for workers.

Alabama, Florida, Louisiana, Mississippi, Texas↗