Search USGS⌕ Search

SEARCH · Search USGS

Results for “Hydrological Data”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
USGS2014

Land-margin ecosystem hydrologic data for the coastal Everglades, Florida, water years 1996-2012

Mangrove forests and salt marshes dominate the landscape of the coastal Everglades (Odum and McIvor, 1990). However, the ecological effects from potential sea-level rise and increased water flows from planned freshwater Everglades restoration on these coastal systems are poorly understood. The National Park Service (NPS) proposed the South Florida Global Climate Change Project (SOFL-GCC) in 1990 to evaluate climate change and the effect from rising sea levels on the coastal Everglades, particularly at the marsh/mangrove interface or ecotone (Soukup and others, 1990). A primary objective of SOFL-GCC project was to monitor and synthesize the hydrodynamics of the coastal Everglades from the upstream freshwater marsh to the downstream estuary mangrove. Two related hypotheses were set forward (Nuttle and Cosby, 1993): 1. There exists hydrologic conditions (tide, local rainfall, and upstream water deliveries), which characterize the location of the marsh/mangrove ecotone along the marine and terrestrial hydrologic gradient; and 2. The marsh/mangrove ecotone is sensitive to fluctuations in sea level and freshwater inflow from inland areas. Hydrologic monitoring of the SOFL-GCC network began in 1995 after startup delays from Hurricane Andrew (August 1992) and organizational transfers from the NPS to the National Biological Survey (October 1993) and the merger with the U.S. Geological Survey (USGS) Biological Research Division in 1996 (Smith, 2004). As the SOFL-GCC project progressed, concern by environmental scientists and land managers over how the diversion of water from Everglades National Park would affect the restoration of the greater Everglades ecosystem. Everglades restoration scenarios were based on hydrodynamic models, none of which included the coastal zone (Fennema and others, 1994). Modeling efforts were expanded to include the Everglades coastal zone (Schaffranek and others, 2001) with SOFL-GCC hydrologic data assisting the ecological modeling needs. In 2002, as a response for a more interdisciplinary science approach to understanding the coastal Everglades ecological system, the SOFL-GCC hydrology project was integrated into the “Dynamics of Land-Margin Ecosystems: Historical Change, Hydrology, Vegetation, Sediment, and Climate” study (Smith and others, 2002). Data from the ongoing study has been useful in providing an empirical hydrologic baseline for the greater Everglades ecosystem restoration science and management needs. The hydrology network consisted of 13 hydrologic gaging stations installed in the southwestern coastal region of Everglades National Park along three transects: Shark River (Shark or SH) transect, Lostmans River (Lostmans or LO) transect, and Chatham River (Chatham or CH) transect (fig. 1). There were five paired surface-water/groundwater gaging stations on the Shark transect (SH1, SH2, SH3, SH4, and SH5) and one stage gaging station (BSC) in the Big Sable Creek; four paired surface-water/groundwater gaging stations on the Lostmans transect (LO1, LO2, LO3, and LO4); and three paired surface-water/groundwater gaging stations on the Chatham transect (CH1, CH2, and CH3). Both surface-water and groundwater levels, salinities, and temperatures were monitored at the paired gaging stations. Rainfall was recorded at marsh and open canopy gaging stations. This report details the study introduction, method, and description of data collected, which are accessible through the final instantaneous hydrologic dataset stored in the USGS South Florida Information Access (SOFIA) South Florida Hydrology Database website, http://sofia.usgs.gov/exchange/sfl_hydro_data/location.html#brdlandmargin .

Florida↗
USGS1989

Summary of hydrologic data for the San Gabriel River basin and Edwards Aquifer, Georgetown area, Texas, water year 1988

The Edwards aquifer is the principle source of freshwater for municipal, domestic, and industrial users in the Georgetown area. Other sources of freshwater are the streams draining the San Gabriel River basin and Lake Georgetown. Lake Georgetown, located on the North Fork San Gabriel River west of Georgetown, is a freshwater supply for some municipalities in the area, water in the San Gabriel River basin also supplies a variety of needs east of Georgetown. Because of the importance of the Edwards aquifer and the surface waters in the area, the U.S. Geological Survey, in cooperation with the city of Georgetown, conducted a monitoring program of the Edwards Aquifer and principal streams during water year 1988. The study area centered on Georgetown and encompassed an area of about 150 square miles (fig. 1). The freshwater resources in the Georgetown area have been the subject of three recent reports. Baker and others (1986) described the Edwards aquifer and the relation between recharge and discharge. Krietier and others (1987) provided fracture analysis, geologic mapping, ground-water chemistry, and the relation between rainfall and recharge in the study area. Land and Dorsey (1988) conducted an investigation to reassess the inclusion of the Georgetown Limestone as one of the geologic units comprising the Edwards aquifer. In addition, the Geological Survey publishes streamflow and water-quality data in the Water Resources Data for Texas report on an annual basis. The primary purpose of this report is to present a summary of the hydrologic data collected from the streams draining the San Gabriel River basin and from the Edwards aquifer during the 1988 water year (October 1987–September 1988). A secondary purpose is to add perspective to the 1988 data by including data from the previous 2 years (1986 and 1987) when available. The scope of the report is limited to the Georgetown area (fig. 1) and to data collected by the Geological Survey.

Texas↗
USGS1978

Hydrologic data for water-table aquifers in the Boulder-Fort Collins-Greeley area, Front Range urban corridor, Colorado

As part of the U.S. Geological Survey 's investigations of the hydrology and geology in the Front Range Urban Corridor of Colorado, hydrologic data relating to water-table aquifers were compiled during 1976-77. These data consisting of records of 446 wells and chemical analyses of water from 208 wells in the Boulder--Fort Collins--Greeley area, are presented in tabular form. The well-data tables contain records that were collected during 1976-77. The chemical analysis tables contain records that were collected during 1956-77. State and local officials in the Boulder--Fort Collins--Greeley area may find these data useful in planning for residential, commercial, and industrial development. (Woodard-USGS)

Open-File Report↗
USGS2012

Geochemical and hydrologic data for San Marcos Springs recharge characterization near San Marcos, Texas, November 2008--December 2010

During 2008–10, the U.S. Geological Survey, in cooperation with the San Antonio Water System, collected geochemical and hydrologic data in Bexar, Comal, and Hays Counties, Texas, to define and characterize the sources of recharge to San Marcos Springs. Precipitation samples were collected for stable isotope analysis at 1 site and water-quality samples were collected at 7 springs, 21 wells, and 9 stream sites in the study area between November 2008 and December 2010. Continuous water-quality monitors were installed in three springs, two wells, and at one stream site. Three continuous stream-gaging stations were installed to measure gage height and a stagedischarge rating was developed at two of the three sites. Depth to water below land surface was continuously measured in two wells.

Texas↗
USGS1993

Hydrologic data for Block Island, Rhode Island

This report was compiled as part of a study to assess the hydrogeology and the quality and quantity of fresh ground water on Block Island, Rhode Island. Hydrologic data were collected on Block Island during 1988-91. The data are pre- sented in illustrations and tables. Data collec- ted include precipitation, surfae-water, ground- water, lithologic, and well-construction and dis- charge information. Precipitation data include total monthly precipitation values from 11 rain gages and water-quality analyses of 14 precipi- tation samples from one station. Surface-water data include water-level measurements at 12 ponds, water-quality data for five ponds, and field specific-conductance measurements at 56 surface- water sites (streams, ponds, and springs). Ground- water data include water-level measurements at 159 wells, water-quality data at 150 wells, and field specific-conductance data at 52 wells. Lithologic logs for 375 wells and test borings, and construc- tion and location data for 570 wells, springs, and test borings are included. In addition, the data set contains data on water quality of water samples, collected by the Rhode Island Department of Health during 1976-91, from Fresh and Sands Ponds and from wells at the Block Island Water Company well field north of Sands Pond.

Open-File Report↗
USGS1997

Flood-hydrology data for the Potomac River and selected tributaries in the vicinity of the Chesapeake and Ohio Canal National Historical Park, Maryland, West Virginia, and the District of Columbia

This report presents flood-hydrology data for the Potomac River and selected tributaries in the vicinity of the Chesapeake and Ohio Canal National Park (C & O Canal NHP). Data were compiled for the floods of (1) March 17-19, 1936; (2) June 22-24, 1972; (3) November 4-7, 1985; (4) January 19-21, 1996; (5) September 6-8, 1996; and (6) the peak of record for 6 U.S. Geological Survey (USGS) streamflow-gaging stations on the Potomac River and 10 streamflow-gaging stations on selected tributaries to the Potomac River. Peak discharge, peak gage height, the date and time of the peak, and approximate recurrence interval are presented for each flood event at these streamflow-gaging stations.Data compiled from selected high-flow discharge measurements on the six Potomac River streamflow- gaging stations are presented. The gage height, top width, cross-sectional area, mean velocity, maximum velocity, and discharge are presented for each selected discharge measurement. Any corresponding discharge on the C & O Canal that was measured or estimated for these dischrge measurements is presented. Ranges of Manning's roughness coefficient were computed for the range of selected discharge measurements, based on estimates of water-surface slope or the channel-bed slope. These data will be used for subsequent hydraulic studies by engineers for maintenance, protection, or restoration of the C & O Canal. An inventory of selected references, flood studies, and additional USGS data along the Potomac River and the C & O Canal NHP also are presented. Included are (1) a listing of selected flood studies and reports, and (2) a listing of USGS indirect flood-discharge measurements that have been made at the six Potomac River streamflow-gaging stations in the vicinity of the C & O Canal NHP. Information on historical streamflow-gaging station records and discharge measurements on the C & O Canal also is presented.

Open-File Report↗
USGS1982

Hydrologic data for urban studies in the San Antonio, Texas, metropolitan area, 1979-80

Hydrologic investigations of urban drainage basins in Texas were begun by the U.S. Geological Survey in 1954. These studies are now in progress in Austin, Houston, and San Antonio. Studies were completed in the Fort Worth metropolitan area at the end of the 1977 water year, and in the Dallas metropolitan area at the end of the 1979 water year. The Geological Survey, in cooperation with the Texas Department of Water Resources, expanded the existing streamflow network in the San Antonio metropolitan area in May 1968 to begin urban hydrology studies in this area. In September 1968, the program was further expanded to include the collection of water-quality data. The operation and maintenance of stations 08178000, San Antonio River at San Antonio; 08178700, Salado Creek (upper station) at San Antonio; and 08178800, Sal ado Creek (lower station) at San Antonio are funded by the San Antonio River Authority in conjunction with the Texas Department of Water Resources and the U.S. Geological Survey. The operation and maintenance and collection of water-quality data at station 08178720, Lorence Creek at Thousand Oaks Blvd., San Antonio, station 08178640, West Elm Creek at San Antonio, and station 08178645, East Eln Creek at San Antonio, are funded by the Edwards Underground Water District in cooperation with the Texas Department of Water Resources and the U.S. Geological Survey. Station 08178640, West Elm Creek at San Antonio, and station 08178645, East Elm Creek at San Antonio will provide hydrologic data on similar and adjacent watersheds. The West Elm watershed is still predominately rural but is undergoing extensive urbanization in some areas. The East Elm watershed is relatively stable and undeveloped. The objectives of the San Antonio urban hydrology study are: To provide data showing the effects of various stages of urbanization on flood discharge and runoff. To provide water-quality data on surface-water runoff from floods of various magnitudes, during all seasons of the year from areas with different types of urban development. Annual publication of the San Antonio urban studies was initiated in 1969. A defination of terms related to streamflow, water quality, and other hydrologic data, as used in this report, are defined in the U.S. Geological Survey's 1979 and 1980 "Water resources data for Texas" reports.

Texas↗
USGS1978

Hydrologic data for the Copper Basin area, a potential mining area in Yavapai County, Arizona

Large low-grade ore bodies have been discovered in Copper Basin, and a large copper-mining operation is anticipated in the near future. Hydrologic data are being collected to provide the data base necessary to determine the effects of a potential mining operation on the water resources of the area. The area of potential depletion or contamination of water supplies is the 50-square-mile alluvial slope downgradient from Copper Basin. In the Copper Basin area the streams generally are dry, except for the perennial flow in a 3-mile-long reach of Kirkland Creek, where the base flow ranges from about 1 to 3 cubic feet per second. The water in the alluvium, which is more than 1,000 feet thick in places, generally is under unconfined conditions. The direction of ground-water movement is generally southwesterly toward Skull Valley Wash and Kirkland Creek. The depth to water in wells ranges from less than 10 to 675 feet below the land surface. Near the center of the area, test wells penetrate a clay confining bed at the base of the alluvium and an underlying sequence of volcanic rocks, which is more than 1,000 feet thick and contains water under confined conditions. Pump tests indicate that the confining bed forms a barrier between the water in the alluvium and the water in the volcanic rocks and that, initially, pumping from the volcanic rocks would not affect the water level in the alluvium. The areal extent of the volcanic sequence is not known.

Arizona↗
USGS2015

Hydrologic data for the Walker River Basin, Nevada and California, water years 2010–14

Walker Lake is a threatened and federally protected desert terminal lake in western Nevada. To help protect the desert terminal lake and the surrounding watershed, the Bureau of Reclamation and U.S. Geological Survey have been studying the hydrology of the Walker River Basin in Nevada and California since 2004. Hydrologic data collected for this study during water years 2010 through 2014 included groundwater levels, surface-water discharge, water chemistry, and meteorological data. Groundwater levels were measured in wells, and surface-water discharge was measured in streams, canals, and ditches. Water samples for chemical analyses were collected from wells, streams, springs, and Walker Lake. Chemical analyses included determining physical properties; the concentrations of major ions, nutrients, trace metals, dissolved gases, and radionuclides; and ratios of the stable isotopes of hydrogen and oxygen. Walker Lake water properties and meteorological parameters were monitored from a floating platform on the lake. Data collection methods followed established U.S. Geological Survey guidelines, and all data are stored in the National Water Information System database. All of the data are presented in this report and accessible on the internet, except multiple-depth Walker Lake water-chemistry data, which are available only in this report.

California, Nevada↗
USGS1990

Hydrologic data collected in the vicinity of the proposed gamma-ray and neutrino detector site, Hot Spring County, Arkansas, 1988-89

An abandoned barite mine in Hot Spring County, Arkansas, has been selected as the location for a proposed gamma-ray and neutrino detector site. As part of the hydrologic evaluation of the site, the U.S. Geological Survey in cooperation with the Arkansas Geological Commission collected hydrologic data at selected locations in the vicinity of the abandoned barite mine. Data collected as part of the project included water quality, pond-evaluation, and precipitation data within the abandoned barite mine and flow and water quality data at selected sites in the vicinity of the mine. Water quality samples from within the abandoned mine were collected at three locations in the pond at selected depths. These data included field measurements of specific conductance, pH, water temperature, dissolved oxygen, major ions, and trace metals. Major ion and trace-metal samples were collected at six stream sites, one lake site, and two wastewater pond sites. Pond elevation and precipitation data from within the abandoned barite mine were measured during the period between July 1, 1988 and June 30, 1989. Twevle discharge measurements during the period between June 21, 1988, and June 26, 1989, were collected at six sites in the vicinity of the abandoned barite mine. (USGS)

Open-File Report↗
USGS1978

Hydrologic data for North Creek, Trinity River basin, Texas, 1976

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 floodwater-retarding structures would be physically and economically feasible in Texas. As of September 30, 1976, 1,673 (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, 1976, data collection in ten of these study areas has been completed and is now in progress in the remaining two. These studies are being made in cooperation with the Texas Water Development Board, 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, 1976, is shown in table 1.

Texas↗
USGS1981

Index to active hydrologic data collection sites in Florida, 1980-81

This index contains a list of active data-collection sites in Florida operated by the U.S. Geological Survey in cooperation with local, State, and Federal agencies during the period from October 1, 1980 through September 30, 1981. It is an update of "Index to Active Hydrologic Data Collection Sites in Florida, 1978-79" by J. D. Simmons, 1980, which was released as U.S. Geological Survey Open-File Report 80-220. The index shows the location of the site, the cooperator or cooperators supporting the data collection activities, the type and frequency of data collection, and the U.S. Geological Survey office responsible for collecting and processing the data.

Florida↗
USGS1994

Geologic and hydrologic data collected at test hole NC-8, Vega Alta, Puerto Rico

Test hole NC-8 was drilled in the municipality of Vega Alta as part of a study of the aquifers in the Northern Coastal Province of Puerto Rico. Test hole NC-8 was drilled to a depth of 1,736 feet below land surface. Geologic and hydrologic data collected during drilling included continuous core, water- quality samples, water-level measurements, and estimates of aquifer yields from the water-bearing zones. Test hole NC-8 penetrated five geologic formations of middle Tertiary age: the Aymamon Limestone, the Los Puertos Formation, the Cibao Formation, the Lares Limestone, and the San Sebastian Formation. Test hole NC-8 penetrated a water-table aquifer and seven artesian aquifers.

Open-File Report↗
USGS2004

Selected hydrologic data for the upper Rio Hondo basin, Lincoln County, New Mexico, 1945-2003

Demands for ground and surface water have increased in the upper Rio Hondo Basin due to increases in development and population. Local governments are responsible for land-use and development decisions and, therefore, the governments need information about water resources in their areas. Hydrologic data were compiled for the upper Rio Hondo Basin and water-level data were collected during two synoptic measurements in March and July 2003. Water-level data from March 2003 were contoured and compared with contours constructed in 1963. The 5,600-, 5,700-, and 5,800-foot March 2003 contours indicate that water levels rose. The 5,500-foot contour for March 2003 indicates a decline in water level. The 5,400-foot contour of March 2003 and the 1963 contour mostly coincide, indicating a static water level. The 5,300- and 5,200-foot contours for March 2003 cross the 1963 contours, indicating a decline in water levels near the Rio Ruidoso but a rise in water levels near the Rio Bonito. In eight hydrographs, 2003 water levels are shown to be higher than water levels from the mid- to late 1950's in five of the eight wells. For the same period of record, water levels in the three remaining wells were lower. Rising and declining water levels were highest in the northern part of the study area; the median rise was 4.01 feet and the median decline was 3.51 feet. In the southern part of the study area, the median water-level rise was 2.21 feet and the median decline was 1.56 feet.

Scientific Investigations Report↗
USGS1972

Compilation of hydrologic data, Little Elm Creek, Trinity River basin, Texas, 1968

The U.S. Soil Conservation Service is actively engaged in the installation of flood and soil erosion reducing measures in Texas under the authority of "The Flood Control Act ot 1936 and 1944" and ''Watershed Protection and Flood Prevention Act" (Public Law 566), as amended. In June 1968, the Soil Conservation Service estimated approximately 3,500 structures to be physically and economically feasible for installation in Texas. As of September 30, 1968, 1,271 of these structures had been built. This watershed-development program will have varying but important effects on the surface- and ground-water resources of river basins, especially where a large number of the floodwater-retarding structures are built. Basic hydrologic data are needed to appraise the effects of the structures on water yield and the mode of occurrence of runoff. Hydrologic investigations of these small watersheds were begun by the Geological Survey in 1951 and are now being made in 11 areas (fig. 1). These studies are being made in cooperation with t he Texas Water Development Board, the Soil Conservation Service, the San Antonio River Authority, the city of Dallas, and the Tarrant County Water Control and Improvement District No. 1. The 11 study areas were choson to sample watersheds having different rainfall, topography, geology, and soils. In four of the study areas (Mukewater, North, Little 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 to the conditions before and after" development. Structures have now been built in three of these study areas. A summary of the development of the floodwater-retarding structures on each study area as of September 30, 1968, is shown in table 1.

Texas↗
USGS1967

Compilation of hydrologic data Green Creek, Brazos River basin, Texas, 1967

The U.S. Soil Conservation Service is actively engaged in the installation of flood and soil erosion reducing measures 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 a total of 3,438 floodwater-retarding structures to be physically and economically feasible in Texas. As of September 30, 1967, 1,196 of these structures had been built. This watershed-development program will have varying but important effects on the natural 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. Hydrologic investigations of these small watersheds, both developed and undeveloped, were begun by the Geological Survey in 1951 and are now being made in 11 areas (fig. 1). These studies are being made in cooperation with the Texas Water Development Board, the Soil Conservation Service, the San Antonio River Authority, the city of Dallas and the Tarrant County Water Control and Improvement District No. 1. The 11 study areas were chosen to sample watersheds having different rainfall, topography, geology, and soils. In four of the study areas (North, Little Elm, Mukewater, 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. Structures have now been built in three of these study areas. A summary of the development of the floodwater-retarding structures in each study area as of September 30, 1967, is shown in table 1.

Texas↗
USGS1972

Annual compilation and analysis of hydrologic data for Honey Creek, Trinity River Basin, Texas, 1970

The U.S. Soil Conservation Service is actively engaged in the installation of flood- and soil-erosion reducing measures 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 a total of approximately 3,500 floodwater-retarding structures to be physically and economically feasible in Texas. As of September 30, 1970, 1,439 of these structures had been built. This watershed-development program will have varying but important effects on the natural 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. Hydrologic investigations of these small watershed study areas were begun by the U.S. Geological Survey in 1951 and are now being made in 12 areas (fig. 1). These investigations are being made in cooperation with the Texas Water Development Board, the Soil Conservation Service, the San Antonio River Authority, the city of Dallas, and the Tarrant County Water 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. Structures have now been built in four of these study areas. A summary of the development of the floodwater-retarding structures in each study area as of September 30, 1970, is shown in table 1.

Texas↗
USGS1971

Annual compilation and analysis of hydrologic data for Pin Oak Creek, Trinity River basin, Texas, 1969

The U.S. Soil Conservation Service is actively engaged in the installation of flood and soil erosion reducing measures 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 a total of approximately 3,500 floodwater-retarding structures to be physically and economically feasible in Texas. As of September 30, 1969, 1,355 of these structures had been built. This watershed-development program will have varying but important effects on the natural 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. Hydrologic investigations of these small watersheds were begun by the U.S. Geological Survey in 1951 and are now being made in 12 areas (fig. 1). These studies are being made in cooperation with the Texas Water Development Board, the Soil Conservation Service, the San Antonio River Authority, the city of Dallas, and the Tarrant County Water 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, North Elm-Little Pond, 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. Structures have now been built in three of these study areas. A summary of the development of the floodwater-retarding structures on each study area as of September 30, 1969, is shown in table 1.

Texas↗