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At least 73 records · Page 4Linked to original sources
USGS2014

Trend analysis and selected summary statistics of annual mean streamflow for 38 selected long-term U.S. Geological Survey streamgages in Texas, water years 1916-2012

In 2013, the U.S. Geological Survey (USGS) operated more than 500 continuous streamgages (streamflow-gaging stations) in Texas. In cooperation with the Texas Water Development Board, the USGS evaluated mean annual streamflow data for 38 selected streamgages that were active as of water year 2012. The 38 streamgages have annual mean streamflow data considered natural and unregulated. Collected annual mean streamflow data for a single streamgage ranged from 49 to 97 cumulative years. The nonparametric Kendall’s tau statistical test was used to detect monotonic trends in annual mean streamflow over time. The monotonic trend analysis detected 2 statistically significant upward trends (0.01 one-tail significance), 1 statistically significant downward trend (0.01 one-tail significance level), and 35 instances of no statistically significant trend (0.02 two-tailed significance level). The Theil slope estimate of a regression slope of annual mean streamflow with time was computed for the three stations where trends in streamflow were detected: 2 increasing Theil slopes were measured (+0.40 and +2.72 cubic feet per second per year, respectively), and 1 decreasing Theil slope (–0.24 cubic feet per second per year) was measured. Selected summary statistics (L-moments) and estimates of respective sampling variances were computed for the 35 streamgages lacking statistically significant trends. From the L-moments and estimated sampling variances, weighted means or regional values were computed for each L-moment. An example application is included demonstrating how the L-moments could be used to evaluate the magnitude and frequency of annual mean streamflow.

Texas↗
USGS2012

Simulation of streamflow and the effects of brush management on water yields in the upper Guadalupe River watershed, south-central Texas, 1995-2010

The U.S. Geological Survey, in cooperation with the Texas State Soil and Water Conservation Board and the Upper Guadalupe River Authority, developed and calibrated a Soil and Water Assessment Tool watershed model of the upper Guadalupe River watershed in south-central Texas to simulate streamflow and the effects of brush management on water yields in the watershed and to Canyon Lake for 1995–2010. Model simulations were done to quantify the possible change in water yield of individual subbasins in the upper Guadalupe River watershed as a result of the replacement of ashe juniper ( Juniperus ashei ) with grasslands. The simulation results will serve as a tool for resource managers to guide their brush-management efforts. Model hydrology was calibrated with streamflow data collected at the U.S. Geological Survey streamflow-gaging station 08167500 Guadalupe River near Spring Branch, Tex., for 1995–2010. Simulated monthly streamflow showed very good agreement with measured monthly streamflow: a percent bias of -5, a coefficient of determination of 0.91, and a Nash–Sutcliffe coefficient of model efficiency of 0.85. Modified land-cover input datasets were generated for the model in order to simulate the replacement of ashe juniper with grasslands in 23 brush-management subbasins in the watershed. Each of the 23 simulations showed an increase in simulated water yields in the targeted subbasins and to Canyon Lake. The simulated increases in average annual water yields in the subbasins ranged from 6,370 to 119,000 gallons per acre of ashe juniper replaced with grasslands with an average of 38,900 gallons. The simulated increases in average annual water yields to Canyon Lake from upstream subbasins ranged from 6,640 to 72,700 gallons per acre of ashe juniper replaced with grasslands with an average of 34,700 gallons.

Texas↗
USGS2016

A plan for study of hexavalent chromium, CR(VI) in groundwater near a mapped plume, Hinkley, California, 2016

The Pacific Gas and Electric Company (PG&E) Hinkley compressor station, in the Mojave Desert 80 miles northeast of Los Angeles, is used to compress natural gas as it is transported through a pipeline from Texas to California. Between 1952 and 1964, cooling water used at the compressor station was treated with a compound containing chromium to prevent corrosion. After cooling, the wastewater was discharged to unlined ponds, resulting in contamination of soil and groundwater in the underlying alluvial aquifer (Lahontan Regional Water Quality Control Board, 2013). Since 1964, cooling-water management practices have been used that do not contribute chromium to groundwater. In 2007, a PG&E study of the natural background concentrations of hexavalent chromium, Cr(VI), in groundwater estimated average concentrations in the Hinkley area to be 1.2 micrograms per liter (μg/L), with a 95-percent upper-confidence limit of 3.1 μg/L (CH2M-Hill, 2007). The 3.1 μg/L upper-confidence limit was adopted by the Lahontan Regional Water Quality Control Board (RWQCB) as the maximum background concentration used to map the plume extent. In response to criticism of the study’s methodology, and an increase in the mapped extent of the plume between 2008 and 2011, the Lahontan RWQCB (Lahontan Regional Water Quality Control Board, 2012) agreed that the 2007 PG&E background-concentration study be updated. The purpose of the updated background study is to evaluate the presence of natural and man-made Cr(VI) near Hinkley, Calif. The study also is to estimate natural background Cr(VI) concentrations in the aquifer upgradient and downgradient from the mapped Cr(VI) contamination plume, as well as in the plume and near its margins. The study was developed by the U.S. Geological Survey (USGS) in collaboration with a technical working group (TWG) composed of community members, the Independent Review Panel (IRP) Manager (Project Navigator, Ltd.), the Lahontan RWQCB, PG&E, and consultants for PG&E.&E.

California↗
USGS2024

Geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within parts of Bandera and Kendall Counties, Texas

The karstic Edwards and Trinity aquifers are classified as major sources of water in south-central Texas by the Texas Water Development Board. During 2019–23 the U.S. Geological Survey, in cooperation with the Edwards Aquifer Authority, mapped and described the geology and hydrostratigraphy of the rocks composing the Edwards and Trinity aquifers within parts of Bandera and Kendall Counties from field observations of the surficial expressions of the rocks. The thicknesses of the mapped lithostratigraphic and hydrostratigraphic units were also estimated from field observations in the study area. The Cretaceous rocks in the study area are part of the Trinity Group and Edwards Group. The groups, formations, and members are composed primarily of layers of marls, shales, and limestones. The limestones are composed of mudstone through grainstone, framestone and boundstone, dolomite, and argillaceous and evaporitic rocks. The principal structural feature in the study area is the Balcones fault zone. The Balcones fault zone is the result of late Oligocene and early Miocene extensional faulting and fracturing that was a result of the eastern Edwards Plateau uplift. In the Balcones fault zone, most of the faults in the study area are high-angle to vertical, en echelon, normal faults that are predominantly downthrown to the southeast. Hydrostratigraphically, the rocks exposed in the study area are those that contain the Edwards aquifer, the upper zone of the Trinity aquifer, and the middle zone of the Trinity aquifer. Descriptions of the hydrostratigraphic units, thicknesses, hydrologic function, porosity types, and field identification and observations are provided, including those for the informal Bandera and Love Creek hydrostratigraphic units of the Edwards aquifer, which were identified through the mapping for this study.

Texas↗
USGS2012

Trends in selected streamflow statistics at 19 long-term streamflow-gaging stations indicative of outflows from Texas to Arkansas, Louisiana, Galveston Bay, and the Gulf of Mexico, 1922-2009

Trends in selected streamflow statistics during 1922-2009 were evaluated at 19 long-term streamflow-gaging stations considered indicative of outflows from Texas to Arkansas, Louisiana, Galveston Bay, and the Gulf of Mexico. The U.S. Geological Survey, in cooperation with the Texas Water Development Board, evaluated streamflow data from streamflow-gaging stations with more than 50 years of record that were active as of 2009. The outflows into Arkansas and Louisiana were represented by 3 streamflow-gaging stations, and outflows into the Gulf of Mexico, including Galveston Bay, were represented by 16 streamflow-gaging stations. Monotonic trend analyses were done using the following three streamflow statistics generated from daily mean values of streamflow: (1) annual mean daily discharge, (2) annual maximum daily discharge, and (3) annual minimum daily discharge. The trend analyses were based on the nonparametric Kendall's Tau test, which is useful for the detection of monotonic upward or downward trends with time. A total of 69 trend analyses by Kendall's Tau were computed - 19 periods of streamflow multiplied by the 3 streamflow statistics plus 12 additional trend analyses because the periods of record for 2 streamflow-gaging stations were divided into periods representing pre- and post-reservoir impoundment. Unless otherwise described, each trend analysis used the entire period of record for each streamflow-gaging station. The monotonic trend analysis detected 11 statistically significant downward trends, 37 instances of no trend, and 21 statistically significant upward trends. One general region studied, which seemingly has relatively more upward trends for many of the streamflow statistics analyzed, includes the rivers and associated creeks and bayous to Galveston Bay in the Houston metropolitan area. Lastly, the most western river basins considered (the Nueces and Rio Grande) had statistically significant downward trends for many of the streamflow statistics analyzed.

Arkansas, Colorado, Louisiana, Oklahoma, New Mexic↗
USGS2014

Sediment characteristics in the San Antonio River Basin downstream from San Antonio, Texas, and at a site on the Guadalupe River downstream from the San Antonio River Basin, 1966-2013

San Antonio and surrounding municipalities in Bexar County, Texas, are in a rapidly urbanizing region in the San Antonio River Basin. The U.S. Geological Survey, in cooperation with the San Antonio River Authority and the Texas Water Development Board, compiled historical sediment data collected between 1996 and 2004 and collected suspended-sediment and bedload samples over a range of hydrologic conditions in the San Antonio River Basin downstream from San Antonio, Tex., and at a site on the Guadalupe River downstream from the San Antonio River Basin during 2011–13. In the suspended-sediment samples collected during 2011–13, an average of about 94 percent of the particles was less than 0.0625 millimeter (silt and clay sized particles); the 50 samples for which a complete sediment-size analysis was performed indicated that an average of about 69 percent of the particles was less than 0.002 millimeter. In the bedload samples collected during 2011–13, an average of 51 percent of sediment particles was sand-sized particles in the 0.25–0.5 millimeter-size range. In general, the loads calculated from the samples indicated that bedload typically composed less than 1 percent of the total sediment load. A least-squares log-linear regression was developed between suspended-sediment concentration and instantaneous streamflow and was used to estimate daily mean suspended-sediment loads based on daily mean streamflow. The daily mean suspended-sediment loads computed for each of the sites indicated that during 2011–12, the majority of the suspended-sediment loads originated upstream from the streamflow-gaging station on the San Antonio River near Elmendorf, Tex. A linear regression relation was developed between turbidity and suspended-sediment concentration data collected at the San Antonio River near Elmendorf site because the high-resolution data can facilitate understanding of the complex suspended-sediment dynamics over time and throughout the river basin.

Texas↗
USGS2023

Flood-inundation maps created using a synthetic rating curve for a 10-mile reach of the Sabinal River and a 7-mile reach of the West Sabinal River near Utopia, Texas, 2021

In 2021, the U.S. Geological Survey (USGS), in cooperation with the Bandera County River Authority and Groundwater District and the Texas Water Development Board, studied floods to produce a library of flood-inundation maps for the Sabinal River near Utopia, Texas. Digital flood-inundation maps were created for a 10-mile reach of the Sabinal River from USGS streamgage 08197936 Sabinal River below Mill Creek near Vanderpool, Tex., at the upstream boundary of the study reach, to USGS streamgage 08197970 Sabinal River at Utopia, Tex. (hereinafter referred to as the “Utopia gage”), at the downstream boundary of the study reach, and for a 7-mile reach of the West Sabinal River. The flood-inundation maps depict estimates of the areal extent and depth of flooding corresponding to selected gage heights (the water-surface elevation at a streamgage, commonly referred to as “stage”) at the Utopia gage. Water-surface elevations were computed for the stream reach by means of a two-dimensional unsteady-state diffusion wave model with the U.S. Army Corps of Engineers Hydrologic Engineering Center River Analysis System program. A synthetic stage-discharge rating curve at the Utopia gage was developed using a regional regression equation to construct the model boundary condition inputs, and the upper bound of the stage-discharge relation was matched to a major flood event in July 2002. The hydraulic model was used to compute water-surface elevations for 35 stages at 0.5-foot (ft) increments referenced to the Utopia gage datum and ranging from 11 ft (near bankfull) to 28 ft (estimated peak stage during the July 2002 flood event). These flood-inundation maps, in conjunction with the real-time stage data from the Utopia gage, are intended to help guide the public in taking individual safety precautions and provide emergency management personnel with a tool to efficiently manage emergency flood operations and postflood recovery efforts.

Texas↗
USGS2020

Geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within northern Medina County, Texas

The karstic Edwards and Trinity aquifers are classified as major sources of water in south-central Texas by the Texas Water Development Board. During 2018–20 the U.S. Geological Survey, in cooperation with the Edwards Aquifer Authority, mapped and described the geologic framework and hydrostratigraphy of the rocks composing the Edwards and Trinity aquifers in northern Medina County from field observations of the surficial expressions of the rocks. The thicknesses of the mapped lithostratigraphic members and hydrostratigraphic units were also estimated from field observations. The Cretaceous-age rocks (listed in ascending order) in the study area are part of the Trinity Group (lower and upper members of the Glen Rose Limestone), Edwards Group (Kainer Formation [and its stratigraphic equivalent, the Fort Terrett Formation] and Person Formation), Devils River Limestone, Washita Group (Georgetown Formation, Del Rio Clay, and Buda Limestone), Eagle Ford Group, Austin Group, Taylor Group, and Late Cretaceous igneous intrusive rocks. The groups and formations are composed primarily of relatively thick layers of clays, shales, and limestone. The igneous rocks are coarse-grained ultramafic in composition. The principal structural feature in northern Medina County is the Balcones fault zone, which is the result of late Oligocene and early Miocene extensional faulting and fracturing resulting from the eastern Edwards Plateau uplift. In the Balcones fault zone, most of the faults in the study area are high-angle to vertical, en echelon, normal faults that are predominately downthrown to the southeast. Hydrostratigraphically, the rocks exposed in the study area (listed in descending order from land surface as they appear in a stratigraphic column) are igneous, the upper confining unit to the Edwards aquifer, the Edwards aquifer, the upper zone of the Trinity aquifer, and the upper part of the middle zone of the Trinity aquifer. The karstic carbonate Edwards and Trinity aquifers developed as a result of their original depositional history, primary and secondary porosity, diagenesis, fracturing, and faulting. These factors have resulted in development of modified porosity, permeability, and transmissivity within and between the aquifers.

Texas↗
USGS2016

Simulation of streamflow and the effects of brush management on water yields in the Double Mountain Fork Brazos River watershed, western Texas 1994–2013

The U.S. Geological Survey, in cooperation with the City of Lubbock and the Texas State Soil and Water Conservation Board, developed and calibrated a Soil and Water Assessment Tool watershed model of the Double Mountain Fork Brazos River watershed in western Texas to simulate monthly mean streamflow and to evaluate the effects of brush management on water yields in the watershed, particularly to Lake Alan Henry, for calendar years 1994–2013. Model simulations were done to quantify the possible change in water yield of individual subbasins in the Double Mountain Fork Brazos River watershed as a result of the replacement of shrubland (brush) with grassland. The simulation results will serve as a tool for resource managers to guide brush-management efforts. The model was calibrated from 1994 through 2008 and validated from 2009 through 2013 with streamflow data collected at the U.S. Geological Survey streamflow-gaging station 08079600 Double Mountain Fork Brazos River at Justiceburg, Texas (hereinafter referred to as the “Justiceburg gage”). Simulated monthly mean streamflow showed agreement with measured monthly mean streamflow for the 1994–2013 study period: the percentage bias was +6, the coefficient of determination was 0.73, and the Nash–Sutcliffe coefficient of model efficiency was 0.71. The calibrated watershed model was used to perform brush-management simulations. The National Land Cover Database 2006, which was the land-cover data used to develop the watershed model, was modified to simulate shrubland replacement with grassland in each of the 35 model subbasins. After replacement of shrubland with grassland in areas with land slope less than 20 percent and excluding riparian areas, the modeled 20-year (1994 through 2013) water yields to Lake Alan Henry increased by 114,000 acre-feet or about 5,700 acre-feet per year. In terms of the increase in water yield per acre of shrubland replaced with grassland, the average annual increase in water yield was 17,300 gallons per acre. Within the modeled subbasins, the increase in average annual water yield ranged from 5,850 to 34,400 gallons per acre of shrubland replaced with grassland. Subbasins downstream from the Justiceburg gage had a higher average annual increase in water yield (21,700 gallons per acre) than subbasins upstream from the streamflow-gaging station (16,800 gallons per acre).

Texas↗
USGS2019

Flood-inundation maps for a 23-mile reach of the Medina River at Bandera, Texas, 2018

In 2018, the U.S. Geological Survey (USGS), in cooperation with the Bandera County River Authority and Groundwater District and the Texas Water Development Board, studied floods through the period of record to create a library of flood-inundation maps for the Medina River at Bandera, Texas. Digital flood-inundation maps for a 23-mile reach of the Medina River at and near Bandera, from the confluence with Winans Creek to English Crossing Road, were developed. The flood-inundation maps depict estimates of the areal extent and depth of flooding corresponding to a range of different gage heights (gage height is commonly referred to as “stage,” or the water-surface elevation at a streamflow-gaging station) at USGS streamflow-gaging station 08178880 Medina River at Bandera, Tex. (hereinafter referred to as the “Bandera station”). Water-surface profiles were computed for the stream reach by means of a one-dimensional step-backwater model. The stage-discharge (streamflow) relation effective in 2018 was used to calibrate the model, and stages from four recent flood events were used to independently validate the model. The calibrated hydraulic model was then used to compute 29 water-surface profiles for stages at 1-foot (ft) increments referenced to the station datum and ranging from 10 ft (near bankfull) to 38 ft, which exceeds the major flood stage of the National Weather Service Advanced Hydrologic Prediction Service of 24 ft. The simulated water-surface profiles were then combined with a geographic information system digital elevation model (derived from light detection and ranging data having a 0.4-ft vertical accuracy and 1.6-ft horizontal resolution) to delineate the area flooded for stages ranging from 10 to 38 ft. The digital flood-inundation maps are delivered through the USGS Flood Inundation Mapper application that presents map libraries and provides detailed information on flood-inundation extents and stages for modeled sites. The flood-inundation maps developed in this study, in conjunction with the real-time stage data from the Bandera station, are intended to help guide the public in taking individual safety precautions and provide emergency management personnel with a tool to efficiently manage emergency flood operations and post-flood recovery efforts.

Scientific Investigations Report↗
USGS2007

Base flow (1966-2005) and streamflow gain and loss (2006) of the Brazos River, McLennan County to Fort Bend County, Texas

During 2006–07, the U.S. Geological Survey (USGS), in cooperation with the Texas Water Development Board, did a study to quantify historical (water years 1966–2005) base flow and streamflow gains and losses from two streamflow-measuring surveys (March and August 2006) in the Brazos River from McLennan County to Fort Bend County, Texas. The Brazos River is hydraulically connected to the Brazos River alluvium aquifer, which in turn is hydraulically connected to several underlying aquifers, the outcrops of which occur in laterally adjacent layers generally parallel to the coast (major aquifers, Carrizo-Wilcox and Gulf Coast, and minor aquifers, Queen City, Sparta, and Yegua-Jackson). Hydrograph separation was done using the USGS computer program Hydrograph Separation and Analysis with historical streamflow from 10 USGS gaging stations, three on the Brazos River and seven on selected tributaries to the Brazos River. Streamflow data for computation of gains and losses were collected in March 2006 from 36 sites on the Brazos River and 19 sites on 19 tributaries to the Brazos River; and in August 2006 from 28 sites on the Brazos River and 16 sites on tributaries. Hydrograph separation and associated analyses indicate an appreciable increase in base flow as a percentage of streamflow in the reach of the Brazos River that crosses the outcrops of the Carrizo-Wilcox, Queen City, Sparta, and Yegua-Jackson aquifers compared to that in the adjacent upstream reach (on average from about 43 percent to about 60 percent). No increase in base flow as a percentage of streamflow in the reach of the Brazos River crossing the Gulf Coast aquifer compared to that in the adjacent upstream reach was indicated. Streamflow gains and losses computed for March 2006 for 35 reaches defined by pairs of sites on the Brazos River indicated that five reaches were verifiably gaining streamflow (computed gain exceeded potential flow measurement error) and none were verifiably losing streamflow. Four of the five gaining reaches are in the outcrop areas of the Carrizo-Wilcox and Yegua-Jackson aquifers. The results of the synoptic gain and loss surveys are consistent with the results of the base-flow analysis of historical streamflow. Appreciable increases in streamflow, apparently the result of increases in base flow, occur in the reach of the Brazos River that crosses the outcrops of the Carrizo-Wilcox, Queen City, Sparta, and Yegua-Jackson aquifers.

Texas↗
USGS2009

Historical Channel Adjustment and Estimates of Selected Hydraulic Values in the Lower Sabine River and Lower Brazos River Basins, Texas and Louisiana

The U.S. Geological Survey, in cooperation with the Texas Water Development Board, evaluated historical channel adjustment and estimated selected hydraulic values at U.S. Geological Survey streamflow-gaging stations in the lower Sabine River Basin in Texas and Louisiana and lower Brazos River Basin in Texas to support geomorphic assessments of the Texas Instream Flow Program. Channel attributes including cross-section geometry, slope, and planform change were evaluated to learn how each river's morphology changed over the years in response to natural and anthropogenic disturbances. Historical and contemporary cross-sectional channel geometries at several gaging stations on each river were compared, planform changes were assessed, and hydraulic values were estimated including mean flow velocity, bed shear stress, Froude numbers, and hydraulic depth. The primary sources of historical channel morphology information were U.S. Geological Survey hard-copy discharge-measurement field notes. Additional analyses were done using computations of selected flow hydraulics, comparisons of historical and contemporary aerial photographs, comparisons of historical and contemporary ground photographs, evaluations of how frequently stage-discharge rating curves were updated, reviews of stage-discharge relations for field measurements, and considerations of bridge and reservoir construction activities. Based on historical cross sections at three gaging stations downstream from Toledo Bend Reservoir, the lower Sabine River is relatively stable, but is subject to substantial temporary scour-and-fill processes during floods. Exceptions to this characterization of relative stability include an episode of channel aggradation at the Sabine River near Bon Wier, Texas, during the 1930s, and about 2 to 3 feet of channel incision at the Sabine River near Burkeville, Texas, since the late 1950s. The Brazos River, at gaging stations downstream from Waco, Texas, has adjusted to a combination of hydrologic, sedimentary, and anthropogenic controls. Since the 1960s, numerous point bars have vertically accreted and vegetation has encroached along the channel margins, which probably promotes channel-bed incision to compensate for a reduction in cross-sectional area. Channel incision was detected at all gaging stations along the Brazos River, and the depth of incision is greatest in the lowermost gaging stations, exemplified by about 5 feet of channel-bed incision between 1993 and 2004 at Richmond, Texas. One notable exception to this pattern of incision was a period of aggradation at U.S. Geological Survey gaging station 08096500 Brazos River at Waco, Texas, during the late 1920s and 1930s, probably associated with upstream dam construction. Lateral channel migration rates along the Brazos River determined from aerial photographs are greatest between Waco and Hempstead, Texas, with numerous bends moving an average of more than 10 feet per year. Migration rates at selected bends downstream from Hempstead were measured as less than 10 feet per year, on average. Two tributaries of the Brazos River, the Little and Navasota Rivers, also were investigated for historical channel adjustment. The Little River near Cameron, Texas (08106500) has incised its channel bed about 12 feet since 1949, and the lower Navasota River shows complex adjustment to bridge construction activities and a channel avulsion.

Scientific Investigations Report↗
USGS2007

Application of surface geophysical methods, with emphasis on magnetic resonance soundings, to characterize the hydrostratigraphy of the Brazos River alluvium aquifer, College Station, Texas, July 2006: A pilot study

The U.S. Geological Survey, in cooperation with the Texas Water Development Board, used surface geophysical methods at the Texas A&M University Brazos River Hydrologic Field Research Site near College Station, Texas, in a pilot study, to characterize the hydrostratigraphic properties of the Brazos River alluvium aquifer and determine the effectiveness of the methods to aid in generating an improved ground-water availability model. Three non-invasive surface geophysical methods were used to characterize the electrical stratigraphy and hydraulic properties and to interpret the hydrostratigraphy of the Brazos River alluvium aquifer. Two methods, time-domain electromagnetic (TDEM) soundings and two-dimensional direct-current (2D–DC) resistivity imaging, were used to define the lateral and vertical extent of the Ships clay, the alluvium of the Brazos River alluvium aquifer, and the underlying Yegua Formation. Magnetic resonance sounding (MRS), a recently developed geophysical method, was used to derive estimates of the hydrologic properties including percentage water content and hydraulic conductivity. Results from the geophysics study demonstrated the usefulness of combined TDEM, 2D–DC resistivity, and MRS methods to reduce the need for additional boreholes in areas with data gaps and to provide more accurate information for ground-water availability models. Stratigraphically, the principal finding of this study is the relation between electrical resistivity and the depth and thickness of the subsurface hydrostratigraphic units at the site. TDEM data defined a three-layer electrical stratigraphy corresponding to a conductor-resistor-conductor that represents the hydrostratigraphic units—the Ships clay, the alluvium of the Brazos River alluvium aquifer, and the Yegua Formation. Sharp electrical boundaries occur at about 4 to 6 and 20 to 22 meters below land surface based on the TDEM data and define the geometry of the more resistive Brazos River alluvium aquifer. Variations in resistivity in the alluvium aquifer range from 10 to more than 175 ohm-meters possibly are caused by lateral changes in grain size. Resistivity increases from east to west along a profile away from the Brazos River, which signifies an increase in grain size within the alluvium aquifer and therefore a more productive zone with more abundant water in the aquifer. MRS data can help delineate the subsurface hydrostratigraphy and identify the geometric boundaries of the hydrostratigraphic units by identifying changes in the free water content, transmissivity, and hydraulic conductivity. MRS data indicate that most productive zones of the alluvium aquifer occur between 12 and 25 meters below land surface in the western part of the study area where the hydraulic conductivity can be as high as 250 meters per day. Hydrostratigraphically, individual hydraulic conductivity values derived from MRS were consistent with those from aquifer tests conducted in 1996 in the study area. Average hydraulic conductivity values from the aquifer tests range from about 61 to 80 meters per day, whereas the MRS-derived hydraulic conductivity values range from about 27 to 97 meters per day. Interpreting an interpolated profile of the hydraulic conductivity values and individual values derived from MRS can help describe the hydrostratigraphic framework of an area and constrain ground-water models for better accuracy.

Texas↗
USGS2004

Hydrogeology and simulation of ground-water flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system, Texas

As a part of the Texas Water Development Board Ground- Water Availability Modeling program, the U.S. Geological Survey developed and tested a numerical finite-difference (MODFLOW) model to simulate ground-water flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system in Texas from predevelopment (before 1891) through 2000. The model is intended to be a tool that water-resource managers can use to address future ground-water-availability issues. From land surface downward, the Chicot aquifer, the Evangeline aquifer, the Burkeville confining unit, the Jasper aquifer, and the Catahoula confining unit are the hydrogeologic units of the Gulf Coast aquifer system. Withdrawals of large quantities of ground water have resulted in potentiometric surface (head) declines in the Chicot, Evangeline, and Jasper aquifers and land-surface subsidence (primarily in the Houston area) from depressurization and compaction of clay layers interbedded in the aquifer sediments. In a generalized conceptual model of the aquifer system, water enters the ground-waterflow system in topographically high outcrops of the hydrogeologic units in the northwestern part of the approximately 25,000-square-mile model area. Water that does not discharge to streams flows to intermediate and deep zones of the system southeastward of the outcrop areas where it is discharged by wells and by upward leakage in topographically low areas near the coast. The uppermost parts of the aquifer system, which include outcrop areas, are under water-table conditions. As depth increases in the aquifer system and as interbedded sand and clay accumulate, water-table conditions evolve into confined conditions. The model comprises four layers, one for each of the hydrogeologic units of the aquifer system except the Catahoula confining unit, the assumed no-flow base of the system. Each layer consists of 137 rows and 245 columns of uniformly spaced grid blocks, each block representing 1 square mile. Lateral no-flow boundaries were located on the basis of outcrop extent (northwestern), major streams (southwestern, northeastern), and downdip limit of freshwater (southeastern). The MODFLOW general-head boundary package was used to simulate recharge and discharge in the outcrops of the hydrogeologic units. Simulation of land-surface subsidence (actually, compaction of clays) and release of water from storage in the clays of the Chicot and Evangeline aquifers was accomplished using the Interbed-Storage Package designed for use with the MODFLOW model. The model was calibrated by trial-anderror adjustment of selected model input data in a series of transient simulations until the model output (potentiometric surfaces, land-surface subsidence, and selected water-budget components) reasonably reproduced field measured (or estimated) aquifer responses. Model calibration comprised four elements: The first was qualitative comparison of simulated and measured heads in the aquifers for 1977 and 2000; and quantitative comparison by computation and areal distribution of the root-mean-square error between simulated and measured heads. The second calibration element was comparison of simulated and measured hydrographs from wells in the aquifers in a number of counties throughout the modeled area. The third calibration element was comparison of simulated water-budget componentsprimarily recharge and dischargeto estimates of physically reasonable ranges of actual water-budget components. The fourth calibration element was comparison of simulated land-surface subsidence from predevelopment to 2000 to measured land surface subsidence from 1906 through 1995.

Texas↗
USGS2021

Hydrogeology and model-simulated groundwater availability in the Salt Fork Red River aquifer, southwestern Oklahoma, 1980–2015

The 1973 Oklahoma Water Law (82 OK Stat § 82-1020.5) requires that the Oklahoma Water Resources Board (OWRB) conduct hydrologic investigations of the State’s groundwater basins to support a determination of the maximum annual yield for each groundwater basin (hereinafter referred to as an “aquifer”). The maximum annual yield allocated per acre of land is known as the equal-proportionate-share (EPS) pumping rate. At present (2021), the OWRB has not yet established a maximum annual yield and EPS pumping rate for the Salt Fork Red River aquifer. To provide updated information to the OWRB that could support evaluation and determination of an appropriate maximum annual yield, the U.S. Geological Survey (USGS), in cooperation with the OWRB, conducted a hydrologic investigation and evaluated the effects of potential groundwater withdrawals on groundwater availability in the Salt Fork Red River aquifer. The Salt Fork Red River aquifer in Greer, Harmon, and Jackson Counties of southwestern Oklahoma is composed of about 274.5 square miles of alluvium and terrace deposits associated with the Salt Fork Red River. The mean annual recharge rate to the Salt Fork Red River aquifer for the period 1980–2015 was estimated to be about 2.94 inches per year, or 10.0 percent of the mean annual precipitation for the same period (29.4 inches per year). This 1980–2015 mean annual recharge rate is equivalent to a mean annual recharge rate of about 38,000 acre-feet per year (acre-ft/yr) for the Salt Fork Red River aquifer excluding about 19,764 acres comprising the Mulberry Creek and Horse Creek terraces. The mean annual recharge rates upgradient and downgradient from USGS streamgage 07300500 Salt Fork Red River at Mangum, Okla. (hereinafter referred to as the “Mangum gage”), apportioned by aquifer area (41.5 and 58.5 percent, respectively), were about 16,000 and 22,000 acre-ft/yr, respectively. Mean annual groundwater use for the study period (1980–2015) was 3,532.7 acre-ft/yr; about 77 percent of that groundwater use was for irrigation, and about 23 percent was for public supply. Most groundwater use for irrigation was associated with wells in the Martha terrace. A hydrogeologic framework was developed for the Salt Fork Red River aquifer and included a definition of the aquifer extent and potentiometric surface, as well as a description of the textural and hydraulic properties of aquifer materials. The hydrogeologic framework was used in the construction of the numerical groundwater-flow model of the Salt Fork Red River aquifer described in this report. A conceptual model for the Salt Fork Red River aquifer that reasonably represents the groundwater-flow system was developed to constrain the construction and calibration of the numerical model. The conceptual-model water budget estimated mean annual inflows to, and outflows from, the Salt Fork Red River aquifer for the period 1980–2015 and included a subaccounting of mean annual inflows and outflows for the portions of the aquifer that were upgradient and downgradient from the Mangum gage. The numerical groundwater-flow model of the Salt Fork Red River aquifer was constructed by using MODFLOW-2005 with the Newton formulation solver. The model of the Salt Fork Red River aquifer was spatially discretized into 1,050 rows, 1,125 columns, about 170,000 active cells measuring 200 by 200 feet (ft), and a single convertible layer. The model was temporally discretized into 432 monthly transient stress periods (each with two time steps to improve model stability). An initial steady-state stress period represented mean annual inflows to, and outflows from, the aquifer and produced a solution that was used as the initial condition for subsequent transient stress periods as well as some groundwater-availability scenarios. The model was calibrated to water-table-altitude observations at selected wells and base-flow observations at selected streamgages. The simulated saturated thickness of the Salt Fork Red River aquifer was determined by subtracting the altitude of the aquifer base from the simulated water-table altitude at the end of the numerical-model period (2015). The simulated saturated thickness was more than 75 ft in a paleochannel in the Dodson terrace near the Texas border. The mean aquifer thickness (sum of saturated and unsaturated) was 49.62 ft, and the mean saturated thickness was 28.55 ft. A simulated mean transmissivity of 1,024 feet squared per day was computed from the calibrated hydraulic conductivity and saturated thickness of each cell. The simulated available water in storage at the end of the numerical-model period (2015) was 526,117 acre-feet (acre-ft); about 42 percent of that total was available upgradient from the Mangum gage, and about 58 percent of that total was available downgradient from the Mangum gage (including the Mangum terrace). Three types of groundwater-availability scenarios were run using the calibrated numerical model. These scenarios were used to (1) estimate the EPS pumping rate that ensures a minimum 20-, 40-, and 50-year life of the aquifer, (2) quantify the potential effects of projected well withdrawals on groundwater storage over a 50-year period, and (3) simulate the potential effects of a hypothetical 10-year drought on base flow and groundwater storage. The 20-, 40-, and 50-year EPS pumping rates under normal recharge conditions were about 0.51, 0.48, and 0.48 acre-foot per acre per year, respectively. Given the 155,929-acre modeled aquifer area, these rates correspond to annual yields of about 78,800, 74,900, and 74,700 acre-ft/yr, respectively. For the 20-year EPS scenario, decreasing and increasing recharge by 10 percent resulted in a 6-percent change in the EPS pumping rate in both cases; for the 40- and 50-year EPS scenarios, decreasing and increasing recharge by 10 percent resulted in a 7-percent change in the EPS pumping rate in both cases. Projected 50-year pumping scenarios were used to simulate the effects of selected well withdrawal rates on groundwater storage of the Salt Fork Red River aquifer and base flows in the Salt Fork Red River. The effects of well withdrawals were evaluated by quantifying differences in groundwater storage and base flow in four 50-year scenarios, which applied (1) no groundwater pumping, (2) mean pumping rates for the study period (1980–2015), (3) 2015 pumping rates, and (4) increasing demand pumping rates at simulated wells. The increasing demand pumping rates assumed a cumulative 20.4-percent increase in pumping over 50 years based on 2010–60 demand projections for southwestern Oklahoma. Groundwater storage after 50 years with no pumping was 535,000 acre-ft, or 8,900 acre-ft (1.7 percent) greater than the initial groundwater storage; this groundwater storage increase is equivalent to a mean water-table-altitude increase of 0.48 ft. Groundwater storage after 50 years of pumping at the mean rate for the study period (1980–2015) was 519,900 acre-ft, or 6,200 acre-ft (1.2 percent) less than the initial groundwater storage; this groundwater storage decrease is equivalent to a mean water-table-altitude decline of 0.34 ft. Groundwater storage at the end of the 50-year period with 2015 pumping rates was 513,100 acre-ft, or 13,000 acre-ft (2.5 percent) less than the initial storage; this groundwater storage decrease is equivalent to a mean water-table-altitude decline of 0.71 ft. Groundwater storage at the end of the 50-year period with increasing demand pumping rates was 509,700 acre-ft, or 16,500 acre-ft (3.1 percent) less than the initial storage; this groundwater storage decrease is equivalent to a mean water-table-altitude decline of 0.89 ft. A hypothetical 10-year drought scenario was used to simulate the effects of a prolonged period of reduced recharge on groundwater storage. The period January 1983–December 1992 was chosen as the simulated drought period. Drought effects were quantified by comparing the results of the drought scenario to those of the calibrated numerical model (no drought) at the end of the simulated drought period (1992). To simulate the hypothetical drought, recharge in the calibrated numerical model was reduced by 50 percent during the simulated drought period (1983–92). Upstream inflows from the Salt Fork Red River, Turkey Creek, and Bitter Creek were reduced by 75 percent. Groundwater storage at the end of the drought period (1992) was 479,200 acre-ft, or 53,200 acre-ft (10.0 percent) less than the groundwater storage of the calibrated numerical model at the end of the drought period. This decrease in groundwater storage is equivalent to a mean water-table-altitude decline of 2.9 ft. At the end of the 10-year hypothetical drought period, simulated base flows at the Mangum gage and USGS streamgage 07301110 Salt Fork Red River near Elmer, Okla., had decreased by about 80 and 70 percent, respectively.

Oklahoma↗
USGS2005

Evaluation of ground-water flow and land-surface subsidence caused by hypothetical withdrawals in the northern part of the Gulf Coast Aquifer system, Texas

During 2003–04 the U.S. Geological Survey, in cooperation with the Texas Water Development Board (TWDB) and the Harris-Galveston Coastal Subsidence District (HGCSD), used the previously developed Northern Gulf Coast Ground-Water Availability Modeling (NGC GAM) model to evaluate the effects of hypothetical projected withdrawals on ground-water flow in the northern part of the Gulf Coast aquifer system and land-surface subsidence in the NGC GAM model area of Texas. The Gulf Coast aquifer system comprises, from the surface, the Chicot and Evangeline aquifers, the Burkeville confining unit, the Jasper aquifer, and the Catahoula confining unit. Two withdrawal scenarios were simulated. The first scenario comprises historical withdrawals from the aquifer system for 1891–2000 and hypothetical projected withdrawals for 2001–50 compiled by the TWDB (TWDB scenario). The projected withdrawals compiled by the TWDB are based on ground-water demands estimated by regional water planning groups. The second scenario is a “merge” of the TWDB scenario with an alternate set of projected withdrawals from the Chicot and Evangeline aquifers in the Houston metropolitan area for 1995–2030 provided by the HGCSD (HGCSD scenario). Under the TWDB scenario withdrawals from the entire system are projected to be about the same in 2050 as in 2000. The simulated potentiometric surfaces of the Chicot aquifer for 2010, 2020, 2030, 2040, and 2050 show relatively little change in configuration from the simulated 2000 potentiometric surface (maximum water-level depths in southern Harris County 150–200 feet below NGVD 29). The simulated decadal potentiometric surfaces of the Evangeline aquifer show the most change between 2000 and 2010. The area of water levels 250– 400 feet below NGVD 29 in western Harris County in 2000 shifts southeastward to southern Harris County, and water levels recover to 200–250 feet below NGVD 29 by 2010. Water levels in southern Harris County recover to 150–200 feet below NGVD 29 by 2020 and remain in that range through 2050. A relatively small cone of depression in southern Montgomery County that did not appear in the 2000 surface develops and enlarges during the projected period, with a maximum depth of 250–300 feet below NGVD 29 in 2030, 2040, and 2050. The simulated decadal potentiometric surfaces of the Jasper aquifer each have a major cone of depression centered in southern Montgomery County that was minimally developed in 2000 but reaches depths of 550–650 feet below NGVD 29 in the 2020, 2030, 2040, and 2050 surfaces. Under the TWDB scenario the percentage of withdrawals supplied by net recharge increases from 75 percent in 2000 to 87 percent in 2050, and the percentage of withdrawals supplied by storage decreases from 25 percent in 2000 to 13 percent in 2050. Under the HGCSD scenario, withdrawals from the Chicot and Evangeline aquifers increase about 74 percent during 1995–2030; Jasper aquifer withdrawals are unchanged from those of the TWDB scenario. For the 2010, 2020, and 2030 potentiometric surfaces of the Chicot and Evangeline aquifers, the substantially greater withdrawals of the HGCSD scenario relative to those of the TWDB scenario result in progressively deeper cones of depression than those in the potentiometric surfaces associated with the TWDB scenario—for the Chicot aquifer in southern Harris County, 400–450 feet below NGVD 29 in 2030; for the Evangeline aquifer in southern Montgomery County, 700–750 feet below NGVD 29 in 2030. Although Jasper aquifer withdrawals are the same for both scenarios, the major cone of depression centered in southern Montgomery County in the 2030 potentiometric surface is 50 feet deeper at its center (600–700 feet below NGVD 29) than the cone in the 2030 surface under the TWDB scenario. Under the HGCSD scenario, the percentage of withdrawals supplied by net recharge decreases from 72 percent in 1995 to 57 percent in 2030, and the percentage of withdrawals supplied by storage increases from 28 percent in 2000 to 43 percent in 2030. About 85 percent of the increase supplied by storage is from the compaction of clay. Land-surface subsidence in the major area of subsidence centered in Harris and Galveston Counties during 2000–50 that results from simulating the TWDB withdrawal scenario expands slightly to the west and increases in places. The maximum change occurs in the Conroe area where subsidence increases from about 4 to about 13 feet during the projected period. Land-surface subsidence in the major area of subsidence during 1995–2030 that results from simulating the HGCSD withdrawal scenario increases substantially. For example, in east-central Harris County maximum subsidence increases from about 10–11 feet in 1995 to 22 feet in 2030. The hypothetical projected withdrawal scenarios are estimates of future withdrawals and might not represent actual future withdrawals. The simplifying assumptions that the downdip limit of freshwater flow in each hydrogeologic unit is a stable, sharp interface across which no flow occurs and that the base of the system is a no-flow boundary become less realistic and thus increase the uncertainty in results as drawdowns increase. The presence of uncertainty dictates that the results of the predictive simulations described in this report be used with caution in any decision-making process.

Texas↗
USGS2017

Characterization of streamflow, suspended sediment, and nutrients entering Galveston Bay from the Trinity River, Texas, May 2014–December 2015

The U.S. Geological Survey (USGS), in cooperation with the Texas Water Development Board and the Galveston Bay Estuary Program, collected streamflow and water-quality data at USGS streamflow-gaging stations in the lower Trinity River watershed from May 2014 to December 2015 to characterize and improve the current understanding of the quantity and quality of freshwater inflow entering Galveston Bay from the Trinity River. Continuous streamflow records at four USGS streamflow-gaging stations were compared to quantify differences in streamflow magnitude between upstream and downstream reaches of the lower Trinity River. Water-quality conditions were characterized from discrete nutrient and sedi­ment samples collected over a range of hydrologic conditions at USGS streamflow-gaging station 08067252 Trinity River at Wallisville, Tex. (hereinafter referred to as the “Wallisville site”), approximately 4 river miles upstream from where the Trinity River enters Galveston Bay. Based on streamflow records, annual mean outflow from Livingston Dam into the lower Trinity River was 2,240 cubic feet per second (ft 3 /s) in 2014 and 22,400 ft 3 /s in 2015, the second lowest and the highest, respectively, during the entire period of record (1966–2015). During this study, only about 54 percent of the total volume measured at upstream sites was accounted for at the Wallisville site as the Trinity River enters Galveston Bay. This difference in water volumes between upstream sites and the Wallisville site indicates that at high flows a large part of the volume released from Lake Livingston does not reach Galveston Bay through the main channel of the Trinity River. These findings indicate that water likely flows into wetlands and water bodies surrounding the main channel of the Trinity River before reaching the Wallisville site and is being stored or discharged through other channels that flow directly into Galveston Bay. To characterize suspended-sediment concentrations and loads in Trinity River inflow to Galveston Bay, a regression model was developed to estimate suspended-sediment concentrations by using acoustic backscatter data as a surrogate. The model yielded an adjusted coefficient of determination value of 0.92 and a root mean square error of 1.65 milligrams per liter (mg/L). The mean absolute percentage error between measured and estimated suspended-sediment concentration was 35 percent. During this study, estimated suspended-sediment concentrations ranged from 2 to 701 mg/L, with a mean of 97 mg/L. Suspended-sediment concentrations varied in response to changes in discharge, with peak suspended-sediment concentrations occurring 1 to 2 days before the peak discharge for each event. The total suspended-sediment load at the Wallisville site during May 2014–December 2015 was approximately 2,200,000 tons, with a minimum monthly suspended-sediment load of 100 tons in October 2014 and a maximum monthly load of 441,000 tons in November 2015. Results from nutrient samples collected at the Wallisville site indicate that total nitrogen and total phosphorus concen­trations fluctuated at a similar rate, with the highest nutrient concentrations occurring during periods of high flow corresponding to releases from Lake Livingston. The mean concen­trations of total nitrogen and total phosphorus were approxi­mately 75 percent higher during high flow releases than during periods of low flow, overshadowing variations in nutrient concentrations caused by seasonality at the Wallisville site. Results from the study indicate nutrient delivery to Galveston Bay from the main channel of the Trinity River is likely controlled primarily by high-flow releases from Lake Livingston. For most samples collected at the Wallisville site, organic nitrogen was the predominant form of nitrogen; however, when discharge increased because of releases from Lake Livingston, the percentage of organic nitrogen typically decreased and the percentage of nitrate increased. The concentrations of total phosphorus also increased during high-flow events, likely as a result of suspended sediment within Lake Livingston releases and mobilization of sediment particles in the river channel and flood plain during these periods of high flow. The predominant source of phosphorous to Galveston Bay from the Trinity River is in particulate form closely tied to suspended-sediment concentrations. The changes in nutrient concentration and composition caused by releases from Lake Livingston during this study indicate the reservoir may play an important role in the delivery of nutrients into Galveston Bay. Further study is required to better understand the processes in Lake Livingston influencing the characteristics of nutrient and sediment inflow to Galveston Bay. With phosphorous concentrations correlated to suspended-sediment concentra­tions (coefficient of determination value of 0.75) and with the concentrations of nutrients changing as the discharge changes, the diversion of water and suspended sediment into surround­ing wetlands and channels outside of the main channel of the Trinity River may play a large role in regulating nutrient inputs into Galveston Bay.

Texas↗
USGS2012

Base flow (1966-2009) and streamflow gain and loss (2010) of the Brazos River from the New Mexico-Texas State line to Waco, Texas

During 2010–11, the U.S. Geological Survey (USGS), in cooperation with the Texas Water Development Board, used hydrograph separation to quantify historical base flow at 11 USGS streamflow-gaging stations between water years 1966–2009 and streamflow gains and losses from two sets of synoptic measurements of streamflow and specific conductance (the first in June 2010, followed by another set in October 2010) in the upper Brazos River Basin from the New Mexico–Texas State line to Waco, Texas. The following subbasins compose the study area: Salt Fork Brazos River Basin, Double Mountain Fork Brazos River Basin, Clear Fork Brazos River Basin, North Bosque River Basin, and the Brazos River Basin (main stem) (including its tributaries). Base-flow analysis was done using historical streamflow data from 11 USGS streamflow-gaging stations in the upper Brazos River Basin to compute yearly base-flow indexes (base flow divided by total streamflow) for each station. The base-flow index was used to indicate the fraction of flow consisting of base flow on an annual basis for the period of record evaluated at each streamflow-gaging station. At nine stations there were long-term streamflow data from water years 1966–2009 (October 1965 through September 2009); at two stations slightly shorter periods of record (water years 1967–2009 and 1969–2009) were available. The median base-flow indexes were 0.16 and 0.15 at USGS streamflow-gaging stations 08082000 Salt Fork Brazos River near Aspermont, Tex., and 08080500 Double Mountain Fork Brazos River near Aspermont, Tex., respectively. The amount of the total streamflow consisting of base flow was larger at sites in the Clear Fork Brazos River Basin compared to sites in the Salt Fork Brazos River Basin or Double Mountain Fork Brazos River Basin; at USGS streamflow-gaging stations 08084000 Clear Fork Brazos River at Nugent, Tex., and at 08085500 Clear Fork Brazos River at Fort Griffin, Tex., the median base-flow indexes were 0.28 and 0.23, respectively. The largest median base-flow index for any station was 0.35 at USGS streamflow-gaging station 08091500 Paluxy River at Glen Rose, Tex. The second largest base-flow index was 0.30 at USGS streamflow-gaging station 08095000 North Bosque River near Clifton, Tex. Median base-flow indexes on the main stem of the Brazos River upstream from Possum Kingdom Lake were 0.22 at USGS streamflow-gaging station 08082500 Brazos River at Seymour, Tex., and 0.24 at USGS streamflow-gaging station 08088000 Brazos River near South Bend, Tex. The base-flow indexes for stations between Possum Kingdom Lake and Lake Granbury were 0.19 and 0.27 at USGS streamflow-gaging stations 08089000 Brazos River near Palo Pinto, Tex., and 08090800 Brazos River near Dennis, Tex., respectively. A median base-flow index of 0.19 was also measured at USGS streamflow-gaging station 08091000 Brazos River near Glen Rose, Tex., located between Lake Granbury and Lake Whitney. A Mann-Kendall trend analysis test was performed on annual base-flow index values from each of the 11 streamflow records that were analyzed. Upward trends in base-flow index values indicating increasing flows during the study period were found for USGS streamflow-gaging stations 08080500 Double Mountain Fork Brazos River near Aspermont, Tex., 08089000 Brazos River near Palo Pinto, Tex., and 08090800 Brazos River near Dennis, Tex. Flows at these three streamflow-gaging stations are regulated by reservoir releases, and additional analyses are needed before these streamflow trends can be characterized as indicative of changes in base flow over time. Streamflow was measured at 66 sites from June 6–9, 2010, and at 68 sites from October 16–19, 2010, to identify reaches in the upper Brazos River Basin that were gaining or losing streamflow. Gaining reaches were identified in each of the five subbasins. The gaining reach in the Salt Fork Brazos River Basin began at USGS streamflow-gaging station 08080940 Salt Fork Brazos River at State Highway 208 near Clairemont, Tex. (site SF–6), upstream from where Duck Creek flows into the Salt Fork Brazos River and continued downstream past USGS streamflow-gaging station 08082000 Salt Fork Brazos River near Aspermont, Tex. (site SF–9), to the outlet of the basin. In the Double Mountain Fork Brazos River Basin, a gaining reach from near Post, Tex., downstream to the outlet of the basin was identified. Two gaining reaches were identified in the Clear Fork Brazos River Basin—one from near Roby, Tex., downstream to near Noodle, Tex., and second from Hawley, Tex., downstream to Nugent, Tex. Most of the North Bosque River was characterized as gaining streamflow. Streamflow gains were identified in the main stem of the Brazos River from where the Brazos River main stem forms at the confluence of the Salt Fork Brazos River and Double Mountain Fork Brazos River near Knox City, Tex., downstream to near Seymour, Tex.

New Mexico, Texas↗