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USGS2008

Characterization of errors in a coupled snow hydrology-microwave emission model

Traditional approaches to the direct estimation of snow properties from passive microwave remote sensing have been plagued by limitations such as the tendency of estimates to saturate for moderately deep snowpacks and the effects of mixed land cover within remotely sensed pixels. An alternative approach is to assimilate satellite microwave emission observations directly, which requires embedding an accurate microwave emissions model into a hydrologic prediction scheme, as well as quantitative information of model and observation errors. In this study a coupled snow hydrology [Variable Infiltration Capacity (VIC)] and microwave emission [Dense Media Radiative Transfer (DMRT)] model are evaluated using multiscale brightness temperature (TB) measurements from the Cold Land Processes Experiment (CLPX). The ability of VIC to reproduce snowpack properties is shown with the use of snow pit measurements, while TB model predictions are evaluated through comparison with Ground-Based Microwave Radiometer (GBMR), air-craft [Polarimetric Scanning Radiometer (PSR)], and satellite [Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E)] TB measurements. Limitations of the model at the point scale were not as evident when comparing areal estimates. The coupled model was able to reproduce the TB spatial patterns observed by PSR in two of three sites. However, this was mostly due to the presence of relatively dense forest cover. An interesting result occurs when examining the spatial scaling behavior of the higher-resolution errors; the satellite-scale error is well approximated by the mode of the (spatial) histogram of errors at the smaller scale. In addition, TB prediction errors were almost invariant when aggregated to the satellite scale, while forest-cover fractions greater than 30% had a significant effect on TB predictions. ?? 2008 American Meteorological Society.

Journal of Hydrometeorology↗

USGS2011

Hydrologic effects of urbanization and climate change on the Flint River Basin, Georgia

The potential effects of long-term urbanization and climate change on the freshwater resources of the Flint River basin were examined by using the Precipitation-Runoff Modeling System (PRMS). PRMS is a deterministic, distributed-parameter watershed model developed to evaluate the effects of various combinations of precipitation, temperature, and land cover on streamflow and multiple intermediate hydrologic states. Precipitation and temperature output from five general circulation models (GCMs) using one current and three future climate-change scenarios were statistically downscaled for input into PRMS. Projections of urbanization through 2050 derived for the Flint River basin by the Forecasting Scenarios of Future Land-Cover (FORE-SCE) land-cover change model were also used as input to PRMS. Comparison of the central tendency of streamflow simulated based on the three climate-change scenarios showed a slight decrease in overall streamflow relative to simulations under current conditions, mostly caused by decreases in the surface- runoff and groundwater components. The addition of information about forecasted urbanization of land surfaces to the hydrologic simulation mitigated the decreases in streamflow, mainly by increasing surface runoff.

Georgia↗

USGS2025

Alaskan hydrology in transition: Changing precipitation and evapotranspiration patterns are projected to reshape seasonal streamflow and water temperature by midcentury (2035-2064)

High spatial and temporal resolution models are essential for understanding future climate impacts and developing effective climate resilience plans. However, existing regional and global river models often lack the resolution needed to accurately capture local conditions. This study uses a series of high-resolution models, including the Regional Arctic System Model, mizuRoute, and the river basin model, to analyze Arctic and sub-Arctic Alaskan hydrology. We compare a historical baseline (1991–2020) with six midcentury (2035–64) futures: two pseudo–global warming scenarios based on historical meteorology and four direct dynamically downscaled global climate models. The six futures reveal significant uncertainty in future annual discharge and peak flows, although a widespread increase in discharge during April (+63%) and October (+31%) is consistently shown across models. Projected increases in rain and shifting weather patterns lead to a transition from snow to rain in spring and autumn, reducing the fraction of snowmelt contributing to river discharge. Rising evapotranspiration moderates discharge changes, particularly in autumn, by offsetting precipitation increases. Average summer river temperatures are projected to increase by approximately 1.5°C, doubling the number of river segments that experience 18°C days, a critical threshold for salmon survival, and intensifying the heat flux to the ocean adding an average of 3.3 × 10 12 MJ yr −1 . These changes in the hydrologic cycle could profoundly impact riverine and oceanic ecosystems, posing substantial challenges to communities reliant on these environments.

Alaska, Yukon↗

USGS2006

One-way coupling of an atmospheric and a hydrologic model in Colorado

This paper examines the accuracy of high-resolution nested mesoscale model simulations of surface climate. The nesting capabilities of the atmospheric fifth-generation Pennsylvania State University (PSU)-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) were used to create high-resolution, 5-yr climate simulations (from 1 October 1994 through 30 September 1999), starting with a coarse nest of 20 km for the western United States. During this 5-yr period, two finer-resolution nests (5 and 1.7 km) were run over the Yampa River basin in northwestern Colorado. Raw and bias-corrected daily precipitation and maximum and minimum temperature time series from the three MM5 nests were used as input to the U.S. Geological Survey's distributed hydrologic model [the Precipitation Runoff Modeling System (PRMS)] and were compared with PRMS results using measured climate station data. The distributed capabilities of PRMS were provided by partitioning the Yampa River basin into hydrologic response units (HRUs). In addition to the classic polygon method of HRU definition, HRUs for PRMS were defined based on the three MM5 nests. This resulted in 16 datasets being tested using PRMS. The input datasets were derived using measured station data and raw and bias-corrected MM5 20-, 5-, and 1.7-km output distributed to 1) polygon HRUs and 2) 20-, 5-, and 1.7-km-gridded HRUs, respectively. Each dataset was calibrated independently, using a multiobjective, stepwise automated procedure. Final results showed a general increase in the accuracy of simulated runoff with an increase in HRU resolution. In all steps of the calibration procedure, the station-based simulations of runoff showed higher accuracy than the MM5-based simulations, although the accuracy of MM5 simulations was close to station data for the high-resolution nests. Further work is warranted in identifying the causes of the biases in MM5 local climate simulations and developing methods to remove them. ?? 2006 American Meteorological Society.

Journal of Hydrometeorology↗

USGS2001

Online bibliographic sources in hydrology

Traditional commercial bibliographic databases and indexes provide some access to hydrology materials produced by the government; however, these sources do not provide comprehensive coverage of relevant hydrologic publications. This paper discusses bibliographic information available from the federal government and state geological surveys, water resources agencies, and depositories. In addition to information in these databases, the paper describes the scope, styles of citing, subject terminology, and the ways these information sources are currently being searched, formally and informally, by hydrologists. Information available from the federal and state agencies and from the state depositories might be missed by limiting searches to commercially distributed databases.

Science and Technology Libraries↗

USGS2012

The hydrology of a drained topographical depression within an agricutlural field in north-central Iowa

North-central Iowa is an agriculturally intensive area comprising the southeastern portion of the Prairie Pothole Region, a landscape containing a high density of enclosed topographical depressions. Artificial drainage practices have been implemented throughout the area to facilitate agricultural production. Vertical surface drains are utilized to drain the topographical depressions that accumulate water. This study focuses on the hydrology of a drained topographical depression located in a 39.5 ha agricultural field. To assess the hydrology of the drained depression, a water balance was constructed for 11 ponding events during the 2008 growing season. Continuous pond and groundwater level data were obtained with pressure transducers. Flows into the vertical surface drain were calculated based on pond depth. Precipitation inflows and evaporative outflows of the ponds were calculated using climatic data. Groundwater levels were used to assess groundwater/pond interactions. Results of the water balances show distinct differences between the inflows to and outflows from the depression based on antecedent conditions. In wet conditions, groundwater inflow sustained the ponds. The ponds receded only after the groundwater level declined to below the land surface. In drier conditions, groundwater was not a source of water to the depression. During these drier conditions, infiltration comprised 30% of the outflows from the depression during declining pond stages. Over the entire study period, the surface drain, delivering water to the stream, was the largest outflow from the pond, accounting for 97% of the outflow, while evapotranspiration was just 2%. Precipitation onto the pond surface proved to be a minor component, accounting for 4% of the total inflows.

Iowa↗

USGS2002

The lacustrine carbon cycle as illuminated by the waters and sediments of two hydrologically distinct headwater lakes in north-central Minnesota, U.S.A

The accumulation rates of CaCO 3 and organic carbon (OC) in lake sediments are delicately balanced between production in the epilimnion and destruction in the hypolimnion. The cycling of these two forms of carbon makes a "carbon pump" that greatly affects the biogeochemical cycles of other elements. To further understand these biogeochemical dynamics, the lakes, streams, and wetlands of the Shingobee River headwater area of north-central Minnesota have been subjected to intensive hydrologic and biogeochemical studies. Williams Lake, situated close to the highest point in the regional flow system, is hydrologically closed, with no surface inlet or outlet, and ground water and precipitation as the only sources of water. Shingobee Lake, situated at the lowest point in the regional flow system, has the Shingobee River as an inlet and outlet. The surface waters of both lakes are oversaturated, and the bottom waters undersaturated, with respect to CaCO 3 during the summer. The small amount of CaCO 3 that is precipitated in the epilimnion of Williams Lake during the summer is dissolved in the undersaturated hypolimnion and sediments with the result that no CaCO 3 is incorporated into the profundal surface sediments. Because of the high phytoplankton productivity of Shingobee Lake, sufficient CaCO 3 is produced in the epilimnion that large amounts survive the corrosive hypolimnion and sediments, and an average of 46 wt. % accumulates in surface sediments. Another consequence of higher phytoplankton productivity in Shingobee Lake is that the hypolimnion becomes oxygen deficient within a month after overturn in both the spring and fall. Because of reducing conditions that develop in the hypolimnion of Shingobee Lake, high concentrations of dissolved Fe and Mn accumulate there during summer stratification. Precipitation of Fe and Mn oxyhydroxides during periods of fall and spring overturn results in high concentrations of Fe and Mn in surface sediments. In Williams Lake, high concentrations of Fe and Mn do not build up in the hypolimnion. The concentration of CaCO 3 is about 80 wt. % in lower Holocene sediments of both lakes. The lower Holocene sediments in both lakes also contain high concentrations of Fe and Mn, and the lower Holocene sediments of Shingobee are laminated. The waters of both lakes had identical values of δ 13 C and δ 18 O during the early Holocene, but the waters of Williams Lake "evolved" during the early Holocene, increasing about 10‰ in both δ 13 C and δ 18 O. Deposits of lacustrine marl occur as much as seven meters above the present elevation of Williams Lake, the highest of the two lakes. Taken together, these observations suggest that the lakes were once connected to form a larger lake called Lake Willobee with a hypolimnion that was anoxic, at least seasonally.

Minnesota↗

USGS2018

Clarifying regional hydrologic controls of the Marañón River, Peru through rapid assessment to inform system-wide basin planning approaches

We use remote sensing to enhance the interpretation of the first baseline dataset of hydrologic, isotopic and hydrochemical variables spanning 620 km of the upper Marañón River, in Andean Peru, from the steep alpine canyons to the lower lying jungle. Remote, data-scarce river systems are under increased hydropower development pressure to meet rising energy demands. The upstream-downstream river continuum, which serves as a conduit for resource exchange across ecosystems, is at risk, potentially endangering the people, environments, and economies that rely on river resources. The Marañón River, one of the final free-flowing headwater connections between the Andes and the Amazon, is the subject of myriad large-scale hydropower proposals. Due to challenging access, environmental data are scarce in the upper Marañón, limiting our ability to do system-wide river basin planning. We capture key processes and transitions in the context of hydropower development. Two hydrologic regimes control the Marañón dry-season flow: in the higher-elevation upper reaches, a substantial baseflow is fed by groundwater recharged from wet season rains, in contrast to the lower reaches where the mainstem discharge is controlled by rain-fed tributaries that receive rain from lowland Amazon moisture systems. Sustainability of the upper corridor’s dry-season baseflow appears to be more highly connected to the massive natural storage capacity of extensive wetlands in the puna (alpine grasslands) than with cryospheric water inputs. The extent and conservation of puna ecosystems and glacier reservoirs may be interdependent, bringing to bear important conservation questions in the context of changing climate and land use in the region. More generally, this case study demonstrates an efficient combined remote sensing and field observation approach to address data scarcity across regional scales in mountain basins facing imminent rapid change.

Marañón River↗

USGS2010

HIMALA: climate impacts on glaciers, snow, and hydrology in the Himalayan region

Glaciers are the largest reservoir of freshwater on Earth, supporting one third of the world's population. The Himalaya possess one of the largest resources of snow and ice, which act as a freshwater reservoir for more than 1.3 billion people. This article describes a new project called HIMALA, which focuses on utilizing satellite-based products for better understanding of hydrological processes of the river basins of the region. With support from the US Agency for International Development (USAID), the International Centre for Integrated Mountain Development (ICIMOD), together with its partners and member countries, has been working on the application of satellite-based rainfall estimates for flood prediction. The US National Aeronautics and Space Administration (NASA) partners are working with ICIMOD to incorporate snowmelt and glacier melt into a widely used hydrological model. Thus, through improved modeling of the contribution of snow and ice meltwater to river flow in the region, the HIMALA project will improve the ability of ICIMOD and its partners to understand the impact of weather and climate on floods, droughts, and other water- and climate-induced natural hazards in the Himalayan region in Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal, and Pakistan.

Himalayas↗

USGS2013

Significance of exchanging SSURGO and STATSGO data when modeling hydrology in diverse physiographic terranes

The Water Availability Tool for Environmental Resources (WATER) is a TOPMODEL-based hydrologic model that depends on spatially accurate soils data to function in diverse terranes. In Kentucky, this includes mountainous regions, karstic plateau, and alluvial plains. Soils data are critical because they quantify the space to store water, as well as how water moves through the soil to the stream during storm events. We compared how the model performs using two different sources of soils data--Soil Survey Geographic Database (SSURGO) and State Soil Geographic Database laboratory data (STATSGO)--for 21 basins ranging in size from 17 to 1564 km 2 . Model results were consistently better when SSURGO data were used, likely due to the higher field capacity, porosity, and available-water holding capacity, which cause the model to store more soil-water in the landscape and improve streamflow estimates for both low- and high-flow conditions. In addition, there were significant differences in the conductivity multiplier and scaling parameter values that describe how water moves vertically and laterally, respectively, as quantified by TOPMODEL. We also evaluated whether partitioning areas that drain to streams via sinkholes in karstic basins as separate hydrologic modeling units (HMUs) improved model performance. There were significant differences between HMUs in properties that control soil-water storage in the model, although the effect of partitioning these HMUs on streamflow simulation was inconclusive.

Kentucky↗

USGS2018

Ecohydrologic changes caused by hydrologic disconnection of ephemeral stream channels in Mojave National Preserve, California

Emplacement of highways and railroads has altered natural hydrologic systems by influencing surface-water flow paths and biotic communities in Mojave National Preserve. Infiltration experiments were conducted along active and abandoned channels to evaluate changes in hydrology and related effects on plant water availability and use. Simulated rainfall infiltration experiments with vegetation monitoring were conducted along an active channel upslope and a comparable abandoned channel down slope of the transportation corridor. We also conducted 90 single-ring, ponded infiltration experiments in adjacent channels to evaluate field-saturated hydraulic conductivity and particle size distributions. The abandoned channels are still morphologically evident, but are disconnected from runoff sources at higher elevations. Infiltration test results show that water infiltrates twice as fast in the active channels. Excavation showed weak soil development with fewer plant roots beneath the abandoned channel. SEM analysis on surface samples showed the presence of cyanobacteria only in abandoned channels. Plants up to three meters away from both channels showed physiological responses to channel water applied in a simulated pulse of rain. The response was short-lived and less pronounced for plants adjacent to the abandoned channel, whereas those adjacent to the active channel showed responses up to two months after the pulse. These responses may explain observed lower plant densities and fewer deep-rooted species along abandoned channels compared to active channels. We infer that the deeper-rooting plants are more abundant where they are able to take advantage of the increased soil-water storage resulting from greater infiltration and flow frequency in active stream channels.

California↗

USGS2001

Effect of the 1997-1998 ENSO-related drought on hydrology and salinity in a Micronesian wetland complex

The potential effects of global climate change on coastal ecosystems have attracted considerable attention, but the impacts of shorter-term climate perturbations such as ENSO (El Niño-Southern Oscillation) are lesser known. In this study, we determined the effects of the 1997–1998 ENSO-related drought on the hydrology and salinity of a Micronesian mangrove ecosystem and an adjacent freshwater swamp. A network of 9 piezometer clusters installed at the study site served as sampling points for continuous and manual measurements of salinity and water level. During the drought period from January through April 1998, mean water table levels in the mangroves and freshwater swamp were approximately 12 and 54 cm lower, respectively, than during May through December when precipitation returned to near normal levels. At the peak of the drought (February 1998), the most dramatic result was a reversal in groundwater flow that sent groundwater from the mangroves upstream toward the freshwater swamp. Flow nets constructed for this period and immediately after illustrate the strong hydrological linkage between the two systems. This linkage was also illustrated by measurements of groundwater salinity in the piezometer network. Ninety-six percent of the salinity measurements taken in the mangroves during the study were at least 10‰ less than the salinity of sea water, indicating that the mangroves were consistently receiving freshwater flows. An analysis of variance of groundwater salinity measurements during and after the drought showed that salinity levels in the 0.5 and 1.0 m depth piezometers were greater during than after the drought. In a comparison of salinity values in 0.5-m wells during low tide, mean salinity was approximately twice as high during the drought than after (14.7‰ versus 6.2‰, respectively). This study demonstrates that short-term climate perturbations such as ENSO can disrupt important coastal processes. Over repeated drought cycles, such perturbations have the potential to affect the structure and function of mangrove forests and upstream ecosystems.

Kosrae↗

USGS2025

Salinas Valley integrated hydrologic and reservoir operations models, Monterey and San Luis Obispo Counties, California

The area surrounding the Salinas Valley groundwater basin in Monterey and San Luis Obispo Counties of California is a highly productive agricultural area, contributes significantly to the local economy, and provides a substantial portion of vegetables and other agricultural commodities to the Nation. This region of California provides about half of the Nation’s lettuce, celery, broccoli, and spinach each year. Thus, this agricultural area provides significant volumes of agricultural products not just for California but the entire United States. Changes in population and increased agricultural development, which includes a shift toward more water-intensive crops, and climate variability, have put increasing demand on both surface water and groundwater resources in the valley. This has resulted in water management challenges in the Salinas Valley that are predominantly related to distribution of water supply throughout the basin. Where and when the water is present in the surface and subsurface does not coincide with where and when the water is needed. To deal with the distribution issue, historically water has been used conjunctively in the valley. Conjunctive use is a water management strategy that coordinates surface water and groundwater use to maximize water availability. Groundwater is used throughout the Salinas Valley to meet water demands when surface water supplies are insufficient. Availability of surface water is constrained by climate. Precipitation and streamflow vary seasonally and year to year. Although there are two reservoirs in the Salinas Valley to capture and store water during wet periods, the only conveyance of reservoir water to coastal agricultural areas is the Salinas River. Increasing demand on groundwater and surface water resources throughout the Salinas Valley has resulted in undesirable effects of unsustainable water use, such as surface water depletion, groundwater level declines, storage depletion in the principal aquifers, and seawater intrusion. To address these escalating issues, local communities, water management agencies, and groundwater sustainability agencies are evaluating how to sustainably manage both their surface water and groundwater resources. To meet water demands and reduce undesirable effects of unsustainable water use, continued conjunctive management of surface water and groundwater would ideally incorporate strategies to deal with increases in demand and a variable climate. To evaluate the challenging water management issues in the Salinas Valley, the U.S. Geological Survey, Monterey County Water Resource Agency, and the Salinas Valley Basin Groundwater Sustainability Agency developed a comprehensive suite of models that represent the Salinas Valley Hydrogeologic system called the Salinas Valley System Model. The Salinas Valley Geologic Framework was developed to characterize the subsurface using various topographic and geologic data sources, including information on hydrogeologic units, their surfaces and extents, geologic structures, lithology, and elevations from borehole data and cross sections, as well as details on faults and existing models. The Salinas Valley Watershed Model simulates the entire Salinas River watershed. Monthly surface water inflows into the integrated hydrologic model domain were simulated using the Salinas Valley Watershed Model. The historical model uses historical climate data, water and land use data, and reservoir releases to simulate agricultural operations, including landscape water demands, diversions, and reclaimed wastewater. The operational model adds an embedded reservoir operations framework to the simulation of the historical model that allows specified operational rules to simulate reservoir releases and changes in reservoir storage. The operational model assumes current reservoir operations and constant land use, which differs from historical conditions. Thus, the operational model is a hypothetical baseline model that can be used by local water managers to evaluate and quantify potential benefits of water supply projects. Together, the geologic framework, watershed, historical, and operational models form a tool that can be used to simulate irrigated agriculture and associated reservoir operations of the integrated hydrologic system of the Salinas Valley.

EarthArXiv↗

USGS1999

1:2,000,000-scale Hydrologic Units of the United States

This file contains hydrologic unit boundaries and codes for the conterminous United States along with Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands. It was revised for inclusion in the National Atlas of the United States of America, and updated to match the streams file created by the USGS National Mapping Division (NMD) for the National Atlas of the United States of America. For the most current data and information relating to hydrologic unit codes (HUCs) please see http://water.usgs.gov/GIS/huc.html. The Watershed Boundary Dataset (WBD) is the most current data available for watershed delineation. See http://www.nrcs.usda.gov/wps/portal/nrcs/main/national/water/watersheds/dataset

Report↗

USGS1999

1:2,000,000-scale Hydrologic Units of the United States

This data set has been superseded by huc2m. This file contains hydrologic unit boundaries and codes for the conterminous United States along with Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands. It was revised for inclusion in the National Atlas of the United States of America, and updated to match the streams file created by the USGS National Mapping Division (NMD) for the National Atlas of the United States of America. For the most current data and information relating to hydrologic unit codes (HUCs) please see http://water.usgs.gov/GIS/huc.html. The Watershed Boundary Dataset (WBD) is the most current data available for watershed delineation. See http://www.nrcs.usda.gov/wps/portal/nrcs/main/national/water/watersheds/dataset

Report↗

USGS1975

Summary of hydrologic data collected during 1974 in Dade County, Florida

This report is ninth in a series documenting the annual hydrologic conditions in Dade County, Florida. The hydrologic conditions in Dade County for the 1974 water year (October 1, 1973 to September 30, 1974) except for rainfall are summarized in tables, graphs, and maps. The locations of ground-water data-collection stations are shown in figure 1, rainfall and surface-water stations in figure 2, and water quality sampling stations in figure 43. As shown, the network of stations is extensive. The long-term records (1940 to 1974) furnish background information vital in the analysis of effects of water-management practices.

Florida↗

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↗

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↗