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At least 1,387 records · Page 77Linked to original sources
USGS2022

Selecting the optimal fine-scale historical climate data for assessing current and future hydrological conditions

High-resolution historical climate grids are readily available and frequently used as inputs for a wide range of regional management and risk assessments, including water supply, ecological processes, and as baseline for climate change impact studies that compare them to future projected conditions. Because historical gridded climates are produced using various methods, their portrayal of landscape conditions differ, which becomes a source of uncertainty when they are applied to subsequent analyses. Here we tested the range of values from five gridded climate datasets. We compared their values to observations from 1231 weather stations, first using each dataset’s native scale, and then after each was rescaled to 270-m resolution. We inputted the downscaled grids to a mechanistic hydrology model and assessed the spatial results of six hydrological variables across California, in 10 ecoregions and 11 large watersheds in the Sierra Nevada. PRISM was most accurate for precipitation, ClimateNA for maximum temperature, and TopoWx for minimum temperature. The single most accurate dataset overall was PRISM due to the best performance for precipitation and low air temperature errors. Hydrological differences ranged up to 70% of the average monthly streamflow with an average of 35% disagreement for all months derived from different historical climate maps. Large differences in minimum air temperature data produced differences in modeled actual evapotranspiration, snowpack, and streamflow. Areas with the highest variability in climate data, including the Sierra Nevada and Klamath Mountains ecoregions, also had the largest spread for snow water equivalent, recharge, and runoff.

Journal of Hydrometeorology↗
USGS2006

Hydrogeochemical investigations in the Osgood Mountains, north-central Nevada

Field investigations performed in the Osgood Mountains during the summers of 1999 and 2000 were designed to test methods of combining geologic, hydrologic, and geochemical investigations. The goals were to develop a more thorough understanding of the movement of water through the study area and to understand the water-rock reactions that may occur along flow paths. The Osgood Mountains were chosen for study because they represent a well-defined geologic system, based on existing and new field data. New work in the area focused on gathering more data about fractures, faults, and joints and on collecting water samples to evaluate the role of geologic structures on hydrologic and geochemical properties of the ground-water/surface-water system. Chemical methods employed in the study included measuring traditional field parameters (e.g., pH, temperature, conductivity, dissolved oxygen) as well as Fe2+ and collecting a variety of samples that were preserved for later laboratory analysis. Hydrologic methods included closely spaced evaluations of substream hydraulic head to define ground-water discharge and recharge zones as well as some measurements of stream discharge. Geologic investigations focused on the locations and orientations of fractures and kinematic indicators of slip observable in outcrops.

Nevada↗
USGS2024

An intercomparison of DOC estimated from fDOM sensors in wildfire affected streams of the western United States

Wildfires in the western United States (US) have been demonstrated to affect water quality, including dissolved organic carbon (DOC), in streams. Elevated post-wildfire DOC concentration poses a potential risk to drinking water treatment systems. In-stream measurements of fluorescent dissolved organic matter (fDOM), a proxy for DOC, have shown potential to detect dynamic changes in DOC. High frequency monitoring of water temperature, turbidity, and fDOM was used in conjunction with discrete sampling during targeted storm events and at fixed intervals to estimate DOC in five western US streams following wildfires in 2020 and 2021 with the objective to characterise and compare responses to wildfire among sites. The elevated turbidity conditions typical after wildfire presented a challenge to fDOM measurements and there was a need to identify appropriate turbidity corrections at burned sites. A combination of established and novel methods corrected fDOM concentrations for turbidity effects up to 800 Formazin nephelometric units (FNU). Pre-wildfire high frequency water quality data in adjacent burned and unburned watersheds allowed for separation of climate effects on DOC at one of the sites. Hydrology, climate and landcover were more important drivers of post-wildfire DOC yield than wildfire characteristics. Seasonal patterns of DOC were unchanged by wildfire in snowmelt-driven watersheds. Large, transient spikes in DOC concentration following frontal and convective storms were observed post-wildfire at all burned sites, but not at the unburned site. These spikes often exceeded operational thresholds for drinking water treatment. This study highlights the ability to develop high frequency DOC estimates in surface waters up to 800 FNU using fDOM sensors and targeted storm sampling and emphasises the value of high frequency pre-wildfire data in adjacent burned and unburned watersheds for separating climate and wildfire effects.

California, Colorado, Montana, Oregon↗
USGS2025

Beavers in the Tualatin River Basin, northwestern Oregon

Growing interest in beaver-assisted restoration in the Tualatin River Basin of northwestern Oregon motivated a series of studies by the U.S. Geological Survey to assess the capacity of the stream network to support beaver dams and to evaluate the effects of beaver dams and ponds on urban streams. This multichapter volume describes the data collection from 2016–17 and the findings of these studies, which were done in partnership with Clean Water Services. Chapter A documents the locations of beaver dams in the Tualatin River Basin and how many beaver dams the stream network could support with existing and improved riparian vegetation. Beaver dam capacity was estimated by modifying existing tools to account for the low gradient of many streams in the Tualatin River Basin. Chapter B describes the effects of beaver dams and ponds on hydrologic and hydraulic responses of storm flows. Hydrologic and hydraulic responses for two urban stream reaches were compared with and without beaver dams and ponds and for a range of streamflow conditions using two-dimensional hydraulic models. Chapter C characterizes the effects of beaver dams and ponds on the transport and deposition of suspended sediment. Continuous turbidity, discrete suspended-sediment samples, and streamflow measurements collected during storms and base-flow periods were used to assess: (1) suspended-sediment loads upstream and downstream from two beaver-affected reaches, and (2) seasonal and longitudinal turbidity patterns. Chapter D describes the effects of beaver dams and ponds on longitudinal, spatial, and seasonal water-quality patterns. Continuous and synoptic water-quality data were collected along urban stream reaches, and net ecosystem production was calculated for two beaver-affected reaches. The findings of these studies illustrate that the effects of beaver dams and ponds on hydrology, hydraulics, suspended-sediment transport and deposition, and water quality are dependent on the characteristics of a stream reach (for example, channel gradient, groundwater exchange, and riparian vegetation) and the characteristics of beaver dams and ponds along that reach. This information can be used to consider the implications of beaver-assisted restoration in the Tualatin River Basin and the effects of beaver dams and ponds in urban streams.

Oregon↗
USGS2015

Hydrologic influences on water-level changes in the Eastern Snake River Plain aquifer at and near the Idaho National Laboratory, Idaho, 1949-2014

The U.S. Geological Survey, in cooperation with the U.S. Department of Energy, has maintained a water-level monitoring program at the Idaho National Laboratory (INL) since 1949 to systematically measure water levels to provide long-term information on groundwater recharge, discharge, movement, and storage in the eastern Snake River Plain (ESRP) aquifer. During 2014, water levels in the ESRP aquifer reached all-time lows for the period of record, prompting this study to assess the effect that future water-level declines may have on pumps and wells. Water-level data were compared with pump-setting depth to determine the hydraulic head above the current pump setting. Additionally, geophysical logs were examined to address changes in well productivity with water-level declines. Furthermore, hydrologic factors that affect water levels in different areas of the INL were evaluated to help understand why water-level changes occur. Review of pump intake placement and 2014 water-level data indicates that 40 wells completed within the ESRP aquifer at the INL have 20 feet (ft) or less of head above the pump. Nine of the these wells are located in the northeastern and northwestern areas of the INL where recharge is predominantly affected by irrigation, wet and dry cycles of precipitation, and flow in the Big Lost River. Water levels in northeastern and northwestern wells generally show water-level fluctuations of as much as 4.5 ft seasonally and show declines as much as 25 ft during the past 14 years. In the southeastern area of the INL, seven wells were identified as having less than 20 ft of water remaining above the pump. Most of the wells in the southeast show less decline over the period of record compared with wells in the northeast; the smaller declines are probably attributable to less groundwater withdrawal from pumping of wells for irrigation. In addition, most of the southeastern wells show only about a 1–2 ft fluctuation seasonally because they are less influenced by groundwater withdrawals for irrigation. In the southwestern area of the INL, 24 wells were identified as having less than 20 ft of water remaining above the pump. Wells in the southwest also only show small 1–2 ft fluctuations seasonally because of a lack of irrigation influence. Wells show larger fluctuation in water levels closer to the Big Lost River and fluctuate in response to wet and dry cycles of recharge to the Big Lost River. Geophysical logs indicate that most of the wells evaluated will maintain their current production until the water level declines to the depth of the pump. A few of the wells may become less productive once the water level gets to within about 5 ft from the top of the pump. Wells most susceptible to future drought cycles are those in the northeastern and northwestern areas of the INL.

Idaho↗
USGS1976

Hydrologic data for urban studies in the San Antonio, Texas metropolitan area, 1976

Hydrologic investigations of urban watersheds in Texas were begun by the U.S. Geological Survey in 1954. These studies are now in progress in Austin, Dallas, Dallas County, Fort Worth, Houston, and San Antonio. The Geological Survey, in cooperation with the Texas Department of Water Resources, expanded the existing streamflow network in the San Antonio metropolitan area in May 1968 to begin urban hydrology studies in this area. In September 1968, the program was further expanded to include the collection of water-quality data.

Texas↗
USGS1995

Hydrology and simulation of ground-water flow in the Aguadilla to Rio Camuy area, Puerto Rico

The aquifers of the Aguadilla to Rio Camuy area, in the northwestern part of Puerto Rico, are the least developed of those on the north coast, and relatively little information is available concerning the ground-water system. The present study, which was part of a comprehensive appraisal of the ground-water resources of the North Coast Province, attempts to interpret the hydrology of the area within the constraints of available data. The study area consists of an uplifted rolling plain that is 200 to 400 feet above sea level and a heavily forested, karst upland. The only major streams in the area are the Rfo Camuy and the Rio Guajataca. Most water used in the area is obtained from Lago de Guajataca, just south of the study area, and ground-water use is minimal (less than 5 million gallons per day). Sedimentary rocks of Tertiary age, mainly limestone and calcareous clays, comprise the aquifers of the Aguadilla to Rio Camuy area. The rocks generally dip from 4 to 7 degrees to the north, and the total sedimentary rock sequence may be as much as 6,000 feet thick near the Atlantic coast. Baseflows for the Rio Camuy are 58 cubic feet per second near Bayaney and 72 cubic feet per second near Hatillo. The ground-water discharge to the Rio Camuy between these stations is estimated to be 15 cubic feet per second, or 2.6 cubic feet per second per linear mile. The flow of the Rio Guajataca is regulated by the Guajataca Dam at Lago de Guajataca. Ground-water discharge to the Rio Guajataca between the dam and the coast is estimated to be about 17 cubic feet per.second, based on the average ground-water discharge per linear mile estimated for the Rio Camuy. Both water-table and artesian aquifers are present in the Aguadilla to Rio Camuy area; how-ever, most ground water occurs within the watertable aquifer, which was the primary focus of this study. The top of the confining unit, below the water-table aquifer, generally is within the unnamed upper member of the Cibao Formation; however, it is within the Los Puertos Formation in the eastern part of the study area. The water-table aquifer primarily is composed of rocks of the Aymam6n Limestone and the Los Puertos Formation. The estimated saturated thickness of the water-table aquifer ranges from zero at the southern limit of the aquifer to more than 600 feet south of Isabela. Hydraulic conductivity of the Aymam6n Limestone, based on specific-capacity test data for seven wells, ranges from about 1 to about 25 feet per day and averages 7.5 feet per day. Hydraulic conductivity of the Los Puertos Formation, based on specific-capacity test data for four wells, generally was less than 7 feet. per day. The average hydraulic-conductivity value for both the Aymam6n Limestone and the Los Puertos Formation, based on specific-capacity test data, is estimated to be about 6.0 feet per day. These hydraulic-conductivity values are much less than average values for the water-table aquifer reported for other parts of the North Coast Province. Transmissivity values, based on the average hydraulic-conductivity value for the aquifer derived from specific-capacity tests, range from zero to about 4,000 feet squared per day; however, these values were adjusted upward during model calibration. Ground water generally moves from the highlands in the south toward the sea to the north and west, and locally, to streams. A major groundwater divide extends from the southeastern corner of the study area to the northwest, and separates flow north and east into the study area from flow to the southwest toward the Rio Culebrinas. Nearly all recharge to the aquifer is from infiltration of rainfall into the karst uplands. Discharge from the aquifer primarily occurs as leakage to streams and to the sea, and to a lesser degree as flow to wells. A two-layer, three-dimensional, steady-state, numerical model was constructed to simulateground-water flow in the water-table aquifer between Aguadilla and the R/o Camuy area. A basic a

Water-Resources Investigations Report↗
USGS1981

Hydrologic data for urban studies in the San Antonio, Texas, metropolitan area, 1978

Hydrologic investigations of urban drainage basins in Texas were begun by the U.S. Geological Survey in 1954. These studies are now in progress in Austin, Houston, and San Antonio. Studies were completed in the Fort Worth metropolitan area at the end of the 1977 water year, and in the Dallas metropolitan area at the end of the 1979 water year. The Geological Survey, in cooperation with the Texas Department of Water Resources, expanded the existing streamflow network in the San Antonio metropolitan area in May 1968 to begin urban hydrology studies in this area. In September 1968, the program was further expanded to include the collection of water-quality data.

Texas↗
USGS2013

Flood-inundation maps for the Flatrock River at Columbus, Indiana, 2012

Digital flood-inundation maps for a 5-mile reach of the Flatrock River on the western side of Columbus, Indiana, from County Road 400N to the river mouth at the confluence with Driftwood River, were created by the U.S. Geological Survey (USGS) in cooperation with the Indiana Department of Transportation. The inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science Web site at http://water.usgs.gov/osw/flood_inundation/ and the Federal Flood Inundation Mapper Web site at http://wim.usgs.gov/FIMI/FloodInundationMapper.html, depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage on the Flatrock River at Columbus (station number 03363900). Near-real-time stages at this streamgage may be obtained on the Internet from the USGS National Water Information System at http://waterdata.usgs.gov/ or the National Weather Service (NWS) Advanced Hydrologic Prediction Service, which also presents the USGS data, at http:/water.weather.gov/ahps/. Flood profiles were computed for the stream reach by means of a one-dimensional step-backwater model. The model was calibrated by using the most current stage-discharge relation at the Flatrock River streamgage, high-water marks that were surveyed following the flood of June 7, 2008, and water-surface profiles from the current flood-insurance study for the City of Columbus. The hydraulic model was then used to compute 12 water-surface profiles for flood stages at 1-foot (ft) intervals referenced to the streamgage datum and ranging from 9 ft or near bankfull to 20 ft, which exceeds the stages that correspond to both the estimated 0.2-percent annual exceedance probability flood (500-year recurrence interval flood) and the maximum recorded peak flow. The simulated water-surface profiles were then combined with a Geographic Information System digital elevation model (derived from Light Detection and Ranging (LiDAR) data having a 0.37 ft vertical accuracy and 3.9 ft horizontal resolution) to delineate the area flooded at each water level. The availability of these maps on the USGS Federal Flood Inundation Mapper Web site, along with Internet information regarding current stage from the USGS streamgage, will provide emergency management personnel and residents with information that is critical for flood response activities, such as evacuations and road closures, as well as for post-flood recovery efforts.

Indiana↗
USGS2001

Water Resources Data, Georgia, 2001, Volume 1: Continuous water-level, streamflow, water-quality data, and periodic water-quality data, Water Year 2001

Water resources data for the 2001 water year for Georgia consists of records of stage, discharge, and water quality of streams; and the stage and contents of lakes and reservoirs published in two volumes in a digital format on a CD-ROM. Volume one of this report contains water resources data for Georgia collected during water year 2001, including: discharge records of 133 gaging stations; stage for 144 gaging stations; precipitation for 58 gaging stations; information for 19 lakes and reservoirs; continuous water-quality records for 17 stations; the annual peak stage and annual peak discharge for 76 crest-stage partial-record stations; and miscellaneous streamflow measurements at 27 stations, and miscellaneous water-quality data recorded by the NAWQA program in Georgia. Volume two of this report contains water resources data for Georgia collected during calendar year 2001, including continuous water-level records of 159 ground-water wells and periodic records at 138 water-quality stations. These data represent that part of the National Water Data System collected by the U.S. Geological Survey and cooperating State and Federal agencies in Georgia. Note: Historically, this report was published as a paper report. For the 1999 and subsequent water-year reports, the Water Resources Data for Georgia changed to a new, more informative and functional format on CD-ROM. The format is based on a geographic information system (GIS) user interface that allows the user to view map locations of the hydrologic monitoring stations and networks within respective river basins.

Georgia↗
USGS2003

Application of artificial neural networks to complex groundwater management problems

As water quantity and quality problems become increasingly severe, accurate prediction and effective management of scarcer water resources will become critical. In this paper, the successful application of artificial neural network (ANN) technology is described for three types of groundwater prediction and management problems. In the first example, an ANN was trained with simulation data from a physically based numerical model to predict head (groundwater elevation) at locations of interest under variable pumping and climate conditions. The ANN achieved a high degree of predictive accuracy, and its derived state-transition equations were embedded into a multiobjective optimization formulation and solved to generate a trade-off curve depicting water supply in relation to contamination risk. In the second and third examples, ANNs were developed with real-world hydrologic and climate data for different hydrogeologic environments. For the second problem, an ANN was developed using data collected for a 5-year, 8-month period to predict heads in a multilayered surficial and limestone aquifer system under variable pumping, state, and climate conditions. Using weekly stress periods, the ANN substantially outperformed a well-calibrated numerical flow model for the 71-day validation period, and provided insights into the effects of climate and pumping on water levels. For the third problem, an ANN was developed with data collected automatically over a 6-week period to predict hourly heads in 11 high-capacity public supply wells tapping a semiconfined bedrock aquifer and subject to large well-interference effects. Using hourly stress periods, the ANN accurately predicted heads for 24-hour periods in all public supply wells. These test cases demonstrate that the ANN technology can solve a variety of complex groundwater management problems and overcome many of the problems and limitations associated with traditional physically based flow models.

Natural Resources Research↗
USGS2001

Selected hydrologic data for Little Cottonwood Creek, Salt Lake County, Utah, September 1998

Metals enter Little Cottonwood Creek in Salt Lake County, Utah, in drainage water that discharges from inactive mines in the watershed (fig. 1). As part of a study to evaluate the effects of this mine drainage on water quality, a sodium chloride tracer was injected into Little Cottonwood Creek during September 17-18, 1998. The purpose of the injection was to quantify stream discharge; to identify inflows, both those observable and those dispersed in the subsurface; and ultimately, to determine which areas within the watershed contribute the most metals to Little Cottonwood Creek. The purpose of this report is to make these data available to agencies responsible for managing the area’ s water resources and to supplement interpretive reports for this study.

Utah↗
USGS2011

Hydrogeomorphic processes of thermokarst lakes with grounded-ice and floating-ice regimes on the Arctic coastal plain, Alaska

Thermokarst lakes cover > 20% of the landscape throughout much of the Alaskan Arctic Coastal Plain (ACP) with shallow lakes freezing solid (grounded ice) and deeper lakes maintaining perennial liquid water (floating ice). Thus, lake depth relative to maximum ice thickness (1·5–2·0 m) represents an important threshold that impacts permafrost, aquatic habitat, and potentially geomorphic and hydrologic behaviour. We studied coupled hydrogeomorphic processes of 13 lakes representing a depth gradient across this threshold of maximum ice thickness by analysing remotely sensed, water quality, and climatic data over a 35-year period. Shoreline erosion rates due to permafrost degradation ranged from < 0·2 m/year in very shallow lakes (0·4 m) up to 1·8 m/year in the deepest lakes (2·6 m). This pattern of thermokarst expansion masked detection of lake hydrologic change using remotely sensed imagery except for the shallowest lakes with stable shorelines. Changes in the surface area of these shallow lakes tracked interannual variation in precipitation minus evaporation (P − E L ) with periods of full and nearly dry basins. Shorter-term (2004–2008) specific conductance data indicated a drying pattern across lakes of all depths consistent with the long-term record for only shallow lakes. Our analysis suggests that grounded-ice lakes are ice-free on average 37 days longer than floating-ice lakes resulting in a longer period of evaporative loss and more frequent negative P − E L . These results suggest divergent hydrogeomorphic responses to a changing Arctic climate depending on the threshold created by water depth relative to maximum ice thickness in ACP lakes.

Alaska↗
USGS2018

Episodic master recession evaluation of groundwater and streamflow hydrographs for water-resource estimation

Hydrograph analysis tools using a master recession curve (MRC) can produce many types of hydrologically important watershed-response quantifications, including aquifer recharge and stormflow characterization. An MRC is the relation between the value of a measured response R and its rate of change with time, d R /d t , occurring on the falling limb when there is no infiltration or other water input. We have developed MRC and episodic hydrograph-evaluation methods for multiple purposes, utilizing both water table and streamflow data. The determination of a parameterized MRC through a structured procedure provides a basis for quantification of hydrologic variables and characteristics that can be validly compared among different events, sites, and periods of time. Application of the MRC to needed hydrologic quantifications is done with our revised episodic master recession (EMR) method. Expert-guided iterative procedures are used to quantify parameters needed in applying the MRC and EMR methods to a given site. Hydrologic judgments such as the significance threshold for response magnitude, and the time window within which the precipitation is assumed to be the cause of an observed response, inherently involve some elements of subjectivity. Our structured iterative approach, however, affords much flexibility in formulating expert judgments and serves to confine them to statements and procedures that can be quantified and documented. Parallel application to streamflow and water table hydrographs can produce new hydrologic insights and understanding, not least in the role of unsaturated zone processes in controlling exchanges among components of the water cycle.

Vadose Zone Journal↗
USGS1995

Water-related scientific activities of the U.S. Geological Survey in Nevada, fiscal years 1993-94

The U.S. Geological Survey has been collecting water-resources data in Nevada since 1890. Most of the projects that constitute the current Nevada District program can be classified as either basic- data acquisition (about 25 percent) or hydrologic interpretation (about 75 percent). About 39 percent of the activities are supported by cooperative agreements with State and local agencies. Technical projects supported by other Federal agencies make up about 32 percent of the program, and the re- maining 29 percent consists of USGS data collection, interpretive projects, and research. Water con- ditions in most of Nevada during fiscal years 1993 and 1994 continued to be dry, a continuation of drought conditions since late 1986. The major water-resource issues in Nevada include: water allocation in the Truckee River and Carson River Basins; water-supply needs of Las Vegas and the Reno/Sparks area, including water-importation plans; hydrologic effects of weapons testing at the Nevada Test Site; assessment of potential long-term effects of the proposed Yucca Mountain Nuclear Waste Repository; and drought. Future water-resources issues in Nevada are likely to center on water supply for, and environmental effects of, the rapidly growing population centers at Las Vegas, Reno, and Elko; impacts of operations at the Nevada Test Site; management of interstate rivers such as the Truckee, Carson, Walker, and Colorado Rivers; hydrologic and environmental impacts at heavily mined areas; and water-quality management in the Lake Tahoe Basin.

Open-File Report↗
USGS1997

Hydrologic investigations in the Mammoth Corridor, Yellowstone National Park and vicinity, U.S.A.

The Mammoth Corridor in and adjacent to Yellowstone National Park encompasses a N-S alignment of geothermal features that extends from the Norris Geyser Basin adjacent to the Yellowstone caldera through Mammoth Hot Springs to the Corwin Springs Known Geothermal Resources Area (KGRA). Thermal springs in this region discharge water that ranges from NaKCl, silica-depositing type to CaNaHC0 3 SO 4 , travertine-depositing type. Although only a few relatively shallow wells have been drilled in the corridor, the region is of special interest because of the environmental issues associated with potential geothermal development adjacent to Yellowstone National Park. The U.S. Geological Survey conducted an intensive hydrogeologic study of this region during 1988–1990 and continued to collect hydrologic and geophysical data until 1994. The results of these investigations document the rates of discharge of thermal water and heat within the corridor, evidence for a magmatic heat source beneath the Mammoth Hot Springs area, and evidence for separate geothermal systems associated with Mammoth Hot Springs and with thermal waters discharging in the KGRA in the vicinity of La Duke Hot Springs. These investigations also indicate that limited development of the 70°C geothermal resource in the La Duke area would not affect thermal springs in Yellowstone National Park.

Geothermics↗
USGS2009

Groundwater availability of the Central Valley Aquifer, California

California's Central Valley covers about 20,000 square miles and is one of the most productive agricultural regions in the world. More than 250 different crops are grown in the Central Valley with an estimated value of $17 billion per year. This irrigated agriculture relies heavily on surface-water diversions and groundwater pumpage. Approximately one-sixth of the Nation's irrigated land is in the Central Valley, and about one-fifth of the Nation's groundwater demand is supplied from its aquifers. The Central Valley also is rapidly becoming an important area for California's expanding urban population. Since 1980, the population of the Central Valley has nearly doubled from 2 million to 3.8 million people. The Census Bureau projects that the Central Valley's population will increase to 6 million people by 2020. This surge in population has increased the competition for water resources within the Central Valley and statewide, which likely will be exacerbated by anticipated reductions in deliveries of Colorado River water to southern California. In response to this competition for water, a number of water-related issues have gained prominence: conservation of agricultural land, conjunctive use, artificial recharge, hydrologic implications of land-use change, and effects of climate variability. To provide information to stakeholders addressing these issues, the USGS Groundwater Resources Program made a detailed assessment of groundwater availability of the Central Valley aquifer system, that includes: (1) the present status of groundwater resources; (2) how these resources have changed over time; and (3) tools to assess system responses to stresses from future human uses and climate variability and change. This effort builds on previous investigations, such as the USGS Central Valley Regional Aquifer System and Analysis (CV-RASA) project and several other groundwater studies in the Valley completed by Federal, State and local agencies at differing scales. The principal product of this new assessment is a tool referred to as the Central Valley Hydrologic Model (CVHM) that accounts for integrated, variable water supply and demand, and simulates surface-water and groundwater-flow across the entire Central Valley system. The development of the CVHM comprised four major elements: (1) a comprehensive Geographic Information System (GIS) to compile, analyze and visualize data; (2) a texture model to characterize the aquifer system;(3) estimates of water-budget components by numerically modeling the hydrologic system with the Farm Process (FMP); and (4) simulations to assess and quantify hydrologic conditions.

Professional Paper↗
USGS2007

Marl prairie vegetation response to 20th century hydrologic change

We conducted geochronologic and pollen analyses from sediment cores collected in solution holes within marl prairies of Big Cypress National Preserve to reconstruct vegetation patterns of the last few centuries and evaluate the stability and longevity of marl prairies within the greater Everglades ecosystem. Based on radiocarbon dating and pollen biostratigraphy, these cores contain sediments deposited during the last ~300 years and provide evidence for plant community composition before and after 20th century water management practices altered flow patterns throughout the Everglades. Pollen evidence indicates that pre-20th century vegetation at the sites consisted of sawgrass marshes in a peat-accumulating environment; these assemblages indicate moderate hydroperiods and water depths, comparable to those in modern sawgrass marshes of Everglades National Park. During the 20th century, vegetation changed to grass-dominated marl prairies, and calcitic sediments were deposited, indicating shortening of hydroperiods and occurrence of extended dry periods at the site. These data suggest that the presence of marl prairies at these sites is a 20th century phenomenon, resulting from hydrologic changes associated with water management practices.

Florida↗