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Results for “Groundwater for Sustainable Development”

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At least 37 records · Page 2Linked to original sources
USGS2010

Groundwater resources of Mosteiros basin, island of Fogo, Cape Verde, West Africa

Groundwater resources in Cape Verde provide water for agriculture, industry, and human consumption. These resources are limited and susceptible to contamination. Additional groundwater resources are needed for continued agricultural development, particularly during times of drought, but increased use and (or) climatic change may have adverse effects on the quantity and quality of freshwater available. In volcanic island aquifers such as those of Cape Verde, a lens of fresh groundwater typically ?floats? upon a layer of brackish water at the freshwater/saltwater boundary, and increased pumping may cause salt water intrusion or other contamination. A recent U.S. Geological Survey study assessed baseline groundwater conditions in watersheds on three islands of Cape Verde to provide the scientific basis for sustainably developing water resources and minimizing future groundwater depletion and contamination.

Island of Fogo, Mosteiros Basin↗
USGS2010

Groundwater resources of Ribeira Paúl basin, island of Santo Antão, Cape Verde, West Africa

Groundwater resources in Cape Verde provide water for agriculture, industry, and human consumption. These resources are limited and susceptible to contamination. Additional groundwater resources are needed for continued agricultural development, particularly during times of drought, but increased use and (or) climatic change may have adverse effects on the quantity and quality of freshwater available. In volcanic island aquifers such as those of Cape Verde, a lens of fresh groundwater typically ?floats? upon a layer of brackish water at the freshwater/saltwater boundary, and increased pumping may cause salt water intrusion or other contamination. A recent U.S. Geological Survey study assessed baseline groundwater conditions in watersheds on three islands of Cape Verde to provide the scientific basis for sustainably developing water resources and minimizing future groundwater depletion and contamination.

Island of Santo Antão, Ribeira Paúl Basin↗
USGS2010

Groundwater resources of Ribeira Fajã basin, island of São Nicolau, Cape Verde, West Africa

Groundwater resources in Cape Verde provide water for agriculture, industry, and human consumption. These resources are limited and susceptible to contamination. Additional groundwater resources are needed for continued agricultural development, particularly during times of drought, but increased use and (or) climatic change may have adverse effects on the quantity and quality of freshwater available. In volcanic island aquifers such as those of Cape Verde, a lens of fresh groundwater typically ?floats? upon a layer of brackish water at the freshwater/saltwater boundary, and increased pumping may cause salt water intrusion or other contamination. A recent U.S. Geological Survey study assessed baseline groundwater conditions in watersheds on three islands of Cape Verde to provide the scientific basis for sustainably developing water resources and minimizing future groundwater depletion and contamination.

Island of São Nicolau, Ribeira Fajã Basin↗
USGS2026

Computation of regional groundwater budgets for the Virginia Coastal Plain aquifer system

Computation of detailed groundwater flow budgets for subdivisions of Virginia’s Coastal Plain aquifer system has enabled quantification and more thorough understanding of groundwater flow within this important water resource. A zone budget analysis conducted on previously published groundwater models of the Virginia Coastal Plain and Virginia Eastern Shore shows that groundwater conditions vary substantially throughout the Coastal Plain aquifer system due to local variations in hydrogeology and historical and ongoing variations in groundwater use and management. Decades of substantial groundwater withdrawal from the Coastal Plain aquifer system have fundamentally altered groundwater flow from pre-development conditions. Rates of sustainable withdrawal are limited because the downward groundwater flow rate into confined aquifers supplying groundwater is a relatively small portion of the total groundwater water budget for the aquifer system. Analyses of groundwater budgets from the Virginia Coastal Plain model show that groundwater flow is generally outward from the surficial aquifer to rivers and coastal water bodies and downward through a series of underlying aquifers and confining units to the Potomac aquifer, which is the deepest aquifer and the source of most groundwater withdrawals. Downward flow into the Potomac aquifer currently is estimated to be only 7 percent of total net precipitation-derived net recharge at the land surface but makes up about 66 percent of inflow to the aquifer in Virginia, with much of the remaining inflow occurring laterally from areas outside of defined groundwater budget regions in Virginia. For several decades prior to 2010, high rates of withdrawal from the Potomac aquifer resulted in substantial decline in groundwater storage in the aquifer and in most overlying aquifers and confining units. From 2010 to 2025, rates of withdrawal substantially lower than the historical maximum have resulted in small net increases in groundwater storage in the confined aquifer system for most regions of the Virginia Coastal Plain. Nevertheless, for the same period, groundwater storage for the entire model domain continues to incrementally decline, indicating that storage recovery in Virginia is offset by a continued decrease in storage in areas beneath the Chesapeake Bay or in adjacent areas of Maryland and North Carolina. Withdrawals from the Potomac aquifer have induced substantial downward flow which is a large part of groundwater budgets for confined aquifers such as the Potomac. Downward groundwater flow continues under current conditions, but because vertical flow rates are a function of the difference between water pressure in the upper surficial systems and lower confined units, those rates are lower than those in earlier decades as the confined water levels partially recover from larger groundwater withdrawals in the past. Geographically, groundwater flow is generally inward from perimeter regions of the Virginia Coastal Plain toward central regions with the largest withdrawal rates. Estimated groundwater inflow from coastal regions could be contributing to saltwater intrusion, though that was not measured directly in this study. Analyses of groundwater budgets from the Virginia Eastern Shore peninsula, a geographic region of the Virginia Coastal Plain, show that groundwater flow for that isolated aquifer system is generally outward from the surficial aquifer to coastal water bodies and downward into the confined Yorktown-Eastover aquifer system, which is the source of most withdrawals. Downward groundwater flow into the confined Yorktown-Eastover aquifer system is estimated to be less than 2 percent of total recharge and less than 9 percent of net recharge at the water table but makes up over 93 percent of all inflow to the confined aquifer system. Decades of substantial but relatively consistent groundwater withdrawals have induced greater downward flow rates into the confined aquifer system but also have resulted in loss of groundwater from storage. Currently, estimated storage loss accounts for slightly under 7 percent of withdrawals from the confined aquifer system. The current withdrawal rate from the confined Yorktown-Eastover system is near the highest reported rate for the Eastern Shore, which means that the storage depletion is expected to continue, even though groundwater levels appear to be relatively stable. Estimated groundwater flow rates upward from the confining unit underlying the Yorktown-Eastover system and small rates of inflow from coastal water bodies underscore ongoing concerns about up-coning and lateral intrusion of salty groundwater.

EarthArXiv↗
USGS2024

Groundwater sustainability and land subsidence in California’s Central Valley

The Central Valley of California is one of the most prolific agricultural regions in the world. Agriculture is reliant on the conjunctive use of surface-water and groundwater. The lack of available surface-water and land-use changes have led to pumping-induced groundwater-level and storage declines, land subsidence, changes to streamflow and the environment, and the degradation of water quality. As a result, in part, the Sustainable Groundwater Management Act (SGMA) was developed. An examination of the components of SGMA and contextualizing regional model applications within the SGMA framework was undertaken to better understand and quantify many of the components of SGMA. Specifically, the U.S. Geological Survey (USGS) updated the Central Valley Hydrologic Model (CVHM) to assess hydrologic system responses to climatic variation, surface-water availability, land-use changes, and groundwater pumping. MODFLOW-OWHM has been enhanced to simulate the timing of land subsidence and attribute its inelastic and elastic portions. In addition to extending CVHM through 2019, the new version, CVHM2, includes several enhancements as follows: managed aquifer recharge (MAR), pumping with multi-aquifer wells, inflows from ungauged watersheds, and more detailed water-balance subregions, streamflow network, diversions, tile drains, land use, aquifer properties, and groundwater level and land subsidence observations. Combined with historical approximations, CVHM2 estimates approximately 158 km 3 of storage loss in the Central Valley from pre-development to 2019. About 15% of the total storage loss is permanent loss of storage from subsidence that has caused damage to infrastructure. Climate extremes will likely complicate the efforts of water managers to store more water in the ground. CVHM2 can provide data in the form of aggregated input datasets, simulate climatic variations and changes, land-use changes or water management scenarios, and resulting changes in groundwater levels, storage, and land subsidence to assist decision-makers in the conjunctive management of water supplies.

California↗
USGS2010

Groundwater sustainability strategies

Groundwater extraction has facilitated significant social development and economic growth, enhanced food security and alleviated drought in many farming regions. But groundwater development has also depressed water tables, degraded ecosystems and led to the deterioration of groundwater quality, as well as to conflict among water users. The effects are not evenly spread. In some areas of India, for example, groundwater depletion has preferentially affected the poor. Importantly, groundwater in some aquifers is renewed slowly, over decades to millennia, and coupled climate–aquifer models predict that the flux and/or timing of recharge to many aquifers will change under future climate scenarios. Here we argue that communities need to set multigenerational goals if groundwater is to be managed sustainably.

Nature Geoscience↗
USGS2019

Groundwater movement and interaction with surface water near the confluence of the Platte and Elkhorn rivers, Nebraska, 2016–18

The State of Nebraska requires a sustainable balance between long-term water supplies and uses of groundwater and surface water and requires Natural Resources Districts to include the effect of groundwater use on surface-water systems as part of their respective integrated management plans. Recent droughts in Nebraska (2000–6; 2012–13) have amplified concerns about the long-term sustainability of groundwater and surface-water resources in the state, and concerns about the effect of groundwater irrigation on both streamflow and the water supplies needed to meet wildlife, recreational, and municipal needs. The lower Platte River provides nearly 100 percent of drinking-water supplies to Lincoln, Nebraska, 40 to 60 percent of drinking-water supplies to Omaha, Nebr., and critical aquatic and riparian habitat for threatened and endangered species. The Lower Platte River Basin-wide Management Plan has been jointly developed by the Nebraska Department of Natural Resources and seven Natural Resources Districts to address some of these concerns by managing groundwater and surface-water resources conjunctively. To sustain flows in the lower Platte River that are needed for municipal water supplies, water managers have proposed projects aimed at temporary storage of surface water in upstream parts of the basin to mitigate periods of low flow in the lower Platte River. To increase scientific understanding and provide support for any potential future streamflow augmentation projects, the Papio-Missouri River Natural Resources District, the Lower Platte North Natural Resources District, and the Nebraska Department of Natural Resources, in cooperation with the U.S. Geological Survey, initiated this study to examine groundwater/surface-water interaction along the lower Platte and Elkhorn Rivers upstream from their confluence. The study design described herein focused on understanding seasonal characteristics of groundwater movement and interaction with surface water during periods of high groundwater demand (June through August) and low groundwater demand (all other months). Understanding how groundwater movement and interaction with surface water are affected by streamflow conditions and local groundwater demand is critical to the development of any streamflow augmentation project intended to sustain streamflow and mitigate periods of low flow in the lower Platte River. The characteristics of groundwater movement and interaction with surface water are affected by hydrologic and local climatic conditions. For the study area, 2016–18 conditions can be broadly characterized as above normal precipitation. The flows measured at the Elkhorn River at Waterloo, Nebr., streamflow-gaging station (U.S. Geological Survey station 06800500) were above the long-term median, and the streamflow of the Platte River near Leshara, Nebr., streamflow-gaging station (06796500) remained normal or slightly above normal for the duration of this study. Continuous streamflow and water-level data were interpreted to examine differences in groundwater movement and interaction with surface water between the Platte and Elkhorn Rivers during high and low groundwater demand periods. Although the streamflow for the Platte and Elkhorn Rivers and their tributaries was less during the high groundwater demand period, the hydraulic gradient along a transect of recorder wells was identical (0.0012 foot per foot) during the high and low groundwater demand synoptic water-level and streamflow surveys. The hydraulic gradient between the Platte and Elkhorn Rivers generally remained between 0.0011 and 0.0012 foot per foot. It can be inferred that the hydraulic gradient, which is the only temporally variable factor in Darcy’s Law, is consistent throughout the study period and that groundwater flow does not vary appreciably along this transect. The northern part of the study area (north of the transect of recorder wells) has consistent groundwater and tributary flow from Big Slough, Rawhide Creek (Old Channel), and Rawhide Creek for low and high groundwater demand periods. In the southern part of the study area (south of the transect of recorder wells), tributary flow is more variable and dependent on local groundwater demand and flow conditions of the Platte River. Small decreases (less than 2 feet) in the groundwater levels, such as those measured during the high groundwater demand period, can have substantial changes in the streamflow in an unnamed tributary to the Elkhorn River. The streamflow measured during the high groundwater demand synoptic water-level and streamflow survey had decreased by nearly a factor of 20 when compared to the low groundwater demand period. The volume of groundwater discharge received by the Elkhorn River was estimated by examining the changes in streamflow between measurement locations. Streamflow measurements indicate that the groundwater discharge received by the Elkhorn River in the southern part of the study area was seasonably variable, making it difficult if not impossible to estimate an annual value. In the Elkhorn River, between the Elkhorn River at Waterloo, Nebr., streamflow-gaging station and the Q Street Bridge, streamflow measurements collected during the low groundwater demand period indicated a gain of 80 cubic feet per second, which is comparable to the gain estimated using aerial thermal infrared imagery and water temperature data. Streamflow measurements collected during the high groundwater demand period indicate a loss of 80 cubic feet per second across this same reach. In assessing water supply conditions in the lower Platte River system, the term “loss” in reference to streamflow in the Elkhorn River should be used with caution. Most likely, flow from the Elkhorn River which is “lost” to the groundwater system will later discharge to surface water closer to the confluence of the Platte and Elkhorn Rivers as underflow. A calibrated groundwater flow model of the study area likely is required to predict the fate of this water and to quantify groundwater discharge during varying hydrologic conditions along this reach. Aerial thermal infrared imagery indicated that much of the groundwater discharge in the southern part of the study area is focused across a 3-mile reach where the Elkhorn River turns southwest, perpendicular to the regional groundwater flow direction. Points of focused groundwater discharge were not detected with aerial thermal infrared imagery, indicating that groundwater discharge is diffuse rather than concentrated at focused points. Temperature-based streambed flux estimates indicated that strong regional groundwater gradients are not driving groundwater discharge and hyporheic flow is the dominant groundwater/surface-water exchange process.

Nebraska↗
USGS2018

Methods used to estimate daily streamflow and water availability in the Massachusetts Sustainable-Yield Estimator version 2.0

The Massachusetts Sustainable-Yield Estimator is a decision support tool that provides estimates of daily unaltered streamflow, water-use-adjusted streamflow, and water availability for ungaged, user-defined basins in Massachusetts. Daily streamflow at the ungaged site is estimated for unaltered (no water use) and water-use scenarios. The procedure for estimating streamflow was developed previously and has been implemented with minor changes and updated water-use data in version 2.0 of the Massachusetts Sustainable-Yield Estimator. Unaltered streamflow at selected exceedance probabilities is estimated by previously published regression equations. Streamflow is interpolated between the regressed quantiles to produce a continuous flow duration curve. A daily streamflow time series is produced for the ungaged site by relating the estimated flow duration curve at the ungaged site to a flow duration curve at a gaged reference site and then transferring the dates from the reference site to the ungaged site. Minor refinements were made to the previously published methods to estimate unaltered and water-use-adjusted streamflow, including a procedure to enforce the monotonic structure of the regression-based unaltered flow quantiles, improvements to the interpolation method used for computing the estimated flow duration curve, and updates to the methods used to compute time-lagged stream alterations from groundwater pumping or discharges. Additionally, a procedure was developed to estimate prediction intervals for daily and monthly unregulated streamflow time series at an ungaged site. The Massachusetts Sustainable-Yield Estimator computes water-use-adjusted streamflow using water-use data provided by the Massachusetts Department of Environmental Protection. Available water-use data included monthly withdrawal and wastewater discharge volumes from 2010 to 2014 for surface-water and groundwater sources. Water-use-adjusted streamflow represents the potential effect of current water use on natural streamflow in the basin over the range of historical hydrologic conditions. Georeferenced water withdrawal and discharge volumes were incorporated into the Massachusetts StreamStats web application for use in version 2.0 of the Massachusetts Sustainable-Yield Estimator. To compute water-use-adjusted streamflow, mean daily withdrawals and discharges within a user-defined basin are subtracted and added to the unaltered time series, respectively. Surface-water volumes are applied directly to the equation. Time-lagged streamflow alterations from groundwater withdrawal or wastewater discharge sources are estimated by using a response-coefficient method developed from results of previously published, calibrated groundwater models in Massachusetts. The Massachusetts Sustainable-Yield Estimator was updated to version 2.0 to improve software stability and usability. The version 2.0 software application was developed in Microsoft Access with a graphical user interface. All geoprocessing steps, including basin delineation and compilation of basin characteristics and water use within the basin, were completed in the Massachusetts StreamStats web application and exported for use by the Massachusetts Sustainable-Yield Estimator version 2.0.

Massachusetts↗
USGS2016

Construction of a groundwater-flow model for the Big Sioux Aquifer using airborne electromagnetic methods, Sioux Falls, South Dakota

The city of Sioux Falls is the fastest growing community in South Dakota. In response to this continued growth and planning for future development, Sioux Falls requires a sustainable supply of municipal water. Planning and managing sustainable groundwater supplies requires a thorough understanding of local groundwater resources. The Big Sioux aquifer consists of glacial outwash sands and gravels and is hydraulically connected to the Big Sioux River, which provided about 90 percent of the city’s source-water production in 2015. Managing sustainable groundwater supplies also requires an understanding of groundwater availability. An effective mechanism to inform water management decisions is the development and utilization of a groundwater-flow model. A groundwater-flow model provides a quantitative framework for synthesizing field information and conceptualizing hydrogeologic processes. These groundwater-flow models can support decision making processes by mapping and characterizing the aquifer. Accordingly, the city of Sioux Falls partnered with the U.S. Geological Survey to construct a groundwater-flow model. Model inputs will include data from advanced geophysical techniques, specifically airborne electromagnetic methods.

South Dakota↗
USGS2016

Sustainability of groundwater supplies in the Northern Atlantic Coastal Plain aquifer system

Groundwater is the Nation’s principal reserve of freshwater. It provides about half our drinking water, is essential to food production, and facilitates business and industry in developing economic well-being. Groundwater is also an important source of water for sustaining the ecosystem health of rivers, wetlands, and estuaries throughout the country. The decreases in groundwater levels and other effects of pumping that result from large-scale development of groundwater resources have led to concerns about the future availability of groundwater to meet all our Nation’s needs. Assessments of groundwater availability provide the science and information needed by the public and decision makers to manage water resources and use them responsibly. The U.S. Geological Survey (USGS) is conducting large-scale multidisciplinary regional studies of groundwater availability as part of its ongoing assessments of the principal aquifers of the Nation. These regional studies are intended to provide citizens, communities, and natural resource managers with knowledge of the status of the Nation’s groundwater resources and how changes in land use, water use, and climate have affected and are likely to affect those resources now and in the future.

Fact Sheet↗
USGS2012

Examining the contradiction in 'sustainable urban growth': an example of groundwater sustainability

The environmental planning literature proposes a set of 'best management practices' for urban development that assumes improvement in environmental quality as a result of specific urban patterns. These best management practices, however, often do not recognise finite biophysical limits and social impacts that urban patterns alone cannot overcome. To shed light on this debate, we explore the effects of different degrees of urban clustering on groundwater levels using a coupled land-use change and groundwater-flow model. Our simulations show that specific urban forms only slow down the impact on groundwater. As population increases, the pattern in which it is accommodated ceases to matter, and widespread depletion ensues. These results are predictable, yet current planning practice tends to take growth for granted and is reluctant to envision either no-growth scenarios or the prospect of depletion. We propose to use simulations such as those presented here to aid in policy discussions that allow decision makers to question the assumption of sustainable growth and suggest alternative forms of development.

Journal of Environmental Planning and Management↗
USGS2013

Recharge sources and residence times of groundwater as determined by geochemical tracers in the Mayfield Area, southwestern Idaho, 2011–12

Parties proposing residential development in the area of Mayfield, Idaho are seeking a sustainable groundwater supply. During 2011–12, the U.S. Geological Survey, in cooperation with the Idaho Department of Water Resources, used geochemical tracers in the Mayfield area to evaluate sources of aquifer recharge and differences in groundwater residence time. Fourteen groundwater wells and one surface-water site were sampled for major ion chemistry, metals, stable isotopes, and age tracers; data collected from this study were used to evaluate the sources of groundwater recharge and groundwater residence times in the area. Major ion chemistry varied along a flow path between deeper wells, suggesting an upgradient source of dilute water, and a downgradient source of more concentrated water with the geochemical signature of the Idaho Batholith. Samples from shallow wells had elevated nutrient concentrations, a more positive oxygen-18 signature, and younger carbon-14 dates than deep wells, suggesting that recharge comes from young precipitation and surface-water infiltration. Samples from deep wells generally had higher concentrations of metals typical of geothermal waters, a more negative oxygen-18 signature, and older carbon-14 values than samples from shallow wells, suggesting that recharge comes from both infiltration of meteoric water and another source. The chemistry of groundwater sampled from deep wells is somewhat similar to the chemistry in geothermal waters, suggesting that geothermal water may be a source of recharge to this aquifer. Results of NETPATH mixing models suggest that geothermal water composes 1–23 percent of water in deep wells. Chlorofluorocarbons were detected in every sample, which indicates that all groundwater samples contain at least a component of young recharge, and that groundwater is derived from multiple recharge sources. Conclusions from this study can be used to further refine conceptual hydrological models of the area.

Idaho↗
USGS1993

Hydrogeology, water quality, and ground-water-development alternatives in the upper Wood River ground-water reservoir, Rhode Island

The 72.4-square-mile Upper Wood River study area is in the Pawcatuck River basin in southern Rhode Island. Stratified drift is the only principal geologic unit capable of producing yields greater than 0.5 Mgal/d. Transmissivity of the aquifer ranges from 7,600 to 49,200 sq ft/d. Water-table conditions prevail and the aquifer is in good hydraulic connection with perennial streams and ponds. Groundwater and surface water in the study area are generally suitable for most uses. Water is soft, slightly acidic, and contains less than 150 mg/L dissolved solids. Locally, however, groundwater has been contaminated with nitrate, chloride, and volatile organic compounds. A model of the groundwater-flow system was used to evaluate the effect of alternative schemes of groundwater development on water levels, pond levels, and streamflow. Till contacts were simulated as specified-flux boundaries, drainage divides as no-flow boundaries, and streams as leaky boundaries. The areas most favorable for development of 1 Mgal/d are along the Flat and Wood Rivers. From 50 to 65 percent of the water withdrawn from wells would be derived from induced recharge. Results of simulation of development alternatives indicate that the groundwater reservoir could sustain withdrawals of 6 to 12 Mgal/d from 11 wells under long-term average annual (1942-89) and simulated drought (1963-66) conditions without causing water-level declines of greater than 25 percent of the unstressed saturated thickness of the aquifer. Pumping 12 Mgal/d, however, would reduce flow of the Wood River at the basin outlet by an amount almost equal to the 7-day, 10-yr low flow of 20.4 cu ft/s.

Water-Resources Investigations Report↗
USGS2013

Enhancements to the Mississippi Embayment Regional Aquifer Study (MERAS) groundwater-flow model and simulations of sustainable water-level scenarios

Arkansas continues to be one of the largest users of groundwater in the Nation. As such, long-term planning and management are essential to ensure continued availability of groundwater and surface water for years to come. The Mississippi Embayment Regional Aquifer Study (MERAS) model was developed previously as a tool to evaluate groundwater availability within the Mississippi embayment, which encompasses much of eastern Arkansas where the majority of groundwater is used. The Arkansas Water Plan is being updated for the first time since 1990 and serves as the State’s primary, comprehensive water-resources planning and guidance document. The MERAS model was selected as the best available tool for evaluation of specific water-use pumping scenarios that are currently being considered by the State of Arkansas. The model, developed as part of the U.S. Geological Survey Groundwater Resources Program’s assessment of the Nation’s groundwater availability, is proving to be invaluable to the State as it works toward development of a sustained yield pumping strategy. One aspect of this investigation was to evaluate multiple methods to improve the match of observed to simulated groundwater levels within the Mississippi River Valley alluvial and middle Claiborne (Sparta) aquifers in the MERAS model. Five primary methods were evaluated: (1) explicit simulation of evapotranspiration (ET), (2) upgrade of the Multi-Node Well (MNW2) Package, (3) geometry improvement within the Streamflow Routing (SFR) Package, (4) parameter estimation of select aquifer properties with pilot points, and (5) modification of water-use estimates. For the planning purposes of the Arkansas Water Plan, three scenarios were developed to evaluate potential future conditions: (1) simulation of previously optimized pumping values within the Mississippi River Valley alluvial and the middle Claiborne aquifers, (2) simulated prolonged effects of pumping at average recent (2000–5) rates, and (3) simulation of drawdown constraints on most pumping wells. The explicit simulation of ET indicated little, if any, improvement of model fit at the expense of much longer simulation time and was not included in further simulations. Numerous attempts to fully utilize the MNW2 Package were unsuccessful in achieving model stability, though modifications made to the water-use dataset remained intact. Final improvements in the residual statistics may be attributed to a single method, or a cumulative effect of all other methods (geometry improvement with the SFR Package, parameter estimation with pilot points, and modification of water-use estimates) attempted. The root mean squared error (RMSE) for all observations in the model is 22.65 feet (ft) over a range in observed hydraulic head of 741.66 ft. The RMSE for water-level observations in the Mississippi River Valley alluvial aquifer is 14.14 ft (an improvement of almost 3 ft) over a range in observed hydraulic head of 297.25 ft. The RMSE for the Sparta aquifer is 32.02 ft (an improvement of approximately 3 ft) over a range in observed hydraulic head of 634.94 ft. Three scenarios were developed to utilize a steady-state version of the MERAS model. Scenario 1 was developed to use pumping values resulting from the optimization of baseline rates (typically 1997 pumping rates) from previous optimization modeling of the alluvial aquifer and the Sparta aquifer. Scenario 2 was developed to evaluate the prolonged effects of pumping from the alluvial aquifer at recent pumping rates. Scenario 3A was designed to evaluate withdrawal limits from the alluvial aquifer by utilizing drawdown constraints equal to an altitude of approximately 50 percent of the predevelopment saturated thickness of the alluvial aquifer or 30 ft above the bottom of the alluvial aquifer, whichever was greater. The results of scenario 1 indicate large water-level declines throughout the area of the alluvial aquifer, regardless of the substitution of the optimized pumping values from earlier model simulations. The results of scenario 2 also indicate large areas of water-level decline, as compared to half of the saturated thickness, throughout the alluvial aquifer. The results of scenario 3A reveal some effects from the inclusion of multiple aquifers in a single simulation. The initial configuration of scenario 3A resulted in water levels well below the defined drawdown constraint, and some areas of depleted aquifer (water levels that are near or below the bottom of the aquifer) in east-central Arkansas. A fourth simulation (scenario 3B) was configured to apply the same drawdown constraints from the alluvial aquifer wells to the Sparta aquifer wells in the depleted area. These drawdown constraints reduce leakage from the alluvial aquifer to the underlying Sparta aquifer. This configuration did not produce depleted areas within the alluvial aquifer. Scenarios 3A and 3B indicate that even when pumping is limited in the alluvial aquifer, water levels in the alluvial aquifer may continue to decline in some areas because of pumping in the underlying Sparta aquifer.

Arkansas↗
USGS2023

Groundwater prospecting using a multi-technique framework in the lower Casas Grandes Basin, Chihuahua, México

Groundwater is a strategic resource for economic development, social justice, environmental sustainability, and water governance. The lower Casas Grandes River Basin, located in the state of Chihuahua, México, is in a semi-arid region with increasing groundwater demand and regional challenges such as drought and depletion of aquifers. Even though there is official information about the availability of groundwater, a comprehensive aquifer characterization requiring an interdisciplinary investigation using a diverse suite of tools and multiple data sources has yet to be carried out. This study presents a multi-technique framework to evaluate potential sites to drill for groundwater resources and reduce the risk of unsuccessful drilling. The main components of the methodology include wellhead leveling correction with a differential global positioning survey to define piezometric levels, principal component analysis using LANDSAT-8 images, application of geospatial tools, geophysics analysis using time domain electromagnetic surveys (TDES) and vertical electric soundings (VES), and structural geohydrology to define aquifer characteristics. The results showed that using the proposed framework steps improved the possibility of identifying subsurface layers with lower resistivity values that could be related to groundwater. Low resistivity values (35 Ohm-m) were found at depths from 50 to 85 m at sites where the regional static water level reached a depth of 245 m, indicating the potential location of a shallow groundwater resource at a site where the intersection of a fracture trace was identified. This procedure can be used in other regions in the world where limited information is available for groundwater exploration, thus reducing the risk of drilling dry wells in complex hydrogeological environments.

Lower Casas Grandes Basin, Chihuahua↗
USGS2012

Groundwater depletion and sustainability of irrigation in the US High Plains and Central Valley

Aquifer overexploitation could significantly impact crop production in the United States because 60% of irrigation relies on groundwater. Groundwater depletion in the irrigated High Plains and California Central Valley accounts for ∼50% of groundwater depletion in the United States since 1900. A newly developed High Plains recharge map shows that high recharge in the northern High Plains results in sustainable pumpage, whereas lower recharge in the central and southern High Plains has resulted in focused depletion of 330 km 3 of fossil groundwater, mostly recharged during the past 13,000 y. Depletion is highly localized with about a third of depletion occurring in 4% of the High Plains land area. Extrapolation of the current depletion rate suggests that 35% of the southern High Plains will be unable to support irrigation within the next 30 y. Reducing irrigation withdrawals could extend the lifespan of the aquifer but would not result in sustainable management of this fossil groundwater. The Central Valley is a more dynamic, engineered system, with north/south diversions of surface water since the 1950s contributing to ∼7× higher recharge. However, these diversions are regulated because of impacts on endangered species. A newly developed Central Valley Hydrologic Model shows that groundwater depletion since the 1960s, totaling 80 km 3 , occurs mostly in the south (Tulare Basin) and primarily during droughts. Increasing water storage through artificial recharge of excess surface water in aquifers by up to 3 km 3 shows promise for coping with droughts and improving sustainability of groundwater resources in the Central Valley.

California, Colorago, Kansas, Nebraska, New Mexico↗
USGS2018

Revised groundwater-flow model of the glacial aquifer system north of Aberdeen, South Dakota, through water year 2015

The city of Aberdeen, in northeastern South Dakota, requires an expanded and sustainable supply of water to meet current and future demands. Conceptual and numerical models of the glacial aquifer system in the area north of Aberdeen were developed by the U.S. Geological Survey in cooperation with the City of Aberdeen in 2012. The U.S. Geological Survey, in cooperation with the City of Aberdeen, completed a study to revise the original numerical groundwater-flow model using data through water year (WY) 2015 to aid the City of Aberdeen in their development of plans and strategies for a sustainable water supply and to increase understanding of the glacial aquifer system and groundwater-flow system near Aberdeen. The original model was revised to improve the fit between model-simulated values and observed (measured or estimated) data, provide greater insight into surface-water interactions, and improve the usefulness of the model for water-supply planning. The revised groundwater-flow model (hereafter referred to as the “revised model”) presented in this report supersedes the original model. The purpose of this report is to describe a revised groundwater-flow model including data collection, model calibration, and model results for the glacial aquifer system including the Elm, Middle James, and Deep James aquifers north of Aberdeen, South Dakota, using updated hydrologic data through WY 2015. The original numerical model was revised in several ways. The model was modified by adding four new layers, which included a surficial layer, two intervening confining layers, and a shale bedrock layer. The revised model provides an improved understanding of the groundwater-flow system in comparison to the original model. The principal aquifers of the model area include portions of the Elm, Middle James, and Deep James aquifers. The lithologic information used to define and describe the aquifers in the model area was unaltered; however, aquifer properties and boundary conditions were reviewed and updated using geological information reported by the South Dakota Department of Environmental and Natural Resources and information obtained from geophysical investigations for this study. The horizontal extent of the Elm, Middle James, and Deep James aquifers was unaltered from the original model. The thickness of the Deep James aquifer was modified based on interpretations from the geophysical investigations. In general, groundwater in the Elm aquifer flowed from northwest to southeast and locally towards rivers and streams. Similarly, in the Middle James and Deep James aquifers, groundwater also typically flowed southeast. The revisions made to the original model include use of the following MODFLOW stress packages: Recharge, Evapotranspiration, Time-Variant Specified Head, Wells, Drains, and Stream Flow Routing, all of which were updated from the original model except for the Stream Flow Routing Package, which replaced the River Package used in the original model. Model calibration is the process of estimating model parameters to minimize the differences, or residuals, between observed data and simulated values; therefore, Parameter ESTimation (PEST) software was used to optimize model input parameters by matching model-simulated values to observed data. Calibration parameters included horizontal hydraulic conductivity, vertical hydraulic conductivity, specific yield, specific storage, and vertical streambed conductance for stream and drain cells. Multipliers were used to calibrate the recharge and evapotranspiration stresses. Evapotranspiration extinction depth also was adjusted during model calibration. Comparisons to the original model are described to highlight the changes made in the revised model. In general, the revised model adequately simulates the natural system and compares favorably with observed hydrologic data. Simulated water levels were evaluated by comparing them to single water-level observations at selected well locations. The selected wells were the same wells used in the original model. The coefficient of determination value between simulated and observed water levels for the revised model was 0.89 and included simulated and observed values from October 1, 1974 (WY 1975), through September 30, 2015 (WY 2015). The coefficient of determination value for the original model was 0.94 and included simulated and observed values from October 1, 1974, through September 30, 2009. The difference may indicate that the original model could have been overfit to hydraulic head observations because base flow was not simulated. The additional data used in the revised model included some climatically wetter, more extreme periods, such as 2011, in which annual precipitation was 30.9 inches. Average annual precipitation for the original model timeframe, which included data from WYs 1975–2009, was 20.26 inches. Additional precipitation data for WYs 2010–15, included in the revised model timeframe, resulted in an average annual precipitation for WYs 1975–2015 in the model area of 20.6 inches. The larger variability in climate data coupled with the additional water-level data could explain the lower coefficient of determination for water levels in the revised model. The revised model was used to calculate various groundwater-budget components for steady-state and transient conditions for WYs 1975–2015. The time-variant specified-head cells in the revised model had the largest change when compared to the original steady-state model for inflows and outflows. Comparing the transient budget components between the original and the revised models indicated that inflow from recharge and time-variant specified-head cells had the greatest effect on groundwater inflows, and outflow from storage had the greatest effect on groundwater outflows. The simulated potentiometric contours from the revised model were compared with (1) the observed (interpreted) potentiometric surface (layer 2) and the hydraulic head values (layers 4 and 6) and (2) the simulated contours from the original model. The simulated hydraulic gradients and general direction of groundwater flow in the Elm aquifer in the revised model generally matched the observed potentiometric contours, the simulated potentiometric contours from the original model, and general flow directions interpreted to be perpendicular to the contours. Minor discrepancies between simulated potentiometric contours from the revised model and the observed potentiometric contours may be due to the lack of observed data in the model area. The revised model was designed to reduce the limitations of the original model. The revisions were validated by comparing the results of the original model with the revised model. A primary benefit of the revised model is the inclusion of the surficial deposits and the confining units as explicit layers in the model. The addition of the surficial layer was beneficial for three primary reasons: (1) more accurate representation of recharge from precipitation, (2) more accurate representation of groundwater evapotranspiration, and (3) more accurate representation of groundwater and surface-water interactions. The groundwater model is a numeric approximation of a complex physical hydrologic system, and the revised model data were interpolated in regions with sparse data. Additionally, model discretization included averaged and interpolated values for water use, withdrawal rates, and hydraulic conductivity. The revised model provides a useful estimate for hydraulic gradients, groundwater-flow directions, and aquifer response to groundwater withdrawals.

South Dakota↗
USGS2022

Assessment of well yield, dominant fractures, and groundwater recharge in Wake County, North Carolina

A cooperative study led by the U.S. Geological Survey and Wake County Environmental Services was initiated to characterize the fractured-rock aquifer system and assess the sustainability of groundwater resources in and around Wake County. This report contributes to the development of a comprehensive groundwater budget for the study area, thereby helping to enable resource managers to make sound and sustainable water-supply and water-use decisions. Construction information was used to analyze the well depth, casing depth, and reported well yield of more than 7,500 inventoried wells. The median well depth and casing depth were 265 feet (ft) below land surface (bls) and 68 ft bls, respectively, and the median well yield was 10 gallons per minute. Generally, well yield increased with depth to around 200 ft bls and then began to decrease with depth within the fractured-rock aquifer. Borehole geophysical logging methods were used to characterize the fractured-rock aquifer by mapping the orientation of geologic structures within the subsurface. Structure measurements were made on resulting log data and mapped to observed general spatial trends within the regional groundwater system and more distinct hydrogeologic units. Many of the fractures observed within the borehole logs are steeply dipping across Wake County, although open fractures with shallow dip angles were also observed in most rock classes. Regional geologic structural trends were observed in proximity to the Jonesboro Fault. Potential groundwater recharge in the study area was estimated using a Soil-Water-Balance (SWB) model, as well as using base flow hydrograph separation. The SWB model calculated net infiltration below the root zone for 1981 through 2019 for a 5,402-square-mile area that extends to the counties surrounding Wake County. The mean annual net infiltration rate for the 39-year period was about 8.6 inches per year for the study area. The mean annual net infiltration results from the SWB model were comparable to annual base flow estimates using the PART hydrograph-separation method at six U.S. Geological Survey streamgages within the study area. Mean annual base flow for all six drainage basins was near 7.5 inches per year and estimates ranged from 2.9 to 8.9 inches. Comparisons of mean annual potential recharge from the SWB model and base flow estimates were generally within 2 inches, except during high flows for most of the drainage basins in the study area.

North Carolina↗