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At least 1,603 records · Page 89Linked to original sources
USGS2024

On connecting hydro-social parameters to vegetation greenness differences in an evolving groundwater-dependent ecosystem

Understanding groundwater-dependent ecosystems (i.e., areas with a relatively shallow water table that plays a major role in supporting vegetation health) is key to sustaining water resources in the western United States. Groundwater-dependent ecosystems (GDEs) in Colorado have non-pristine temporal and spatial patterns, compared to agro-ecosystems, which make it difficult to quantify how these ecosystems are impacted by changes in water availability. The goal of this study is to examine how key hydrosocial parameters perturb GDE water use in time and in space. The temporal approach tests for the additive impacts of precipitation, surface water discharge, surface water mass balance as a surrogate for surface–groundwater exchange, and groundwater depth on the monthly Landsat normalized difference vegetation index (NDVI). The spatial approach tests for the additive impacts of river confluences, canal augmentation, development, perennial tributary confluences, and farmland modification on temporally integrated NDVI. Model results show a temporal trend (monthly, 1984–2019) is identifiable along segments of the Arkansas River at resolutions finer than 10 km. The temporal impacts of river discharge correlate with riparian water use sooner in time compared to precipitation, but this result is spatially variable and dependent on the covariates tested. Spatially, areal segments of the Arkansas River that have confluences with perennial streams have increased cumulative vegetation density. Quantifying temporal and spatial dependencies between the sources and effects of GDEs could aid in preventing the loss of a vulnerable ecosystem to increased water demand, changing climate, and evolving irrigation methodologies.

Colorado↗
USGS2014

Development of a shared vision for groundwater management to protect and sustain baseflows of the Upper San Pedro River, Arizona, USA

Groundwater pumping along portions of the binational San Pedro River has depleted aquifer storage that supports baseflow in the San Pedro River. A consortium of 23 agencies, business interests, and non-governmental organizations pooled their collective resources to develop the scientific understanding and technical tools required to optimize the management of this complex, interconnected groundwater-surface water system. A paradigm shift occurred as stakeholders first collaboratively developed, and then later applied, several key hydrologic simulation and monitoring tools. Water resources planning and management transitioned from a traditional water budget-based approach to a more strategic and spatially-explicit optimization process. After groundwater modeling results suggested that strategic near-stream recharge could reasonably sustain baseflows at or above 2003 levels until the year 2100, even in the presence of continued groundwater development, a group of collaborators worked for four years to acquire 2250 hectares of land in key locations along 34 kilometers of the river specifically for this purpose. These actions reflect an evolved common vision that considers the multiple water demands of both humans and the riparian ecosystem associated with the San Pedro River.

Arizona↗
USGS2017

Atoll groundwater movement and its response to climatic and sea-level fluctuations

Groundwater resources of low-lying atoll islands are threatened due to short-term and long-term changes in rainfall, wave climate, and sea level. A better understanding of how these forcings affect the limited groundwater resources was explored on Roi-Namur in the Republic of the Marshall Islands. As part of a 16-month study, a rarely recorded island-overwash event occurred and the island’s aquifer’s response was measured. The findings suggest that small-scale overwash events cause an increase in salinity of the freshwater lens that returns to pre-overwash conditions within one month. The overwash event is addressed in the context of climate-related local sea-level change, which suggests that overwash events and associated degradations in freshwater resources are likely to increase in severity in the future due to projected rises in sea level. Other forcings, such as severe rainfall events, were shown to have caused a sudden freshening of the aquifer, with salinity levels retuning to pre-rainfall levels within three months. Tidal forcing of the freshwater lens was observed in electrical resistivity profiles, high-resolution conductivity, groundwater-level well measurements and through submarine groundwater discharge calculations. Depth-specific geochemical pore water measurements further assessed and confirmed the distinct boundaries between fresh and saline water masses in the aquifer. The identification of the freshwater lens’ saline boundaries is essential for a quantitative evaluation of the aquifers freshwater resources and help understand how these resources may be impacted by climate change and anthropogenic activities.

Water↗
USGS2022

Understanding the impacts of surface-groundwater conditions on stream fishes under altered baseflow conditions

Persistence of aquatic fauna depends on the conditions and connectivity of surface water and groundwater. In light of altered baseflows and both current and future predicted increases in stream temperatures, it is important to assess current thermal conditions, examine thermal responses of aquatic fauna, and evaluate water-management practices. Our study objectives were to determine (1) how changes in baseflow levels in the Kiamichi River influence hyporheic exchange, which correspondingly influences temperature at the reach scale; (2) temperature tolerances of stream fishes as a means for predicting how habitat complexity influences stream-fish populations; and (3) assess how dam releases influence the downstream temperature and dissolved oxygen regime during the low-flow period. We quantified hyporheic exchange at four reaches and, as expected, found higher groundwater exchange via transient storage occurred at the upstream sites. The net groundwater flux estimation was negative for the majority of reaches indicating that surface water is lost to groundwater during summer (i.e., losing), baseflow conditions. We determined critical thermal maximum (CTMax) for 17 stream fishes and thermal tolerances ranged 32-38°C. We determined the average thermal tolerance for two habitat fish guilds to calculate changes in thermal stress due to hypothetical reservoir release scenarios. We developed a process-based Water Quality Analysis Simulation Program model to predict downstream temperature conditions over 74-km of river in response to reservoir releases that corresponded to discharges of 0.00 (control), 0.34, 0.59, 0.76, 1.13, and 1.50 m3/s. Based on the dissolved oxygen conditions observed in 2015 and 2017 and biological oxygen demand sampling results, reservoir releases did not directly reduce dissolved oxygen concentrations in the Kiamichi River (though dissolved oxygen concentrations are limited to current water-release strategies by the managing agency). We simulated three scenarios using three water-release temperatures: 27.64°C, 26.00°C and 24.07°C that corresponded to average reservoir temperatures at gate locations on the dam. We compared the predicted temperature time series with CTMax of two fish-habitat guilds to quantify the cumulative time when stream fishes experienced severe thermal stress downstream from Sardis Reservoir. According to our simulations, reservoir releases would be capable of regulating downstream water temperature during the summer baseflow period. The 0.00 m3/s scenario resulted in 130 h of thermal stress for benthic fishes, and 73 h for mid-column fishes. As expected, thermal relief increased with increasing release magnitude and decreasing release water temperature. The 0.34 m3/s release scenario reduced thermal stress (range is simulations from the top and bottom gate) by 11-18% for mid-column fishes and 8-12% for benthic fishes with an effective distance (where the cumulative time above CTMax was reduced by half) of 1-2 km for both guilds. The 0.59 m3/s release scenario reduced thermal stress by 18-25% for mid-column fishes and 12-20% for benthic fishes with effective distances of 4-8 km and 2-7 km, respectively. Three releases representing pre-dam flow magnitudes (0.76, 1.13 and 1.50 m3/s released from top gate) reduced thermal stress up to 46% for mid-column fishes and 41% for benthic fishes with an effective distance of 13-16 km, respectively. Lastly, we quantified temperature-induced stress via whole-body cortisol concentration of six stream fishes in response to prolonged thermal exposure at two temperatures (27°C and 32°C). We found no difference in cortisol levels between temperatures for any of the six species, indicating acclimation to elevated temperatures during the test period. However, Highland Stoneroller Campostoma spadiceum expressed cortisol concentrations greater than typical basal levels at both temperatures, suggesting stress from factors other than temperature (i.e., captivity). Our results suggest different reservoir-release options could improve downstream thermal-fish habitat during the summer baseflow period.

Cooperator Science Series↗
USGS2006

Groundwater-transported dissolved organic nitrogen exports from coastal watersheds

We analyzed groundwater-transported nitrogen (N) exports from 41 watershed segments that comprised 10 Cape Cod, Massachusetts watersheds to test the hypotheses that chemical form of N exports is related to land use and to length of flow paths through watersheds. In the absence of human habitation, these glacial outwash-plain watersheds exported largely dissolved organic N (DON) but at relatively low annual rate. Addition of people to watersheds increased rates of both total dissolved N (TDN) and DON export through groundwater. Percent of TDN as DON in groundwater was negatively related to path length of groundwater through aquifers, but %DON was not significantly related to population density on the watersheds. DON was often the dominant form of N exported from the watersheds, even at high population densities. Our results suggest that natural sources are not entirely responsible for organic N exports from watersheds, but, instead, a substantial portion of anthropogenic N introduced to watersheds is exported as DON. This finding is in disagreement with previous results, which suggest that anthropogenic N is exported from watersheds largely as NO 3- and that DON exported from watersheds is from natural sources.

Massachusetts↗
USGS2018

GSFLOW-GRASS v1.0.0: GIS-enabled hydrologic modeling of coupled groundwater–surface-water systems

The importance of water moving between the atmosphere and aquifers has led to efforts to develop and maintain coupled models of surface water and groundwater. However, developing inputs to these models is usually time-consuming and requires extensive knowledge of software engineering, often prohibiting their use by many researchers and water managers, thus reducing these models' potential to promote science-driven decision-making in an era of global change and increasing water resource stress. In response to this need, we have developed GSFLOW–GRASS, a bundled set of open-source tools that develops inputs for, executes, and graphically displays the results of GSFLOW, the U.S. Geological Survey's coupled groundwater and surface-water flow model. In order to create a robust tool that can be widely implemented over diverse hydro(geo)logic settings, we built a series of GRASS GIS extensions that automatically discretizes a topological surface-water flow network that is linked with an underlying gridded groundwater domain. As inputs, GSFLOW–GRASS requires at a minimum a digital elevation model, a precipitation and temperature record, and estimates of channel parameters and hydraulic conductivity. We demonstrate the broad applicability of the toolbox by successfully testing it in environments with varying degrees of drainage integration, landscape relief, and grid resolution, as well as the presence of irregular coastal boundaries. These examples also show how GSFLOW–GRASS can be implemented to examine the role of groundwater–surface-water interactions in a diverse range of water resource and land management applications.

Geoscientific Model Development↗
USGS2016

Influence of groundwater on distribution of dwarf wedgemussels (Alasmidonta heterodon) in the upper reaches of the Delaware River, northeastern USA

The remaining populations of the endangered dwarf wedgemussel (DWM) ( Alasmidonta heterodon ) in the upper Delaware River, northeastern USA, were hypothesized to be located in areas of greater-than-normal groundwater discharge to the river. We combined physical (seepage meters, monitoring wells and piezometers), thermal (fiber-optic distributed temperature sensing, infrared, vertical bed-temperature profiling), and geophysical (electromagnetic-induction) methods at several spatial scales to characterize known DWM habitat and explore this hypothesis. Numerous springs were observed using visible and infrared imaging along the river banks at all three known DWM-populated areas, but not in adjacent areas where DWM were absent. Vertical and lateral groundwater gradients were toward the river along all three DWM-populated reaches, with median upward gradients 3 to 9 times larger than in adjacent reaches. Point-scale seepage-meter measurements indicated that upward seepage across the riverbed was faster and more consistently upward at DWM-populated areas. Discrete and areally distributed riverbed-temperature measurements indicated numerous cold areas of groundwater discharge during warm summer months; all were within areas populated by DWM. Electromagnetic-induction measurements, which may indicate riverbed geology, showed patterning but little correlation between bulk streambed electromagnetic conductivity and areal distribution of DWM. In spite of complexity introduced by hyporheic exchange, multiple lines of research provide strong evidence that DWM are located within or directly downstream of areas of substantial focused groundwater discharge to the river. Broad scale thermal-reconnaissance methods (e.g., infrared) may be useful in locating and protecting other currently unknown mussel populations.

Delaware River↗
USGS2010

Simulated impacts of artificial groundwater recharge and discharge of the source area and source volume of an Atlantic Coastal Plain Stream, Delaware, USA

A numerical groundwater-flow model was used to characterize the source area and volume of Phillips Branch, a baseflow-dominated stream incising a highly permeable unconfined aquifer on the low relief Delmarva Peninsula, USA. Particle-tracking analyses indicate that the source area (5.51 km 2 ) is ~20% smaller than the topographically defined watershed (6.85 km 2 ), and recharge entering ~37% of the surface watershed does not discharge to Phillips Branch. Groundwater residence time within the source volume ranges from a few days to almost 100 years, with 95% of the volume "flushing" within 50 years. Artificial discharge from groundwater pumping alters the shape of the source area and reduces baseflow due to the interception of stream flow paths, but has limited impacts on the residence time of groundwater discharged as baseflow. In contrast, artificial recharge from land-based wastewater disposal substantially reduces the source area, lowers the range in residence time due to the elimination of older flow paths to the stream, and leads to increased discharge to adjacent surface-water bodies. This research suggests that, in this and similar hydrogeologic settings, the "watershed" approach to water-resource management may be limited, particularly where anthropogenic stresses alter the transport of soluble contaminants through highly permeable unconfined aquifers.

Delaware↗
USGS1982

Preliminary model of regional Mesozoic groundwater flow and uranium deposition in the Colorado Plateau.

Qualitative and numerical simulation of regional groundwater flow in the Colorado Plateau during Late Jurassic and Early Cretaceous time has led to a model of U deposition in areas of upwelling solutions. Palaeographic reconstruction shows that surface drainage and groundwater flow was generally to the NE and E. Groundwater flowing in these directions, principally through Triassic-Jurassic and Permian sandstones, encountered sediments of variable thickness due to buried uplifted or downdropped Precambrian blocks. The buried uplifted blocks caused upward movement of groundwater around them. These inferred zones of upwelling are closely associated with concentrations of Jurassic- and Cretaceous-age U deposits. The results are consistent with hypotheses of an upwelling brine mixing and reacting with descending meteoric water and causing U precipitation at the fluid interface. Whether the U came from above or below the interface is an unsolved problem.-A.P.

Geology↗
USGS1996

Using remote sensing and GIS techniques to estimate discharge and recharge fluxes for the Death Valley regional groundwater flow system, USA

The recharge and discharge components of the Death Valley regional groundwater flow system were defined by techniques that integrated disparate data types to develop a spatially complex representation of near-surface hydrological processes. Image classification methods were applied to multispectral satellite data to produce a vegetation map. The vegetation map was combined with ancillary data in a GIS to delineate different types of wetlands, phreatophytes and wet playa areas. Existing evapotranspiration-rate estimates were used to calculate discharge volumes for these area. An empirical method of groundwater recharge estimation was modified to incorporate data describing soil-moisture conditions, and a recharge potential map was produced. These discharge and recharge maps were readily converted to data arrays for numerical modelling codes. Inverse parameter estimation techniques also used these data to evaluate the reliability and sensitivity of estimated values.The recharge and discharge components of the Death Valley regional groundwater flow system were defined by remote sensing and GIS techniques that integrated disparate data types to develop a spatially complex representation of near-surface hydrological processes. Image classification methods were applied to multispectral satellite data to produce a vegetation map. This map provided a basis for subsequent evapotranspiration and infiltration estimations. The vegetation map was combined with ancillary data in a GIS to delineate different types of wetlands, phreatophytes and wet playa areas. Existing evapotranspiration-rate estimates were then used to calculate discharge volumes for these areas. A previously used empirical method of groundwater recharge estimation was modified by GIS methods to incorporate data describing soil-moisture conditions, and a recharge potential map was produced. These discharge and recharge maps were readily converted to data arrays for numerical modelling codes. Inverse parameter estimation techniques also used these data to evaluate the reliability and sensitivity of estimated values.

Application of geographic information systems in h↗
USGS1995

Mobilization of major and trace constituents of highway runoff in groundwater potentially caused by deicing chemical migration

The quality of water in unsaturated zones and groundwater is affected by the major ions in deicing chemicals applied to roads and highways. The assessment of the environmental effects of highway runoff requires investigations to determine whether other major and trace constituents are mobilized during deicing chemical migration through the unsaturated zone and groundwater. In this regard, groundwater samples were analyzed in February and August 1991, and March, August, and November 1993 at a test site along Route 25 in southeastern Massachusetts. Analyses indicated that concentrations of major and trace chemical constituents of highway runoff in groundwater are substantially higher downgradient than upgradient from the highway.

Transportation Research Record↗
USGS2003

Incorporating uncertainty into high-resolution groundwater supply models

Groundwater modeling is a useful tool for evaluating whether an acquifer system is capable of supporting groundwater withdrawals over long periods of time and what effect, if any, such activity will have on the regional flow dynamics as well as on specific public water, agricultural and industrial supplies. An overview is given of an ongoing groundwater modeling study of the Chicot Aquifer in southwestern Louisiana where a low-resolution groundwater model is being used to study the regional flow in the Chicot acquifer and to provide boundary conditions for higher-resolution inset models created using telescopic mesh refinement (TMR).

Conference Paper↗
USGS2006

The importance of submarine groundwater discharge to the nearshore nutrient supply in the Gulf of Aqaba (Israel)

We used two short-lived radium isotopes (223Ra, 224Ra) and a mass balance approach applied to the radium activities to determine the nutrient contribution of saline submarine groundwater discharge to the coastal waters of the northern Gulf of Aqaba (Israel). Radium isotope activities were measured along transects during two seasons at a site that lacked any obvious surficial water input. An onshore well and an offshore end member were also sampled. For all samples, nutrients and salinity data were collected. Radium isotope activities generally decreased with distance offshore and exhibited significant tidal variability, which is consistent with a shore-derived tidally influenced source. Submarine groundwater contributes only 1-2% of the water along this coast, but this groundwater provides 8-46% of the nutrients. This saline groundwater is derived predominately from tidally pumped seawater percolating through the unconfined coastal aquifer and leaching radium and nutrients. This process represents a significant source of nutrients to the oligotrophic nearshore reef. ?? 2006, by the American Society of Limnology and Oceanography, Inc.

Limnology and Oceanography↗
USGS2010

Groundwater sampling

Groundwater is protected in most areas as it is a primary source of drinking water. In the United States, 50% of the population relies on groundwater supplies (Reilly et al., 2008). Groundwater sampling in the United States became commonplace in the 20th century as contaminated water resources became apparent and a growing public concern emerged to protect water resources. In response to this concern, the U.S. government mandated a study in which scientists identified six categories of groundwater contaminant sources (OTA, 1984): Category 1-sources designed to discharge substances (e.g., injection well) Category 2-sources designed to store, treat, and/or dispose of substances; discharge through unplanned release (e.g., landfills) Category 3-sources designed to retain substances during transport or trans-mission (e.g., pipelines) Category 4-sources discharging as consequence of other planned activities (e.g., pesticide application) Category 5-sources providing conduit or inducing discharge through altered flow patterns (e.g., construction excavation) Category 6-naturally occurring sources whose discharge is created and/or exacerbated by human activity (e.g., salt water intrusion).

Book chapter↗
USGS2010

Summary of groundwater-recharge estimates for Pennsylvania

Groundwater recharge is water that infiltrates through the subsurface to the zone of saturation beneath the water table. Because recharge is a difficult parameter to quantify, it is typically estimated from measurements of other parameters like streamflow and precipitation. This report provides a general overview of processes affecting recharge in Pennsylvania and presents estimates of recharge rates from studies at various scales. The most common method for estimating recharge in Pennsylvania has been to estimate base flow from measurements of streamflow and assume that base flow (expressed in inches over the basin) approximates recharge. Statewide estimates of mean annual groundwater recharge were developed by relating base flow to basin characteristics of HUC10 watersheds (a fifth-level classification that uses 10 digits to define unique hydrologic units) using a regression equation. The regression analysis indicated that mean annual precipitation, average daily maximum temperature, percent of sand in soil, percent of carbonate rock in the watershed, and average stream-channel slope were significant factors in the explaining the variability of groundwater recharge across the Commonwealth. Several maps are included in this report to illustrate the principal factors affecting recharge and provide additional information about the spatial distribution of recharge in Pennsylvania. The maps portray the patterns of precipitation, temperature, prevailing winds across Pennsylvania’s varied physiography; illustrate the error associated with recharge estimates; and show the spatial variability of recharge as a percent of precipitation. National, statewide, regional, and local values of recharge, based on numerous studies, are compiled to allow comparison of estimates from various sources. Together these plates provide a synopsis of groundwater-recharge estimations and factors in Pennsylvania. Areas that receive the most recharge are typically those that get the most rainfall, have favorable surface conditions for infiltration, and are less susceptible to the influences of high temperatures, and thus, evapotranspiration. Areas that have less recharge in Pennsylvania are typically those with less precipitation, less permeable soils, and higher temperatures that are conducive to greater rates of evapotranspiration.

Pennsylvania↗
USGS2012

Effects of groundwater pumping in the lower Apalachicola-Chattahoochee-Flint River basin

USGS developed a groundwater-flow model of the Upper Floridan aquifer in lower Apalachicola-Chattahoochee-Flint River basin in southwest Georgia and adjacent parts of Alabama and Florida to determine the effect of agricultural groundwater pumping on aquifer/stream flow within the basin. Aquifer/stream flow is the sum of groundwater outflow to and inflow from streams, and is an important consideration for water managers in the development of water-allocation and operating plans. Specifically, the model was used to evaluate how agricultural pumping relates to 7Q10 low streamflow, a statistical low flow indicative of drought conditions that would occur during seven consecutive days, on average, once every 10 years. Argus ONETM, a software package that combines a geographic information system (GIS) and numerical modeling in an Open Numerical Environment, facilitated the design of a detailed finite-element mesh to represent the complex geometry of the stream system in the lower basin as a groundwater-model boundary. To determine the effects on aquifer/stream flow of pumping at different locations within the model area, a pumping rate equivalent to a typical center-pivot irrigation system (50,000 ft3/d) was applied individually at each of the 18,951 model nodes in repeated steady-state simulations that were compared to a base case representing drought conditions during October 1999. Effects of nodal pumping on aquifer/stream flow and other boundary flows, as compared with the base-case simulation, were computed and stored in a response matrix. Queries to the response matrix were designed to determine the sensitivity of targeted stream reaches to agricultural pumping. Argus ONE enabled creation of contour plots of query results to illustrate the spatial variation across the model area of simulated aquifer/streamflow reductions, expressed as a percentage of the long-term 7Q10 low streamflow at key USGS gaging stations in the basin. These results would enable water managers to assess the relative impact of agricultural pumping and drought conditions on streamflow throughout the basin, and to develop mitigation strategies to conserve water resources and preserve aquatic habitat.

Alabama, Georgia, Florida↗
USGS2010

Development of a conceptual model of groundwater flow, Chesterfield County, South Carolina

Chesterfield County is located in the north central part of South Carolina (SC) and is adjacent to the North Carolina border. The County lies along the Fall Line, the geologic boundary between the Atlantic Coastal Plain (ACP) and Piedmont physiographic provinces. Between 2000 and 2007, the population increased from 42,768 to 43,191 people (U.S. Census Bureau, 2007). Associated with this population growth is an increased demand for domestic, public, industrial, and agricultural water supplies. The ACP sediments underlying Chesterfield County contain abundant supplies of highquality groundwater (Newcome, 2004). The U.S. Geological Survey, in cooperation with the South Carolina Department of Natural Resources is investigating the ACP groundwater resources of Chesterfield County. The initial task of the study is to establish a hydrologic data-collection network for the ACP part of the County. A groundwater-flow model and derived water budgets for the ACP aquifer that underlies most of the County will be constructed and calibrated later in the study. Both anthropogenic and natural groundwater contaminants that have been identified in the study area will be quantified and described as part of a companion study.

South Carolina↗
USGS2011

Using dissolved gases to observe the evolution of groundwater age in a mountain watershed over a period of thirteen years

Baseflows in snowmelt-dominated mountain streams are critical for sustaining ecosystems and water resources during periods of greatest demand. Future climate predictions for mountainous areas throughout much of the western U.S. include increasing temperatures, declining snowpacks, and earlier snowmelt periods. The degree to and rate at which these changes will affect baseflows in mountain streams remains unknown, largely because baseflows are groundwater-fed and the relationship between climate and groundwater recharge/discharge rates in mountain watersheds is uncertain. We use groundwater age determinations from multiple dissolved gas tracers (CFCs, SF6, and 3H/3He) to track changes in groundwater age over a period of thirteen years in the Sagehen Creek watershed, Sierra Nevada Mountains, CA. Data were collected from springs and wells in 2009 and 2010 and combined with those obtained in prior studies from 1997 to 2003. Apparent ages range from 0 to >60 years. Comparison between variations in age and variations in snow water equivalent (SWE) and mean annual air temperature reveals the degree of correlation between these climate variables and recharge rate. Further, comparison of apparent ages from individual springs obtained at different times and using different tracers helps constrain the age distribution in the sampled waters. The age data are generally more consistent with an exponential age distribution than with piston-flow. However, many samples, even those with relatively old mean ages, must have a disproportionately large very young fraction that responds directly to annual SWE variations. These findings have important implications for how future baseflows may respond to decreasing SWE.

California↗