USGS Science⌕ Search

SEARCH · USGS Science

Results for “Water Resources Research”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 469 records · Page 26Linked to original sources
USGS2007

Global impacts of conversions from natural to agricultural ecosystems on water resources: Quantity versus quality

Past land use changes have greatly impacted global water resources, with often opposing effects on water quantity and quality. Increases in rain‐fed cropland (460%) and pastureland (560%) during the past 300 years from forest and grasslands decreased evapotranspiration and increased recharge (two orders of magnitude) and streamflow (one order of magnitude). However, increased water quantity degraded water quality by mobilization of salts, salinization caused by shallow water tables, and fertilizer leaching into underlying aquifers that discharge to streams. Since the 1950s, irrigated agriculture has expanded globally by 174%, accounting for ∼90% of global freshwater consumption. Irrigation based on surface water reduced streamflow and raised water tables resulting in waterlogging in many areas (China, India, and United States). Marked increases in groundwater‐fed irrigation in the last few decades in these areas has lowered water tables (≤1 m/yr) and reduced streamflow. Degradation of water quality in irrigated areas has resulted from processes similar to those in rain‐fed agriculture: salt mobilization, salinization in waterlogged areas, and fertilizer leaching. Strategies for remediating water resource problems related to agriculture often have opposing effects on water quantity and quality. Long time lags (decades to centuries) between land use changes and system response (e.g., recharge, streamflow, and water quality), particularly in semiarid regions, mean that the full impact of land use changes has not been realized in many areas and remediation to reverse impacts will also take a long time. Future land use changes should consider potential impacts on water resources, particularly trade‐offs between water, salt, and nutrient balances, to develop sustainable water resources to meet human and ecosystem needs.

Water Resources Research↗
USGS2007

A method to estimate groundwater depletion from confining layers

Although depletion of storage in low‐permeability confining layers is the source of much of the groundwater produced from many confined aquifer systems, it is all too frequently overlooked or ignored. This makes effective management of groundwater resources difficult by masking how much water has been derived from storage and, in some cases, the total amount of water that has been extracted from an aquifer system. Analyzing confining layer storage is viewed as troublesome because of the additional computational burden and because the hydraulic properties of confining layers are poorly known. In this paper we propose a simplified method for computing estimates of confining layer depletion, as well as procedures for approximating confining layer hydraulic conductivity ( K ) and specific storage ( S s ) using geologic information. The latter makes the technique useful in developing countries and other settings where minimal data are available or when scoping calculations are needed. As such, our approach may be helpful for estimating the global transfer of groundwater to surface water. A test of the method on a synthetic system suggests that the computational errors will generally be small. Larger errors will probably result from inaccuracy in confining layer property estimates, but these may be no greater than errors in more sophisticated analyses. The technique is demonstrated by application to two aquifer systems: the Dakota artesian aquifer system in South Dakota and the coastal plain aquifer system in Virginia. In both cases, depletion from confining layers was substantially larger than depletion from the aquifers.

Water Resources Research↗
USGS2007

Assessing the likely value of gravity and drawdown measurements to constrain estimates of hydraulic conductivity and specific yield during unconfined aquifer testing

Pumping of an unconfined aquifer can cause local desaturation detectable with high‐resolution gravimetry. A previous study showed that signal‐to‐noise ratios could be predicted for gravity measurements based on a hydrologic model. We show that although changes should be detectable with gravimeters, estimations of hydraulic conductivity and specific yield based on gravity data alone are likely to be unacceptably inaccurate and imprecise. In contrast, a transect of low‐quality drawdown data alone resulted in accurate estimates of hydraulic conductivity and inaccurate and imprecise estimates of specific yield. Combined use of drawdown and gravity data, or use of high‐quality drawdown data alone, resulted in unbiased and precise estimates of both parameters. This study is an example of the value of a staged assessment regarding the likely significance of a new measurement method or monitoring scenario before collecting field data.

Water Resources Research↗
USGS2007

Transport and degradation of chlorofluorocarbons (CFCs) in the pyritic Rabis Creek aquifer, Denmark

Vertical profiles of the chlorofluorocarbons CFC‐11, CFC‐12, and CFC‐113 penetrating aerobic and anaerobic parts of a shallow sandy aquifer show that the CFC gases are degraded in the <1 m thick transition zone from aerobic to anaerobic groundwater in a pyritic sand aquifer at Rabis Creek, Denmark. Two‐dimensional solute transport simulations with either zero‐order or first‐order degradation in the anaerobic zone corroborate this interpretation. The transport model was previously calibrated against detailed tritium profiles in the same wells. First‐order degradation is found to best match the observed CFC profiles yielding an approximate half‐life of a few months for CFC‐11. Degradation is not as clearly recognized for CFC‐12 and CFC‐113, but it may occur with rates corresponding to a half‐life of a few years or more. Data indicate a geochemical control of the CFC concentration gradient at the redox front and that denitrification and denitrifiers are not of major importance for the observed CFC degradation. The responsible mechanism behind the observed degradation is not known but we suggest that reductive dehalogenation by surface‐bound Fe(II) on pyrite possibly enhanced by the presence of Fe(III)‐bearing weathering products (green rust) may be a plausible mechanism. The observed data and the performed simulations confirm the potential application of the CFC gases as age‐dating tools in the aerobic part of the investigated aquifer, but also that CFC data must be analyzed carefully before it is used as a dating tool in reducing aquifers because degradation may have occurred. The use of multiple or alternative tracers should be considered in anaerobic environments.

Rabis Creek aquifer↗
USGS2007

Evaluation of the applicability of the dual‐domain mass transfer model in porous media containing connected high‐conductivity channels

This paper evaluates the dual‐domain mass transfer (DDMT) model to represent transport processes when small‐scale high‐conductivity (K) preferential flow paths (PFPs) are present in a homogenous porous media matrix. The effects of PFPs upon solute transport were examined through detailed numerical experiments involving different realizations of PFP networks, PFP/matrix conductivity contrasts varying from 10:1 to 200:1, different magnitudes of effective conductivities, and a range of molecular diffusion coefficients. Results suggest that the DDMT model can reproduce both the near‐source peak and the downstream low‐concentration spreading observed in the embedded dendritic network when there are large conductivity contrasts between high‐K PFPs and the low‐K matrix. The accuracy of the DDMT model is also affected by the geometry of PFP networks and by the relative significance of the diffusion process in the network‐matrix system.

Water Resources Research↗
USGS2007

Cloud water in windward and leeward mountain forests: The stable isotope signature of orographic cloud water

Cloud water can be a significant hydrologic input to mountain forests. Because it is a precipitation source that is vulnerable to climate change, it is important to quantify amounts of cloud water input at watershed and regional scales. During this study, cloud water and rain samples were collected monthly for 2 years at sites on windward and leeward East Maui. The difference in isotopic composition between volume‐weighted average cloud water and rain samples was 1.4‰ δ 18 O and 12‰ δ 2 H for the windward site and 2.8‰ δ 18 O and 25‰ δ 2 H for the leeward site, with the cloud water samples enriched in 18 O and 2 H relative to the rain samples. A summary of previous literature shows that fog and/or cloud water is enriched in 18 O and 2 H compared to rain at many locations around the world; this study documents cloud water and rain isotopic composition resulting from weather patterns common to montane environments in the trade wind latitudes. An end‐member isotopic composition for cloud water was identified for each site and was used in an isotopic mixing model to estimate the proportion of precipitation input from orographic clouds. Orographic cloud water input was 37% of the total precipitation at the windward site and 46% at the leeward site. This represents an estimate of water input to the forest that could be altered by changes in cloud base altitude resulting from global climate change or deforestation.

Water Resources Research↗
USGS2008

Pathogen and chemical transport in the karst limestone of the Biscayne aquifer: 1. Revised conceptualization of groundwater flow

The Biscayne aquifer is a highly transmissive karst limestone that serves as the sole source of drinking water to over two million residents in south Florida. The aquifer is characterized by eogenetic karst, where the most transmissive void space can be an interconnected, touching‐vug, biogenically influenced porosity of biogenic origin. Public supply wells in the aquifer are in close proximity to lakes established by surface mining. The mining of the limestone has occurred to the same depths as the production wells, which has raised concerns about pathogen and chemical transport from these surface water bodies. Hydraulic and forced gradient tracer tests were conducted to augment geologic and geophysical studies and to develop a hydrogeologic conceptual model of groundwater flow and chemical transport in the Biscayne aquifer. Geologic and geophysical data indicate multiple, areally extensive subhorizontal preferential flow zones of vuggy limestone separated by rock with a matrix pore system. The hydraulic response from an aquifer test suggests that the Biscayne aquifer behaves as a dual‐porosity medium; however, the results of the tracer test showed rapid transport similar to other types of karst. The tracer test and concurrent temperature logging revealed that only one of the touching‐vug flow zones dominates transport near the production wells. On the basis of the rising limb of the breakthrough curve, the dispersivity is estimated to be less than 3% of the tracer travel distance, which suggests that the fastest flow paths in the formation are likely to yield limited dilution of chemical constituents.

Water Resources Research↗
USGS2008

Pathogen and chemical transport in the karst limestone of the Biscayne aquifer: 2. Chemical retention from diffusion and slow advection

A tracer experiment, using a nonreactive tracer, was conducted as part of an investigation of the potential for chemical and pathogen migration to public supply wells that draw groundwater from the highly transmissive karst limestone of the Biscayne aquifer in southeastern Florida. The tracer was injected into the formation over approximately 1 h, and its recovery was monitored at a pumping well approximately 100 m from the injection well. The first detection of the tracer occurred after approximately 5 h, and the peak concentration occurred at about 8 h after the injection. The tracer was still detected in the production well more than 6 days after injection, and only 42% of the tracer mass was recovered. It is hypothesized that a combination of chemical diffusion and slow advection resulted in significant retention of the tracer in the formation, despite the high transmissivity of the karst limestone. The tail of the breakthrough curve exhibited a straight‐line behavior with a slope of −2 on a log‐log plot of concentration versus time. The −2 slope is hypothesized to be a function of slow advection, where the velocities of flow paths are hypothesized to range over several orders of magnitude. The flow paths having the slowest velocities result in a response similar to chemical diffusion. Chemical diffusion, due to chemical gradients, is still ongoing during the declining limb of the breakthrough curve, but this process is dwarfed by the magnitude of the mass flux by slow advection.

Water Resources Research↗
USGS2008

Pathogen and chemical transport in the karst limestone of the Biscayne aquifer: 3. Use of microspheres to estimate the transport potential of Cryptosporidium parvum oocysts

The vulnerability of a municipal well in the Northwest well field in southeastern Florida to potential contamination by Cryptosporidium parvum oocysts was assessed in a large‐scale, forced‐gradient (convergent) injection and recovery test. The field study involved a simultaneous pulse introduction of a nonreactive tracer (SF 6 , an inert gas) and oocyst‐sized (1.6, 2.9, and 4.9 μ m diameter) carboxylated polystyrene microspheres into karst limestone of the Biscayne aquifer characterized by a complex triple (matrix, touching‐vug, and conduit) porosity. Fractional recoveries 97 m down gradient were inversely related to diameter and ranged from 2.9% for the 4.9 μ m microspheres to 5.8% for 1.6 μ m microspheres. Their centers of mass arrived at the pumping well approximately threefold earlier than that of the nonreactive tracer SF 6 (gas), underscoring the need for use of colloid tracers and field‐scale tracer tests for these kinds of evaluations. In a modified triaxial cell using near in situ chemical conditions, 2.9 and 4.9 μ m microspheres underestimated by fourfold to sixfold the attachment potential of the less electronegative 2.9–4.1 μ m oocysts in the matrix porosity of limestone core samples. The field and laboratory results collectively suggested that it may take 200–300 m of transport to ensure even a 1‐log unit removal of oocysts, even though the limestone surfaces exhibited a substantive capability for their sorptive removal. The study further demonstrated the utility of microspheres as oocyst surrogates in field‐scale assessments of well vulnerability in limestone, provided that differences in attachment behaviors between oocysts and microspheres are taken into account.

Water Resources Research↗
USGS2008

Simulation assessment of the direct‐push permeameter for characterizing vertical variations in hydraulic conductivity

The direct‐push permeameter (DPP) is a tool for the in situ characterization of hydraulic conductivity (K) in shallow, unconsolidated formations. This device, which consists of a short screened section with a pair of pressure transducers near the screen, is advanced into the subsurface with direct‐push technology. K is determined through a series of injection tests conducted between advancements. Recent field work by Butler et al. (2007) has shown that the DPP holds great potential for describing vertical variations in K at an unprecedented level of detail, accuracy and speed. In this paper, the fundamental efficacy of the DPP is evaluated through a series of numerical simulations. These simulations demonstrate that the DPP can provide accurate K information under conditions commonly faced in the field. A single DPP test provides an effective K for the domain immediately surrounding the interval between the injection screen and the most distant pressure transducer. Features that are thinner than that interval can be quantified by reducing the vertical distance between successive tests and analyzing the data from all tests simultaneously. A particular advantage of the DPP is that, unlike most other single borehole techniques, a low‐K skin or a clogged screen has a minimal impact on the K estimate. In addition, the requirement that only steady‐shape conditions be attained allows for a dramatic reduction in the time required for each injection test.

Water Resources Research↗
USGS2009

Use of heat to estimate streambed fluxes during extreme hydrologic events

Using heat as a tracer, quantitative estimates of streambed fluxes and the critical stage for flow reversal were calculated for high‐flow events that occurred on the Bogue Phalia (a tributary of the Mississippi River) following the 2005 Hurricanes Katrina and Rita. In June 2005, piezometers were installed in the Bogue Phalia upstream from the stream gage near Leland, Mississippi, to monitor temperature. Even with the hurricanes, precipitation in the Bogue Phalia Basin for the months of June to October 2005 was below normal, and consequently, streamflow was below the long‐term average. Temperature profiles from the piezometers indicate that the Bogue Phalia was a gaining stream during most of this time, but relatively static streambed temperatures suggested long‐term data was warranted for heat‐based estimates of flux. However, the hurricanes caused a pair of sharp rises in stream stage over short periods of time, increasing the potential for rapid heat‐based modeling and for identification of the critical stage for flow reversal into the streambed. Heat‐based modeling fits of simulated‐to‐measured sediment temperatures show that once a critical stage was surpassed, flow direction reversed into the streambed. Results of this study demonstrate the ability to constrain estimates of streambed water flux and the critical stage of flow reversal, with little available groundwater head data, by using heat as a tracer during extreme stage events.

Water Resources Research↗
USGS2007

Identifying spatial variability of groundwater discharge in a wetland stream using a distributed temperature sensor

Discrete zones of groundwater discharge in a stream within a peat‐dominated wetland were identified on the basis of variations in streambed temperature using a distributed temperature sensor (DTS). The DTS gives measurements of the spatial (±1 m) and temporal (15 min) variation of streambed temperature over a much larger reach of stream (>800 m) than previous methods. Isolated temperature anomalies observed along the stream correspond to focused groundwater discharge zones likely caused by soil pipes within the peat. The DTS also recorded variations in the number of temperature anomalies, where higher numbers correlated well with a gaining reach identified by stream gauging. Focused zones of groundwater discharge showed essentially no change in position over successive measurement periods. Results suggest DTS measurements will complement other techniques (e.g., seepage meters and stream gauging) and help further improve our understanding of groundwater–surface water dynamics in wetland streams.

Water Resources Research↗
USGS2008

Dating groundwater with trifluoromethyl sulfurpentafluoride (SF 5CF3), sulfur hexafluoride (SF6), CF 3Cl (CFC-13), and CF2Cl2 (CFC-12)

[1] A new groundwater dating procedure using the transient atmospheric signal of the environmental tracers SF5CF3, CFC-13, SF6, and CFC-12 was developed. The analytical procedure determines concentrations of the four tracers in air and water samples. SF 5CF3 and CFC-13 can be used to date groundwaters in some environments where the CFCs and SF6 have previously failed because these new tracers have increasing atmospheric input functions, no known terrigenic source, and are believed to be stable under reducing conditions. SF5CF3 has a dating range from 1970 to modern; the mixing ratio (mole fraction) in North American air has increased from the detection limit of 0.005 parts per trillion (ppt) to the 2006 mole fraction of about 0.16 ppt. No evidence was found for degradation of SF5CF3 in laboratory anaerobic systems. The solubility of SF5CF3 was measured in water from 1 to 35??C. Groundwater samples that contained large amounts of terrigenic SF6 did not contain terrigenic SF 5CF3. CFC-13 is a trace atmospheric gas with a dating range in groundwater of about 1965 to modem. CFC-13 has been used primarily in very low-temperature refrigeration; thus groundwater environments are less likely to be contaminated with nonatmospheric sources as compared to other widely used CFCs. Because of the low solubility of SF5CF3 and CFC-13 in water, an excess air correction must be applied to the apparent ages. The new dating procedure was tested in water samples from wells and springs from Maryland, Virginia, and West Virginia.

Water Resources Research↗
USGS2008

Influence of perched groundwater on base flow

Analysis with a three‐dimensional variably saturated groundwater flow model provides a basic understanding of the interplay between streams and perched groundwater. A simplified, layered model of heterogeneity was used to explore these relationships. Base flow contribution from perched groundwater was evaluated with regard to varying hydrogeologic conditions, including the size and location of the fine‐sediment unit and the hydraulic conductivity of the fine‐sediment unit and surrounding coarser sediment. Simulated base flow was sustained by perched groundwater with a maximum monthly discharge in excess of 15 L/s (0.6 feet 3 /s) over the length of the 2000‐m stream reach. Generally, the rate of perched‐groundwater discharge to the stream was proportional to the hydraulic conductivity of sediment surrounding the stream, whereas the duration of discharge was proportional to the hydraulic conductivity of the fine‐sediment unit. Other aspects of the perched aquifer affected base flow, such as the depth of stream penetration and the size of the fine‐sediment unit. Greater stream penetration decreased the maximum base flow contribution but increased the duration of contribution. Perched groundwater provided water for riparian vegetation at the demand rate but reduced the duration of perched‐groundwater discharge nearly 75%.

Water Resources Research↗
USGS2008

Source and transport controls on the movement of nitrate to public supply wells in selected principal aquifers of the United States

In 2003–2005, systematic studies in four contrasting hydrogeologic settings were undertaken to improve understanding of source and transport controls on nitrate movement to public supply wells (PSW) in principal aquifers of the United States. Chemical, isotopic, and age tracer data show that agricultural fertilizers and urban septic leachate were the primary sources of large nitrate concentrations in PSW capture zones at Modesto, California (Central Valley aquifer system) and York, Nebraska (High Plains aquifer). Urban septic leachate and fertilizer (possibly nonfarm) were the primary sources of large nitrate concentrations in PSW capture zones at Woodbury, Connecticut (glacial aquifer system), and Tampa, Florida (Floridan aquifer system), respectively. Nitrate fluxes to the water table were larger in agricultural settings than urban settings, indicating that it would be beneficial to reduce PSW capture zone areas in agricultural regions. Mixing calculations indicate that about 50 to 85% of the nitrate in water from the PSW could be from those modern anthropogenic sources, with the remainder coming from sources in old (>50 years) recharge or sources in young recharge in undisturbed settings such as forests. Excess N 2 concentrations and age tracers showed that denitrification at Modesto occurred gradually (first‐order rate constant of 0.02/a) in a thick reaction zone following a ∼30‐year lag time after recharge. Denitrification generally was not an important nitrate sink at Woodbury. At York and Tampa, denitrification occurred rapidly (0.5 to 6/a) in thin reaction zones in fine‐grained sediments that separated the anoxic PSW producing zones from overlying oxic, high‐nitrate ground water. Particle tracking showed that a major pathway by which anthropogenic nitrate reached the York and Tampa PSW was by movement through long well screens crossing multiple hydrogeologic units (York) and by movement through karst features (Tampa), processes which reduced ground water residence times in the denitrifying zones. These results illustrate how PSW vulnerability to nitrate contamination depends on complex variations and interactions between contaminant sources, reaction rates, transit times, mixing, and perturbation of ground water flow in contrasting hydrogeologic settings.

Water Resources Research↗
USGS2008

Advection, dispersion, and filtration of fine particles within emergent vegetation of the Florida Everglades

The movement of particulate matter within wetland surface waters affects nutrient cycling, contaminant mobility, and the evolution of the wetland landscape. Despite the importance of particle transport in influencing wetland form and function, there are few data sets that illuminate, in a quantitative way, the transport behavior of particulate matter within surface waters containing emergent vegetation. We report observations from experiments on the transport of 1 ??m latex microspheres at a wetland field site located in Water Conservation Area 3A of the Florida Everglades. The experiments involved line source injections of particles inside two 4.8-m-long surface water flumes constructed within a transition zone between an Eleocharis slough and Cladium jamaicense ridge and within a Cladium jamaicense ridge. We compared the measurements of particle transport to calculations of two-dimensional advection-dispersion model that accounted for a linear increase in water velocities with elevation above the ground surface. The results of this analysis revealed that particle spreading by longitudinal and vertical dispersion was substantially greater in the ridge than within the transition zone and that particle capture by aquatic vegetation lowered surface water particle concentrations and, at least for the timescale of our experiments, could be represented as an irreversible, first-order kinetics process. We found generally good agreement between our field-based estimates of particle dispersion and water velocity and estimates determined from published theory, suggesting that the advective-dispersive transport of particulate matter within complex wetland environments can be approximated on the basis of measurable properties of the flow and aquatic vegetation. Copyright 2008 by the American Geophysical Union.

Water Resources Research↗
USGS2008

Rain‐induced subsurface airflow and Lisse effect

Water‐level increase after rainfall is usually indicative of rainfall recharge to groundwater. This, however, may not be true if the Lisse effect occurs. This effect represents the water‐level increase in a well driven by airflow induced by an advancing wetting front during highly intensive rains. The rainwater, which may behave like a low‐permeability lid, seals the ground surface so that the air pressure beneath the wetting front is increased because of air compression due to downward movement of the wetting front. A rapid and substantial rise of the water level in the well screened below water table, which bears no relationship to groundwater recharge, can be induced when various factors such as soil properties and the rain‐runoff condition combine favorably. A transient, three‐dimensional and variably saturated flow model was employed to study the air and groundwater flows in the soil under rain conditions. The objectives of this paper are two‐fold: to evaluate the reliability of the theory of the Lisse effect presented by Weeks to predict its magnitude in modeled situations that mimic the physical complexity of real aquifers, and to conduct parametric studies on the sensitivity of the water‐level rise in the well to soil properties and the rain event. The simulation results reveal that the magnitude of the Lisse effect increases with the ponding depth. Soil permeability plays a key role in generating the Lisse effect. The water‐level rise in the well is delayed relative to the air‐pressure rise in the unsaturated zone when the soil permeability is low, and the maximum water‐level rise is less than the maximum air pressure induced by rain infiltration. The simulation also explores the sensitivity of the Lisse effect to the van Genuchten parameters and the water table depth.

Water Resources Research↗
USGS2008

An exact solution for ideal dam-break floods on steep slopes

The shallow‐water equations are used to model the flow resulting from the sudden release of a finite volume of frictionless, incompressible fluid down a uniform slope of arbitrary inclination. The hodograph transformation and Riemann's method make it possible to transform the governing equations into a linear system and then deduce an exact analytical solution expressed in terms of readily evaluated integrals. Although the solution treats an idealized case never strictly realized in nature, it is uniquely well‐suited for testing the robustness and accuracy of numerical models used to model shallow‐water flows on steep slopes.

Water Resources Research↗