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

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At least 739 records · Page 41Linked to original sources
USGS1996

Direct simulation of groundwater age

A new method is proposed to simulate groundwater age directly, by use of an advection-dispersion transport equation with a distributed zero-order source of unit (1) strength, corresponding to the rate of aging. The dependent variable in the governing equation is the mean age, a mass-weighted average age. The governing equation is derived from residence-time-distribution concepts for the case of steady flow. For the more general case of transient flow, a transient governing equation for age is derived from mass-conservation principles applied to conceptual “age mass.” The age mass is the product of the water mass and its age, and age mass is assumed to be conserved during mixing. Boundary conditions include zero age mass flux across all noflow and inflow boundaries and no age mass dispersive flux across outflow boundaries. For transient-flow conditions, the initial distribution of age must be known. The solution of the governing transport equation yields the spatial distribution of the mean groundwater age and includes diffusion, dispersion, mixing, and exchange processes that typically are considered only through tracer-specific solute transport simulation. Traditional methods have relied on advective transport to predict point values of groundwater travel time and age. The proposed method retains the simplicity and tracer-independence of advection-only models, but incorporates the effects of dispersion and mixing on volume-averaged age. Example simulations of age in two idealized regional aquifer systems, one homogeneous and the other layered, demonstrate the agreement between the proposed method and traditional particle-tracking approaches and illustrate use of the proposed method to determine the effects of diffusion, dispersion, and mixing on groundwater age.

Water Resources Research↗
USGS1996

Modeling reservoir density underflow and interflow from a chemical spill

An integral simulation model has been developed for understanding and simulating the process of a density current and the transport of spilled chemicals in a stratified reservoir. The model is capable of describing flow behavior and mixing mechanisms in different flow regimes (plunging flow, underflow, and interflow). It computes flow rate, velocity, flow thickness, mixing parameterized by entrainment and dilution, depths of plunging, separation and intrusion, and time of travel. The model was applied to the Shasta Reservoir in northern California during the July 1991 Sacramento River chemical spill. The simulations were used to assist in the emergency response, confirm remediation measures, and guide data collection. Spill data that were available after the emergency response are used to conduct a postaudit of the model results. Predicted flow parameters are presented and compared with observed interflow intrusion depth, travel time, and measured concentrations of spilled chemicals. In the reservoir, temperature difference between incoming river flow and ambient lake water played a dominant role during the processes of flow plunging, separation, and intrusion. With the integral approach, the gross flow behavior can be adequately described and information useful in the analysis of contaminated flow in a reservoir after a spill is provided.

Water Resources Research↗
USGS1996

Groundwater inflow measurements in wetland systems

Our current understanding of wetlands is insufficient to assess the effects of past and future wetland loss. While knowledge of wetland hydrology is crucial, groundwater flows are often neglected or uncertain. In this paper, groundwater inflows were estimated in wetlands in southwestern Wisconsin using traditional Darcy's law calculations and three independent methods that included (1) stable isotope mass balances, (2) temperature profile modeling, and (3) numerical water balance modeling techniques. Inflows calculated using Darcy's law were lower than inflows estimated using the other approaches and ranged from 0.02 to 0.3 cm/d. Estimates obtained using the other methods generally were higher (0.1 to 1.1 cm/d) and showed similar spatial trends. An areal map of groundwater flux generated by the water balance model demonstrated that areas of both recharge and discharge exist in what is considered a regional discharge area. While each method has strengths and weaknesses, the use of more than one method can reduce uncertainty in the estimates.

Water Resources Research↗
USGS1996

Nitrate in groundwater and water sources used by riparian trees in an agricultural watershed: A chemical and isotopic investigation in southern Minnesota

This study evaluates processes that affect nitrate concentrations in groundwater beneath riparian zones in an agricultural watershed. Nitrate pathways in the upper 2 m of groundwater were investigated beneath wooded and grass-shrub riparian zones next to cultivated fields. Because trees can be important components of the overall nitrate pathway in wooded riparian zones, water sources used by riparian trees and possible effects of trees on nitrate concentrations in groundwater were also investigated. Average nitrate concentrations in shallow groundwater beneath the cultivated fields were 5.5 mg/L upgradient of the wooded riparian zone and 3.5 mg/L upgradient of the grass-shrub zone. Shallow groundwater beneath the fields passed through the riparian zones and discharged into streams that had average nitrate concentrations of 8.5 mg/L (as N). Lateral variations of δD values in groundwater showed that mixing among different water sources occurred beneath the riparian zones. In the wooded riparian zone, nitrate concentrations in shallow groundwater were diluted by upwelling, nitrate-poor, deep groundwater. Upwelling deep groundwater contained ammonium with a δ 15 N of 5‰ that upon nitrification and mixing with nitrate in shallow groundwater caused nitrate δ 15 N values in shallow groundwater to decrease by as much as 19.5‰. Stream water penetrated laterally beneath the wooded riparian zone as far as 19 m from the stream's edge and beneath the grass-shrub zone as far as 27 m from the stream's edge. Nitrate concentrations in shallow groundwater immediately upgradient of where it mixed with stream water averaged 0.4 mg/L in the wooded riparian zone and 0.8 mg/L near the grass-shrub riparian zone. Nitrate concentrations increased toward the streams because of mixing with nitrate-rich stream water. Because nitrate concentrations were larger in stream water than shallow groundwater, concentrated nitrate in the streams cannot have come from shallow groundwater at these sites. Water sources of riparian trees were identified by comparing δD values of sap water, soil water, groundwater, and stream water. Soil water was the main water source for trees in the outer 4 to 6 m of one part of the wooded riparian zone and outer 10 m of another part. Groundwater was a significant water source for trees closer to the streams where the water table was less than about 2.1 to 2.7 m below the surface. No evidence was found in the nitrate concentration profiles that trees close to the streams that took up groundwater through their roots also took up nitrate from groundwater. The lack of such evidence is attributed to the nitrate concentration profiles being insufficiently sensitive indicators of nitrate removal by trees.

Minnesota↗
USGS1997

The travel times of solutes at the Cape Cod Tracer Experiment: Data analysis, modeling, and structural parameters inference

A method for analyzing and interpreting travel times of solutes in heterogeneous aquifers is presented based on the peak concentration arrival times as measured at various samplers in the aquifer. The method allows separation of the effects of pore-scale dispersion from the effects of the large-scale aquifer heterogeneity. An analysis of data from the Cape Cod field experiment is presented, and we found that the values of the hydrogeological parameters inferred from the travel times match very well the values obtained from direct interpretation of cores. Analysis of the spatial correlations of the travel times also allows inference of spatial covariances of the log conductivity and the anisotropy ratio of the correlation lengths. Separate analyses of the travel times carried over planes at different travel distances show that the variance of the log conductivity increases with travel distance.

Massachusetts↗
USGS1996

Age dating of shallow groundwater with chlorofluorocarbons, tritium/helium: 3, and flow path analysis, southern New Jersey coastal plain

Groundwater age dating through the combination of transient tracer methods (chlorofluorocarbons (CFCs) and tritium/helium 3 ( 3 H/ 3 He)) and groundwater flow path analysis is useful for investigating groundwater travel times, flow patterns, and recharge rates, as demonstrated by this study of the homogeneous shallow, unconfined Kirkwood-Cohansey aquifer system in the southern New Jersey coastal plain. Water samples for age dating were collected from three sets of nested observation wells (10 wells) with 1.5-m-long screens located near groundwater divides. Three steady state finite difference groundwater flow models were calibrated by adjusting horizontal and vertical hydraulic conductivities to match measured heads and head differences (range, 0.002–0.23 m) among the nested wells, with a uniform recharge rate of 0.46 m per year and porosities of 0.35 (sand) and 0.45 (silt) that were assumed constant for all model simulations and travel time calculations. The simulated groundwater travel times increase with depth in the aquifer, ranging from about 1.5 to 6.5 years for the shallow wells (screen bottoms 3–4 m below the water table), from about 10 to 25 years for the medium-depth wells (screen bottoms 8–19 m below the water table), and from about 30 to more than 40 years for the deep wells (screen bottoms 24–26 m below the water table). Apparent groundwater ages based on CFC- and 3 H/ 3 He-dating techniques and model-based travel times could not be statistically differentiated, and all were strongly correlated with depth. Confinement of 3He was high because of the rapid vertical flow velocity (of the order of 1 m/yr), resulting in clear delineation of groundwater travel times based on the 3 H/ 3 He-dating technique. The correspondence between the 3 H/ 3 He and CFC ages indicates that dispersion has had a minimal effect on the tracer-based ages of water in this aquifer. Differences between the tracer-based apparent ages for seven of the 10 samples were smaller than the error values. A slight bias toward older apparent ages, found not to be statistically significant, was noted for the 3 H/ 3 He-dating technique relative to the CFC-dating technique. This result may be caused by enrichment of local air in CFC-Il and CFC-12 from urban and industrial sources in the northeastern United States and minor contamination from sampling equipment. The demonstrated validity of the combined tracer-dating techniques to determine the age of water in the Kirkwood-Cohansey aquifer system indicates that groundwater flow models can be refined when apparent ages based on 3 H/ 3 He- and CFC- dating are used as calibration targets.

New Jersey↗
USGS1996

Identification of hydraulic conductivity structure in sand and gravel aquifers: Cape Cod data set

This study evaluates commonly used geostatistical methods to assess reproduction of hydraulic conductivity (K) structure and sensitivity under limiting amounts of data. Extensive conductivity measurements from the Cape Cod sand and gravel aquifer are used to evaluate two geostatistical estimation methods, conditional mean as an estimate and ordinary kriging, and two stochastic simulation methods, simulated annealing and sequential Gaussian simulation. Our results indicate that for relatively homogeneous sand and gravel aquifers such as the Cape Cod aquifer, neither estimation methods nor stochastic simulation methods give highly accurate point predictions of hydraulic conductivity despite the high density of collected data. Although the stochastic simulation methods yielded higher errors than the estimation methods, the stochastic simulation methods yielded better reproduction of the measured In (K) distribution and better reproduction of local contrasts in In (K). The inability of kriging to reproduce high In (K) values, as reaffirmed by this study, provides a strong instigation for choosing stochastic simulation methods to generate conductivity fields when performing fine-scale contaminant transport modeling. Results also indicate that estimation error is relatively insensitive to the number of hydraulic conductivity measurements so long as more than a threshold number of data are used to condition the realizations. This threshold occurs for the Cape Cod site when there are approximately three conductivity measurements per integral volume. The lack of improvement with additional data suggests that although fine-scale hydraulic conductivity structure is evident in the variogram, it is not accurately reproduced by geostatistical estimation methods. If the Cape Cod aquifer spatial conductivity characteristics are indicative of other sand and gravel deposits, then the results on predictive error versus data collection obtained here have significant practical consequences for site characterization. Heavily sampled sand and gravel aquifers, such as Cape Cod and Borden, may have large amounts of redundant data, while in more common real world settings, our results suggest that denser data collection will likely improve understanding of permeability structure.

Water Resources Research↗
USGS2010

Inferring shallow groundwater flow in saprolite and fractured rock using environmental tracers

The Ridge and Valley Province of eastern Tennessee is characterized by (1) substantial topographic relief, (2) folded and highly fractured rocks of various lithologies that have low primary permeability and porosity, and (3) a shallow residuum of medium permeability and high total porosity. Conceptual models of shallow groundwater flow and solute transport in this system have been developed but are difficult to evaluate using physical characterization or short‐term tracer methods due to extreme spatial variability in hydraulic properties. In this paper we describe how chlorofluorocarbon 12, 3 H, and 3 He were used to infer groundwater flow and solute transport in saprolite and fractured rock near Oak Ridge, Tennessee. In the shallow residuum, fracture spacings are <0.05 m, suggesting that concentrations of these tracers in fractures and in the matrix have time to diffusionally equilibrate. The relatively smooth nature of tracer concentrations with depth in the residuum is consistent with this model and quantitatively suggests recharge fluxes of 0.2 to 0.4 m yr −1 . In contrast, groundwater flow within the unweathered rock appears to be controlled by fractures with spacings of the order of 2 to 5 m, and diffusional equilibration of fractures and matrix has not occurred. For this reason, vertical fluid fluxes in the unweathered rock cannot be estimated from the tracer data.

Water Resources Research↗
USGS1996

Evaluating the reliability of the stream tracer approach to characterize stream-subsurface water exchange

Stream water was locally recharged into shallow groundwater flow paths that returned to the stream (hyporheic exchange) in St. Kevin Gulch, a Rocky Mountain stream in Colorado contaminated by acid mine drainage. Two approaches were used to characterize hyporheic exchange: sub-reach-scale measurement of hydraulic heads and hydraulic conductivity to compute streambed fluxes (hydrometric approach) and reachscale modeling of in-stream solute tracer injections to determine characteristic length and timescales of exchange with storage zones (stream tracer approach). Subsurface data were the standard of comparison used to evaluate the reliability of the stream tracer approach to characterize hyporheic exchange. The reach-averaged hyporheic exchange flux (1.5 mL s −1 m −1 ), determined by hydrometric methods, was largest when stream base flow was low (10 L s −1 ); hyporheic exchange persisted when base flow was 10-fold higher, decreasing by approximately 30%. Reliability of the stream tracer approach to detect hyporheic exchange was assessed using first-order uncertainty analysis that considered model parameter sensitivity. The stream tracer approach did not reliably characterize hyporheic exchange at high base flow: the model was apparently more sensitive to exchange with surface water storage zones than with the hyporheic zone. At low base flow the stream tracer approach reliably characterized exchange between the stream and gravel streambed (timescale of hours) but was relatively insensitive to slower exchange with deeper alluvium (timescale of tens of hours) that was detected by subsurface measurements. The stream tracer approach was therefore not equally sensitive to all timescales of hyporheic exchange. We conclude that while the stream tracer approach is an efficient means to characterize surface-subsurface exchange, future studies will need to more routinely consider decreasing sensitivities of tracer methods at higher base flow and a potential bias toward characterizing only a fast component of hyporheic exchange. Stream tracer models with multiple rate constants to consider both fast exchange with streambed gravel and slower exchange with deeper alluvium appear to be warranted.

Water Resources Research↗
USGS1996

Subsidence of agricultural lands in the Sacramento‐San Joaquin Delta, California: Role of aqueous and gaseous carbon fluxes

To examine the causes of land subsidence on marshes drained for agriculture, carbon fluxes and changes in land‐surface elevation were determined on three islands in the Sacramento‐San Joaquin Delta, California. Over the time period of March 1990 to May 1992, gaseous CO 2 fluxes were determined approximately monthly using closed chambers, and dissolved carbon fluxes were determined from the dissolved carbon loads of drainage ditches adjacent to each field site. Surface elevation changes were measured continuously by measuring the distance between the land surface and an elevated structure anchored beneath the organic soil layer. Gaseous CO 2 fluxes accounted for most of the permanent subsidence measured over the monitoring period. Gaseous CO 2 fluxes are strongly affected by soil temperature. Net subsidence rates for the three islands, which have different depths of organic soils and water‐management practices, range from 0.46 to 1.06 cm/yr. Estimates of dissolved organic carbon fluxes for all three islands were small relative to gaseous CO 2 losses and represent <1% of the measured subsidence.

California↗
USGS1996

Analysis of nitrate in near-surface aquifers in the midcontinental United States: An application of the inverse hyperbolic sine Tobit model

A nonnormal and heteroscedastic Tobit model is used to determine the primary factors that affect nitrate concentrations in near-surface aquifers, using data from the U.S. Geological Survey collected in 1991. Both normality and homoscedasticity of errors are rejected, justifying the use of a nonnormal and heteroscedastic model. The following factors are found to have significant impacts on nitrate concentrations in groundwater: well screen interval, depth to top of aquifers, percentages of urban residential, forest land, and pasture within 3.2 km, dissolved oxygen concentration level, and presence of a chemical facility and feedlot. The effects of explanatory variables on nitrate concentration are explored further by calculating elasticities. Dissolved oxygen concentration level has more notable effects on nitrate concentrations in groundwater than other variables.

Water Resources Research↗
USGS1996

Mineral nitrogen transformations in and under seasonal snow in a high-elevation catchment in the Rocky Mountains, United States

In an effort to understand sources of nitrate (NO 3 − ) in surface waters of high-elevation catchments, nitrogen (N) transformations in and under seasonal snow were investigated from 1993 to 1995 on Niwot Ridge, an alpine ecosystem at 3,500 m located in the Colorado Front Range of the Rocky Mountains. Ammonium (NH 4 + ) and NO 3 − labeled with 15 N applied as nonconservative tracers to the snow showed no evidence of nitrification in the snowpack. Furthermore, NH 4 + movement through the amended snowpack was highly correlated with a conservative chloride tracer ( r 2 = 0.99). In an unamended snowpack NH 4 + concentrations in meltwater before contact with the ground were highly correlated with NO 3 − concentrations ( r 2 = 0.98), which is consistent with no nitrification in the snowpack. The isotopically labeled 15 NH + 4 applied to the snowpack was found in underlying soils, showing that NH 4 + released from snow can be rapidly immobilized. Resin bag (mixed-bed ion-exchange resins) measurements (n = 22) showed that 80% of the mobile inorganic N in unamended subnivial soils was NO 3 − . Measurements of KCl-extractable inorganic N from surface soils showed that highest values were prior to the initiation of snowmelt and lowest values were during the growing season. The natural δ 15 N abundance of unamended soils was negative and ranged from −12 to −2, suggesting that atmospheric deposition of δ 15 N-depleted N is an important component of N cycling in these alpine soils. These results suggest that soil mineralization under seasonal snow, rather than snowmelt release of NO 3 − , may control NO 3 − concentrations in surface waters of high-elevation catchments.

Water Resources Research↗
USGS1997

Analysis of the Cape Cod tracer data

An analysis of the Cape Cod test was performed using several first- and higher-order theoretical models. We compare conditional and unconditional solutions of the transport equation and employ them for analysis of the experimental data. We consider spatial moments, mass breakthrough curves, and the distribution of the solute mass in space. The concentration measurements were also analyzed using theoretical models for the expected value and variance of concentration. The theoretical models we employed are based on the spatial correlation structure of the conductivity field, without any fitting of parameters to the tracer data, and hence we can test the predictive power of the theories tested. The effects of recharge on macrodispersion are investigated, and it is shown that recharge provides a reasonable explanation for the enhanced lateral spread of the Cape Cod plume. The compendium of the experimental results presented here is useful for testing of theoretical and numerical models.

Water Resources Research↗
USGS1997

Effects of solution mining of salt on wetland hydrology as inferred from tree rings

Radial growth and concentrations of selected elements within rings were studied in white pine ( Pinus strobus ) trees from a wetland in central New York approximately 5 km north of a salt-solution mining field that operated from 1889 to 1988. Trees seemingly document three sequential episodes of mine-induced alterations of groundwater discharge irrigating the wetland during the 100-year period. The radial growth of trees established before the onset of mining declined abruptly in the early 1890s and remained suppressed until about 1960, as did growth of numerous other trees that became established after the onset of mining. Suppressed pre-1960 radial growth coincided with the interval that surface water was injected into the saltbeds, suggesting that losses of injected water to the bedrock and/or unconsolidated deposits increased groundwater flow into the wetland. An abrupt and sustained enhancement of radial growth beginning about 1960 indicates that the wetland became drier, and thus more conducive to tree growth, when injection practices were discontinued in the late 1950s despite the continued pumping of brine. Following the cessation of mining in the late 1980s, head pressures again increased in the upper valley, driving chloride-enriched flow northward along regional bedding-plane fractures and into the wetland. Large concentrations of chloride were detected within the most recently formed rings of some trees. As the result of chloride-enriched irrigation, the radial growth of some trees declined, and some trees died. Thus trees have preserved evidence of a century of hydrologic alterations, unobtainable by other means, where the effects of brine mining have not been documented previously.

Water Resources Research↗
USGS1997

Deep well injection of brine from Paradox Valley, Colorado: Potential major precipitation problems remediated by nanofiltration

Groundwater brine seepage into the Dolores River in Paradox Valley, Colorado, increases the dissolved solids load of the Colorado River annually by ∼2.0 × 10 8 kg. To abate this natural contamination, the Bureau of Reclamation plans to pump ∼3540 m 3 /d of brine from 12 shallow wells located along the Dolores River. The brine, with a salinity of 250,000 mg/L, will be piped to the deepest (4.9 km) disposal well in the world and injected mainly into the Mississippian Leadville Limestone. Geochemical modeling indicates, and water-rock experiments confirm, that a huge mass of anhydrite (∼1.0 × 10 4 kg/d) likely will precipitate from the injected brine at downhole conditions of 120°C and 500 bars. Anhydrite precipitation could increase by up to 3 times if the injected brine is allowed to mix with the highly incompatible formation water of the Leadville Limestone and if the Mg in this brine dolomitizes the calcite of the aquifer. Laboratory experiments demonstrate that nanofiltration membranes, which are selective to divalent anions, provide a new technology that remediates the precipitation problem by removing ∼98% of dissolved SO 4 from the hypersaline brine. The fluid pressure used (50 bars) is much lower than would be required for traditional reverse osmosis membranes because nanofiltration membranes have a low rejection efficiency (5–10%) for monovalent anions. Our results indicate that the proportion of treatable brine increases from ∼60% to >85% with the addition of trace concentrations of a precipitation inhibitor and by blending the raw brine with the effluent stream.

Water Resources Research↗
USGS1997

Regional streamflow regimes and hydroclimatology of the United States

The dominant regions of interannual streamflow variability in the United States are defined, and their seasonality and persistence characteristics identified, using an orthogonally rotated principal components analysis (RPCA) of a climatically sensitive network of 559 stream gages for the period 1941–1988. This classification of streamflow regimes is comprehensive and unique in that separate analyses of the streamflow record, for each month of the year, are carried out to detail the month-to-month changes in the dominant streamflow patterns. Streamflow variations, or anomalies, in the Upper Mississippi, South Atlantic/Gulf, Far West, Ohio Valley, Northeast, and Eastern/Mid- Atlantic regions, as well as a pattern of opposing streamflow anomalies in the West, are observed in all seasons of the year. Anomalies in the Southern Plains and New England regions are observed in autumn, winter, and spring; those in the Rocky Mountains and Middle Mississippi regions occur in late spring and summer.

Water Resources Research↗
USGS1997

Strontium 87/strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine/subalpine watershed, Loch Vale, Colorado

Sr isotopic ratios of atmospheric deposition, surface and subsurface water, and geologic materials were measured in an alpine/subalpine watershed to characterize weathering reactions and identify sources of dissolved Ca in stream water. Previous studies have noted an excess of Ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals. Mixing calculations based on 87 Sr/ 86 Sr indicate that on an annual basis, 26 ± 7% of Ca export in streams is atmospherically derived, 23 ± 1% is from weathering of plagioclase, and the remainder is from weathering of calcite present in trace amounts in the bedrock. A potential source of error when applying Sr isotopes in catchment studies is determination of the 87 Sr/ 86 Sr of Sr released by mineral weathering, which is complicated by the wide range of mineral isotopic compositions, particularly in older rocks, and the variable rates at which the minerals weather. In this study, base-flow stream chemistry was used to represent the 87 Sr/ 86 Sr of Sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of Sr released by weathering in the alpine environment.

Colorado↗
USGS1997

Multiphase flow modeling of a crude-oil spill site with a bimodal permeability distribution

Fluid saturation, particle-size distribution, and porosity measurements were obtained from 269 core samples collected from six boreholes along a 90-m transect at a subregion of a crude-oil spill site, the north pool, near Bemidji, Minnesota. The oil saturation data, collected 11 years after the spill, showed an irregularly shaped oil body that appeared to be affected by sediment spatial variability. The particle-size distribution data were used to estimate the permeability ( k ) and retention curves for each sample. An additional 344 k estimates were obtained from samples previously collected at the north pool. The 613 k estimates were distributed bimodal lognormally with the two population distributions corresponding to the two predominant lithologies: a coarse glacial outwash deposit and fine-grained interbedded lenses. A two-step geostatistical approach was used to generate a conditioned realization of k representing the bimodal heterogeneity. A cross-sectional multiphase flow model was used to simulate the flow of oil and water in the presence of air along the north pool transect for an 11-year period. The inclusion of a representation of the bimodal aquifer heterogeneity was crucial for reproduction of general features of the observed oil body. If the bimodal heterogeneity was characterized, hysteresis did not have to be incorporated into the model because a hysteretic effect was produced by the sediment spatial variability. By revising the relative permeability functional relation, an improved reproduction of the observed oil saturation distribution was achieved. The inclusion of water table fluctuations in the model did not significantly affect the simulated oil saturation distribution.

Water Resources Research↗