Stream-aquifer System Research Articles

Development of a Model for Simulation of Solute Transport in a Stream–Aquifer System

A model for simulation of solute transport in a dynamic stream–aquifer system is developed by integrating four existing sub-models. Interface packages are created to link the sub-models. The developed model is successfully used to simulate chloride transport in the stream–aquifer system of the Arkansas River and the Equus Beds Aquifer in Kansas and demonstrates that chloride concentration in the aquifer decreases in the vicinity of the simulated channel over time.

Hydraulics of Stream Flow Routing with Bank Storage

Bank storage is a process in which volumes of water are temporarily retained by alluvial stream banks during storm events and gradually released to partially sustain baseflow. This process has important hydrologic and ecological implications. In this paper, analytical solutions are developed for routing stream flow, lateral stream-aquifer interactions, and aquifer storage. In effect, the streamflow routing Muskingum method is modified for bank storage. The analysis is based on one-dimensional lateral groundwater flow in semiinfinite homogeneous unconfined aquifers, which are in contact with streams through semipervious bed sediments. Impulse response and unit step response functions are derived for the stream-aquifer system, using Laplace transformations. These response functions relate stream outflow, stream-aquifer flow, bank storage, and cumulative reach discharge volume to discrete-time inflow hydrographs through convolution integrals. The impulse response function decreases with increasing aquifer hydraulic conductivity at earlier times, but increases with the conductivity and persists at later times. The unit step response function decreases with aquifer conductivity uniformly in time. The dependence of stream flow and bank storage on aquifer hydraulic conductivity, streambed leakance, stream width, and aquifer diffusivity is investigated. The analysis is extended to discrete input data, and modification of the methodology to route discrete-time inflow hydrographs of general form is achieved, using discrete-time kernels. The presented analysis establishes the time domain for validity of the analytical solutions in terms of the Muskingum parameters and an aquifer-related parameter.

Drawdown and stream depletion produced by pumping in the vicinity of a partially penetrating stream.

Commonly used analytical approaches for estimation of pumping-induced drawdown and stream depletion are based on a series of idealistic assumptions about the stream-aquifer system. A new solution has been developed for estimation of drawdown and stream depletion under conditions that are more representative of those in natural systems (finite width stream of shallow penetration adjoining an aquifer of limited lateral extent). This solution shows that the conventional assumption of a fully penetrating stream will lead to a significant overestimation of stream depletion (> 100%) in many practical applications. The degree of overestimation will depend on the value of the stream leakance parameter and the distance from the pumping well to the stream. Although leakance will increase with stream width, a very wide stream will not necessarily be well represented by a model of a fully penetrating stream. The impact of lateral boundaries depends upon the distance from the pumping well to the stream and the stream leakance parameter. In most cases, aquifer width must be on the order of hundreds of stream widths before the assumption of a laterally infinite aquifer is appropriate for stream-depletion calculations. An important assumption underlying this solution is that stream-channel penetration is negligible relative to aquifer thickness. However, an approximate extension to the case of nonnegligible penetration provides reasonable results for the range of relative penetrations found in most natural systems (up to 85%). Since this solution allows consideration of a much wider range of conditions than existing analytical approaches, it could prove to be a valuable new tool for water management design and water rights adjudication purposes.

STREAMFLOW DEPLETION: MODELING OF REDUCED BASEFLOW ANI INDUCED STREAM INFILTRATION FROM SEASONALLY PUMPED WELLS1

ABSTRACT: Numerical modeling techniques are used to analyze streamflow depletion for stream‐aquifer systems with baseflow. The analyses calculated two flow components generated by a pumping well located at a given distance from a river that is hydraulically connected to an unconfined aquifer. The two components are induced stream infiltration and reduced baseflow; both contribute to total streamflow depletion. Simulation results suggest that the induced infiltration, the volume of water discharged from the stream to the aquifer, has a shorter term impact on streamflow, while the reduced baseflow curves show a longer term effect. The peak impacts of the two hydrologic processes on streamflow occur separately. The separate analysis helps in understanding the hydrologic interactions between stream and aquifer. Practically, it provides useful information about contaminant transport from stream to aquifer when water quality is a concern, and for areas where water quantity is an issue, the separate analysis offers additional information to the development of water resource management plan.

Aquifer response to stream-stage and recharge variations. II. Convolution method and applications

In this second of two papers, analytical step-response functions, developed in the companion paper for several cases of transient hydraulic interaction between a fully penetrating stream and a confined, leaky, or water-table aquifer, are used in the convolution integral to calculate aquifer heads, streambank seepage rates, and bank storage that occur in response to stream-stage fluctuations and basinwide recharge or evapotranspiration. Two computer programs developed on the basis of these step-response functions and the convolution integral are applied to the analysis of hydraulic interaction of two alluvial stream–aquifer systems in the northeastern and central United States. These applications demonstrate the utility of the analytical functions and computer programs for estimating aquifer and streambank hydraulic properties, recharge rates, streambank seepage rates, and bank storage. Analysis of the water-table aquifer adjacent to the Blackstone River in Massachusetts suggests that the very shallow depth of water table and associated thin unsaturated zone at the site cause the aquifer to behave like a confined aquifer (negligible specific yield). This finding is consistent with previous studies that have shown that the effective specific yield of an unconfined aquifer approaches zero when the capillary fringe, where sediment pores are saturated by tension, extends to land surface. Under this condition, the aquifer's response is determined by elastic storage only. Estimates of horizontal and vertical hydraulic conductivity, specific yield, specific storage, and recharge for a water-table aquifer adjacent to the Cedar River in eastern Iowa, determined by the use of analytical methods, are in close agreement with those estimated by use of a more complex, multilayer numerical model of the aquifer. Streambank leakance of the semipervious streambank materials also was estimated for the site. The streambank-leakance parameter may be considered to be a general (or lumped) parameter that accounts not only for the resistance of flow at the river–aquifer boundary, but also for the effects of partial penetration of the river and other near-stream flow phenomena not included in the theoretical development of the step-response functions.

Development of a Comprehensive Watershed Model Applied to Study Stream Yield under Drought Conditions

AbstractWe developed a model code to simulate a watershed's hydrology and the hydraulic response of an interconnected stream‐aquifer system, and applied the model code to the Lower Republican River Basin in Kansas. The model code links two well‐known computer programs: MODFLOW (modular 3‐D flow model), which simulates ground water flow and stream‐aquifer interaction; and SWAT (soil water assessment tool), a soil water budget simulator for an agricultural watershed. SWAT represents a basin as a collection of subbasins in terms of soil, land use, and weather data, and simulates each subbasin on a daily basis to determine runoff, percolation, evaporation, irrigation, pond seepage, and crop growth. Because SWAT applies a lumped hydrologic model to each sub‐basin, spatial heterogeneities with respect to factors such as soil type and land use are not resolved geographically, but can instead be represented statistically. For the Republican River Basin model, each combination of six soil types and three land uses, referred to as a hydrologic response unit (HRU), was simulated with a separate execution of SWAT. A spatially weighted average was then taken over these results for each hydrologic flux and time step by a separate program, SWBAVG. We wrote a package for MODFLOW to associate each subbasin with a subset of aquifer grid cells and stream reaches, and to distribute the hydrologic fluxes given for each subbasin by SWAT and SWBAVG over MODFLOW's stream‐aquifer grid to represent tributary flow, surface and ground water diversions, ground water recharge, and evapotranspiration from ground water. The Lower Republican River Basin model was calibrated with respect to measured ground water levels, streamflow, and reported irrigation water use. The model was used to examine the relative contributions of stream yield components and the impact on stream yield and base flow of administrative measures to restrict irrigation water use during droughts. Model results indicate that tributary flow is the dominant component of stream yield and that reduction of irrigation water use produces a corresponding increase in base flow and stream yield. However, the increase in stream yield resulting from reduced water use does not appear to be of sufficient magnitude to restore minimum desirable streamflows.

Integrated numerical modeling for basin-wide water management: The case of the Rattlesnake Creek basin in south-central Kansas

The objective of this article is to develop and implement a comprehensive computer model that is capable of simulating the surface-water, ground-water, and stream-aquifer interactions on a continuous basis for the Rattlesnake Creek basin in south-central Kansas. The model is to be used as a tool for evaluating long-term water-management strategies. The agriculturally-based watershed model SWAT and the ground-water model MODFLOW with stream-aquifer interaction routines, suitably modified, were linked into a comprehensive basin model known as SWATMOD. The hydrologic response unit concept was implemented to overcome the quasi-lumped nature of SWAT and represent the heterogeneity within each subbasin of the basin model. A graphical user-interface and a decision support system were also developed to evaluate scenarios involving manipulation of water rights and agricultural land uses on stream-aquifer system response. An extensive sensitivity analysis on model parameters was conducted, and model limitations and parameter uncertainties were emphasized. A combination of trial-and-error and inverse modeling techniques were employed to calibrate the model against multiple calibration targets of measured ground-water levels, streamflows, and reported irrigation amounts. The split-sample technique was employed for corroborating the calibrated model. The model was run for a 40 y historical simulation period, and a 40 y prediction period. A number of hypothetical management scenarios involving reductions and variations in withdrawal rates and patterns were simulated. The SWATMOD model was developed as a hydrologically rational low-flow model for analyzing, in a user-friendly manner, the conditions in the basin when there is a shortage of water.

Modeling CO 2 degassing and pH in a stream–aquifer system

Pinal Creek, Arizona receives an inflow of ground water with high dissolved inorganic carbon (57–75 mg/l) and low pH (5.8–6.3). There is an observed increase of in-stream pH from approximately 6.0–7.8 over the 3 km downstream of the point of groundwater inflow. We hypothesized that CO 2 gas-exchange was the most important factor causing the pH increase in this stream–aquifer system. An existing transport model, for coupled ground water–surface water systems (OTIS), was modified to include carbonate equilibria and CO 2 degassing, used to simulate alkalinity, total dissolved inorganic carbon ( C T), and pH in Pinal Creek. Because of the non-linear relation between pH and C T, the modified transport model used the numerical iteration method to solve the non-linearity. The transport model parameters were determined by the injection of two tracers, bromide and propane. The resulting simulations of alkalinity, C T and pH reproduced, without fitting, the overall trends in downstream concentrations. A multi-parametric sensitivity analysis (MPSA) was used to identify the relative sensitivities of the predictions to six of the physical and chemical parameters used in the transport model. MPSA results implied that C T and pH in stream water were controlled by the mixing of ground water with stream water and CO 2 degassing. The relative importance of these two processes varied spatially depending on the hydrologic conditions, such as stream flow velocity and whether a reach gained or lost stream water caused by the interaction with the ground water. The coupled transport model with CO 2 degassing and generalized sensitivity analysis presented in this study can be applied to evaluate carbon transport and pH in other coupled stream–ground water systems.

Seasonal variation in surface‐subsurface water exchange and lateral hyporheic area of two stream‐aquifer systems

We used two‐dimensional unconfined transient groundwater flow models to investigate the interface between stream and groundwater flow systems, or hyporheic zone, of two first‐order streams that drain catchments with distinctly different alluvial sediments and bedrock lithology. Particle tracking showed that lateral hyporheic area (planimetric area of flow paths lateral to the stream that are recharged by and return to the stream with travel times of 10 days or less) differed between the two study streams and varied with discharge within each system. At the Rio Calaveras (welded tuff), lateral hyporheic area ranged from 1.7 to 4 m2 over the annual cycle. In the Aspen Creek system (sandstone), lateral hyporheic area (1–1.5 m2) was restricted to roughly half of that observed at Rio Calaveras. The size of the hyporheic zone lateral to the streams at both sites decreased by approximately 50% during high flows. Sensitivity analyses indicated that changes in the hydraulic conductivity of alluvial and streambed sediments and variation in recharge rates have greatest impact on the magnitude, direction, and spatial distribution of stream‐groundwater exchange.

Denitrification and mixing in a stream—aquifer system: effects on nitrate loading to surface water

Ground water in terrace deposits of the South Platte River alluvial aquifer near Greeley, Colorado, USA, had a median nitrate concentration of 1857 μmol l −1. Median nitrate concentrations in ground water from adjacent floodplain deposits (468 μmol l −1) and riverbed sediments (461 μmol l −1), both of which are downgradient from the terrace deposits, were lower than the median concentration in the terrace deposits. The concentrations and δ 15N values of nitrate and N 2 in ground water indicated that denitrifying activity in the floodplain deposits and riverbed sediments accounted for 15–30% of the difference in nitrate concentrations. Concentrations of Cl − and SiO 2 indicated that mixing between river water and ground water in the floodplain deposits and riverbed sediments accounted for the remainder of the difference in nitrate concentrations. River flux measurements indicated that ground-water discharge in a 7.5 km segment of river had a nitrate load of 1718 kg N day − and accounted for about 18% of the total nitrate load in the river at the downstream end of that segment. This nitrate load was 70% less than the load predicted on the basis of the median nitrate concentration in the terrace deposits and assuming no denitrification or mixing in the aquifer. Water exchange between the river and aquifer caused ground water that originally discharged to the river to reenter denitrifying sediments in the riverbed and floodplain, thereby further decreasing the nitrate load in this stream—aquifer system. Results from this study indicated that denitrification and mixing within akluvial aquifer sediments may substantially decrease the nitrate load added to rivers by discharging ground water.

Hazardous wastes assessment, management, and minimization

Hazardous wastes assessment, management, and minimization

Calibrated models as management tools for stream-aquifer systems: the case of central Kansas, USA

We address the problem of declining streamflows in interconnected stream-aquifer systems and explore possible management options to address the problem for two areas of central Kansas: the Arkansas River valley from Kinsley to Great Bend and the lower Rattlesnake Creek-Quivira National Wildlife Refuge area. The approach we followed implements, calibrates, and partially validates for the study areas a stream-aquifer numerical model combined with a parameter estimation package and sensitivity analysis. Hydrologic budgets for both predevelopment and developed conditions indicate significant differences in the hydrologic components of the study areas resulting from development. The predevelopment water budgets give an estimate of natural ground-water recharge, whereas the budgets for developed conditions give an estimate of induced recharge, indicating that major ground-water development changes the recharge-discharge regime of the model areas with time. Such stream-aquifer models serve to link proposed actions to hydrologic effects, as is clearly demonstrated by the effects of various management alternatives on the streamflows of the Arkansas River and Rattlesnake Creek. Thus we show that a possible means of restoring specified streamflows in the area is to implement protective stream corridors with restricted ground-water extraction.

On the relationship between river-basin geomorphology, aquifer hydraulics, and ground-water flow direction in alluvial aquifers

The delineation of ground-water flow in alluvial valley stream-aquifer systems is important in studies of water availability, environmental impact, and aquifer remediation and is required by some states' water laws. Published potentiometric surfaces and head data, however, are not always available. When data are absent, it is commonly assumed that ground water and dissolved solutes flow toward the river. Analysis of published geomorphologic and hydraulic data in 24 alluvial systems and the results of digital simulations indicate that in some cases this assumption is only valid immediately adjacent to an effluent river. Ground-water flow in the remaining portions of an alluvial valley aquifer may be dominated by downstream or underflow components. This paper investigates the nature of ground-water flow in alluvial valleys and presents a new classification scheme for alluvial aquifers. The geomorphologic conditions that may allow underflow to be the predominant regional ground-water flow component are described. In order to classify alluvial aquifers, two Darcy flux end-member components are defined. The baseflow component is that portion of the ground-water flux that moves perpendicular to the river. The baseflow component may flow toward the river or away from the river depending on whether the river is effluent or influent, respectively. The underflow component of the Darcy flux moves parallel to the river and in the same direction as the stream flow. The alluvial stream-aquifer systems are classified based on the predominant regional ground-water flow component as underflow-component dominated, baseflow-component dominated, or mixed. On the basis of the results of this study, we conclude that the dominant regional ground-water flow component, base-flow or underflow, can be inferred in an alluvial valley aquifer from geomorphologic data. These data include the channel slope, the river sinuosity, the degree of penetration (incision through the alluvium) of the river, the width-to-depth ratio, and the fluvial depositional system. The underflow component is demonstrably predominant when the following conditions exist: (1) the channel gradient exceeds .0008, (2) the sinuosity is less than 1.3, (3) the river penetration is less than 20%, (4) the width-to-depth ratio is greater than 60, and (5) the fluvial depositional system is either valley fill or mixed load to bed-load. The underflow component can also be dominant on flood plains where the lateral valley slope is negligible.

Benefits of an irrigation water rental market in a saline stream‐aquifer system

The hydrologic and economic effects of a water market are evaluated for an irrigated, stream‐aquifer system. In the hypothetical rental market, surface water is traded annually among farmers, while ground water is used to augment irrigation supplies. Market simulations account for changes in the value of groundwater and surface water due to salinity differences. Results show that the market increases long‐term profit for all participants, reduces the risk of loss due to drought, and decreases average short‐term groundwater salinity. The market becomes active during dry years, when farmers without groundwater rights buy surface water from farmers with groundwater rights, who increase pumping to replace sold surface water. Under the rental market the distribution of additional profits partially depends on the pumping costs and higher salinity associated with increased groundwater use. Farmers reduce risk without sacrificing profit, by utilizing higher rates of groundwater pumping to mitigate drought damage. Increased withdrawals may diminish irrigation supplies for downstream users.

Simulating physical processes and economic behavior in saline, irrigated agriculture: model development

A model of an irrigated, saline stream‐aquifer system is constructed to simulate economic, agronomic, and hydrologic processes. The model is applied to a section of the Arkansas Valley in southeastern Colorado and is used to examine the effect of crop‐mixing strategies on long‐term profits. Mixing in excess of crop rotation requirements provides an index of farmers' willingness to exchange some profit for a reduction in the risk of short‐term loss. The model contains three components. The economic component simulates water use decisions that maximize annual profit for each farm. The hydrologic component simulates salt transport by employing regression equations that predict changes in groundwater salinity as a function of hydrologic conditions and water use decisions. The agronomic component approximates changes in corn and alfalfa production in response to the depth and salinity of irrigation applications. Results from the entire economic‐hydrologic‐agronomic model are consistent with the few historical observations available for the site.

An Indirect Method for Determination of the Parameters of Flood Plain Aquifers

An indirect method of determining flood plain aquifer parameters from estimated autocorrelation of groundwater table data is presented. For this purpose a stream-aquifer system is approximated by a cascade of linear reservoirs. The response of groundwater piezometric head to an arbitrarily varying flood pulse in the river is given by the convolution equation. The autocorrelation function of groundwater piezometric head is expressed as a function of the parameters of the aquifer and the autocorrelation function of the water stage in the river. Observations performed in Gaupne in western Norway are used to determine the parameters of a flood plain aquifer.

Recalibration and predictive reliability of a solute-transport model of an irrigated stream-aquifer system

A solute-transport model of an irrigated stream-aquifer system was recalibrated because of discrepancies between prior predictions of ground-water salinity trends during 1971–1982 and the observed outcome in February 1982. The original model was calibrated with a 1-year record of data collected during 1971–1972 in an 18-km reach of the Arkansas River Valley in southeastern Colorado. The model is improved by incorporating additional hydrologic processes (salt transport through the unsaturated zone) and through reexamination of the reliability of some input data (regression relationship used to estimate salinity from specific conductance data). Extended simulations using the recalibrated model are made to investigate the usefulness of the model for predicting long-term trends of salinity and water levels within the study area. Predicted ground-water levels during 1971–1982 are in good agreement with the observed, indicating that the original 1971–1972 study period was sufficient to calibrate the flow model. However, long-term simulations using the recalibrated model based on recycling the 1971–1972 data alone yield an average ground-water salinity for 1982 that is too low by about 10%. Simulations that incorporate observed surface-water salinity variations yield better results, in that the calculated average ground-water salinity for 1982 is within 3% of the observed value. Statistical analysis of temporal salinity variations of the applied surface water indicates that at least a 4-year sampling period is needed to accurately calibrate the transport model.

A discrete kernel simulation model for conjunctive management of a stream—Aquifer system

A stream—aquifer simulation model was developed to conduct a conjunctive use management study in the South Platte River in Colorado. This model simulates both the physical and operational behavior of the system. The physical system modeled is comprised of the river and the saturated and unsaturated zones of the aquifer. A technique referred to as the “discrete kernel approach” was used to model the saturated zone of the aquifer. This technique is based on the classical Green's function method of solution of partial differential equations. The physical simulator was coupled to an allocation model which simulates the operational behavior of the system. The management model was applied to conduct a conjunctive use study involving the evaluation of a stream flow augmentation scheme. A summary of the results of this case study is presented.

Modeling efficient water allocation in a conjunctive use regime: The Indus Basin of Pakistan

Efficient resource use where ground‐ and surface waters are used conjunctively may require special policies to rationalize the interaction between water use by farmers and the response of the stream aquifer system. In this paper, we examine alternative policies for achieving more efficient conjunctive use in the Indus Basin of Pakistan. Using a simulation model which links the hydrology of a conjunctive stream aquifer system to an economic model of agricultural production for each of 53 regions of the basin together with a network model of the flows in river reaches, link canals, and irrigation canals, we have studied the joint effect of various canal water allocation and associated private tube well tax or subsidy policies on overall system efficiency. The results suggest that large gains in agricultural production and employment are possible, given more efficient policies.

Ground‐Water Contamination Due to Transient Sources of Pollution

This paper presents simple analytical solutions to predict the temporal and spatial distribution of concentrations in one, two, or three‐dimensional fully saturated uniform flow fields caused by instantaneous or finite‐time release of contaminants from a point, line, plane, or parallelepiped source in an isotropic porous medium. The effects of the nonflux boundaries provided by bedrock, water table, or ground‐water divides are accounted for by the method of images. The same technique is used to model the contribution of a constant concentration boundary such as the one provided by a fully penetrating perennial stream. Sensitivity analyses show the effect of the number of images considered and the time‐step size used to evaluate the Duhamel integral. An example is presented to demonstrate the use of the method to analyze the distribution of concentrations due to seepage from an ashpond located in a streamaquifer system.