bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic identification of transmissivity and effective recharge in steady groundwater flow: 1. Theory
Authors: Rubin Yoram , Dagan Gedeon
Published: February 2008

The study is a continuation and extension of a previous work (Dagan, 1985a) whose aim was to identify the values of the log‐transmissivity Y for steady flow. The common basic assumptions are that Y is a normal and stationary random space function, the aquifer is unbounded, and a first‐order approximation of the flow equation is adopted. The expected value of the water head H, as well as the Y unconditional autocovariance, are supposed to have analytical expressions which depend on a parameters vector θ. The proposed solution of the inverse problem consists of identifying θ with the aid of the model and of the measurements of Y and H and subsequently computing the statistical moments of Y conditioned on the same data, The additional features of the present study are (1) incorporation of a constant, but random, effective recharge and its identification and (2) accounting for the fact that θ estimation is associated with some uncertainty, whereas before θ was assumed to be identified with certainty. Analytical expressions are derived for the Y and H covariances for an exponential autocovariance of Y. Paper 2 (Rubin and Dagan, this issue) of the study illustrates the applications of the method to a real‐life case.
Regional underpressuring in Deep Brine Aquifers, Palo Duro Basin, Texas: 1. Effects of hydrostratigraphy and topography
Authors: Senger Rainer K. , Fogg Graham E.
Published: February 2008

Deep brine aquifers of the Palo Duro Basin, Texas Panhandle, ranging in depth from about 1000 to 3000 m below land surface, are underpressured compared with the shallow Ogallala aquifer. Two‐dimensional simulations of flow in an east‐west regional cross‐sectional model through the basin reveal the causes of underpressuring as well as mechanisms of groundwater circulation in the basin. The regional groundwater flow regime consists of a shallow flow system governed primarily by topography and a deeper flow system recharging in the New Mexico area and passing deep beneath the Pecos River into the deep brine aquifers of the Palo Duro Basin. The low‐permeability Evaporite aquitard limits flow between the shallow and deep systems, although leakage through the aquitard is important on a regional scale and could contribute a significant portion of water to the deep aquifers: Repeated simulations with the model demonstrate that chief causes of underpressuring are regional topography and geology. The elevated position of the Ogallala aquifer on the High Plains together with its segregation from the deep brine aquifers by the low‐permeability Evaporite aquitard creates an apparent underpressuring that is further accentuated by efficient drainage through the permeable granite wash deposits in the Deep‐Basin Brine aquifer. The Pecos River serves as a discharge area of some of the ground water from the west that would otherwise move downdip into the deep aquifers; thus capture of recharge water enhances underpressuring in the deep section beneath the western half of the High Plains.
Geochemical evolution of groundwater in stratified‐drift and arkosic bedrock aquifers in north central Connecticut
Authors: Rogers Robert J.
Published: February 2008

Groundwaters in both stratified‐drift and arkosic bedrock aquifers are dilute (dissolved solid concentration less than 300 mg/L), of similar chemical composition, and evolve along similar reaction paths. Calcite, potassium feldspar, sodic plagioclase, accessory silicates, and probably pyrite and barite are reactants in both aquifer types. Water in the stratified‐drift aquifers is in chemical equilibrium with kaolinite and generally has reached equilibrium with chalcedony, which controls H2SiO4 concentrations. In the bedrock aquifers, kaolinite forms as a product in the less evolved water, and calcium‐montmorillonite and calcite form as products in the more highly evolved water. CO2 is a major reactant in both types of aquifers, which are probably open with respect to CO2. The absolute dissolution rates of reactant minerals have a greater effect on groundwater chemistry than do their relative abundance. Calcite, a minor constituent, contributes to water chemistry significantly more than silicates in both types of aquifers. The greater degree of geochemical evolution of water in the bedrock aquifers compared to that of water in the stratified‐drift aquifers is attributed to its longer residence time in the bedrock.
An approximate semianalytical solution for tracer injection tests in a confined aquifer with a radially converging flow field and finite volume of tracer and chase fluid
Authors: Guvanasen Varut , Guvanasen Victoria M.
Published: February 2008

An approximate analytical solution describing the movement of a conservative tracer of finite volume in a radially converging flow field is proposed. The solution is divided into two phases: injection and transport. During the injection phase, an injection of chase fluid immediately following the tracer is allowed. Hydrodynamic dispersion effects are assumed to be negligible during this phase. The geometry of the tracer plume is determined by a particle‐tracking technique. During the plume transport phase, the tracer plume is approximated by a series of contiguous pulses. An approximate analytical solution for each pulse has been derived through linearization of the transport equation. The approximate solution has been verified by comparison with numerical solutions. The distribution of tracer in space and time is obtained by summing the contributions from all the pulses. Four geometrical parameters governing the geometry of the tracer plume immediately after injection are presented and discussed. The solution shows that the geometry of the initial tracer plume has an effect on the breakthrough curves. The volume of tracer and chase fluid has to be taken into account in tracer test design and data analysis. Limitations of the proposed solution are also discussed.
The influence of rainfall distribution in numerical simulation of evapotranspiration from a multilayer model pine canopy
Authors: Cooper T. A. , Lockwood J. G.
Published: February 2008

A multilayer canopy model is used to simulate the water balance of a pine forest. The role of advected energy in sustaining evapotranspiration from tall canopies in low‐radiation environments is reproduced. The surface water balance of temperate forested areas is not necessarily dominated by evapotranspiration in conditions of high radiation receipt. Interception loss is greater where the rainfall regime consists of shorter events, since long‐duration storms tend to fully saturate the canopy. The achievement of the potential evaporation rate and the onset of drainage then combine to limit interception loss totals. This result is important in considering the possible effect of climatic change on water resources. Catchment yield may be as sensitive to the temporal distribution of rainfall as to seasonal or annual totals.
Parameter estimation through groundwater tracer tests
Authors: Rainwater Kenneth A. , Wise William R. , Charbeneau Randall J.
Published: February 2008

In situ estimation of parameters in chemical models describing groundwater pollutant transport and fate is considered. During tracer tests, the observed breakthrough of a conservative species yields information characterizing the hydraulic behavior of a multiple‐well system. A streamline advective solute transport model incorporating the chemical model of interest is scaled so that it applies to all streamlines in the flow system. The hydraulic and chemical data are coupled through a combination integral which calculates the production well effluent concentration of a reactive tracer as a function of time. This mathematical model is combined with the measured effluent data and a nonlinear estimation procedure to estimate the parameters in the chemical models. The procedure is tested in controlled laboratory experiments. A later paper will present a field application.
Operational water quality management: Problem context and evaluation of a model for river quality
Authors: Beck M. B. , Finney B. A.
Published: February 2008

In river basins where water is used intensively and by many activities and facilities, the essential questions of water quality management are changing from being issues of planning alone to being problems of operational decision making. In the past 10 years in the United Kingdom, for example, the technology, economics, legislation, and institutional structure of management have all changed substantially. Together these changes have overturned the traditional assumptions made about the nature of managing river water quality. This paper discusses the foundations for a case study in operational water quality management. The basis of the case study is a dynamic model for stream discharge and quality covering a 54‐km stretch of the Bedford Ouse River in England. The model describes interactions among biochemical oxygen demand, dissolved oxygen, ammonium N, nitrate N, and chlorophyll a concentrations at various points along the river; preliminary identification results are presented using daily time series data for the whole of 1974. The behavior of the river, which relates the effects of a major upstream discharger to a downstream abstractor, is dominated by the dynamics of algal population growth and mortality. In addition to the presentation of these results the paper sets out the technical, economic, and policy questions central to the practical feasibility and potential of operational water quality management. This includes questions in quantifying the stochastic, dynamic aspects of river basin management, the development of improved operating strategies, and the development of operational decision support systems.
Transport of reactive solute in spatially variable soil systems
Authors: van der Zee S. E. A. T. M. , Van Riemsdijk W. H.
Published: February 2008

Transport is studied for reactive solutes and one‐dimensional fluid flow with sorption described by the Freundlich equation (Q = kcn). For a physically and chemically homogeneous soil column and if the constant feed concentration is larger than the initial concentration, the transport occurs in a traveling wave–type displacement, with a constant shape of the solute concentration front and constant front propagation velocity, provided 0 < n < 1. For a negligible initial concentration it is shown that a shock front may be assumed if n is small enough. Field scale transport is described as an ensemble of shock fronts in parallel columns with different flow velocities ν, retardation factors r, and times of solute input, tc. These stochastic variables are characterized by probability density functions (PDF). If we assume lognormal distributions, a simple expression for the field‐averaged profile of dimensionless sorbed solute 〈Γ〉 at a particular time is derived. If tc is not a distributed variable, but equal to the total time τ the profile 〈Γ〉 coincides with the field‐averaged dimensionless concentration profile. It is shown how scaling theory, leading to the PDF of the fluid velocity, may be incorporated in the model. For reasonable parameter values and statistics of the stochastic variables the 〈Γ〉 profiles are calculated. Notably, the effect of a stochastic retardation factor, with statistics derived from the distributions of pH and oc (organic carbon content) found for 84 soils, appears to be profound. The field‐averaged displacement calculated is nonsigmoid for the PDFs of oc, pH, and tc chosen. This phenomenon is amplified if v and r are assumed negatively correlated. From the results it is clear that modeling of horizontally large soil systems with averaged properties will in general lead to an underestimation of the moment of first breakthrough at a particular reference level, such as the phreatic water level.
The implicit stochastic model for reservoir yield optimization
Authors: Simonovic Slobodan
Published: February 2008

The implicit stochastic model is aimed at solving the specific problem of the optimal reservoir yield when the demand is not known. The model is created to assist in the long‐term comprehensive water management planning. The presented treatment of the reservoir as a water resource for satisfying demand differs from the present practice. Knowing the character of different water demands, represented by relative demand coefficients, the implicit stochastic model provides planners with the optimal value of reservoir yield. The lack of strong and reliable economic criteria, which is common for development countries, is in this approach replaced by optimizing the reliability of satisfying water demand from the reservoir. A three‐level algorithm is proposed for the reservoir yield computation. At the first level, the simulation is used for computing the value of objective function. At the second level, computation of the seasonal reservoir operating rules is presented. The approach used for deriving the reservoir operating rules is based on the nonlinear unconstrained multivariable search of M.J.D. Powell. The third level is used for estimating the single multipurpose reservoir yield. The Fibonacci search procedure is used for the optimization of the reservoir yield at this level. The model is used in reservoir analysis for the water resources master plan of the Republic of Serbia, Yugoslavia. In this case, 49 reservoirs Were analyzed.
Freezing and thawing of soils and permafrost containing unfrozen water or brine
Authors: Osterkamp T. E.
Published: February 2008

An analytical solution is presented for freezing and thawing of soils and permafrost containing unfrozen water or brine and with temperature dependent thermal properties. Latent heat effects are incorporated into an apparent heat capacity. The partially frozen soil is divided into layers, each with constant thermal properties and with fixed temperatures at the layer boundaries which move with time in a multiple moving boundary problem. Solutions are obtained for the positions of the layer boundaries and for the temperature distribution within each layer. The theory is used to predict the maximum depth of ice penetration and the temperature profile in a large artificial island. Maximum ice penetration in the island is greater than that determined from the two‐layer Neumann solution. Predicted temperature profiles are relatively smooth and do not exhibit a sharp break at the phase boundary. The solution procedure is also applicable to other heat conduction problems in permafrost containing unfrozen water or brine.
Dissolved oxygen systematics in the Tucson Basin Aquifer
Authors: Rose S. , Long A.
Published: February 2008

Dissolved oxygen (DO) is ubiquitous in Tucson basin groundwater; however, its distribution is systematic and distinct facies are apparent. Dissolved oxygen concentrations approach a minimum of 15% of the saturation limit in a chemically immature recharge facies and then rapidly increase downgradient. Groundwater throughout most of the central basin remains nearly saturated with dissolved oxygen for thousands of years during the course of its chemical evolution. DO concentrations were lowest where the water table was highest, indicative of the oxidation of phreatophyte detritus. Transverse dispersive influx of dissolved oxygen from the vadose atmosphere into the shallow phreatic zone represents an inferred process controlling the electrochemical evolution of groundwater within this aquifer. Traditional models which describe a progressive reduction of the electrochemical state of groundwater along the flow path cannot be directly applied to the Tucson basin which is a “dispersive influx‐dominated” system.
Constant rate rainfall infiltration: A versatile nonlinear model: 1. Analytic solution
Authors: Broadbridge P. , White I.
Published: February 2008

Analytic solutions are presented for a nonlinear diffusion‐convection model describing constant rate rainfall infiltration in uniform soils and other porous materials. The model is based on the Darcy‐Buckingham approach to unsaturated water flow and assumes simple functional forms for the soil water diffusivity D(θ) and hydraulic conductivity K(θ) which depend on a single free parameter C and readily measured soil hydraulic properties. These D(θ) and K(θ) yield physically reasonable analytic moisture characteristics. The relation between this model and other models which give analytic solutions is explored. As C→ ∞, the model reduces to the weakly nonlinear Burgers' equation, which has been applied in certain field situations. At the other end of the range as C→1, the model approaches a Green‐Ampt‐like model. A wide range of realistic soil hydraulic properties is encompassed by varying the C parameter. The general features of the analytic solutions are illustrated for selected C values. Gradual and steep wetting profiles develop during rainfall, aspects seen in the laboratory and field. In addition, the time‐dependent surface water content and surface water pressure potential are presented explicitly. A simple traveling wave approximation is given which agrees closely with the exact solution at comparatively early infiltration times.
Effects of acidic deposition on the chemistry of headwater streams: A comparison between Hubbard Brook, New Hampshire, and Jamieson Creek, British Columbia
Authors: Driscoll Charles T. , Johnson Noye M. , Likens Gene E. , Feller Michael C.
Published: February 2008

Streamwater samples were collected from watersheds in Jamieson Creek, British Columbia, and the Hubbard Brook Experimental Forest, New Hampshire, to compare the chemistry of drainage waters which are unimpacted and impacted by acidic deposition. Qualitative and quantitative differences in the chemistry of headwater streams were evident. Principal among these were a shift from acidification by organic acids to strong acids, increased concentrations of aqueous Al, and a change in Al speciation from largely organic to inorganic forms. In both watersheds, streamwater acidity is ultimately neutralized by the release of basic cations.
Contaminated groundwater remediation design using simulation, optimization, and sensitivity theory: 2. Analysis of a field site
Authors: Ahlfeld David P. , Mulvey John M. , Pinder George F.
Published: February 2008

An optimization approach to designing contaminated groundwater aquifer remediation systems is described and used to analyze alternate hypothetical remediation strategies at a Superfund site in Woburn, Massachusetts. The methodology combines two‐dimensional convective‐dispersive transport simulation, nonlinear optimization, and sensitivity theory. Remediation strategies are generated based on different design criteria as represented by two alternate optimization formulations. It is demonstrated that field scale simulation models can be successfully incorporated into a nonlinear optimization framework to solve important design problems. Through the use of sensitivity theory for the transport simulation model it is possible to solve field scale problems with at least an order of magnitude less computational effort than when using perturbation methods.
Linear and nonlinear solutions for one‐dimensional compaction flow in sedimentary basins
Authors: Bethke Craig M. , Corbet Thomas F.
Published: February 2008

We consider the effects of assuming linearity in solving the moving boundary problem that describes one‐dimensional groundwater flow in compacting sedimentary basins. The linear problem in which specific storage and hydraulic conductivity do not vary can be solved analytically. This solution should be applied to geological problems with caution because of the implications of assuming that specific storage is constant over the range of stresses typical of sedimentary basins. A nonlinear equation in which specific storage and hydraulic conductivity vary with effective stress describes compaction flow more realistically. This equation can be solved accurately by a numerical method. Solutions to the nonlinear equation show that the solution to the linear equation can significantly overpredict excess heads in compacting basins. Large excess heads develop by compaction in sediments of lesser conductivity and over a smaller conductivity interval than suggested by the linear solution. The nonlinear solutions predict that geopressured zones should develop in shaly basins undergoing rapid sedimentation but fail to explain the abrupt transition from hydrostatic to near‐lithostatic pressures observed in these basins. The transition is better explained as the result of a facies change or a discontinuity in conductivity caused by diagenetic reactions than a decrease in hydraulic conductivity during compaction.
Response of well aquifer systems to Earth tides: Problem revisited
Authors: Hsieh Paul A. , Bredehoeft John D. , Rojstaczer Stuart A.
Published: February 2008

Two recent works cause us to reexamine Bredehoeft's (1967) analysis of earthtide response of water wells. Narasimhan et al. (1984) raise several questions regarding Bredehoeft's (1967) analysis and suggest that the analysis is internally inconsistent. They argue that one cannot directly estimate the specific storage, which characterizes the drained behavior of a porous medium, from earth tide response, which is an undrained phenomenon. We resolve the questions raised by Narasimhan et al. (1984) and show that Bredehoeft's analysis is internally consistent. In addition, we show that it is possible to determine the specific storage from undrained loading. While Bredehoeft's analysis is somewhat heuristic and neglects grain compressibility, Van der Kamp and Gale (1983) present a more rigorous analysis that is based on Biot's (1941) constitutive relationships and accounts for grain compressibility. However, their results reduce to Bredehoeft's results when grains are assumed incompressible. This suggests that Bredehoeft's analysis has incorporated all the essential features of Biot's relationships except for grain compressibility. Upon reexamining Bredehoeft's analysis we find that this is indeed the case.
An evaluation of the equilibrium calculations within acidification models: The effect of uncertainty in measured chemical components
Authors: Schecher William D. , Driscoll Charles T.
Published: February 2008

There is much concern over the effects of acidic deposition on soils and drainage waters. To better understand the processes regulating the acidification of surface waters, computer models have been developed which utilize equilibrium calculations to predict the concentration of chemical parameters such as pH, acid neutralizing capacity, dissolved inorganic carbon, Al and SO42−. A simple chemical equilibrium model (ALCHEMI) was used to evaluate the effect of uncertainty in the measurement of chemical constituents on thermodynamic calculations. For calculations where pH was not allowed to vary (fixed pH calculations), uncertainty in Al speciation was small (maximum of 7%) and largely due to imprecision in the measurement of total F and pH. When calculations were made from electroneutrality based on measured constituents (variable pH calculations), most of the uncertainty associated with the values of output parameters was due to imprecision in the determination of SO42−.
The effect of intersite dependence on regional flood frequency analysis
Authors: Hosking J. R. M. , Wallis J. R.
Published: February 2008

Regional flood frequency analysis usually assumes that flood records from different sites are statistically independent. This assumption is unlikely to be valid in practice, so it is important to know how intersite dependence affects flood quantile estimates obtained by regional analysis. We use Monte Carlo simulation to assess the effect of realistically specified intersite dependence on the regional probability weighted moment algorithm, a robust and efficient procedure for regional flood frequency analysis. Our principal conclusions are as follows. Any bias in flood quantile estimates is unchanged by the presence of intersite dependence. The accuracy of flood quantile estimates decreases when intersite dependence is present, but this effect is less important for practical applications than the bias in flood quantile estimates due to heterogeneity (inequality of the flood frequency distributions in the region). Even when both heterogeneity and intersite dependence are present and the form of the flood frequency distribution is misspecified, regional flood frequency analysis is more accurate than at‐site analysis.
Developing joint probability distributions of soil water retention characteristics
Authors: Carsel Robert F. , Parrish Rudolph S.
Published: February 2008

A method is presented for developing probability density functions for parameters of soil moisture relationships of capillary head [h(θ)] and hydraulic conductivity [K(θ)]. These soil moisture parameters are required for the assessment of water flow and solute transport in unsaturated media. The method employs a statistical multiple regression equation proposed in the literature for estimating [h(θ)] or [K(θ)] relationships using the soil saturated water content and the percentages of sand and clay. In the absence of known statistical distributions for either [h(θ)] or [K(θ)] relationships, the method facilitates modeling by providing variability estimates that can be used to examine the uncertainty associated with water flow or solute transport in unsaturated media.
Pressure interference data analysis for two‐phase (water/steam) geothermal reservoirs
Authors: Garg S. K. , Pritchett J. W.
Published: February 2008

A previously published approximate solution by Garg (1980) is used to develop a practical procedure for analyzing pressure interference (drawdown) data from a hot‐water geothermal reservoir which evolves into a two‐phase system as a result of fluid production. The observation well is assumed to remain in the single‐phase (liquid) part of the reservoir. A numerical geothermal reservoir simulator is employed in a series of calculations to test the limits of applicability of the interpretation procedure. The numerical results suggest that the accuracy of the computed reservoir transmissivity depends somewhat on the size of the induced two‐phase region. Even if the two‐phase zone is extensive, the method can still be used to provide a good first approximation for the reservoir transmissivity; forward modeling with a numerical reservoir simulator may then be employed to refine this transmissivity estimate. Numerical results also show that the observation well pressure buildup data will obey the superposition principle after the return of the reservoir to single‐phase conditions.
Alkalinity regulation in softwater Florida lakes
Authors: Baker L. A. , Pollman C. D. , Eilers J. M.
Published: February 2008

Major ion chemistry data collected as part of the Environmental Protection Agency (EPA) Eastern Lake Survey was examined to evaluate the mechanisms and extent of alkalinity regulation in 37 undisturbed, softwater lakes in Florida. Comparison of major ion‐Cl ratios in atmospheric deposition and in lakewater shows the reactions resulting in retention of sulfate and nitrate are the dominant sources of alkalinity; production of organic acids and ammonium retention are the major alkalinity‐consuming processes. Based on average reactions, enrichment of major cations accounted for only 12% of net alkalinity generation in the study lakes. In general, calcium and potassium were depleted in low ANC lakes, presumably by in‐lake sinks, and were enriched in most higher ANC lakes by groundwater inputs. Differences in alkalinity among these lakes reflect hydrologic factors and the proximity of clay and carbonate deposits to the lake bed. Overall, net alkalinity generation nearly balanced H+ predicted from evaporative concentration of atmospheric acid inputs; this close balance suggests that the alkalinity status of these lakes is very sensitive to changes in atmospheric loadings and groundwater alkalinity inputs.
Steady unsaturated seepage above a sloping impermeable base
Authors: Philip J. R.
Published: February 2008

We establish the nonexistence of steady unsaturated flows in regions infinite in the horizontal and bounded below by a horizontal impermeable base. Asymptotic analyses are given of two‐ and three‐dimensional seepage above a sloping impermeable base, valid far from the water supply source(s). The solutions depend only on total source discharge: details of source configuration are irrelevant. We require only that the total discharge be positive and finite and that the sources be contained in a finite region. Two‐dimensional results are found both for quasi‐linear and for general nonlinear flows. The general results apply also to mixed saturated‐unsaturated flows. The asymptotic three‐dimensional quasi‐linear results involve the same functional forms as analogous two‐dimensional flows in unbounded regions. An upper bound on unsaturated total discharge exists for two‐dimensional systems. Use of the potential Ω, a line integral of the Kirchhoff potential, effectively reduces by one the dimensionality of the problems treated. In one instance the dimensionality is reduced by two after a second integration.
Assessing the Birkenes Model of stream acidification using a multisignal calibration methodology
Authors: Hooper Richard P. , Stone Alex , Christophersen Nils , de Grosbois Ed , Seip Hans M.
Published: February 2008

A revision of the Birkenes model of streamwater acidification has been attempted to incorporate additional chemical and hydrologic information gained in the last 6 years since its original construction. The first stage of this effort has been an analysis of the hydrologic submodel with the goal of extending it to predict concentrations of a conservative tracer in streamwater. An objective calibration of the model indicated that the model is overparameterized. Only one passive store is identifiabile, not two as currently contained in the model and the routing between the two reservoirs is not determined by the data. Inclusion of the conservative tracer improved the identifiability of the dimensional parameters, but had little effect on the rate or routing parameters. If the hydrologic structure is to be determined from the hydrograph and conservative tracer alone, it must be simplified to eliminate unidentifiable parameters. The validity of using more complex rainfall‐runoff models in hydrochemical models which seek to test chemical mechanisms is called into question by this analysis.
The fractal nature of river networks
Authors: Tarboton David G. , Bras Rafael L. , Rodriguez‐Iturbe Ignacio
Published: February 2008

Ever since Mandelbrot (1975, 1983) coined the term, there has been speculation that river networks are fractals. Here we report analyses done on river networks to determine their fractal structure. We find that the network as a whole, although composed of nearly linear members, is practically space filling with fractal dimension near 2. The empirical results are backed by a theoretical analysis based on long‐standing hydrologic concepts describing the geometric similarity of river networks. These results advance our understanding of the geometry and composition of river networks.
Management of a tributary aquifer
Authors: Burness H. Stuart , Martin Wade E.
Published: February 2008

Much work has been done concerning the integration of hydrologic and economic considerations for a nontributary aquifer. Moreover, some fairly sophisticated hydrologic models concerning tributary aquifers have been developed, but to date there has been a paucity of economic analyses concerning tributary aquifers, and most of these analyses have incorporated the hydrologic link between surface water and groundwater only as a secondary phenomenon. We develop an analytical economic model which focuses primarily on this hydrologic link as it relates to efficient plans for water pumping and then examine the allocative efficiency of competitive markets for such water. The efficiency of alternative state management of tributary aquifer water systems is also analyzed.
Erosion of cohesionless sediment by groundwater seepage
Authors: Howard Alan D. , McLane Charles F.
Published: February 2008

Surface grains of noncohesive sediment eroded by emerging groundwater are acted upon by three forces, the tractive force of the cumulative surface flow contributed by upslope seepage, the local seepage force, and gravity. The balance of the force moments determines the mode and rate of transport. Seepage forces are strong in a narrow “sapping zone” at the upstream end of the emerging flow, where erosion occurs by mass movement and the surface gradient is determined by the balance of the seepage and gravity moments. Most of the erosion occurs in this zone, and the resultant backcutting triggers intermittent failure of overlying slopes in a “undermining zone” maintained at the angle of repose of the dry or damp sediment. In the “fluvial zone” downstream from the sapping zone the seepage force is small compared to the tractive force, and transport occurs by normal fluvial traction. The overall rate of sapping erosion in noncohesive sediments is determined by the capacity of fluvial transport to remove sediment eroded in the sapping zone. Prediction of sapping rates is complicated by the interaction between the geometry of the fluvial and sapping zones and the quantity and spatial distribution of seepage. A simulation model incorporating a groundwater flow model and sediment transport relationships closely replicates the observed evolution of sapping erosion in a two‐dimensional tank filled with noncohesive sand subjected to lateral groundwater flow.
Stochastic identification of recharge, transmissivity, and storativity in aquifer transient flow: A quasi‐steady approach
Authors: Dagan Gedeon , Rubin Yoram
Published: February 2008

In this paper, a stochastic method to identify aquifer natural recharge, storativity, and transmissivity under transient conditions is developed. Four main assumptions were adopted: Y, the log transmissivity, is a normal random space function, the aquifer is unbounded, a first‐order approximation of the flow equation is adopted, and the transients are slowly varying. Based on these assumptions, the expected value of Y and of the head H, as well as their covariances and crosscovariances, are expressed by analytical equations which depend on a parameters vector θ. A major part of the first paper is devoted to the development of these expressions, based on the two‐dimensional flow equation. The proposed solution of the inverse problem is a double‐stage procedure. First, θ is identified stochastically, by a maximum likelihood procedure applied to the measurements of Y and H. Then, θ serves to estimate the spatial distributions of Y and H through their conditional mean and variances of estimation. The three main new features of the approach are the possibility to identify the spatial distributions of Y and H through their first two statistical moments based on transient head data and in the presence of pumping‐recharching wells; the identification of the storativity and the stochastic identification of natural recharge. Since the proposed method make use of the analytic solution of the flow equation, it saves the need of laborious numerical schemes. Application of the method to a section of the Israeli Coastal Aquifer illustrates its potential in a real‐life case.
Multicomponent mass transport with homogeneous and heterogeneous chemical reactions: Effect of the chemistry on the choice of numerical algorithm: 2. Numerical Results
Authors: Reeves Howard , Kirkner David J.
Published: February 2008

This paper is the second in a two‐part series which studies the efficiency of several algorithms for solving the problem of multicomponent mass transport with equilibrium chemical reactions. In particular, the relative efficiency of competing algorithms is evaluated as a function of the nature of the chemistry. The first, formulation A, introduces the total soluble concentration of each component as the primary dependent variable. The second, with variants B and C, introduces the total component concentration, aqueous plus all solid forms, as the primary dependent variable. Finite element discretization in space and a single‐step, implicit time marching scheme reduces the problem to a set of nonlinear algebraic equations in each time step. Several versions of Newton‐Raphson iteration and Picard iteration are evaluated for the basic formulations by studying a set of single‐ and three‐component problems. The specific cases studied are each designed in order to emphasize a particular aspect of the equilibrium chemical reactions. Results indicate that overall, a modified Newton‐Raphson iteration is the most efficient solution strategy for the range of problems considered.
Episodic response of aluminum chemistry in an acid‐sensitive Massachusetts catchment
Authors: McAvoy Drew C.
Published: February 2008

A field investigation was conducted to evaluate factors that regulate episodic variations of Al chemistry in an acid‐sensitive Massachusetts catchment. Stream water was collected from an upland subcatchment, a wetland subcatchment, and below the confluence of these two drainage areas in the West Wachusett Brook at 6 hour intervals during the first 2 weeks of November 1985. All major solutes and three Al fractions were analyzed. During the monitoring period, two different rainfall events of contrasting origin (i.e., a coastal storm and an inland storm) occurred. Rainfall volume, intensity, and duration were important factors regulating short‐term acidification of this stream. Ion exchange processes rather than mineral phase solubility appear to control stream water Al concentrations during high‐flow periods. The episodic acidification and subsequent release of Al in the upland stream were associated with a decrease in basic cations. In contrast, Al chemistry from the wetland drainage was regulated by the release of organic acids which served as mobile anions and were responsible for chelating and transporting Al. Chemical equilibrium calculations showed that waters draining the upland subcatchment were potentially toxic to fish during high‐flow periods, whereas the wetland stream exhibited minimal potential for Al toxicity.
Flow through porous media from a pressurized spherical cavity
Authors: Lockington D. , Hara M. , Hogarth W. , Parlange J.‐Y.
Published: February 2008

The saturated‐unsaturated flow generated by injecting water into a soil from a pressurized spherical cavity is modeled mathematically. Approximate solutions are obtained analytically for arbitrary pressure head when the soil water diffusivity varies rapidly with water content. In particular, the relationship between the cavity pressure and cumulative absorption is established, and formulae for the position of the saturation and wetting fronts are derived. The accuracy of these results improves with increasing cavity pressure. Consequently, they are compared with a numerical solution obtained for the case of flow through Hanford sandy loam when the cavity pressure is zero. The solutions prove to be in excellent agreement. The steady state solution is used to evaluate gravity effects and the application of the formulae to injection problems, particularly subsurface trickle irrigation, is briefly discussed.
Streamflow changes after clear‐cut logging of a pine beetle‐infested watershed in southern British Columbia, Canada
Authors: Cheng J. D.
Published: February 2008

The paired watershed technique was used to assess the streamflow changes of Camp Creek in interior British Columbia after clear‐cut logging occurred over 30% of its 33.9 km2 watershed. Existing hydrometric data for Camp Creek and those of an adjacent control, Greata Creek, were analyzed for both the 1971–1976 prelogging and 1978–1983 postlogging periods. Postlogging Camp Creek streamflow changes are characterized by increases in annual and monthly water yields and annual peak flows, as well as earlier annual peak flow and half flow volume occurrence dates. The direction and magnitude of these postlogging streamflow increases are clear and consistent. The results are in good agreement with the findings of most previous studies conducted on watersheds which generally have been smaller than 2.5 km2. This study provides strong evidence that changes in streamflow from a large forested watershed can be significant if a sizeable portion of its drainage area is clear‐cut. Possible causes for the streamflow changes are discussed.
The direct inverse problem in aquifers
Authors: Weir G. J.
Published: February 2008

Solution of the inverse problem for aquifers requires identification of a distributed parameter system. In addition to ill‐posedness, the inverse problem may be underdetermined if recharge is treated as a spatially and temporally variable distribution parameter. Galerkin's method is applied to a weak formulation of the direct inverse problem, leading to a (possibly nonlinear) weighted least squares problem. Consideration of generic errors suggests that if the estimate for some derivative of head contains a significant error on one element for all time, then significant estimation errors are possible for all nodes and for all reservoir parameters. In contrast, if some derivative of head is small in some spatial region, for all time, causing the matrix to be inverted in the least squares algorithm to be nearly singular, then significant estimation errors can occur in the corresponding reservoir parameters in that spatial region; although it is still possible that other reservoir parameters in that region, as well as all reservoir parameters elsewhere, may be satisfactorily estimated.
On boundary conditions and point sources in the finite element integration of the transport equation
Authors: Galeati Giorgio , Gambolati Giuseppe
Published: February 2008

In the finite element integration of the convection‐dispersion equation over a groundwater domain, boundary conditions of the third (or Cauchy) type may or may not be incorporated with the variational statement. While the former development (formulation A) requires the application of Green's first identity to both the convective and the dispersive terms, the latter (formulation B) does not. Although both approaches are equivalent at the theoretical level, they behave differently from a computational standpoint. The numerical solution proves more accurate and stable if Green's lemma is not applied to the convective term, since significant errors arising from the representation of the Darcy velocity over the elements are avoided. Point sources or sinks representing injection or pumping wells can be treated as either sources (sinks) distributed over a small volume or external boundaries with prescribed contaminant flux. It is shown that when the well bore is excluded from the flow field, formulation A yields the same matrix addition for an injection (abstraction) well as formulation B does for an abstraction (injection) well (reciprocity of the results). The computational behaviors of these alternative modeling procedures are illustrated with a number of significant numerical examples.
Spatial and temporal gradients in aquifer oxidation‐reduction conditions
Authors: Barcelona Michael J. , Holm Thomas R. , Schock Michael R. , George Gregory K.
Published: February 2008

The study was undertaken to identify principal oxidizing and reducing chemical species in groundwater with the goal of determining the utility of platinum electrode (Eh) measurements to characterize subsurface redox conditions. Serial measurements of Eh and groundwater analyses were conducted in oxic and suboxic environments over more than a 2‐year period for major ionic, oxidized, and reduced species. Vertical gradients in measured Eh values in the oxic groundwater environments can exceed −40 mV/m depth. In the poorly poised, oxic groundwaters, the Eh measurements correlated reasonably well with calculated values based on analytical determinations of O2 and H2O2 which was detected persistently in the 10−8 to 10−9 M range. The equilibrium calculated Eh values from this and other redox couples did not correlate well with measured Eh values over the 2‐year study period. In the suboxic range, the average calculated values based on the Fe3+/Fe2+ coupled correlated well with averaged measured values. The results support the need to determine redox pairs in groundwater as a supplement to either calculated “equilibrium” Eh values or Pt electrode Eh measurements.
Evaluation of a linear bank erosion equation
Authors: Pizzuto J. E. , Meckelnburg T. S.
Published: February 2008

Field surveys and aerial photographs were used to measure the rate of migration of a bend of the Brandywine Creek near Chadds Ford, Pennsylvania. Velocities near the bank were measured in the field during high flows and also estimated by solving a form of the St. Venant equations. Engineering properties of the bank soils and the spatial density of trees growing along the bank were also measured. The data indicate that rates of bank migration are linearly related to the magnitude of the near‐bank velocity. If the St. Venant equations are used to estimate the near‐bank velocity, the data also suggest that erosion rates are proportional toub‐U, whereubis the near‐bank velocity andUis the reach‐averaged velocity. In addition, rates of bank migration are reduced where the density of silver maples (Acer saccharinum) is high. Boxelder (Acer negundo) and white ash (Fraxinus americana) are also found along the bend, but these species do not noticeably influence rates of bank migration.
Export of dissolved organic carbon and acidity from peatlands
Authors: Urban N. R. , Bayley S. E. , Eisenreich S. J.
Published: February 2008

Because of the vast areal extent and high rates of organic matter production of peatlands, such ecosystems have a significant but poorly quantified impact on large numbers of lakes. This study reports the export of dissolved organic carbon (DOC) and acidity from two bogs and one fen in north central North America. Rates of export of DOC are high for all three peatlands (8–40 g m−2 yr−1), and variations are largely dependent on water yield. Dissolved organic matter from all sites exhibits a charge density between 7 and 24 μeq (mg DOC)−1, and rates of acidity export from all three sites are similar (100–200 meq m−2 yr−1). Variation in elemental composition of dissolved organic matter suggests a seasonal change in relative proportions of organic matter fractions and indicates direct incorporation of microbially reduced sulfur into organic matter. Current definitions and measurement techniques for alkalinity are inappropriate for such high DOC waters, and fixed end point titration to pH 4 is suggested as an alternative.
Ion elution through shallow homogeneous snow
Authors: Bales Roger C. , Davis Robert E. , Stanley Deena A.
Published: February 2008

Controlled melting of snowpacks in the laboratory demonstrates the importance of the initial distribution of chemical species within the pack (mesoscale) and within the snow grains (microscale) to the timing and relative concentrations of meltwater released from the base of the pack. Acid and salt tracers were applied to homogeneous snow in order to investigate these effects. Species deposited near the top of the pack eluted out considerably before those more uniformly distributed with depth. Also, about 80% of the salts dosed at the top of a 0.4‐m pack were removed in the first 20% of the meltwater, versus 70% of a salt dosed at middepth. Both the top and middepth tracers were present in the first fractions of meltwater draining from the pack, however, indicating that there is partial mixing of percolating meltwater with solutes in an immobile surface phase on grains deeper in the pack. Concentration of species on the outside of grains by seasonal metamorphism and on the outside of multigrain particles and clusters during melt freeze will enhance their early removal. Different ions that were present in the snow with the same mesoscale and microscale conditions prior to melt came out at the same relative concentrations; i.e., they did not exhibit preferential elution.