bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors affecting the efficiency of some estimators of fluvial total phosphorus load
Authors: Young Thomas C. , DePinto Joseph V. , Heidtke Thomas M.
Published: February 2008

The accuracy of estimating total phosphorus (TP) loads to receiving waters usually is constrained by availability of concentration data, as discharge (flow) data normally are comparatively abundant. Using 4 years of daily observations from three tributaries to the Great Lakes (Grand, Saginaw, and Sandusky Rivers), annual TP loads were tested for accuracy by five methods, including regression, ratio, and robust estimators. Monte Carlo methods were employed to simulate replicated flow‐stratified sampling of the datasets with various allocations of samples to flow strata. Each of the load calculation methods was applied to each group of simulated samples, and response was quantitated as load estimation error (computed minus “true” load). The results show the most consistently accurate estimator was Beale's stratified ratio estimator. It was, however, the only stratified estimator tested and should have been more accurate. Most accurate of the unstratified estimators was a straightforward least squares regression (log‐log) method. The response of estimation bias to flow cut point and sample allocation manipulations indicated (1) beneficial results generally (but not always) obtained from high flow weighting of sampling and (2) postsampling stratification generally may yield improved accuracy for load estimation and deserves additional research.
Optimization of storm water storage‐release strategies
Authors: Nix Stephan J. , Heaney James P.
Published: February 2008

Storage‐release systems, in one form or another, are often used to improve the quality of urban storm water. Analytical methods to determine optimal storm water storage‐release strategies are difficult to apply because of difficulties in providing accurate functional representations of the problem components and in solving nonlinear programing problems with economies of scale. In order to circumvent these obstacles robust procedures for selecting an optimal storage‐release strategy are presented. One method takes a graphical approach, the other is based on an application of microcomputer‐based spreadsheet and spatial analysis software. Both methods are demonstrated with an example application.
An improvement to the one‐step outflow method for the determination of soil water diffusivities
Authors: Valiantzas John D. , Kerkides Petros G. , Poulovassilis Alex
Published: February 2008

A simple, quick, and reliable iterative method for the determination of the D‐Θ relationship, based on the outflow analysis, is presented. This method imposes no restriction on the functional D(Θ) relationship and gives better results than other previous methods even in cases of extreme nonlinearities in the InD(Θ) relationship and in cases where the D(Θ) relationship is not monotonous. The present method, an improvement to the already existing methods, has been verified against simulated and measured one‐step pressure outflow data.
Parameter estimation for coupled unsaturated flow and transport
Authors: Mishra S. , Parker J. C.
Published: February 2008

This paper deals with the estimation of soil hydraulic and transport parameters from transient unsaturated flow and tracer experiments using a combined simulations‐optimization approach. Hydraulic properties are defined by a modified form of van Genuchten's (1980) parametric model for two‐phase permeability‐saturation‐pressure relations, and transport properties are defined by an empirical parametric dispersion model. A nonlinear weighted least squares algorithm is used to estimate unknown model parameters by minimizing deviations between concentrations, water contents, and pressure heads obtained from hypothetical infiltration/redistribution/evaporation experiments, and those predicted by solving a numerical model of coupled unsaturated flow and transport. Simultaneous estimation of hydraulic and transport properties is found to yield smaller estimation errors for model parameters than sequential inversion of hydraulic properties from water content and pressure head data followed by inversion for transport properties from concentration data. Effects of random noise in data measurements, soil layering, and choice of improper parametric model on the parameter estimation process are discussed.
The seepage exclusion problem for parabolic and paraboloidal cavities
Authors: Philip J. R. , Knight J. H. , Waechter R. T.
Published: February 2008

The problems of water exclusion from, or entry into, parabolic‐cylindrical and paraboloidal cavities during steady downward unsaturated seepage are solved. Both the quasi‐linear and the full nonlinear solutions are found exactly and simply. The identical general mathematical character of the two types of solution, and the good agreement of numerical details, attest to the reliability and utility of the (very much simpler) quasi‐linear analysis. A remarkable result is that for both the parabolic cylinder and the paraboloid, the potential at the cavity wall is spatially uniform. These geometries thus constitute separatices between apically blunter ones (circular cylinder, sphere), where the potential at the wall decreases downstream, and sharper ones (wedge, cone, hyperbolic cylinder, hyperboloid), where it increases. The parabolic geometries are optimal in leaking nowhere or everywhere: blunter ones leak first at the apex and and sharper ones at a low point of the wall. Implications for the design of seepage‐excluding tunnels and underground repositories are indicated. Comparison of the present results with those for the circular cylinder and the sphere reveals the significance of two dimensionless parameters of cavity geometry: σ(=½ ακ−1, with α sorptive number and κ apical total curvature); and ω, apical sharpness.
Simulation of calcite dissolution and porosity changes in saltwater mixing zones in coastal aquifers
Authors: Sanford Ward E. , Konikow Leonard F.
Published: February 2008

Thermodynamic models of aqueous solutions have indicated that the mixing of seawater and calcite‐saturated fresh groundwater can produce a water that is undersaturated with respect to calcite. Mixing of such waters in coastal carbonate aquifers could lead to significant amounts of limestone dissolution. The potential for such dissolution in coastal saltwater mixing zones is analyzed by coupling the results from a reaction simulation model (PHREEQE) with a variable density groundwater flow and solute transport model. Idealized cross sections of coastal carbonate aquifers are simulated to estimate the potential for calcite dissolution under a variety of hydrologic and geochemical conditions. Results show that limestone dissolution in mixing zones is strongly dependent on groundwater flux and nearly independent of the dissolution kinetics of calcite. The amount of dissolution varies within a mixing zone, depending on the properties, physical dimensions, and boundary conditions of the aquifer system. Nearly all of the dissolution occurs in the fresher side of the mixing zone, with the maximum dissolution occurring in water that is fresher than that predicted solely by geochemical reaction models. The greatest porosity and permeability development occur at the toe and at the top of the mixing zone. If permeability increases as porosity increases, asymmetry in the dissolution causes the mixing zone to migrate landward over time. Dissolution rates indicated by the model show that this mechanism can produce significant increases in porosity and permeability over time spans on the order of tens of thousands of years. Given the comparatively long span of geologic time, this process may be largely responsible for porosity and permeability development observed in those carbonate rocks through which a freshwater‐saltwater mixing zone had at one time migrated.
Accounting for intracell flow in models with emphasis on water table recharge and stream‐aquifer interaction: 1. Problems and concepts
Authors: Jorgensen Donald G. , Signor Donald C. , Imes Jeffrey L.
Published: February 2008

Intracell flow is important in modeling cells that contain both sources and sinks. Special attention is needed if recharge through the water table is a source. One method of modeling multiple sources and sinks is to determine the net recharge per cell. For example, for a model cell containing both a sink and recharge through the water table, the amount of recharge should be reduced by the ratio of the area of influence of the sink within the cell to the area of the cell. The reduction is the intercepted portion of the recharge. In a multilayer model this amount is further reduced by a proportion factor, which is a function of the depth of the flow lines from the water table boundary to the internal sink. A gaining section of a stream is a typical sink. The aquifer contribution to a gaining stream can be conceptualized as having two parts; the first part is the intercepted lateral flow from the water table and the second is the flow across the streambed due to differences in head between the water level in the stream and the aquifer below. The amount intercepted is a function of the geometry of the cell, but the amount due to difference in head across the stream bed is largely independent of cell geometry. A discharging well can intercept recharge through the water table within a model cell. The net recharge to the cell would be reduced in proportion to the area of influence of the well within the cell. The area of influence generally changes with time. Thus the amount of intercepted recharge and net recharge may not be constant with time. During periods when the well is not discharging there will be no intercepted recharge even though the area of influence from previous pumping may still exist. The reduction of net recharge per cell due to internal interception of flow will result in a model‐calculated mass balance less than the prototype. Additionally the “effective transmissivity” along the intercell flow paths may be altered when flow paths are occupied by intercepted recharge.
Solute transport in porous media with solid‐liquid mass transfer limitations: Application to ion exchange
Authors: Nicoud R. M. , Schweich D.
Published: February 2008

Assuming that exchange equilibrium can be described by mass action laws, we show how to properly model the kinetic process with external and internal diffusion limitations using average concentrations and characteristic diffusion times. These characteristic diffusion times are defined as those used to describe linear interactions whereas the overall process is nonlinear due to the equilibrium constraints. The characteristic times are expressed in terms of the diffusion coefficients, characteristic dimensions of the exchanging aggregates, and relevant parameters of the flow regime. These expressions allow one to extrapolate laboratory measurements to field scale systems. The internal diffusion time is shown to be related to the selectivity factor. The analysis shows that external diffusion prevails in most situations, and specially at trace levels. A new criterion incorporating the nonlinear equilibrium law is proposed to determine whether the rate‐limiting step is internal or external diffusion.
Tritium as an indicator of recharge and dispersion in a groundwater system in central Ontario
Authors: Robertson W. D. , Cherry J. A.
Published: February 2008

The detailed distribution of tritium (3H) in the recharge area of a shallow unconfined sand aquifer near Sturgeon Falls, Ontario, is described. At this forested, shallow water table site, bomb tritium has penetrated uniformly to a depth of 8–12 m indicating recharge of 15 cm/year, which is 16% of precipitation. The zone of bomb tritium contains 3H concentrations of from 16 to 269 tritium unit (TU), whereas much lower values (<1 TU) are observed in groundwaters recharged only a few years prior to 1953, the year when significant fallout of bomb tritium began. Tritium distribution is accurately simulated, using one‐ and two‐dimensional models, when the Ottawa record is used for the post‐1953 tritium input function, when dispersion is low and when a prebomb tritium input value of 3 TU is used. This prebomb value is slightly lower than that suggested by Kaufman and Libby (1954), based on precipitation and surface water samples from the early 1950s. The simulations indicate and field data corroborate, that in 1986, 3H levels of more than 100 TU occur only in groundwaters recharged between 1957 and 1971, while levels in excess of 200 TU occur only in groundwaters recharged during 1961–1967. The 1960s tritium peak is observed within a narrow distinct depth zone at all locations along the flow section investigated.
Atmospheric sulfur deposition 1950–1985 inferred from sulfate in groundwater
Authors: Robertson W. D. , Cherry J. A. , Schiff S. L.
Published: February 2008

Groundwater sulfate that occurs at concentrations of 6–27 mg/L in a shallow water table sand aquifer, at a forested site 100 km east of Sudbury, Ontario, is used to deduce the trend in atmospheric sulfur deposition between 1950 and 1985. The simple geologic nature of the aquifer made feasible this trend reconstruction. The age of groundwater that entered the aquifer during the past 60 years was determined with unusual accuracy (±3 years) from tritium analyses and flow modeling. Sulfur isotopes and mass balances indicate that the sulfate in the groundwater zone is of atmospheric origin and is not derived from solid phase material in the sediments. Evapotranspiration enriches atmospheric sulfate by a factor of about three as it enters the aquifer. Adsorption of sulfate is not significant. Groundwater sulfate indicates a decrease of 37% in sulfur deposition at the site between a maximum in the 1960s and lower values observed in the 1980s. We attributed most of the decrease ((bout 80%) to lower SO2 emissions from the Sudbury smelters. These emissions are now about one third of the 1960s levels. Further major decreases in sulfur deposition at this site can be achieved only if emissions from sources distant from Sudbury are lowered as well because Sudbury now contributes less than 25% of total sulfur deposition.
Conditioning stochastic daily precipitation models on total monthly precipitation
Authors: Wilks Daniel S.
Published: February 2008

Chain‐dependent stochastic daily precipitation models are fit to dry, near‐normal, and wet subsets of monthly total precipitation data, using category definitions consistent with the 30‐day forecasts issued by the Climate Analysis Center of the National Oceanic and Atmospheric Administration. The resulting models are compared to those derived unconditionally from entire data records. It is found that for the 10 selected North American stations investigated, the unconditional models produce distributions of total monthly precipitation having too few dry and wet months as compared to the observations, while appropriate probability mixtures of the three conditional models can accurately reproduce the climatological distributions of total monthly precipitation. Application of the conditional precipitation models to generation of daily data consistent with certain longer‐term aspects of the observations is also illustrated.
The Impeller Meter for measuring aquifer permeability variations: Evaluation and comparison with other tests
Authors: Molz Fred J. , Morin Roger H. , Hess Alfred E. , Melville Joel G. , Güven Oktay
Published: February 2008

A knowledge of the variation of horizontal hydraulic conductivity with vertical position, K(z), is important in understanding the transport and dispersive properties of aquifers. Using an impeller meter to measure the discharge distribution in a screened well while pumping at a constant rate is a promising technique for obtaining the K(z) function. Such an application is described herein, and the resulting K(z) functions are compared with those obtained previously using tracer tests and multilevel slug tests. Impeller meter data were the most convenient to obtain, and tracer data the most difficult. The K(z) functions obtained by the three methods were not identical but quite similar overall. This similarity between both borehole tests and the larger‐scale tracer test showed that nonstationary hydraulic conductivity trends, in a stochastic hydrologic sense, exist in the test aquifer. The impeller meter method was better able to detect the higher K layers than was the multilevel slug approach. Overall, the results suggest that a practical strategy for “fitting” impeller meter, tracer, or multilevel slug test data to a given aquifer is to use the selected testing procedure to obtain a dimensionless
distribution and then a standard pumping test to measure
. Combining both types of information enables dimensional values for K(z) to be calculated. In low permeability aquifers or near the bottom of a test well the fluid velocity due to pumping may be below the stall velocity of an impeller. Thus there is a definite need for the commercial development of more sensitive flow‐measuring devices such as heat pulse flowmeters (Hess, 1986), which will extend the resolution of this field method.
Salt redistribution during freezing of saline sand columns at constant rates
Authors: Baker G. C. , Osterkamp T. E.
Published: February 2008

Columns of sand with grain sizes from about 250 to 600 μm were saturated with a sodium chloride solution with a concentration of 35 parts per thousand (ppt) and frozen at constant rates ranging from 1 to 20 mm d−1. Electrical conductivity of the soil solution, water content, and temperature were measured during the experiments. The interface between the frozen and unfrozen regions was sharply defined and mechanically hard with no evidence for a soft, ice‐bearing transition region thicker than a millimeter. Ice content near the interface was less than 50%. Substantial salt redistribution occurred with downward freezing but not with upward freezing. For downward freezing, the amount of salt rejected near the interface decreased with increasing freezing rate and increased with the salinity of the soil solution in the unfrozen region. Salt redistribution consisted of salt rejection and brine drainage from an extended partially frozen region just above the interface. Brine drained from this partially frozen region until the ice content reached about 900–950 ppt. Brine drained through the interface and mixed rapidly in the unfrozen region, apparently by salt fingering. No evidence could be found for a salt‐enriched layer just below the interface. There was a layer just above the interface, moving with it, which was undersaturated at low and oversaturated at high freezing rates. An effective distribution coefficient may be useful in describing salt redistribution during freezing of saline sands.
Water content dependence of trapped air in two soils
Authors: Stonestrom David A. , Rubin Jacob
Published: February 2008

An improved air pycnometer method was used to examine the water content dependence of trapped‐air volumes in two repacked, nonswelling soils. Trapped‐air volumes were determined at a series of hydrostatic equilibrium stages which were attained during water pressure‐controlled wetting and drying cycles over a range of 0 to −10 kPa for a sand and 0 to −20 kPa for a loam. Small pressure perturbations, between 0.2 and 0.6 kPa, were used in the air pycnometer method. Volumes of trapped air obtained at each hydrostatic equilibrium stage were independent of perturbation level and remained relatively constant over the time required to make repeated determinations. In contrast with most of the results obtained in previous studies, which often showed irregular relations, in this study the volume fraction of trapped air was found to be a regular, monotonically increasing (though possibly hysteretic) function of water content. For the soils studied, the function definitely exceeded zero only at water contents greater than 70% of saturation. However, during the initial drying from complete water saturation, the volume fraction of trapped air was virtually zero. Air trapping influenced the water retention curves significantly only at water contents higher than about 60% of saturation. Except at zero water pressure, however, not all of the differences between the initial and the other drying retention curves were accounted for by observed differences in trapped‐air volumes. Air trapping was not required for the onset of hysteresis in the water retention relation for the cases studied, i.e., when drying‐to‐wetting reversals were imposed at about 27% and 40% of saturation for the sand and loam soils, respectively.
Water yield from forest snowpack management: Research findings in Arizona and New Mexico
Authors: Ffolliott Peter F. , Gottfried Gerald J. , Baker Malchus B.
Published: February 2008

Snow falling in high‐elevation forests is an important source of water for much of the arid Southwest. Snowpack conditions in Arizona and New Mexico differ from those in more northern regions, because of the variability in annual accumulations and the intermittent melting throughout the winter season. Snow management research in Arizona and New Mexico over the past 25 years has indicated the possibilities of increasing snowmelt water yields through forest management activities. The effects of management can be predicted from forest inventory data. Other research has resulted in the development of snow‐runoff forecasting procedures and computer simulation models of forest snowpack dynamics, as well as increasing the general knowledge of snow hydrology.
A consistent set of parametric models for the two‐phase flow of immiscible fluids in the subsurface
Authors: Luckner L. , Van Genuchten M. Th. , Nielsen D. R.
Published: February 2008

Accurate estimates of the unsaturated hydraulic properties are needed for any quantitative description of multiphase flow in porous media. This paper presents a consistent set of parametric models for the isothermal, hysteretic unsaturated fluid phase content (retention) and hydraulic conductivity functions of typical two‐phase systems like water and air, or water and hydrocarbons. The equations are obtained by combining expressions for the hysteretic fluid retention curves with the statistical pore size distribution model of Mualem (1976) which predicts the hydraulic conductivity from more easily measured fluid retention data. Hysteresis is described using the model of Scott et al. (1983). The existence of residual fluid saturations for both the wetting and non wetting fluids is justified. Theoretical and experimental considerations indicate a need to match predicted and observed hydraulic conductivities at fluid phase contents less than full saturation.
Field‐scale transport of interacting solutes through the unsaturated zone: 2. Analysis of the spatial variability of the field response
Authors: Russo David
Published: February 2008

The effect of physicochemical interactions between the soil solution and the soil matrix on the spatial variability of the soil‐dependent variables during transient transport of mixed Na/Ca−Cl salts through the unsaturated zone of a large field‐scale soil is analyzed. The spatial variability of the soil water and solute transport properties evaluated in part I were used as inputs to a conceptual stochastic model describing one‐dimensional vertical transport of water and soil‐interacting solutes through the unsaturated zone of a spatially variable soil, viewed as a collection of vertically homogeneous and independent soil columns. Using data of the spatial distributions of pertinent soil properties from the Bet Dagan field, the transport process was simulated for boundary and initial conditions pertinent to the application of low‐salinity and low‐alkalinity waters (rain) to the surface of a saline‐alkaline soil, considering effects of the soil solution concentration and composition on the soil water and solute transport properties. The spatial variability (in terms of field averages and coefficients of variation CV) of the profiles of the soil water content θ, the chloride concentration C, and the sodium adsorption ratio SAR of the soil solution and the soil hydraulic conductivity K at given elapsed times t were presented and compared with those evaluated from simulations of the same boundary value problem where the effect of the soil solution concentration and composition on the water and solute transport properties was disregarded. Results of the analyses suggested that because of soil solution‐soil matrix interactions the field‐average movement of both the water and the solutes may be retarded and their spatial variability may be increased relative to the case where these interactions had not been considered. In the Bet Dagan field, after t = 5 hours of continuous infiltration, the field averages of the positions of the wetting front and the chloride front were retarded by 10 and 15%, respectively; the relative variabilities of the positions of these fronts were increased by 16 and 38%, respectively; and the equivalent effective dispersivity was increased by 18%, relative to the reference inert case.
Determinants of household water conservation retrofit activity: A discrete choice model using survey data
Authors: Cameron T. A. , Wright M. B.
Published: February 2008

Economic analyses of residential water demand have typically concentrated on price and income elasticities. In the short run a substantial change in water prices might induce only small changes in consumption levels. As time passes, however, households will have the opportunity to “retrofit” existing water‐using equipment to make it less water‐intensive. This produces medium‐ to long‐run demand elasticities that are higher than short‐run studies suggest. We examine responses to water conservation questions appearing on the Los Angeles Department of Water and Power's 1983 residential energy survey. We find that households' decisions to install shower retrofit devices are influenced by the potential to save money on water heating bills. We attribute toilet retrofit decisions more to noneconomic factors which might be characterized as “general conservation mindedness.” The endogeneity of these retrofit decisions casts some doubt on the results of studies of individual households that treat voluntary retrofits as exogenous.
Exact integral solutions for two‐phase flow
Authors: McWhorter David B. , Sunada Daniel K.
Published: February 2008

Exact integral solutions for the horizontal, unsteady flow of two viscous, incompressible fluids are derived. Both one‐dimensional and radial displacements are calculated with full consideration of capillary drive and for arbitrary capillary‐hydraulic properties. One‐dimensional, unidirectional displacement of a nonwetting phase is shown to occur increasingly like a shock front as the pore‐size distribution becomes wider. This is in contrast to the situation when an inviscid nonwetting phase is displaced. The penetration of a nonwetting phase into porous media otherwise saturated by a wetting phase occurs in narrow, elongate distributions. Such distributions result in rapid and extensive penetration by the nonwetting phase. The process is remarkably sensitive to the capillary‐hydraulic properties that determine the value of knw/kw at large wetting phase saturations, a region in which laboratory measurements provide the least resolution. The penetration of a nonwetting phase can be expected to be dramatically affected by the presence of fissures, worm holes, or other macropores. Calculations for radial displacement of a nonwetting phase resident at a small initial saturation show the displacement to be inefficient. The fractional flow of the nonwetting phase falls rapidly and, for a specific example, becomes 1% by the time one pore volume of water has been injected.
Real‐time control of a system of large hydropower reservoirs
Authors: McLaughlin Dennis , Velasco Horacio L.
Published: February 2008

This paper describes a real‐time optimal control approach for operating a system of large hydropower reservoirs. The operating objective is to track specified power output targets, subject to a variety of physical constraints. The constraints describe the hydrologie behavior of the tributary watershed and the dynamics of the reservoir system. The decision variables are monthly average releases from each of the system reservoirs. These releases are derived in real time, as functions of available measurements of reservoir storage and tributary inflow. Inflow and measurement uncertainty are explicitly included in the state and measurement equations. The stochastic operations problem is first formulated in general terms and then simplified to allow the use of classical linear‐quadratic stochastic control concepts. The solution to the simplified control problem is implemented by combining a linear deterministic control law with a linear estimation algorithm. The resulting stochastic controller is applied to a two‐reservoir system in the Caroni River basin of Venezuela. Preliminary tests indicate that the controller performs well in this application, even when some of its underlying assumptions are violated.
Comparison of biodegradation kinetics with an instantaneous reaction model for groundwater
Authors: Rifai Hanadi S. , Bedient Philip B.
Published: February 2008

Biodegradation modeling is gaining more attention as a useful tool for predicting the attenuation of organic contaminants in groundwater. In this paper we compare two conceptual models. The first approximates biodegradation with an instantaneous reaction between the organics and oxygen. The advantage of this model is its simplicity and minimal biotransformation data requirements. Inherent in this model is the assumption that biodegradation in groundwater is oxygen transport limited. The second conceptual model utilizes a dual substrate Monod kinetic relationship to calculate biodegradation. While theoretically more accurate, the model suffers from being numerically more complex to implement. The kinetic model also requires more biotransformation data for each organic contaminant than the instantaneous reaction model. The analysis presented in this paper is intended to determine the requirements that must be placed on a system's Damköhler number to guarantee that reaction mechanisms are not kinetically limited. Results indicate that the instantaneous reaction is an adequate assumption when nondimensionalized reaction rates are large.
Multiyear trends in snowpack ion accumulation and loss, northern Michigan
Authors: Stottlemyer Robert , Rutkowski Darcy
Published: February 2008

From December 1982 to May 1987 the quality and quantity of snowfall and snowpack were measured at four stations in a small (176 ha) gauged watershed adjacent to Lake Superior's south shore. Annual precipitation was less than and winter precipitation greater than observed east and south of the Lake Superior basin. Snowfall averaged 37% of annual precipitation but was quite variable. Snowfall significantly increased (from 21.1 to 35.7 cm, P < 0.001) with 150 m increase in elevation. Hydrogen and SO42− were the dominant ions in precipitation and snowpack while Ca2+ and HCO3− dominated stream water. No significant time trends in winter precipitation chemistry were found. Snowpack ionic retention rarely matched precipitation input. Generally, midwinter freeze‐thaw periods resulted in elevated concentrations of solutes in snow meltwater and greatly reduced snowpack ion loads prior to peak stream water discharge. All ions exhibited pulses in snowmelt each year. Preferential elution from the snowpack of SO42− and K+ was observed. Stream water H+, NH4+ and most NO3− pulses were associated with midwinter thaws. Stream water SO42− pulses were rare. For those years exhibiting the most pronounced spring increase in stream H+, NO3− and SO42− concentration, the magnitude and rate of concentration change was as great in a year of small peak snowpack ion load as it was following a more rapid ion loss from a larger snowpack load. This suggests that the pattern of snowpack melt and especially the pathway the meltwater follows to the stream may be important factors in determining whether stream water chemical pulses occur.
A reductionist physical approach to unsaturated aquifer recharge from a circular spreading basin
Authors: Morel‐Seytoux Hubert J. , Miracapillo Cinzia , Abdulrazzak Mohamed J.
Published: February 2008

In this paper the process of aquifer recharge from a circular area through the unsaturated zone is investigated. The same basic methodology described previously by the authors for the case of a long strip recharging area (Morel‐Seytoux et al., 1988) is applied. An approximate solution to the three‐dimensional problem is obtained by matching two unidimensional flows, a vertical and a radial one. The mathematical formulation is obtained first for the case of a constant infiltration rate and then for a time‐dependent rate through the unsaturated zone. The formulation leads to an integrodifferential equation whose solution is obtained numerically using the “discrete kernel” approach (Morel‐Seytoux et al., 1973; Morel‐Seytoux and Daly, 1975). In both cases, concrete examples illustrate the influence of the parameters on the discharge into the saturated zone and on the water table level. Also, a criterion to evaluate the efficiency of the recharge is provided for practical purposes. This criterion allows comparison between different recharge designs.
Mapping saturated areas with a helicopter‐borne C band scatterometer
Authors: Brun C. , Bernard R. , Vidal‐Madjar D. , Gascuel‐Odoux C. , Merot P. , Duchesne J. , Nicolas H.
Published: February 2008

The “contributing area” concept is one of several basic concepts in modeling hydrologic processes used to explain storm runoff production. The main difficulty in using this concept of variable source areas is the identification and characterization of saturated areas according to the temporal and spatial variability during a storm event. In this experiment a helicopter‐borne C band scatterometer has been used to locate the saturated areas within a small watershed. In contrast to the general results, where radar cross section increases with soil moisture, calibration shows a backscatter coefficient decreasing for the high gravimetric water contents of the saturated areas, which may be due to the increasing importance of specular reflection processes. It appears that a threshold on the backscatter coefficient may be determined which would allow the location of saturated areas, independent of the nature of the field surface (vegetation cover or slope). These experiments, which were intended partly as ERS 1 satellite simulations, show that active microwaves may be a good tool for partial hydrology.
R‐5 revisited: 2. Reevaluation of a quasi‐physically based rainfall‐runoff model with supplemental information
Authors: Loague Keith
Published: February 2008

In this paper a new set of infiltration data for a small rangeland catchment, described in the companion paper (Loague and Gander, this issue), is used to reexcite and reevaluate a quasi‐physically based rainfall‐runoff model that was previously tested by Loague and Freeze (1985). The rainfall‐runoff model is an event‐based simulator of the Horton overland flow mechanism. The performance of the model is shown to be somewhat improved in this study with the supplemental information over the original study. However, the model does not fully approximate the rainfall‐runoff processes for the catchment, a combination of Horton and Dunne overland flow, and therefore the new data do not lead to an overwhelming improvement in the model performance.
Effective hydraulic conductivity for gradually varying flow
Authors: Kitanidis Peter K.
Published: February 2008

Consider the problem of flow in a porous medium with hydraulic conductivity which fluctuates locally about a mean value. The flow is unsteady but gradually or slowly varying, i.e., the correlation length of head fluctuations is considerably larger than the correlation length of hydraulic‐conductivity fluctuations. The equations which must be satisfied by the effective conductivity tensor are derived under general conditions using a method of volume averaging and spatial moments. The generality of the derived equations is shown by replicating some known results.
Fourier domain shape analysis methods: A brief review and an illustrative application to rainfall area evolution
Authors: Kumar Praveen , Foufoula‐Georgiou Efi
Published: February 2008

Morphological shape analysis techniques offer valuable tools for the study of several hydrologic and atmospheric processes. Detailed description of patterns, as well as evolution and comparison of patterns can be efficiently performed in the Fourier domain and by means of a finite number of Fourier descriptors. In this technical note we present a brief summary of three Fourier domain shape analysis methods: the complex plane method, the angular direction method, and the polar coordinates method. We illustrate the use of the complex plane method for studying the evolution of rainfall areas within a radar‐depicted rainfall field for the purpose of short‐term precipitation forecasting.
Evaluation of regional flood frequency analysis with a region of influence approach
Authors: Burn Donald H.
Published: February 2008

A novel approach to regional flood frequency analysis is presented and evaluated. The technique is referred to as the region of influence approach in that every site can have a potentially unique set of gauging stations for use in the estimation of at‐site extremes. The rationale for the methodology is discussed, and several options for incorporating the approach into regional flood frequency analysis are developed and compared with traditional regional estimation procedures. Through a Monte Carlo experiment, the region of influence approach is demonstrated to provide improved at‐site estimates of extreme flow quantlies in terms of network average root mean squared error and comparable results for bias. The method is further shown to have attractive features for estimating extremes for unusual sites in a network of gauging stations.
Aquifer thermal energy storage: A numerical simulation of field experiments in China
Authors: Xue Yuqun , Xie Chunhong , Li Qingfen
Published: February 2008

This paper describes the results of computer simulations for three seasonal aquifer thermal energy storage experiments which have been carried out recently in China. The governing equation of the mathematical model used to simulate the experiments contains convection, conduction and heat dispersion terms. A general description of the experiments, three‐dimensional mathematical model and numerical method used is presented. The simulated temperatures agree very well with the observed field data. Total mean values of the absolute errors are 0.5°C for the single‐well experiment, 0.7°C for the double‐well experiment and 0.4°C for the multiwell experiment; relative error ranges from 2.8% to 4.5%. The simulated production temperatures and energy recovery ratios, ϵ, (ϵsimu = 0.638 versus ϵobs = 0.640 and ϵsimu = 0.729 versus ϵobs = 0.753 for different experiments) also agree very well with the field data. Discussions are also given on the determination and choice of various parameters used in the simulations. The results strongly indicate the validity of the model and simulation procedures used. It is necessary to consider the heat transfer through the fluid phase by heat dispersion in the governing equation.
Identification of large‐scale spatial trends in hydrologic data
Authors: Rajaram Harihar , McLaughlin Dennis
Published: February 2008

It is often useful to distinguish different scales of variability in hydrologic properties such as hydraulic conductivity. In the simplest two‐scale case, large‐scale variations can be viewed as a trend, while small‐scale fluctuations about this trend can be viewed as a random residual. This paper describes a method for estimating spatial trends from scattered field measurements. The basic concept is to treat both the trend and the residual as stationary random functions. These functions are distinguished by their spatial spectral (or covariance) properties, which may be estimated from available data or simply hypothesized. We present two versions of a general algorithm for estimating spatial trends: (1) a discrete version which is useful in practical applications where data are limited and irregularly spaced and (2) a continuous version which can be used to study the effects of using incorrect spectral parameters. Applications of the discrete algorithm to both synthetically generated data and field measurements yield satisfactory trend estimates. An analysis based on the continuous algorithm shows that the estimation error lower bound for these applications depends on two dimensionless ratios, that is, the scale disparity (ratio of the trend and residual correlation scales) and the signal‐to‐noise ratio (ratio of the trend and residual variances). These ratios may be used to evaluate the feasibility of trend estimation before field samples are actually collected.
Analytical traveling wave solutions for transport with nonlinear and nonequilibrium adsorption
Authors: van der Zee Sjoerd E. A. T. M.
Published: February 2008

Transport was modeled for a soil with dual porosity, or with chemical nonequilibrium, assuming first‐order kinetics. The equilibrium sorption equation in the immobile region is nonlinear. Two equilibrium equations for sorption were considered, that is, the Langmuir and the Van Bemmelen‐Freundlich equations. The sorption equation in the mobile region is assumed to be linear. Analytical solutions were obtained that describe the traveling wave displacement found for initial resident concentrations that are smaller than the feed concentration and for infinite displacement times, neglecting the coupled effects of dispersion and nonequilibrium conditions. These waves travel with a fixed shape and a fixed velocity through the homogeneous flow domain. Besides expressions for the front shape, expressions for the front thickness and the front position were also presented. Differences with respect to the linear sorption case are the smaller front thickness and the non‐Fickian type of displacement. The non‐Fickian behavior is intrinsic to the traveling wave assumption as the front does not spread with the square root of time. The analytical solutions obtained for the equilibrium and for the nonequilibrium situations are mathematically equivalent. Only the effective diffusion/dispersion coefficient needs to be adapted to account for nonequilibrium effects, as for linear dual‐porosity models. Apart from early time behavior, the traveling wave solutions agree well with numerical approximations. The front steepness depends sensitively on the degree of nonlinearity. The sensitivity on the dispersion coefficient and first‐order rate coefficient may be large but depends on which mechanism controls front spreading.
Assessment of Runoff and Suspended Sediment Yield in a Partially Forested Catchment in Southern Chile
Authors: Iroumé Andrés
Published: February 2008

A 12‐month study of runoff and suspended sediment yield was undertaken in a 0.93 km2 catchment in southern Chile. Rainfall and total runoff for the period December 1983–November 1984 were estimated at 2170 and 1150 mm, respectively, representing a runoff coefficient of 0.53. Suspended sediment concentrations ranged between 14 and 186 mg L−1, with an average of 71 mg L−1. Suspended sediment yield was estimated at 84 t or 90 t km−2 yr−1.
Evaluation of Five Simulation Models for Predicting Aldicarb and Bromide Behavior Under Field Conditions
Authors: Pennell K. D. , Hornsby A. G. , Jessup R. E. , Rao P. S. C.
Published: February 2008

Five pesticide simulation models (Chemical Movement in Layered Soils (CLMS), Method of Underground Solute Evaluation (MOUSE), Pesticide Root Zone Model (PRZM), Groundwater Leading Effects of Agriculture Management Systems (GLEAMS), and Leaching Estimation and Chemistry Model‐Pesticides (LEACHMP)) were evaluated using data for the transport and transformation of aldicarb and bromide in the unsaturated zone. Although these models have been tested separately, to date no effort has been made to evaluate all of them using a comprehensive data set from a single field study. Model performance was evaluated based on their ability to predict: the depth of solute center of mass, solute dissipation, and solute concentration distributions within the soil profile. GLEAMS and MOUSE underestimated bromide and aldicarb dissipation, while the other models provided satisfactory predictions of both solute center of mass and pesticide degradation. None of the models accurately described measured solute concentration distributions. Recommendations are made for the selection and use of the models based on objective and subjective criteria including graphical analysis, objective functions, intended model use, and the difficulty in obtaining model input data.
Regional Surface Fluxes From Remotely Sensed Skin Temperature and Lower Boundary Layer Measurements
Authors: Sugita Michiaki , Brutsaert Wilfried
Published: February 2008

During First International Satellite Land Surface Climatology Project Field Experiment in north‐eastern Kansas, surface temperature was measured by infrared radiation thermometers at some 12 stations spread over the 15 × 15 km experimental area. These data, together with wind and temperature profiles in the unstable atmospheric boundary layer measured by means of radiosondes, were analyzed within the framework of Monin‐Obukhov similarity. The radiometric scalar roughness corresponding to the radiometric surface temperature was found to increase as the season progressed; for the spring campaign the mean value was zoh,r = 4.56 × 10−7 m and for the fall zoh, r = 1.01 × 10 −2 m. The radiometric scalar roughness could also be expressed as a function of solar elevation and to a lesser extent, of canopy height or leaf area index. For an elevation range 10° ≤ α ≤ 75° the regression equation is zoh,r = exp [−0.735 ‐ 3.61 tan (α)]. With this function good agreement (r = 0.87) was obtained between the profile‐derived regional surface flux of sensible heat and the mean flux measured independently at ground‐based stations under unstable conditions. Similarly, regional values of evaporation, obtained by means of the energy budget method from these sensible heat flux estimates, were in good agreement (r = 0.96).
Preferential Flow and the Generation of Runoff: 1. Boundary Layer Flow Theory
Authors: Germann Peter F.
Published: February 2008

Approaches to soil water flow, which are based on the theory of potential flow, often overestimate either the volume of flow or the response time at the hillslope scale when their results are compared with observations. Macropore flow is frequently thought to be the reason for the discrepancy between observations and model performance. The expression macropore flow is considered to be too restricting. It confines the rapid flow and transport processes to the easily observed channels, concealing the more general question as to what degree potential flow theory adequately describes flow in porous media. The application of potential flow theory to infiltration leads to the Richards equations only when hydrodynamic dispersion of soil water and capillary potential are perfectly correlated. In this paper a boundary layer infiltration model is presented, which is based on kinematic theory. It is also expanded to lateral flow in a sloping soil.
Effect of ion beam irradiation on the structure of ZnO films deposited by a dc arc plasmatron
Authors: Penkov Oleksiy V. , Lee Heon-Ju , Plaksin Vadim Yu. , Ko Min Gook , Joa Sang Beom , Yim Chan Joo
Published: February 2008

The deposition of polycrystalline ZnO film on a cold substrate was performed by using a plasmatron in rough vacuum condition. Low energy oxygen ion beam generated by a cold cathode ion source was introduced during the deposition process. The change of film property on the ion beam energy was checked. It is shown that irradiation by 200eV ions improves crystalline structure of the film. Increasing of ion beam energy up to 400eV leads to the degradation of a crystalline structure and decreases the deposition rate.