bluuebunny/crossref_metadata_2025 huggingface dataset:
Empirical equations for some soil hydraulic properties
Authors: Clapp Roger B. , Hornberger George M.
Published: February 2008

The soil moisture characteristic may be modeled as a power curve combined with a short parabolic section near saturation to represent gradual air entry. This two‐part function—together with a power function relating soil moisture and hydraulic conductivity—is used to derive a formula for the wetting front suction required by the Green‐Ampt equation. Representative parameters for the moisture characteristic, the wetting front suction, and the sorptivity, a parameter in the infiltration equation derived by Philip (1957), are computed by using the desorption data of Holtan et al. (1968). Average values of the parameters, and associated standard deviations, are calculated for 11 soil textural classes. The results of this study indicate that the exponent of the moisture characteristic power curve can be predicted reasonably well from soil texture and that gradual air entry may have a considerable effect on a soil's wetting front suction.
Gravity‐induced cross‐formational flow of formation fluids, red earth region, Alberta, Canada: Analysis, patterns, and evolution
Authors: Tóth J.
Published: February 2008

Three zones of different generations of formation‐fluid flow systems were identified from analyses of the potentiometric surface, hypsographic distribution of fresh water heads, pressure‐depth relations, water table elevations, and dynamic pressure increments observed in five extensive water‐bearing units in a 20,400‐mi2 (52,840 km2) geologically mature area in northern Alberta. In each zone, fluids move in gravity‐induced flow systems maintained by cross‐formational energy transfer and subject to past or present boundary conditions. The force fields and associated flow systems in the basal zone of Middle Devonian aquifers were generated by and adjusted to the topography of the Pliocene continental surface. However, subsequent to the erosional exposure of the sub‐Cretaceous unconformity about Pleistocene times, the drainage of the middle zone disrupted the supply of energy from the land surface to the Pliocene flow systems and changed them into slowly decaying relicts of regional fluid dynamics tending toward hydrostatic equilibrium. The same event resulted in the formation of the Pleistocene flow systems of the middle zone which straddles the sub‐Cretaceous unconformity and comprises Paleozoic and basal Cretaceous strata. It is recharged mainly in the area's major hill ranges through the overlying thick succession of Cretaceous clastic rocks which include major aquitards also, and partly through reef ‘chimneys’ from the underlying basal zone. Fluids from the middle zone discharge by ascending cross‐formational flow in the major valleys and also by flow along the bedding planes through the unconformity's outcrops at low elevations beyond the boundaries of the area. These fluids are therefore at relatively low potential, which is adjusted to present boundary conditions. The upper hydrodynamic zone is perched on top of the principal Lower Cretaceous aquitard of the area and includes Cretaceous and Quaternary aquifers. Its flow systems are generated by local differences of the Holocene (present) topography and extend only a few hundred feet in depth. Downward leakage from this zone supplies recharge to the middle hydrodynamic zone. Solution of the diffusion equation for transient fluid potentials suggests a halflife time of approximately 0.7 m.y. for the excess hydraulic heads in the basal zone, indicating pre‐Pleistocene origin for the observed flow distributions in that zone and thus supporting conclusions derived from the steady state patterns of formation‐fluid pressures.
Three‐dimensional modeling of groundwater flow systems
Authors: Frind Emil O. , Verge Murray J.
Published: February 2008

Practical aspects of three‐dimensional (3‐D) modeling of groundwater flow systems are closely examined. A Galerkin finite element model is designed with a view to providing flexibility, user convenience, and a high degree of efficiency, qualities which are critical to the success of 3‐D modeling of real systems. The model is based on the general saturated‐unsaturated continuity equation. Several integration schemes and matrix solvers are compared, and relative costs are expressed as functions of grid size. Examples presented include a hypothetical system and a real system. Simulation costs are generally found to be reasonable for grids of the size encountered with real systems. It is found that a remaining obstacle to the unified treatment of saturated‐unsaturated systems is that the optimum element sizes required for saturated and unsaturated flow are not always compatible because of constraints arising from the physical properties of the materials. In general, however, it appears that with presently available tools, 3‐D analysis is a practical option.
Hydrologic behavior of a forested mountain soil in coastal British Columbia
Authors: De Vries J. , Chow T. L.
Published: February 2008

Inferences with respect to the hydrologic behavior of a West Coast forested mountain soil are based on measurement of the water potential field during the wetting and drainage phases of simulated rainfall events. The field was measured as a continuous function of time with an array of 13 tensiometers in combination with pressure transducers and a data collection system. Measurements were carried out with the forest floor intact, partly disturbed, and totally removed. Inferences were made by interpreting the water potential fields as ‘fingerprints of hydrologic behavior.’ It was concluded that during a simulated rainfall event, water flow through the profile was partitioned between root channels and the soil matrix which is transversed by the channels. The proportion of the flow conducted by the channels was at its maximum during the non‐steady state phase of the event, decreasing to a minimum as steady state was approached. During the drainage phase of the event the channels did not contribute to downward flow. The process of internal infiltration is discussed. It causes the soil matrix to wet up both from the surface of the H horizon of the forest floor and from the wetted periphery of the root channels. Results indicated that simulated disturbance of the forest floor down to the mineral soil caused a shift in the water flow pathway from the channels to the soil matrix. It was speculated that this shift was due to closure of the channel openings. It was speculated that the flashy response of streams to rainfall events is related to rapid subsurface storm flow through root channels. Also, because water flow through the soil matrix is much slower than that through root channels, it is likely that forest floor disturbance on a watershed‐wide scale would result in an increase in the time lag between the rainfall event and the corresponding streamflow event.
Simulation procedures for Box‐Jenkins Models
Authors: McLeod Angus Ian , Hipel Keith William
Published: February 2008

New simulation procedures are presented for generating synthetic data from either a nonseasonal or a seasonal Box‐Jenkins model. The simulation techniques are designed so that random realizations of the underlying stochastic process are employed for starting values. Because fixed beginning values are not utilized, systematic bias is not introduced into the synthetic trace. When the data have been transformed by a Box‐Cox transformation, the inverse transformation can be conveniently incorporated into the simulation process. Also a new algorithm is presented for simulating integrated models. A method is developed for incorporating parameter uncertainty into simulation studies, and it is explained how this technique can be used in the design of reservoirs. Practical applications are presented to demonstrate the efficacy of the aforesaid simulation methods. In addition, the Fortran computer subroutines for the simulation procedures are included in an appendix with the microfiche edition of this paper.

Appendix is available with entire article on microfiche. Order from American Geophysical Union, 1909 K Street, N.W., Washington, D.C. 20006. Document W78‐006; $1.00. Payment must accompanyorder.
Bank‐full discharge of rivers
Authors: Williams Garnett P.
Published: February 2008

Eleven possible definitions of ‘bank‐full’ have been used by various investigators. The active floodplain is the most meaningful bank‐full level to the fluvial geomorphologist, whereas the banks of the valley flat are the most important to engineers. Comparison of 16 ways of determining bank‐full discharge suggests that bank‐full discharge at gaged sites should be obtained from the station's rating curve, where bank‐full gage height is determined from a longitudinal profile of the floodplain along the entire reach. At ungaged sites, bank‐full discharge can be estimated from the empirical equation of this study or from the Gauckler‐Manning equation. In the latter case the resistance coefficient n should be estimated at the field site for bank‐full flow; a measured low‐flow n should not be used. Bank‐full discharge does not have a common recurrence frequency among the rivers studied, and the discharge corresponding to the 1.5‐year recurrence interval in most cases does not represent the bank‐full discharge.
Evolution of contaminated groundwater in Holt County, Nebraska
Authors: Exner Mary E. , Spalding Roy F.
Published: February 2008

The theoretical absence of the in situ formation of most common mineral phases and the high vertical permeability of the relatively inert soils and unsaturated layer permit detection of man‐induced environmental changes in the dilute groundwater of Holt County. Correlation coefficients show many significant associations for the major ions in groundwater affected by point and nonpoint‐source contamination. Large areas of nonpoint contamination are attributed to fertilization and irrigation of the sandy soils. In these areas increases in the average annual groundwater concentrations of Cl−, SO42−, and NO3− average 0.44, 0.57, and 4.9 mg/l/yr, respectively. A proposed model suggests that 50% of the applied nitrogen fertilizer infiltrates to the groundwater reservoir.
Energy budget evaluation of the transpiration‐pF relationship in a young pine forest
Authors: Tajchman S. , Hädrich F. , Lee R.
Published: February 2008

By using the Bowen ratio method, hourly and daily evapotranspiration totals were determined during a drying period for a 9‐year‐old pine forest (Pinus sylvestris) situated in the upper Rhine area of Germany. A relationship between the soil water suction, expressed by pF, and the ratio Q of the latent heat of evapotranspiration to the available energy was obtained. For 2 < pF < 3, Q ≈ 0.6, and for pF > 3, Q decreases exponentially when pF increases. For pF ≈ 4.2, Q = 0.11. These and other empirical and theoretical results discussed in the paper suggest that the Q−pF relationship can be useful for calculating evapotranspiration from complex terrain situations where the micrometeorological approach is inapplicable.
Identification of suspended sediment sources by means of magnetic measurements: Some preliminary results
Authors: Oldfield F. , Rummery T. A. , Thompson R. , Walling D. E.
Published: February 2008

Rapid, nondestructive magnetic measurements of initial low‐field susceptibility x, saturation isothermal remanent magnetization (IRMsat), and coercivity of IRM provide a means of identifying the source of suspended sediments in rivers. Preliminary results derived from the application of these measurements both to suspended sediment and to potential sources within the instrumented catchment of the Jackmoor Brook near Exeter, United Kingdom, demonstrate the value of this approach in an area of Permian sandstone bedrock where the contrast in magnetic properties between parent material and topsoil is easily characterized. High flows are shown to be associated with suspended sediment, the magnetic properties of which are indistinguishable from those of the cultivated soils of the catchment.
An advection‐aridity approach to estimate actual regional evapotranspiration
Authors: Brutsaert Wilfried , Stricker Han
Published: February 2008

Actual regional evapotranspiration is calculated by means of a procedure requiring only meteorological data, which are those commonly used in the various versions of the combination approach for potential evaporation. The approach is based on a conceptual model involving, first, the effect of regional advection on potential evaporation, and second, an assumed symmetry between potential and actual evaporation with respect to the evaporative power of the air in the absence of advection. Thus the degree of nonavailability of water for evapotranspiration, that is the aridity of the region, is deduced from the regional advection of drying power of the air, as implied by the atmospheric conditions. The approach was found to give good agreement with daily data of evapotranspiration obtained by means of an energy budget method for a period of severe drought in a rural watershed in a sandy region. One of the advantages is that no soil moisture data, no stomatal resistance properties of the vegetation, nor any other additional aridity parameters are required to determine actual evapotranspiration.
Water quality in river systems: Monte‐Carlo Analysis
Authors: Whitehead Paul , Young Peter
Published: February 2008

Water quality models are described for a 55‐km stretch of the Bedford Ouse River in central eastern England. The dynamic models relate time‐varying upstream influents to downstream water quality and are stochastic to account for the uncertainty in the system. A stochastic simulation provides forecasts of water quality at a downstream abstraction point in terms of probability distributions, and these are compared with water quality standards, also defined in probabilistic terms. Effluent from the new city of Milton Keynes enters the river at an upstream point, and the impact of the effluent on the aquatic environment is assessed together with the sensitivity of the water quality model to parametric uncertainty.
A statistical view of a class of water quality indices
Authors: Landwehr Jurate Maciunas
Published: February 2008

Water quality indices are treated as random variables; the class of quality ‘averaging’ indices is examined and several statistics are derived. It is seen that the probability density functions of the water quality constituents as well as the structure of the transform functions (rating curves) influence the ability of indices to measure policy performance.
A statistical approach to the inverse problem of aquifer hydrology: 1. Theory
Authors: Neuman Shlomo P. , Yakowitz Sidney
Published: February 2008

A new statistically based approach to the problem of estimating spatially varying aquifer transmissivities on the basis of steady state water level data is presented. The method involves solving a family of generalized nonlinear regression problems and then selecting one particular solution from this family by means of a comparative analysis of residuals. A linearized error analysis of the solution is included. This analysis allows one to estimate the covariance of the transmissivity estimates as well as the square error of the estimates of hydraulic head. In addition to the explicitly statistical orientation of the method, it has an additional feature of permitting the user to incorporate a priori information about the transmissivities. This information may be based on actual field data such as pumping tests, or on statistical data accumulated from similar aquifers elsewhere in the world. A highly efficient explicit numerical scheme for solving the inverse problem in an approximate manner when errors in water level data are sufficiently small is also described. When these errors are large, the explicit scheme may still be useful for obtaining a rapid initial idea about the approximate location of the optimum solution. Paper 1 presents the theory and illustrates it by a theoretical example. The purpose of this example is to demonstrate the effectiveness of our method in dealing with noisy data obtained from a known model. Application of the method to real data will be described in paper 2.
Management model of a groundwater system with a transient pollutant source
Authors: Gorelick Steven M. , Remson Irwin , Cottle Richard W.
Published: February 2008

A management model is presented for determining the maximum concentration of a transient pollutant source such that space‐dependent groundwater quality requirements are met. The method is illustrated using a one‐dimensional groundwater system with a single pollutant source at an adjacent stream. The chloride concentration of the source is to be managed to meet variable groundwater quality constraints. Management of the pollutant source is demonstrated for a single‐period as well as for repeated‐period pollutant discharges. The Crank‐Nicolson numerical approximation of the convective‐dispersive equation is used in the management model. The pollutant source concentration is treated as a parameter in the resulting system of linear equations. Taking advantage of the block structure of the matrix, the concentrations throughout the system are defined and manipulated as functions of this parameter for each time step. The parameter is maximized by comparison of groundwater quality limits with the groundwater solute concentrations at the corresponding nodes. The minimum value of the parameter over the entire time frame is the maximum concentration allowable in the source water over the management period or periods.
Estimation of parameters and quantiles of Wakeby Distributions: 1. Known lower bounds
Authors: Landwehr J. Maciunas , Matalas N. C. , Wallis J. R.
Published: February 2008

An algorithm based on the use of probability weighted moments allows estimation of the parameters of the Wakeby distribution. In the case where the lower bound is known, the quantile estimates, unlike the parameter estimates, tend to be neither highly biased nor highly variable, even for samples of small size (n = 5).
Rainfall measurements by weather radar: Applications to hydrology
Authors: Barge B. L. , Humphries R. G. , Mah S. J. , Kuhnke W. K.
Published: February 2008

Surface precipitation measurements are of prime importance in studies of hydrology, climatology, and meteorology. These measurements can be improved by using both weather radar and conventional rain and snow gages. Recent advances in digital radar data management make possible improved precipitation estimates for hydrological applications such as flood forecasting. A project undertaken in Alberta provides areal precipitation data for operational flood forecasting. Maps depicting rainfall intensities are generated at specified time intervals from the Alberta Research Council's S band weather radar. Transmitted 150 km by telecopier to the Flow Forecasting Branch, Alberta Environment, the real‐time radar‐derived areal maps of precipitation are used with point surface observations to specify more precisely the precipitation events that lead to floods. During precipitation events, weather radar data provide an indication of the applicability of point surface observations, leading to better operational flow forecasts. In one example the radar showed that high rainfall amounts observed at a conventional surface rain gage fell over a localized area. Using only surface gage information, a flood forecast likely would have been issued. However, radar intelligence suggested otherwise, so the forecast was not issued. The potential benefit of weather radar to hydrologists is assessed using rainfall within a representative subbasin. The precipitation was estimated from radar observations and from an independent gage network used by operational hydrologists. Throughout a stormy 6‐day period, the accumulated precipitation for a subbasin estimated by the two methods agreed to within 15%. Shortcomings of typical rain gage networks in assessment of areal rainfall are evident. In one case, weather radar data revealed that although rain fell on the network gages, the subbasin itself received little rain, so the gage estimate was high. In another example, the weather radar demonstrated that rain fell in the subbasin but missed the network gages. The spatial variability of precipitation, evident in weather radar observations, is generally not observed by gage networks. Therefore radar measurements of rainfall intensity and rainfall amount can be of considerable benefit to operational and applied hydrologists.
Stochastic analysis of macrodispersion in a stratified aquifer
Authors: Gelhar Lynn W. , Gutjahr Allan L. , Naff Richard L.
Published: February 2008

The longitudinal dispersion produced as a result of vertical variations of hydraulic conductivity in a stratified aquifer is analyzed by treating the variability of conductivity and concentration as homogeneous stochastic processes. The mass transport process is described using a first‐order approximation which is analogous to that of G. I. Taylor for flow in tubes. The resulting stochastic differential equation describing the concentration field is solved using spectral representations. The results of the analysis demonstrate that for large time the longitudinal dispersivity approaches a constant value which is dependent on statistical properties of the medium. The analysis also describes the transient development of the dispersive process and some non‐Fickian effects which occur early in the displacement process.
Analytical solution of a velocity dependent dispersion problem
Authors: Tang D. H. , Babu D. K.
Published: February 2008

A complete description of the convective‐dispersive transport of a contaminant from an injection well requires consideration of a velocity dependent dispersion coefficient. An analytical solution of this equation for steady fluid flow conditions can be obtained. The solution is significantly different from existing approximate analytical solutions. A numerical solution to this problem converges to the new analytical solution upon refinement of the finite difference net.
Thermal energy storage in a confined aquifer: Experimental results
Authors: Molz F. J. , Parr A. D. , Andersen P. F. , Lucido V. D. , Warman J. C.
Published: February 2008

To aid in testing the idea of storing thermal energy in aquifers, an experiment was performed by Auburn University in which 54,784 m3 of water was pumped from a shallow supply aquifer, heated to an average temperature of 55°C, and injected into a deeper confined aquifer where the ambient temperature was 20°C. After a storage period of 51 days, 55,345 m3 of water were produced from the confined aquifer. Throughout the experiment, which lasted approximately 6 months, groundwater temperatures were recorded at six depths in each of 10 observation wells, and hydraulic heads were recorded in five observation wells. In order to prevent errors due to thermal convection, most of the observation wells recording temperature had to be backfilled with sand. During the 41‐day production period, the temperature of the produced water varied from 55° to 33°C, and 65% of the injected thermal energy was recovered. At no time was an appreciable amount of free thermal convection observed in the storage formation. The dominant heat dissipation mechanisms appeared to be hydrodynamic thermal dispersion and possible mixing of cold and hot water induced by clogging and unclogging of the injection‐production well. On the basis of laboratory and field studies, it was concluded that clogging of the injection well, which constituted the major technical problem during the experiment, was caused by the freshwater‐sensitive nature of the storage aquifer. Due to the relatively low concentration of cations in the supply water, clay particles would swell, disperse, and migrate until they became trapped in the relatively small pores connecting the larger pores. Surging the pump and back washing the injection well would dislodge the clogging particles and temporarily improve the storage formation permeability. The phenomenon seems largely independent of temperature because it was reproduced in the laboratory with unheated water. It may, however, depend on pore velocity. Future research should be directed toward procedures for selecting storage aquifers that will have minimal susceptibility to clogging and other geochemical problems. Procedures for overcoming such difficulties are needed also because clogging and related phenomena will be more the rule than the exception. Designing an aquifer thermal storage system for maximum energy recovery would involve selecting an appropriate aquifer, analyzing the effects of hydrodynamic thermal dispersion and thermal convection if it is predicted to occur, anticipating geochemical problems, designing the optimum supply‐injection‐production well configuration and injecting a sufficiently large volume of heated water to realize economies of scale related to increasing volume‐surface area ratio.
Design of operational precipitation and streamflow networks for river forecasting
Authors: Jettmar R. Uwe , Young G. Kenneth , Farnsworth Richard K. , Schaake John C.
Published: February 2008

A methodology is presented for assessing the value of river forecasting to possible changes in existing precipitation and streamflow networks. This study was undertaken as a part of an effort to evaluate the expected benefit of automating all or part of the data gathering networks used by the National Weather Service. A surrogate measure of benefits, called the ‘mean forecast lead time,’ is related indirectly to benefits because the value of river forecasting depends on the lead time available for the flood plain dweller to take action and respond to the forecast. Presented here is the rationale for the methodology and the results of part of the research using streamflow generated by Hurricane Agnes (June 1972) and Hurricane Eloise (September 1975) for the Susquehanna River basin.
Kriging in the design of streamflow sampling networks
Authors: Villeneuve Jean‐Pierre , Morin Guy , Bobee Bernard , Leblanc Denis , Delhomme Jean‐Pierre
Published: February 2008

Kriging is of particular interest in network design because of its ability to estimate streamflow values using existing stations. Another possibility offered by kriging is the estimation of variance reduction gained by addition of fictitious stations in regions of high variance. In this article we give a brief description of kriging theory as developed at the Ecole des Mines de Paris. In order to improve and optimize the Quebec streamflow recording network design we kriged specific streamflows with a given return period over the Quebec province, using the data observed at existing stations. For the evaluation of the given return period flow and its sampling variance at each gauged site we use the log Pearson type 3 distribution model. Kriging is an optimal estimation technique, in terms of minimum variance, and contrary to other methods it gives an estimation variance for any point in the kriged domain, which is essential in network design.
An analysis of hydrodispersive transfer in aquifers
Authors: Sauty Jean‐Pierre
Published: February 2008

This work is concerned with the nonreactive transport of solute materials in groundwater, or hydro‐dispersive transfer. Several types of flow fields are considered: linear (or uniform) flow with one‐ and two‐dimensional dispersion and radial flow under diverging and converging conditions. The analysis includes the two main possibilities for introduction of solutes into an aquifer: continuous and instantaneous (or slug) injection. Different solutions from the literature plus some original solutions for dispersion in a linear flow field have been unified by transposing the solutions into dimensionless variables of concentration (CR), time (tR), and the Peclet number (P). This permits an analysis of the errors committed in some commonly used approximations for dispersion as a function of P. In the case of radial flow, a numerical method using finite differences has been developed that can be applied to either diverging or converging flow problems. Results in dimensionless form when compared to the only analytical approximations that could be found (for continuous injection in a diverging flow field) indicate that the approximate solutions are in error when P ≤ 10. The radial flow results are also compared to those for linear flow fields to demonstrate that in most cases either approach can be used as long as P > 3. A series of dimensionless type curves has been developed showing CR versus tR for practical ranges of P. A simple method of interpreting tracer tests is proposed using these type curves. One is able to directly determine dispersivity and kinematic porosity using curve matching techniques. Results from some recent field tests in France are analyzed using this approach. There is definite confirmation from these investigations that the apparent (macroscopic) dispersivity can vary depending on the distances used in the field.
On the definition of droughts
Authors: Dracup John A. , Lee Kil Seong , Paulson Edwin G.
Published: February 2008

In this paper, several considerations for developing a practical, analytical definition of droughts are discussed. These considerations include (1) selection of the nature of the water deficit to be studied (hydrological, meteorological, or agricultural); (2) selection of the averaging period used to discretize a continuous time series (months, seasons, or years); (3) selection of the truncation level used to separate droughts from the remainder of the time series (mean or median); and (4) method of regionalization or standardization. These decisions are discussed in terms of their impacts on various approaches to drought frequency analysis. In this paper, drought events are considered to be composed of duration, magnitude (average water deficiency), and severity (cumulative water deficiency). An application of the proposed drought definition procedure is presented for the case of a frequency analysis of multiyear hydrologic droughts.
Trace metal budgets for a forested watershed in the New Jersey pine barrens
Authors: Swanson Karen A. , Johnson Arthur H.
Published: February 2008

Deposition of Pb, Cu, Ni, Fe, Mn, and Cd on the McDonalds Branch Basin in bulk precipitation was 25.4, 5.3, 6.6, 64.6, 20.7, and <2 mg m−2 yr−1 for a 1 year period in 1978–1979. Output in streamflow was 1.7, 0.7, 1.9, 148, 12.8, and <1 mg m−2 yr−1, respectively, and loss to deep groundwater was 1.4, 1.9, 2.3, 123, 20.4, and <1 mg m−2 yr−1. Pb, Cu, and Ni accumulated in the basin, while there was a net loss of Fe and Mn from the ecosystem. The major mechanism for movement of Fe and Pb out of the basin was interpreted to be complexation with and transport by mobile organic matter.
On Jacob's Approximation in flow through porous media
Authors: Singh Sita Ram , Sagar Budhi
Published: February 2008

The equation of flow of slightly compressible fluids through nondeformable, or consolidating, porous media is a nonlinear parabolic partial differential equation of the second order. Hitherto, the equation has been approximately linearized by neglecting its nonlinear term. This method of linearization, hereafter called Jacob's method, was first introduced by C. E. Jacob (1950) for flow of groundwater in confined aquifers. In this article the method of functional transformation was used to find a transformation which exactly linearized the equation. A problem of constant drawdown well in extensive homogeneous and isotropic consolidating, or nondeformable, porous media was solved. Solution of the approximately linearized differential equation for the aforesaid problem was compared with the exact one, and the error due to the neglect of the nonlinear term was analyzed. It is shown that the error resulting from Jacob's approximate method of linearization for flow of water through confined aquifers is negligible. However, in the case of the transport of other compressible fluids through nondeformable formations the error is not insignificant.
A note on the meaning of storage coefficient
Authors: Narasimhan T. N. , Kanehiro B. Y.
Published: February 2008

The term storage coefficient and the related expressions, storativity, specific storage, and total compressibility, are frequently used in hydrogeology, petroleum engineering, and other fields. These parameters seek to express the quantity of water required to be added to or removed from storage in order to change (under conditions of drainage) the average hydraulic head or pore pressure of a porous material by a given amount. Originally introduced over 4 decades ago, the storage parameter is still used by many in the restricted sense of a coefficient occurring in the partial differential equation describing fully saturated flow. However, with the significant increase in our computational abilities using powerful numerical integration techniques, there presently exists a need to have a more fundamental appreciation of the storage parameter as it relates to transient fluid flow in porous media. Such a fundamental approach requires consideration of the type of loading to which the porous medium is subject as well as certain conventions followed by various workers in actually defining the parameter. While no new derivations or results are presented, this paper attempts to assemble in a single place the various ideas relevant to the storage parameter in order to obtain a generalized perspective.
Risk of dam failure in benefit‐cost analysis
Authors: Baecher Gregory B. , Paté M. Elisabeth , De Neufville Richard
Published: February 2008

A procedure is presented for calculating the costs of failure of a dam and for incorporating these risk costs into the evaluation process. Basically, it involves a calculation of expected value. One critical issue is what the probability of failure should be; given that research will not provide accurate values for some time, a default value (of 10−4 per dam year) is proposed to be used until better information becomes available. Another critical question is whether the refinement of incorporating risk costs is worthwhile; here, the risk‐benefit factor α is introduced to be used as a screening tool to decide the question. The importance of implicit value ascribed to lives lost through failure is discussed.
Electromagnetic determination of soil water content: Measurements in coaxial transmission lines
Authors: Topp G. C. , Davis J. L. , Annan A. P.
Published: February 2008

The dependence of the dielectric constant, at frequencies between 1 MHz and 1 GHz, on the volumetric water content is determined empirically in the laboratory. The effect of varying the texture, bulk density, temperature, and soluble salt content on this relationship was also determined. Time‐domain reflectometry (TDR) was used to measure the dielectric constant of a wide range of granular specimens placed in a coaxial transmission line. The water or salt solution was cycled continuously to or from the specimen, with minimal disturbance, through porous disks placed along the sides of the coaxial tube.

Four mineral soils with a range of texture from sandy loam to clay were tested. An empirical relationship between the apparent dielectric constant Ka and the volumetric water content θv, which is independent of soil type, soil density, soil temperature, and soluble salt content, can be used to determine θv, from air dry to water saturated, with an error of estimate of 0.013. Precision of θv to within ±0.01 from Ka can be obtained with a calibration for the particular granular material of interest. An organic soil, vermiculite, and two sizes of glass beads were also tested successfully. The empirical relationship determined here agrees very well with other experimenters' results, which use a wide range of electrical techniques over the frequency range of 20 MHz and 1 GHz and widely varying soil types. The results of applying the TDR technique on parallel transmission lines in the field to measure θv versus depth are encouraging.
Competition versus optimal control in groundwater pumping
Authors: Gisser Micha , Sánchez David A.
Published: February 2008

This article considers one of the most important issues in water resources research, namely, the management of groundwater. Economists have long taken it for granted that the temporal allocation of groundwater would lead to welfare losses if left to the free market because all farmers pump from a common aquifer. Hence water economists studied extensively optimal control of temporal groundwater allocation. They never paused to compare the temporal allocation yielded by optimal control with the free market. In this article we prove by comparing the two strategies analytically that if the storage capacity of the aquifer is relatively large, the difference between them is so small that it can be ignored for practical consideration.
Multiport diffuser as line source of momentum in shallow water
Authors: Lee Joseph H. , Jirka Gerhard H.
Published: February 2008

Multiport diffusers are linear structures consisting of many closely spaced nozzles which inject a series of high‐velocity jets into an ambient fluid. The discharge of heated water into the shallow coastal zone is considered herein as a typical practice for cooling water disposal from steam electric power generation. The flow and temperature fields, induced in the otherwise stagnant and homogeneous fluid layer, are analyzed by representing the diffuser as a line source of fluid momentum in a two‐dimensional coordinate system, thus neglecting the initial momentum transfer zone in which the three‐dimensional jets merge to produce a vertically fully mixed flow. A scaling argument which considers the effect of pressure deviations, turbulent bottom friction, and lateral turbulent diffusion shows that the flow field can be divided into the near field, of order of the diffuser length, and into the far field, at longer distances. The near field is characterized by a predominantly inviscid behavior and gives rise to a contracting slipstream motion, qualitatively similar to the slipstream produced by an airscrew. The shape of the slip streamline is found by mapping the complex potential of the flow into the log hodograph plane. The boundary conditions at the diffuser line are assumed to be a uniform normal velocity and a uniform longitudinal acceleration. The interior velocity and pressure distribution are determined through a finite difference solution using the known geometry of the slipstream. Results indicate a strong separation angle (60°) of the slipstream at the diffuser and a rapid approach to the asymptotic contraction value (½). An integral model is developed for the depth‐averaged temperature and velocity in the far field of the ‘diffuser plume’ (i.e., a localized current with elevated temperatures with weaker velocities and a uniform temperature outside). The model includes the effect of turbulent friction at the plume bottom, described by a quadratic friction law, and of lateral turbulent entrainment, described by the entrainment hypothesis of Morton et al. (1956). The far‐field model is combined with the inviscid near‐field solution, thus superimposing the real fluid effects onto the properties of the contracting slipstream. Two distinctive features characterize the diffuser plume. First, it experiences an exponential loss of fluid momentum through turbulent bottom friction which leads to an ultimate plume stagnation at a characteristic distance ƒ0LD/(16H), where ƒ0 is a quadratic friction coefficient, LD the diffuser length, and H the water depth, and also puts a limit on the total lateral entrainment flow. Second, the initial plume characteristics, and thus its rate of entrainment, are controlled by the accelerating high‐velocity slipstream in the vicinity of the line source. Experiments in a shallow laboratory basin corroborate the theoretical results, both as regards the qualitative features of the contracting slipstream and the quantitative observations of induced velocities and flow rates.
A clear‐sky spectral solar radiation model for snow‐covered mountainous terrain
Authors: Dozier Jeff
Published: February 2008

A clear‐sky spectral solar radiation model for direct and diffuse fluxes, combined with topographic calculations from digital terrain data, computes either incident, net, or reflected solar radiation at any point on a snow surface in mountainous terrain. The radiation may be integrated over any wavelength range from 250 to 5000 nm, or over any time step. Atmospheric attenuation parameters are ozone, water vapor, the Angstrom turbidity coefficient and exponent, and the absorptance to reflectance ratio of the atmospheric aerosols. The model derives these, from measurements which may contain both systematic and random errors, by finding the least squares solution to an overdetermined set of nonlinear equations. For calculations over a specified area, it employs table look‐up procedures, so that computation speed for the spectral model approaches that for a lumped model. Thus it may be useful as part of a snow surface energy budget calculation over a drainage basin.
A representation of an instantaneous unit hydrograph from geomorphology
Authors: Gupta Vijay K. , Waymire Ed , Wang C. T.
Published: February 2008

The channel network and the overland flow regions in a river basin satisfy Horton's empirical geo‐morphologic laws when ordered according to the Strahler ordering scheme. This setting is presently employed in a kinetic theoretic framework for obtaining an explicit mathematical representation for the instantaneous unit hydrograph (iuh) at the basin outlet. Two examples are developed which lead to explicit formulae for the iuh. These examples are formally analogous to the solutions that would result if a basin is represented in terms of linear reservoirs and channels, respectively, in series and in parallel. However, this analogy is only formal, and it does not carry through physically. All but one of the parameters appearing in the iuh formulae are obtained in terms of Horton's bifurcation ratio, stream length ratio, and stream area ratio. The one unknown parameter is obtained through specifying the basin mean lag time independently. Three basins from Illinois are selected to check the theoretical results with the observed direct surface runoff hydrographs. The theory provided excellent agreement for two basins with areas of the order of 1100 mi2 (1770 km2) but underestimates the peak flow for the smaller basin with 300‐mi2 (483‐km2) area. This relative lack of agreement for the smaller basin may be used to question the validity of the linearity assumption in the rainfall runoff transformation which is embedded in the above development.
Is transport in porous media always diffusive? A counterexample
Authors: Matheron G. , De Marsily G.
Published: February 2008

For the special case of a stratified porous medium with flow parallel to the bedding it is shown that the transport of solute cannot, in general, be represented by the usual convection‐diffusion equation, even for large time. The necessary conditions for the appearance of a Fickian diffusive process are discussed and compared with previous work done by Gelhar et al. (1979) and Marie et al. (1967). It is shown, however, that when the flow is not exactly parallel to the stratification, diffusive behavior is much more likely to appear. The need for further work on the mechanism of transport in porous media is then emphasized.
Survey of methods for soil moisture determination
Authors: Schmugge T. J. , Jackson T. J. , McKim H. L.
Published: February 2008

Increased interest in soil moisture information for applications in such disciplines as hydrology, meteorology, and agriculture has necessitated an overview of both existing and proposed methods for determination of soil moisture. This paper thus discusses methods of in situ soil moisture determination including gravimetric, nuclear, and electromagnetic techniques; soil physics models that track the behavior of water in the soil in response to meteorological inputs (precipitation) and demands (evapotranspiration); and remote sensing approaches that use the solar, thermal infrared, and microwave portions of the electromagnetic spectrum. The abilities of these approaches to satisfy various user needs for soil moisture information vary from application to application. Therefore we have proposed a conceptual scheme for merging these approaches into an integrated system. This system should provide soil moisture information having the potential for meeting the requirements of various applications.
Validity of Cubic Law for fluid flow in a deformable rock fracture
Authors: Witherspoon P. A. , Wang J. S. Y. , Iwai K. , Gale J. E.
Published: February 2008

The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.