bluuebunny/crossref_metadata_2025 huggingface dataset:
On One Difference between the Gould and Moran Storage Models
Authors: Klemeš V.
Published: February 2008

Whereas in the Moran model, the matrix of the transition probabilities specifies transitions that are safe and those during which a failure occurs, the transition matrix in the Gould model does not provide such information. To make the Gould model applicable to problems concerning reservoir behavior in two or more successive years, the governing equation of the Gould model is decomposed into two parts, one involving only the safe transitions, the other involving only the failure transitions.
Microwave Evapotron
Authors: McGavin R. E. , Uhlenhopp P. B. , Bean B. R.
Published: February 2008

A microwave evapotron is described in which a modified microwave refractometer and a vertical sonic anemometer are combined to measure the vertical transport of water vapor directly by the eddy correlation method. The instrument was used successfully in the field. Ten‐minute samples from this instrument compare favorably with the results from conventional methods. In terms of evaporation, the accuracy is within 0.02 cm/day, and the resolution is within 0.002 cm/day.
Economic Evaluation of Some Watershed Management Alternatives on Forest Land in West Virginia
Authors: Worley David P. , Patric James H.
Published: February 2008

Timber and water research conducted at the Fernow Experimental Forest provides a 10‐year record of timber growth and streamflow increases. An approach for evaluating streamflow increases in terms of timber growth forgone is modeled. Light cutting (up to one‐fourth of the timber volume) slightly increased the value of timber growth as well as the amount of streamflow. Cutting one‐third to one‐half of the merchantable volume sacrificed timber regrowth for streamflow gain. Cutting one‐half to three‐fourths of the timber volume resulted in small streamflow increases for large sacrifices of timber regrowth. Cutting three‐fourths or more of the forest vegetation provided major increases in streamflow but no return from timber during the 10‐year period of regrowth. Average annual water costs ranged from 0 to $1.30 per thousand gallons. Although these water costs may be invalid outside the Fernow Experimental Forest, they nevertheless suggest a magnitude for water costs under similar forest conditions.
Unit and Total Cost Functions for Water Treatment Based on Koenig's Data
Authors: Hinomoto Hirohide
Published: February 2008

Whether a water treatment plant is installed as an independent facility or as an addition to an existing system of such plants, the determination of its capacity depends to a great extent on its total cost, which is composed of the amortization of capital investment and the fixed and variable operating costs. This total cost is formulated as a function of capacity and use rate on the basis of data reported by Koenig on surface water treatment.
Application of Thermocouple Psychrometers to Soil Water Transport
Authors: Enfield C. G. , Hsieh J. J. C.
Published: February 2008

The energy status (potential) of water can be used to calculate water flux. Thus, field measurement of water potential is superior to conventional gravimetric soil moisture content measurements for dynamic soil water studies and is useful for steady state analysis of soil water transport. Data presented show that soil thermocouple psychrometers give sufficiently sensitive, in situ measurements of water potential to apply energy concepts to dynamic soil water movement. Thus the soil thermocouple psychrometer can be used to obtain soil water potential information needed to determine the direction of water flow and the magnitude of the driving force. This technique is not limited to studies of the penetration of rainfall in the arid region but also has application in evapotranspiration studies, and might be adaptable to such studies as groundwater hazards of sanitary land fills.
Projections of Darcy's Law as Related to the Ellipse of Direction
Authors: Case C. M.
Published: February 2008

The concept of projecting the tensor form of Darcy's law in a given direction is examined mathematically. The conclusions drawn from this analysis are (1) the projections in a given direction of each term in the tensor expression for Darcy's law cannot in general be assembled to give a valid expression for Darcy's law, and (2) an ellipse of direction cannot be used to find the projection of the permeability tensor at a point in any direction other than that parallel to the resultant velocity at that point.
Estimating Truncation Error in Image Well Theory
Authors: Bostock Charles A.
Published: February 2008

Assume that groundwater production from wells located beyond a distance, say r1, that is large relative to the spacing between adjacent image wells may be treated as an equivalent, continuous, constant production rate per unit of ground surface area. By means of the Theis [1935] equation and the usual symbol nomenclature, the result is s (r1, ∞) = QNw (t/S) [e−u1 − u1 W(u1)[, where s(r1, ∞) is the drawdown at the observation point due to all image wells beyond distance r1, and Nw is the density of wells per unit area. This equation is useful for calculating the minimum radius r1 min of the image well model in which image wells must be included for a given pumping time t to keep the truncation error due to omitted image wells less than some predesignated value s(r1, ∞)max. On the other hand, if an image well model exists and is composed of a fixed number of image wells for approximating an areally infinite system, then the equation will give the maximum allowable pumping time for a given allowable truncation error s(r1, ∞)max.
Problems choosing irrigation techniques in a developing country
Authors: Soltani‐Mohammadi G. R.
Published: February 2008

A linear programing model is developed to select between modern surface and portable or semiportable sprinkler systems in two irrigation projects in Iran. Skilled labor is included in the model as one of the major limiting factors in the development of modern irrigated agriculture in a developing country.

Under the specified conditions and assumptions, a portable or semiportable sprinkler system is indicated to be economically superior to a modern surface irrigation system for the development of new lands. However, in lands where a modern surface irrigation system has already been installed the transformation to sprinkler irrigation is not feasible. A completely automated sprinkler system is not indicated for either set of conditions in Iran. Primitive irrigation was not included in this study because of lack of data. Finally, the welfare effects of the choice of techniques are indicated.
Effects of random data errors on the parameter values for a conceptual model
Authors: Ibbitt R. P.
Published: February 2008

A conceptual model was used to generate synthetic error‐free runoff data from precipitation and potential evaporation records. Random errors were then introduced into all three data records. By automatically and objectively fitting the model to different combinations of error‐free and error‐contaminated records, the effects of the errors on the fitting were studied. The value of the fitting criterion was found to depend largely on the errors in the runoff record. The variations in the final parameter values for fittings to error‐contaminated data were shown to be no greater than for the error‐free case. The data were then used to find the sensitivity figures for each parameter by a method that is less localized than the standard perturbation technique.
Principles of groundwater data acquisition
Authors: Gilliland John A.
Published: February 2008

Any data acquisition program, must be planned and designed to attain some objective, and since the objectives of different types of groundwater programs differ, each case must be considered on its own merits.

Groundwater programs can be broken into three different categories, each requiring a different type of data: (1) water resource allocation and management, (2) water resource evaluation, and (3) research. Any water resource program involves significant costs, against which the probability of success must be weighed. Data acquisition costs cannot be considered separately from other costs because the individual processes involved in attaining the overall objective are all interrelated; e.g., a saving in data acquisition costs may lead to increased processing costs. The way in which the various tools of hydrogeology (instruments, techniques, and so on) affect the costs, the precision, and the reliability of results for the three types of programs are considered, and ways by which costs can be reduced and efficiency increased are examined.
Definition hydrologic units for water studies in Arkansas
Authors: Bedinger M. S. , Sniegocki R. T.
Published: February 2008

Water studies that use cause‐effect models are planned for Arkansas. Cause‐effect models that incorporate the physical and flow characteristics of the hydrologic system in the state can serve as tools to predict the effects of various stresses on the system. Another very important use of models is to evaluate the adequacy of the data networks in meeting the data needs of the state. Arkansas is divided into several flow subsystems for use as study units. Natural hydrologic boundaries of a stream and of the groundwater flow parts of a system commonly do not coincide. In the coastal plain, the natural aquifer boundaries are taken as the principal boundaries of the hydrologic subsystems, and natural surface water boundaries may enclose an additional peripheral area that must be considered. In the interior highlands, surface water divides are the principal boundaries of the hydrologic subsystems.
On the tensor concept of unsaturated anisotropic hydraulic conductivity
Authors: Cisler Jaromir
Published: February 2008

Unsaturated hydraulic conductivity can be regarded as a second order tensor, the coefficients of which depend on soil moisture suction or soil moisture content. General equations for the three‐dimensional anisotropic unsaturated flow of water in porous media must involve nine coefficients of the hydraulic conductivity tensor, all of which are, in general, nonzero. Equations for horizontal anisotropic unsaturated flow can be reduced to an orthotropic form with principal hydraulic conductivities Kx′,Ky′, and Kz′ provided the principal axes of the conductivity tensor do not rotate when the moisture content or the soil moisture suction changes. This condition is fulfilled only for a certain constant ratio of hydraulic conductivities in different directions that is independent of the soil moisture suction or soil moisture content. In this case the flow velocity is given by the simple Darcy type equation without the cross coefficients of hydraulic conductivity. A simple experimental method is proposed to determine the diagonal and cross coefficients of the hydraulic conductivity as functions of the soil moisture suction for horizontal unsaturated steady flow in anisotropic porous media.
Digital simulation of the Boussinesq equation for a water table aquifer
Authors: Lin Chang L.
Published: February 2008

A mathematical model has been developed to simulate the Boussinesq equation for a two‐dimensional water table aquifer. Transient solutions to the finite difference approximations based on an irregular mesh matrix were obtained by the alternating direction implicit method. The precision of the model was evaluated by comparing the volume of water pumped with the amount of water released from storage and the amount received from a nearby recharging river. Preliminary results indicate that the model is suitable for the study of transient flow in a permeable sand and gravel aquifer.
Accounting for apparatus‐induced dispersion in analyses of miscible displacement experiments
Authors: James R. V. , Rubin Jacob
Published: February 2008

Investigators studying hydrodynamic dispersion in porous media have had some difficulty in theoretically predicting experimental breakthrough curves from laboratory columns. The greatest discrepancies occur for short‐column experiments or studies of unsaturated media. Some of the disagreement apparently can be eliminated by a quantitative treatment of apparatus‐induced dispersion. The experimental system is treated as a two‐layer construct in which the porous medium and the apparatus are considered as separate layers. The dispersion characteristics of the apparatus layer are determined independently in the absence of the porous material. The dispersion coefficient for the porous medium is obtained from a two‐layer dispersion equation. The hydrodynamic dispersion coefficients calculated in this manner were found to be as much as 40% lower than those obtained by the usual, one‐layer approach.
North Atlantic Regional Supply Model
Authors: DeLucia Russell J. , Rogers Peter
Published: February 2008

In the North Atlantic regional (NAR) study the supply model was designed to complement the demand model. The level of complexity of the supply model was developed from a balance of limits of resources and time available and the need to capture certain characteristics of the system. The resulting model is a mathematical programing model minimizing efficiency costs expressed in annual terms. Those cost curves that are nonlinear are approximated by using piecewise linear functions. It is a static annual model based on a critical period analysis and selected risk levels. The model incorporates the cost curves for supply from the headwater and mainstream storage, groundwater, desalting for 50 subbasins of the planning area and for selected interbasin transfer possibilities. Hydrologic and in‐stream use constraints are incorporated. The costs are minimized subject to meeting these and the set of demand constraints. The model produces a configuration of supplies for the 50 subbasins to meet the particular demand sets produced by analyzing the demand model. Objectives other than efficiency can be reflected to some extent through manipulation of the objective function and the constraints.
System relationships for a Panama Canal Water Supply Study
Authors: Hulman Lewis G.
Published: February 2008

Increased shipping through the Panama Canal has begun to tax the capability of the water supply system to provide lockage water. To investigate the use of existing and supplemental water supplies, the operation of the canal was simulated by using detailed data on the water used during ship transits, the storage capability of the reservoir system serving the canal, the hydropower capability of each reservoir, the operating constraints for shipping, the anticipated municipal water supply diversion, the historical shipping use, the economics of shipping, the hydropower production, and the supplemental water supplies. Canal operation for different operation criteria and different shipping levels was used with chronological run‐off data for simulation. This paper contains a description of the canal and its operational characteristics and a detailed summary of the system relationships.
Conceptual analysis of rainfall and runoff data with a hybrid computer
Authors: McCarthy J. R.
Published: February 2008

A watershed is represented by a serial multistage system in which each stage employs a generalized conceptual element. The stages are initial abstractions, surface storage, translation, intermediate abstractions, channel storage, final abstractions, and outlet storage. The specific character of each stage is determined by using data from an actual watershed and a hybrid computer. Data compiled from a 16‐acre tract on the Atterbury Experimental Watershed near Tucson, Arizona, are used. A broad spectrum of recorded conditions gives rise to typical problems involving rainfall‐runoff relations on arid land watersheds. Infiltration becomes the important initial abstraction, and Horton's equation is modified to make the capacity rate of infiltration a function of time and precipitation intensity. The analysis relates depression losses to storm variables so that the starting time of the runoff can be estimated. A provision is included, for subsequent depression losses that may occur, for example, during multiple peak flows. The translation model developed permits the shifting of the computed hydrograph to coincide with the actual runoff. Linear reservoirs are used in storage stages. A suggested ‘parameter matrix’ increases the reliability of predictions.
Approximate solution to the freezing of the ice‐water system
Authors: Foss Stephen D. , Fan Stephen S. T.
Published: February 2008

A simplified solution to the Stefan problem for the ice‐water system is presented. The solution is based on the assumption that the freezing process is the rate‐controlling step and hence that the temperature of the solid phase is represented by a linear function of thickness. Our solution is compared with the series solution of Westphal. The two solutions agree remarkably well for small Stefan numbers and deviate from one another for larger Stefan numbers. This comparison indicates that when the freezing process is the rate‐controlling mechanism, the proposed simplified solution yields satisfactory results.
Evaporative cooling of a body of water
Authors: Dake Jonas M. K.
Published: February 2008

Known physical laws and empirical evaporation formulas are correlated to provide a simple means for estimating evaporative heat losses from water bodies. The result also provides an adjustment for atmospheric stability to established evaporation formulas.
Some evidence of stomatal restriction of evaporation from well‐watered plant canopies
Authors: Shepherd W.
Published: February 2008

Various aspects of stomatal control of evaporation and their practical significance have been considered in a recent exchange of opinions in this journal. The present paper describes some considerable departures from potential evaporation rates observed under conditions of generous soil water supply. These departures occurred on days of high potential rates and represented reductions of up to about 20% from levels that might otherwise have been expected under the prevailing atmospheric conditions. However, the reductions represented only a few percent of the seasonal or annual evaporation. Accompanying symptoms of plant moisture stress are discussed.
New approach to water allocation under uncertainty
Authors: Thomas George , Whinston Andrew , Wright Gordon
Published: February 2008

This paper discusses some new water allocation policies that maximize expected profit when the central authority controlling a reservoir faces deterministic demand functions and a stochastic supply of water. The demand functions are distinguished by price and a guaranteed probability of receiving water. A penalty cost is incurred if the guaranteed probability of delivery is not met by the reservoir manager. The demand functions could represent, for example, consumers of water for the purposes of hydroelectric power, recreation, irrigation, and dilution for pollution control. The optimal contract policies (optimal prices and associated optimal guaranteed delivery probabilities) are characterized. The analysis shows that the use of price discrimination may be superior (Pareto's law) to a uniform contract for all consumers of water. The results are illustrated by a stochastic model of two classes of water consumers.
Dynamic surface temperature structure of thermal plumes
Authors: Scarpace F. L. , Green T.
Published: February 2008

Airborne thermal imagery is used to show that thermal plumes often vary rapidly in space and time, although both the initial thermal effluent and the receiving water change very little. The imagery is buttressed by simultaneous data taken from boats. The rapid variations can cast doubt on the validity of some standard methods of measuring thermal plumes. The plume is shown to be sometimes dominated by a series of concentric thermal fronts that spread radially outward from the outfall. These are described, and various tentative explanations for their occurrence are given.
I would if I could (self‐denial by conditional models)
Authors: Slack J. R.
Published: February 2008

Since a finite sample of a random process rarely has statistics equal to the population values, a random process model (including the associated estimators of driving parameters) may be conditional in the sense that functional constraints on allowable driving parameters may be numerically violated. A conditional model then may generate finite samples yielding estimates of driving parameters unacceptable to its own restrictions and thereby may deny that it was the source of the sample.
Entropy as a measure of the areal concentration of water‐oriented industry
Authors: Paulson Albert S. , Garrison Charles B.
Published: February 2008

The concepts of entropy and numbers equivalent are applied to the configuration of water intensive and non‐water intensive employment data by county in the Tennessee Valley region to provide an overall measure of the areal concentration of employment and population. If the underlying distribution of employees is assumed to be governed by the multinomial distribution, it is shown that there have been shifts in microlocational characteristics, since the role chance can play is minimal. Non‐water intensive manufacturing employment has become much more areally dispersed over the study period 1959–1968, but it appears that there has been neither a decrease nor an increase in concentration in water intensive employment. Finally, the two types of employment are concentrated to markedly different degrees.
Approximate solutions for nonsteady column drainage
Authors: Arbhabhirama Anat , Ahmed Zahir Uddin
Published: February 2008

An application of pore size distribution to a capillary analogy is introduced to obtain approximate solutions for nonsteady column drainage. The analysis is based on the assumption that the drainable pore space of porous media can be represented by a set of capillary tubes of various sizes having a size distribution that provides the same capillary pressure‐saturation relationship as the real media. The solutions obtained approximately describe the cumulative outflow and the saturated front as functions of time and measurable soil parameters. Theoretical solutions are verified by using experimental and numerical results of the present work and the work of others.
Effect of a water table aquitard on drawdown in an underlying pumped aquifer
Authors: Cooley Richard L. , Case Clinton M.
Published: February 2008

A theoretical derivation of the convolution integral produced by N. S. Boulton's originally empirical ‘delayed yield’ theory shows that it describes the vertical velocity at the base of a water table aquitard having negligible compressibility. The derivation requires that fluid compressibility be neglected and that water be obtained from storage by instantaneous desaturation (or saturation) with a declining (or rising) water table. An expression for the ‘delay index’ shows that it is a function of hydraulic conductivity, specific yield, and thickness of the aquitard. To evaluate the effect that gradual desaturation may have on flow in a water table aquitard, flow in the unsaturated zone was approximated by an analytical solution of Richards' equation assuming time invariant power law functions for change of both capillary conductivity and moisture content in the vertical. An equation was derived that shows that the length of time for which gradual desaturation could influence flow in the saturated zone is a function of the hydraulic conductivity and specific yield of the aquitard and the thickness of the capillary fringe. To investigate the effect that delayed yield could have on flow in the aquifer, analytical solutions were made for flow to a well pumping at a constant rate in a compressible aquifer overlain by a compressible water table aquitard. Comparison of results that consider delayed yield effects with those that do not suggests that the unsaturated zone has little effect on flow in the aquifer, and comparison of these solutions with numerical solutions that treat the unsaturated zone explicitly conforms with this result.
Creation of conditional dependency matrices based on a stochastic streamflow synthesis technique
Authors: Clainos D. M. , Roefs T. G. , Duckstein L.
Published: February 2008

The construction of transition probability matrices by the streamflow synthesis technique developed by the Hydrologie Engineering Center of the U.S. Army Corps of Engineers was tried. In certain cases it was found to be necessary to use a transform different from the Wilson‐Hilferty transform used in the stated routine in order to produce reasonable results. Other details of the numerical considerations necessary for the definition of discrete conditional probability matrices between monthly flow volumes are described.
Use of cross correlation between hydrological time series to improve estimates of lag one autoregressive parameters
Authors: Frost Jean , Clarke R. T.
Published: February 2008

The problem considered requires estimation of parameters characterizing a serially correlated hydrologic time series {yt}, where data are also available from a longer time series {xt}, itself serially correlated and cross correlated with {yt}. On the assumption that both series are lag one autoregressions (when {yt} is characterized by three parameters μy, β, and σϵ2), large‐sample variances for the autoregressive parameter β are derived from the short series {yt} alone or from both series {xt} and {yt}, and the relative information is investigated numerically. It is concluded that, when the two serial correlations are approximately equal and the length of {xt} is twice that of {yt}, the gain in precision of the estimate β is about 4% when the cross correlation is 0.2, about 15% when the cross correlation is 0.4, about 31% when the cross correlation is 0.6, and about 49% when the cross correlation is 0.8. The equations giving maximum likelihood (ML) estimates are examined, and a relatively simple numerical technique is developed for one particular case of some practical importance. Small‐sample properties of both ML estimates and an estimate derived from work by Matalas are investigated, and tentative conclusions are that (1) the modified Matalas estimates have smaller mean square error than ML estimates, and (2) ML estimates of μy and β derived from both series have smaller mean square error than ML estimates of μy and β derived from the single series only, the converse being true for σϵ2.
Modified Monte Carlo application to groundwater movement— The simultaneity procedures
Authors: Shih Sun‐Fu
Published: February 2008

The advantages of applying the Monte Carlo methods to problems of water movement in soils have shown that very difficult problems can often be treated easily and that solutions at only a few points in a flow system can be obtained independently. A modified Monte Carlo application presented herein, termed the simultaneity procedure, has been developed to hasten the classical Monte Carlo application. So that the simultaneity procedure can be adapted more widely, the techniques of a parallel simultaneity procedure and a successive simultaneity procedure are devised and demonstrated. Examples are presented not only for the problems of groundwater movement and Thiessen coefficients but also for the problems of general mathematics. Comparisons of results indicate that the simultaneity procedure has the same accuracy as the classical Monte Carlo method, but the computing time is reduced by approximately 30–60% by using the simultaneity procedure.
Least‐cost allocation and valuation model for water resources
Authors: Young H. Peyton , Thompson Russell G.
Published: February 2008

A mathematical economic model of water use and water quality is formulated that allows for trade‐offs between the technologies of water use and waste treatment and the capacities of different regions for waste assimilation. The input‐output coefficients of water‐using production processes are written as functions of intake water quality so that the feedback effects of waste discharge on the economic process itself may be evaluated. The model determines the combination of production processes in each region that minimizes the overall cost of meeting a given bill of final demands, including demands for water quality (i.e., water quality standards). Such a model could be used to evaluate water development projects on a consistent basis; in particular it would calculate the marginal values of water in different regions and the marginal costs of meeting different water quality objectives.
Steady state ground motions caused by single‐well pumping
Authors: Brown Colin B. , Burges Stephen J.
Published: February 2008

Surface motions caused by well pumping have often caused technical as well as legal problems. Here a small deformation theory of such motions is formally developed for a single‐well axially symmetric case. The theory involves no coupling between the fluid and solid phase; linear elasticity is used. Numerical comparison with field results suggests that this theory may be adequate to describe steady state long‐term ground motions.
Economic feasibility of irrigating southern pines
Authors: Manogaran Chelvadurai
Published: February 2008

A climatic model developed for estimating the depressing effect of drought on the diameter growth of loblolly pines in the southern United States is used to project potential pine growth under conditions of no soil moisture deficit, which irrigation could assure. The regional distribution of the additional growth demonstrates that the benefits of irrigation would increase from the Atlantic coast toward east Texas. The dollar value of the additional growth based on the current price of pulpwood is compared with the costs necessary to irrigate southern pines. Under present conditions of technology, costs of irrigation would exceed benefits. Technological changes, higher pulpwood prices, or decisions of the federal government to improve southern forests may justify the irrigation costs necessary to increase southern pine production.
Application of the implicit method to surges in open channels
Authors: Chaudhry Y. M. , Contractor D. N.
Published: February 2008

A technique is proposed by which continuous numerical computation of flows with surges in open channels can be handled with an implicit formulation. The one‐dimensional gradually varied flow equations of continuity and momentum are written in finite difference form for the point (I + ½, J + θ) in the x, t plane, where I is the distance counter, J is the time counter, and θ is a weighting parameter that is varied from 0.5 to 1.0. A computer program was written to solve the problem in which the discharge hydrograph is given at the upstream end of a channel and a stage‐discharge relationship is specified at the downstream end. This program was applied to different flow situations in laboratory channels and natural rivers. It was found that θ = 0.5 produced results with a steep wave front but with considerable numerical instability. The use of θ = 1.0 gave results with considerable diffusion of the wave front. The use of θ = 0.60 produced results that had a steep wave front and only a minor degree of numerical instability. This value of θ resulted in good agreement between calculated and measured hydrographs at the downstream end of the channel in most applications. However, the optimum value of θ depends on channel friction and the steepness of the wave front.
Optimum Reservoir Operating Policies and the Imposition of a Reliability Constraint
Authors: Askew Arthur J.
Published: February 2008

Stochastic dynamic programing can be used to derive optimum operating policies that maximize the expected net dollar benefits for a water resource system. It is shown that these policies may give rise to significant probabilities of system failure. Such probabilities can be estimated by system simulation. A procedure is proposed in which the combined use of dynamic programing and simulation allows an optimum operating policy to be derived that will maximize the expected net benefit and yet not violate constraints on the probability of failure. Limitations to failure are applied directly by imposing a fixed penalty on the system whenever it fails, thus inducing amendments in the optimum policies derived. Further developments of the technique are foreshadowed.
Application of seasonal parametric linear stochastic models to monthly flow data
Authors: McKerchar A. I. , Delleur J. W.
Published: February 2008

Stochastic linear models are fitted to hydrologic data for two main reasons: to enable forecasts of the data one or more time periods ahead and to enable the generation of sequences of synthetic data. These techniques are of considerable importance to the design and operation of water resource systems. Short sequences of data lead to uncertainties in the estimation of model parameters and to doubts about the appropriateness of particular time series models. A premium is placed on models that are economical in terms of the number of parameters required. One such family of models is multiplicative seasonal autoregressive integrated moving average (Arima) models that have been described by G. E. P. Box and G. M. Jenkins. In this paper we illustrate the process of identifying the particular member of the family that fits logarithms of monthly flows, estimating the parameters, and checking the fit. The seasonal Arima model accounts for the seasonal variability in the monthly means but not the seasonal variability of the monthly standard deviations: for this reason its value is limited. The forecasting of flows one or more months ahead is described with an example.
Seepage through a hillside: The steady water table
Authors: Warrick A. W. , Lomen D. O.
Published: February 2008

An analytical solution is developed for seepage through a hillside in which a curved water table is maintained by steady percolating water. The two‐dimensional surface is assumed to be a straight slope from the base to a seepage point but may be irregular at higher elevations. Conformal transformations are used to determine seepage elevations and water table profiles as a function of the seepage rate and the slope. For small slopes and small percolation rates the seepage elevation is equal to the rainfall rate times the width of the slope divided by the saturated hydraulic conductivity.
A note on the use of spectral analysis to detect leads and lags in annual cycles of water quality
Authors: Dowling J. Malcolm
Published: February 2008

The conditions necessary for interpreting spectral analytic phase statistics as absolute delays in physical time are examined. This interpretation is justified only if the two series are related as input and output by a simple delay process. For all other linear input‐output systems it is incorrect to interpret phase as if there is a simple delay between input and output series.
Isotopic and chemical characteristics of high‐level groundwaters on Oahu, Hawaii
Authors: Hufen T. H. , Buddemeier R. W. , Lau L. S.
Published: February 2008

High‐level dike‐confined groundwaters and high‐level perched groundwaters on Oahu, Hawaii, were analyzed for tritium, radiocarbon, carbon 13, and several chemical constituents. Discharges from several tunnels that tap dike compartments contain postbomb tritium, indicating the presence of modern (since 1954) recharge. The amount of postbomb tritium in samples taken inside one of the tunnels is a function of the distance between sampling point and overlying surface. Chemical and carbon isotopic compositions of dike waters, established in the soil zone of the overlying ground surface, remain unchanged while the water is passing through the basaltic carbonate‐free compartments. Dike water carbon isotope data are sufficiently consistent to serve as initial values for the dating of water in the Honolulu basal aquifers. The radiocarbon and carbon 13 data for perched waters are similar to those for the dike waters, in spite of the much larger bicarbonate concentrations in the former.
Expected range and adjusted range of hydrologic sequences
Authors: Salas‐La Cruz Jose D. , Boes Duane C.
Published: February 2008

Because of the stochastic nature of hydrologic sequences such as streamflow the needed capacity of a reservoir is a random variable. Studies of storage capacity of reservoirs, under the assumption of infinite storage, lead to the problem of finding the distribution of the range Rn or adjusted range Rn* of partial sums Si* = Si−1* + (Xi − αω), where ω = μ = ε [Xi] or
. Previous studies led to separate formulas for the expected range ε [Rn] and the expected adjusted range ε [Rn*] for independent standard normal variables and for a ‘degree of development’ α=1. In a recent study it was demonstrated that for any 0 ≤ α ≤ 1 and for any underlying distribution of the streamflow variables Xi, both the expected range and the expected adjusted range can be obtained from a single formula by changing an appropriate parameter. This paper elaborates on this previous study. Among other things it graphically exhibits the ‘transient’ nature of the general formulas for the expected adjusted range.
Approximate solution to the freezing of the ice‐water system with constant heat flux in the water phase
Authors: Foss Stephen D. , Fan Stephen S. T.
Published: February 2008

By utilizing the assumption of a quasi steady state temperature profile for the solution to the Stefan problem an approximate solution to the ice‐water problem in which a constant heat flux exists in the water phase is developed. Two hypothetical cases are studied. Case 1 considers a step change in the ambient air temperature. Case 2 considers the effect of sinusoidal ambient air temperature fluctuations. A method is developed for determining the characteristic heat flux in the water phase.
Two‐dimensional seepage in layered soil—Destabilizing effects of flows with an unsteady free surface
Authors: Dicker D. , Babu D. K.
Published: February 2008

An analytic study has been made about the destabilizing effects of a prolonged rainfall over the sides of a long symmetric hill. The assumptions underlying the analysis are that (1) the soil consists of layers parallel to the hillslope, (2) the flow domain is bounded from below by an unknown free surface (the interface between dry and saturated wet soil), and (3) this free boundary moves downward with passage of time. The resulting flow pattern is therefore unsteady or time dependent. The motion is described by Darcy's law as applied to a saturated porous medium (heterogeneous) having variable conductivity. Perturbation techniques have been applied in constructing the solution to this nonlinear problem. For certain portions of the flow region the perturbation becomes singular, and the singularities are removed by the methods of matched asymptotic expansions. Properties of singular integrals with Cauchy kernels are employed in certain quantitative estimates. Only the first‐order effects are presented here. It has been shown that one large‐time effect of prolonged rainfall is to generate outward horizontal velocity components in the distant regions of the slope; these components grow in time. It is known in soil mechanics that such tendencies to outward flow have serious destabilizing effects on the soil slope. This paper demonstrates that the underlying causes for such disasters as landslides can be traced in a significant fashion to the hydrodynamic nature of the seepage that evolves naturally as a result of prolonged rainfall.
Seepage rates and the horizontal flow approximation
Authors: Youngs E. G.
Published: February 2008

This note draws attention to a particular case of seepage through a porous body in which the flow is everywhere horizontal and hence easily calculated. In an appendix the seepage through a dam core with a cross section in the shape of an isosceles triangle is shown to be estimated with sufficient accuracy for practical purposes by the horizontal flow approximation.
Modeling of stochastic‐deterministic hydrologic systems
Authors: Laurenson E. M.
Published: February 2008

Combined modeling of the stochastic and deterministic aspects of systems can lead to advances in many areas of hydrologic practice. Such modeling is achieved by the matrix multiplication of a probability distribution of the stochastic system input with a transition matrix derived from the deterministic operation of the system and any stochastic parameter. This method is surprisingly general and flexible. Its use is demonstrated for a wide range of applications.
Second‐order theory of flow in three‐dimensional deforming media
Authors: Gambolati Giuseppe
Published: February 2008

A basic assumption in groundwater flow theory is that consolidation occurs in the vertical direction only. In real three‐dimensional media this condition is not satisfied a priori. In the present paper a second‐order theory of flow is developed including the consideration of horizontal soil displacements. The ‘strain nucleus’ or ‘tension center’ approach, well‐known in thermoelasticity, is used. The formulation of the theory shows that volume strain in a point P of the system may be viewed as being distinctly contributed by pore pressure variations in and outside P. The latter contribution, which vanishes identically in one‐dimensional media, is called the ‘three‐dimensional effect’. Solutions applied to a semi‐infinite mechanically homogeneous medium show that the three‐dimensional effect is negligible and the diffusion equation is good as long as the ratio W between the average depth and the thickness of aquifer is ≥2, whatever its areal exent. If W < 2 (shallow and thick aquifers), the above effect produces an additional compression of soil during an intermediate stage after pumping has begun and hence a slowing down of the rate of pressure head decline, as has been predicted by standard solutions. The most critical conditions occur for W=1/2, i.e., in unconfined aquifers. The present theory also allows for a short qualitative analysis of the ‘Noordbergum effect’ or reverse water level fluctuation.
Birth‐Death Models for differential persistence
Authors: Jackson Barbara Bund
Published: February 2008

Birth‐death models can generate synthetic flow sequences that demonstrate differential persistence, i.e., sequences in which low flows show more persistence than high flows do. A simple phenomenological model helps justify the assumption of differential persistence. The use of a birth‐death model, together with a set of modeling precepts, shows that differential persistence is a phenomenon of considerable descriptive importance but at least in some planning situations does not carry corresponding prescriptive importance.
The evaporation of intercepted rainfall from a forest stand: An analysis by simulation
Authors: Murphy Charles E. , Knoerr Kenneth R.
Published: February 2008

A model of the energy exchange between the atmosphere and a vegetated surface has been developed and used to investigate the sources of energy available for evaporation of precipitation intercepted by a forest canopy. Simulations with this model have demonstrated that a forest canopy wetted by rainfall will partition more of the absorbed radiant energy into latent heat exchange than an unwetted canopy in the same environment. This energy diversion creates a decrease in sensible heat transfer from the canopy to the atmosphere and a smaller decrease in a long‐wave radiation emitted by the canopy.
A submerged hypolimnion aerator
Authors: Fast Arlo W. , Dorr Victor A. , Rosen Robert J.
Published: February 2008

A new hypolimnetic aeration system is described. This system increased the hypolimnetic oxygen concentrations of Lake Waccabuc, New York, from 0.0 mg/1 to over 4.0 mg/1, while at the same time preserving thermal stratification. These improvements and others created a suitable habitat for cold‐water fish, but care must be exercised in the use of the system to avoid problems of nitrogen gas supersaturation.
Hydrologic estimation and economic regret
Authors: Jettmar R. U. , Young G. K.
Published: February 2008

The purpose of this research is to determine the consequence of using Markovian and self‐similar synthetic data generators in the economic design of a multipurpose reservoir. This leads to the study of two engineering problems: sizing a reservoir and operating a reservoir. This work is the sequel to the paper ‘Practical Application of Fractional Brownian Motion and Noise to Synthetic Hydrology’ (Chi et al., 1973). To study the effects of synthetic data generators, a one‐reservoir model is used as a case study and typical flood, water supply, and recreation cost functions are employed to answer the questions: Does the complex model yield a more accurate economical answer? What are the trade offs between using simple or complex hydrologic models in operating and in sizing analysis? Is it worth the extra effort in analysis cost over ranges of simulation periods? The optimum reservoir size is found to agree within 15% for the two hydrology models. A higher variance for the self‐similar solution is present. Both streamflow generators give cost plus loss estimates which differ about 5% under optimal conditions. A 95% confidence band for total cost (i.e., expected present value of losses plus fixed cost of the reservoir( shows the historic result to be conservative. Computing times for the generation of synthetic streamflow differ by an order of magnitude for simple and complex models. The problem of sizing is sensitive to the different streamflow generators; regret is of the order of 5%. Operating rules of a reservoir are fairly insensitive to the choice of the streamflow model. Furthermore, one can state that given limited resources, a Markovian model can be used for both sizing and operating a multipurpose reservoir. And no discrimination between a simple Markovian model and a complex self‐similar model could be found.
A possible relation of albedo to the density and grain size of natural snow cover
Authors: Bergen James D.
Published: February 2008

A simple model is proposed for the solar albedo of natural snow cover, based on an approximation to the specific surface by a function of grain size and density derived from air permeability measurements. Agreement with limited observational material is good. The model suggests that for grain sizes greater than 1.5 mm, density is the primary factor governing albedo.
Regional skew in search of a parent
Authors: Matalas N. C. , Slack J. R. , Wallis J. R.
Published: February 2008

The relationship between the mean and the standard deviation of regional estimates of skewness for historical flood sequences is not compatible with the relations derived from several well‐known distribution functions.
An efficient transition definition for discrete state reservoir analysis: The divided interval technique
Authors: Doran D. G.
Published: February 2008

Discrete state‐discrete time stochastic matrix methods of reservoir analysis may be used to estimate the relationships between reservoir capacity, yield, and probability of emptiness for given inflow distributions. To avoid excessive computation and computer storage demands, these methods most commonly use models in which the state variable is discretized into a small number of finite states. This, however, generally leads to inaccurate solutions. To improve computational efficiency and allow solutions with reasonable accuracy with small numbers of finite states, a method is proposed of modeling the storage process which has been called ‘the divided interval technique.’ This method is described, and its results compared, by means of examples, with those from the existing method.
Using parametric models of runoff to improve parameter estimates for stochastic models
Authors: Carey D. I. , Haan C. T.
Published: February 2008

The problem of evaluating and improving stochastic model parameter estimates is examined. A methodology is described for evaluating the ability of a parametric runoff model to improve short‐record estimates of stochastic model parameters by extension of existing runoff records.