bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear decision rule in reservoir management and design: 4. A rule that minimizes output variance
Authors: ReVelle Charles , Gundelach Jose
Published: February 2008

A linear decision rule (LDR) in reservoir management and design is reviewed and transformed. A generalized formulation of a new LDR is presented, and the necessary steps to implement it are carried out for a particular form of the new rule. The proposed rule permits further minimization of expected losses arising from deviations of releases from prespecified target levels. The use of the rule also makes possible a larger minimum commitment of water. The problem is solved for historical data from the Gunpowder River in Maryland under both the previous and the new form of the LDR. Results obtained are compared for the two cases.
A stochastic analysis of extreme droughts
Authors: Gupta Vijay K. , Duckstein Lucien
Published: February 2008

A stochastic analysis is performed on the extreme drought duration defined to be the maximum dry interval for a point rainfall process. The assumptions underlying previous analyses are generalized to those of a nonhomogeneous Poisson process. Analytical results, which seem intractable in general, are derived for two particular forms of the intensity function of the Poisson process; for a general intensity function, simulation is recommended. Next, small time intervals such as the growing season of a crop are considered so that the assumption of a homogeneous Poisson rainfall process may be made and the effect of parameter estimation on the theoretical results may be studied qualitatively. To illustrate this point, four estimates of the intensity parameter are calculated by using precipitation data from Chicago and Austin. A good agreement is found between the theoretical and empirical distribution functions for the two parameter estimates calculated by use of the model developed in this investigation; on the other hand, a substantial bias is present for parameters calculated directly from the data. Finally, an approach is schematically indicated to extend the model to regional droughts by using stochastic superposition.
Nonlinear kinematic wave approximation for water routing
Authors: Li Ruh‐Ming , Simons Daryl B. , Stevens Michael A.
Published: February 2008

Herein a simple numerical model for both overland and channel water routing is presented. A second‐order nonlinear scheme is developed to solve the kinematic wave equation with the boundary condition of time variant inflows. The numerical solutions agree very well with analytical solutions which are available for some particular cases. This model includes the effects of rainfall on flow resistance and simulates hydrographs which agree very well with experimental results for both constant rainfall and variable rainfall cases. The interesting phenomena of ‘pip’ and ‘dip’ in overland flow hydrographs are successfully simulated. These phenomena are found to be the results of sudden changes of flow resistance due to ceasing or starting of rainfall. The same routing procedure for overland flow is employed to route flow in natural channels.
Observations of stage, discharge, pH, and electrical conductivity during periods of ice formation in a small subarctic stream
Authors: Osterkamp T. E. , Gilfilian R. E. , Benson C. S.
Published: February 2008

Ice formation in a small subarctic stream modified the stage, velocity profiles, discharge, and electrical conductivity, while the pH remained nearly constant. Frazil ice crystals suspended in the flow reduced the velocity profiles and increased the stage. Anchor ice and border ice growth decreased the discharge by 31 and 55% for two periods of underwater ice production. These reductions in discharge may be attributed to storage in the form of ice and to upstream water storage caused by increased flow resistance in the stream. The increase in the electrical conductivity of the stream water during periods of ice production was related to the concentration of ice in the stream. Ice concentrations calculated from this increase in conductivity were 1.8, 0.9, and 4.7% (by volume) for the first 150 min of three different periods of ice production.
Predicting recessions through convolution
Authors: Yates Paul , Snyder W. M.
Published: February 2008

The recession of streamflow following storm periods has been studied for a long time. Flow during recessions is important as a dependable minimum supply of water. However, quantitative mathematical expressions are still lacking for accurately predicting flow during recession periods. A convolutional model of streamflow recession has been formulated and tested utilizing sequential values of mean daily discharge. Parameters of the model are determined by optimization with historical streamflow records. Preliminary relationships of parameters to rate of flow and size of drainage area are explored.
Computer time and memory requirements for DP and DDDP in water resource systems analysis
Authors: Chow Ven Te , Maidment David R. , Tauxe George W.
Published: February 2008

The computer time required for a water resource optimization problem by dynamic programing (DP) or discrete differential dynamic programing (DDDP) may be considered as the sum of the compiling time for programing language translation, the initiating time for the program, and the execution time TE. The execution time is the dominant component of the total computer time and may be formulated as TE = TaMN Пi=1S Qi Пj=1D Pj, in which Ta is the time for one unit operation, M is the number of iterations involved in optimization, N is the number of stages, and Qi and Pj are the number of feasible values that state variable i (i = 1, 2, …, S) and decision variable j(j = 1,2,…, D), respectively, can take in each iteration or in the optimizational procedure. The value of Ta depends on nature of problem, type of computer, method of coding, kind of compiler, and other factors. The computer memory required for this optimization problem may be considered as the sum of the machine memory which is relatively constant, the code memory which increases slowly with the problem size, and the data memory which increases rapidly with the problem size. The data memory consists of the basic data memory, the performance data memory P = 2 Пi=1s Qi, and the optimal decision data memory T = ND Пi=1s Qi. The cost trade offs involved in replacing core memory by slow‐speed memory (disks or tapes) are investigated. The computers used in the analysis include: IBM 360/50, IBM 360/75, IBM 360/91 and Burroughs B‐6700. The problems verifying the formulas include operations of single‐and multiple‐purpose reservoir networks and optimal design of storm sewer systems and aqueducts.
Longitudinal dispersion in natural channels
Authors: Day Terry J.
Published: February 2008

The longitudinal dispersion of fluid particles in natural channels is investigated in an extensive series of experiments in small mountain streams (New Zealand). These experiments extend over a maximum distance of 2250 m, a mean velocity range of 0.32–1.57 m/s, and a mean flow width range of 2.7–21.8 m. It is conclusively shown for these channels and others as well that the spread or standard deviation of an initially concentrated mass increases linearly with distance and not as its square root, as is necessary for the application of Taylor's mixing model. One consequence of the linearity is an ever‐increasing dispersion coefficient along the channel. It is also shown that the time‐concentration curve of a dispersing tracer mass maintains a persistent asymmetry. This persistent asymmetry and the continued linear spreading appear to be characteristic of dispersion in natural channels and as such show the inadequacies of applying Taylor's analysis.
An optimization model for regional water quality management
Authors: McNamara John R.
Published: February 2008

A nonlinear programing model for water quality management is developed and applied to the case of the upper Hudson River. The model is formulated as a geometric programing problem. It is shown that this formulation permits the simultaneous consideration of waste treatment processes, bypass piping, flow regulation, and artificial aeration in determining a least‐cost solution to a given water quality management problem.
Estimating groundwater evapotranspiration from streamflow records
Authors: Daniel James F.
Published: February 2008

Methods for determining groundwater outflow from a drainage basin following sudden or constant recharge were presented by Rorabaugh in 1964. He then developed, but did not publish, a method for computing outflow from an aquifer underlain by a leaky boundary. This method can be extended to determine outflow from an aquifer subjected to constant evapotranspiration (ET). The unaffected aquifer outflow (streamflow) recession following recharge becomes a straight line on a semilogarithmic graph after sufficient time has elapsed. The slope of this recession is, in logarithm to base 10 form, − Tt/0.933a2S, where T and S are the transmissivity and storage coefficient of the aquifer, a is the distance from the stream to the groundwater divide, and t is the time since recharge occurred (sudden case) or began (constant case). A set of dimensionless type curves are developed for the case of constant ET (leakage) which diverge from and lie below the unaffected case. Streamflow records for the basin, Indian Creek near Troy, Alabama, were analyzed by using the method described. A constant ET rate of 0.037 m3/s was computed for the 23.00‐km2 basin during the period April through June 1963.
Estimation of response surface gradients in multiobjective water resources planning
Authors: McBean Edward A. , Schaake John C.
Published: February 2008

A probabilistic Markov model of reservoir state transitions is developed which, in combination with a simulation model, offers a computational tool for estimating response surface gradients of water resources planning problems. Use of the gradient estimation capability provides a substantial improvement in efficiency of the search for improved water resources configurations. The estimation capability arises by recognizing and using the reservoir state transition changes that would result from a modification of decision variables. The procedure is highly flexible in that it functions under such complicated situations as multiple‐objective environments, nonlinear benefit loss functions, and complex connectivity of river basin components.
Energy balance computations of snowmelt in a subarctic area
Authors: Price A. G. , Dunne T.
Published: February 2008

A physically based model was used to predict daily snowmelt on 2000‐m2 plots in the subartic. The plots had a range of aspects and inclinations under boreal forest and on the tundra. The energy balance, computed for each of the plots, was compensated for differences in radiative and turbulent energy fluxes caused by varied slope geometry and vegetative cover. The turbulent energy fluxes were also corrected for the effects of the stable stratification of the air over the snow surface. The predictions of the model were compared with daily melts derived from runoff measured on the snowmelt plots. The results show that the method is a good predictor of daily amounts of snowmelt, although some uncertainties are introduced by changes in the snow surface during the melt period. In a companion paper we show how hourly snowmelt rates, calculated from the energy balance, can be used to predict runoff hydrographs from hillside plots.
The relationship between light and photosynthetic rate in a river community and implications for water quality modeling
Authors: Hornberger George M. , Kelly Mahlon G. , Eller Richard M.
Published: February 2008

Saturation of photosynthesis at naturally occurring high light intensities has widely been reported for aquatic communities. Contrary to this, using free water measurement methods, we found a relationship between light intensity and photosynthesis in a small river that was unmistakably linear on cloudless days and on days when points corresponding to times of highly variable radiation were discarded. The linear relationship obtained through the year. Simulations of nutrient‐limited growth in light‐dark bottles show that nutrient depletion effects can explain the cases of light saturation and inhibition previously reported in the literature. If light saturation and inhibition of photosynthesis are due even in part to artificially induced nutrient limitation, then the inclusion of nonlinear light terms in water quality models is inappropriate.
Nitrate and chloride pollution of aquifers: A regional study with the aid of a single‐cell model
Authors: Mercado Abraham
Published: February 2008

A single‐cell model was used to study the regional chloride and nitrate pollution patterns in part of the coastal aquifer of Israel. The model integrates pollution sources on the land surface, hydrologic parameters of the aquifer and the unsaturated zone, and variations of chloride and nitrate concentration distribution in pumping wells. Complicated hydrologic and biochemical processes in the unsaturated zone are simplified and represented by two basic parameters, transit time from land surface to the aquifer and nitrogen losses in the soil. A working hypothesis is used here to show that linear relationships exist between nitrogen quantities released on the surface and the quantities reaching the water table. Chloride and nitrate balances have been studied simultaneously. The effective volume of groundwater in the mixing zone of the aquifer was interpreted from the concentration variations of the chloride ion which is a conservative tracer. This value was used later for determining other parameters of the nitrogen terrestrial cycle. The calibration of the model, by reconstructing present pollution levels, enabled its use for prediction purposes. The Monte Carlo technique was introduced to determine the range of predicted average groundwater concentrations as a function of time; this gives a probabilistic expression to the uncertainty in defining the pollution mechanism and difficulties in calibrating the model parameters. The forecasts presented here call for urgent protection measures in order to meet drinking water standards for maximum nitrate concentrations. An aggravating factor is the time lag between measures taken to decrease the pollutant load on the surface and the response of the aquifer system. Thirteen alternative protection measures are examined here and compared to predictions based on present nitrogen loads and hydrologic regime. They include advanced treatment of sewage waters prior to their recharge to the aquifer, reduction of fertilizer dosage to crops, and exchange of nitrate‐contaminated groundwater by low‐nitrate surface waters. The exchange relationships between these measures are derived, and they can be used later for evaluating economic criteria for protecting groundwater quality.
A drawdown prediction model based on regression analysis
Authors: Maddock Thomas
Published: February 2008

A technique for determining algebraic technological functions (ATF) relating the drawdown at wells to the quantity of water withdrawn from those wells is developed. The technique does not rely on the development of an analog or digital groundwater model to calculate the ATF's, nor does it rely on a determination of distributions of transmissivity and storage coefficient. The inputs are the time series of historical pumping and water levels, the distances between wells, the radius of the well, and the duration of a pumping period. A stepwise regression analysis is then used to determine the coefficients of the ATF. The functional form of the regression equation is based on standard results from groundwater analysis.
Multiobjective programing in watershed management: A study of the Charleston Watershed
Authors: Goicoechea Ambrose , Duckstein Lucien , Fogel Martin M.
Published: February 2008

A multiple‐objective approach to decision making in watershed management is developed and demonstrated within the framework of nonlinear programing by means of the case study of the Charleston watershed in southern Arizona. The effects of various land treatments and management practices on water runoff, sediment, recreation, wildlife levels, and commercial potential of a study area are investigated, constraints on the available land and capital being observed. This leads to a model with five objective functions to be maximized under 18 constraints. In an iterative manner the decision maker proceeds from one noninferior solution to another, comparing sets of land management activities for reaching specified goals and evaluating trade‐offs between individual objective functions. This technique, labeled Trade, involves the formulation of a surrogate objective function and the use of the cutting plane method to solve the general nonlinear problem; it hopefully provides a compromise between computationally intractable and excessively simplified approaches to truly multiobjective watershed management.
Heat storage and advection in Lake Erie
Authors: Derecki Jan A.
Published: February 2008

Heat content and net advection based on long‐term monthly mean input data covering 17 yr (1952–1968) were derived for Lake Erie. The lake heat storage changes and net advection, with major components, are presented for the average monthly periods, indicating normal values for these parameters. Data limitations for the lake heat content precluded computation of monthly values by individual years. Derivation of the necessary input data (water temperature profiles, water supply and loss factors with appropriate temperatures, and ice conditions) is briefly described.
A single‐potential solution for regional interface problems in coastal aquifers
Authors: Strack O. D. L.
Published: February 2008

An analytic technique for solving three‐dimensional interface problems in coastal aquifers is presented in this paper. Restriction is made to cases of steady state flow with homogeneous isotropic permeability where the vertical flow rates can be neglected in relation to the horizontal ones (the Dupuit‐Forchheimer assumption). The aquifer is divided into zones defined by the type of flow occurring. These types of flow may be either confined, unconfined, confined interface, or unconfined interface flow, where the interfaces separate freshwater from salt water at rest. The technique is based upon the use of a single potential which is defined throughout all zones of the aquifer. This potential in each zone can be represented in a way similar to that suggested by Girinskii in 1946 and 1947. The potential introduced in this paper is single valued and continuous throughout the multiple‐zone aquifer, and its application does not require that the boundaries between the zones be known in advance. The technique thus avoids the difficulties that result from the discontinuity of both the velocity gradients and the Girinskii potentials at the boundaries between the zones and from the unknown locations of these boundaries. The use of the single‐valued potential is illustrated in this paper for an analytic technique, but it may be used with some advantage in numerical methods such as finite difference or finite element techniques. Applications discussed in this paper involve two interface flow problems in a shallow coastal aquifer with a fully penetrating well. The first problem is one of unconfined interface flow where the upper boundary is a free water table. The second is one of confined interface flow where the upper boundary is horizontal and impervious. Each problem involves two zones. One zone is adjacent to the coast and is bounded below by an interface between freshwater and salt water at rest. The other zone is bounded below by an impervious bottom. It is shown that saltwater intrusion in the well occurs when the discharge of the well surpasses a certain value for which the interface becomes unstable. The conditions that must be met to prevent such saltwater intrusion are established for each problem and are represented graphically.
A chlorophyll a model and its relationship to phosphorus loading plots for lakes
Authors: Chapra Steven C. , Tarapchak Stephen J.
Published: February 2008

A model predicting the summer concentration of cholorophyll a in a phosphorus‐limited lake is derived from simple empirical and semitheoretical relationships. The model is rearranged and expressed as a phosphorus loading plot which agrees closely with the predictions of Vollenweider's model. The model can be used to gain insight into the phosphorus loading concept. The primary conclusion is that a lake's tolerance to phosphorus loading is a function of two processes: sedimentation and flushing rate. At low areal water loads, in‐lake forces which remove phosphorus to the sediments predominate. At high areal water loads, flushing of phosphorus through the lake's outlet is the factor governing eutrophication. The importance of the steady state assumption is also demonstrated by using data for Lake Washington.
Deviations from the Theis Solution in aquifers undergoing three‐dimensional consolidation
Authors: Gambolati Giuseppe
Published: February 2008

Previously, a new mathematical model based on the ‘tension center’ or ‘strain nucleus’ concept was proposed by the author for the response characterizing flow in a confined aquifer undergoing three‐dimensional consolidation. The new approach differs from Bio's [1941] in that it leads to the development of a unique integrodifferential equation for the pressure head decline occurring within the porous system. The consideration of the horizontal strain components results in a conceptually simple modification of the classical diffusion equation to which a further integrodifferential term accounting for the three‐dimensional effect is added. In the present paper the new equation of flow is solved in a pumped artesian aquifer enclosed in a half space by an iterative finite element technique. It is shown that in shallow and relatively thick units (with W ≃ 0.5, where W is the ratio between the average depth and the thickness of the aquifer), downward vertical components of flow develop and that the average drawdown deviates moderately from the Theis solution and is no longer uniquely represented against the dimensionless time. The three‐dimensional effect produces an additional soil compression which retards the piezometric decline. At large values of time the horizontal strain components vanish, the diffusion equation holds, and the solution becomes parallel to the Theis profile. As a major consequence the traditional aquifer tests can still be applied to assess the formation permeability, but they yield a 40% overestimate of the elastic storage coefficient. In deeper units (W > 0.5) the importance of the three‐dimensional effect diminishes, is already small when W = 1, and becomes negligible for W ≥ 2. In this case the diffusion equation and its solutions are sufficiently accurate. From a practical standpoint the quantitative results given herein are limited by the condition that a mechanically homogeneous and isotropic half space is required.
Linked models for managing river basin salt balance
Authors: Helweg Otto J. , Labadie John W.
Published: February 2008

One of the pressing problems facing the irrigation intensive areas of the world is the increasing salinity of groundwater. A cost‐effective salinity management technique, called the accelerated salt transport (Astran) method, has been developed which may be feasible for many stream aquifer systems. The basic idea is to encourage application of pumped water downstream of the well from which it is pumped rather than within its vicinity. In this way a mechanism is established for accelerating the downstream transport of salts in the groundwater at a more rapid rate than would occur naturally through convection and dispersion while still satisfying irrigation demands. A management algorithm is developed for implementing the Astran method which combines an optimizing model with a detailed quantity‐quality simulation model. The optimizing model generates least‐cost alternatives for distributing water over the basin. These alternatives are subsequently examined by the simulation model as to their effectiveness in controlling the salt balance. A parameter in the optimizing model can be adjusted so as to produce a desired degree of salinity control. The management algorithm has been applied to the Bonsall Subbasin in the San Luis Rey River Basin in order to test its effectiveness. Results of the case study indicate that the Astran method (1) is cost‐effective, requiring roughly 10% of the cost of tiling for this area, (2) encourages balanced conjunctive use of surface water and groundwater, and (3) is flexible enough to respond to future management needs.
Vertical infiltration in dry soil
Authors: Brutsaert Wilfried
Published: February 2008

An approximate method is proposed to integrate the ordinary differential equations governing the terms in Philip's (1957) series formulation of the water content profile. The method is related to the weighting solution used earlier (Brutsaert, 1976) for the sorption problem, and it is intermediate between the quasi‐steady state method and the sharp front method. In a comparison with an available exact solution (Brutsaert, 1968b) it is shown that the derived solution is usually accurate to within less than 1%. The water content profile and the infiltration rate can be expressed concisely in terms of soil physical parameters by making use of suitable expressions for the soil water diffusivity and the capillary conductivity. As an illustration, the infiltration rate is calculated for the Averjanov‐Irmay capillary conductivity and the author's three‐parameter power function diffusivity. Inspection of two extreme cases in this calculation finally leads to a new infiltration equation in closed form which is valid not only for short but also for large time of infiltration.
Floodplain zoning: Implications of hydrologic and legal uncertainty
Authors: Dingman S. Lawrence , Platt Rutherford H.
Published: February 2008

Implementation of floodplain regulations in the United States has been very slow. There is a danger that regulation will not be widely adopted before floodplains become largely developed. Important among the reasons for failure to regulate floodplains appear to be the misconceptions that precise floodplain delineation is (1) hydrologically possible and (2) legally required. Our analysis shows that wide confidence intervals are unavoidably associated with even the most elaborate and expensive delineation techniques. Application of the ‘fairly debatable rule’ legally supports regulation based on expedient techniques, as long as they are fairly applied, and issues of constitutional purpose and taking of property are properly considered. Thus there is hydrologic and legal justification for floodplain regulation based on expedient delineation methods, and it is imperative that such methods be used if regulation is to be an effective tool for flood damage reduction.
Advances in Box‐Jenkins modeling: 1. Model construction
Authors: Hipel Keith William , McLeod Angus Ian , Lennox William C.
Published: February 2008

Box‐Jenkins modeling of time series data can be improved and simplified by adhering to contemporary modeling procedures. This paper gives the theory and techniques of the application of many recent advances that have been made at the identification, estimation, and diagnostic check stages of model development. The inverse autocorrelation function and the inverse partial autocorrelation function are demonstrated to be useful identification tools for both nonseasonal and seasonal models. Parameters can be estimated more efficiently by employing the modified sum of squares technique. At the estimation stage it is also possible to obtain a maximum likelihood estimate for a Box‐Cox power transformation. The Akaike information criterion is introduced to formalize mathematically the concept of model parsimony. When checking for model adequacy, knowing the distribution of the residual autocorrelation allows for a sensitive test for residual whiteness. Diagnostic checks are given for verifying the assumption of homoscedasticity of the model residuals. In practice, heteroscedasticity and nonnormality of the residuals can often be removed by a Box‐Cox transformation.
Viscoelastic aquifer model applied to subsidence due to pumping
Authors: Corapcioglu M. Yavuz , Brutsaert Wilfried
Published: February 2008

A viscoelastic aquifer model, proposed earlier by the authors, is applied to analyze and predict the piezometric drawdown and the compaction observed in a major confined aquifer system in the San Joaquin Valley in California. A field approach is used based on a minimal number of ‘bulk’ parameters. These parameters, which are the transmissivity, the compressibilities of primary and secondary consolidation, and the viscosity of the secondary consolidation, were derived by calibration of the model by means of trial and error simulation of 2 years of records of drawdown and compaction. It was found that in the absence of drawdown records the identification may also be accomplished with compaction records in addition to a standard pumping test. Comparison of computed results with available records shows that the viscoelastic model yields a satisfactory prediction of compaction which is far better than that obtainable with the elastic model of the classical Theis‐Jacob approach. The elastic model may be adequate to represent the hydraulic properties of the aquifer in the analysis of the piezometric drawdown; however, it appears to be unsatisfactory to represent the mechanical properties of the aquifer as related to surface subsidence.
Numerical model for saturated‐unsaturated flow in deformable porous media 1. Theory
Authors: Narasimhan T. N. , Witherspoon P. A.
Published: February 2008

A theory is presented for numerically simulating the movement of water in variably saturated deformable porous media. The theoretical model considers a general three‐dimensional field of flow in conjunction with a one‐dimensional vertical deformation field. The governing equation expresses the conservation of fluid mass in an elemental volume that has a constant volume of solids. Deformation of the porous medium may be nonelastic. Permeability and the compressibility coefficients may be non‐linearly related to effective stress. Relationships between permeability and saturation with pore water pressure in the unsaturated zone may be characterized by hysteresis. The relation between pore pressure change and effective stress change may be a function of saturation. In the transition zone where pore water pressure is less than atmospheric but greater than air entry value, soil moisture diffusivity as used in soil physics and coefficient of consolidation as used in soil mechanics are shown to be conceptually equivalent. It is believed that this model will be of practical interest in studying saturated‐unsaturated systems undergoing simultaneous desaturation and deformation.
An analysis of flood levee reliability
Authors: Wood Eric
Published: February 2008

In most studies of flood levee reliability the probability of failure is taken to be equal to the probability that the flood peak discharge will exceed the capacity of the channel‐levee system. Such an analysis assumes that levees fail only by overtopping, whereas in many cases, levees fail at discharges much below the channel capacity. In the present paper the discharge at which levees fail is assumed to be a random variable with a particular distribution. The results on the flood frequency curve are presented for two conditions: one for the failure discharge having a uniform probability density function and the other for failure discharges having a quadratic distribution. In a similar manner the effects on the net benefits from levee construction were also analyzed and results are given.
Fitting the Pearson type 3 distribution in practice
Authors: Buckett J. , Oliver F. R.
Published: February 2008

The three‐parameter Pearson type 3 distribution is frequently fitted to streamflow data, partly in order to estimate percentiles. This practical study confirms that maximum likelihood methods can give very different, and much more satisfactory, estimates than the more usual method of moments.
Internalization in a stochastic pollution model
Authors: Hochman Eithan , Zilberman David , Just Richard
Published: February 2008

This paper develops and applies a stochastic model for internalizing pollution externalities. Pollution occurs or does not, depending on factors related to a stochastic environment and human error. But the probability of pollution can be altered by adopting various technologies. The model is applied to the problem of effluent runoff from dairies near the San Francisco Bay, which can prevent shellfish harvest in the bay. With runoff holding areas, pollution occurs if a rainstorm is severe enough to cause overflow. Standards rather than taxes are used as policy instruments in the model. Results generally indicate that an accurate approximation of stochastic distribution is a necessity. Specific implications for the dairy problem are that present regulations are too lenient.
The log Pearson type 3 distribution: The T‐year event and its asymptotic standard error by maximum likelihood theory
Authors: Condie R.
Published: February 2008

The maximum likelihood estimators for the three distribution parameters of a log Pearson type 3 distribution are derived from the logarithmic likelihood function and a solution method is given.The T‐year event is then derived as a function of these parameters and the standard normal deviate t. These parameters are subject to sampling variances and covariances, whereas t is not. By using the logarithmic likelihood function the inverse dispersion matrix is derived, hence the variances and covariances of the parameters. Entering these in the general variance of the estimate equation of a function of three variables leads to an estimate of the asymptotic standard error of estimate of the T‐year event. Flood data from 37 hydrometric stations on Canadian rivers were analyzed by this method and compared with the more common moment analysis. In all cases the maximum likelihood analysis is markedly superior in terms of the estimate of standard error of estimate, but the asymptotic nature of the result must always be borne in mind. Possible sources of bias in the maximum likelihood estimate of the T‐year event are discussed.
Measurement of sediment control impacts on agriculture
Authors: Wade James C. , Heady Earl O.
Published: February 2008

Environmental policy has been explicitly expanded to consider nonpoint or dispersed sources of water pollutants. This study utilizes a national agricultural model to evaluate hypothetical policies of sediment control viewing the problem as primarily a national problem of agricultural land use. A sediment sector is added to the basic Center for Agricultural and Rural Development‐National Water Assessment model in order to test the impacts of sediment control policies on the agricultural production system. The primary function of this paper is to present the formulation of this model and a short summary analysis of some results. Specifically, costs of alternative control policies are analyzed. These costs are defined as the additional costs to agriculture of several alternative sediment control policies.
A kinematic model for surface irrigation
Authors: Sherman Bernard , Singh Vijay P.
Published: February 2008

A kinematic wave model is developed to study surface irrigation. Depending on the variability of infiltration and the kinematic wave friction parameter, three cases are distinguished. Explicit analytical solutions are obtained for the case when infiltration is constant, and a possible approach is suggested for the case when it is not.
Sensitivity of groundwater models with respect to variations in transmissivity and storage
Authors: McElwee Carl D. , Yukler M. Arif
Published: February 2008

Sensitivity analysis is the study of a system's response to various disturbances. In this study, disturbances of aquifer parameters are considered. In the simulation of an aquifer the investigator must establish tolerances within which the parameters of the physical system may vary without appreciably affecting the model results. By means of a first‐order sensitivity formalism it is shown how to evaluate the perturbed hydraulic head for a small change in aquifer parameter. An expression for the sensitivity coefficient is obtained in this study by taking the partial derivative of the flow equation with respect to a particular parameter. The sensitivity coefficient is evaluated either analytically or by numerical techniques for some common models. The sensitivity formalism is applied to the Theis equation to study the general behavior of sensitivity coefficients and to determine the range of validity of the first‐order sensitivity formalism. The formalism is also applied to one‐ and two‐dimensional numerical models to see the effect of barrier and constant head boundaries. The perturbed hydraulic head is obtained for a change of transmissivity (T) and storage coefficient (S) by applying the first‐order sensitivity formalism. This procedure should be a valuable tool in calibrating models or establishing tolerances on T and S for a given acceptable error in hydraulic head. In general, a ±20% deviation in T or S may be handled adequately by the first‐order formalism discussed in this work.
The statistical mechanical theory of water transport through unsaturated soil: 2. Derivation of the Buckingham‐Darcy Flux Law
Authors: Sposito Garrison
Published: February 2008

The Buckingham‐Darey flux law, an empirical equation that relates the volumetric flux density of water in an unsaturated soil to the gradient of the total potential, is derived from first principles by using the methods of statistical mechanics. The derivation given, a direct application of well‐known techniques in nonequilibrium statistical mechanics, proceeds through a detailed molecular description of two laboratory experiments for measuring the hydraulic conductivity tensor of a homogeneous unsaturated soil. In the first experiment the steady flow of water is induced by a gradient in the matric potential, while in the second, flow is induced by a gradient in the gravitational potential. In both cases the appropriate form of the Buckingham‐Darcy law is derived on the basis of a linear response approximation, and an expression for the hydraulic conductivity is given in terms of a time integral of the correlation function for the velocities of the water molecules in the soil. The problem of calculating the hydraulic conductivity of a soil thereby is reduced to quadrature and to the task of developing a molecular model of the velocity correlations among the water molecules. A recent successful model of this type is discussed briefly.
Preservation of the rescaled adjusted range: 3. Fractional Gaussian noise algorithms
Authors: Hipel Keith William , McLeod Angus Ian
Published: February 2008

Improved modeling procedures are available for use with a discrete time fractional Gaussian noise (FGN) model. These advancements in FGN modeling consist of an exact simulation procedure, a maximum likelihood approach to obtain efficient estimates of the model parameters, and a technique for calculating the model residuals so that they can be subjected to rigorous diagnostic checks. The computer algorithms for the aforementioned modeling improvements are available on microfiche. The intention of this article is to summarize the essential ingredients of the complete paper, which appears on microfiche.

Summary and entire article are available on microfiche. Order from American Geophysical Union, 1909 K Street, N.W., Washington, D.C. 20006. Document W78‐004; $1.00. Payment must accompany order.
Longitudinal and transverse dispersion coefficients in unsaturated plainfield sand
Authors: Yule D. F. , Gardner W. R.
Published: February 2008

The relationship between the longitudinal and transverse dispersion coefficients (DL and Dτ) and the pore water velocity (υ) and the effective diffusion coefficient (De) was determined for 0.01 < υ < 0.28 cm/min in a vertical unsaturated column (L = 23 cm) of C horizon Plainfield sand. The inflow and outflow control systems on the soil column consisted of rows of porous ceramic tubes with individual adjustable pressure controls. Uniform inflow and outflow were achieved across the column, and υ was maintained constant during each experiment. An analysis of the transverse spread produced indicated that the effect of apparatus‐induced dispersion was <10%. DL (cm2/min) was linearly related to υ (cm/min) (DL = 0.216υ + 0.0032; r2 = 0.90). Slightly larger DL was found in experiments with H2O replacing Cl than in experiments with Cl replacing H2O. DL at the lowest υ was 2 orders of magnitude greater than De. DT(cm2/min) was essentially independent of υ(DT = 0.0035υ + 0.0031; r2 = 0.15) and was about 2 orders of magnitude greater than De at the lowest υ studied. The spread of tracer at the outflow was inversely proportional to υ, and transverse dispersion had reduced the concentration peak of the inflow by 84% at L = 23 cm and υ = 0.01 cm/min. The ratio DL/DT was proportional to υ and ranged from ∼ 1 (υ = 0.01 cm/min) to ∼20 (υ = 0.28 cm/min).
Circulation patterns in the Fox Chain of lakes in Illinois
Authors: Bhowmik Nani G. , Stall John B.
Published: February 2008

Extensive circulation data were collected at seven locations on five different occasions during 1975 in the Fox Chain of Lakes in Illinois. In areas of negligible inflow the circulation patterns in all of the lakes were governed by the wind. Even in areas of significant inflow the wind dominated the movement of water as soon as diffusion of the inflow jets reduced the flow velocity. Generally, the surface water moved with the wind, and there was some return flow below certain depths. Measured wind‐generated current profiles in the lakes indicated that they generally follow a logarithmic distribution. The wind factor defined as the ratio of surface water velocity to wind velocity varied from 2 to 7%. Theoretical circulation patterns in Pistakee Bay for a few selected wind conditions were computed by a finite element method. Computer plots were developed, and the theoretical circulation patterns were compared with the measured circulation patterns. Correlation between the theoretical and measured circulation patterns was found to be good.
A sediment graph model based on an instantaneous unit sediment graph
Authors: Williams J. R.
Published: February 2008

A model was developed for predicting sediment graphs from agricultural watersheds. Storm sediment graphs are predicted by convolving source runoff with an instantaneous unit sediment graph (IUSG). The IUSG is the distribution of sediment from an instantaneous burst of rainfall producing one unit of runoff. The IUSG is the product of an instantaneous unit hydrograph and the sediment concentration distribution. Initial sediment concentration of the IUSG is assumed to vary linearly with source runoff volume. A sediment‐routing function, based on travel time and sediment particle size, is used to predict the sediment concentration distribution. Tests with 50 storms from five watersheds showed that the model is applicable to agricultural watersheds in the Texas blacklands. It should be useful in designing reservoirs or in waterquality‐modeling problems.
Climate change: Detection and its impact on hydrologic design
Authors: Lettenmaier Dennis P. , Burges Stephen J.
Published: February 2008

Controversy regarding origins of the so‐called Hurst phenomenon has continued since the first appearance of Hurst's work. There appear to be at least two general mechanisms which might generate geophysical time series displaying the Hurst phenomenon. The first is nonstationarity of process mean level, perhaps owing to dynamic characteristics of the entire earth geophysical system. The second generating mechanism is a stationary model structure such as the Box‐Jenkins models with parameters such that substantial low‐frequency effects are present. A series of Monte Carlo tests have been performed which show that it will generally be very difficult to distinguish between the two generating mechanisms on the basis of geophysical records of lengths usually available. The Monte Carlo experiments are augmented by analysis of several series of tree ring growth indices ranging in length from 506 to 1164 years. Analysis of these sequences for nonstationarity in mean level showed that the sequences were entirely compatible with stationary Box‐Jenkins models earlier fit to the data by Hipel (1975). However, a similar analysis of the variance of the time series showed that there was evidence of nonstationarity in the variances of the records such that the time series were not compatible with the constant variance assumption of the stationary Box‐Jenkins models. Finally, several reservoir simulations were made by using the sequent peak algorithm for type A (nonstationary mean) and type B (constant mean) models which had been found to be statistically indistinguishable in the Monte Carlo experiments. The results showed that so long as nonstationarity in mean level was modest and demand levels were not too high the models give very similar results; however, at high demand levels or large nonstationarity in process mean, substantial differences in storage requirements may result.
A note on packer, slug, and recovery tests in unconfined aquifers
Authors: Dagan G.
Published: February 2008

Packer, slug, and recovery tests are common procedures for determining the hydraulic conductivity of unconfined formations of low permeability. The volumes of water injected or removed from the borehole are small, so that the water table remains horizontal and the flow is steady. The flow problem is solved by source distributions along the well axis. A simple numerical method and numerical results covering a wide range of the parameters of the problem are presented. The main limitation of the method is the requirement that the active portion of the well length should be much larger (say, 50 times) than the well radius.
A new function for use in the Hodograph Method
Authors: Strack O. D. L. , Asgian M. I.
Published: February 2008

A new function, the reference function, is introduced for combined use with the hodograph. The function is applicable to two‐dimensional problems of steady groundwater flow through homogeneously permeable porous media. The reference function is applicable to all problems of the above class with the restriction that the boundary in the hodograph plane be composed of segments of straight lines and circular arcs. The function is determined by application of elementary conformal transformations. Use of the reference function is illustrated for the case of unconfined flow toward a riverbank. A graph is presented that gives the length of the seepage face as a function of the flow parameters. The approach for solving the general problem of the above class by use of the reference function is outlined.
Toward more detailed field monitoring of variable source areas
Authors: Anderson M. G. , Burt T. P.
Published: February 2008

Variable source area storm flow generation is now a well‐accepted process in natural catchments. Although the concept of variable source areas, together with more theoretical modeling, has received much recent attention, detailed field delineation, both seasonally and for short storms, has not. The work reported here uses an automatic tensiometer system to obtain continuous data on soil water potential status in a hillslope hollow. The results discussed demonstrate that source areas can be accurately delineated by such equipment and that hollows are significant source areas at all stages of drainage. Moreover, the convergence shown by the soil water flow nets in such source areas remains almost constant throughout the year.