bluuebunny/crossref_metadata_2025 huggingface dataset:
A model for water reuse planning
Authors: Ocanas Gerardo , Mays Larry W.
Published: February 2008

A water reuse planning model has been developed for use in determining the optimum reuse of waste‐water on a regional basis that minimizes the overall cost of water supply for single period planning. Wastewater from all use sectors, along with fresh water, are considered as candidate sources or origins of water for other elements within the use sector and also for elements of other use sectors. Quality parameters of various sources of flows are explicitly considered. The model allows for economies of scale in treatment and transportation through the use of a nonlinear objective function and consists of both linear and nonlinear constraints. The model is solved using a large‐scale generalized reduced gradient technique. The analysis of hypothetical examples shows how the model can evaluate various planning scenarios, allowing the planner a broad spectrum of solutions to choose from.
Aquifer models of pressure drawdown in the Wairakei‐Tauhara Geothermal Region
Authors: Wooding R. A.
Published: February 2008

The analytical theory of porous horizontal aquifers is applied to the problem of pressure response of the Tauhara geothermal field to drawdown from Wairakei. In a ‘bounded’ model the Tauhara field is regarded as a sector from an axisymmetric solution in the horizontal plane, having a permeability contrast at the curved outer boundary. The straight sides of the sector are impermeable. In a second model the only barrier to horizontal flow is a straight boundary situated to the southeast of the Tauhara field, the presence of which is suggested by a high gradient in the field resistivity. Features shared by both models include a steady horizontal outflow from Wairakei, which was present before development and probably arises from natural convection, and a superimposed downward pressure gradient, which may be a consequence of the efficient horizontal propagation of the pressure drawdown at Wairakei. Statistical tests indicate that these features are important. The best fit to the field pressure data is obtained by using the second model with impermeable upper and lower boundaries.
Hydromythology and ethnohydrology in the new world
Authors: Back William
Published: February 2008

From mythology, archeology, and chronicles of early explorers we can learn how early Americans viewed the cause and effect relations of hydrologic phenomena. Hopes and fears are the basis of religion, and it was through religion that water management was first practiced. Early people used their water resources to develop diverse civilizations in various parts of the western hemisphere. Not only was the rise of these earlier civilizations hydrologically influenced, but also the downfall of some was related to natural or man‐made hydrological crises in which gods and mythology continued to play a role.
Stream system evaluation with emphasis on spawning habitat for salmonids
Authors: Shirazi Mostafa A. , Seim Wayne K.
Published: February 2008

This paper presents a comprehensive procedure for evaluating sedimentation impact on the streambed gravels used for spawning by salmonids. It establishes a relationship between embryo survival of incubating eggs and the geometric mean diameter of the substrate. It outlines simple procedures for estimating the overall composition of the gravel in spawning sites along stream reaches and provides the rationale for interpretation of these estimates in terms of overall embryo survival in a stream system.
Groundwater contaminant transport with adsorption and ion exchange chemistry: Method of characteristics for the case without dispersion
Authors: Charbeneau Randall J.
Published: February 2008

Contaminant transport in the groundwater environment with adsorption and ion exchange reactions is considered. For the case where the influence of dispersion is negligible, the method of characteristics is used to formulate the solution for any adsorption isotherm and an arbitrary number of exchanging cations. The approach applies equally well to linear flow systems and to nonlinear systems along streamlines in a nonuniform flow field. Transport problems related to the emerging technologies of in situ gasification of lignite and in situ leach mining of uranium are discussed. The first example considers migration of organics using the nonlinear Freundlich isotherm for adsorption of organics on lignite. Other examples consider ammonia migration and site restoration using the mass action law of ion exchange chemistry in in situ leach mining of uranium.
Hydraulic geometry and minimum rate of energy dissipation
Authors: Yang Chih Ted , Song Charles C. S. , Woldenberg Michael J.
Published: February 2008

The theory of minimum rate of energy dissipation states that a system is in an equilibrium condition when its rate of energy dissipation is at its minimum value. This minimum value depends on the constraints applied to the system. When a system is not at equilibrium, it will adjust in such a manner that the rate of energy dissipation can be reduced until it reaches the minimum and regains equilibrium. A river system constantly adjusts itself in response to varying constraints in such a manner that the rate of energy dissipation approaches a minimum value and thus moves toward an equilibrium. It is shown that the values of the exponents of the hydraulic geometry relationships proposed by Leopold and Maddock for rivers can be obtained from the application of the theory of minimum rate of energy dissipation in conjunction with the Manning‐Strickler equation and the dimensionless unit stream power equation for sediment transport proposed by Yang. Theoretical analysis is limited to channels which are approximately rectangular in shape. The width and depth exponents thus derived agree very well with those measured in laboratory experiments by Barr et al. Although the theoretical width and depth exponents are within the range of variations of measured data from river gaging stations, the at‐station width adjustment of natural rivers may also depend on constraints other than water discharge and sediment load.
Channel instability in a braided, sand bed river
Authors: Graf William L.
Published: February 2008

The Gila River of central Arizona is representative of braided, sand bed rivers in alluvial valleys that have inherent unstable behavior and destructive channel migration. The 112‐year record of channel conditions along a portion of the Gila River provides data for the construction of locational probability maps for main flow channels. Zones of stability and hazardous instability alternate with each other at 3.2 km (2 mi) intervals. During the past century the overall sinuosity of the main flow channel has remained close to 1.18, despite numerous changes in actual location. Spatial and temporal variation of sinuosity have occurred in subreaches as a result of sedimentation behind a dam and fluctuations in the density of phreatophyte growth, which both affect the hydraulics of flood flows. Unstable zones of the channel correspond to the surface of the sediment wedge behind the dam and areas dense phreatophyte growth. Stable zones correspond to areas controlled by bedrock or man‐made structures, as well as locations determined by these external factors plus the requirement to maintain a consistent sinuosity. Channels such as that of the Gila River do not meet most assumptions of equilibrium and are best understood through probabilistic approaches with an assumption of catastrophic adjustment.
Simple in situ determination of hydraulic conductivity by power function descriptions of drainage
Authors: Chong She‐Kong , Green Richard E. , Ahuja Lajpat R.
Published: February 2008

A simple method is presented to calculate soil hydraulic conductivity, K(θ), from in situ measurements during infiltration and redistribution. Equations for calculating K(θ) and K(h) were derived with the assumption of unit hydraulic gradient. The derivation employed power functions to describe the change of water content θ and pressure head h with time during the redistribution period. The validity of this assumption was tested because measured pressure head profiles during drainage showed that the total hydraulic head gradient varied from extremes of about 0.3 during the early stage of drainage to 2.0 after several days. Unit gradient was most frequently approached during the intermediate stages of drainage. K(θ) values obtained with this simple method should therefore be most reliable at intermediate water contents. This expectation was confirmed by comparison of K(h) values from the simple method with K values determined by the detailed Darcy method. The simple method appears to provide a practical means of characterizing K(θ) of well‐drained soils, even when the surface is tilled and the conductivity at high water contents decreases with depth. Such methods are needed to adequately characterize large areas to which hydrologic models, which require K(θ), are to be applied.
Estimation of impervious‐area Washoff Parameters
Authors: Alley William M.
Published: February 2008

In recent years many models have been developed which simulate the quality of rainfall runoff from urban areas. Common to many of these models is the use of an exponential washoff equation. This washoff equation is often modified by an availability equation to account for the effects of runoff intensity on constituent washoff. Optimization techniques for estimating the values of coefficients used in these equations have been developed. Application of these techniques to a small urban watershed in south Florida demonstrated considerable variability in the optimized parameter values among different storms and among different constituents.
Scale‐dependent dispersion in a stratified granular aquifer
Authors: Pickens John F. , Grisak Gerald E.
Published: February 2008

The magnitude of longitudinal dispersivity in a sandy stratified aquifer was investigated using laboratory column and field tracer tests. The field investigations included two‐single‐well injection‐withdrawal tracer tests using 131I and a two‐well recirculating withdrawal‐injection tracer test using 51Cr‐EDTA. The tracer movement within the aquifer was monitored in great detail with multilevel point‐sampling instrumentation. A constant value for dispersivity of 0.7 cm was found to be representative (and independent of travel distance) at the scale of an individual level within the aquifer. A dispersivity of 0.035 cm was determined from laboratory column tracer tests as a representative laboratory‐scale value for sand from the field site. The scale effect observed between the laboratory dispersivity and the dispersivity from individual levels in the aquifer is caused by the greater inhomogeneity of the aquifer (e.g., laminations within individual layers) and the averaging caused by the groundwater sampling system. Full‐aquifer dispersivities of 3 and 9 cm obtained from the single‐well tests indicate a scale effect with the value obtained being dependent mainly on the effect of transverse migration of tracer between the layers and the total injection volume. The full‐aquifer dispersivity of 50 cm from the two‐well test is scale‐dependent, controlled by the distance between the injection and withdrawal wells (8 m) and hydraulic conductivity distribution in the aquifer. Scale‐dependent full‐aquifer dispersivity expressions were derived relating dispersivity to the statistical properties of a stratified geologic system where the hydraulic conductivity distribution is normal, log normal or arbitrary. In the developed expressions, dispersivity is a linear function of the mean travel distance. Proportionality constants ranged from 0.041 to 0.256 for the hydraulic conductivity distributions obtained from the field tracer tests.
The mathematical structure of rainfall representations: 2. A review of the theory of point processes
Authors: Waymire Ed , Gupta Vijay K.
Published: February 2008

Part 2 constitutes the second of three parts devoted to the mathematical structure of rainfall. An expository, yet current, treatment of those features of point process theory which are essential to descriptions of the hydrologic processes is developed. A general overview of this three‐part series is given in part 1.
Water reuse planning models: Extensions and applications
Authors: Ocanas Gerardo , Mays Larry W.
Published: February 2008

A water reuse planning model has been developed for determining the optimum allocation of water and reuse of wastewater on a regional basis for multiperiod planning that minimizes the overall cost of water supply. Both water quantity and water quality parameters of various sources of flows are considered. Wastewater from all use sectors, along with freshwater, can be considered as candidate sources or origins of water. The model considers the capacity expansion of treatment facilities and allows for economies of scale in treatment and transportation through the use of nonlinear objective functions. Either the large‐scale generalized reduced gradient or the successive linear programing methods can be used to obtain solutions to the models. Both single‐period and multiperiod models are applied to a region including San Antonio, Texas. The single‐period model was applied to planning scenarios for the years 1980, 2000, and 2030. The multiperiod model was applied using a planning horizon consisting of three periods, 1980–2000, 2000–2030, and 2030–2060. Comparisons were made of the single‐period model applications and the multiperiod applications. The solution of a sequence of single‐period problems does not correctly represent the dynamic nature of the systems.
Electrical resistivity—hydraulic conductivity relationships in glacial outwash aquifers
Authors: Urish Daniel W.
Published: February 2008

Empirical field relationships between the apparent formation factors from surface resistivity soundings and hydraulic conductivity from pumping tests in fresh water granular aquifers usually show positive correlations. These relationships can be adequately explained by theory if consideration is taken of in situ field conditions. A sound theoretical basis for relating apparent formation factor to pertinent hydrogeophysical parameters in homogeneous isotropic sand is a three‐phase parallel resistor model which explicity includes parameters of porewater resistivity, grain size and shape, porosity, tortuosity, and intergranular surface conductance. The veracity of the theoretical model is supported by data from laboratory tests. The model demonstrates that intergranular surface conductance is an important factor at small grain sizes and high porewater resistivities, operating to lower the apparent formation factor. The model further shows that direct relationships between hydraulic conductivity and formation factor are weak in the normal range of porewater resistivity, being strongly dependent on porosity. When systematic variation of in situ porosity and aquifer layering effects are considered, a simulated field curve relating the apparent formation factor to hydraulic conductivity is shown to compare favorably with the comparable curve from field data for thirteen pumping test sites in southern Rhode Island. Both theoretical and empirical results demonstrate a useful positive correlation between aquifer apparent formation factor and hydraulic conductivity. Quantitative interpretation, however, is imprecise because of nonuniqueness of interpretation and inherent variation in important aquifer parameters, especially porosity.
Description of soil chemistry during transient solute transport
Authors: Dudley L. M. , Wagenet R. J. , Jurinak J. J.
Published: February 2008

Leaching studies were conducted in six instrumented field plots to establish the validity of a soil chemistry‐solute transport model. The model was designed to predict the transport and solution concentrations of Ca2+, Mg2+, Na+, K+, HCO3−, CO32−, SO42−, and Cl− in a soil containing CaCO3 (lime) and CaSO4·2H2O (gypsum). The model includes description of the precipitation and dissolution of both lime and gypsum and considers cation exchange. Evaluations were made of the sensitivity and accuracy of model simulations under transient and steady state flow regimes and in cropped and noncropped situations. The leaching plots were instrumented with porous ceramic suction samplers, tensiometers, and neutron probe access tubes. Five different quality waters and three types of water management were used. The soil solution was sampled following each irrigation and analyzed for the cations and anions of interest. Comparisons of measured and predicted data showed the model to be reliable as a simulation tool to predict electrical conductivity under cropped conditions but unreliable in uncropped situations.
Random differential equations in river water quality modeling
Authors: Finney Brad A. , Bowles David S. , Windham Michael P.
Published: February 2008

A one‐dimensional steady state probabilistic river water quality model is developed to compute the joint and marginal probability density functions of BOD and DO at any point in a river. The model can simultaneously consider randomness in the initial conditions, inputs, and coefficients of the water quality equations. Any empirical or known distribution can be used for the initial conditions. Randomness in each of the water quality equation inputs and coefficients is modeled as a Gaussian white noise process. The joint probability density function (pdf) of BOD and DO is determined by numerically solving the Fokker‐Plank random differential equation. In addition, moment equations are developed which allow the mean and variance of BOD and DO to be calculated independently of their joint pdf. The probabilistic river water quality model is examined through sensitivity study and an application to a hypothetical river system.
An operational net shortwave radiation model for glacier basins
Authors: Munro D. S. , Young G. J.
Published: February 2008

An operational net shortwave radiation model, which may be used to map radiation distributions under clear and cloudy skies, is described. Construction is achieved by modifying existing total spectrum approaches to allow a minimum of observational data to be used in its operation. Application to the Peyto Glacier Basin, Alberta, shows that realistic and diagnostically useful results can be produced from information contained in a topographic map, monitoring of the snowline, and routine weather observations. Net shortwave radiation estimates from the model are found to be a fair approximation of energy equivalents of ablation derived from stake measurements. It is concluded that net shortwave radiation should be a principal component of any realistic meltwater discharge model.
Dynamic programming applications in water resources
Authors: Yakowitz Sidney
Published: February 2008

The central intention of this survey is to review dynamic programming models for water resource problems and to examine computational techniques which have been used to obtain solutions to these problems. Problem areas surveyed here include aqueduct design, irrigation system control, project development, water quality maintenance, and reservoir operations analysis. Computational considerations impose severe limitation on the scale of dynamic programming problems which can be solved. Inventive numerical techniques for implementing dynamic programming have been applied to water resource problems. Discrete dynamic programming, differential dynamic programming, state incremental dynamic programming, and Howard's policy iteration method are among the techniques reviewed. Attempts have been made to delineate the successful applications, and speculative ideas are offered toward attacking problems which have not been solved satisfactorily.
An analysis of input errors in precipitation‐runoff models using regression with errors in the independent variables
Authors: Troutman Brent M.
Published: February 2008

Errors in runoff prediction caused by input data errors are analyzed by treating precipitation‐runoff models as regression (conditional expectation) models. Independent variables of the regression consist of precipitation and other input measurements; the dependent variable is runoff. In models using erroneous input data, prediction errors are inflated and estimates of expected storm runoff for given observed input variables are biased. This bias in expected runoff estimation results in biased parameter estimates if these parameter estimates are obtained by a least squares fit of predicted to observed runoff values. The problems of error inflation and bias are examined in detail for a simple linear regression of runoff on rainfall and for a nonlinear U.S. Geological Survey precipitation‐runoff model. Some implications for flood frequency analysis are considered. A case study using a set of data from Turtle Creek near Dallas, Texas illustrates the problems of model input errors.
Incorporation of prior information on parameters into nonlinear regression groundwater flow models: 1. Theory
Authors: Cooley Richard L.
Published: February 2008

Prior information on the parameters of a groundwater flow model can be used to improve parameter estimates obtained from nonlinear regression solution of a modeling problem. Two scales of prior information can be available: (1) prior information having known reliability (that is, bias and random error structure) and (2) prior information consisting of best available estimates of unknown reliability. A regression method that incorporates the second scale of prior information assumes the prior information to be fixed for any particular analysis to produce improved, although biased, parameter estimates. Approximate optimization of two auxiliary parameters of the formulation is used to help minimize the bias, which is almost always much smaller than that resulting from standard ridge regression. It is shown that if both scales of prior information are available, then a combined regression analysis may be made.
Bayesian analysis of underground flooding
Authors: Bogardi Istvan , Duckstein Lucien , Szidarovszky Ferenc
Published: February 2008

An event‐based stochastic model is used to describe the spatial phenomenon of water inrush into underground works located under a karstic aquifer, and a Bayesian analysis is performed because of high parameter uncertainty. The random variables of the model are inrush yield per event, distance between events, number of events per unit underground space, maximum yield, and total yield over mine lifetime. Physically based hypotheses on the types of distributions are made and reinforced by observations. High parameter uncertainty stems from the random characteristics of karstic limestone and the limited amount of observation data. Thus, during the design stage, only indirect data such as regional information and geological analogies are available; updating of this information should then be done as the construction progresses and inrush events are observed and recorded. A Bayes simulation algorithm is developed and applied to estimate the probability distributions of inrush event characteristics used in the design of water control facilities in underground mining. A real‐life example in the Transdanubian region of Hungary is used to illustrate the methodology.
A stochastic‐convective transport representation of dispersion in one‐dimensional porous media systems
Authors: Simmons C. S.
Published: February 2008

A stochastic‐convective transport formulation based upon solute travel time probability is presented and is shown to include Fickian transport as a special subcase. It is further demonstrated that a travel time probability associated with a lognormal distribution of hydraulic conductivity will yield concentration breakthrough curves nearly equivalent to those of Fickian transport when the coefficient of variation in travel time is sufficiently small, i.e., less than unity. When applied to column tracer experiments, the results suggest that typical laboratory‐measured hydrodynamic dispersion may be ascribed to local variations in hydraulic conductivity. Moreover, stochastic‐convective transport is shown to conserve solute mass under a flux boundary condition but to fail to do so under a held concentration condition. This result indicates the importance of boundary conditions for properly formulated stochastic transport. The travel time formulation is shown to provide a direct link between measured dispersivity and the autocovariance of local flow velocity variations that are a consequence of media inhomogeneity and the system boundary conditions. Dispersivity is shown to manifest a scale effect by increasing in proportion to the length of a system when the velocity correlation range is greater than that length. An expression for the effective dispersivity is derived for the case of long‐range velocity correlations and is shown to represent non‐Fickian behavior.
Stability analysis of water movement in unsaturated porous materials: 1. Theoretical considerations
Authors: Diment G. A. , Watson K. K. , Blennerhassett P. J.
Published: February 2008

The occurrence of wetting front instability during water movement in unsaturated porous materials under certain conditions is discussed and a brief review presented of relevant stability studies. The principles of hydrodynamic stability analysis are summarized and then used in developing a linear perturbation equation for vertical water movement with nonsharp fronts. A numerical approach for determining the stability parameters involving the eigenvalues of a matrix solution is outlined, and the numerical results are checked against an analytical solution for a profile exhibiting a uniform distribution of capillary potential.
The Turning Bands Method for simulation of random fields using line generation by a spectral method
Authors: Mantoglou Aristotelis , Wilson John L.
Published: February 2008

The turning bands method (TBM) for the simulation of multidimensional random fields is presented. These fields commonly occur in the Monte Carlo simulation of hydrologic processes, particularly groundwater flow and mass transport. The general TBM equations for two‐ and three‐dimensional fields are derived with particular emphasis on the more complicated two‐dimensional case. For stationary two‐dimensional fields the unidimensional line process is generated by a simple spectral method, a technique which can be generally applied to any two‐dimensional covariance function and which is easily extended to anisotropic and areal averaged processes. Theoretically and by example the TBM is shown to be ergodic even for a finite number of lines, and it is demonstrated that it rapidly converges to the true statistics of the field. Guidelines are presented for the selection of model parameters which will be helpful in the design of simulation experiments. The TBM is compared to other methods in terms of cost and accuracy, demonstrating that the TBM is as accurate as and much less expensive than multidimensional spectral techniques and more accurate than the most expensive approaches which use matrix inversion, such as the nearest neighbor approach. The unidimensional spectral technique presented here permits, for the first time, the inexpensive and accurate TBM simulation of any proper two‐dimensional covariance function and should be of some help in the stochastic analysis of hydrologic processes.
Effect of viewing angle on the infrared brightness temperature of snow
Authors: Dozier Jeff , Warren Stephen G.
Published: February 2008

Remote sensing of snowpack temperatures from satellites requires knowledge of the spectral emissivity of snow. A model for spectral emissivity is combined with the Planck function to calculate brightness temperature of snow in thermal infrared wavelengths for a range of grain sizes and viewing angles. Emissivity variations caused by density, grain shape, liquid water, and grain size are apparently unimportant, but emissivity varies with viewing angle to produce differences between thermodynamic temperature and brightness temperature as large as 3 K at wavelengths 12 to 14 μm, within the major atmospheric infrared window. This difference is also verified by experimental measurements. An equation to convert brightness temperatures to thermodynamic temperatures is presented, and this is also combined with a dual‐wavelength atmospheric correction method. The spectral emissivity model is also used to calculate an ‘all‐wave’ emissivity of snow: 0.985–0.990 for all grain sizes.
Adaptive explicit‐implicit quasi three‐dimensional finite element model of flow and subsidence in multiaquifer systems
Authors: Neuman Shlomo P. , Preller Christian , Narasimhan T. N.
Published: February 2008

A quasi three‐dimensional finite element model is presented for the analysis of groundwater flow and land subsidence due to pumpage in multiaquifer systems. In the model, aquifers are simulated with the aid of two‐dimensional horizontal finite element grids. Each aquifer is connected to its neighbors above and below by one‐dimensional vertical finite element strings which allow leakage to take place across aquitards and aquicludes. Land subsidence is modeled by varying the void ratio of each vertical element according to a nonlinear version of Terzaghi's one‐dimensional consolidation theory. A major feature of the new method is its ability to solve the finite element equations explicitly in one part of the mesh and implicitly in another part, depending on the ratio between the stability limit of each node and any given time step size. Since the hydraulic diffusivity of aquitards is usually very small compared to that of aquifers, it is often possible to solve the finite element equations explicitly for most, and sometimes all, aquitard nodes. This leads to a virtual decoupling of the aquifer equations during a given time step, which results in a significant saving of computer time and storage.
Analysis of flow through heterogeneous random aquifers: 2. Unsteady flow in confined formations
Authors: Dagan G.
Published: February 2008

The direct problem of determining the head field in a formation of given stationary isotropic random structure is solved approximately for unsteady flow conditions. Under restrictive assumptions of sufficiently small conductivity variance and average head gradient slowly varying in time and space, closed form expressions are derived for the effective conductivity or storativity and for the head variogram. Two types of unsteady flow are considered: transients and periodic flows. In the case of transients, it is assumed that initially the head is constant (no flow) and that ultimately the flow becomes uniform. It is found that the effective conductivity and transmissivity are time‐dependent and drop from the arithmetic mean (initially) to the steady state value during a relaxation time. The latter is much larger for one‐dimensional flows than for two‐ or three‐dimensional ones. The head variogram also relaxes from the one corresponding to the initial lack of correlation to the steady state variogram during a relaxation time which grows with the lag. While in three‐dimensional structure the relaxation time scales are relatively short and steady state analysis can be used accurately even under transient conditions, the tendency to steady state may be very slow in the case of transmissivity because of its large integral scale. Hence steady state analysis for transients might not be warranted for regional transient flows. In the case of periodic flows of seasonal nature, the head gradient is assumed to be made up from a steady component and a periodic one. If the amplitude of the latter is sufficiently small compared to the steady one, steady state value of effective transmissivity and storativity can be adopted. The head variogram has also its steady state form for large lags and quasisteady for small lags. Hence the variogram lies between the steady one (steady component of head gradient) and the quasisteady one (instantaneous head gradient).
Time‐dependent, linearized two‐dimensional infiltration and evaporation from nonuniform and nonperiodic strip sources
Authors: Batu Vedat
Published: February 2008

Using a linearized equation describing unsaturated homogeneous and isotropic porous media flow, a general, two‐dimensional, time‐dependent mathematical model is presented for infiltration and/or infiltration‐evaporation from nonuniform and nonperiodic strip sources located at the soil surface. The analysis is based on an exponential relationship between the unsaturated hydraulic conductivity and the soil water pressure head and also assumes a constant value for the derivative of unsaturated hydraulic conductivity with respect to water content. In the mathematical analysis, Laplace transform and Fourier analysis techniques are used simultaneously, and a general equation in an integral form for the distribution of matric flux potential has been obtained. The result of Warrick and Lomen (1976) for a single strip source is shown to be a special case of this general model. The solution for infiltration from two strip sources is presented as another special case. Also, a third special case is presented for infiltration from two strip sources and evaporation from another strip located in the middle part. The horizontal and vertical flux components for these cases are presented. All results are expressed in integral forms and calculated with a computer using a numerical integration method. The solutions predict the matric flux potential and flux components as functions of space and time. Examples that illustrate the applicability of some of the solutions are presented. These solutions are of interest in the design of both sprinkler and furrow irrigation systems. The results may also be used for different purposes in civil and agricultural engineering applications.
Extremal hypotheses for river behavior
Authors: Davies Timothy R. H. , Sutherland Alex J.
Published: February 2008

The hypotheses of minimum energy dissipation, minimum stream power, and minimum unit stream power are summarized and compared. Their derivation from analogies with laminar flow and linear thermodynamics is criticized on the grounds that these situations differ fundamentally from river flows, which are usually highly turbulent and strongly nonlinear. The authors' empirical hypothesis of maximum friction factor seems preferable to the minimization hypotheses because it is compatible with the known behavior of turbulent flows and nonlinear processes, it is applicable with a wider range of independent variables, and it is more in keeping with trends shown by experimental data under all constraints. The minimization hypotheses seem likely to give incorrect predictions when flow rate and depth are independent variables. The empirical success of the minimization hypotheses is confined to situations in which they predict similar behavior to the maximum friction factor hypothesis; they may be considered as special cases of this more general hypothesis.
Uniqueness and observability of conceptual rainfall‐runoff model parameters: The percolation process examined
Authors: Gupta Vijai Kumar , Sorooshian Soroosh
Published: February 2008

Many researchers have expressed concerns regarding the uniqueness of parameter estimates for conceptual rainfall‐runoff (R‐R) models obtained through calibration. Recent studies (Sorooshian et al., this issue; Sorooshian and Gupta, this issue) have revealed that even though stochastic parameter estimation techniques can help, the problems are not all due to inefficiencies in the calibration techniques used but are caused by the manner in which the model is structurally formulated. Thus even when calibrated under ideal conditions (simulation studies), it is often impossible to obtain unique estimates for the parameters. It is possible to resolve this problem, at least in part, by appropriate reparameterizations of the pertinent model equations. In this paper the percolation equation of the soil moisture accounting model of the National Weather Service River Forecast System (SMA‐NWSRFS) will be discussed. It is shown that a logical reparameterization of this equation can result in conditions that improve the chances of obtaining unique parameter estimates. It is believed that these results have implications for other conceptual R‐R models in which similar approaches are used in the representation of the percolation/infiltration process.
Economics of irrigation water mixing within a farm framework
Authors: Feinerman E. , Yaron D.
Published: February 2008

Linear programing models, deterministic in the short run and stochastic (random rainfall) in the long run, aimed at guiding annual decision making with regard to crop mix and saline irrigation water mixing from various sources within a farm framework, are presented. The short‐run model incorporates the physical, biological, and economic relationships involved in one endogenous system and enables an in depth analysis of them but is limited to a single year. The long‐run model considers the effects of the short‐run decisions on the future but several relationships are incorporated exogenously. The short run model's results are utilized for the determination of some of these predetermined relationships. The models are applied to a potential farm situation in southern Israel. The results provide priorities in the allocation of water and soil plots of varying salinity levels and empirical estimates of the shadow prices and the rates of substitution between the limited resources.
Groundwater geochemistry and calcite cementation of the aquia aquifer in southern Maryland
Authors: Chapelle Francis H.
Published: February 2008

The Aquia aquifer in southern Maryland exhibits three regions that are characterized by distinctly different water composition. Region I is about 26 mi (42 km) wide and is parallel to the outcrop area. Water in region I has relatively high calcium (∼30 mg/l), magnesium (∼10 mg/l), and bicarbonate (∼150 mg/l) concentrations and relatively low sodium (∼2 mg/l) concentrations. Region II, parallel to and downgradient from region I, is about 24 mi (38 km) wide. Water in region II is characterized by constant bicarbonate, increasing sodium, decreasing calcium, and decreasing magnesium concentrations. Region III is downgradient from region II and is characterized by low calcium (∼2 mg/l), low magnesium (∼1 mg/l), high bicarbonate (∼300 mg/l), and high sodium (∼100 mg/l) concentrations. The major lithologic constituents of the Aquia aquifer are quartz sand (∼55%), glauconite (∼30%), and carbonate shell material (∼8%). Heavy minerals, clay minerals, and finely disseminated lignite make up about 2% of the aquifer material. Calcite cementation is commonly observed in and near the outcrop area of the Aquia. Stoichiometric chemical models were constructed based on this lithology to describe the water chemistry of each region. These models are (region I) (Ca1−x, Mgx)CO3(s) + CO2(g) + H2O(1) ⇌ (1 − x)Ca(aq)2+ + xMg(aq)2+ + 2HCO3(aq)−, (region II) (1 − x)Ca(aq)2+ + xMg(aq)2+ + Na2 · glauconite(ad) ⇌ Ca(1−x)Mgx · glauconite(ad) + 2Na(aq)+, and (region III) (Ca(1−x)Mgx)CO3(s) + CO2(g)) + H2O(1)) + Na2 · glauconite(ad) ⇌ 2Na(aq)+ + 2HCO3(aq) +Ca(1−x)Mgx · glauconite(ad). The applicability of these models was verified by comparing predicted and observed molar ratios of dissolved species using linear regression techniques. In all cases, close matches were found between predicted and measured curves. Mass balance calculations using the verified chemical models predict a spatial distribution of calcite cementation that closely matches the observed distribution in the Aquia aquifer. This suggests that the observed calcite cementation is postdepositional in origin and has resulted from reaction of groundwater with aquifer material.
Modeling the effects of a time‐dependent wetted perimeter on infiltration from ephemeral channels
Authors: Freyberg David L.
Published: February 2008

The effects of a time‐dependent wetted perimeter on infiltration from ephemeral stream channel cross sections are explored using a conceptually simple mathematical model. The model is based on the assumptions of vertical soil moisture flow and the validity of the Green‐Ampt model for vertical infiltration. By using a simple channel geometry, an analytic solution is found for the case in which the gravitational component of soil moisture flow may be neglected. An efficient, accurate numerical technique provides approximate solutions in the general case. Application of the model demonstrates that cross‐sectional infiltration, that is, infiltration per unit length of channel, is a complex function of soil properties, channel geometry, and hydrograph shape. For the channel geometry considered, the direct effects of variable water pressure at the ground surface are overshadowed by the effects of variation in the wetted perimeter, with the result that the temporal variation in infiltration rate is quite unlike that which would be predicted assuming ponded infiltration alone.
Reservoir management: A reliability programming approach
Authors: Mariño Miguel , Mohammadi Behzad
Published: February 2008

A reliability programming model is developed to determine the optimum monthly releases from a multipurpose reservoir. The model is based on chance‐constrained linear programming (CCLP) and dynamic programming (DP). The flood and drought reliabilities are represented in the CCLP in the form of chance constraints. These reliabilities are varied parametrically from their minimum required levels to their maximum possible values. The trade‐offs between flood and drought reliabilities are made using a forward two‐dimensional DP routine. The model does not require equal flood and/or drought reliabilities during the year. Folsom reservoir of the California Central Valley Project is modeled to demonstrate the use of this reliability programming approach. The resulting operation policy shows high reliabilities of flood and drought during winter and summer months, respectively. The variable risk levels avoid unnecessary releases during summer (for flood protection) and unnecessary storage of water during winter (for drought protection).
Incorporation of prior information on parameters into nonlinear regression groundwater flow models: 2. Applications
Authors: Cooley Richard L.
Published: February 2008

This paper investigates factors influencing the degree of improvement in estimates of parameters of a nonlinear regression groundwater flow model by incorporating prior information of unknown reliability. Consideration of expected behavior of the regression solutions and results of a hypothetical modeling problem lead to several general conclusions. First, if the parameters are properly scaled, linearized expressions for the mean square error (MSE) in parameter estimates of a nonlinear model will often behave very nearly as if the model were linear. Second, by using prior information, the MSE in properly scaled parameters can be reduced greatly over the MSE of ordinary least squares estimates of parameters. Third, plots of estimated MSE and the estimated standard deviation of MSE versus an auxiliary parameter (the ridge parameter) specifying the degree of influence of the prior information on regression results can help determine the potential for improvement of parameter estimates. Fourth, proposed criteria can be used to make appropriate choices for the ridge parameter and another parameter expressing degree of overall bias in the prior information. Results of a case study of Truckee Meadows, Reno‐Sparks area, Washoe County, Nevada, conform closely to the results of the hypothetical problem. In the Truckee Meadows case, incorporation of prior information did not greatly change the parameter estimates from those obtained by ordinary least squares. However, the analysis showed that both sets of estimates are more reliable than suggested by the standard errors from ordinary least squares.
Sensitivity of Florida lakes to acidic precipitation
Authors: Canfield Daniel E.
Published: February 2008

To assess the potential vulnerability of Florida lakes to damage by acidic precipitation, data from a survey of 165 lakes located in the major physiographic and geologic regions of Florida were used to determine pH, total alkalinity, calcium hardness, and calcite saturation index values. Mean lake pH ranged from 4.1 to 8.9. Mean total alkalinity concentrations ranged from 0 to 4100 µeq/l and mean calcium hardness concentrations ranged from 20 to 4300 µeq/l. Total alkalinity averaged below 200µeq/l in 49% of the sampled lakes. Calcite saturation index values were greater than 4 in 36% of the sampled lakes. Based on these data, Florida has a large number of lakes that are vulnerable to reductions in pH and alkalinity by acidic precipitation. Data on chlorophyll a concentrations, Zooplankton abundance, and recent fisheries data, however, suggest that Florida lakes may not be as biologically sensitive as the alkalinity and calcite saturation indices might suggest. Low phosphorus and nitrogen concentrations are primarily responsible for reduced animal and plant populations in acidic Florida lakes. Consequently, predictions of future impacts or trends based on current sensitivity indices should be regarded with caution.
A mathematical model for border strip irrigation
Authors: Weir G. J.
Published: February 2008

A kinematic model is developed to discuss surface irrigation when the infiltration function consists of a long‐time gravity term plus a short‐time capilliary or sorbtivity term. The corresponding model equations are solved either exactly or numerically, and several graphical solutions are presented. Using the kinematic solution, we suggest a condition for the validity of the corresponding Lewis‐Milne problem, and from the shallow water or dynamic equations we suggest a condition for the validity of our kinematic solution.
Improved parameter inference in catchment models: 1. Evaluating parameter uncertainty
Authors: Kuczera George
Published: February 2008

A Bayesian methodology is developed to evaluate parameter uncertainty in catchment models fitted to a hydrologic response such as runoff, the goal being to improve the chance of successful regionalization. The catchment model is posed as a nonlinear regression model with stochastic errors possibly being both autocorrelated and heteroscedastic. The end result of this methodology, which may use Box‐Cox power transformations and ARMA error models, is the posterior distribution, which summarizes what is known about the catchment model parameters. This can be simplified to a multivariate normal provided a linearization in parameter space is acceptable; means of checking and improving this assumption are discussed. The posterior standard deviations give a direct measure of parameter uncertainty, and study of the posterior correlation matrix can indicate what kinds of data are required to improve the precision of poorly determined parameters. Finally, a case study involving a nine‐parameter catchment model fitted to monthly runoff and soil moisture data is presented. It is shown that use of ordinary least squares when its underlying error assumptions are violated gives an erroneous description of parameter uncertainty.