bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of aquifer transmissivities: The comparison model method
Authors: Ponzini Giansilvio , Lozej Alfredo
Published: February 2008

A method for solving the inverse problem in hydrogeology is presented. This method is suitable for computing the interblock transmissivities (harmonic mean or others) referred to the sides of the network blocks of a nonhomogeneous, anisotropic aquifer in steady state flow. The interblock transmissivities computing procedure is based on the comparison between real gradients and the ones generated by a ‘comparison model’ whose initial transmissivity value is arbitrarily chosen and constant through out the surveyed area. Alternative solutions of interblock transmissivities, one for each constant initial transmissivity value utilized in the comparison model, are obtained. Generally, these solutions differ from each other, but all of them present the characteristics of being able to reproduce, with the precision of an arbitrarily small ϵ, the real piezometrie heads, respecting the geometry and the boundary conditions of the real aquifer. The selection of the value, or set of values, of the initial transmissivity to put into the comparison model in order to obtain one solution of computed interblock transmissivities close to the real ones, both as trends and as absolute values, is rather critical. The minimum head anomaly criterion and the bottleneck criterion enable one to select a value or a set of values of initial transmissivity. These criteria exploit only the data needed for the solution of the inverse problem (real piezometric heads, geometry, and boundary conditions), and they lead to a suitable initial transmissivity that, put into the comparison model, allow one to obtain a good and meaningful solution of computed interblock transmissivities. The comparison model method and the two aforementioned criteria have been applied to a numerical case study bearing good results. The method has been tested, in order to evaluate its effectiveness, even in the case of noisy piezometric heads (piezometric heads with random errors). Even in this case the method bore satisfactory and useful results. Finally, a promising approach to the inverse problem solution, when one has at his disposal at least four sets of data coming from as many hydraulic situations, has been briefly described.
On the mutually beneficial cooperative scheme: Dynamic change in the payoff matrix of international river basin schemes
Authors: Dufournaud Christian M.
Published: February 2008

Mutual benefit is the most common criterion by which scholars view international cooperative river basin schemes. Since all riparians are not equally committed financially to the completion of such a project and since the benefits of the project will accrue to each party at different rates over time, a probability exists that one of the partners will opt out at a point advantageous to suit himself. Utilizing metagame theory, this paper explores the possibilities open to riparians in the Columbia and Lower Mekong River Basin schemes by demonstrating the various dynamic paths of the net benefits of such cooperative and sovereign schemes. The paper concludes by arguing that the traditional view of the criterion of mutual benefit is not valid in all cases.
Analysis of length distribution of drainage basin perimeter
Authors: Werner Christian
Published: February 2008

To establish a theoretical base for the study of the length distribution of basin perimeters, the paper introduces a descriptive model of the topology of interlocking channel and ridge networks. Assuming topological randomness within and between both, the expected number of links of basin perimeters is derived; for large basin magnitudes n, it approximates a square root function in n. Observed link numbers of perimeters deviate significantly, showing a 0.69 regression exponent for their growth rate relative to the basin magnitude rather than the expected value of 0.5. The spatial constraint of possible perimeter/(area;)½ proportions as defined by the circle is translated into a corresponding topological constraint but fails to provide a sufficient explanation. The paper then explores the possibility that the relatively large length of the perimeter reflects the basin elongation which, following Hack, might be linked to the length of the mainstream. Although basin perimeter, elongation, and mainstream length are highly correlated and the elongation axis is oriented to the outlet in two‐thirds of the sample basins, the data indicate that the mainstream link number does not account for the basin elongation, nor does it account for the number of links of the basin perimeter.
Passive microwave sensing of soil moisture under vegetation canopies
Authors: Jackson Thomas J. , Schmugge Thomas J. , Wang James R.
Published: February 2008

Vegetation cover has a significant effect on the ability of passive microwave radiometers to detect changes in near‐surface soil moisture. A quantitative technique for isolating the effect of vegetation was developed using a theoretical model as the basis of a parametric approach. This approach was evaluated using data collected by truck‐mounted sensors over experimental plots. Results show that a microwave radiometer operating at a 21‐cm wavelength can provide volumetric surface soil moisture estimates to ∼5% of accuracy for fields covered with moderate vegetation. In addition, all of the data required for applying the parametric model can be measured using remote sensing.
Multidimensional numerical simulation of fluid flow in fractured porous media
Authors: Narasimhan T. N.
Published: February 2008

Isothermal flow of water in a variety of fractured systems is discussed in the context of a unified, integral framework. Three commonly used conceptualizations, namely, porous systems, fractured systems, and composite porosity systems, are analyzed. The integral equations are directly replaced by discretized expressions based on an integral finite difference scheme (IFDM). Because of the manner in which the IFDM scheme chooses to handle geometric inputs, it handles the three aforesaid conceptualizations with equal facility. Six illustrative examples are provided to give an idea of the variety of fracture‐related problems that are of common interest, to identify the common denominators that unify these problems and to demonstrate the power of the IFDM.
Macropores and water flow in soils
Authors: Beven Keith , Germann Peter
Published: February 2008

This paper reviews the importance of large continuous openings (macropores) on water flow in soils. The presence of macropores may lead to spatial concentrations of water flow through unsaturated soil that will not be described well by a Darcy approach to flow through porous media. This has important implications for the rapid movement of solutes and pollutants through soils. Difficulties in defining what constitutes a macropore and the limitations of current nomenclature are reviewed. The influence of macropores on infiltration and subsurface storm flow is discussed on the basis of both experimental evidence and theoretical studies. The limitations of models that treat macropores and matrix porosity as separate flow domains is stressed. Little‐understood areas are discussed as promising lines for future research. In particular, there is a need for a coherent theory of flow through structured soils that would make the macropore domain concept redundant.
Model experiments on mobile, paved gravel bed streams
Authors: Parker Gary , Dhamotharan Sundararajan , Stefan Heinz
Published: February 2008

Laboratory experiments which model streams with poorly sorted gravel beds at reduced scale reveal that pavement is a mobile bed phenomenon. It acts to decrease the inherent difference in mobility between large and small grains by overrepresenting the percentage of large grains exposed to the flow. Pavement can coexist with the motion of all available grain sizes because motion is sporadic, so that at any given time only a small percentage of surface grains are actually in motion. Particles in the immediate subpavement are only occasionally moved, and deeper particles are hardly ever moved. The experiments were conducted at constant discharges. They provide accurate quantitative models of two field streams in that they obey the same bedload law as field data. Both sediment feed and recirculating configurations were utilized. The only systematic difference between the two is in the behavior of the finer grains.
Consumptive water use response of maize to changes in environment and management practices: Sensitivity analysis of a model
Authors: Terjung W. H. , Hayes J. T. , O'Rourke P. A. , Burt J. E. , Todhunter P. E.
Published: February 2008

WATER, a parametric crop water use model, employs climatic data to calculate water consumption for a variety of crops, using a modification of the Penman equation which included specific crop and growth stage effects. The objective of this paper was to demonstrate the response of WATER, for a grain corn crop, to changes in a variety of important environmental and decision‐making inputs: air temperature, solar radiation, relative humidity, irrigation frequency, and amount of irrigation water applied. Five temperature, five solar radiation, and six relative humidity regimes were examined for an entire growing season. Also, five different water application schemes and four irrigation frequencies were included in this experiment. Additionally, the effect of different soil types, wind regimes, and groundwater depths on crop water requirements were investigated. These analyses were performed using four annual climatic scenario combinations. Among the results, evapotranspiration (ET) increased on the average by about 2.5%/1°C increase in air temperature. One percent change in solar radiation resulted in a 1.5% change in ET, while a similar change in relative humidity caused a 0.4% response in ET. Contrasting soil types, in addition to affecting irrigation frequency, were capable of changing the responding ET by over 10%.
Agricultural vs. hydropower tradeoffs in the operation of the High Aswan Dam
Authors: Oven‐Thompson Katherine , Alercon Luis , Marks David H.
Published: February 2008

This paper defines a tradeoff relationship between hydropower and agriculture for the monthly operations of the High Aswan Dam under current water availability conditions. A stochastic dynamic programming model is employed which incorporates the physical constraints (e.g., reservoir storage limits, turbine capacity, allowable reservoir releases, etc.) of the High Aswan Dam system. Variations of monthly reservoir releases for agricultural purposes are imposed on the system through this model, and consequent impacts on hydropower production at the high dam are studied. The results show that once operating rules are optimized for current agricultural demands an 11–20% increase in firm monthly hydropower production can be gained when summer irrigation allocations are reduced by 25%. A simple benefit/cost analysis concludes that potential benefits obtained by gains in firm monthly hydropower are nearly equal to potential losses in the agricultural sector when summer allocations are reduced by 5–10%. Operation questions raised by the introduction of a new emergency flood control spillway at Toshka are addressed. Recommendations are made for the operating guidelines of the high dam releases in light of these results.
Preliminary studies of the reservoir capacity and the generating potential of the Baca Geothermal Field, New Mexico
Authors: Bodvarsson G. S. , Haar S. Vonder , Wilt M. , Tsang C. F.
Published: February 2008

A 50‐MWe geothermal power plant is being considered for the Baca site in the Valleys Caldera, New Mexico, as a joint venture of the Department of Energy (DOE) and Union Oil Company of California. To date, over 20 wells have been drilled on the prospect, and the data from these wells indicate the presence of a high‐temperature, liquid‐dominated reservoir. In this paper, data from the open literature on the physical characteristics of the field are used to estimate the amount of hot water in place (reservoir capacity) and the length of time the reservoir can supply steam for a 50‐MWe power plant (reservoir longevity). The reservoir capacity is estimated to be 1012 kg of hot fluid by volumetric calculations using existing geological, geophysical, and well data. The criteria used are described and the sensitivity of the results discussed. The longevity of the field is studied using a two‐phase numerical simulator (SHAFT79). A number of cases are simulated based upon different boundary conditions and upon injection and production criteria. The results obtained from the simulation studies indicate that it is questionable that the Baca field can supply enough steam for a 50‐MWe power plant for 30 years. Although the estimated reservoir reserves greatly exceed those needed for a 50‐MWe power plant, the low transmissivity of the reservoir would cause localized boiling and rapid pressure decline during exploitation. It is therefore apparent that the conventional zero‐dimensional (lumped parameter models) cannot be used to evaluate the generating capacities of low‐permeability fields such as the Baca field.
Experimental investigation on irreversible changes of hydraulic conductivity on the seawater‐freshwater interface in coastal aquifers
Authors: Goldenberg L. C. , Magaritz M. , Mandel S.
Published: February 2008

Seawater and fresh groundwater were made to flow through columns filled with samples from a ‘good aquifer’ that contained 5% or less clay minerals. Hydraulic conductivities decreased very sharply whenever seawater was flushed by fresh groundwater. The extent of the decrease depended mainly on the percentage of clays and reached maximum values of 10−1 to 10−3 of the original hydraulic conductivity. Subsequent flushing with seawater restored hydraulic conductivity only in a slight measure, if at all. The mechanism of this process was investigated by using CaCl2 and NaCl solutions with the ionic strengths of seawater and fresh groundwater. It appears that the decrease of hydraulic conductivity is caused by an incipient stage of gel formation. The small water‐clay configurations that are formed during this stage behave as practically rigid particles and close the bottlenecks between adjacent pores. The major implications of these findings for groundwater hydrology are as follows: (1) In natural coastal aquifers the seawater‐freshwater interface is likely to undergo shifts on a semigeologic time scale. If the aquifer contains even a small percentage of clays, these shifts may create an almost impermeable boundary in the zone of the interface. Hitherto existing theories on movements of the interface regard permeability as constant. (2) The attempt to repel a fresh water‐seawater interface by the injection of fresh water may create a practically impermeable boundary within a relatively short time, and thus defeat its own purpose.
Simulation of solute transport in a mountain pool‐and‐riffle stream: A transient storage model
Authors: Bencala Kenneth E. , Walters Roy A.
Published: February 2008

The physical characteristics of mountain streams differ from the uniform and conceptually well‐ defined open channels for which the analysis of solute transport has been oriented in the past and is now well understood. These physical conditions significantly influence solute transport behavior, as demonstrated by a transient storage model simulation of solute transport in a very small (0.0125 m3s−1) mountain pool‐and‐riffle stream. The application is to a carefully controlled and intensively monitored chloride injection experiment. The data from the experiment are not explained by the standard convection‐dispersion mechanisms alone. A transient storage model, which couples dead zones with the one‐dimensional convection‐dispersion equation, simulates the general characteristics of the solute transport behavior and a set of simulation parameters were determined that yield an adequate fit to the data. However, considerable uncertainty remains in determining physically realistic values of these parameters. The values of the simulation parameters used are compared to values used by other authors for other streams. The comparison supports, at least qualitatively, the determined parameter values.
A stochastic‐dynamic model for real time flood forecasting
Authors: Chow K. C. A. , Watt W. E. , Watts D. G.
Published: February 2008

A stochastic‐dynamic model for real time flood forecasting was developed using Box‐Jenkins modelling techniques. The purpose of the forecasting system is to forecast flood levels of the Saint John River at Fredericton, New Brunswick. The model consists of two submodels: an upstream model used to forecast the headpond level at the Mactaquac Dam and a downstream model to forecast the water level at Fredericton. Inputs to the system are recorded values of the water level at East Florenceville, the headpond level and gate position at Mactaquac, and the water level at Fredericton. The model was calibrated for the spring floods of 1973, 1974, 1977, and 1978, and its usefulness was verified for the 1979 flood. The forecasting results indicated that the stochastic‐dynamic model produces reasonably accurate forecasts for lead times up to two days. These forecasts were then compared to those from the existing forecasting system and were found to be as reliable as those from the existing system.
Identifying sources of groundwater pollution: An optimization approach
Authors: Gorelick Steven M. , Evans Barbara , Remson Irwin
Published: February 2008

Least squares regression and linear programing for least absolute error estimation are each combined with groundwater solute transport simulation to identify the locations and magnitudes of aquifer pollutant sources. Pollutant sources are identified by matching simulated and measured nonreacting solute concentration data. We have assumed known hydraulic parameters but considered concentration data errors explicitly. The identification models are demonstrated and compared using two hypothetical aquifer systems, one for the steady state case and the other for the transient case. Steady state models identified unknown pipe leak locations and leak magnitudes based upon sparse and spatially distributed chloride and tritium data. The number of likely leak locations was restricted in the models by employing mixed integer programing and stepwise multiple regression. Transient models identified several annual disposal fluxes in the aquifer based upon concentration histories collected at observation wells. In this case, conservative solute concentration data were abundant and contained substantial errors. Minimizing either least absolute or least squared errors was successful in identifying pollutant sources. Furthermore, we demonstrate error analysis for the results given by either method.
A mathematical model for regional land subsidence due to pumping: 3. Integrated equations for a phreatic aquifer
Authors: Corapcioglu M. Yavuz , Bear Jacob
Published: February 2008

A mathematical model is developed for the areal distribution of drawdown, land subsidence, and horizontal displacements due to groundwater pumping from a deformable phreatic aquifer. This paper is a continuation of earlier works published by the authors (Bear and Corapcioglu, 1981a, b) on the subject of regional land subsidence due to pumping in confined and leaky aquifers. All the basic assumptions underlying these previous works are also valid here. However, in this case the same methodology is extended to the case of a phreatic aquifer. The main additional feature in the present paper is that due to the decline of the water table, the total stress at points within the flow domain changes continuously. Following the development of a three‐dimensional mathematical model consisting of a mass conservation equation, quasi‐static equilibrium equations, and stress‐strain relations for an assumed perfectly elastic solid matrix, a regional, horizontal two‐dimensional model is derived by averaging the three‐dimensional model over the vertical thickness of the aquifer, taking into account the continuous variation in total stress as a result of water table fluctuations. The separation of an initially coinciding phreatic surface, which serves as the Upper boundary of the aquifer, and a surface consisting of a set of solid particles during the lowering of the water table and the compaction of the aquifer has been incorporated into the averaging procedure. An analytical solution is given for the case of a single pumping well. The solution, which is expressed in terms of the classical well function for a confined aquifer but with a modified storativity, provides estimates of drawdown, vertical subsidence, and horizontal displacement. The displacements for a sample problem are compared with those of a confined aquifer under similar conditions. The results indicate that under the conditions of the studied case of radial flow, vertical and horizontal displacements due to pumping from a phreatic aquifer with the same discharge rate would be less than those of a confined one. Furthermore, the same averaging procedure is extended for a system of phreatic and leaky confined aquifers and for the unsaturated zone above the water table. An additional change in total stress is obtained in terms of moisture content of the zone above the phreatic surface.
Stability analysis of water movement in unsaturated porous materials: 2. Numerical studies
Authors: Diment G. A. , Watson K. K.
Published: February 2008

In an earlier paper a detailed theory was presented in which the principles of hydrodynamic stability analysis were used to develop a linear perturbation equation for vertical water movement with nonsharp fronts. In the present study the analysis is applied to the stability of several soil water systems some of which are potentially unstable. The first stage in the analysis requires the generation of water content and pressure head profiles using a computer‐based numerical solution for the flow equation for unsaturated porous materials. These profiles permit the calculation of certain differential terms which appear in the specification of the coefficients required in the stability analysis. Results for the growth rate of imposed disturbances of wavelengths of 1, 5, and 25 cm together with the appropriate eigenvectors are presented for infiltration into a homogeneous profile, redistribution following infiltration, infiltration into a scale heterogeneous medium, and infiltration into a fine‐over‐coarse stratified profile. Although instability was expected for the redistribution, heterogeneous, and layered systems, the results, whilst showing a noticeable trend towards instability, did not predict the occurrence of such a condition. The reason for this is discussed, in particular the evidence which suggests that small amounts of initial water can have a significant effect on the damping‐out of instabilities that otherwise would occur under dry initial conditions. Reference is made to a projected further paper documenting the effect of initial water content on wetting front instability and to the need for additional numerical studies at very low initial water contents.
Influence of the point bar on flow through curved channels
Authors: Dietrich William E. , Smith J. Dungan
Published: February 2008

In a channel with bed topography that does not vary in the downstream direction, a secondary circulation composed of outward flow at the surface and inward flow near the bottom extends across the entire width. If the curvature is constant, the cross‐stream velocity component near the bed and the pattern of boundary shear stress can be estimated by assuming fluid accelerations to be small. Unfortunately, this procedure cannot be used in analyzing the flow through natural river meanders, or through channels with downstream constant bottom topography but with rapidly changing curvature. In these latter cases, effects arising from bed‐ and bank‐induced momentum changes must be accounted for. Evidence for a substantial topographically induced alteration in the cross‐stream flow pattern relative to that for the analogous constant bottom topography case is provided through new analyses of several sets of laboratory and field data. Shoaling over the point bar in the upstream part of the bend is shown to force the high‐velocity core of the flow toward the pool. This is accomplished by a convective acceleration‐caused decrease in the cross‐stream water surface slope and a resulting dominance of the vertically averaged centrifugal force. The primary effect is a velocity component toward the outside or concave bank throughout the flow depth over the upstream, shallow part of the point bar and an outward component of boundary shear stress in this region. The channel curvature‐induced inward component of boundary shear stress consequently is confined to 20 or 30% of the channel width at the pool. Outward transfer of momentum over the point bar, as manifested by a rapid crossing of the high‐velocity core from the inside bank to the outside one, contributes to an enhanced decrease in boundary shear stress along the convex side of the stream as the top of the bar is approached. Forces arising from topographically induced spatial accelerations are of the same order of magnitude as the downstream boundary shear stress and water surface slope force components, so they must be modeled as zero‐order, not first‐ or second‐order, effects.
A stochastic analysis of macroscopic dispersion in fractured media
Authors: Schwartz Franklin W. , Smith Leslie , Crowe Allan S.
Published: February 2008

A stochastic modeling technique has been developed to investigate mass transport in a network of discrete fractures. The model is based on the repetitive generation of realizations of a fracture network from probability distributions, describing the fracture geometry, and on a solution for mass transport within each network, using a particle‐tracking technique. The system we work with consists of two orthogonal fracture sets of finite length, oriented at various angles with respect to the direction of the mean hydraulic gradient. Emphasis is placed on describing the character of dispersion, which develops as a consequence of fracture interconnectivity, and on testing the validity of the conventional diffusion‐based model of dispersion in describing transport in fractured media. Results show that mass distributions have a complex form. Marked longitudinal dispersion can develop even a short distance from a source. The distribution of mass in the direction of flow has a consistent negative skew. This pattern of dispersion arises from the limited number of pathways for mass to migrate through the network. Controlling factors in the transport process are the orientation of the fracture sets with respect to the mean hydraulic gradient, the difference in the mean flow velocity in the two fracture sets, and the standard deviation in velocity for fracture set 1. Transport patterns can change greatly as the orientation of the hydraulic gradient changes with respect to the two fracture sets. A conventional diffusion‐based model of dispersion cannot characterize transport in these fracture networks. A skewed spatial distribution of mass is observed much more frequently than a Gaussian distribution. When the mean velocities in the two fracture sets are not equal, the form of mass spreading is described by a more general, skewed distribution that accounts for the bias in the probability of mass moving along one fracture set over another. There is a tendency for mass to form a more symmetric distribution as the orientation of the two fracture sets is rotated toward a 45° angle with respect to the direction of the mean hydraulic gradient. Furthermore, constant dispersivity values or simple dispersivity functions are not definable because of the sensitivity of transport to the local velocity field in the fracture network.
Regional management of an aquifer for mining under fuzzy environmental objectives
Authors: Bogárdi István , Bárdossy András , Duckstein Lucien
Published: February 2008

A methodology is developed for the dynamic multiobjective management of a multipurpose regional aquifer. In a case study of bauxite mining in Western Hungary, ore deposits are often under the piezometric level of a karstic aquifer, while this same aquifer also provides recharge flows for thermal springs. N + 1 objectives are to be minimized, the first one being total discounted cost of control by dewatering or grouting; the other N objectives consist of the flow of thermal springs at N control points. However, there is no agreement among experts as to a set of numerical values that would constitute a “sound environment”; for this reason a fuzzy set analysis is used, and the N environmental objectives are combined into a single fuzzy membership function. The constraints include ore availability, various capacities, and the state transition function that describes the behavior of both piezometric head and underground flow. The model is linearized and solved as a biobjective dynamic program by using multiobjective compromise programming. A numerical example with N = 2 appears to lead to realistic control policies. Extension of the model to the nonlinear case is discussed.
Solute Transfer Through Columns of Glass Beads
Authors: De Smedt F. , Wierenga P. J.
Published: February 2008

Miscible displacement experiments were conducted in a 30‐cm‐long column filled with glass beads that had diameters in the range of 74–125 µm. Breakthrough curves were determined at various leaching rates for saturated or unsaturated conditions. The breakthrough curves of the unsaturated experiments showed early breakthrough and tailing. These could be described with the classical dispersion equation, provided dispersion coefficients were used, which were about 20 times larger than for saturated columns leached at comparable pore water velocities. A better description of these breakthrough curves was obtained with a model accounting for mobile and immobile water. With this model the dispersion coefficients, as obtained from the saturated experiments, could be used directly. The immobile water content was found to increase linearly with the total water content, while the transfer coefficient for solute transport into the immobile water increased proportionally with the pore water velocity. It is shown, based on the mobile and immobile water and solute transport model, that breakthrough curves of long unsaturated columns should exhibit no early breakthrough and tailing but that the presence of immobile water will result in predictably larger dispersion coefficients than those expected on the basis of saturated flow experiments alone.
Water Conservation: The Struggle Over Definition
Authors: Baumann Duane D. , Boland John J. , Sims John H.
Published: February 2008

During the 1970's much attention was focused on the role of water conservation in the planning and management of urban water supplies, and actions to implement water conservation were taken at all levels of government. Yet many policies and programs appear to rely on conceptions of water conservation which confuse supply and demand oriented strategies or which inefficiently conserve water at the expense of other scarce resources. Through an analysis of the underlying concepts and values, a definition of water conservation is reached which is both precise and practical and which provides a sound basis for the development of water conservation policies. Examples drawn from recent field studies illustrate the application of the definition.
Optimal Estimation of the Average Areal Rainfall and Optimal Selection of Rain Gauge Locations
Authors: Bastin G. , Lorent B. , Duqué C. , Gevers M.
Published: February 2008

We propose a simple procedure for the real‐time estimation of the average rainfall over a catchment area. The rainfall is modeled as a two‐dimensional random field. The average areal rainfall is computed by a linear unbiased minimum variance estimation method (kriging) which requires knowledge of the variogram of the random field. We propose a time‐varying estimator for the variogram which takes into account the influences of both the seasonal variations and the rainfall intensity. Our average areal rainfall estimator has been implemented in practice. We illustrate its application to real data in two river basins in Belgium. Finally, it is shown how the method can be used for the optimal selection of the rain gauge locations in a basin.
Income Distribution Impacts of Irrigation Water Distribution Policy
Authors: Sampath Rajan K.
Published: February 2008

In the majority of lesser developed countries (LDC's) there is acute inequality in income distribution in the rural sector, particularly between large and small farms on the one hand and between land owners and the landless on the other. Irrigation water distribution policy of the government is both an economic and political problem. It has both equity and efficiency implications. It has effects on both the level and distribution of income. This paper deals with the conditions under which using water redistribution as an effective governmental policy variable can reduce inequality in the distribution of income. This paper also deals with the relationship between the objectives of equity and efficiency in water distribution under different objective realities, such as dualistic versus nondualistic conditions, two‐sector versus three‐sector modeling, optimum versus equal water distribution, specifically to derive the conditions under which promotion of equity promotes efficiency and vice versa and the conditions under which it does not.
A Statistical Exploration of the Relationships of Soil Moisture Characteristics to the Physical Properties of Soils
Authors: Cosby B. J. , Hornberger G. M. , Clapp R. B. , Ginn T. R.
Published: February 2008

Stochastic modeling of soil water fluxes in the absence of measured hydraulic parameters requires a knowledge of the expected distribution of the hydraulic parameters in different soil types. Predictive relationships describing the hydraulic parameter distributions must be developed based on the common descriptors of the physical properties of soils (e.g., texture, structure, particle size distribution). Covariation among the hydraulic parameters within these relationships must be identified. Data for 1448 soil samples were examined in an evaluation of the usefulness of qualitative descriptors as predictors of soil hydraulic behavior. Analysis of variance and multiple linear regression techniques were used to derive quantitative expressions for the moments of the hydraulic parameters as functions of the particle size distributions (percent sand, silt, and clay content) of soils. Discriminant analysis suggests that the covariation of the hydraulic parameters can be used to construct a classification scheme based on the hydraulic behavior of soils that is analogous to the textural classification scheme based on the sand, silt, and clay content of soils.
Simulation of Runoff From Snow‐Covered Hillslopes
Authors: Akan A. Osman
Published: February 2008

A physics‐based mathematical model of springtime runoff from snow‐covered hillslopes is presented. The model accounts for liquid water flow, heat conduction, and vapor diffusion simultaneously within a snow cover. The physics‐based approach is verified by testing the model with two sets of observed data. Also, by applying the model to a hypothetical snow‐covered plot, it is demonstrated that springtime diurnal changes are not restricted to a thin layer near the snow surface, but they may influence the entire depth of a wet snowpack.
A Nonparametric Trend Test for Seasonal Data With Serial Dependence
Authors: Hirsch Robert M. , Slack James R.
Published: February 2008

Statistical tests for monotonic trend in seasonal (e.g., monthly) hydrologic time series are commonly confounded by some of the following problems: nonnormal data, missing values, seasonality, censoring (detection limits), and serial dependence. An extension of the Mann‐Kendall test for trend (designed for such data) is presented here. Because the test is based entirely on ranks, it is robust against nonnormality and censoring. Seasonality and missing values present no theoretical or computational obstacles to its application. Monte Carlo experiments show that, in terms of type I error, it is robust against serial correlation except when the data have strong long‐term persistence (e.g., ARMA (1, 1) monthly processes with ϕ > 0.6) or short records (∼ 5 years). When there is no serial correlation, it is less powerful than a related simpler test which is not robust against serial correlation.
Dependence of Hypolimnetic Oxygen Consumption on Ambient Oxygen Concentration: Fact or Artifact?
Authors: Cornett R. J. , Rigler F. H.
Published: February 2008

Ten lakes studied in this investigation and the data presented by previous authors are all consistent with the hypothesis that rates of oxygen depletion in the hypolimnion of lakes do not depend upon the ambient oxygen concentration over the range of concentrations from 12 mg/L to 1.0 mg/L. By definition, aerobic respiration must stop when there is no more oxygen present. Therefore the hypolimnetic oxygen deficit can be modeled as a zero‐order chemical process that is independent of oxygen concentration. Predictions of seasonal changes in hypolimnetic oxygen concentrations can be made by estimating the slope of the linear regression of oxygen concentration against the Julian day when the sample was collected.
Nash Model Relation to Horton Order Ratios
Authors: Rosso Renzo
Published: February 2008

The Nash model of the instantaneous unit hydrograph (IUH) is parameterized in terms of Horton order ratios of a catchment on the basis of a geomorphologic model of catchment response. The shape parameter of the Nash model is found to depend on Horton's numbers RA, RB, and RL of a catchment; thus catchment geomorphology can provide a synthesis of the shape of the hydrologic response. The scale parameter of the Nash model results to be a time‐varying character depending on both geomorphology and average streamflow velocity along the stream network; thus the time scale of the IUH could account for the variability of the hydrologic response for different storms and throughout a storm.
Pressure Transient Analysis for Two‐Phase Geothermal Wells: Some Numerical Results
Authors: Garg S. K. , Pritchett J. W.
Published: February 2008

A numerical geothermal reservoir simulator is used in a series of calculations to help devise interpretation techniques for analyzing pressure transient data from two phase geothermal reservoirs. The investigations include (1) the drawdown/buildup behavior of initially two‐phase (liquid water/steam) reservoirs, (2) the drawdown/buildup response of initially single‐phase reservoirs which undergo flashing as a result of fluid production, and (3) the effects of cold water injection into hot two‐phase reservoirs. Production (drawdown/buildup) data from two‐phase (either initially or due to production‐induced boiling) reservoirs may be analyzed in the usual manner to yield kinematic mobility; buildup data from reservoirs which undergo flashing on production also offer the possibility of determining absolute formation permeability. Injection data can be interpreted in a straightforward manner to yield absolute formation permeability; the corresponding falloff data appear, however, to be of little value.
A Model for Flow in Meandering Streams
Authors: Smith J. Dungan , Mclean S. R.
Published: February 2008

Erosion and deposition in streams and tidal channels depend on the divergence of the sediment‐flux field, and this is governed by the distribution of boundary shear stress. As a consequence, erosion arid deposition patterns in such systems are sensitive to spatial variations in boundary shear stress, which in turn, can be induced by the complex interplay between the flow and bed and bank topography. A method whereby variations in boundary shear stress can be calculated is presented herein for flows that are broad in relation to their depth and for which the bed slopes are small. The formal scheme employs a regular perturbation expansion around a zero‐order state that includes vertically integrated, topographically induced convective accelerations. Use of a zero‐order velocity field that includes these accelerative effects yields a model that is applicable to streams with typical bed slopes and channel curvatures, one that can be employed in the majority of situations of interest to geomorphologists, sedimentologists, and hydraulic engineers concerned with fluvial and estuarine systems. In order to verify the model, our calculations are shown to reproduce, with reasonable accuracy, the free‐surface topography and boundary shear stress distribution measured by Hooke (1975) when applied to a channel of the geometry that he investigated. The latter part of the paper describes how the interplay of the various components of flow through a curved channel with bar‐pool topography is affected by the parameters of the problem.
Statistical Inference for Point Process Models of Rainfall
Authors: Smith James A. , Karr Alan F.
Published: February 2008

In this paper we develop maximum likelihood procedures for parameter estimation and model selection that apply to a large class of point process models that have been used to model rainfall occurrences, including Cox processes, Neyman‐Scott processes, and renewal processes. The statistical inference procedures are based on the stochastic intensity λ(t) = lims→0,s>0 (1/s)E[N(t + s) − N(t)|N(u), u < t]. The likelihood function of a point process is shown to have a simple expression in terms of the stochastic intensity. The main result of this paper is a recursive procedure for computing stochastic intensities; the procedure is applicable to a broad class of point process models, including renewal Cox process with Markovian intensity processes and an important class of Neyman‐Scott processes. The model selection procedure we propose, which is based on likelihood ratios, allows direct comparison of two classes of point processes to determine which provides a better model for a given data set. The estimation and model selection procedures are applied to two data sets of simulated Cox process arrivals and a data set of daily rainfall occurrences in the Potomac River basin.
Interactive Data Management for Resource Planning and Analysis
Authors: Loucks Daniel P. , Taylor Marshall R. , French Peter N.
Published: February 2008

Since the mid‐1970's, a number of research projects at Cornell University have focused on the development and application of interactive models and computer programs for studying water resources and environmental management problems. These models and programs have been adapted for use with computer graphics display devices. This interactive computer‐aided planning system has been designed to facilitate data input, editing, and display; model building and solution; and analysis and synthesis of alternative resource management plans or policies. This paper discusses the approaches taken for managing and displaying data that are needed for, and derived from, this interactive modeling system. Several applications are presented and some conclusions on how such systems might be developed or expanded in the future are proposed.
The Dual Formulation of Flow for Contaminant Transport Modeling: 2. The Borden Aquifer
Authors: Frind E. O. , Matanga G. B. , Cherry J. A.
Published: February 2008

The dual formulation of flow in terms of potentials and stream functions is applied to a groundwater system containing a well‐monitored chloride plume. It is found that field measurements of head alone, regardless of detail, are not sufficient to arrive at a description of the flow system that is meaningful within the context of a contaminant transport modeling study. Problems identified include the incompatibility of the time‐specific hydraulic data with the longer time frame of the transport phenomenon and the susceptibility of the potential solution to numerical error. In overcoming these problems, plumebased data are used in the dual model of potentials and stream functions to determine the hydrogeologic parameters that are needed for the description of the flow system in a transport model. A companion paper reviews the underlying theory.
Seepage to Collection Gallery Near Seacoast
Authors: Hunt B.
Published: February 2008

Conformal mapping is used to obtain a solution for seepage to a collection gallery (a horizontal ditch or slotted pipe) that is parallel to a seacoast. The solution permits calculation of the gallery drawdown that is required to withdraw any given flow rate and also allows calculation of the maximum flow rate that can be abstracted without causing sea water intrusion. The results are applied to a numerical example.
Optimal urban water distribution design
Authors: Morgan D. R. , Goulter I. C.
Published: February 2008

A heuristic linear programming‐based procedure has been developed for the least cost layout and design of water distribution networks. The methodology is capable of analyzing a wide range of demand pattern and pipe failure combinations. Hydraulic consistency is ensured throughout the procedure through the use of the Hardy‐Cross network solver technique. The procedure can also be extended for use in the expansion or reinforcement of existing network systems. While the techniques used to reduce the size of the constraint set to enable the procedure to handle a wide range of loading conditions do not guarantee global optimality, a pragmatic “reasonable” optimum is achieved. The method is demonstrated by application to the design of a new network and the expansion of an existing network. In the expansion of the existing network problem the solution obtained was less expensive than any previously published solution.