bluuebunny/crossref_metadata_2025 huggingface dataset:
A mixed numerical analytical method for groundwater flow simulation
Authors: Ramm Dov , Chazan Dan
Published: February 2008

When finite difference or finite element schemes are used to solve the equations of ground water flow, it is not possible to obtain an accurate representation of the flow field near singularities without a considerable refinement of the grid. This difficulty is readily overcome by the use of a mixed numerical analytic scheme which is proposed in this work. Functions which accurately represent the effect of the singularity near its center but die off away from it are subtracted from the solution. The difference is a smooth function which is adequately represented by existing schemes. In addition to wells which are discussed here, springs and extended singularities can also be handled. The scheme is mainly of interest when it is of importance to trace the flow of pollutants in an area where many singularities may be present.
Theoretical head variograms for steady flow in statistically homogeneous aquifers
Authors: Chirlin G. R. , Dagan G.
Published: February 2008

Flow through two‐dimensional porous formations is modeled as a random process using an approximate formulation of flow physics in order to obtain an expression for the head variogram. (The variogram is related to the variance of the head difference between two points separated by a vector h and has leapt into prominence owing to its central role in kriging.) The model domain investigated here is unbounded, composed of arbitrarily placed circular blocks of random, statistically homogeneous dimension and transmissivity, these two properties being independently distributed. The model medium can represent only transmissivity autocorrelation functions which decline monotonically from 1 to 0. Steady, uniform average flow is investigated. Flow physics are simplified by ignoring any differences among blocks of the same size and transmissivity and then using their random setting to ease spatial integrations involved in head statistics. The head variogram proves significantly anisotropic, with heads differing more widely on average for a fixed lag parallel to the head gradient than perpendicular to it. Field practice presently ignores anisotropy; the implications are examined for a hypothetical case and indicate that kriged standard deviation is overestimated perpendicular to the mean flow and underestimated parallel to it. For lag magnitude greater than the largest block diameter the variogram is logarithmic in the lag magnitude and proportional to the head gradient squared. This leads to a technique to reduce data scatter in empirically fitted variograms. Once an empirical head variogram is selected, the inverse problem may be solved for a particularly simple medium structure.
Optimal design and operation of permanent irrigation systems
Authors: Oron Gideon , Walker Wynn R.
Published: February 2008

Solid‐set pressurized irrigation system design and operation are studied with optimization techniques to determine the minimum cost distribution system. The principle of the analysis is to divide the irrigation system into subunits in such a manner that the trade‐offs among energy, piping, and equipment costs are selected at the minimum cost point. The optimization procedure involves a nonlinear, mixed integer approach capable of achieving a variety of optimal solutions leading to significant conclusions with regard to the design and operation of the system. Factors investigated include field geometry, the effect of the pressure head, consumptive use rates, a smaller flow rate in the pipe system, and outlet (sprinkler or emitter) discharge.
A traveling wave solution to the problem of simultaneous flow of water and air through homogeneous porous media
Authors: Nakano Yoshisuke
Published: February 2008

A traveling wave solution was derived for the problem of simultaneous flow of water and air through homogeneous porous media. It is found that the properties of the solution generally depend upon the hydraulic characteristics of a given problem. The properties of the solution are presented for a specific case in which the hydraulic characteristics are given in specific functional forms. For this specific case it is found that a singularity occurs in the solution at both a saturated‐unsaturated boundary and a wetting front. Some applications of the solution are discussed.
A comparison of predictions and measurements of the radiation field in a shallow water layer
Authors: Incropera F. P. , Wagner T. R. , Houf W. G.
Published: February 2008

The problem of solar radiation transfer in a body of water is complicated by several factors, which include the directional distribution of the incident radiation, reflection and refraction at the air‐water interface, absorption and multiple scattering within the water, and reflection off the bottom surface. Although theoretical methods have been developed to treat the problem, little has been done to test the accuracy of the methods through a comparison of predictions with measurements under controlled laboratory conditions. In this study, measurements of the directional and spatial distribution of the spectral radiation have been made in a diffusely irradiated aqueous medium, and the results have been compared with predictions based on the discrete ordinate and three‐flux methods. For the prescribed laboratory conditions the radiation is concentrated within a cone of half angle θ ≈ 0.85 rad, and for this region, good agreement is obtained between intensity measurements and predictions based on the discrete ordinate method. Good agreement is also obtained between radiation fluxes measured for the forward direction and predictions based on both the discrete ordinate and three‐flux methods. Discrepancies between predicted and measured results for θ ≳0.85 rad are attributed to uncertainties in the radiation intensity and phase function measurements.
A technique in using integrodifferential equations for model simulation of multiaquifer systems
Authors: Premchitt Jerasak
Published: February 2008

A numerical technique for modeling a multiaquifer system is developed on the basis of a quasi three‐dimensional flow model. The model consists of many horizontal aquifers interconnected by leakage flux from aquitards. The direct flow across aquitards and yield from aquitard storage are taken into account in leakage flux terms in the form of convolution integrals. Mathematical formulation results in flow functions which diminish with time and can be approximated by few exponential terms. They have been proved to be very convenient in a numerical solution scheme involving the convolution integrals. The approach reduces the dimensionality of the problem and uncouples the equations corresponding to each of the aquifers. The technique is flexible and can be used for any basin geometry with an arbitrary pumping scheme. The validity of the technique is demonstrated by comparing the model results with available analytical solutions. In general, it appears that this technique is more economical than the full three‐dimensional model or even the quasi three‐dimensional models that use one‐dimensional elements to represent the aquitards.
Bifurcation analysis of rainfall infiltration
Authors: Nguyen V. V. , Wood E. F.
Published: February 2008

The understanding of local characteristics within the global behavior of catchment dynamics is an important concern to both theorists and field hydrologists. The law of averages, when applied to local infiltration behavior, often fails to render representative information as to the nonlinear response of a catchment due to runoff thresholds, feedback with soil moisture, and infiltration hysteresis. As an alternative to current conceptual approaches, this paper analyzes the bifurcation (nonlinear) behavior of point infiltration using the equation of unsaturated flow. The result is a geometric framework in which the relationships between rainfall, infiltration, and soil properties are better understood. By using standard experimental data a nonlinear infiltration model can be easily parameterized that exhibits bifurcations in bulk infiltration rates.
Long‐term distributions of annual sediment yields from small watersheds
Authors: Van Sickle John
Published: February 2008

Annual sediment yields from small (<20 km2) mountain watersheds in the northwestern United States are approximately log normally distributed over time. Stochastic sediment yield models, based on brief, infrequent transport events, reproduce the log normal property. Observed cumulative distributions of annual yields from several Pacific Northwest drainages also appear to be log normal. The property gives a statistical basis for interpreting annual yield data. For example, impacts of watershed disturbance should be assessed by median rather than mean annual yield.
Estimating evapotranspiration from the Sonoita Creek Watershed near Patagonia, Arizona
Authors: Ben‐Asher J.
Published: February 2008

In a study that was proposed to evaluate the water balance of the Sonoita Creek watershed near Tucson, Arizona, monthly evapotranspiration was defined by Morton's conceptual approach for large areas. The objective of this study was to test the model. The available climatological data were solar radiation, dew point temperature, mean monthly temperature, and humidity. The model was evaluated by testing the relationship between potential and actual evapotranspiration in Africa. Data for Africa were found to be in agreement with the concept of a complementary relationship. When applied to a small watershed such as Sonoita Creek, the model performance was good on an annual basis and in the hot seasons. In the cold seasons, however, an alternative approach was used. Error analysis indicated that a major source of error lies in the fact that the model neglects the effect of surface moisture content on net radiation. It assumes a single value of net radiation for both the Priestley‐Taylor and Penman’s formulae. However, the assumption of a well‐watered surface, which is inherent in the first formula, must be associated with net radiation which is higher than that associated with Penman's formula. As a result, a maximum error as large as 52% of the annual evapotranspiration may occur.
Comparison of first‐order error analysis and Monte Carlo Simulation in time‐dependent lake eutrophication models
Authors: Scavia Donald , Powers William F. , Canale Raymond P. , Moody Jennie L.
Published: February 2008

Estimates of variance for a nonlinear, seasonal food chain, nutrient cycle eutrophication model of Saginaw Bay, Lake Huron, calculated by first‐order variance propagation and Monte Carlo analyses, do not always agree. A comparison of estimates of state variables indicates that Monte Carlo means are most like the measurements, whereas Monte Carlo medians are most like the deterministic model output. Best agreement between Monte Carlo and first‐order estimates of both state variable values and their variances occurs when Monte Carlo output distributions are symmetric. Under these conditions, both estimates are measures of variance associated with total populations (i.e., all algae). Those distributions, however, change dramatically in time for most state variables. For asymmetric distributions, first‐order variance estimates measure variability about the typical component of the total population (i.e., the typical algal species) and Monte Carlo variance estimates measure variability of the mean component (which is more reflective of the total). One must be cognizant of these differences when estimating variance associated with model projections.
A comparison of the incomplete cholesky‐conjugate gradient method with the strongly implicit method as applied to the solution of two‐dimensional groundwater flow equations
Authors: Kuiper L. K.
Published: February 2008

This paper compares the efficiency of the strongly implicit procedure (SIP) and the incomplete Cholesky‐conjugate gradient method (ICCG) applied to the solution of the finite difference approximating equations for groundwater flow. Results for five isotropic two‐dimensional test problems are presented. Three are linear confined aquifer problems, and two are nonlinear water table aquifer problems; in all but one of the test problems the aquifer was considered to be nonhomogeneous. Both SIP and ICCG as applied to water table aquifer problems make use of iteration parameters. These were varied for each of the test problems to reduce the amount of computational work needed to find a solution. ICCG was usually substantially more efficient than SIP when applied to the confined aquifer test problems. For the water table aquifer test problems, SIP and ICCG performed equally well.
The irrigation scheduling problem and evapotranspiration uncertainty
Authors: Rhenals Alonso E. , Bras Rafael L.
Published: February 2008

Scheduling and determining of irrigation water applications are important considerations given limited water resources and increasing concern about agricultural productivity. Past literature has repeatedly been concerned with the influence of the variability of actual evapotranspiration on crop irrigation needs. This work investigates the above issue. A model, based on stochastic dynamic programing, is formulated to maximize net benefits from a crop facing uncertain, correlated evapotranspiration demands. Weekly irrigation decisions are made after observing current soil moisture and available irrigation water, as well as potential evapotranspiration in the past week. The model is similar to the traditional reservoir control algorithms popular in the surface water literature. A case study example indicates that although the model formulation is useful and feasible, the effect of uncertain evapotranspiration on irrigation performance measures is apparently minimal. This work should be of interest to researchers of agricultural management and to those studying the applications and use of operation research techniques in water resources. Computer programs utilized in this paper are available from the authors.
A multiobjective branch and bound method for network‐structured water resources planning problems
Authors: Nakamura Masahisa , Riley James M.
Published: February 2008

A multiobjective branch and bound algorithm is proposed for use in analyzing multiobjective fixed charge network flow problems which are found commonly in water resources planning situations. Also proposed is a multiobjective imputed value analysis which makes use of the branch and bound tree structure and allows the comparison of the importance of facilities in the network as represented by individual arcs or sets of arcs. The mathematical formulation and the analysis procedure of the method are described, and the potential usefulness of the method is demonstrated using a hypothetical example problem dealing with a regional wastewater treatment and residual management system. A Fortran program for implementing the algorithm is available from the first author.
Coping with increased stream erosion in urbanizing areas
Authors: Whipple William , DiLouie James
Published: February 2008

This paper discusses the increasing channel degradation being experienced in many urbanizing area streams. Increased flooding caused by intensive land development is related to stream erosion through bed load transport theory. Analysis of these relationships leads to conclusions as to channel design criteria. Current design criteria for culverts crossing such streams should be modified.
An alternative development of the dispersion equation
Authors: Soerjadi R.
Published: February 2008

A mathematical approach to dispersion of particles may start with the development of the governing equation. Such an equation has been derived in 1972 by de Josselin de Jong using a so‐called canal model. He introduced this model in 1957 for computing the spreading of salt by water flowing through porous media. This paper deals with another mathematical treatment based upon the same model. The properties of the model can be characterized by a stochastic spreading mechanism, in which the stochastical displacement of a particle plays the role of fundamental random variable. In a simplified case, where the spreading mechanism is place and time independent, the governing differential equation appears to possess constant coefficients. These coefficients turn out to be the moments of the random particle displacement per unit time. Another aspect is the symmetrical behaviour of the time and place coordinates. This leads to a duality in the problem formulation: the original problem requires the particle density in space at a given instant, whereas the dual problem questions how the particles pass through at a given place. If the spreading mechanism is time and place dependent, the governing equation can also be derived. The results are in agreement with the ones found by de Josselin de Jong.
Estimation of extreme low flows for pumped storage reservoir design
Authors: Metcalfe A. V. , Mawdsley J. A.
Published: February 2008

A method for estimating the probability of nonexceedance of low flows for a reservoir fed directly by one river with additional pumped inflow from a second river is described, The method is based on the joint probability distribution of an extreme value distribution and a truncated extreme value distribution. The estimates of the probabilities of given low flows are given by integrals. These are evaluated numerically for a range of low flows and maximum daily pumping rates. Details are given for the particular case of total inflow during a period of three consecutive months, but the method could be used for any duration.
Hydrodynamic dispersion during absorption in a fine sand: 1. The constant concentration case
Authors: Watson K. K. , Jones M. J.
Published: February 2008

The quasianalytical approach to hydrodynamic dispersion during horizontal absorption under constant concentration conditions is discussed, and an integral solution presented for the case of a constant dispersion coefficient. Experimental results for Bungendore fine sand, obtained during constant concentration absorption, are compared with concentration profiles calculated using the integral solution. The comparison is good when a constant dispersion coefficient of 10−8 m2 s−1 is used. An explicit computer‐based numerical analysis is then described briefly and checked against the integral result with excellent correspondence being achieved. The numerical analysis is used to determine concentration profiles for the case when the dispersion coefficient is velocity dependent. These profiles are compared with the experimental data, and it is observed that the bandwidth of the scatter of the data is greater than the spread of the concentration profiles. It is concluded that a definitive statement on the existence and magnitude of a velocity‐dependent effect cannot be made solely on the basis of the experimental data. However, the Péclet numbers appropriate to the system are greater than unity, suggesting that the dispersion coefficient is velocity dependent and that the parameters used in the numerical analysis to express this dependence are satisfactory for Bungendore fine sand under constant concentration absorption.
Establishing contributions to an insurance fund
Authors: Fiering Myron B.
Published: February 2008

The recent literature in water resource planning suggests several techniques for resolution of conflict and uncertainty in the planning process. Multiobjective planning is a societal reality which must be handled if rational plans are to be developed and assessed in an unambiguous fashion. This paper considers the application of an insurance or sinking fund to cases with stochastic system response and in particular deals with the theory of decision‐making for projects in which the uncertainties in benefit to the competing parties or interest groups are not independent. In effect, the paper develops a rule for incentive or side payments which accommodate the extent to which benefits to the parties cannot be decoupled.
Topologic model for drainage networks with lakes
Authors: Mark David M. , Goodchild Michael F.
Published: February 2008

Shreve's probabilistic‐topologic model for drainage network topology is herein extended and generalized to allow for the presence of lakes. Drainage network topology is represented by an integer string directly analogous to the binary strings used for channel networks without lakes. Validity constraints on integer strings are presented, along with combinatorial results and methods for generating ‘topologically random’ networks. The hypothesis that network element degree and type is independent of position within the integer string leads to good predictions of the relative frequencies of various classes of small subnetworks within a 596‐link network in northern Ontario. For the special case of networks without lakes the model is equivalent to Shreve's.
Regional water balance on the Arctic Tundra in summer
Authors: Ohmura Atsumu
Published: February 2008

The regional distributions of evaporation and precipitation were investigated on the arctic tundra on Axel Heiberg Island, Northwest Territory, Canada, during the summers of 1969 and 1970. The measurements were made using small weighing lysimeters and Canadian standard rain gauges installed at eight locations ranging in altitude from the sea level to 800 m above mean sea level. The mean evaporation rate for the snow‐free period increases slightly with altitude. The total evaporation for the snow‐free period at high altitudes, however, is cut short due to the longer duration of the snow cover. Consequently, the total summer evaporation shows a maximum value in the altitude zone between 100 and 600 m. Summer total precipitation increases steadily with altitude, exceeding evaporation at about 500 m. Below this altitude, most of the annual runoff takes place during and immediately after the melt of the winter snow cover. At higher altitudes, runoff is observed throughout summer.
Diffusivity, storativity, and the Dupuit Assumptions for periodic flow in a vertical Hele‐Shaw Model
Authors: Williams John A.
Published: February 2008

The linear theory of shallow phreatic aquifers and the role of storativity are investigated by using data from a periodic flow in a vertical Hele‐Shaw model. Results indicate that the theory is valid if (z¯/λ)2 ≤ 0.08 and if η0/z ≤ 0.083, where λ is the length of the periodic fluctuation in the phreatic surface, η0 is the amplitude of the fluctuation applied at the boundary, and z¯ is the average depth. These values are not necessarily upper limits. The results also show that the storativity varies with depth and frequency and assumes a maximum value at that depth for which the dominant meniscus configuraton produces a minimum specific retention. In addition, analyses of amplitudes indicate that local variations in the storativity, some of the order of 50%, occur systematically without any significant effect on the theoretically predicted amplitude behavior. Consequently, the linear theory requirement of a constant diffusivity may be relaxed.
Identification of multivariate time series and multivariate input‐output models
Authors: Cooper David M. , Wood Eric F.
Published: February 2008

The problem of linear model structure identification for multivariate time series or multiple input‐output models is presented and solved. The identification is obtained using canonical correlations to determine model order. The equivalence between state‐space model structure and multivariate autoregressive moving average with exogenous inputs (ARMAX) models is presented. The class of models open to analysis includes rainfall‐runoff models, multivariate streamflow models, and time invariant state‐space models used in Kaiman filtering. Examples include a rainfall‐runoff model using three precipitation inputs, a four‐site monthly streamflow model, and a four‐season streamflow model.
An approximate integral solution of vertical infiltration under changing boundary conditions
Authors: Prasad S. N. , Römkens M. J. M.
Published: February 2008

An approximate solution of the Richards equation was obtained with a spectral series solution for rain infiltration under changing boundary conditions. Prior to surface ponding a flux boundary condition was employed, which was followed by a concentration boundary condition. During this latter stage a flux matching boundary condition was used to describe the movement of the interface between the saturated and unsaturated zones. The solutions yield a general expression for ponding time, wetting front advance, and soil water profile. Infiltration rates beyond ponding include the effect of time dependent ponding height and saturation depth.
Parameter estimation of multiple input‐output time series models: Application to rainfall‐runoff processes
Authors: Cooper David M. , Wood Eric F.
Published: February 2008

In time series modeling of hydrologic systems the model structure either is determined a priori from physical considerations or is identified statistically. This paper sets forth a maximum likelihood procedure for estimating the parameters of a class of statistical models (linear time‐invariant state‐space) once a suitable member of the class has been identified. Using the innovation form of the state‐space model, the parameters of the transition, input weighting, gain and output, or measurement matrices are estimated as well as the innovation covariance matrix. Procedures for estimating process and measurement covariances in the state‐space model, and the parameters of the equivalent multivariate autoregressive moving average with exogenous inputs (ARMAX) model are also developed. A convergent and asymptotically efficient on‐line method of estimation is derived from the off‐line algorithm. Four examples are presented: daily rainfall‐runoff forecasting, four‐site monthly streamflow, seasonal model, and river flow input‐output model with a tributary.
On Lagrangian residual currents with applications in south San Francisco Bay, California
Authors: Cheng Ralph T. , Casulli Vincenzo
Published: February 2008

The Lagrangian residual circulation has often been introduced as the sum of the Eulerian residual circulation and the Stokes' drift. Unfortunately, this definition of the Lagrangian residual circulation is conceptually incorrect because both the Eulerian residual circulation and the Stokes' drift are Eulerian variables. In this paper a classification of various residual variables are reviewed and properly defined. The Lagrangian residual circulation is then studied by means of a two‐stage formulation of a computer model. The tidal circulation is first computed in a conventional Eulerian way, and then the Lagrangian residual circulation is determined by a method patterned after the method of markers and cells. To demonstrate properties of the Lagrangian residual circulation, application of this approach in South San Francisco Bay, California, is considered. With the aid of the model results, properties of the Eulerian and Lagrangian residual circulation are examined. It can be concluded that estimation of the Lagrangian residual circulation from Eulerian data may lead to unacceptable error, particularly in a tidal estuary where the tidal excursion is of the same order of magnitude as the length scale of the basin. A direction calculation of the Lagrangian residual circulation must be made and has been shown to be feasible.
Analysis of an incongruity in the standard Galerkin Finite Element Method
Authors: Cooley Richard L.
Published: February 2008

In the standard Galerkin finite element method applied to equations of groundwater flow, the development to incorporate second and third type boundary conditions implicitly assumes that the basis functions satisfy these boundary conditions. Because the basis functions normally employed are not required to satisfy these boundary conditions, a theoretical incongruity is created. If the Galerkin procedure is reformulated by adding a term to explicitly consider failure of the basis functions to satisfy the boundary conditions, the incongruity is eliminated; however, the resulting set of operational equations is unchanged from the set resulting from applying the boundary conditions in the normal manner. An analysis demonstrates that if the differential equation has a variational equivalent, the same error functional is minimized whether or not the basis functions satisfy second and third type boundary conditions.
Precipitation chemistry at the marcell experimental forest in north central Minnesota
Authors: Verry Elon S.
Published: February 2008

Concentration (milligrams and microequivalents per liter) values are presented for major ions occurring in rain and snow from July 1978 to July 1980. Ammonium, sodium, and calcium are the largest equivalent weight cations which are largely balanced by sulfate and nitrate anions. Hydrogen is the fourth most abundant cation; but high combined concentrations of other cations in 27% of the sample events mask positive correlations with high hydrogen concentrations. Field‐measured pH averaged 4.3, but the range (3.5 to 6.5) fluctuated with a combination of earth and air mass conditions. When high cation (and anion) data are deleted, low pH correlates well with high nitrate. Sulfate concentrations are similar to those measured in 1936 and do not correlate with pH. Calcium and, to a lesser extent, ammonium tend to increase pH values. High nitrate values also correlate positively with high excess acidity, while high sodium and calcium values correlate with high excess alkalinity.
Capacity Expansion model for large‐scale water‐energy systems
Authors: Matsumoto Junji , Mays Larry W.
Published: February 2008

A mathematical optimization model has been developed to help investigate various alternatives for the capacity expansion of water‐energy systems. The system consists of four subsystems: water, coal, electricity, and gas systems. Expressing new capacities, production, and distribution activities mathematically, the mathematical structure of the problem is defined and formulated as a multisystem, multiperiod capacity expansion problem. Benders decomposition is applied to the original problem to decompose it into three problems: capacity, production, and distribution problems. Each problem is solved by specialized algorithms. An example problem was solved, and the results are presented.
Resource allocation to interrelated projects
Authors: Mehrez Abraham , Sinuany‐Stern Zilla
Published: February 2008

A multiattribute utility function was used to specify the decision‐maker's preferences, along with a zero‐one budget model, to solve the problem of selecting among interrelated multiobjective long‐range projects. Increasing the number of projects increases the complexity of the problem. The advantages of the model for relatively small problems are demonstrated by a case study dealing with a subset of Israeli water development projects for 1981.
Mathematical simulation of interdependent surface and subsurface hydrologic processes
Authors: Smith R. E. , Hebbert R. H. B.
Published: February 2008

It has become popular with some hydrologists to consider runoff produced by rainfall intensities in excess of soil infiltration capacity (‘Horton’ excess) and runoff produced by rain falling on saturated soil zones (saturation excess) to be alternative or competitive models for describing surface runoff. On the contrary, we contend with Freeze (1972) that these two mechanisms, along with subsurface stormflow, are three parts of a continuum of hydrologic response that are controlled by the relative properties of the soil and the rainfall. We introduce a model which trades some of the generality of the Freeze (1972) hillslope model for increased efficiency, by selecting efficient approximations for key elements in hillslope hydrodynamics: infiltration and movement in the unsaturated flow zone. The hillslope is considered to consist of two soil layers with the lower soil capable of restricting vertical flow at the interface to create a perched aquifer and subsurface stormflow. The slope of the interface is arbitrary. A kinematic method for routing unsaturated vertical flow is described and is linked consistently with a modern analytically derived infiltration model, which operates when rainfall exceeds surface saturated hydraulic conductivity Ks. The model is used to demonstrate several of the relationships between rainfall flux, soil hydraulic properties, hillslope geometry, and runoff characteristics. The model is also applied to simulate experimental data from a hillslope in Western Australia. Subsurface stormflow recessions are demonstrated to be affected by the ratio Ks/ql, anisotropy, and spatial distribution of saturated hydraulic conductivity Ks, where ql is the rate of loss from the perched aquifer. Vertical growth of the saturated zone depth is demonstrated to have a potentially greater effect on runoff than horizontal movement in cases where anisotropy and/or slope is not severe.
The effects of a change in the variability of irrigation water
Authors: Lyon Kenneth S.
Published: February 2008

This paper examines the short‐run effects upon several variables of an increase in the variability of an input. The measure of an increase in the variability is the “mean preserving spread” suggested by Rothschild and Stiglitz (1970). The variables examined are real income (utility), expected profits, expected output, the quantity used of the controllable input, and the shadow price of the stochastic input. Four striking features of the results follow: (1) The concepts that have been useful in summarizing deterministic comparative static results are nearly absent when an input is stochastic. (2) Most of the signs of the partial derivatives depend upon more than concavity of the utility and production functions. (3) If the utility function is not “too” risk averse, then the risk‐neutral results hold for the risk‐aversion case. (4) If the production function is Cobb‐Douglas, then definite results are achieved if the utility function is linear or if the “degree of risk‐aversion” is “small.”
Some algorithms for parameter estimation in water resources systems
Authors: Sehitoglu H.
Published: February 2008

This paper is concerned with the development of algorithms for the estimation of the unknown model parameters of some water resources systems. The proposed algorithms are of recursive form and therefore are suitable for real‐time estimation purposes. Proportional and proportional plus integral type algorithms are developed by using Lyapunov's stability theorem. This way, asymptotic convergence of the algorithms is guaranteed in the space of unknown parameters. The finite‐element method is used to discretize the spatial domain of the distributed system. The method developed does not require prior knowledge of the unknown parameters and the system initial conditions. The numerical examples presented include the convection‐diffusion equation and Burgers' equation.
Measuring water surface and streambed elevation changes with the acoustic velocity metering system
Authors: Laenen Antonius
Published: February 2008

Acoustic velocity metering systems used to measure the water velocity along a diagonal path across a stream can also be used to measure stage and streambed changes. Underwater acoustic transmissions reflected from the water surface can accurately measure depth above transducers. Similarly, signals reflected from the streambed can indicate streambed changes in the vicinity midway between transducers.
The risks of drinking water
Authors: Crouch E. A. C. , Wilson R. , Zeise L.
Published: February 2008

Exposures to the low levels of organic compounds found in drinking water might cause a variety of health effects, cancer being one of great concern. The estimation of cancer risk is uncertain, which may in part explain why cancer risk is not properly considered in establishing drinking water standards. Current standards for a given chemical or class of chemicals do not account for the presence of other pollutants, chemicals which have not been tested in long term oral bioassays are generally ignored, and the uncertainties of risk calculations are not explicitly considered. To better quantify risks from drinking waters, we apply procedures which incorporate measures of uncertainty into the risk calculation and consider all chemicals included in a water analysis. This procedure is demonstrated by calculating risks for several U.S. water supplies. Our results show that some might pose moderately high risks.
Microclimate at Arctic Tree Line 1. Radiation Balance of Tundra and Forest
Authors: Rouse Wayne R.
Published: February 2008

Components of the radiation balance were measured or calculated for upland tundra and adjacent open spruce forest for the period from April to September 1979 at Churchill, Manitoba, Canada, which is positioned near the tree line and which is underlain by continuous permafrost. Because of deep winter snow accumulations, snow melt in the forest lags behind that of the tundra by almost a month. The tundra undergoes a stepwise change in albedo from 0.78 to 0.09 over a period of a few days of final snow melt. Its albedo is constant over the summer. On clear days for both surfaces there is a strong diurnal pattern of raised albedos in morning and evening due to specular reflection. On cloudy days there is almost no daily change. The tundra radiative surface temperatures are almost always larger than those of the forest, but differences decrease systematically as the summer progresses. In late winter, on clear days, the forest canopy averages 6.6°C warmer than the surrounding air and 12.6°C warmer than the snow beneath. This results from an absorption of incident and reflected solar radiation by the nontranspiring trees. In winter the forest canopy serves as a convective and radiative heat source to the snow beneath. This hastens snow melt in later winter. The forest has a larger net radiation than the tundra at all times, but this is particularly pronounced with the large solar radiation input of late winter before any snow melt takes place. Destruction of the forest will lead to a greatly modified radiation and surface temperature regime.
Nonlinear Stochastic Model of Rainfall Runoff Process
Authors: Rao Srinivas G. , Rao Ramachandra A.
Published: February 2008

A nonlinear stochastic model is proposed to model the rainfall runoff process in which higher order derivatives of rainfall are used in addition to the magnitude of rainfall as inputs. The rainfall, runoff, and derivatives of rainfall are considered as stochastic. The model consists of several subsystems in parallel. The first subsystem utilizes the observed rainfall and runoff as input and output, respectively. The subsequent subsystems use higher order derivatives of rainfall as input and forecast error from the previous subsystems as output. The subsystems improve the performance of the overall model by using higher order derivatives of input. The error in forecasting the runoff is progressively reduced by each subsystem. The method of analysis and parameter estimation of each of the subsystems are the same except that different inputs and outputs are used to characterize the subsystems. The optimal output of each of the subsystems is computed by minimizing the corresponding mean square error, and the estimation procedure is based on the statistical theory of filters involving the marginal and joint probability density functions of rainfall, runoff, and rainfall derivative sequences. The model is tested using daily rainfall runoff data from the Rough River basin in Kentucky, and its prediction performance is discussed. Testing the residuals of the model for whiteness is emphasized in order to improve the prediction performance of the model.
Transport of Cationic Solutes in Sorbing Porous Media
Authors: Van Eijkeren J. C. H. , Loch J. P. G.
Published: February 2008

A model simulating transport of a cationic solute through soil under steady state water flux conditions is described, and model simulations are reported. Chemical interaction of each cation with the solid soil matrix was assumed to occur by exchangeable adsorption and was described by a general formulation of the Gapon equation. Physical interaction with the soil system was described by lateral diffusion between a mobile and an immobile liquid phase. A mathematical model was derived from the physicochemical model. The resulting system of two algebraically coupled partial differential equations was solved numerically by applying a Crank‐Nicolson time discrete Galerkin approximation. This approximation resulted in a system of nonlinear equations that was solved by Newton‐Raphson iterations. Model simulations indicated the particular and combined effects of the physicochemical processes involved. Model computations were compared with the results of a laboratory experiment employing a cation exchanger column. Considering the uncertainty of some of the parameter estimations, the model simulations and experimental results compared reasonably well.
Irrigated Agricultural Expansion Planning in Developing Countries: Income Redistribution Objective
Authors: Allam Mohamed N. , Marks David H.
Published: February 2008

The role of agricultural expansion investment in improving the income redistribution conditions in society has been of considerable concern to planners. In this paper an approach based on distributing the newly developed land to a poorer sector (landless farmers) in society to gain agricultural revenues and improve their income is investigated. A mathematical optimization model is built to determine the distribution of land and a pricing policy established for the new areas in such a way that (1) a specified (by the government) income increase to the farmers can be achieved, (2) a predetermined level of recovery of the expansion cost can be insured, (3) high agricultural efficiency in the new land can be maintained, and (4) redistribution benefits can be maximized. In a case study application of the model, no conflict is found between the economic efficiency and income redistribution cirtieria in agricultural expansion investment within the planning framework presented in the companion paper (Allam and Marks, this issue). For a specified cost recovery condition it is found that the least cost planning alternatives give the opportunity to the largest number of landless farmers to own the new land and receive a specified income increase from the agricultural revenues, but a conflict between government return from the investment and redistribution objectives is found. This conflict is addressed and the trade‐off between the two objectives is illustrated.
Effect of Clear‐Cut Silviculture on Dissolved Ion Export and Water Yield in the Piedmont
Authors: Hewlett J. D. , Post H. E. , Doss R.
Published: February 2008

A paired watershed experiment in Putnam County, Georgia, was carried out from 1973 to 1980 to determine the effects of a typical southern clear‐cut operation on water quality, timing, and yield. This report shows that increases in monthly exports of dissolved N, P, K, Ca, Mg, Na, TKN, and total electrolytes were short‐lived and less than 0.5 kg ha−1 month−1 and may therefore be considered minor for practical purposes. Stream water concentrations were mostly diluted by clear‐cutting, but a monthly water yield increase of 1 to 2 cm flushed an extra 0.15 kg ha−1 month−1 of nitrate‐nitrogen from the basin during a 2‐year period following harvest. Twenty surrounding forested basins (7 to 165 ha in area) were sampled monthly for 1 year, showing that the experimental pair was representative of the general levels of dissolved ions in forested Piedmont streams. Results suggest that clear‐cut silviculture in this region will neither reduce soil fertility by flushing ions into streams nor eutrophy stream water.
Cost Sharing With Irrigated Agriculture: Promise Versus Performance
Authors: Franklin Douglas R. , Hageman Ronda K.
Published: February 2008

Financial data from various federal water projects is analyzed to determine the extent of the deviation between projected private user cost sharing and actual payments collected. Evidence is presented which shows that irrigated agriculture is heavily subsidized not only with respect to capital expenditures but also for operation, maintenance, and replacement (OM&R) costs. The latter result is especially surprising since agricultural users are required to pay 100% of their allocated share of OM&R costs. Since actual user payments are found to fall far short of those projected in water project feasibility reports, reasons for the deviation are explored.
A Heuristic Method for Measurement and Characterization of River Meander Wavelength
Authors: Sinnock Scott , Rao A. Ramachandra
Published: February 2008

Historically, meander planform data have been analyzed by various statistical and geometrical techniques, but uncertainty persists about the wavelength, frequency, and reference geometry. Therefore meander wavelength was analyzed in the Fourier frequency domain by power spectral analysis in terms of hierarchical centerlines as a reference geometry, eliminating some of the subjective bias associated with wavelength measurements. Equally spaced sampling points were located along the talweg of meandering streams. Sample values were measured as the perpendicular distance to a reference line connecting meander belt midpoints. This line, itself meandering, constitutes a river's second‐order meander frequency, which is analyzed with respect to a still higher‐order reference line. Sampling along the talweg attenuates the spectral estimates of natural frequencies of meanders. Corrections are obtained by multiplying frequency peaks by the sinuosity of the study reach. Power spectra obtained from hierarchical reference lines of first‐ and second‐order meanders of the White River in southern Indiana indicate discrete frequencies in each order. First‐ and second‐order harmonics are observed at high and low frequencies. Complex meandering along the Dolores River in western Colorado is characterized by very low‐frequency energy in third‐order meanders and successively higher frequency energy in second‐ and first‐order meanders. A comparison of power spectra for hierarchical and arbitrary reference lines shows that arbitrary references condense spectral estimates of meander energy within artificially averaged frequency bands. Another comparison, using the theory of minimum variance for meander formation, confirms that hierarchical reference lines improve meander characterization.
Major Ion Chemistry and Sensitivity to Acid Precipitation of Sierra Nevada Lakes
Authors: Melack John M. , Stoddard John L. , Ochs Cliff A.
Published: February 2008

Most alpine and subalpine lakes of the Sierra Nevada (California) are very dilute, weakly buffered calcium bicarbonate waters. Seventy‐three lakes selected to lie in basins representative of Sierran bedrocks were sampled in the summers of 1981 and 1982 and have a median alkalinity of 50 μeq 1−1 (range 5–1137) and a pH of 7 (range 5.7–9.4). The alkalinity of Sierran lakes cannot be predicted from altitude, basin area, or lake area. The concentrations of sulfate, calcium, or alkalinity in lake waters are positively correlated with the percent areal coverage of volcanic or calcareous rocks in the basins. The lakes are not acidified but are extremely sensitive to increases in acidity of atmospheric precipitation.
Interactive Computer Technology for Planning and Policy Modeling
Authors: Fedra Kurt , Loucks Daniel P.
Published: February 2008

This paper speculates on the potential impacts of our increasing access to and use of computer technology and communication, especially with respect to planning and policy making. The focus of the discussion is on the interaction between the users of this expanding technology and the technology itself. Those involved in its development, whether it be the hardware or software of this technology, are in a position to make substantial contributions toward a more effective use of the models and their data bases by planners and policy analysts. Specific features of the technology and of environmental planning and policy‐making processes are examined to identify where and how interactive computer‐based models and associated hardware can best serve individuals, their organizations or institutions. Finally, the necessary conditions for the successful implementation of such tools and methods are identified.