bluuebunny/crossref_metadata_2025 huggingface dataset:
Parameter Identification in Field Problems
Authors: Bruch John C. , Lam Chok M. , Simundich Thomas M.
Published: February 2008

In water resources field problems, unknown physical parameters are present in the governing partial differential equations that must be determined before relevant numerical results can be obtained. The identification of these parameters is formulated in this paper as a minimization problem in which the function to be minimized is a least squares comparison between the model equation and the systems responses, the field data. The minimization technique utilized is the Fletcher‐Powell method. Three typical water resources field problems are used as examples to demonstrate the technique.
Water Flow Through Snow Overlying an Impermeable Boundary
Authors: Colbeck S. C.
Published: February 2008

A two‐layer model is constructed in order to describe water flow over an impermeable boundary. The model consists of vertical flow through an unsaturated layer and flow along a boundary in a saturated layer. The governing equations are solved for the nonsteady case, where the gradient of the thickness of the saturated layer is small compared with the slope of the impermeable boundary. It is shown that in most cases the discharge from shallow snowpacks will preserve the diurnal cycles of input at the surface, although for deep snowpacks (such as temperate glacier firn) the diurnal cycle is smoothed and only long‐term responses are expected. The flow of a diurnal meltwater wave through a small (2.10 m deep by 100 m long) snowpack is calculated as an example. The case of steady flow is also described.
Light and Temperature Relations in a Small Desert Pond as Influenced by Phytoplanktonic Density Variations
Authors: Idso Sherwood B. , Foster Joyce M.
Published: February 2008

Measurements of incoming and reflected solar radiation, down‐welling solar radiation in the water, and air temperature and water temperature at four different depths were recorded every half hour over a 3‐month period in a small man‐made pond of reclaimed waste water at Phoenix, Arizona. At intervals of a few days, chlorophyll a and b values were also assayed to determine density variations in the phytoplanktonic community of the pond. During this period the extinction coefficient far solar radiation was found to be a linear function of both chlorophyll a and b concentrations, and the shape of the midafternoon temperature profile of the pond was found to be highly correlated with the extinction coefficient. Water surface temperature increased during three distinct algal blooms to such a degree that the water‐air vapor pressure difference increased by approximately 25% during the short periods of the blooms, an indication that phytoplanktonic density variations may exert a significant influence on evaporation.
Optimal timing and sizing of a conjunctive urban water supply and waste water system with nonlinear programing
Authors: Mulvihill Michael E. , Dracup John A.
Published: February 2008

A mathematical model of a conjunctively operated urban water supply and waste water system is formulated and applied to the city of Los Angeles. The objectives are (1) to minimize the cost of supplying water from several sources, including the provision for recycling reclaimed water, and (2) to determine the capacity expansion schedule of the water and waste water treatment processes. The water sources vary in quality, quantity, and cost. Constraints on water quality constituents as well as on quantity are included. The model formulated consists of the minimization of a concave objective function subject to linear constraints. A multilevel solution technique is developed to determine the minimum cost alternative for a selected planning horizon. The mathematical model is flexible in that it can be expanded to include additional water quality constituents, advanced waste water treatment processes, and variations in water quality standards.
Streamflow simulation: 3. The broken line process and operational hydrology
Authors: Mejia Jose M. , Dawdy David R. , Nordin Carl F.
Published: February 2008

This paper reports on the use of the broken line process in the synthesis of multivariate sequences exhibiting the Hurst phenomenon.
Industrial application of Whitford's demand forecasting procedure
Authors: Collins Michael A. , Plummer Alan H.
Published: February 2008

A probabilistic method developed by Whitford (1972) for residential water demand forecasting is applied to water demand for steam‐electric power generation in the Trinity River basin in Texas in order to reduce reliance upon single isolated estimates of future demand. The resulting time‐dependent cumulative probability distributions provide useful information for water quality planning in the basin. It is suggested that this probabilistic approach has significant advantages that warrant its further refinement.
Surface water network design by regression analysis simulation
Authors: Moss M. E. , Karlinger M. R.
Published: February 2008

The statistical characteristics of the accuracy of regression analyses as used in surface water regionalization are investigated by simulating logarithmic regressions of the streamflow parameters, mean and standard deviation, derived from synthetic streamflow sequences. Accuracy is measured in terms of equivalent years of at site record. A procedure for the design of surface water data networks that accounts for the statistical nature of the estimates of parameter accuracy is presented.
Sorption of orthophosphate on the surface of water sample containers
Authors: Latterell J. J. , Timmons D. R. , Holt R. F. , Sherstad E. M.
Published: February 2008

Orthophosphate sorption studies on borosilicate glass, polyethylene, and coated and uncoated galvanized metal are reported. The concentration range of orthophosphate in the solutions studied was 0.0075–1.00 ppm P, and the pH range was 5.8–8.8. The exposure of solution to surface ranged up to 14 days, ratios of surface area to milliliters of solution being in the range 0.04–1.14 cm2/ml. The percent of the original orthophosphate sorbed was determined by the use of radioactive 32P and by orthophosphate analysis using the ascorbic acid method. Studies indicate that aqueous solutions containing 0.03–0.112 ppm orthophosphate may be stored in either borosilicate or polyethylene bottles with less than 0.5% adsorption during the initial 24‐hour storage period. The amount of sorption for a given sample was observed to increase as the contact time and/or the ratio of surface area to solution volume increased. Measurable quantities of orthophosphate were sorbed on galvanized sheet metal in all the studies made, indicating that sample‐collecting equipment made of this material should be coated to minimize orthophosphate sorption. Various coatings were tested, and their effectiveness in minimizing sorption is reported.
Benefit‐cost analysis reconsidered: An evaluation of the Mid‐State Project
Authors: Hanke Steve H. , Walker Richard A.
Published: February 2008

The Bureau of Reclamation has traditionally been accused of distorting benefit‐cost analysis to serve political ends. Economists and other critics have usually believed that if only the theoretical tools of benefit‐cost were sharpened sufficiently and its logic applied impartially by government analysts, the politics of water resource investment decisions could be neutralized. This study of the controversial Mid‐State reclamation project serves both to point out the politically expedient elements of bureau analysis that remain after almost 30 years of refinement and criticism by economists and to act as a lesson to reformers who fail to recognize the limitations on benefit‐cost analysis in replacing the inherently political choices of democratic government.
Distribution of contaminants in porous media flow
Authors: Marino Miguel A.
Published: February 2008

A mathematical analysis is presented of simultaneous dispersion and adsorption of a solute within homogeneous and isotropic porous media in steady unidirectional flow fields. The dispersion systems are adsorbing the solute at rates proportional to their concentration and are subject to input concentrations that vary exponentially with time. Mathematical solutions are developed for predicting the concentration of contaminants in adsorbing and nonadsorbing porous media for prescribed media and fluid parameters.
Optimization of real time operation of a multiple‐reservoir system
Authors: Becker Leonard , Yeh William W‐G.
Published: February 2008

This paper addresses a typical requirement of real time multiple‐reservoir operation. A methodology is evolved utilizing a form of dynamic programing (DP) for the selection of an optimal reservoir storage policy path through a specified number of policy periods, and a linear programing (LP) routine is used for period by period optimization. The policy periods, in case of the real time operation, correspond to the number of time periods for which a streamflow prediction model is reasonably reliable. The method results in relatively easy computer implementation and high flexibility in that changes in constraints are simply made and additional reservoirs easily added. The method is of considerable value for the determination of release policies in real time operation of an existing system. As an example, application is made to a real system of reservoirs and hydroelectric facilities associated with the Shasta and Trinity sub‐systems of the California Central Valley Project.
Inconsistent matrices in estimating ungaged streamflow data
Authors: Fuller G. A. , Fuller N. E.
Published: February 2008

Least squares estimated correlation coefficients between gaged and ungaged streams are sometimes used in the estimation of ungaged streamflow. Constructed correlation matrices containing actual and estimated correlation coefficients may not be positive semidefinite and thus may cause computational problems. To overcome this problem, an algorithm, based on Rosenbrock's hill‐climbing technique, was used. The maximum absolute deviation from the least squares estimates was minimized subject to the constraints that each leading principal minor be nonnegative and that the correlation coefficients must lie within the range −1.0 to 1.0 inclusive. With this algorithm, only the estimated correlation coefficients are modified.
An economic analysis of water resource investments and regional economic growth
Authors: Cicchetti Charles J. , Smith V. Kerry , Carson John
Published: February 2008

The purpose of this paper is to analyze the effects of the Bureau of Reclamation's water resource projects over the period 1930–1970 on regional economic growth in the Southwest. The empirical results indicate that these investments have had an impact on regional economic growth and that the extent of the effect depends on the nature of the water investment, the state of the regional economy, and the amount and nature of other investments in the region.
Confidence limits for design events
Authors: Kite G. W.
Published: February 2008

Frequency analysis is commonly used in hydrology to define flood plains, design hydraulic structures, and aid in watershed planning and management. Although design event magnitudes may be determined analytically by using probability distributions, the analytical determination of confidence limits for the design event is not easy. Using the alternate method of moments to determine confidence limits involves an assumption of normality of the distribution of design events. It is shown by data generation that this assumption is valid for quite small samples. Tables are given to compute confidence limits in this manner for several common probability distributions.
A theory of the combined Mole‐Tile Drain System
Authors: Unhanand Komain , Kadir Tariq N.
Published: February 2008

A theory of water movement in the combined mole‐tile drain system based on the transient state condition was developed. Two general equations were derived to describe the height of the water table at any location in the system at any elapsed time after the drainage process begins. One of the equations is applicable for the stage in which the water table is above the mole drains, and the other equation is for the stage in which the water table falls below the mole drains. The two general equations were simplified for the point located at midpoint between the tile drains and mole drains in the system. In the derivation, assumptions regarding the flow condition of groundwater and shape of the water table profile at certain boundaries were made. Field experiments were then conducted, and the test data were used in verifying the equation for the first stage. A reasonably good agreement between the theoretical analysis and field data was obtained for this type of research.
Water level fluctuations due to earth tides in a well pumping from slightly fractured crystalline rock
Authors: Marine I. Wendell
Published: February 2008

At the Savannah River plant of the Atomic Energy Commission near Aiken, South Carolina, there are three distinct groundwater systems: the coastal plain sediments, the crystalline metamorphic rocks, and a buried Triassic basin. The coastal plain sediments include several Cretaceous and Tertiary granular aquifers and aquicludes, the total thickness being about 305 m. Below these sediments, water occurs in small fractures in crystalline metamorphic rock (hornblende schist and gneiss with lesser amounts of quartzite). Water level fluctuations due to earth tides are recorded in the crystalline metamorphic rock system and in the coastal plain sediments. No water level fluctuations due to earth tides have been observed in wells in the Triassic rock because of the very low permeability. The water level fluctuations due to earth tides in the crystalline rock are about 10 cm, and those in the sediments are about 1.8 cm. The use of water level fluctuations due to earth tides to calculate porosity appears to present practical difficulties both in the crystalline metamorphic rock system and in the coastal plain sediments. In a 1‐yr pumping test on a well in the crystalline metamorphic rock the flow was controlled to within 0.1% of the total discharge, which was 0.94 l/s. The water level fluctuations due to earth tides in the pumping well were 10 cm, the same as when this well was not being pumped.
Linear decision rule in reservoir management and design: 5. A general algorithm
Authors: Gundelach Jose , ReVelle Charles
Published: February 2008

An algorithm is derived that determines the capacity and decision constants for a reservoir to be operated by use of the linear decision rule (LDR). The new algorithm supplants an earlier technique, which was fitted to a specialized problem format. The new algorithm will serve for any feasible formulation of a reservoir operating by the linear rule and may easily be implemented without the computer.
Response of an unsaturated soil to forest transpiration
Authors: Parlange Jean‐Yves , Aylor Donald E.
Published: February 2008

Diurnal cycles in water outflow from a small watershed due to forest transpiration were observed 4 times during the summer. Each time the daytime outflow was reduced significantly below that during the following night. The recovery of the outflow to the steady night level takes place for several hours after sunset, and this time of recovery is shown to be controlled by the unsaturated soil water movement in the root zone.
Steady vertical flows in swelling soils
Authors: Sposito Garrison
Published: February 2008

A thermodynamic description is presented of the isothermal, isohaline steady vertical flow of water in a swelling porous medium. An expression for the rate of steady flow is derived which is a straightforward generalization of well‐known results in standard flow theory but which differs considerably from an equation derived previously by Philip to describe the same process. This difference, aside from changes in notation, is shown to be the artifact of an error in procedure. An application of the flow equation derived is made to a simple model of steady evaporation from a bare soil containing a shallow water table. A significant result of the calculation is that the standard flow theory, applicable only to nonswelling porous media, will always underestimate the rate of evaporation when it is applied to a swelling porous medium.
Use of environmental isotope methods as a reconnaissance tool in groundwater exploration near San Antonio de Pichincha, Ecuador
Authors: Moser Heribert , Stichler Willibald
Published: February 2008

In a semiarid area in the Sierra of Ecuador (about 20 km north of Quito), measurements of deuterium, oxygen 18, and tritium content in spring water, surface water, and precipitation have been performed. The results, together with some meteorological and hydrogeological data, furnished information on the recharge area and on the recharge rate of groundwater. On the basis of the results a groundwater exploitation does not appear feasible.
A direct method for the identification of the parameters of dynamic nonhomogeneous aquifers
Authors: Sagar Budhi , Yakowitz Sidney , Duckstein Lucien
Published: February 2008

A method to solve the inverse problem is developed. This method does not require the iterative solution of the aquifer equation, which is an essential characteristic of many current identification schemes. The shape of the surface representing the observed dependent variable (which may be hydraulic head, chemical concentration, or temperature) is approximated from measured samples by means of various interpolation algorithms. Once the various derivatives of the dependent variable are approximated, the identification problem reduces locally to algebraic equations of small dimension. It is shown that aquifer conditions of general heterogeneity and anisotropy are amenable to this method. Input may be treated as an unknown to be evaluated. The method is appraised by application to scattered solution points of a simulated solution to a nonhomogeneous aquifer equation.
A Hele‐Shaw Model Study of steady state flow in an unconfined acquifer resting on a sloping bed
Authors: Jaiswal C. S. , Chauhan H. S.
Published: February 2008

Experiments were conducted on a vertical Hele‐Shaw model to study the effect of slope of an impermeable layer on flow profiles and flow rates in an unconfined aquifer. Experimental results were compared with the solutions of Pavlovsky (1930) and Childs (1971) for nonuniform seepage on a small sloping impermeable bed. These studies showed that the solution of Pavlovsky may be used for the prediction of the flow profile downslope up to 30% slope and upslope up to 15% slope. Pavlovsky's equations also predicted flow rates and normal depths satisfactorily up to 30% slope. Childs’ equations also predicted similar results. None of these equations predicted the flow rate on negative slope satisfactorily.
Simulation of evapotranspiration and drainage from mature and clear‐cut deciduous forests and young pine plantation
Authors: Swift Lloyd W. , Swank Wayne T. , Mankin J. B. , Luxmoore R. J. , Goldstein R. A.
Published: February 2008

Prosper, a phenomenological model of water exchange between soil, plant, and atmosphere, was used to simulate evapotranspiration and annual drainage for 2 years from a mature oak‐hickory forest in the southern Appalachians. The simulation was tested by comparing drainage to measured streamflow. In a year of unusually high precipitation the simulated annual drainage was within 1.5% of measured streamflow. Simulations were also performed by using the same 2 years of meteorologic data, but vegetation parameters were changed to represent a young white pine plantation and a regrowing hardwood forest 1 year after clear‐cutting. The model estimated that drainage for an average rainfall year was reduced 20 cm by a 16‐year‐old white pine plantation and increased 36 cm by clear‐cutting. These results were comparable to changes of −20 and +38 cm observed in watershed experiments at Coweeta Hydrologic Laboratory. Simulated evapotranspiration during the summer was nearly identical for hardwood and pine forests, while winter and early spring water loss was greater for pine. Simulation suggests that the greater evapotranspiration by pine was due to increased interception in all seasons and increased transpiration in the dormant season. For the clear‐cut area, simulated evapotranspiration was considerably less than it was for the pine or hardwood forest and thus caused simulated soil moisture contents to be greater during the summer season.
New tritium data on movement of groundwater in western Fresno County, California
Authors: Poland Joseph F. , Stewart Gordon L.
Published: February 2008

Well waters along two traverse lines were sampled in 1963 and tested for tritium concentration. Haskell et al. [1966] estimated from the apparent thermonuclear tritium concentrations that groundwater had moved westward in the lower water‐bearing zone at a maximum velocity of 14–16.5 mi (23–27 km) in 9 yr. The maximum velocities and permeabilities estimated from the 1963 sampling were about an order of magnitude greater than the velocities and permeabilities suggested by prior hydrologic and geologic evidence. Consequently, in 1966–1970 the U.S. Geological Survey sampled and tested the tritium concentrations of well waters along the same two traverses but also extended the sampling eastward. On the basis of these analyses it is concluded that (1) thermonuclear tritium had not invaded the lower zone by 1970 within the extent of the 1963 sampling and (2) although the maximum westward movement of groundwater in the lower zone from 1955 to 1970 is indeterminate, it has been less than 4 mi (6.5 km) from the recharge area in 15 yr.
The Galerkin Method for nonlinear parabolic equations of unsteady groundwater flow
Authors: Yoon Yong Sup , Yeh William W‐G.
Published: February 2008

This paper suggests a relatively simple way for solving nonlinear parabolic partial differential equations associated with unsteady groundwater flow. The Galerkin formulation is discretized in the space domain by using piecewise polynomial equations, and the trapezoidal formula is employed to approximate the time derivative. The resulting system of nonlinear equations is then solved by the Newton method. Rapid rate of convergence and easy computer implementation are demonstrated by numerical examples. Results compare favorably with published experimental data.
Quality of life and environmental social overhead impact
Authors: McKean John R. , Ericson Raymond K.
Published: February 2008

Conventional benefit‐cost analysis is criticized with respect to the measurement of benefits resulting from the provision of environment‐improving capital. It is argued that a population feedback similar to the Pigovian congestion externality may tend to thwart efforts to improve quality of life unless projects explicitly plan for these external effects.
Correction of bias in the estimation of the coefficient of skewness
Authors: Bobée B. , Robiataille R.
Published: February 2008

By using the data of Wallis et al. (1974) regarding the distribution of the coefficient of skewness of a sample of size N taken from Pearson type 3, log normal, and Weibull distributions, formulae are proposed for adjusting the average of the estimates to give a better estimation of the skewness of the population.
Spatial variability of the leaching characteristics of a field soil
Authors: Biggar J. W. , Nielsen D. R.
Published: February 2008

Solute distributions within a soil profile during the leaching of water‐soluble salts applied to the soil surface were measured at six depths to 182.4 cm within 20 subplots of a 150‐ha field. Estimates of the pore water velocity based upon measures of solute displacement within each subplot and the entire field were found to be logarithmically normally distributed and in agreement with volumetric measures of water infiltration rates. Such agreement was only possible because it was recognized that the observed values were not normally distributed, and their mean values were calculated accordingly. The number of observations required to yield an estimate of the mean pore water velocity within a prescribed accuracy is shown to depend upon the nature and extent of the spatial variability of the field soil. For the field examined, 100 observations would allow the mean pore water velocity to be estimated within ±50% of its true value. The functional relation between field‐measured values of the apparent diffusion coefficient, also found to be logarithmically normally distributed, and pore water velocity is examined and interpreted in terms of solute distributions likely to be measured at specific sampling sites.
On the general equations for flow in porous media and their reduction to Darcy's Law
Authors: Gray William G. , O'Neill Kevin
Published: February 2008

A technique of local averaging is applied to obtain general equations which describe mass and momentum transport in porous media. The averaging is performed without significantly idealizing either the porous medium or the pertinent fluid mechanical relations. The resulting general flow equation is simplified to treat flow of a Newtonian fluid in a slowly deforming solid matrix for two special cases. For flow in an isotropic medium where convective and inertial terms are important, an equation is developed which is dependent only on five medium parameters which could be evaluated by experiment. Flow in an anisotropic medium is also analyzed, and the general equation is reduced to Darcy's law when the convective and inertial terms are neglected.
Pulsed dispersion of trace chemical concentrations in a saturated sorbing porous medium
Authors: Lindstrom F. T.
Published: February 2008

A rather simple, yet complete, mathematical model for the pulsed dispersion of trace chemical concentrations in a water‐saturated sorbing porous medium is stated, and the resulting integrodifferential equation of transport is solved via Laplace transform methods. A typical example of a soil water dispersion system is discussed with the aid of free and sorbed phase concentration distribution curves.
Irrigation systems in Taiwan: Management of a decentralized public enterprise
Authors: Abel Martin E.
Published: February 2008

The efficiency of the management of irrigation systems in Taiwan, viewed as decentralized public enterprises, depends on four interrelated factors. These factors are (1) the recognition that water is a scarce factor in agricultural production, (2) the legal administrative basis for centralized planning of irrigation investments but decentralized management of irrigation systems, (3) the information systems which permit the exchange of agronomic and engineering information between the users of water and the managers of a system, and (4) the use of incentive structures for both the managers of irrigation systems and the users of water that appear to be compatible with the efficient use of water within the irrigation system.
Rainfall generation: A nonstationary time‐varying multidimensional model
Authors: Bras Rafael L. , Rodríguez‐Iturbe Ignacio
Published: February 2008

Most existing rainfall models concentrate on storm exterior characteristics. Those that generate storm interiors generally do so at only one point. Very few models attempt to generate exterior and interior rainfall characteristics everywhere in space, and those that do have limiting assumptions of stationary behavior at all levels of storm activity. This work suggests a nonstationary multidimensional rainfall generator. The model, capable of simulating historical storm exteriors and interiors, assumes the validity of Taylor's hypothesis of turbulence within the storm interior. First‐order statistics of storm interiors as well as the correlation in time and space of the storm interiors are preserved.
A distributed converging overland flow model: 1. Mathematical solutions
Authors: Sherman Bernard , Singh Vijay P.
Published: February 2008

In models for overland flow based on kinematic wave theory the friction parameter is assumed to be constant. This paper studies a converging geometry and allows continuous spatial variability in the parameter. Parameter variability results in a completely distributed approach, reduces the need to use a complex network model to simulate watershed surface runoff, and saves much computational time and effort. This paper is the first in a series of three. It develops analytical solutions for a converging geometry with no infiltration and temporally constant lateral inflow. Part 2 discusses the effect of infiltration on the runoff process, and part 3 discusses application of the proposed model to natural agricultural watersheds.
A distributed converging overland flow model: 3. Application to natural watersheds
Authors: Singh Vijay P.
Published: February 2008

The proposed distributed converging overland flow model is utilized to predict surface runoff from three natural agricultural watersheds. The Lax‐Wendroff scheme is used to obtain numerical solutions. For determination of the kinematic wave friction relationship parameter a simple relation between the parameter and topographic slope is hypothesized. The simple relation contains two constants which are optimized for each watershed by the Rosenbrock‐Palmer optimization algorithm. The model results are in good agreement with runoff observations from these watersheds. It is shown that if the model structure is sound, it will suffice to optimize model parameters on hydrograph peak only even for prediction of the entire hydrograph. The model results suggest that a distributed approach to kinematic wave modeling of watershed surface runoff is potentially promising and warrants further investigation.
A variable source area model of the rainfall‐runoff process based on the Watershed Stream Network
Authors: Lee M. T. , Delleur J. W.
Published: February 2008

A model of the dynamic contributing area during a storm is formulated in terms of the history of precipitation in excess of B horizon permeability. The spatial dynamic contributing area along the main stream is obtained under the assumptions that the velocity of flow along the stream network is uniform, the drainage density is a constant within a given watershed, and the first‐order streams are uniformly distributed in the basin. The runoff from the dynamic contributing area is then routed through the synthesized stream network to obtain the direct runoff at the basin outlet by making use of a method based on the linearized Saint Venant equations. The model has been tested in several watersheds in the central United States.
The concise formulation of diffusive sorption of water in a dry soil
Authors: Brutsaert Wilfried
Published: February 2008

Several formulations for the sorption of water in a dry soil obtained on the basis of approximate solutions of the nonlinear diffusion equation are considered, and their relative merits are investigated. In addition, new solutions are developed by the application of a simple weighting of the available approximations. In a comparison with one of Philip's (1960) exact solutions it was found that the error involved in all these solutions is at most of the order of 3 or 4% however, Parlange's (1975a) optimization result and the weighting solutions appear to be accurate to within a few thousandths. The sorptivity and the position of the wetting front can be expressed concisely as functions of soil physical parameters by applying either the two‐parameter exponential diffusivity of Gardner and Mayhugh (1958) or the three‐parameter power function diffusivity of the author. The mathematical form suggests that on a field or basinwide scale the sorptivity of the surface soil is log normally distributed.
A comparison of techniques for solving the diffusion equation with an exponential diffusivity
Authors: Parlange J.‐Y. , Babu D. K.
Published: February 2008

A recent solution obtained by Babu when the soil water diffusivity has an exponential behavior is compared with two earlier solutions. It is shown that with a slight modification, Babu's perturbation solution is identical to the iterative solution using Cisler's correction. It is also shown that solutions which optimize the sorptivity and the front position are numerically indistinguishable from either the perturbation or the iterative solution but have in general a much simpler analytical form.
Management of groundwater and surface water via decomposition
Authors: Haimes Y. Y. , Dreizin Y. C.
Published: February 2008

This paper develops a methodology for solving the problems of conjunctive use of a large‐scale complex groundwater system, a network of streams, and reservoirs all interacting with one another. Decomposing the model of a large‐scale aquifer system as well as that of a stream network into interacting submodels provided an improved mathematical model of the entire physical system. A theorem is proved that establishes the necessary conditions for the existence of a solution to the optimal control problem associated with the management of the groundwater system. A sample problem was formulated in which the options of groundwater operations and surface water supply are conjunctively utilized to meet the water needs of several water users in a basin. The management problem was solved via decomposition and multilevel approach.
Shot noise models for the generation of synthetic streamflow data
Authors: Weiss Gideon
Published: February 2008

A shot noise process consisting of a series of events at random times and of random magnitudes, each of which produces a fixed shaped rise and recession, is used as the basis for describing continuous time streamflows. This type of model is chosen for its ability to model recessions. Recession shapes consisting of one or two exponential curves are considered. The fitting of the models to multisite daily data and the generation of synthetic daily data are described. The application of the models to some English streamflow data is illustrated.
Apparent regional skew
Authors: Wallis J. R. , Matalas N. C. , Slack J. R.
Published: February 2008

Differences in the relationships between the mean and standard deviation of regional estimates of skewness for historical flood sequences and the relations derived from several well‐known distribution functions may be explained in terms of spatial or temporal distribution of values of skewness. Unless skewness is large, variations in estimates of skewness for different time periods are unlikely to be ascribable to chance.
Toward an analytical theory of water flow through inhomogeneous porous media
Authors: Gupta Vijay K. , Sposito Garrison , Bhattacharya R. N.
Published: February 2008

Some rigorous mathematical results for the Buckingham‐Darcy flux law for water flow through an isotropic, nondeformable, inhomogeneous porous medium are presented. It is shown that the volumetric flux density vector, aside from the component due to gravity, may always be expressed in terms of a scalar and a vector matric flux potential. The vector matric flux potential will vanish for a homogeneous porous medium and for a one‐dimensional inhomogeneous porous medium. It follows from this result that the hydraulic conductivity will be a function only of the water potential in any one‐dimensional porous medium if its space derivative at constant water potential vanishes identically. In addition, it is shown that the vector matric flux potential is of no physical consequence insofar as the flow equation is concerned, regardless of the number of dimensions of space. The specification of that part of the flux density vector contributed by the vector potential appears in the law of momentum balance instead of in the law of mass balance.
Distributed numerical model for estimating runoff and sediment discharge of ungaged rivers: 3. Comparison with other simple techniques
Authors: Gupta S. K. , Solomon S. I.
Published: February 2008

In two earlier papers published by the authors Gupta and Solomon, 1977; Solomon and Gupta, 1977; the development of an information system and of a distributed hydrologic model based on it was described. The model can be used to estimate flow and sediment at ungaged river sections. In this paper the authors compare, in detail, the results obtained in estimating flows and sediment discharges by means of the model at two stations with estimates of the same hydrologic characteristics obtained by means of other simpler techniques. The results of the comparison indicate improvement over the simpler techniques, the indication being that the application of the model is justified where a higher accuracy of flow and sediment data is required or where lack of basic measurement data makes it impossible to apply the simpler techniques.
Macroscopic dispersion in porous media: The controlling factors
Authors: Schwartz Franklin W.
Published: February 2008

One of the most important limitations to the application of modeling techniques for the analysis of mass transfer in groundwater systems is the difficulty in characterizing the dispersive character of natural systems. Although large quantities of experimental data exist for laboratory scale experiments, the handful of measurements which have been obtained from regional systems suggest that dispersion produced by large‐scale porous medium nonidealities is considerably more important. In this paper the effects of macroscopic dispersion are simulated for uniform heterogeneous porous media under conditions of one‐ dimensional flow. The idealized media considered for detailed analysis consist of low permeability inclusions within a higher‐permeability medium. When the inclusions are not arranged rather homogeneously within the region, a unique dispersivity value for the medium cannot be defined, and dispersivity changes as a function of space. The magnitude of dispersion is controlled by the contrast in hydraulic conductivity between the inclusions and the remainder of the medium, the number of inclusions, and the mode of aggregation. Generally, dispersivity is found to decrease as the conductivity contrast decreases and the structure of the medium is regularized. It will be possible to estimate the dispersivity of a medium by using stochastic analysis. Hypothetical porous media with characteristics similar to those of some actual medium will yield a range of dispersivity values. The basic data for this technique will be detailed statistical analysis of the mode of porous medium aggregation and the conductivity contrasts within the medium.
Physical and chemical parameters affecting transport of 137Cs in arid watersheds
Authors: McHenry J. Roger , Ritchie Jerry C.
Published: February 2008

The occurrence and amount of fallout 137Cs were determined in 12 watersheds in the arid southwestern United States. The factors believed to influence the distribution of 137Cs in the watershed soils and in the reservoir sediments were investigated by using stepwise regression techniques. Seventeen parameters, in the case of soils, and 21 parameters, in the case of sediments, were used in the study. Ninety percent of the variation in the 137Cs content of soils, per unit weight, could be predicted in terms of the percentage of soil nitrogen, the R factor (rainfall intensity) of the universal soil loss equation, the percentage of sand in the soils, and the soil cation exchange capacity. Also, 90% of the variation in the content of 137Cs in the watershed soils, per unit area, could be predicted in terms of the fallout intensity, the percentages of silt and clay, and the cation exchange capacity. For reservoir sediments the equivalent predictors of 137Cs accumulation in the sediment profile, per unit weight, were the soil cation exchange capacity, the January–March average precipitation, and the soil contents of total P and N. The distribution Of 137Cs in sediments per unit area was similarly predicted by watershed area, percentage of total soil C, reservoir surface area, areal concentration of 137Cs in the watershed soils, and soil organic matter.
Steady state river quality modeling by sequential extended Kalman filters
Authors: Bowles David S. , Grenney William J.
Published: February 2008

Sequential extended Kalman filters (EKF) are applied as a technique for steady state river water quality modeling. The approach was demonstrated by using water quality data collected over a 36.4‐mi (58.6 km) stretch of the Jordan River, Utah. Each EKF was used to represent a river reach in which hydraulic and quality characteristics were judged fairly uniform. Mean and variance boundary conditions between successive filters were adjusted to represent the effects of point loads and tributaries discharging into the main river. Approximate minimum variance estimates of the system state (water quality parameters) and confidence intervals on these estimates were provided by combining two independent estimates of the system)state. The independent estimates were based on (1) predictions from an ‘internally meaningful’ model of the stream transport processes and biochemical transformations and (2) measurements of the water quality parameters. The estimates were combined by a weighting procedure based on uncertainties associated with each estimate. A smoothing algorithm was also applied in order that estimates from passes of the filter procedure in both the downstream and upstream directions could be combined. In this way, information contained in the measurements was used both upstream and downstream of the location of the measurement. The calibration capability of the filter procedure was demonstrated by simultaneous estimation of the state vector and one of the model coefficients. This capability was also used to estimate simultaneously the rate of lateral loading for one of the water quality parameters. Simultaneous estimation of coefficients of lateral loading was shown to increase the uncertainty associated with filter estimates because of the inclusion of uncertainty associated with these coefficients and lateral loading rates.
Remote sensing of agricultural water demand information: A California study
Authors: Estes John E. , Jensen John R. , Tinney Larry R.
Published: February 2008

This study focuses on the use of Landsat image‐processing techniques to produce cropland and crop type statistics for input into agricultural water demand prediction procedures currently being employed by the Kern County Water Agency in Kern County, California. The potential of remote sensing to provide input to the Kern County Water Agency's groundwater basin model in a more accurate and timely fashion is the goal of the research discussed herein. Current accuracies associated with Landsat cropland/noncropland identifications are of the order of 98% absolute accuracy. These data are being operationally incorporated into model calculations on a quarterly basis. Crop specific accuracies, although somewhat lower, are steadily being improved, and prospects for eventual incorporation appear good.
Solutions of Boussinesq's Equation for seepage flow
Authors: Gureghian A. B.
Published: February 2008

Solutions of Boussinesq's equation for groundwater seepage from a ditcn with vertical sides extending in depth to a horizontal impermeable floor were obtained numerically by using the finite difference and finite element methods for the case when the seepage rate from the ditch into the soil is constant with time. Both solutions agreed satisfactorily with experimental results from a Hele‐Shaw analog. It was found, however, that the execution time in the computer for the finite difference method was an order shorter than that for the finite element method, and thus the finite difference method is to be preferred. The finite difference method was also used to obtain a numerical solution for the reverse situation when water seeps out of the soil into the ditch at a constant rate.
Numerical model for saturated‐unsaturated flow in deformable porous media: 2. The algorithm
Authors: Narasimhan T. N. , Witherspoon P. A. , Edwards A. L.
Published: February 2008

An integrated finite difference algorithm is presented for numerically solving the governing equation of saturated‐unsaturated flow in deformable porous media. In recognition that stability of the explicit equation is a local phenomenon a mixed explicit‐implicit procedure is used for marching in the time domain. In this scheme the explicit changes in potential are first computed for all elements in the system, after which implicit corrections are made only for those elements for which the stable time step is less than the time step being used. Time step sizes are automatically controlled in order to optimize the number of iterations, to control maximum change in potential during a time step, and to obtain desired outputs. Time derivatives, estimated on the basis of system behavior during two previous time steps, are used to start the iteration process and to evaluate nonlinear coefficients. Boundary conditions and sources can vary with time or with the dependent variable. Input data are organized into convenient blocks. Accuracy of solutions can be affected by modeling errors, different types of truncation errors, and convergence errors. The algorithm constitutes an efficient tool for analyzing linear and nonlinear fluid flow problems in multidimensional heterogeneous porous media with complex geometry. An important limitation is that the model cannot conveniently handle arbitrary anisotropy and other general tensorial quantities.
Sensitivity of optimized parameters in watershed models
Authors: Mein R. G. , Brown B. M.
Published: February 2008

A procedure is developed by which the variance of each fitted parameter of a watershed model can be determined. This information can be used to determine the degree to which the model parameters can be related to physical watershed characteristics. The method is illustrated by applying the Boughton model to several watersheds and examining the coefficient of variation of each optimized parameter.
Flood frequency analysis with a generalized skew coefficient
Authors: Tasker Gary D.
Published: February 2008

The Hydrology Committee of the Water Resources Council (1976) has recently issued guidelines for flood frequency analyses. One aspect of these guidelines concerns the estimate of skewness. Monte Carlo experiments are used to gain some insights into sensitivity of estimates of peak flows to errors in mapped skew coefficients. The optimum factor by which to weight a sample skew coefficient and a generalized skew coefficient is a function of sample size, population skew coefficient, and map error.
Dissipation and fine‐scale structure in turbulent open channel flow
Authors: Nowell Arthur R. M.
Published: February 2008

Turbulent open channel flows are studied in a laboratory by using ‘Lego’ blocks at various spacings on the bed to examine the effect of different shear Reynolds numbers on the fine‐scale structure. Measurements of dissipation rates, computed by various methods, are compared and the high values shown to be reasonable when viewed against local mean shear values. The fine‐scale structure and the intermittent nature of the small‐scale motions are examined spectrally and by studying the moments. The ‘rescaled range,’ a technique developed in communications work (Mandelbrot and Van Ness, 1968) and in geophysical time series analysis (Klemes, 1974), is utilized to investigate the possible scale interactions among the various processes of production and dissipation in a turbulent boundary layer.