bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil water flow model with two‐dimensional automatic gamma ray attenuation scanner
Authors: Dirksen Christiaan , Huber Michael J.
Published: February 2008

This paper describes a physical laboratory model to study two‐dimensional transient water and solute transport in unsaturated soil, including water uptake by roots. It features an automatic two‐dimensional gamma ray attenuation scanner for measuring soil water content. Automation is obtained with a simple closed loop control circuit. After a gamma count is transmitted to the teletypewriter, a signal is sent to the hydraulically moved scanner to search for the next grid point. Upon arrival the scanner sends a signal back to initiate another data acquisition sequence, and so on. In this way, synchronization between counter and scanner is assured independent of counting time, travel time, configuration of grid points, temporary slowdown, etc. It also eliminates dead time between grid points for any recording pattern. Grid points are established by an array of holes that trap the core of a solenoid actuator. The configuration of grid points can be changed easily by opening and closing the desired holes. This mechanical trapping was found to be simpler and more accurate than a potentiometric control. The soil water flow model is constructed in modules. It can be used as one unit of 3.15 by 1.07 by 0.178 m and inclined up to 30°, or it can be subdivided into up to eight compartments, each with its own drainage filter tubes. The front glass walls allow visual observations of soil packing, wetting fronts, root distribution, etc. The back aluminum walls allow installation of instruments, such as tensiometers, salinity sensors, and psychrometers.
Choice of distribution functions for hydrologic design
Authors: Castano Eugenio , Duckstein Lucien , Bogardi Istvan
Published: February 2008

The problem of selecting a bivariate probability density function (pdf) for the simultaneous water stages at both ends of a confluence reach is considered. This pdf is used to compute the expected flood losses in the design of a levee with minimum expected yearly cost. A case study in Hungary illustrates the methodology throughout the paper. Two model selection procedures are compared: ranking the candidate pdf's by the likelihood of the X2 statistic and ranking them by their sample likelihoods. A composite model consisting of a linear combination of candidate pdfs weighted proportionally to their sample likelihoods is also considered. It is found that the two selection procedures lead to different choices, which in the example represent a significant cost variation. Although the ranking of the distributions reduces the uncertainty by imposing an ordering within the candidate set, a unique pdf does not fully account for the model uncertainty. In this sense the composite model seems a more reasonable choice, especially if the decisions are based on expected values.
On the Cobb‐Douglas Functions in multiobjective optimization
Authors: Passy Ury
Published: February 2008

Properties of Pareto optimum solutions of multiobjective problems with Cobb‐Douglas production type functions were analyzed. This type of production function is widely used in economic theory and is therefore used in the related literature on water resources. It was found that under the defined conditions, every feasible point is a Pareto solution.
Numerical techniques for estimating best‐distributed Manning's Roughness Coefficients for open estuarial river systems
Authors: Davidson Burton , Vichnevetsky Robert , Wang Howard T.
Published: February 2008

A finite difference version of the Levenberg‐Marquardt method for nonlinear least squares problems has been extended to include inverse problems in distributed estuarial hydraulic systems. The objective in solving the inverse problems was to establish a numerical simulation procedure for estimating best‐distributed Manning's roughness coefficients from sets of observed tide heights. As an illustration, spatially varying Manning's roughness coefficients for the Upper Delaware River Estuary system were determined for several representative sets of tide height data for the period October 1973 to June 1974. The roughness coefficients were modeled as polynomial functions of distance. Manning's n was thus found generally to vary inversely with distance from the head of tide at Trenton to Wilmington. The spatially distributed tidal‐averaged Reynolds number Re was used to correlate Manning's n and Darcy‐Weisbach's f. The resultant n‐Re relationships displayed three distinct hydrodynamic flow regimes characterized as having turbulence. Both n and f were found to be independent of Re for Re > 1.52 × 106 but inversely related to Re for Re < 1.2 × 106. Among the numerical techniques used to simulate tidal hydraulic transients it was found that a ‘hopscotch’ finite difference method yielded the best compromise between computational economy and overall accuracy.
unit sediment graph
Authors: Rendon‐Herrero Oswald
Published: February 2008

The unit Hydrograph method is extended to sediment graph analysis, thus yielding a unit sediment graph. The method is applicable to small uniform watersheds where the main contribution to suspended sediment transported in the drainage channels as the result of runoff derives from upslope erosion, that is, from wash load and not from entrained bed load material. Bixler Run, a small wash load‐producing watershed near Loysville, Pennsylvania, was used as a data source in deriving unit sediment graphs. The hydrographs and concomitant sediment graphs used are generally parallel in shape and coincide during peak flow.
Bulk precipitation and streamflow quality relationships in an urban area
Authors: Betson Roger P.
Published: February 2008

A systems study of urban hydrology was undertaken in Knoxville, Tennessee. Measurements of bulk precipitation quality were related to streamflow quality in several small watersheds. The yields of streamflow in these catchments are affected to varying degrees because they are located in carbonate terrain. Compared with bulk precipitation concentrations measured in other urban areas and in rural areas, the quality of bulk precipitation in Knoxville was found to be similar to that measured elsewhere for some 20 constituents. Input‐output studies for various constituents revealed that the relationships were considerably influenced by the effect of subdrainage losses through the carbonate rock system and by urbanization. In each case, however, the atmosphere was found to provide important sources for many constituents. Comparisons of the water quality data with those from equivalent rural areas revealed the quality of these urban streams to be similar to rural streams. These findings lead to the conclusion that bulk precipitation may be an important source for many constituents found in streamflow from rural and urban areas.
Water balance estimate for Georgian Bay in 1974
Authors: Schertzer W. M. , Bennett E. B. , Chiocchio F.
Published: February 2008

Current meter observations and hydrological and meteorological data collected primarily during 1974 formed the basis upon which the monthly water balance of Georgian Bay could be estimated. The data were used to derive a first approximation of the exchange of water between Georgian Bay and main Lake Huron. The net exchange across Main Channel at depths greater than 5 m was determined from extensive current meter observations while the exchange in the upper 5 m was the residual necessary to achieve a balanced water budget. The results illustrate that during the stratified season (May through November) the transport of water through Main Channel is also stratified with surface water moving into Georgian Bay from main Lake Huron while continuity is maintained by net outflow at depths greater than 5 m. Total annual supply from runoff and direct precipitation is nearly twice as large as combined losses from evaporation and flow to North Channel. Residence and flushing times for water in the bay are estimated at 5.1 and 5.7 years, respectively.
Radiative property measurements for selected water suspensions
Authors: Incropera F. P. , Privoznik K. G.
Published: February 2008

Although transport of the visible component of solar radiation in a water body strongly influences thermal structure and the growth of photosynthetic organisms, little is known about the inherent radiative properties which govern this transport. These properties include the extinction, scattering, and absorption cross sections, as well as the scattering phase function. In this study, systematic property measurements have been made for two special cases: the wastewater suspension and the symbiotic algal culture. In both cases, extinction is dominated by scattering processes (rather than by absorption), but cross sections associated with the symbiotic cultures are typically a factor of 6 larger than those associated with the wastewater. In both cases the scattering phase function is strongly peaked in the forward direction.
Prediction of drainage density from surrogate measures
Authors: Richards K. S.
Published: February 2008

A number of surrogate indices have been proposed as alternatives to, or predictors of, drainage density. These involve quadrat‐ and line‐sampling methods, which avoid the problems of watershed definition and irregular area measurement, and counts of segments, junctions, and sources, which avoid measurement of irregular line lengths. These techniques are evaluated, and the number of Shreve segments within a quadrat‐sampling unit is found to be consistently the best predictor of both quadrat and basin drainage density, although differences occur according to the nature of network definition (blue line or contour crenulated). A number of tests of the suggested prediction relationships are described, and these indicate that the method can successfully predict drainage densities in areas other than the area for which the relationship is derived and on different map editions at the same scale.
Tributary diameter in topologically random channel networks
Authors: Flint Jean‐Jacques , Proctor Jean R.
Published: February 2008

The concept of channel diameter can be extended to define the number of links along the trunk channel of tributaries in a basin. In topologically random channel networks, the occurrence of tributaries with a specified diameter can be expressed by recursive equations for basins of given magnitude. Comparison with two sets of stream data indicate a close resemblance with calculated values.
A model to generate rent surfaces: Applications and results for a public project
Authors: Ricci Paolo F. , Glaser Edward R. , Laessig Robert E.
Published: February 2008

This paper suggests an alternative approach to modeling rents generated by a public investment. The formulation adopted adds direction, through a Fourier series expansion, to distance, the independent variable of potential models. The coefficients of the enhanced model are estimated statistically and the resulting equation is utilized to generate rent equipotentials. The proposed formulation enables the representation of the various influences that intervene to disturb the otherwise smooth rent surfaces normally obtained from a potential model. The economic impact of a newly developed park‐lake complex is studied to provide an application of the methodology developed. Land values from deed records, the dependent variable of the model, are regressed against distance and direction from the centroid of the park‐lake complex. The findings show that rent surfaces change in configuration as different project‐related activities take place. For example, construction of the reservoir increases land values nearby the park‐lake, while the lack of visible activities does not affect land values.
Systematic sampling of Gaussian random processes and fields
Authors: Veneziano Daniele , Queiroz Celso S.
Published: February 2008

Linear observation of Gaussian random functions always results in reduction of uncertainty and since the posterior central moments are precomputable, optimal linear sampling schemes for variance reduction are nonsequential. In particular, systematic sampling of homogeneous Gaussian processes and fields, the latter on rectangular grids, leads to simple variance‐updating equations. Cases when measurements are noisy, when linear transformations of the uncertain function are observed or estimated, and when nonparametric uncertainty is superposed to a random parametric trend lead to simple variants of the direct observation/estimation model. The basic analytical tool is the Kolmogorov‐Wiener filter, either in the frequency or in the space domain. Application areas include the design of rainfall collection networks, inference of soil properties for geotechnical use, mineral exploration, biological and environmental sampling, materials testing, and quality control.
Atmospheric contributions to stream water chemistry in the North Cascade Range, Washington
Authors: Dethier David P.
Published: February 2008

Bulk precipitation contributes significant quantities of cations and trace metals to a subalpine catchment located in the North Cascade Range of Washington. Precipitation loadings account for 30% of the major and more than 50% of the minor element export from the catchment. Preliminary data from larger basins in the North Cascades suggest similar values. Calcium and potassium measured in bulk precipitation are largely derived from continental dusts, while sodium and magnesium originate as marine aerosols. Lead, copper, and arsenic, products of anthropogenic activity in the Puget Lowland, are deposited downwind in the Cascade Mountains; mean precipitation pH at the study site was 4.85 during 1974 and 1975. Elements contributed by precipitation become part of complex upland biogeochemical cycles. With the exception of highly mobile ions like sodium, elemental levels in streamflow reflect biologic and pedogenic cycling processes rather than direct precipitation influence.
Influence of cover slab diameter on solute travel time to wells
Authors: Kirkham Don , Sotres M. Olga
Published: February 2008

Travel times are computed for solute, moving by assumed piston flow, in steady state along streamlines in a phreatic (water table) aquifer in which a tube well is located to determine the influence of a well cover slab on the travel times. Flow nets are first computed by potential theory; then travel times along sets of streamlines are derived for 12 geometries. Parameters are cover slab radius, screened and unscreened casing depth, thickness of aquifer, well radius, and radius of influence. For example, for a well of cover slab radius 1.8 m, screened casing depth 0.5 m, unscreened casing depth 1.5 m, thickness of aquifer 6 m, well radius 0.6 m, and radius of influence 30 m, hydraulic conductivity 35 m/d, head difference across the system 0.15 m, and aquifer porosity 0.25, the travel time for solute injected at the edge of the cover slab to reach the well is 5.4 days, whereas solute introduced at the top of the aquifer next to the well pipe with no cover slab is 0.17 day (4.1 hours). The longer travel time, 5.4 days versus 0.17 day for ‘no cover slab,’ provides a longer time for biochemical and biophysical degradation of the solute, which may be pollutants as nitrates and acids originating from agriculture, industry, strip mines, sanitary landfills, or other groundwater pollution sources near a well.
Developing best management practices for salinity control in Grand Valley, Colorado
Authors: Walker Wynn R. , Skogerboe Gaylord V. , Evans Robert G.
Published: February 2008

The development of ‘best management practices’ (BMP) for controlling the salinity associated with irrigation return flows involves (1) delineation of the hydro‐salinity systems, (2) linkage of salinity impacts and irrigation practices, and (3) determining the least cost or most beneficial program for salinity management. The Grand Valley in western Colorado is one of the most significant contributors to the salinity problem in the Colorado River Basin and has been studied intensively to develop and apply the concepts of BMP. The hydro‐salinity system is described by research data collected over an 8‐year period. A mathematical simulation of the cost‐effectiveness relationships for various agricultural and desalination salinity control alternatives for reducing salt pickup by irrigation return flows was developed. Cost‐effectiveness functions developed from the model were then optimized using a least cost criterion to determine the most cost‐effective strategies for salinity control in the Valley. The analysis indicates that lining small conveyance channels to reduce seepage and increasing the efficiency of the existing furrow irrigation systems should be given the highest priority in any future salinity management programs. Canal lining and desalination of return flows are costly alternatives, but are feasible when the level of salinity control requires nearly total alleviation of the problem.
Extension of annual streamflow record by correlation with precipitation subject to heterogeneous errors
Authors: Clarke R. T.
Published: February 2008

Mean annual streamflow, μY, from a basin must frequently be estimated from short streamflow records. Where longer precipitation records are available, regression methods are commonly used to ‘extend’ the record of annual streamflow with the objective of improving the precision of the estimate of μY. However, the longer record of annual precipitation consists of mean areal estimates derived from a network of gages, and each year's estimate will be subject to a within‐year sampling error with a variance that is a function of the density of the rain gage network used in calculating it. This paper examines the consequences of neglecting to take account of heterogeneous variance of mean areal precipitation where regression of annual streamflow on annual precipitation is used to improve the precision of
. Two correlation models are used; in the first, it is assumed that annual streamflow and estimated mean areal annual precipitation are bivariate‐normally distributed, and that the rain gage network increased from g2 to g1 gages at the time when streamflow records began. If spatial correlation in rain gage catch is neglected, and if Δ = 1/g2 − 1/g1, then it is shown that the bias in
which results from neglecting to take account of change in gage density, is of the order of Δ2; the large‐sample variance var
, neglecting change in network density, underestimates the true variance, although the extent of the underestimation is not large for the typical situations that are evaluated numerically. The second correlation model assumes a bivariate gamma distribution of annual precipitation and runoff; this distribution has advantages over the bivariate Normal, but is not without its own drawbacks. For this correlation model, a qualitative assessment of the effect on var
that results from neglect of variation in network density shows that this effect is also small for typical situations.
The transition problem in pumped aquifers
Authors: Johnson Mark L. , Brutsaert Willem F.
Published: February 2008

Confined aquifers may develop water table conditions near the well bore and under prolonged pumping stresses this condition may spread to the recharge area. This situation is defined as the transition problem. The physics of the transition problem is examined by modeling well flow with a finite difference computer simulator. The computer simulator is based on two‐dimensional, two‐phase flow and takes into consideration formation compressibility, fluid (air and water) compressibility, solubility of air in water and a seepage face boundary condition at the well bore. A fully implicit finite difference scheme is used to solve the nonlinear flow equations by employing a modified Newton iteration process. The results obtained in this study agree with field data. Current analytical approaches seem to overestimate drawdown levels in time. The analysis shows that the transition problem is a unique combination of confined and unconfined flow. Gravity flow near the well bore appears to dominate the total flow pattern and affects drawdown at farther distances from the well bore where flow is radial. It was also shown that partially penetrating wells behave much like fully penetrating wells at certain radial distances from the well bore.
Waste water reuse and water quality planning in new England: Attitudes and adoption
Authors: Johnson Branden B.
Published: February 2008

Consideration of waste water reuse as a waste water management method is required in federal water quality planning. This paper reports the result of a survey of major participants in such planning in New England. It found that only cursory consideration was given to waste water reuse. Where one sits in the water management system significantly influences one's evaluation of reuse. Further, considerations other than economic and engineering factors will influence, indeed often determine, waste water reuse decisions; New England officials' views of reuse were generally very conservative.
Turbidity‐induced meromixis in an Oregon reservoir: Hypothesis
Authors: Larson Douglas W.
Published: February 2008

Flood flows into a river impoundment early in its history are believed to have produced a deepwater layer of highly turbid water that persisted owing to the slow settling of suspended material and poor reservoir flushing ability. Subsequent inflows of considerably cleaner water, superimposed on the turbid layer, created a pronounced middepth density gradient. Possibly, circulation of water between the two layers was restricted for several years, and a condition regarded as meromictic may have been established.
The National Water Data Network: A case history
Authors: Langford R. H. , Kapinos F. P.
Published: February 2008

In 1964 the Bureau of the Budget (now the Office of Management and Budget) issued Circular A‐67 to coordinate water data acquisition activities by federal agencies. Under Circular A‐67 the Department of the Interior's Office of Water Data Coordination (OWDC) has the responsibility to (1) maintain a catalog of information on water data, (2) undertake a continuing review of water data requirements, (3) prepare a federal plan for efficient utilization of water data activities, and (4) design a national water data network. A concept of three levels of information was developed as the rationale for national network planning. The three levels are level I, a base level of information for national and regional planning and assessment; level II, data needs for subregional planning and assessment; and level III, data for operation and management at the local level. Several elements of level I of the national network have been totally or partially implemented, including (1) the streamflow and stream quality accounting elements, (2) the water use accounting element, (3) the water quality surveillance element, and (4) the flood surveillance element. The National Water Data Network is coordinated through an interagency process involving more than 30 federal agencies and numerous nonfederal organizations interested in water data acquisition. As part of this coordination process the Catalog of Information on Water Data is maintained and is used as the basis for planning and operation of the network. Through the National Water Data Exchange, established as an outgrowth of the coordination activity, the water data information base is being expanded continually.
Spatial and temporal aggregation effects in a regional water supply planning model
Authors: Kirshen Paul H.
Published: February 2008

In applying mathematical programing water supply planning models, water supplies and demands must be spatially and temporally aggregated. An assessment is made of the effects of aggregation on the results of a planning model for West Africa. The assessment uses a detailed hydroeconomic simulation model to study the solution set of the planning model when it has been applied to several representative subareas. Comparisons are made between the design reliability intended for the supply system and the actual reliabilities of sources as estimated by the detailed simulation model. Comparisons are also made between the system suggested by the planning model and the estimated least cost reliable system. (The least cost reliable system was found using a trial and error search method and the detailed simulation model.) It was found that the aggregation assumptions primarily affect the modeling of sources that depend directly on the highly variable precipitation (e.g., ephemeral aquifers). These sources should, in general, be excluded from the planning model and analyzed separately. Overall, unless a planner is particularly interested in studying the use of such unreliable sources, the spatial and temporal aggregation assumptions of the planning model do not hinder its use as an effective regional planning tool.
Alternative choices in measurement systems for artificial river aeration
Authors: Olgac Nejat M. , Cooper C. Anthony , Longman Richard W.
Published: February 2008

Artificial in‐stream aeration is an economical and, under appropriate conditions, desirable method for alleviating symptoms of water pollution in rivers. Some measurement of the degree of pollution is generally required for this and other aquatic reclamation applications. Our objective is to optimize the selection of such measurements for use as feedback in aeration systems in order to improve performance under variable conditions. A special case of our mathematical results can also give the optimized measurement selection for water quality estimators. Two widely accepted measures of water quality are dissolved oxygen and biochemical oxygen demand, the latter being available only through time‐consuming and rather inaccurate observations. This time delay can be avoided by correlating biochemical oxygen demand with measurements of total organic carbon but only with a further sacrifice of accuracy. We examine a hierarchy of feedback structures, which includes the measurement of a variety of water quality parameters, and compare these structures to determine their relative performance. Finally, a trade‐off between time lag and accuracy of biochemical oxygen demand measurements is developed to optimize per formance.
Application of error analysis to a Marsh Hydrology Model
Authors: Gardner R. H. , Huff D. D. , O'Neill R. V. , Mankin J. B. , Carney J. , Jones J.
Published: February 2008

The contribution of errors on individual parameters to uncertainties in model predictions is studied in a hydrologic model of a marsh. Daily values of water level and storage are calculated in the model as a function of precipitation, storm runoff from the urban watershed, physical properties of soil, groundwater movement, and daily values of evapotranspiration. Errors associated with each parameter were propagated through the model calculations by Monte Carlo simulation. The distribution of each hydrologic parameter, considered as a random variable, was specified by mean, variance, maximum, and minimum values. Random numbers drawn from these distributions were used to simulate 244 days of water level and storage in the marsh. Errors for the marsh model are bounded, returning toward zero rather than growing monotonically through time. Although the simulations show considerable error for some days, the overall behavior of the model is robust. The seasonal contribution of specific parameters has important implications for model calibration and validation. Our analysis indicates that Monte Carlo analysis using actual estimates of parameter error leads to different conclusions than sensitivity analysis.
Piezometric determination of inhomogeneous hydraulic conductivity
Authors: Irmay Shragga
Published: February 2008

The hydraulic conductivity of inhomogeneous, isotropic, or anisotropic saturated stable porous media is computed from the observed or known field of the piezometric head ϕ in Cartesian and curvilinear orthogonal coordinates, in the general case, and for some special forms of ϕ. The method can be applied to aquifer flow and to heat transfer, and its accuracy can be assessed.
Correction for bias in estimation of the standard deviation and coefficient of skewness of the log Pearson 3 distribution
Authors: Lettenmaier Dennis P. , Burges Stephen J.
Published: February 2008

Estimated bias correction factors αG and αS for the coefficient of skewness and standard deviation of the log Pearson 3 distribution are presented. In contrast to similar results for other distributions commonly used in water resource applications, both αG and αS depend on the coefficient of variation Cv as well as the skew coefficient γ. The αG is not monotonie with γ for some values of Cv, and both αG and αS may assume values less than unity, unlike other commonly used distributions. It is shown that some of these differences are attributable to the peculiar forms which the probability density function of the log Pearson 3 distribution may assume.

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Bivariate gamma distributions for extending annual streamflow records from precipitation: Some large‐sample results
Authors: Clarke R. T.
Published: February 2008

This paper discusses the extension of streamflow records (commonly for annual time intervals) by correlation with longer records of precipitation for the purpose of estimating μY, the mean of the extended streamflow record. It is assumed that streamflow and precipitation have a bivariate gamma distribution, incorporating physical constraints on both variables, with μY estimated by maximum likelihood, by a ratio estimate, and by a regression estimate. Large‐sample variances of estimates given by these three estimation procedures are compared, and the effect on the ratio estimate of serial correlation in streamflow is calculated.
Derivation of monthly reservoir release policies
Authors: Bhaskar Nageshwar R. , Whitlatch Elbert E.
Published: February 2008

A single multiple‐purpose reservoir is analyzed using a backward looking dynamic program algorithm to obtain optimal releases. The dynamic program is solved for both one‐sided and two‐sided quadratic loss functions. Monthly policies are derived by regressing the optimal set of releases on the input and state variables. Linear and nonlinear release policies are developed, then verified and compared through simulation. For a two‐sided quadratic loss function, linear policies are as good or better than nonlinear policies. However, for a one‐sided quadratic loss function, nonlinear policies give improved performance over linear policies. It is also illustrated that the maximum R2 criterion for selecting release policies may not always be appropriate. Hoover Reservoir, located on Big Walnut Creek in central Ohio, is used as a case example.
On the expected diameter of random channel networks
Authors: Moon J. W.
Published: February 2008

The mainstream length of river networks tends to be proportional to the area of the corresponding drainage basin raised to a power that decreases from about 0.6 for small basins to near 0.5 for large basins. Shreve (1974) calculated the expected diameter μ(D) of random channel networks with n sources for values of n up to 500. On the basis of this numerical data he concluded that it seems likely that the ratio log μ(D)/log n approaches ½ as n increases indefinitely. Our object here is to prove that this is indeed the case.
Model for the optimal planning of structural flood control systems
Authors: Windsor James S.
Published: February 2008

A mixed integer programing approach is described in this paper for the planning and design of composite multiunit flood control systems. The model is intended to be a preliminary selection device permitting the planner to compare alternative configurations and determine roughly the optimal solution to a given flood control problem. Such a solution may then be used to establish the guidelines and specifications for the design of the individual components. The flexibility of the method enables a large number of alternatives to be considered simultaneously, even though they may be at different stages of planning. It also recognizes that optimal operation is a function of system design.
Constructive derivation in dynamic programing modeling
Authors: Young Donovan , Sherali Hanif D.
Published: February 2008

Constructive derivation of dynamic programing recursive equations proceeds by straightforward rearrangement of standard formulation as a constrained optimization problem. The advantage of constructive derivation over direct writing of recursive equations is demonstrated by application to a sequencing problem for which incorrect and correct formulations have been published. The problem is to find a minimal present cost sequence of N water supply projects having known capacities and installation costs to meet a given schedule of nondecreasing demands for total installed capacity.
A model for the water relations, photosynthesis, and expansive growth of crops
Authors: Zur B. , Jones J. W.
Published: February 2008

A conceptual model was developed for studying the integrated effects of soil, crop, and climatic conditions on the expansive growth, photosynthesis, and water use of agricultural crops. The plant was represented by water storage capacity, leaf area index, and osmotic, turgor, and total leaf water potentials. Water loss from the leaves was based on Monteith's combination equation for vapor flux. The resulting gradient between leaf and root water potentials caused a liquid water flux through the xylem resistance. The water potential gradient between root xylem and bulk soil causes water flux as the system departs from thermodynamic equilibrium. Resistances to water flux into the root depended on soil hydraulic conductivity, root density, and root radial resistance as defined by Taylor and Klepper (1978). Failure of the root system to supply water rapidly enough to replace water lost by the leaves resulted in decreased turgor and osmotic potentials. Stomatal control and expansive growth of leaves was a function of leaf turgor pressure. The model was used to simulate 10‐day drying conditions for sand and clay soils and for various combinations of root densities, root zone depths, and potential evapotranspiration rates. Diurnal and total daily values of transpiration and photosynthesis predictions suggest that soil root zone depth and soil hydraulic conductivities are very important factors in determining the maintenance of favorable turgor potential in the plant. Results also suggest that the relationship between daily transpiration and soil water potential is not unique but highly dependent on soil properties. The model is intended for developing simpler relationships for specific soils for describing the effects of various atmospheric conditions on plant growth processes such as transpiration, photosynthesis, and growth.
The use of weighted discount rates in cost‐benefit analysis: A further analysis
Authors: McDonald John F.
Published: February 2008

The weighted discount rate for cost‐benefit analysis is derived from a general formulation of the benefit and cost streams. The conditions under which the simple weighted discount rate procedure can be used are specified. Assuming that some private investment which would have generated a perpetual return is foregone to finance a public expenditure and assuming that the returns to the foregone private investment cannot be reinvested, the weighted discount rate can be used if there are costs only in the initial time period and a perpetual stream of benefits beginning in the next time period. Otherwise, the more general formulation must be used.
Determination of rainfall duration statistics for rain‐out models from daily records
Authors: Alexander K.
Published: February 2008

We discuss two methods by which the parameters of a simple model of the occurrence of rainy and dry episodes can be estimated from data. We first apply the method of moments to the mean and variance of the fraction of a fixed time period during which it is raining. The second method derives maximum likelihood estimates from observations of the weather at regular intervals.
Reliability programing in reservoir management: 2. Risk‐loss functions
Authors: Simonovic Slobodan P. , Mariño Miguel A.
Published: February 2008

The reliability programing approach for reservoir management is based on the concept of risk‐loss functions. This paper presents a methodology for deriving the risk‐loss functions associated with the violations of a freeboard constraint (flood risk) and a water supply storage constraint (drought risk). A relation between the amount of water excess or shortage and its corresponding reliability level is first established. The excesses or shortages are then related to damages (losses). This provides the basis for a final relation of the reliability levels and the damages. A similar approach can be followed in developing the risk‐loss functions associated with other reservoir purposes, such as recreation, navigation, and water quality enhancement. The hydrologie, hydraulic, and economic data necessary for developing the riskloss functions are discussed. The methodology is illustrated using data from the Blue Marsh Reservoir on Tulpehochen Creek, Schuylkill River basin, Pennsylvania.
A mathematical model of water table fluctuation in a semi‐infinite aquifer induced by localized transient recharge
Authors: Rai Shivendra Nath , Singh Rishi Narain
Published: February 2008

A mathematical model of the water table fluctuation in an unconfined aquifer subjected to a typical localized transient recharge is presented. The aquifer is taken to be homogeneous, isotropic, underlain by a horizontal impermeable base, and linked with a surface reservoir on one side. Sensitivity characteristics of the water table due to variations in the rate of recharge, hydraulic conductivity, and specific yield are illustrated with the help of a numerical example.
Extension of the integrodifferential approach to inhomogeneous multiaquifer systems
Authors: Hennart J. P. , Yates R. , Herrera I.
Published: February 2008

In the original integrodifferential model developed by Herrera and his co‐workers for multiaquifer systems and based on the quasi‐three‐dimensional theory for such systems, homogeneity was assumed at least in the vertical direction. This restriction is eliminated here, and the integrodifferential approach is extended to general heterogeneous multiaquifer systems. Finite element approximations in time and space are also introduced which include as particular cases most of the well‐known time integration schemes and lead to consistent updating schemes for the influence and memory terms.
Apportionment of net recharge in landfill covering layer into separate components of vertical leakage and horizontal seepage
Authors: Lentz John J.
Published: February 2008

In order to assess the probable impact on groundwater of contaminated leachate from landfill waste, it is necessary to estimate the quantity of leachate. This requires an accounting of the water surplus in a sloping cover placed over a freestanding landfill. By using input‐output analysis, water surplus is separated into a lateral seepage fraction and a vertical leakage fraction. The equation used is differentiable to the Boussinesq equation. By linearization the partial differential input‐output equation is transformed into an ordinary differential equation solvable by standard techniques. An example is given.
Surface heat fluxes from Lake Ontario: Further verification of lake thermal model
Authors: Tucker William A.
Published: February 2008

The components of heat flux at the surface of Lake Ontario during the stratified season of 1972 are estimated using a lake thermal model, which has previously been verified with respect to temperature simulation. The model inputs are lake geometry and optical properties and surface weather observations. The heat flux components are compared with independent observationally based estimates. The net flux is simulated accurately by the model; the radiative input to the lake is significantly overestimated. The error in the radiative flux is traced to the expression accounting for the effect of cloud cover on insolation. This error leads to compensating errors in sensible and latent heat fluxes, resulting in accurate simulation of the net heat flux. Evaporation rates estimated by the model are approximately 50% higher than other estimates. The use of observed insolation, or a more accurate formula for the effect of clouds, would probably lead to accurate simulation of evaporation rates.
An approximate method of estimating soil water diffusivity for different soil bulk densities
Authors: Libardi P. L. , Reichardt K. , Jose C. , Bazza M. , Nielsen D. R.
Published: February 2008

The effect of soil bulk density on soil water diffusivity and on infiltration is studied using data from 13 soils, widely ranging in texture. It is shown for horizontal infiltration of water into initially air dry soil that although changes in the slopes of plots of the distance to the wetting front as a function of square root of infiltration time corresponding to different bulk density values actually depend on soil type, they may be considered independent. Hence a generalized exponential equation is developed which expresses the soil water diffusivity of any soil as a function of soil water content and soil bulk density, knowing only the rate at which the wetting front advances for only one value of the bulk density.
Improved principles, standards, and procedures for evaluating federal water projects
Authors: Eisel Leo M. , Seinwill Gerald D. , Wheeler Richard M.
Published: February 2008

Over the past 40 years, many attempts have been made to develop improved evaluation criteria for Federal water resources development projects. The scope of evaluation expanded markedly with the introduction of multiobjective planning embodied in the 1973 principles and standards adopted by the U.S. Water Resources Council. Recent improvement efforts by the Council included revisions to the principles and standards and the development of an accompanying manual of evaluation procedures for use in determining the overall attractiveness of alternative plans for water resources development. Analysis of these improvements indicates that the revised procedures for evaluating beneficial and adverse economic effects of water resources development are more consistent with theoretical principles, although in some cases the new procedures include compromises necessitated by limited data, computation complexity, and political and legal contraints. Furthermore, these revisions to the principles and standards stress nonstructural measures and water conservation, which should make these planning guidelines more responsive to the increasing need for cost efficient as well as environmentally sound water resources development.
Sample selection bias in analysis of consumer choice: An application to warmwater fishing demand
Authors: Ziemer Rod F. , Musser Wesley N. , White Fred C. , Hill R. Carter
Published: February 2008

A theoretical model and empirical application are presented which account for the individual's decision concerning whether or not to recreate as well as the amount of participation once the decision is made. Results for warmwater fishing demand data yielded least squares parameter estimates fairly similar to those provided by an estimator which corrects for sample selection bias. Further research appears warranted regarding the general degree of potential selection bias inherent in outdoor recreation demand data.
Generating alternative solutions for dynamic programing models of water resources problems
Authors: Hopkins Lewis D. , Brill E. Downey , Wong Benedict
Published: February 2008

For a decision maker to bring implicit knowledge, that is, knowledge that cannot be incorporated into a model, to bear on a problem, he must be confronted with alternatives that are perceivable as different with respect to this implicit knowledge. A technique is presented to generate alternatives that are different from each other, but good with respect to modeled objectives, for problems that can be modeled by dynamic programing. The technique is argued to be better than alternative techniques. An application to floodplain management shows that the technique can produce sets of different alternatives for water resources problems.
Stochastic daily precipitation models: 2. A comparison of distributions of amounts
Authors: Woolhiser David A. , Roldán José
Published: February 2008

Chain‐dependent and independent exponential, gamma, and mixed exponential distributions are compared as models for the distribution of daily precipitation. Parameters for each distribution are estimated by maximum likelihood techniques for 14‐day periods. The Akaike information criterion is used to select the most appropriate distribution for each period and for the entire year. For the five U.S. stations studied, the independent mixed exponential distribution was the best on the basis of the Akaike information criterion, and the independent gamma and chain‐dependent gamma ranked second and third, respectively. Fourier series are fit to the parameters by least squares to provide starting values for subsequent numerical maximum likelihood estimates of the Fourier coefficients. According to the Akaike information criterion, the Fourier series description of model parameters for the mixed exponential model is superior to the specification of parameters for each 14‐day period.
Stochastic estimation of states in unconfined aquifers subject to artificial recharge
Authors: Schmidke Klaus D. , McBean Edward A. , Sykes Jonathan F.
Published: February 2008

An extended Kalman filter model for characterizing minimum variance estimates of the piezometric heads and coefficients defining an unconfined aquifer subject to artificial recharge is developed. The system evolution model employs Hantush's (1967) model. Sensitivity analyses are used to test the estimation capability of the technique. The ability of the extended Kalman filter to use all available information from both the system model and measurements of the state to provide approximate minimum variance estimates of the state and confidence limits is shown. The extended Kalman filter version of Hantush's model is applied to a record data length of one year obtained at the study area located in Norwood, Ontario.
On subsurface stormflow: Predictions with simple kinematic theory for saturated and unsaturated flows
Authors: Beven Keith
Published: February 2008

This paper provides analytical solutions for some simple cases of subsurface stormflow. The solutions are based on kinematic approximations in both unsaturated and saturated zones. Solutions for rising, falling, and partial equilibrium hydrographs are given. The analytical model has been applied to data collected on a hillslope of the East Twin Brook catchment, Mendip, United Kingdom. Measured and predicted hillslope hydrographs were in good agreement.
Improvements to the transition definition for the Lloyd Model of discrete state storage with correlated inflows
Authors: Doran D. G.
Published: February 2008

The transition probability matrices which result from the Lloyd model of storage are very large, and when these matrices are constrained to be of manageable size, loss of accuracy in the performance of the model results. A description is given of an extension to a previous technique, the divided interval scheme, which makes possible the practical use of Markov chain analysis with given inflow distributions to provide comparatively accurate results in a probabilistic account of reservoir behaviour. The extension is applied specifically to the Lloyd model of storage for single reservoirs, and the results of such analyses are obtained with modest computer storage requirements.