bluuebunny/crossref_metadata_2025 huggingface dataset:
Value of Streamflow Data for Project Design—A Pilot Study
Authors: Dawdy D. R. , Kubik H. E. , Close Edward R.
Published: February 2008

The value of streamflow data for project design is related to benefits forgone because of insufficient streamflow data. Stochastic simulation of a long‐term hypothetical record for a sample station is used to determine a reservoir design based on full (hypothetical) information. Shorter segments of the long‐term trace are then used for design under the same criteria in order to compute benefits forgone as a result of lack of full information. For the station used in this study, a low mean flow, high variability station, the marginal value of streamflow data approaches the marginal cost at some time beyond the length of 100 years. The manner in which the value of streamflow data for project design can be evaluated is illustrated.
Application of Linear Random Models to Four Annual Streamflow Series
Authors: Carlson Robert F. , MacCormick A. J. A. , Watts Donald G.
Published: February 2008

A simple method for describing random time series is illustrated by application to the annual streamflow data of the St. Lawrence, the Missouri, the Neva, and the Niger rivers. The technique is illustrated for identifying the appropriate form of the general autoregressive‐moving average model by use of the sample autocorrelation function of each series. The values of the parameters of the suggested model of each series are estimated and the results checked to suggest further modification of the model. The best model for each of the four samples showed a reduction in the variance value to 0.49, 0.64, 0.59, and 0.62 of the original variance with the use of one or two parameters. The use of the model for one year ahead forecasting on the Missouri River data is shown.
Effect of a Porous Sand Bed on Incipient Sediment Motion
Authors: Martin C. S.
Published: February 2008

Incipient motion tests were conducted for flow into and out of a porous bed. Seepage out of a bed does not affect incipient motion measurably because the seepage force is lost once a sediment particle rocks. Seepage into a bed may either enhance or hinder incipient motion, depending upon the relative effect of the boundary shear stress and the seepage force, both of which depend on the seepage flow. For a given hydraulic gradient the size of the sand grains is critical regarding incipient motion. For turbid water flow over a bed, fine particles of the mixture may become deposited in the bed, resulting in a concrete‐like, more resistant bed. Typical values of the hydraulic gradient are given for flow out of a canal and in an ocean bed under oscillatory waves.
Frequency of Design Drought
Authors: Joseph E. S.
Published: February 2008

Certain problems associated with a drought frequency analysis are exposed and their solutions are proposed. The techniques are based on a probabilistic framework. Return period of a project's design drought, the annual drought for which a water resource project such as a treatment plant or a low flow augmentation system has to be designed, is treated as a function of the project's useful life and the desired level of ‘assurance.’ (‘Assurance’ here stands for the probability of nonoccurrence of droughts equal to or smaller than the design drought during the project's useful life.) A method is shown for estimating the probability and return period associated with the design drought of a project. The paper presents a chart that gives recurrence intervals of design droughts for various combinations of the estimated useful life of a project and the desired level of assurance.
Implications of a Type of Empirical Evaporation Formula for Lakes and Pans
Authors: Brutsaert Wilfried , Yeh Gour‐Tsyh
Published: February 2008

Empirical mass transfer formulas for evaporation from lakes and from pans at ground level are compared with the theoretical solution based on semiempirical turbulent diffusion theory in conjunction with Reynolds' analogy and the power law for the wind profile. It was found that although the theory has its limitations, it is a useful tool for the study of evaporation, especially under conditions of lateral advection. The empirical formulas should be adequate for many design problems.
Fluid Model Studies of the Storage of Freshwater in Saline Aquifers
Authors: Kimbler Oscar K.
Published: February 2008

Flow studies in artificial sandstone models have been used to test and validate a computational technique for predicting the recovery of freshwater stored in saline aquifers. These studies indicate the physical and operational conditions under which such storage should be technically feasible, and show that gravitational effects are usually a much more important cause of poor freshwater recovery than is dispersion.
Flood Series Compared to Rainfall Extremes
Authors: Reich Brian M.
Published: February 2008

Annual series of maximum instantaneous flood peaks from 26 Pennsylvanian watersheds smaller than 200 square miles were analyzed by the Gumbel, log Gumbel, and log Pearson 3 methods. An empirical appraisal of how well each of these mathematical curves fits the data shows the general applicability of the straight Gumbel line. Consistent overestimation of long return period extremes results from using the log Gumbel analysis. Advantages of slight flattening for very rare expectations, which can result from the log Pearson 3 and the types of data sets preventing this from happening, are discussed. Corresponding histories of daily and clock hourly extreme rainfall annual series were compared to flood series for 24 watersheds that had more than one half of their drainage areas within a 14‐mile radius of the rain gage. Extreme rains that occur during the spring are more strongly linked to annual floods than yearly maximum rainfalls are. No usable relationship could be found between the extreme value statistics of rainfall and floods.
Stream Channels and Flow Relations
Authors: Brown Dwight A.
Published: February 2008

This paper considers the use of channel capacity as a reconnaissance technique for estimating mean flow and the magnitude of floods at various expected frequencies. Channel capacity is shown to be a valuable tool in estimating mean flow and flood values. Low flows are examined briefly and are shown to have diminishing relationships to channel capacity with increasing severity of low flow. Derived equations to estimate flood magnitudes provided good results when tested within the same environment. The coefficients of the derived equations are shown to lack transferability to different physical environments.
Use of Harmonic Analysis To Study Tidal Fluctuations in Aquifers near the Sea
Authors: Carr P. A.
Published: February 2008

Sixteen days of water level records were collected from a tidal gage and from four wells situated in a line perpendicular to the shore at Borden, Prince Edward Island. These two sets of records are separated by harmonic analysis into three tidal components. In a confined aquifer, groundwater flow obeys linear potential theory so that each component represents a distinct test on the aquifer, which is analyzed for hydraulic conductivity and specific storage. The use of a line of wells permits the determination of the effective distance and an accurate determination of true tidal efficiency by two different plots. The values of hydraulic conductivity determined this way agree very closely with the values determined by packer tests on nearby wells. These results permitted examination of the composite wave and the single well technique. The unseparated composite wave was analyzed by using the maxima and minima from four days of records and by assuming a periodicity of 745 minutes. The calculated values of aquifer parameters differed very little from those determined by the individual components. In addition, each well was analyzed individually and the results were compared with those determined from the line of wells. The individual analyses can produce large errors because they do not permit an accurate determination of the effective distance.
Use of Monte Carlo Techniques in the Design and Operation of a Multipurpose Reservoir System
Authors: Askew Arthur J. , Yeh William W‐G. , Hall Warren A.
Published: February 2008

The output from most analytical procedures used to set firm output levels for water projects is not associated with any given probability of failure to meet those output objectives. As a result, such output cannot always be used with confidence in the design and operation of water resource systems. A simple procedure is proposed that uses Monte Carlo techniques in deriving the optimum contract levels for a multipurpose system subject to constraints imposed by stated maximum permissible probabilities of failure to meet firm contract deliveries. The procedure is tested by analyzing a particular reservoir system. Similar procedures can be designed to handle multireservoir, multipurpose systems with a large number of such constraints and can be used to choose between alternative designs and fix optimum contract levels and release rules. Probability tables derived from such analyses can be used to improve the operational efficiency of water resource systems.
Influence of the Unsaturated Flow Domain on Seepage Through Earth Dams
Authors: Freeze R. Allan
Published: February 2008

This paper presents an integrated analysis of flow through earth dams in which the entire porous domain is considered. The mathematical model provides a finite difference solution to two‐ or three‐dimensional problems involving transient or steady state flow in the saturated and unsaturated domains of nonhomogeneous, anisotropic dam sections. In general, the water table is not a streamline; in many zoned cross sections, a significant proportion of the stream tubes may take unsaturated flow routes for some part of their traverse. In addition, the position of the water table may be quite different from that determined from the classic saturated‐only analysis. Unsaturated flow components take on greater importance in small dams rather than in large, in dams with sloping cores and downstream filter blankets rather than more homogeneous sections, and in the fine‐grained, well‐graded soils common to internal cores rather than in the more permeable and more uniform soils of the external sections. A simulation of the transient initial advance problem shows that the rate of growth of the saturated zone is highly dependent on the unsaturated properties of the soils and on the initial moisture contents. In the early stages of seepage following a rapid rise in the upstream reservoir level, inflow rates into the dam may be as much as 100 times the steady state seepage rate. Consideration of the unsaturated zone in the analysis of seepage through earth dams involves added mathematical complexity and requires data on unsaturated soil properties that are not commonly available.
Drainage of Groundwater Resting on a Sloping Bed
Authors: Childs E. C.
Published: February 2008

The Dupuit‐Forchheimer convention for horizontal impermeable beds is that the gradient of hydraulic potential is synonymous with the absolute slope of the water table. When the impermeable bed is sloping, however, the gradient is normally better approximated by dZ/dl, where l is the distance measured along the bed and Z is the height of the intersection with the water table of the perpendicular through l. Thus the solution of the resulting flow equation for drainage to a transverse ditch in the absence of surface recharge provides a family of branched curves for different slopes, instead of the single branched curve currently accepted. When there is surface recharge and a system of parallel equidistant drains, there is no simple analytic solution. However, numerical solutions show that the water table peak, as compared with a horizontal bed, is shifted downhill; its height is often not greatly affected.
Application of the Thomas and Fiering Model to Skewed Hydrologic Data
Authors: McMahon T. A. , Miller A. J.
Published: February 2008

An inconsistency is noted in the transformation to modify random normal variates to random skewed variates used in the Thomas and Fiering hydrologic generation model.
Mathematical Model for Beach Groundwater Fluctuations
Authors: Dominick Thomas F. , Wilkins Bert , Roberts Harry
Published: February 2008

The measurement of changing water levels across a tropical carbonate beach profile over three tidal cycles has provided basic data for the development of a predictive mathematical model of the fluctuation in the level of a beach water table. The model is based on partial differential equations governing transient, one‐dimensional movement of groundwater through porous media. A finite difference algorithm for the digital computer was developed to solve the equations. Beach homogeneity and nonlinear boundary conditions imposed by tidal fluctuations were assumed in these calculations.

Field measurements of water table fluctuations in Galleon Beach, Grand Cayman Island, show that the mathematical model simulates this system within the limits of accuracy of the experimental measurements. A method for in situ determination of the permeability‐porosity ratio is proposed and demonstrated for the beach studied. The mathematical model of the beach water table is used to develop an accurate method of calculating inflow and outflow at the beach‐ocean interface.
A Topologically Optimum Water‐Sampling Plan for Rivers and Streams
Authors: Sharp W. E.
Published: February 2008

It is postulated that the topologically optimum sequential sampling procedure for a stream network is to sample by successive elimination through division of the network at the centroid. The total number of samples is bounded by a minimum of [log3Mo] and a maximum of 2 {1 + [log3Mo]}. The mode is given by 1 + [log2Mo] where Mo is the link magnitude of the stream at the outlet. The results are used to develop a uniform sampling plan for the Edisto River in South Carolina.
Stochastic modeling of temperature and flow in rivers
Authors: McMichael Francis Clay , Hunter J. Stuart
Published: February 2008

Forecast models using historical time series data for temperature and flow are constructed by means of parametric time series models recently proposed by G. E. P. Box and G. Jenkins. An exposition of the new methods and two examples of data illustrative of the iterative procedures necessary to construct a good forecast model are given. The daily water temperature and Ohio River discharge at Wheeling, West Virginia, for January 1, 1963–December 31, 1968, provide the raw material for the models. The methods are easily extended to other problems.
Application of Galerkin's Procedure to aquifer analysis
Authors: Pinder George F. , Frind Emil O.
Published: February 2008

The groundwater flow equations may be solved using the Galerkin procedure to generate the approximating equations. The integrals in the resulting equations may be efficiently evaluated by using isoparametric quadrilateral elements and numerical integration. A comparison of solutions for an idealized problem obtained by using Galerkin techniques and finite difference techniques indicates they achieve approximately the same degree of accuracy. A field application of the two methods shows that the Galerkin procedure provided satisfactory solutions with far fewer nodes than were required for the finite difference approach. In selecting one of the above methods for a particular hydrologic problem the flexibility of the irregular subspaces used in the Galerkin approach must be weighed against the very efficient equation solving schemes applicable to the finite difference equations.
Analyses of selected statistical methods for estimating groundwater withdrawal
Authors: Luckey Richard R.
Published: February 2008

A procedure for estimating groundwater withdrawal ideally should (1) maintain an acceptable level of accuracy and (2) significantly reduce data collection. Two procedures that were investigated, random sampling and regression analysis, meet these objectives. Random sampling theory allows the calculation of sample size for any combination of accuracy limit and probability level, once the population type and parameters have been determined. Groundwater withdrawals in the Arkansas River valley in southeastern Colorado exhibit an approximately log normal distribution with a standard deviation of 1.25. Gross annual withdrawal can be estimated within 15% at the 0.90 probability level from a sample of 225 wells (about one‐fourth the number presently monitored). Random samples of actual data show errors that agree closely with errors predicted by sampling theory. Annual withdrawal can be related to certain independent variables using regression techniques. The independent variables used in this study were (1) annual precipitation, (2) total annual canal diversion, (3) annual electrical energy used by pumps, and (4) change in groundwater storage during the irrigation season. The standard errors of estimate of the four regressions, which used four or five data points each, ranged from 8900 ac ft/yr for the relation between annual withdrawal and change in groundwater storage during the irrigation season to 17,700 ac ft/yr for the relation between annual withdrawal and precipitation. The mean annual groundwater withdrawal was 122,000 acre‐feet.
Optimum gaging of thunderstorm rainfall in southeastern Arizona
Authors: Osborn H. B. , Lane L. J. , Hundley J. F.
Published: February 2008

About 70% of the annual precipitation on the Walnut Gulch Experimental Watershed in southeastern Arizona occurs as thunderstorm rainfall during the 3‐month period from July through September. The summer thunderstorms produce high intensity, short duration rains of limited areal extent. Records from long‐term stations give good estimates of the average annual and seasonal precipitation for a region, but networks of recording gages are necessary to describe individual storms and seasonal rainfall on finite watersheds. The optimum rain gage density varies inversely with watershed size and directly with the required accuracy. For example, to correlate rainfall and runoff, a 1‐mi2 watershed with a length‐width ratio of 4 requires a network of three recording rain gages. For watersheds of approximately 120 acres or less, the optimum network for rainfall‐runoff correlation is one recording rain gage. Generally, the number of gages required per unit area decreases as the watershed size increases up to about 10 mi2. A network of gages located at 1.5‐mile intervals is necessary to correlate adequately the thunderstorm rainfall and runoff for watersheds of 10 mi2 and more.
Analysis of the feasibility of interim water supplies
Authors: Hall Warren A. , Haimes Yacov Y. , Butcher William S.
Published: February 2008

The general problem of the feasibility criteria for interim water supplies is analyzed. Two forms are presented: (1) a combination of an interim supply and a long‐term supply and (2) the possibility of multiple interim supply projects and a long‐term supply. Both forms are compared with an immediate long‐term conventional water system. A problem formulation that yields to the optimal deferment period of the long‐term supply system is presented. The cost effectiveness of a combined desalting‐surface supply system is discussed, and a numerical example is presented. A table relating the different costs of the interim and long‐term projects with the water requirement is calculated. This table provides the optimal deferment period for the long‐term projects. The numerical results show that although the desalting system described clearly would not be competitive as a complete substitute for the surface system, the combination system of desalting for 10 years followed by the surface system is fully competitive.
Review of the influences of the Great Lakes on weather
Authors: Changnon Stanley A. , Jones Douglas M. A.
Published: February 2008

The considerable influence of the masses of water in the Great Lakes on the weather over and around the Lakes is reviewed and the average lake‐related weather alterations are indicated. Particular emphasis is placed on delineating the known facts and those that are inadequately known. The lack of extensive continuous weather measurements, particularly over the lakes, makes definitive areal assessments of lake influences on the weather around them difficult. Whether the lakes act as the energy sources or sinks on a daily or seasonal basis depends on the relative temperature of the waters and the overlying air. Over the lakes and their downwind shore areas, the lake‐caused average changes in cloud and precipitation amounts represent 5–15% reductions in summer and 5–45% increases in winter in comparison with upwind values.
Generation of serially correlated nonnormally distributed rainfall durations
Authors: Raudkivi A. J. , Lawgun N.
Published: February 2008

A practical and simple technique is used to generate a long series of serially correlated nonnormally distributed rainfall duration events. Rainfall durations are defined as the length of a continuous spell of nonzero 10‐minute interval rainfall depths. The serial correlation of the historical data is modeled by the autoregression scheme, and the skewness is described by the Pearson type 3 distribution functions. The model is tested with rainfall data from Auckland, New Zealand. The results are good in that the serial correlation, the first three moments, and the distribution of the historical data are reproduced. Preliminary results are also given for rainfall data generated by the model for two other locations with differing climatic conditions.
Managing a Ponderosa pine forest to increase water yield
Authors: Rich Lowell R.
Published: February 2008

A forest ecosystem, managed for social goals of water, wood production, wildlife, scenic values, and sediment control was applied to the West Fork watershed, Castle Creek, after a 10‐year calibration period. Water yields have improved significantly following this timber harvest and improvement cut. During the posttreatment period an increase of 1.4 inches of water was measured during a year of high runoff when 8.77 inches was yielded from the control watershed. In contrast, during years of low runoff when the water yield averaged 0.5 inch from the control watershed, the increase averaged more than 0.4 inch. Streamflow is intermittent. Winter precipitation has been the major source of water yields. Summer rains during June through September have accounted for nearly 46% of the annual precipitation but less than 10% of the streamflow. No measurable quantities of sediment have been trapped in the pond above the measuring weir.
Factor analysis of drainage basin properties: Evidence for stream abstraction accompanying the degradation of relief
Authors: Abrahams Athol D.
Published: February 2008

Factor analyses are carried out on five parameters measured in third order basins in five landscapes in eastern Australia: basin area, stream length, basin relief, basin perimeter, and stream number. A comparison of the factor solutions for the five landscapes suggests that departures from topological randomness are associated with the evolutionary decline of relief. Regressions between the geometric mean bifurcation ratio and relief indicate that very small headwater streams have been abstracted from the drainage networks in the two landscapes where relief has been erosionally reduced below 200 feet.
Longitudinal dispersion in nonuniform flow
Authors: Carter H. H. , Okubo A.
Published: February 2008

Nonuniform flow is defined as a flow in which the velocity at any given time changes from point to point along a streamline. Such a flow occurs in an estuary in which the cross‐sectional area increases in the longitudinal or downstream direction. A general solution to the one‐dimensional equation that describes the fate of a pollutant introduced into such an estuary has not been found; only certain special solutions have been given for various simple analytical expressions for the longitudinal variation of area and longitudinal dispersion coefficient. Furthermore solutions to this equation are given in terms of the longitudinal dispersion coefficient, the value of which is not determinable a priori. A peak concentration model is developed that is applicable to estuaries and rivers whose lengths are large in comparison to their widths and depths. This model permits the estimation of the longitudinal dispersion coefficient Ke from the geometry of the system and from measurements of the peak dye concentration determined by the release of a known quantity of a tracer material such as rhodamine WT. The geometry need not be specified analytically; it need be specified only numerically at the positions of the peak concentration. The tracer experiments and the manner in which the longitudinal dispersion coefficients are estimated are described. A method for estimating the applicability of the procedure is also presented.
Modeling the pore structure of porous media
Authors: Farrell D. A. , Larson W. E.
Published: February 2008

A physicomathematical alternative to capillaric modeling of the pore structure of porous media is proposed. With this model, the hydraulic conductivity of porous materials is determined from a ‘pore domain’ characterization of the pore space by using an appropriate conductance theory for estimating the flux contribution of the various components of heterogeneous media. The proposed model is versatile yet mathematically tractable and is capable of analyzing fluid flow through porous materials of widely differing structure including anisotropic and structured media. A comparative study of the predictions of this model with those of a model proposed by E. C. Childs and N. Collis‐George and now widely used in soil science is made for several media. The findings indicate that indiscriminate use of the latter model may be responsible for the gross overpredictions of hydraulic conductivity for some porous materials and also for the reported distortions in the relationships between conductivity and the degree of saturation for some soils.
Transformation of the tensor form of Darcy's law in inhomogeneous and anisotropic soils
Authors: Case C. M. , Cochran G. F.
Published: February 2008

The transformation of the tensor form of Darcy's law from an arbitrary cartesian coordinate system to one in which the permeability tensor is diagonal is discussed. Matrix equations are developed that allow this transformation to be conveniently performed. This transformation leads in a natural way to a discussion of the ellipses of permeability, which have been used in attempts to find geometrically the direction of the gradient of head given the velocity, and vice versa, in anisotropic media. Equations are derived that allow the magnitude, as well as the direction, of the gradient of head or velocity, as the case may be, to be found from the geometrical constructions; thus the utility of the equations is extended. Finally, the connection between the permeability ellipse and the ellipse of direction, which does not seem to have been previously noted in the literature, is demonstrated, and the implications of the connection are briefly discussed.
Methods for apportioning costs among participants in regional systems
Authors: Giglio Richard J. , Wrightington Robert
Published: February 2008

This paper first examines three methods currently used for apportioning the costs of joint waste water treatment facilities among users. The methods are cost sharing based on the measure of pollution, cost sharing based on single plant costs with a rebate proportional to the measure of pollution, and cost sharing based on the separable costs remaining benefit method. Through the use of numerical and theoretical arguments it is demonstrated that often these methods do not provide an apportionment that satisfies all the people involved and that a potential participant may find it economically advantageous not to join the regional plan and may thereby force the adoption of a system that is, in total, more costly. These difficulties will frequently arise when any plan is subjected to the pressures of ‘free market‘ bargaining. Two additional methods relying on game‐theoretic concepts are then introduced to deal with the problem. These methods, which are practical, can satisfactorily solve problems that are not tractable when other techniques are used. Also, the basically perverse characteristics of situations requiring cost sharing are demonstrated by using the bargaining methods to prove that some cost‐sharing problems have no unique solutions and that others have no viable solution at all unless the regional authority can obtain a subsidy.
Computer‐oriented Wilson‐Hilferty transformation that preserves the first three moments and the lower bound of the Pearson type 3 distribution
Authors: Kirby W.
Published: February 2008

The modification in this paper of the familiar Wilson‐Hilferty transformation has exactly the same mean, variance, skew, and lower bound as the Pearson type 3 variate that it is intended to approximate. Although the original Wilson‐Hilferty approximation is adequate only at skews of less than about 3.0, the new one remains satisfactory throughout the range of hydrologic interest.
Note on the finite element solution of the diffusion‐convection equation
Authors: Guymon G. L.
Published: February 2008

An improved formulation of the finite element procedure, based on a variational principle, yields superior results to a previous formulation of the finite element method. Numerical dispersion, introduced into the previous formulation by a transformation procedure that is unnecessary, is substantially reduced by the new procedure. The improved formulation of the problem yields a stable solution for a hypothetical stream mass transport problem.
Stability and the conservation of mass in drainage basin evolution
Authors: Smith Terence R. , Bretherton Francis P.
Published: February 2008

Drainage basin evolution is modeled as the time development of an initial surface subject to conservation of sediment and water and a transport law qs = F(S, q) connecting the sediment flux qs with the local slope S and the discharge of surface water q. Two models are presented. The first is appropriate to a smooth surface on which no discrete channels have formed, and the second is appropriate to a family of V‐shaped valleys, each containing a separate stream of negligible width. For the first model, some solutions are presented that describe the evolution of a long ridge for which the profile is independent of one spatial coordinate. The stability of such surfaces is then discussed. It is shown that, if F/q < ∂F/∂q, disturbances of small amplitude and small lateral scale will grow rapidly and presumably will lead to the formation of closely spaced channels directed down the slope, whereas, if F/q ≥ ∂F/∂q, such channels will tend to disappear. For a surface eroding without change of shape, convex portions are stable, and concave segments are unstable. The second model is less well developed, since conservation principles alone are insufficient to determine its evolution without some additional postulate describing the sideways migration of individual streams. It is shown how, if each stream moves so that the sediment fluxes entering from its two side slopes remain equal, a system of similar parallel valleys is unstable, and neighbors will tend to coalesce on a time scale comparable to that for erosion through a layer as thick as a valley is deep.
Management model as a tool for studying the worth of data
Authors: Maddock Thomas
Published: February 2008

Groundwater simulation modeling, mathematical programing, and decision theory are combined to plan and manage an irrigated farm, subject to variation in economic factors such as pumping costs and crop prices, in hydrologic factors such as transmissivity and storage coefficient, and in physical factors such as the choice of a physical model of the groundwater system. Those factors that are most critical to planning and managing the farm are identified and analyzed. The results of the analysis are a decision on cropping and pumping patterns over a design period, a choice of a physical model of the groundwater system that meets the needs of the farm, a ranking of data by the worth to the farm (worth being related to the regret incurred by the farm when an undesirable decision is made), and a ranking of data by priority for further data collection activities.
Effect of longitudinal dispersion on dynamic water quality response of streams and rivers
Authors: Thomann Robert V.
Published: February 2008

The amplitude and phase characteristics of a river subjected to a time variable waste input are computed for two cases: zero dispersion with no mixing and dispersion levels representative of streams and large rivers. The amplitude characteristic provides a guideline on the efficacy of using a no‐dispersion model for river water quality studies. The frequency response depends on a set of dimensionless numbers that characterize the reactive and dispersive nature of the river. The results show that for upland streams and rivers small amounts of dispersion may be important when the input varies with periods of about 7 days or less. For large, deep rivers the effect of dispersion can generally not be neglected when the input is time variable.
Seepage steps in the New Forest, Hampshire, England
Authors: Tuckfield C. G.
Published: February 2008

Seepage steps are erosional scarps produced on hillslopes by the removal of material on the downslope side by concentrated seepage. In plan, the scarps form arcuate lines approximately following the contour. In profile, four elements can be distinguished: a convex slope above the step, an almost vertical face, a convex debris slope below the face, and often a concave slope beyond the debris slope. In the New Forest, Hampshire, England, the seepage is caused by concentration of water above the junction between a permeable sandstone and an underlying impermeable clay. The seepage face is composed partly of superficial material and partly of the permeable rock, the contact between the two strata being obscured by the debris and found in one case to be 8 meters below the level of the base of the step. The water table was always found to be <1 meter below the level of the base of the step. It is concluded that the position of the step is determined directly by the level of the water table and indirectly by the clay‐sandstone junction. The height of the step varies considerably: the mean maximum height for 54 valley sides is 2.16 meters; the absolute maximum height recorded is 6 meters. Erosion of the face is active at some points; at other points the feature appears to be relict. It is usually most active near the heads of valleys.
An environmental evaluation system for water resource planning
Authors: Dee Norbert , Baker Janet , Drobny Neil , Duke Ken , Whitman Ira , Fahringer Dave
Published: February 2008

The Environmental Evaluation System (EES) is a methodology for conducting environmental impact analysis. It was developed by an interdisciplinary research team and is based on a hierarchical arrangement of environmental quality indicators, an arrangement that classifies the major areas of environmental concern into major categories, components, and ultimately into parameters and measurements of environmental quality. The EES provides for environmental impact evaluations in four major categories: ecology, environmental pollution, esthetics, and human interest. These four categories are further broken down into 18 components and finally into 78 parameters. The EES provides a means for measuring or estimating selected environmental impacts of large‐scale water resource development projects in commensurate units termed ‘environmental impact units’ (EIU). Results of using the EES include a total score in EIU ‘with’ and ‘without’ the proposed project; the difference between the two scores is one measure of environmental impact. Environmental impact scores developed in the EES are based on the magnitude of specific environmental impacts and their relative importance. Another major output from the EES is an indication of major adverse impacts called ‘red flags’, which are of concern of and by themselves. These flags indicate ‘fragile’ elements of the environment, which must be studied in more detail.
Effects of artificial destratification on primary production and Zoobenthos of El Capitan Reservoir California
Authors: Fast Arlo W.
Published: February 2008

El Capitan reservoir was continually and artificially mixed by using compressed air during the summers of 1965 and 1966. Mixing and reservoir volume increases resulted in more uniform physical and chemical conditions, aerobic conditions throughout the lake, increased primary production, increased depth distributions of zoobenthos, and zoobenthos population increases. Increased primary production was related to a decrease in algal depth distribution. This decrease was caused by incomplete destratification, since thermal microstratification persisted near the lake surface. Zoobenthos were distributed throughout the lake during mixing, whereas they were confined to shallow depths during well‐stratified times. Water volumes increased three‐fold during the study and greatly confounded interpretation of the mixing effects.
Moisture variation at the soil surface and the advance of the wetting front during infiltration at constant flux
Authors: Braester Carol
Published: February 2008

The problem of infiltration at constant flux at the soil surface has been solved approximately in an analytical closed form. The solutions may be valuable to the practicing engineer when dealing with sprinkler irrigation or infiltration of rain. Infiltration into a semi‐infinite soil column as well as infiltration into a soil column of finite length with a constant water table were considered. Analytical and numerical results were compared for a few cases. It was found that the analytical solutions provide quite a satisfactory prediction of the moisture content at the soil surface and the advance of the wetting front. The results are presented in a dimensionless form; the analytical results are the same for all soils, and apparently the numerical results are also the same for all soils.
Behavior of groundwater flow subject to time‐varying recharge
Authors: Tseng M. T. , Ragan R. M.
Published: February 2008

The objective of this paper is to investigate the dynamic response of two‐dimensional unconfined aquifers subject to localized recharge. The variations of free surface profiles, discharges, and the flow patterns with respect to time in both fully penetrated and partially penetrated aquifer systems have been obtained by solving the governing partial differential equations numerically. The method treats the nonlinear free surface boundary as an initial condition, and the overall flow region has been solved as a boundary value problem at a given time. The numerical results agree with experimental data obtained from Hele‐Shaw models. The method may be applied to study the quantitative and qualitative changes in groundwater reservoirs resulting from artificial or natural recharge. The method gives a point of departure for study of groundwater pollution.
Technique for implicit dynamic routing in rivers with tributaries
Authors: Fread D. L.
Published: February 2008

The prediction of transient flow in a river having a major tributary poses a challenging problem for the streamflow forecaster. The interaction of storage and dynamic effects between the two rivers can be simulated efficiently by a mathematical model consisting of the two unsteady flow differential equations and of known stage time, discharge time, or stage discharge relationships at the extremities of the rivers. Numerical solutions of discharge and water surface elevation are obtained from the differential equations at specified time intervals by an implicit finite difference technique. This produces successive systems of nonlinear equations that are efficiently solved by the Newton‐Raphson iterative method in combination with an extrapolation procedure and a specialized direct method for solving a system of linear equations. The length of the specified time interval is not limited by computational stability; however, accuracy constraints may limit its size. Some numerical results are presented to illustrate the interaction between a river and a tributary when they are subjected to a flood wave of long duration.
Simultaneous transport of solutes and water under transient unsaturated flow conditions
Authors: Bresler Eshel
Published: February 2008

Theoretical and mathematical tools for analyzing transient one‐dimensional (vertical) simultaneous transfer of noninteracting solute and water in unsaturated soils are developed. The transient diffusion convection equation is solved numerically by an approach that eliminates the effect of numerical dispersion. The numerical results are compared with some analytical solutions for steady water flow. For transient infiltration the results are compared with field data reported by Warrick et al. These comparisons indicate that the theory as well as the numerical method is reliable and can be used with confidence. Results are given for typical cases of infiltration, redistribution, and evaporation of water from the soil and their effect on dispersion coefficients and salt concentration profiles.
Integrodifferential equations for systems of leaky aquifers and applications: 1. The nature of approximate theories
Authors: Herrera Ismael , Rodarte Leopoldo
Published: February 2008

The dynamics of leaky aquifers are governed by a system of integrodifferential equations derived in this paper. Alternative expressions for the memory functions are obtained, and it is shown that approximate theories of leaky aquifers correspond to several ways of approximating the memory functions.
Analytic solution of spatially discretized groundwater flow equations
Authors: Kuiper L. K.
Published: February 2008

The Galerkin procedure when it is applied to the equation for horizontal two‐dimensional flow of groundwater in a nonhomogeneous isotropic aquifer generates approximating equations of the following form: Rc + G [dc/dt] + f = 0, where R and G are square matrices, c and f are column matrices, and t is time. This matrix equation is decoupled and solved for the unknown column matrix c(t). In the case of a confined aquifer that approaches a steady state solution, R, G, and f are constant. An analytic solution to the matrix equation for c(t) is given for this case. In the case of a water table aquifer that approaches a steady state solution, R and f are explicitly dependent on c(t), and G is constant. For this case, c(t = ∞) is found in a simple iterative manner, and an iterative procedure is given to approximate c(t). These methods are compared with the approximate numerical Crank‐Nicholson procedure by applying both to a particular problem for which the unknown column matrix c(t) has 49 elements. The Crank‐Nicholson procedure is found usually to require less computation time to evaluate c(t) for the confined aquifer case but to give errors for drawdown averaging approximately 10%. The Crank‐Nicholson procedure is found to take considerably more computation time to evaluate c(t =∞) for both the confined and the water table cases but to take considerably less time to evaluate c(t) for the water table case.
Wheat response to soil moisture and the optimal irrigation policy under conditions of unstable rainfall
Authors: Yaron D. , Strateener G. , Shimshi D. , Weisbrod M.
Published: February 2008

An approach to irrigation decisions for wheat under conditions of unstable rainfall is presented, and a simulation model designed for tracing the variation of moisture in the soil profile during the growing season of wheat is described. Empirical estimates of the response function of wheat yield derived on the basis of 4 years of irrigation experiments are presented. The paper concludes with the simulation and comparison of several irrigation policies for wheat under conditions of stochastic rainfall.
Capacity decisions in a multipurpose multireservoir system
Authors: Nayak Satish , Arora Sant R.
Published: February 2008

A mathematical programing model is proposed to solve the common and formidable water resource planning problem of finding the best sites from a number of potential sites for constructing a system of reservoirs that will optimally meet the various water demands. Since flood damages and shortage costs (the primary problems the reservoirs are designed to solve) usually vary nonlinearly with the flow values, a nonlinear programing model is proposed. The fact that the variables in the objective function, which minimizes the sum of the annual amortized cost of the reservoirs and the annual flood and shortage losses less the annual recreational benefits, and the variables in the constraints are separable has been used to reduce the nonlinear problem to a separable problem. The common approximate approach to the problem, which chooses the optimal design parameters on the basis of straight historical inflow data for a specified period, was selected over the more complex ideal approach, which quantifies the stochastic nature of the historical inflows and uses the inflow distributions in an optimization model to select the design parameters. The optimization in this paper considers the flood inflows (based on a given flood frequency) and the drought inflows (based on the severest drought on record) simultaneously. The damages due to shortages may be weighted further in the objective function. The present model differs from other models in that releases are constrained only by the availability of water and their optimal values are determined by balancing damages downstream against the cost of providing storage to prevent them. The model is applied to U.S. Army Corps of Engineers data for the Minnesota River basin, and the results are compared with the plan proposed by the Corps.
Entropy in the assessment of uncertainty in hydrologic systems and models
Authors: Amorocho J. , Espildora B.
Published: February 2008

In the representation of natural catchment systems with mathematical models, a relatively wide range of choice exists among models of various degrees of completeness and sophistication. When the cost, as well as the appropriateness, of a model is considered for a particular purpose, it is desirable to have an objective criterion to make this selection. The concept of entropy as used in information theory provides one such criterion. Entropy is a measure of the degree of uncertainty of a particular outcome in a process; therefore, in dealing with the prediction of a hydrologie variable such as streamflow, one can compute the entropy of this variable from historical data and thus characterize the unexpectedness or variability inherent in the process. This represents a property of the system and is called marginal entropy. It is likewise possible to evaluate the uncertainty of the predictions made by a given mathematical model of the catchment by comparing these predictions with the measured flow. This is done through the conditional entropy. By combination of these two entropy functions a criterion called ‘transinformation,’ providing an objective evaluation of the goodness of the model, is obtained. The important point to note is that this assessment depends not only on the model but on the characteristics of the output series resulting from the natural process. The above criteria, which have been discussed in other contexts, were applied to a basin for which a number of years of historical flow record and concurrent model simulations were available. The results show the value of the entropy criterion in judging model performance as well as the difficulties and limitations of the method.