bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of evaporation from Lake Ontario during IFYGL by a modified mass transfer equation
Authors: Phillips David W.
Published: February 2008

Daily evaporation from Lake Ontario during the International Field Year for the Great Lakes (April 1972 to March 1973) was computed by a modified mass transfer technique. Turbulent energy flux was calculated by using upwind land station data and the surface water temperature at 88 grid points on the lake. Wind speed and humidity at each grid point were determined through multiregression equations that take into account stability, fetch, and water temperature. Daily, monthly, and annual evaporation amounts obtained in this study are compared to amounts obtained by conventional mass transfer, energy balance, and terrestrial water budget methods. Discrepancies in the results of the various approaches are examined and discussed.
Numerical simulation of steady state three‐dimensional groundwater flow near lakes
Authors: Winter Thomas C.
Published: February 2008

Numerical simulation of three‐dimensional groundwater flow near lakes shows that the continuity of the boundary encompassing the local groundwater flow system associated with a lake is the key to understanding the interaction of a lake with the groundwater system. The continuity of the boundary can be determined by the presence of a stagnation zone coinciding with the side of the lake nearest the downgradient side of the groundwater system. For most settings modeled in this study the stagnation zone underlies the lakeshore, and it generally follows its curvature. The length of the stagnation zone is controlled by the geometry of the lake's drainage basin divide on the side of the lake nearest the downgradient side of the groundwater system. In the case of lakes that lose water to the groundwater system, three‐dimensional modeling also allows for estimating the area of lake bed through which outseepage takes place. Analysis of the effects of size and lateral and vertical distribution of aquifers within the groundwater system on the outseepage from lakes shows that the position of the center point of the aquifer relative to the littoral zone on the side of the lake nearest the downgradient side of the groundwater system is a critical factor. If the center point is downslope from this part of the littoral zone, the local flow system boundary tends to be weak or outseepage occurs. If the center point is upslope from this littoral zone, the stagnation zone tends to be stronger (to have a higher head in relation to lake level), and outseepage is unlikely to occur.
A two‐dimensional linearized view of one‐dimensional unsaturated‐saturated flow
Authors: Cushman John , Kirkham Don
Published: February 2008

A numerical analysis of the one‐dimensional unsaturated‐saturated flow problem is presented. Both the pressure head and moisture content equations were studied for vertical and horizontal infiltration, respectively. The problems were considered in a two‐dimensional setting in which time was considered the second dimension. The numerical scheme used was finite element analysis coupled with a simple linearizing assumption. The numerical process is compared with various other analytic and numerical solutions of the same problems. It is shown that if the size of the elements is not too large, the method is very accurate.
Infiltration during an unsteady rain
Authors: Chu Shu Tung
Published: February 2008

Infiltration during a rainfall event can be divided into two distinct stages: a stage with surface ponding and a stage without surface ponding. Few of the infiltration models in current use are suitable to describe infiltration for both stages. In this paper the Green and Ampt equation was applied to determine the time that separates these two stages so that infiltration for the different stages can be treated separately. To obtain an integrated form of the Green and Ampt equation, it is traditionally assumed that the cumulative infiltration is zero at the time when surface ponding starts. But in a rainfall event the cumulative infiltration equals the water infiltrated into the soil profile prior to the ponding time, which is usually not zero. Therefore a modification in the traditional Green and Ampt equation is needed to describe infiltration during a rainfall event. It is shown in this paper that this modification is equivalent to a shift of the time scale by an amount which is referred to as the pseudotime by the author. The modified version of the Green and Ampt equation was applied to determine rainfall excess and to predict total runoff for three major storms recorded by the Agricultural Research Service from 1957 to 1959 on a watershed near Oxford, Mississippi. A comparison of the prediction and the measured total runoff appeared to be promising.
Sampling frequency for river quality monitoring
Authors: Sanders Thomas G. , Adrian D. Dean
Published: February 2008

Sampling frequency for a water quality monitoring network is presented, and for illustrative purposes the criterion is applied to the Massachusetts portion of the Connecticut River basin. The proposed frequency criterion is based upon the assumption that the primary objectives of future river quality monitoring networks are the determination of ambient water quality conditions and an assessment of yearly trends rather than detection of stream or effluent standards violations. The sampling frequency criterion is derived as a function of the random variability of the river flow. The criterion is specifically related to the magnitude of the expected half width of the confidence interval of the mean of the random component of the annual statistic‐mean log river flow. The appropriate sampling intervals (at each sampling station within the river basin) are determined by specifying equality of this confidence interval half width, which insures a uniform reliability of the annual statistic.
A study of the Kalamos Springs in Greece with environmental isotopes
Authors: Payne B. R. , Leontiadis J. , Dimitroulas Ch. , Dounas A. , Kallergis G. , Morfis A.
Published: February 2008

Variations in the stable isotopic composition of water were used to define the area of recharge to the Kalamos springs, issuing brackish water near the coast. The two possible areas of recharge differed in elevation, so that their stable isotope indices were different owing to the altitude effect, whereby the stable isotopic composition of precipitation contains less deuterium and 18O with an increase of elevation. The results of the study showed that the area of recharge is located in the Parnis system at elevations greater than 570 m.
Serially linked reservoir system design using stochastic programing
Authors: Prékopa András , Rapcsák Tamás , Zsuffa István
Published: February 2008

A stochastic programing model formulated for a serially linked reservoir system design is presented, and a numerical solution method is proposed. The model has already been formulated by Prékopa (1973) in a concise form. Here we give a more detailed explanation, apply the sequential unconstrained minimization technique for the solution of the optimization problem, and present a numerical example. The example is taken from a larger model which arose in the first implementation of this reservoir system design method in practice.
Climate, soil, and vegetation: 7. A derived distribution of annual water yield
Authors: Eagleson Peter S.
Published: February 2008

The average annual soil moisture balance, as derived from the mechanics of storm and interstorm soil moisture movement and from the statistics of the climatic variables, is used to define the average annual soil moisture. This soil moisture is used in the equation for average annual yield to give a first‐order approximation of the annual precipitation yield function. This function is used to transform the cumulative distribution function (cdf) of annual precipitation into the cdf of annual yield, and application is made in a subhumid and in an arid climate. The derived yield frequency function is seen to be sensitive to the soil and vegetal properties. Proper selection of these parameters brings close agreement with observed streamflow‐frequency and suggests the model's utility for parameterizing drainage basins with respect to effective average soil and vegetal properties.
Time‐averaged areal mean of precipitation: Estimation and network design
Authors: Bras Rafael L. , Colón Raul
Published: February 2008

Rainfall is recognized as a random process in time and space. With this in mind, data collection is treated as an estimation problem in which discrete, noisy, and incomplete information is used to estimate the true rainfall process. The estimation of the unknown time‐averaged areal mean of precipitation is accomplished through a state augmentation procedure and the use of multivariate linear estimation concepts, in particular, the Kalman‐Bucy filter. A technique results which can be used to analyze existing data networks, design new networks, and process data from existing networks. The procedure can handle any network configuration and explicitly accounts for the number of stations, their particular locations, the duration of observations, and the measurement errors. Results are presented.
Delayed aquifer yield as a phenomenon of delayed air entry
Authors: Bouwer Herman , Rice R. C.
Published: February 2008

Delayed release of pore water from a pumped, unconfined aquifer is treated as a situation of restricted air movement in the vadose zone due to layers of high water content. This restricted movement produces below‐atmospheric pressures in the pore air above the water table, which cause the water table initially to drop faster than the dewatered zone. The initial yield thus is less than the full specific yield, which develops after a certain water table drop. Equations are derived that relate delayed yield to air entry value and height above water table of saturated layers in the vadose zone. These equations agreed with results from a delayed yield experiment on a vertical soil column and produced ratios between initial and final yield that resembled those calculated by others from actual pumping tests. An axisymmetric flow system, simulated by interconnected jars with narrow standpipes, produced delayed yield drawdown curves that were amenable to Boulton's analysis.
Birth of a parent: The Wakeby Distribution for modeling flood flows
Authors: Houghton John C.
Published: February 2008

Traditional distributions, such as the log normal distribution, inadequately model flood flows for certain records. The Wakeby distribution is defined to overcome this deficiency, and its analytical form proves easy to use in many applications. Tests show that a significant number of flood records are inadequately fit by the three‐parameter log normal. The Wakeby demonstrates the ‘separation effect’ that other distributions fail to show. Most other distributions can be mimicked by the Wakeby but not always vice versa. Thus choosing to use the Wakeby does not limit the shape of the resulting curve to as great a degree as choosing a conventional distribution.
Time and length scales for the one‐dimensional assumption and its relation to ecological models
Authors: Ford Dennis E. , Thornton Kent W.
Published: February 2008

The vertical one‐dimensional assumption is examined with respect to its validity for mathematical ecological models of lakes or reservoirs. Analysis of the time and length scales characterizing the hydrodynamics, chemistry, and biology shows that the two scales are inexorably coupled and their interaction dictates both upper and lower bounds for the lake size that can be characterized by a one‐dimensional model. For an update frequency or forcing time scale of 1 day the one‐dimensional model is restricted to lakes characterized by length scales of 0.5–10 km. This range is preliminary and dependent on model formulation and update frequency. Inconsistencies between the model formulation scales for the hydrodynamics, chemistry, and biology may result in erroneous model predictions.
Multiple objectives under uncertainty: An illustrative application of protrade
Authors: Goicoechea Ambrose , Duckstein Lucien , Fogel Martin M.
Published: February 2008

A decision making method labeled Protrade has been developed to account for both multiple objectives and uncertainty aspects. This method is applied to the case study of the Black Mesa Region in Northern Arizona which is being strip mined for coal. One important concern in large‐scale surface mining is the reclamation of mine spoils to bring about beneficial land uses while observing economic, social, environmental, and legal constraints. Protrade considers a set of linear objective functions with random parameters, subject to a set of physical constraints; the preferences of the decision maker are articulated in a progressive manner, and alternative solutions are generated. Nonlinear deterministic equivalents are introduced to account for uncertainty in some of the parameters involved. While no final policy recommendations are made, this illustration of Protrade is carried out to investigate the potential of the method for trading off multiple objectives and measures of uncertainty in water and other natural resource system design problems.
On the influence of the spatial distribution of rainfall on storm runoff
Authors: Wilson Charles B. , Valdes Juan B. , Rodriguez‐Iturbe Ignacio
Published: February 2008

This study is an assessment of the importance of precipitation accuracy on the rainfall‐runoff modeling of a small catchment. Two mathematical models were used in the investigation: a deterministic rainfall‐runoff model based on the kinematic wave approximation and a nonstationary time‐varying multidimensional rainfall generation model. It is implicitly assumed that this rainfall generation model is an appropriate mathematical representation of the natural phenomenon of rainfall. The deterministic rainfall‐runoff model is used to represent the 26.5‐mi2 catchment of the Rio Fajardo in northeastern Puerto Rico. The rainfall model generates synthetic rainfall which serves as the input to this runoff model. The influence of the spatial distribution of the rainfall input on the discharge is analyzed by using 1 rain gage or 20 rain gages to record the synthetic storms. The isohyetal maps and hyetographs of the synthetic storms, together with the storm hydrographs produced by the runoff model, are analyzed, with specific attention given to the volume of storm runoff, time‐to‐peak runoff, and peak runoff. The experiments show that the spatial distribution of rain and the accuracy of the precipitation input have a marked influence on the outflow hydrograph from a small catchment.
Trichlorofluoromethane in groundwater—A Possible tracer and indicator of groundwater age
Authors: Thompson Glenn M. , Hayes J. M.
Published: February 2008

Trichlorofluoromethane, an entirely man‐made material, has become a detectable component of the atmosphere. Because of its unique atmospheric history, the presence of CCl3F in groundwater is potentially significant in terms of groundwater age. The age relationship stems from the fact that precipitation, exposed to CCl3F in the atmosphere, will pick up an amount that is proportional to the atmospheric CCl3F concentration. If a portion of this water infiltrates into the subsurface to become groundwater, it can be differentiated from older groundwater (that infiltrated prior to the buildup of CCl3F in the atmosphere) on the basis of its CCl3F content. In order to evaluate the temporal significance of CCl3F in groundwater, preliminary investigations were conducted in three areas where the hydrology was well understood and where tritium measurements had been made in the past. They were: the Wharton tract of southern New Jersey; Hot Springs National Park in Hot Springs, Arkansas; and the Edwards aquifer of south central Texas. Good agreement was observed between the CCl3F data and the hydrologic controls. The Texas study also revealed a series of anomalous CCl3F concentrations (up to 35 × 10−9g CCl3F/I H2O) that were too high to be of atmospheric origin. The anomalous points occurred in a line extending from the northwest corner of San Antonio for a distance of 74 km northeast along the Balcones fault zone and are interpreted as representing the migration of CCl3F from a point source, thus indicating the potential of this and similar compounds as hydrologic tracers.
Modeling groundwater flow fields containing point singularities: A technique for singularity removal
Authors: Charbeneau Randall J. , Street Robert L.
Published: February 2008

Artificial recharge of groundwater resources through wells leads to a need for computer simulation of the hydraulics and transport of contaminants in a flow field. The basic numerical technique used is the Galerkin finite element method (FEM). Greatly improved accuracy of the simulation near wells is achieved first by removing the singular behavior of the flow with an analytic solution for the near‐well zone, second by solving the remaining nonsingular problem, and third by combining the results. The resulting solutions compare favorably with known analytic solutions for confined and leaky aquifers (both isotropic and anisotropic). No additional computation time is required for this method compared to standard FEM programs. The resulting combined velocity fields are accurate enough throughout the flow field for direct use in contaminant transport simulations.
Optimal management of a multireservoir water supply system
Authors: Gal Shmuel
Published: February 2008

This paper presents a pilot study of a method for finding an approximation for the optimal policy of a dynamic system which depends on stochastic state variables. The systems being considered are multi‐reservoir water supply systems whose (stochastic) state variables are the quantities of water in each reservoir and some previous inflows which affect future inflows. Of special importance is the three‐reservoir system which represents the major part of Israel's water supply system: Lake Kinneret and two underground aquifers. This system can be represented by five stochastic state variables: the quantities of water in each of the three reservoirs and the inflows into the Kinneret for the two previous months. Since this system is too large to be solved by the usual dynamic programing approach, a method was devised in this study for obtaining an approximate solution which does not consume too much time or space. This method will be referred to as the parameters iteration method. It has been tested on a smaller system which contains only three stochastic state variables: the amount of water in the Kinneret and two previous monthly inflows. The results were satisfactory in the sense that the approximate solution obtained by this method was as good as the optimal solution obtained by a dynamic programing approach to this problem. Thus it can be expected that the parameter iteration method would be efficient for the three reservoir problems as well and for larger problems.
Screening objectives and uncertainties in water resources planning
Authors: Byer Philip H.
Published: February 2008

A procedure for helping analysts to choose the objectives and uncertainties to be considered in the evaluation of alternative system designs has been developed. Two models are described, one for screening system attributes (and their related objectives) and one for screening uncertainties about the levels of these attributes. The models use first‐order estimates of utilities and probabilities to calculate a measure of the maximum expected effect on the results of the evaluation of not considering an objective or of assuming certainty, rather than uncertainty, about the levels of an attribute. The models are applied to the problem of planning a hypothetical multipurpose dam and reservoir system.
Trade‐offs for multiple objective planning through linear programing
Authors: Thampapillai Dodo J. , Sinden J. A.
Published: February 2008

Benefit transformation curves are derived from a multiple objective linear programing model. These transformation curves are used to assess the relationship between objectives. The model consists of a weighted objective function which can be parametized. Procedures are suggested to narrow the search for an efficient management strategy on the transformation curve. However, the validity of the transformation curve depends on how non‐commensurables are valued and so different methods of valuation are presented and used. The model is illustrated through application to a policy problem in northern New South Wales, Australia.
Infiltration and drainage calculations using spatially scaled hydraulic properties
Authors: Warrick A. W. , Amoozegar‐Fard A.
Published: February 2008

Infiltration and drainage results are calculated for spatially varying hydraulic properties. The soil water flow equation is solved in a form valid for scaled soil water characteristics and unsaturated hydraulic conductivities. The single solution can then be utilized for individual sites chosen randomly by using a scaling coefficient. This procedure reduces repeated tedious individual calculations to simple algebra or interpolations. Examples include infiltration using semi‐analytical forms and drainage based on a single finite difference solution. Monte Carlo simulations were used in most cases.
Estimating solute transport in streams from grab samples
Authors: Johnson Arthur H.
Published: February 2008

Several combinations of weighting procedures and schedules of sample collection resulted in substantial differences in calculated P transport by Fall Creek, New York. Calculation of P flux using regressions of concentration on flow are the most satisfactory for grab sample studies where solute concentration is correlated with stream discharge because regressions account for solute export at the highest flows better than other methods. Acceptable estimates of yearly solute flux in a stream can probably be obtained from samples collected weekly and representing all flow stages.
Multiobjective optimization in water quality and land management
Authors: Das Prasanta , Haimes Yacov Y.
Published: February 2008

A multiobjective planning framework for a river basin that considers both point and nonpoint source pollutants is presented. The need for an intergrated approach to pollution abatement originating from these two sources is discussed in the light of Public Law 92‐500. The need for including multiple objective functions in their noncommensurable formats and units are also discussed. Two broad‐based planning objectives considered are: economic development and environmental quality. The environmental quality model includes the following multiple objectives: (1) soil erosion, (2) phosphorus, (3) biological oxygen demanding load in the stream. Noninferior solutions and trade‐offs among the objectives are examined for several alternative planning scenarios using the surrogate worth trade‐off (SWT) method. The decision‐maker's role in obtaining the basin‐wide plan is discussed. Finally, the planning framework is applied to the Maumee River Basin study.
Climatological estimate of the average monthly energy and water budgets of Lake Tahoe California‐Nevada
Authors: Myrup L. O. , Powell T. M. , Godden D. A. , Goldman C. R.
Published: February 2008

An estimate of the average monthly energy and water budgets of Lake Tahoe, California‐Nevada is made from commonly available meteorological, hydrological, and limnological data. The water budget indicates that precipitation, discharge, runoff, and evaporation dominate the water balance in seasonal succession, each associated with an appropriate minimum or maximum in the lake water storage. The annual energy budget is dominated by the net radiation and evaporation terms with 93% of the radiation input used to evaporate water. The seasonal energy budget indicates that (1) energy storage is in phase with the radiation input and is a dominant term in the periods November–January and May–July, (2) evaporation reaches a maximum value in the fall, 3 months after the radiation maximum, (3) upward transfer of sensible heat from the lake surface reaches a maximum another 3 months later, in the winter, and (4) the sensible heat flux is downward in late spring and early summer, indicating stable stratification in the atmospheric surface layer over the lake during this period, a result of possible significance to air quality in the Tahoe basin. The energy storage and sensible heat transfer terms show large fluctuations in the fall which may be associated with large‐scale meteorological events during a season in which energy is trapped in the surface waters by stable stratification in the thermocline layer.
An energy budget analysis of water use by Saltcedar
Authors: Gay L. W. , Fritschen L. J.
Published: February 2008

Bowen ratio estimates of evapotranspiration (ET) over a stand of saltcedar (Tamarix chinensis) on the Rio Grande floodplain in central New Mexico provide (1) estimates of water use by saltcedar during hot, dry weather, (2) comparisons of ET measured at two different locations within the same stand, and (3) comparison of ET over natural stands with results obtained from four constant‐level lysimeters. The mean ET for 5 consecutive days (June 14–18, 1977) was 8.2 mm d−1 by the Bowen ratio and 7.9 mm d−1by the lysimeters. Vegetation on the lysimeters and at the Bowen ratio sites differed in density and vigor in a manner consistent with the evapotranspiration measurements. Given these differences, the agreement between methods is judged excellent.
Analysis of Arizona Flood Data Network for regional information
Authors: Tasker Gary D. , Moss Marshall E.
Published: February 2008

The technique known as Network Analysis for Regional Information is used for a network of stream‐gaging stations in northwest Arizona in order to suggest a logical gaging strategy for the area. This procedure uses a Bayesian estimation scheme to arrive at the relationship between information content of a regional regression and the level of data availability (measured by the number pf stations and harmonic mean record length). Superimposed on this relationship is the relationship between estimated network operating costs for planning periods of 10, 20, and 30 years for alternative gaging strategies. These relationships are used to develop the relationship between expected information content of the network and estimated cost of network operation, which, in turn, can be used to suggest the best gaging strategy to pursue in an uncertain future.
A statistical approach to station discontinuance
Authors: Wood Eric F.
Published: February 2008

The sequential probability ratio test (SPRT) is developed and applied to the station discontinuance problem. The decision whether to discontinue a station is dependent upon statistical considerations that include the error probabilities of accepting a model when it is incorrect as well as rejecting it when it is correct. Both error probabilities can be explicitly set by using the SPRT approach so that the decision rules are: accept model 1, accept model 2, continue to sample (cannot accept either). The error probability levels are a decision variable that depends upon the use of the data and the cost of collection. Procedures are developed for determining the expected benefits from sampling one additional time within the SPRT framework. The SPRT approach was applied to the Susquehanna River at Harrisburg, Pennsylvania.
Overview of conference on hydrologic data networks
Authors: Langbein W. B.
Published: February 2008

This conference is the latest involving conferences whose research includes work in what is called the design of data networks. The broader scope of this conference reflects, in my view, movement toward greater sophistication in research and in subject matter, and it is good that these kinds of critical inquiry are going on. The rough estimates mentioned at the conference show data collection to be big business, even though data storage and retrieval tend to attract most public attention. The design of data systems, that is, the efficiency and effectiveness, must also be concerned with the manner of collection, the places and numbers of observations, their costs, and their utility. These matters constitute the fundamentals. Yet in the face of the wide range of present and prospective uses, the complex range of objectives, and the diversity of variables the products of research and critical inquiry appear to find few applications. That subject as well as the needs and opportunities were examined at this conference.
Technology‐based effluent standards: The U.S. case
Authors: Freeman A. Myrick
Published: February 2008

This paper discusses the role of technology‐based standards in U. S. environmental policy, procedures used by EPA in establishing standards, issues in their implementation, and economic consequences. Technology‐based standards are shown to have complexities of their own and to involve difficult judgments about technology, feasibility, and the degree to which cost and benefit considerations should influence standard setting. Technology‐based standards are not necessarily easier to implement than other strategies.
Infiltration under rapidly varying surface water depths
Authors: Reeder John W. , Freyberg David L. , Franzini Joseph B. , Remson Irwin
Published: February 2008

Effects of fluctuations in surface water depth on infiltration rates into initially unsaturated soils were investigated by numerically solving the Richards equation. The numerical model was verified through comparison with published solutions of Philip and with the results of laboratory experiments on a well‐graded crushed dune sand. It was found that infiltration rates may incease with time in response to rapid rates of increase in water depth. Conditions under which this will occur are identified.
Water storage on forest foliage: A general model
Authors: Massman William J.
Published: February 2008

A model for the prediction of water accumulation on forest foliage is presented. It is general enough to include linear, exponential, or logarithmic forms for the buildup of accumulated water and to go from any one of these three limiting forms to any other in a continuous manner by varying a single dimensionless parameter. This equation unifies into a single form many other models used to predict water accumulation (from either rain or fog) on forest foliage. An exploration of the underlying assumptions relating drip rate to interception intensity shows how these other models differ from one another. Evaporation is included in the model by using another dimensionless parameter which may be very useful in regions where only an approximate estimate of the evaporation rate is available. However, to include evaporation correctly into the model it is necessary to define the water storage capacity first in order to properly interpret the model predictions.
A variance‐constrained reservoir control problem
Authors: Sniedovich Moshe
Published: February 2008

A dynamic programing solution procedure is developed for a class of variance‐constrained reservoir control problems. The variance constraint is incorporated as a penalty term in a nonseparable Lagrangian problem which is solved by a two‐stage procedure. First, the difficulty associated with the nonseparability of the problem is resolved by the consideration of a modified simpler separable problem which is solved by a simple additive dynamic programing recursion. Then the optimal solution to the nonseparable problem is found by a simple search algorithm. The entire discussion is devoted to the mathematical aspects of the problem and no consideration is given to the applicability of variance constraints as far as water resources management problems are concerned. The procedure is applied to a simple numerical example.
The incidence of water quality: A county level analysis
Authors: Asch Peter , Seneca Joseph J.
Published: February 2008

Relationships between nine quality characteristics of domestic water systems and the income and racial composition of the using populations are examined for a national sample of counties. Simple correlations suggest a regressive distribution for some but not all pollutants. More detailed analysis of two pollutants adjusts for variation in size of county population and shows a regressive distribution of fecal coliform but an income neutral distribution of cadminum. The findings are far from definitive but point to the type of analysis required to draw broader incidence conclusions.
Quantile estimation with more or less floodlike distributions
Authors: Landwehr J. Maciunas , Matalas N. C. , Wallis J. R.
Published: February 2008

The desirable properties of an estimator relative to a hypothetical population may be irrelevant in practice unless the population at issue more or less resembles the hypothetical population. Evidence that floods are distributed with long, stretched upper tails suggests that use of the more common distributions results in a rather precise underestimation of the extreme quantiles and thereby in the underdesign of flood protection measures.
Effects of lily pads on evaporation
Authors: Cooley Keith R. , Idso Sherwood B.
Published: February 2008

Measurements of evaporation from open water and water partially covered by lily pads have indicated that for the portion of the surface area covered by lily pads, evaporation is reduced to about 84% of that occurring from open water.
Completion of the list of analytical solutions for nutrient transport to roots: 1. Exact linear models
Authors: Cushman John H.
Published: February 2008

Solutions to a linear transport model for nutrient flow to roots are presented. The solutions concern no interroot competition and various types of interroot competition. Among the interroot competition problems considered are an imaginary cylinder a short distance out from the root through which no nutrient can pass and a cylinder for which only convective transport to the root exists. The solutions are for either a high nutrient concentration or a low concentration. All solutions presented are exact in the sense that they exactly solve the initial boundary value problems under consideration.
A depth‐area‐duration model of storm rainfall in the Southern Great Plains
Authors: Nicks A. D. , Igo F. A.
Published: February 2008

A depth‐area‐duration model for Oklahoma rainstorms was developed using 10 years of data from a dense network of recording rain gages covering a 3885‐km2 area. A nonlinear least squares procedure was used to fit the data to the model. The model developed can be used to convert storm center point rainfall amounts to mean rainfall in areas up to 3100 km2 and durations up to 24 hours. The model seems to have predictive value, especially for storms occurring in the Great Plains. Comparison of the model curves with actual depth‐area curves for two storms, Black Hills, South Dakota, and north central Oklahoma, showed that the model‐simulated depth‐area curves were within the experimental error of model development. Data from a network of gages located in the Chicago urban area were used to evaluate the model parameters with similar results.
A semianalytical solution for partial penetration in two‐layer aquifers
Authors: Javandel I. , Witherspoon P. A.
Published: February 2008

A semianalytical solution is presented for the problem of drawdown distribution in a two‐layer aquifer when the system is pumped from a well that is partially penetrating in one of the layers. The solution is used to illustrate the effects on aquifer behavior of partial penetration as well as the effect of a contrast in flow properties between the two layers. The validity of the solution has been verified against four available limiting cases. A method for analyzing field data is proposed, and an example is given to illustrate the procedure.
Physically based probabilistic models of infiltration, soil moisture, and actual evapotranspiration
Authors: Cordova Jose R. , Bras Rafael L.
Published: February 2008

Real‐time control of irrigation in areas of sparse rainfall requires probabilistic description of infiltration, soil moisture, and actual evapotranspiration. This work develops the probability density function of infiltrated water volumes as a function of climatic and soil parameters. This stochastic input is used with a physical‐conceptual model of the soil moisture depletion process to derive analytic expressions for the soil moisture transition probabilities over a given time period and the first two moments of associated actual evapotranspiration. Analytic results are corroborated with a case study example. A forthcoming paper by the authors illustrates the use of the derived expressions in an optimal decision model for deficit irrigation practices.
A similarity method for geothermal well test analysis
Authors: O'Sullivan Michael J.
Published: February 2008

The nonlinear partial differential equations governing mass and energy transport in a geothermal reservoir are reduced to simpler ordinary differential equations by the use of a similarity variable rt. For the idealization of a constant flow rate line source in a uniform horizontal reservoir the resulting equation can be numerically integrated for either two‐phase, single‐phase, or flashing flow.
Age dating of groundwater in fissured rock: Influence of water volume in micropores
Authors: Neretnieks Ivars
Published: February 2008

Age dating of groundwater by 14C measurements is sometimes used to indicate the residence time of the water. In fissured rock with a porous rock matrix the flow is in the fissures. The water‐filled pores of the rock may, however, be accessed by the tracer by diffusion. The residence time for a tracer can then be longer than the flow time. Model calculations were performed using data for granitic rock. For flow in large fissures (1 mm) the 14C age is 10–70 times larger than the water residence time. For small fissures (0.01 mm) the 14C age may be more than 1000 times larger.
Economics of rainfed cropping systems: Northeast Thailand
Authors: Johnson Sam H. , Charoenwatana Terd
Published: February 2008

Using a computer model to simulate effective rainfall, it is shown that a flexible rainfed cropping system based on a legume crop planted before rice has a greater expected return than present subsistent rainfed cropping systems. Combining a legume crop intercropped with cassava or kenaf further increases the expected returns yet maintains the stability of the new system. Further research is required to bring the farmer's yields up to match experiment station results and to facilitate effective transfer policies.
A leaky reservoir model for ephemeral flow recession
Authors: Peebles Roger W. , Smith R. E. , Yakowitz Sidney J.
Published: February 2008

The flood wave in ephemeral streams can often be portrayed accurately by assuming ‘instantaneous ’ rise to peak flood stage (depth) and specifying a recession curve. Here recession is modeled as a conceptual analog of discharge from a single leaky reservoir. Physically, the reservoir may be considered to approximate that portion of the ephemeral stream channel that is flowing at the onset of recession. The discharging reservoir is described by a continuity equation and by discharge‐stage (stream rating) and storage‐stage (reservoir configuration) relations. No input is routed through the reservoir; at the onset of recession the reservoir has water in storage. A good fit to observed curves is obtained by calibrating two parameters, reservoir leakage rate and initial storage (reservoir shape). The agreement is most sensitive to changes in initial storage. The best fit parameter values are physically plausible.
Determination of hydrogeological parameters using sinusoidal pressure tests: A theoretical appraisal
Authors: Black J. H. , Kipp K. L.
Published: February 2008

A method for determining the hydrogeological parameters of formations of interest based on a sinusoidal pressure fluctuation in an excitation borehole is proposed. Equations are derived which describe the dependence of pressures and phase lags outside the excitation borehole on distance, signal frequency, specific storage, hydraulic conductivity, and flow rates. These cover two distinct configurations: that of a point source deep within a water‐saturated elastic formation and that of a line source totally penetrating a confined aquifer. The ranges of application of these two arrangements are appraised using existing data on hydraulic diffusivities to derive likely excitation and response pressures for various flow rates and signal frequencies. The two configurations require the accurate measurement of phase shifts in the case of the point source and of amplitudes in the line source case, and it is concluded that the ranges of applications are useful but limited.
A mathematical model for predicting moisture flow in an unsaturated soil under hydraulic and temperature gradients
Authors: Dakshanamurthy V. , Fredlund D. G.
Published: February 2008

A theoretical model is presented to predict the moisture flow in an unsaturated soil as the result of hydraulic and temperature gradients. A partial differential heat flow equation (for above‐freezing conditions) and the two partial differential transient flow equations (one for the water phase and the other for the air phase), are derived in this paper and solved using a finite difference technique. Darcy's law is used to describe the flow in the water phase, while Pick's law is used for the air phase. The constitutive equations proposed by Fredlund and Morgenstern are used to define the volume change of an unsaturated soil. The simultaneous solution of the partial differential equations gives the temperature, the pore water pressure, and the pore air pressure distribution with space and time in an unsaturated soil. The pressure changes can, in turn, be used to compute the quantity of moisture flow.
Effects of floods on nutrient and metal concentrations in a coastal plain stream
Authors: Mulholland Patrick J. , Yarbro Laura A. , Sniffen Robert P. , Kuenzler Edward J.
Published: February 2008

Water quality in Creeping Swamp, a coastal plain stream in North Carolina, was monitored during two floods in 1976. The concentrations of most of the filterable substances studied remained relatively constant, particularly at the upstream station, CP‐20, which drained the least disturbed portion of the watershed. Concentrations of NO3 and dissolved organic carbon increased, and concentrations of Cl decreased during the floods at CP‐20. At the downstream station, CP‐10, which received effluents from a hog farm, concentrations of the filterable forms of N, P, K, and Fe increased markedly during floods. Indications were that increases in concentration of filterable substances during floods may be a better indicator of watershed disturbance than ambient concentrations. Despite the dominance of overland flow in the hydrologic regime and the abundance of organic material in the stream channel and floodplain, concentration patterns of the filterable constituents of streamflow during floods in Creeping Swamp are similar to the patterns in streams draining upland watersheds, where contact between runoff waters and the inorganic strata of watershed soils is likely to be much greater. The concentrations of particulate forms of phosphorus, silicon, and most of the metals studied increased during the rising limb of the hydrograph, peaked prior to peak streamflow, and decreased thereafter. The contribution of floods to total annual flux of P, Fe, Si, and Al in Creeping Swamp is especially great because of large increases in concentrations of the particulate forms of these elements as streamflow increases.
Risk models for flood levee design
Authors: Tung Yeou‐Koung , Mays Larry W.
Published: February 2008

In the design of flood levee systems there are many parameters and variables with associated uncertainties. This paper presents models which systematically analyze the various types of uncertainties in the hydrologic aspect as well as hydraulic aspect of design and analysis to define the risk and reliability of overtopping. Both static and time dependent risk models are developed. Results show that risk evaluated by the simple return period method can be underestimated by 10% to 50%, depending on the loading distribution model used. The risk‐safety factor relationships are shown to be very sensitive to the hydrologic loading probability model adopted, so that composite models are suggested for risk analysis.
A probe method for soil water sampling and subsurface measurements
Authors: Harrison W. D. , Osterkamp T. E.
Published: February 2008

A technique employing lightweight driving and sampling equipment to obtain interstitial soil water samples is described. It can also be used for hydraulic conductivity, temperature, and water pressure measurements. The sampler consists of a probe, with a shield, a porous metal filter and a check valve which are connected to the surface by plastic tubing inside standard EW or A drill rod. The water sample is collected with a bailer lowered inside the tubing from the surface. The tubing can then be cleared and sealed without pulling the drill rod and the sampler driven to the next depth. A method of estimating the probe shape factor is given. Some of the difficulties unique to sampling interstitial water in thawed subsea permafrost are discussed.
Numerical simulation of the transport and speciation of nonconservative chemical reactants in rivers
Authors: Chapman Bernard M.
Published: February 2008

A computer model, previously used to simulate the transport of conservative chemical components in streams, has been used as a basis for a more complex model which includes the effects due to processes such as precipitation and sedimentation and adsorption onto stationary reactive surfaces which render the reactants nonconservative with respect to the flowing waters. The model uses, as before, the program MINEQL as a basis for the chemical equilibrium submodel. The physical transport submodel employs a convolution integral procedure, with an approximate form of the impulse function to solve a one‐dimensional convective‐diffusion equation. Although the model essentially assumes chemical equilibrium, a pseudokinetic treatment is necessary to deal with redissolution of precipitates and dissociation of surface species. Simple hypothetical examples are given to illustrate the operation of the model. The model is then applied to an experiment in which the base NaOH is injected into a creek draining an abandoned base metal mine. Concentrations of the metals Zn, Al, Cu, Fe, and Na in the flowing waters, expressed in terms of total metals and as suspended solids, are followed as a function of time and distance downstream. Significant sedimentation of the precipitates formed is evident, and the existence of substantial quantities of protons and/or metal ions, adsorbed on the streambed, is implied from the model calculations. The model was able to simulate successfully the major features observed. This simulation involved the simultaneous formation of five distinct precipitates and one surface species.