bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrodynamic dispersion during absorption in a fine sand: 2. The constant flux case
Authors: Watson K. K. , Jones M. J.
Published: February 2008

The conclusions of an earlier paper involving hydrodynamic dispersion during absorption in a fine sand under constant concentration conditions are discussed in relation to the support they provide for the concept of a velocity dependent dispersion coefficient. The present study analyzes the more exacting constant flux case using influent boundary fluxes of water ranging from 3.28 × 10−7 ms−1 to 1.05 × 10−5 ms−1. These values allow the ratio of the mechanical dispersion component of the dispersion coefficient to the molecular diffusion component to vary from 0.43 to 5.81. For all cases, computer‐based numerical solutions are compared with experimental results using reduced space and time variables in the presentation of the data. It is observed that the bandwidth of the scatter of the experimental data is generally greater than the spread of the computed concentration profiles. In keeping with the constant concentration results, this suggests that the form of the experimental data is not inconsistent with the concept of a hydrodynamic dispersion coefficient which is velocity dependent. In all cases a dispersion length of 0.0001 m was used.
A derived flood frequency distribution using Horton Order Ratios
Authors: Hebson Charles , Wood Eric F.
Published: February 2008

A flood frequency distribution is derived from assumed climatic distributions and the geomorphologic unit hydrograph (GUH) model of catchment response. The derived distribution is tested on two Appalachian Mountain catchments and shows good agreement with historical data. Because the GUH is rooted in catchment shape and geomorphology, this derived frequency distribution may be a promising vehicle for studying the effect of catchment shape on flood frequency characteristics. Furthermore, it is felt that the question of catchment homogeneity and similarity, necessary for regional flood estimation, can also be studied through the GUH derived flood distribution.
Estimation of Pearson type 3 moments
Authors: Lall Upmanu , Beard Leo R.
Published: February 2008

Estimates of frequencies of floods and other events are based on statistical distributions estimated from sample data. The most common and generally the most robust technique used is the fitting of data by the method of moments. It is well known that moments of the data of an order higher than 1 are biased estimates of the moments of the population from which the data represent a sample. Much work has been done in deriving factors or functions by which the bias can be corrected. All of such work has been based on considering the variation of statistics of various samples drawn from a specified population, whereas the real interest is in the range of likely parent population parameters corresponding to a statistic obtained from a unique sample. It is recognized that there is no solution to this problem without an assumption of the range and distribution of such parameters as they occur in nature. The study described herein examines this question with regard to a particular functional form of parent distribution and for the case where the a priori distributions of the parameters are uniform, that is, where all values of a particular parameter are equally likely on an arithmetic scale. The distribution function studied is the Pearson type 3, and the parameter of primary attention is the skew coefficient.
Benefits from joint treatment of municipal and poultry‐processing wastewater
Authors: Epp Donald J. , Young C. Edwin , Rossi Daniel
Published: February 2008

The costs of treating wastewater from poultry‐processing plants and municipalities are simulated for joint treatment and separate facilities. Three sizes of poultry processing plants (51,000 to 207,000 birds per day) and six sizes of communities (3,000 to 20,000 people) were studied, and costs were developed for lagoon, activated sludge, and trickling filter systems. Lagoon systems are cost effective both for separate and joint treatment. Trickling filter systems cost less than activated sludge systems when only domestic wastes are treated. The reverse is true when poultry processing wastes are introduced. When activated sludge or lagoon treatment is used, joint treatment gives a substantial cost saving for any size of poultry processing plant, regardless of community size. The potential savings from joint treatment are sufficient to pay for up to 6 miles (9.6 km) of gravity main transmission of poultry processing plant wastes to a municipal treatment plant.
Asymptotic distribution of the maximum deficit with correlated, partially regulated outflows
Authors: Troutman Brent M.
Published: February 2008

The asymptotic distribution of the maximum accumulated deficit with partially regulated, Markov‐dependent net outflows having a Bernoulli distribution is derived, and the distribution for independent, continuous outflows is presented. It is demonstrated that under partial regulation the maximum deficit behaves as log n, where n is the length of the series; this is to be contrasted with the n½ behavior exhibited by fully regulated outflows. Also, as would be expected, the presence of correlation tends to increase the magnitude and variability of the maximum deficit.
Chemical composition and spatial variation of bulk precipitation at a coastal plain watershed in South Carolina
Authors: Richter Daniel D. , Ralston Charles W. , Harms William R.
Published: February 2008

Bulk precipitation was collected for analysis of ionic constituents at eight rainfall stations over a 4‐year period at a 500‐ha watershed in the Lower Coastal Plain of South Carolina. Mean annual deposition rates of ions in greatest supply, Cl−, SO42− ‐S, Ca2+, and Na+, were respectively 14.2, 7.51, 5.69, and 5.66 kg/ha. Annual deposition rate for total inorganic N (NH4+ −N plus NO3− −N) was about 2.6 kg/ha and for orthophosphate‐P about 0.12 kg/ha. Spatial variation of annual depositions to the eight rainfall stations was smallest for SO42−, NO3−, and Ca2+, with coefficients of variation (CV) less than 10%. Variation of annual inputs to the eight collectors was intermediate for Mg2+, Cl−, H+, and Na+ with CV ranging between 13.9 and 21.5%, whereas the CV for annual inputs of NH4+, PO43−, and K+ exceeded 30%. Sample size estimates for this 500‐ha watershed indicated that 19 collectors should provide estimates of the annual bulk precipitation inputs within 10% of true means for 7 of 10 ions (SO42−, NO3−, Ca2+, Mg2+, Cl−, H+, and Na+) and that more than 35 collectors would be necessary to provide similar confidence intervals for annual inputs of NH4+, PO43−, and K+ (± 10% at P < 0.05). Although estimates of annual bulk precipitation inputs may be quite variable over local areas, control of sampling errors can be gained by increasing the number of collectors.
Approximate sampling distribution of the serial correlation coefficient for small samples
Authors: Tasker Gary D.
Published: February 2008

The probability density function for the sample serial correlation coefficient r can be approximated byf(r) = (β(½, ½(T + 1)))−1(1 − r2)½(T− 1)(1+ c2 − 2cr)−½(T), whereβ is the Beta function, T = n− 2, c = ρ − [(1 + ρ)/(n − 3)], n is the number of observations, and ρ is the population lag one serial correlation. This distribution is derived from a large Monte Carlo study at points between ρ= −0.9 and ρ = 0.9 and for n =10, 20, and 30.
Hydrologic effects of clearcutting and wildfire on steep granitic slopes in Idaho
Authors: Megahan Walter F.
Published: February 2008

Many of the environmental impacts of logging and wildfire are caused by changes in the hydrologic response of slopes after disturbances. This study was conducted to evaluate changes in inflow, storage, and outflow for 3‐year periods before and after clearcut logging and wildfire on two steep, granitic microwatersheds in Idaho. Clearcutting alone and clearcutting plus wildfire increased annual peak snow water equivalent and snowmelt rates an average of 41% and 30%, respectively. The greater volume and rate of snowmelt caused respective increases in the peak piezometric rise and in total piezometric storage, amounting to 47% and 27%. Accordingly, the total volume of subsurface flow intercepted by the roadcut was increased 96% and was accompanied by 27% greater peak flow rates. None of the above responses were detectable on an adjacent watershed that was burned by wildfire alone. Evapotranspiration was reduced on both watersheds after clearcutting or wildfire, as indicated by increases in the unsaturated soil water content at the end of the growing season amounting to 44 and 72%, respectively. Accelerated mass erosion on clearcut slopes, and accelerated surface and mass erosion on roads and in channels below roads, can result from such changes.
Control of DO level in a river under uncertainty
Authors: Spear R. C. , Hornberger G. M.
Published: February 2008

A previously developed regionalized sensitivity analysis for exposing critical uncertainties in models of environmental systems is extended to study control of systems for which there is a good deal of uncertainty in the mathematical model used to describe the appropriate physical, chemical, and biological processes. The method is based on a binary classification of Monte Carlo simulation results as being either satisfactory or unsatisfactory in terms of controller performance. Contrasts in parameters associated with the two classes are elucidated by statistical analysis. This allows the selection of a set of control parameters that maximizes the probability of acceptable behavior in the presence of uncertainty in process parameters. The method is applied to the problem of regulating the discharge from a lagoon with the object of preventing DO from falling below a predetermined standard. It was found that for this system the desired behavior of the controlled process can be achieved with a probability of 0.84 with a particularly simple controller design. Nevertheless, the results suggest that even modest levels of uncertainty in the process parameters can have a considerable effect on the controller performance and that additional attention should be devoted to the design of robust controllers for environmental systems.
A methodology for evaluation of flood forecast‐response systems: 2. Theory
Authors: Krzysztofowicz Roman , Davis Donald R.
Published: February 2008

A methodology for evaluation of the performance of flood forecast‐response (FFR) systems is presented. It is built of (1) a model of the FFR process and (2) a set of performance measures. The FFR process is formulated as a finite, random duration, Markovian decision process which outputs the expected annual loss (cost of response plus flood damage sustained). The sequence of forecasts of the flood crest and the actual river stages are described by a two‐branch Markov chain of order one. The decision maker's response is represented by a strategy defined on a three‐dimensional state vector and time. The performance measures consist of a value, an efficiency, and an expected opportunity loss for each system component as well as the total system. They are defined on a vector of outputs, each output being computed for a distinct scenario of system operation. Two evaluation models are constructed: one for a single decision maker and another for an arbitrary collection of decision makers along a reach (e.g., a community).
A proposed upstream weight numerical method for simulating pollutant transport in groundwater
Authors: Sun Ne‐Zheng , Yeh William W.‐G.
Published: February 2008

An alternative upstream weighting numerical method is proposed to simulate the transport process in groundwater under a variety of conditions. The discretized system of the solute transport equations is derived from the integral form that expresses the balance of mass in each element. An upstream weight that depends on the local Peclet number is directly added to the basis functions. When convective transport dominates the dispersive transport, this technique can eliminate the oscillation of solutions efficiently, with only a nominal increase of computation effort over that of the general linear triangular Galerkin finite element method. The accuracy of the proposed numerical model is tested against two classical problems for which analytical solutions exist. The agreement is nearly exact. An additional numerical example is used to illustrate the applicability of this model.
A Simple Analytical Solution for the Boussinesq One‐Dimensional Groundwater Flow Equation
Authors: Tolikas Panagiotis K. , Sidiropoulos Epaminondas G. , Tzimopoulos Christos D.
Published: February 2008

An approximate analytical solution to the Boussinesq equation is presented here. Uniform initial conditions and a step function increase of piezometric head on the boundary are assumed. The one‐dimensional problem is reduced to an ordinary differential equation through Boltzmann's transformation, and a technique exploiting some basic characteristics of the exact solution leads to an approximate polynomial solution of the problem. The technique presented here can also be applied to one‐dimensional nonlinear diffusion problems. A numerical procedure incorporating some of the analytical characteristics of the exact solution is presented. A discussion concludes the paper.
Microclimate of Arctic Tree Line 2. Soil Microclimate of Tundra and Forest
Authors: Rouse Wayne R.
Published: February 2008

Forest and tundra soils display distinctive microclimates for a climatically normal year at Churchill. Forest soils are substantially warmer in the active layer than those of the tundra but the tundra active layer is deeper. Forest soils are much wetter than those of the tundra. This results from the deep winter snow pack, which provides abundant meltwater to already thawed soils. The soils remain wet throughout the year, and the large latent heat release delays the freezing of forest soils until a snow pack is established. As a result, soils stay relatively warm throughout winter and thaw rapidly and deeply before snow pack melting in the spring. The thaw period in the tree rooting zone is about 6 months, compared to 4 months at the same depth in tundra. The magnitude of soil heat storage is large, comprising 18% and 16% of net radiation in tundra and forest, respectively, during the thaw season. During freeze back it is the dominant heat exchange process. Between 80% and 90% of the total soil heat storage is involved in the latent heat exchange accompanying thawing and freezing. Soil heat flux plates strongly underestimate the ground heat exchange and are unreliable in permafrost terrain.
Specification of Objectives by Group Processes in Multiobjective Water Resources Planning
Authors: Deason J. P. , White K. P.
Published: February 2008

A weak link in previous attempts to apply multiobjective decision‐aiding tools to actual decision problems has been the initial specification of a usable set of objectives. One new approach to this difficult problem applies findings about group processes to the development of a suitable procedure for generating and structuring ideas. The procedure, in turn, is applied to determine a set of objectives for the selection of a portfolio of water projects. The procedure results in the definition of a set of objectives that is minimal, operational, complete, decomposable, nonredundant, and hierarchically structured.
Optimal Determination of Loss Rate Functions and Unit Hydrographs
Authors: Ünver Olcay , Mays Larry W.
Published: February 2008

An optimization model is presented that can be used in the determination of loss rate functions and unit hydrographs using observed rainfall and runoff data. Composite unit hydrographs and loss rate parameters can be determined by using several multiperiod storms simultaneously or using individual multiperiod storms. The model is a nonlinear programming problem so that a generalized reduced gradient method is used as the solution technique. Kostiakov's, Philip's, Horton's, and the ϕ index methods are used to illustrate the model for comparative purposes. An infiltration equation that includes rainfall intensity is also introduced and is compared with the others by using the optimization model. The model is applied to storms for a hypothetical example, Shoal Creek watershed in Austin, Texas, and Wills Creek watershed near Cumberland, Maryland. A comparison of the new model with earlier optimization procedures is also presented.
The Performance of LDR Models for Preliminary Design and Reservoir Operation
Authors: Stedinger Jery R.
Published: February 2008

Since their introduction, linear decision rule (LDR) chance‐constrained reservoir models have held out promise of developing into simple reservoir screening models and of producing reasonable operating policies. Single and multiple LDR models using two release rule structures are examined in the context of a multiple‐purpose reservoir operating problem. The LDR models were of questionable value for screening purposes in this instance. As operating policies, computed LDR policies were found to be less efficient than simple alternatives at meeting water supply and minimum storage targets when subject to constraints on available active or control storage capacity.
Link Length Distributions in Drainage Networks With Lakes
Authors: Mark David M. , Averack Richard
Published: February 2008

A classification system for stream links in drainage networks containing lakes is introduced. For two study areas the observed frequencies of these link types differ significantly from expected values predicted by topological randomness. Mean link lengths vary significantly across link types, with links beginning at point sources tending to be longer than other types. The mixed‐gamma distribution provides a good fit to link length distributions. The mixing parameters for link types beginning at point sources are similar to values reported for exterior links in lake‐free networks. Shape parameters for most other link types are near or below 2. Because the glacially deranged drainage systems studied are not adjusted to fluvial processes, frequency distributions of link lengths more closely approach the exponential distribution which should characterize randomly merging links.
The Distribution of Catchment Coverage by Stationary Rainstorms
Authors: Eagleson Peter S.
Published: February 2008

The occurrence of wetted rainstorm area within a catchment is modeled as a Poisson arrival process in which each storm is composed of stationary, nonoverlapping, independent random cell clusters whose centers are Poisson‐distributed in space and whose areas are fractals. The two Poisson parameters and hence the first two moments of the wetted fraction are derived in terms of catchment average characteristics of the (observable) station precipitation. The model is used to estimate spatial properties of tropical air mass thunderstorms on six tropical catchments in the Sudan.
Objective Identification of Pools and Riffles
Authors: O'Neill Michael P. , Abrahams Athol D.
Published: February 2008

This paper presents a new technique for objectively identifying pools and riffles. The technique is termed the bed form differencing technique and as its data base has bed elevations surveyed at a fixed interval along the channel. These elevations are differenced, and the difference or elevation change values are used to identify pools and riffles. Where the cumulative elevation change since the last bed form exceeds a certain tolerance value, a new bed form is considered to exist, the type of bed form being determined by the direction of the elevation change. Analysis of a small stream in western New York suggests that the most realistic pool‐riffle sequence is obtained where the tolerance value is 0.75 times the standard deviation of the difference values. The bed form differencing technique can be used to identify bed forms other than pools and riffles, such as ripples and dunes, by simply modifying the surveying interval to reflect the scale of the bed forms.
An Evaluation of Methods for Calculating the Concentration of Suspended Bed Material in Rivers
Authors: Pizzuto J. E.
Published: February 2008

A modified Rouse equation is used to predict the average concentration of suspended bed material in rivers and canals with sandy, dune‐covered beds. Equations of Einstein, Itakura and Kishi, and Engelund and Fredsoe are used to calculate the absolute concentration near the bed, Ca. Calculations based on the Engelund‐Fredsoe equation are consistently about 31 times too high. A modified Einstein equation overpredicts high concentrations and underpredicts low concentrations. The median predicted con‐ centration is only 20% too high, however. The Itakura and Kishi equation is the most successful theory; predicted concentrations are overestimated by only 50% on the average. Better results, however, are obtained using a constant value of 22,258 ppm for Ca in the Rouse equation, suggesting that Ca varies within a much smaller range than is predicted by current theories. A simple regression equation (r = 0.88) for the average concentration is also obtained. The regression equation is the most successful of all of the methods tested here.
An eigenvalue solution continuous in time to the spatially discretized solute transport equation in steady groundwater flow
Authors: Hwang Jack C. , Cho Woncheol C. , Yeh G. T.
Published: February 2008

The spatially discretized two‐dimensional solute transport equation in a steady groundwater flow was solved by an eigenvalue technique. The solution is exact in time. An explicit expression was obtained for each nodal point as a function of time. Thus the computer code can be implemented to calculate solute concentration at any nodal point at any given instant with a direct computation. The general solution can be obtained explicitly for transient boundary conditions and variable constant source loads. The solution for steady boundary conditions can readily be derived from the general solution. The method presented herein can provide convenience of data retrieval, particularly in groundwater management modeling.
Variational‐Lagrangian Analysis of Aquifers With Application to Artesian Wells
Authors: Biot M. A. , Delmer A.
Published: February 2008

A unifying variational principle of virtual dissipation of wide interdisciplinary generality is discussed in the more restricted context of aquifer analysis. It is applied to artesian well problems, one with constant drawdown, the other with constant pumping rate for both small and large well capacity. Numerical agreement with known result is excellent. Drawdown is also derived for ranges of values not covered by standard results. The computational work is simple and performed on a hand computer.
Detection of Linear Boundaries by Drawdown Tests: A Semilog Type Curve Matching Approach
Authors: Sageev Abraham , Horne Roland N. , Ramey Henry J.
Published: February 2008

A new method for pressure drawdown analysis in reservoirs affected by linear boundaries is developed. This method is based on a semilog curve matching approach and may be applied to both constant pressure and impermeable linear boundary cases. A semilog type curve is presented by which the distance between a well and the linear boundary may be estimated. The new analysis method is an improvement over the current double straight line analysis method. The pressure response of the well is matched without the need to find two straight lines, and several advantages result. First, the analysis may be performed for interference tests for which the first semilog straight line never develops. Second, the duration of the test required for the new method is shorter by an order of magnitude than that required for existing semilog methods, since it is not necessary to wait for the second straight line to develop.
An alternating direction galerkin technique for simulation of contaminant transport in complex groundwater systems
Authors: Daus A. D. , Frind E. O.
Published: February 2008

A general contaminant transport simulation technique based on a Galerkin finite element representation in space and an alternating direction time‐stepping scheme is developed. The formulation, which is in terms of natural coordinates following the principal directions of hydraulic conductivity of the medium, decouples the spatial components of the equations, leading to tridiagonal matrices. The numerical accuracy can be easily controlled in each principal direction through the well‐established Peclet and Courant numbers. Results are found to be comparable to those from the classic finite element scheme, but the cost of computation is generally much less because the computational effort varies only linearly with the grid size. The technique is thus well suited for transport simulations with complex layered anisotropic groundwater systems requiring large and detailed grids.
Reservoir Impacts: A Synthesis of a 10‐Year Research Project
Authors: Napier Ted L. , Goe W. Richard , Carter Michael V.
Published: February 2008

The purpose of this paper is to present a synthesis of research findings derived from longitudinal monitoring of a reservoir affected community group located in the urban fringe of a major metropolitan community in central Ohio. Data were collected at three time periods to assess the social impacts of rapid change on local people. Data were collected over a 10‐year period using standardized measurement devices to ensure comparability of the information collected. The research findings demonstrate that extensive modification of social and physical environments did not result in the destruction of the social fabric of the affected group. Observations over time suggest that the affected group has accommodated many of the changes introduced in the community and has accepted the lake project.
Reply [to “Comment on ‘Conjunctive Use of Groundwater and Surface Water for Irrigated Agriculture: Risk Aversion’ by John D. Bredehoeft and Robert A. Young”]
Authors: Bredehoeft John D. , Young Robert A.
Published: February 2008

This serves as an introduction for the following sequence of five papers on interactive water resources and environmental management, policy modeling, and model use. We review some important shortcomings of many management and policy models and argue for improved human‐computer‐model interaction and communication. This interaction can lead to more effective model use which in turn should facilitate the exploration, analysis, and synthesis of alternative designs, plans, and policies by those directly involved in the planning, management, or policy making process. Potential advantages of interactive modeling and model use, as well as some problems and research needs, are discussed.
Evaluating Alternative Investment Programs for the Mediterranean‐Dead Sea Project
Authors: Gross Amnon , Zahavi Jacob
Published: February 2008

A methodology, geared toward the prefeasibility study, is devised for evaluating alternative investment programs in the Mediterranean‐Dead Sea (MDS) project, which is based on comparing the optimal configuration for each alternative route of the water carrier. The maximal energetic benefits are calculated using two interrelated optimization problems: a multiperiod optimization, involving dynamic programming, to find the optimal operating regime of the system over time, and a one‐period optimization, imbedded in the multiperiod optimization, involving probabilistic methods, to find the loading point of the hydro unit that maximizes the value of the energy displaced. Cost‐benefit analysis is used to find the optimal size of the hydroelectric components, including the hydro unit size and the water carrier diameter. The model has been applied to evaluate the economic feasibility of the MDS project and to rank the various alternatives by economic merit, and some of the results are discussed.
A Two‐Phase Numerical Model for Prediction of Infiltration: Case of an Impervious Bottom
Authors: Morel‐Seytoux Hubert J. , Billica Judith A.
Published: February 2008

A numerical procedure to describe soil moisture evolution in a column with an impervious bottom for varied boundary conditions at the soil surface is presented. The procedure accounts for viscous resistance to simultaneous flow of water and air and for air compression. The method was programmed for the computer. In one case study a 10‐cm‐deep soil column is subjected to a steady rainfall at the surface. Moisture profiles and infiltration rates are calculated by both the one‐ and two‐phase approaches. Comparison demonstrates the magnitude of the error incurred when air effects are not incorporated in the analysis. In a second case study a 100‐cm‐deep soil column is subjected to a sequence of two different rainfall rates. Again comparison of results by the two approaches (traditional versus two phase) provides a measure of the error resulting from the neglect of air effects in the analysis. Not only is capacity infiltration rate greatly reduced after ponding of soil surface but the ponding times themselves are greatly reduced due to increased viscous resistance to flow when airflow is considered in the analysis. The more rigorous analysis complicates little the basic numerical procedures and performs the calculations at essentially no extra cost.
Analysis of Hydrodynamic Dispersion in Discrete Fracture Networks Using the Method of Moments
Authors: Rasmuson Anders
Published: February 2008

Recent field investigations in crystalline rock give strong indications that water flows in largely isolated channels in fissured rock. The channels are located in fracture planes and may or may not connect to other channels in the same plane or at fracture intersections. In the present paper, hydrodynamic dispersion in such fracture networks is investigated using the concepts of residence time distribution theory. It is shown that from a set of simple relations, at least the first four statistical moments for the system response are easily obtained even for complicated networks. In particular, an equivalent dispersion coefficient may be calculated from the second central moment (variance). The effect of channeling generally decreases in systems with many mixing steps. A criterion, based on the coefficients of skewness and kurtosis, is derived for when the response of the system is in accordance with the diffusion‐dispersion model. Examples show that this limit may not be obtained under realistic repository conditions in fissured rock.
Scattering Functions and Infiltration
Authors: Philip J. R.
Published: February 2008

In the theory of the scattering of plane harmonic waves by an obstacle Van de Hulst theorems give simple connections between the forward scattering function and the total extinction cross section. In this paper analogous theorems are proved for two‐ and three‐dimensional quasi‐linear steady flows in saturated soils from finite cavities of arbitrary size and shape, with arbitrary boundary conditions on the cavity surface. These theorems connect “downward wetting functions” and total cavity flow rates. Simple relations are established between scattering functions in the wave context and wetting functions in the soil water context. The important consequence is that flow rates for a large range of cavity shapes can be inferred simply and directly from extant results on forward scattering functions. It is proved that at large r (dimensionless radius), flow is concentrated in a small angular region vertically beneath the cavity and has a Gaussian distribution with angular standard deviation (sr)−½ (s=½αl; α, sorptive number; l, characteristic cavity length.)
Adaptation of the Carter‐Tracy Water Influx Calculation to Groundwater Flow Simulation
Authors: Kipp Kenneth L.
Published: February 2008

The Carter‐Tracy calculation for water influx is adapted to groundwater flow simulation with additional clarifying explanation not present in the original papers. The Van Everdingen and Hurst aquifer‐influence functions for radial flow from an outer aquifer region are employed. This technique, based on convolution of unit‐step response functions, offers a simple but approximate method for embedding an inner region of groundwater flow simulation within a much larger aquifer region where flow can be treated in an approximate fashion. The use of aquifer‐influence functions in groundwater flow modeling reduces the size of the computational grid with a corresponding reduction in computer storage and execution time. The Carter‐Tracy approximation to the convolution integral enables the aquifer influence function calculation to be made with an additional storage requirement of only two times the number of boundary nodes more than that required for the inner region simulation. It is a good approximation for constant flow rates but is poor for time‐varying flow rates where the variation is large relative to the mean. A variety of outer aquifer region geometries, exterior boundary conditions, and flow rate versus potentiometric head relations can be used. The radial, transient‐flow case presented is representative. An analytical approximation to the functions of Van Everdingen and Hurst for the dimensionless potentiometric head versus dimensionless time is given.
A Point Rainfall Generator With Internal Storm Structure
Authors: Marien J. L. , Vandewiele G. L.
Published: February 2008

A point rainfall generator is a probabilistic model for the time series of rainfall as observed in one geographical point. The main purpose of such a model is to generate long synthetic sequences of rainfall for simulation studies. The present generator is a continuous time model based on 13.5 years of 10‐min point rainfalls observed in Belgium and digitized with a resolution of 0.1 mm. The present generator attempts to model all features of the rainfall time series which are important for flood studies as accurately as possible. The original aspects of the model are on the one hand the way in which storms are defined and on the other hand the theoretical model for the internal storm characteristics. The storm definition has the advantage that the important characteristics of successive storms are fully independent and very precisely modelled, even on time bases as small as 10 min. The model of the internal storm characteristics has a strong theoretical structure. This fact justifies better the extrapolation of this model to severe storms for which the data are very sparse. This can be important when using the model to simulate severe flood events.
A Soil Water Extractor That Minimizes CO2 Degassing and pH Errors
Authors: Suarez D. L.
Published: February 2008

Soil water extractors that are presently used to sample the unsaturated zone cause substantial CO2 degassing within the sampler. The resultant pH errors are sufficiently large that the measured pH values are unacceptable for determining specific mineralogic controls on solution composition. The pH increases can also result in oxide and carbonate precipitation within the extractor thereby altering solution composition. The soil water samplers described here reduce CO2 degassing by minimizing the gas‐liquid ratio in the extractor and by flushing several volumes of solution through the liquid‐filled sampling container before a sample is removed. The construction of both shallow and deep samplers is described.
Statistical Inference of Spatial Random Functions
Authors: Feinerman E. , Dagan G. , Bresler E.
Published: February 2008

A methodology to infer the spatial distribution of the statistical moments of a stationary normal random spatial function based on a finite set of measured values is described. The uncertainty of estimation of the parameters characterizing the probability density function (pdf) is incorporated in the process of inferring and conditioning. Relationships generalizing the traditional approach of stochastic interpolation and simulation have been derived. They yield: (i) an estimate of the conditional expectation; (ii) an estimate of the conditional multivariate normal (MVN) covariance and variance; and (iii) a new quantity, the variance of the estimated variance. The method is illustrated for a two‐dimensional synthetic example with both estimated mean and variance regarded as random. A set of 60 points was generated within a square of sides equal to unity from a MVN population with zero mean, unity variance and exponential covariance with a linear integral scale of 0.3. Contour maps of the inferred expected values and variances are drawn and compared with maps of kriged values and maps of kriged variances. Contour maps of variances of estimation of the variance are given to demonstrate the uncertainty of variance estimates. The unconditional and conditional statistical moments of the space average (block value), , were also evaluated. The reduction of the uncertainty of the inferred random variable as the number of measured points increases is demonstrated with the same synthetic example.
Synopsis of Analytic Solutions for the Temperature Distribution in a River Downstream From a Dam or Reservoir
Authors: Gosink J. P.
Published: February 2008

A synopsis of analytic solutions for river temperature downstream from a dam is presented. Transient, convective, and diffusive effects are considered as well as periodic and spatially varying surface heat exchange. Two new solutions of the transient equation for heat transport in a river with fluctuating surface heat exchange have been developed. The first describes the transient‐convective temperature response in a river subjected to a combination of fluctuating and spatially varying surface heat transfer. The second new solution represents a complete transient‐convective‐diffusive solution to the equation for river temperature when surface heat exchange is dependent upon periodically varying meteorological conditions. The parameters determining the amplitude of the river response, as well as the lag between atmospheric forcing and river response, are delineated.
A Conjugate Gradient Finite Element Model of Flow for Large Multiaquifer Systems
Authors: Gambolati Giuseppe , Sartoretto Flavio , Uliana Fiore
Published: February 2008

A quasi three‐dimensional finite element model based on the conjugate gradient technique is developed and applied to the analysis of subsurface flow occurring in complex heterogeneous multiaquifer systems. Transient leakage across the aquitards is fully taken into consideration using the convolution approach originally derived by Herrera (1970). The convolution integrals enhance the favorable features of the modified conjugate gradients (MCG), which prove to be a very efficient tool for the solution of the integrodifferential model. The high performance of MCG results from two combined factors: (1) the diagonal dominance of the assembled finite element matrix, which is emphasized by the integral contributions; (2) the essential reducibility of the matrix for a wide range of time step values, which is due to the virtual decoupling of the aquifer equations. The preconditioning of the conjugate gradient scheme is therefore improved, and a good convergence occurs after a number of iterations smaller than (N/n)½, N and n being the overall number of nodes and aquifers, respectively. The computational cost of the model is generally low, and its relative efficiency tends to increase for small to moderate time steps and for complex multiaquifer systems where several interconnected aquifers are simulated.
A Heuristic Solution Procedure for Expansion Sequencing Problems
Authors: Kim Sheung K. , Yeh William W‐G.
Published: February 2008

A heuristic solution procedure is developed for capacity expansion problems encountered in water resources development. The heuristic solution procedure consists of two steps. In the first step, project sequence is generated and capacity refinement is done in the second step. A shortest path dynamic programming solution scheme is used as a “return function” for the sequence generation step, and a univariate direct search algorithm is used for capacity refinement. The proposed solution procedure is tested for both capacitated and uncapacitated example problems with a finite planning horizon. The results indicate that the proposed heuristic solution procedure is superior to other solution procedures selected for comparison in finding an optimum expansion policy consisting of a sequence of project developments, investment timing, and sizing for each project.
Radionuclide Transport in Fast Channels in Crystalline Rock
Authors: Rasmuson Anders , Neretnieks Ivars
Published: February 2008

Recent field investigations in crystalline rock give strong indications that water flows in largely isolated channels in fissured rock. The present paper sets out to investigate radionuclide transport in such channels including diffusion into the rock matrix. It is shown that the uptake from a cylindrical hole in a matrix is much more effective, per unit contact area, than a flat surface (semi‐infinite solid). Comparison of diffusion from cylindrical and slit‐formed channels shows that the differences in interfacial flux are minor. A slit‐formed channel may therefore be approximated by a cylindrical one. Diffusional transport in the matrix is then treated as one dimensional instead of two dimensional, which gives a considerable numerical simplification. A simple estimate of the “penetration depth” into the cylindrical region, i.e., the location of the diffusional front, is proposed. By using the integrated finite difference method a number of radionuclide transport calculations are performed for the case of flow and dispersion in a cylindrical channel coupled to diffusion and sorption in the matrix.
The inverse problem for confined aquifer flow: Identification and estimation with extensions
Authors: Loaiciga Hugo A. , Mariño Miguel A.
Published: February 2008

The contributions of this work are twofold. First, a methodology for estimating the elements of parameter matrices in the governing equation of flow in a confined aquifer is developed. The estimation techniques for the distributed‐parameter inverse problem pertain to linear least squares and generalized least squares methods. The linear relationship among the known heads and unknown parameters of the flow equation provides the background for developing criteria for determining the identifiability status of unknown parameters. Under conditions of exact or overidentification it is possible to develop statistically consistent parameter estimators and their asymptotic distributions. The estimation techniques, namely, two‐stage least squares and three stage least squares, are applied to a specific groundwater inverse problem and compared between themselves and with an ordinary least squares estimator. The three‐stage estimator provides the closer approximation to the actual parameter values, but it also shows relatively large standard errors as compared to the ordinary and two‐stage estimators. The estimation techniques provide the parameter matrices required to simulate the unsteady groundwater flow equation. Second, a nonlinear maximum likelihood estimation approach to the inverse problem is presented. The statistical properties of maximum likelihood estimators are derived, and a procedure to construct confidence intervals and do hypothesis testing is given. The relative merits of the linear and maximum likelihood estimators are analyzed. Other topics relevant to the identification and estimation methodologies, i.e., a continuous‐time solution to the flow equation, coping with noise‐corrupted head measurements, and extension of the developed theory to nonlinear cases are also discussed. A simulation study is used to evaluate the methods developed in this study.
Tidal and tidally averaged circulation characteristics of Suisun Bay, California
Authors: Smith Lawrence H. , Cheng Ralph T.
Published: February 2008

Availability of extensive field data permitted realistic calibration and validation of a hydrodynamic model of tidal circulation and salt transport for Suisun Bay, California. Suisun Bay is a partially mixed embayment of northern San Francisco Bay located just seaward of the Sacramento‐San Joaquin Delta. The model employs a variant of an alternating direction implicit finite‐difference method to solve the hydrodynamic equations and an Eulerian‐Lagrangian method to solve the salt transport equation. An upwind formulation of the advective acceleration terms of the momentum equations was employed to avoid oscillations in the tidally averaged velocity field produced by central spatial differencing of these terms. Simulation results of tidal circulation and salt transport demonstrate that tides and the complex bathymetry determine the patterns of tidal velocities and that net changes in the salinity distribution over a few tidal cycles are small despite large changes during each tidal cycle. Computations of tidally averaged circulation suggest that baroclinic and wind effects are important influences on tidally averaged circulation during low freshwater‐inflow conditions. Exclusion of baroclinic effects would lead to overestimation of freshwater inflow by several hundred m3/s for a fixed set of model boundary conditions. Likewise, exclusion of wind would cause an underestimation of flux rates between shoals and channels by 70–100%.
A method of streamflow drought analysis
Authors: Zelenhasić Emir , Salvai Atila
Published: February 2008

A method of completely describing and analyzing the stochastic process of streamflow droughts has been recommended. All important components of streamflow droughts such as deficit, duration, time of occurrence, number of streamflow droughts in a given time interval [0, t], the largest streamflow drought deficit, and the largest streamflow drought duration in a given time interval [0, t] are taken into consideration. A streamflow drought is related here to streamflow deficit. Following the theory of the supremum of a random number of random variables a stochastic model is presented for interpretation and analysis of the largest streamflow drought deficit below a given reference discharge and the largest streamflow drought duration concerning a time interval [0, t], at a given location of a river. The method is based on the assumption that streamflow droughts are independent, identically distributed random variables and that their occurrence is subject to the Poisson probability law. This paper is actually a continuation of the previous E. Zelenhasić (1970, 1979, 1983) and P. Todorović (1970) works on the extremes in hydrology. Application of the method is made on the 58‐year record of the Sava River at Sr. Mitrovica and on the 52‐year record of Tisa River at Senta, Yugoslavia, and good agreement is found between the theoretical and empirical distribution functions for all analyzed drought components for both rivers. Only one complete example, the Sava River at Sr. Mitrovica, is given in the paper. The proposed method deals with hydrograph recessions of daily or instantaneous discharges in the region of low flows, and not with mean annual flows which were used by other investigators.