bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of long‐wave radiation calculation methods over the United States
Authors: Hatfield J. L. , Reginato R. J. , Idso S. B.
Published: February 2008

Several long‐wave radiation models have been developed which provide different methods of evaluating the emittance of the atmosphere. Most of these methods are derived for a location using the relationship provided by a researcher but utilizing local empirical coefficients. There are several, however, which are thought to be more universal in their predictive ability and these were tested on a data set collected in 1979, 1980, and 1981. Data were collected at 15 locations in the United States over a range in latitude from 26°13′N to 47°46′N and over an elevation range from −30 m to 3342 m, relative to sea level. The models evaluated in this study were the Brunt model with the original coefficients, the Swinbank, Idso‐Jackson, and Brutsaert models, each with two different empirical coefficients, and two recent methods proposed by Idso. Pooling all the information, the Brutsaert 1 model best described the data. However, with the Beartooth Pass and Estes Park data at elevations above 2500 m excluded, the Brunt, Idso‐2 and two Brutsaert relationships provided the best fit. In all cases the Swinbank and Idso‐Jackson equations, which correct for emittance solely on temperature, provided the poorest fit. An evaluation of the models for the 1981 season at Five Points, California, showed the Brunt, Brutsaert 1 and 2, and Swinbank models to best describe the data at that location. These analyses suggest that the original Brunt equation, the Brutsaert equation with a coefficient of 0.575, and the Idso 2 model would adequately predict long‐wave radiation amounts with errors less than 5% for most agricultural locations in the United States and that local correction for water vapor effects should not be necessary.
Estimating profile water storage from surface zone soil moisture measurements under bare field conditions
Authors: Arya Lalit M. , Richter John C. , Paris Jack F.
Published: February 2008

A linear regression approach was used to estimate profile water storage from the storage in the surface zone. For a given thickness of the surface zone the correlations between the surface zone and profile water storages decreased as the profile depth increased; for a given profile depth, these correlations increased as the surface zone thickness increased. In general, the correlations were higher for irrigated corn fields than for bare fields. Results show that the profile depth for which water storage can be predicted from surface zone soil moisture data depends on the thickness of the surface zone, the cultural condition of the field, and the coefficient of determination considered adequate. An alternative procedure to estimate water storage in a deep profile under bare field conditions is based on the assumption that change in profile water storage over a period of time equals net surface flux over the same time. Surface fluxes are computed from surface zone soil moisture data and hydrologic properties of the soil. In a simulation study, net surface fluxes very nearly equaled changes in water storage of a 2.25‐m‐deep profile. For a field‐measured data set, computed surface fluxes and those measured by a weighing lysimeter showed good overall agreement.
Modeling tritium and chloride 36 transport through an aggregated oxisol
Authors: Nkedi‐Kizza P. , Biggar J. W. , van Genuchten M. Th. , Wierenga P. J. , Selim H. M. , Davidson J. M. , Nielsen D. R.
Published: February 2008

Breakthrough curves (BTC's) of 3H2O and 36Cl simultaneously displaced through columns of various‐sized aggregates of an Ione Oxisol soil were measured under water‐saturated steady flow conditions. The data were simulated using two conceptual models. In model I, all soil water was assumed to be mobile with a physical equilibrium existing in the system. For model II, soil water was partitioned into mobile and immobile regions. Convective diffusive solute transport was limited to the mobile water region. Transfer of a tracer between the two soil water regions was assumed to occur at a rate proportional to the difference in tracer concentration between the two regions. Sorption Of 3H2O and 36Cl was considered to be an instantaneous linear and reversible process. The two unknown parameters in model I and the four unknown parameters in model II were estimated by fitting model predictions to the experimental data. Model I could only describe BTC's obtained from columns packed with small aggregates (0.5–1 mm) and for displacements run at small fluxes (0.2 cm/h), whereas model II described all the BTC's well. Peclet numbers P in model II, as measured on each separate column, were essentially constant, indicating a linear relationship between the apparent diffusion coefficient D and the mobile pore water velocity vm. The fraction of soil water that is mobile, Φ, and the mass transfer coefficient α were found to be a function of the physical and chemical properties of the porous medium (aggregate size, pore water velocity, and solution concentration).
Simulation of solute transport in a mountain pool‐and‐riffle stream with a kinetic mass transfer model for sorption
Authors: Bencala Kenneth E.
Published: February 2008

In natural channels there are often long periods of low flow during which solutes have repeated opportunity for contact with relatively immobile bed materials. Such conditions can exist in very small pool‐and‐riffle mountain streams. If a solute can sorb onto bed materials, then both hydrodynamic and chemical processes control solute transport. A simulation of these processes is presented for a carefully controlled and intensively monitored strontium injection experiment. The numerical model couples nonreactive, transient storage with a kinetic mass transport model for sorption. The results are compared to both in‐stream and on‐sediment strontium measurements. In mountain streams the stream hydrology is complex and is governed by a wide variety of time and distance scales. The present simulations assist in interpreting the relative roles of hydrologic and sorptive kinetic processes, and indicate the practical limits of our process and parameter knowledge. The simulations are relatively insensitive to the details of the kinetic mechanisms and to the spatial variability of the stream parameters.
A new derivation of the Taylor‐Aris Theory of solute dispersion in a capillary
Authors: Gupta Vijay K. , Bhattacharya R. N.
Published: February 2008

The transport of a dilute solute under viscous motion in a straight capillary is described at three distinct space‐time scales. These are the kinetic, fluid mechanical, and Taylorian scales. The transition from one scale to the next higher scale is shown to be a consequence of the central limit theorem (CLT) of probability theory. The Taylor‐Aris dispersion equation is derived by an application of a recently proved CLT for Markov processes. An alternative computation of the dispersion coefficient is given using a ‘differential equation averaging’ approach. A third method, which also applies to solute transport in porous media, is illustrated for an approximate computation of the dispersion coefficient.
An analysis of dissolved oxygen concentrations in tail waters of hydroelectric dams and the implications for small‐scale hydropower development
Authors: Cada Glenn F. , Kumar K. D. , Solomon Jean A. , Hildebrand Stephen G.
Published: February 2008

One of the environmental issues affecting small‐scale hydropower development in the United States is water quality degradation. The extent of this potential problem, as exemplified by low dissolved oxygen concentrations in reservoir tail waters, was analyzed by pairing operating hydroelectric sites with dissolved oxygen measurements from nearby downstream U.S. Geological Survey water quality stations. These data were used to calculate probabilities of noncompliance (PNC's), that is, the probabilities that dissolved oxygen concentrations in the discharge waters of operating hydroelectric dams will drop below 5 mg/l. The continental states were grouped into eight regions based on geographic and climatic similarities. Most regions had higher mean PNC's in summer than in winter, and summer PNC's were greater for large‐scale than for small‐scale hydropower facilities. Cumulative probability distributions of PNC also indicated that low dissolved oxygen concentrations in the tail waters of operating hydroelectric dams are phenomena largely confined to sites with large‐scale facilities.
Market simulations for irrigation water rights: A hypothetical case study
Authors: Wong Benedict D. C. , Eheart J. Wayland
Published: February 2008

The efficiency of two marketable water rights systems in a lentic (lakelike) structure is assessed quantitatively for a case study based on hypothetical irrigation water use. Water rights are simulated on the bases of (1) the expected values of water rights to the users and (2) perfect foresight on the parts of users, and the economic outcomes of these markets are evaluated from both ex ante and ex post perspectives. The market outcomes are compared to the optimal (efficient) scheme and to two alternative nonmarket policies. Distributional aspects of the markets are examined on the basis of individual payoff. Simulation results show that higher efficiency is obtained for the two market systems than for the nonmarket policies and that the market systems recoup about 95% of the economic value of the optimal distribution. The results suggest that most of the 5% efficiency loss should be attributed to the design of the market system itself (i.e., the restrictions imposed by the definition of the rights and/or the water rights allocation policy), rather than the users' inability to predict future events.
Monitoring the unfrozen water content of soil and snow using time domain reflectometry
Authors: Stein Jean , Kane Douglas L.
Published: February 2008

Time domain reflectometry is a technique that can be used to indirectly measure the in situ moisture content of soil. Previously, this method was not used in the field to continuously monitor the liquid water content because of the influence it had on the wetting, drying, freezing and thawing cycles of the soil. The principal objectives of this field investigation were, apply the TDR technique to monitor the unfrozen water content in the soil, utilize this technique to determine snowmelt infiltration into seasonally frozen soils, and explore the feasibility of using the TDR technique to monitor snowmelt percolation in the snowpack. An additional goal of this paper was to explain in a straightforward manner how to use the TDR technique to obtain the liquid water profile in a soil. Various configurations of parallel transmission lines were installed horizontally at various depths in the soil and also in the snowpack. This technique gave a good delineation of the unfrozen water content with depth in frozen soils. Results looked promising in snow if in situ snow density measurements were taken along with the TDR measurements.
Sediment Sampling in Different Aquatic Environments: Statistical Aspects
Authors: Håkanson Lars
Published: February 2008

The aim of this paper is to discuss statistical aspects on sediment sampling and sample representativity. The study is based on empirical data from three different sedimentological environments: a river, a river mouth area, and a lake. The sediments have been analyzed for physical sediment character (water content and loss on ignition) and chemical/contaminational status (Pb, Cu, and Cd). The prevalent bottom dynamics influence the character of the sediments and the representativity and information value of sediment samples. An informative fraction is defined by the portion of a sediment sample that passes a 63‐μm mesh by wet sieving. This fraction corresponds approximately to deposits from areas of accumulation. Direct analysis of surficial sediment samples from areas of erosion or transportation, such as in rivers and river mouths, yield low information, i.e., many samples would be required to obtain a given statistical certainty. Correction with the water content (or similar parameters, e.g., grain size and bulk density) or organic content would improve the information but still not yield optimal results. Simple wet sieving through a 63‐μm mesh seems to yield best information, i.e., the lowest number of necessary analysis for the least amount of work. Fractionated centrifugation (or similar approach, e.g., ultrafiltration) would not improve the information value.
Evaporation From a Bare Soil Evaluated Using a Soil Water Transfer Model and Remotely Sensed Surface Soil Moisture Data
Authors: Prevot L. , Bernard R. , Taconet O. , Vidal‐Madjar D. , Thony J. L.
Published: February 2008

Daily surface soil moisture data, obtained with a C band scatterometer on a bare soil, provide the upper boundary condition for a numerical soil water transfer model. The model uses an implicit finite difference scheme to solve the nonlinear Richards equation. The soil is represented by two layers differing in hydraulic conductivity. Following calibration by comparison of calculated and measured soil moisture profiles, the model provides estimates of the water budget and the boundary fluxes. The estimates of evaporation computed from the model compare favorably to those derived from soil water content measurements by the neutron probe when only the radar data are used to define the surface boundary condition. When known precipitation rates are also used, evaporation is underestimated.
Forest Management for Increased Timber and Water Yields
Authors: Bowes Michael D. , Krutilla John V. , Sherman Paul B.
Published: February 2008

In some regions of the country where timber management alone affords at best only indifferent economic prospects, it may be possible that joint “production” of both water and timber is economic. The Colorado subalpine forests of the West Slope, in combination with the extensive development of the Upper Colorado River, provide conditions that merit examination. The release of water available for streamflow from the reduction in evapotranspiration and other features of a vegetation manipulation‐snow management regime is the basic mechanism for joint production. Unless other values are realized from joint production not realized from the manipulation of vegetation for water alone, it may be that the Colorado subalpine forests are not being managed to produce the most valuable, if unconventional, output.
Laboratory Studies of the Effects of the Capillary Fringe on Streamflow Generation
Authors: Abdul A. S. , Gillham R. W.
Published: February 2008

This paper describes laboratory experiments that were conducted to investigate the groundwatersurface water interactions during the process of streamflow generation. In particular, the experiments were designed to examine the role of the capillary fringe in the runoff processes and its influence on the groundwater response to precipitation. The experimental results clearly show that if the zone of tension saturation extends to, or near, ground surface, the application of a small amount of water can cause an immediate rise in the water table, and the magnitude of the rise is much greater than would be expected on the basis of normal specific yield values for sandy materials. Because of the sloping surface of the laboratory model the rising water table caused the rapid generation of hydraulic gradients directed towards the toe of the slope (the stream) resulting in the immediate generation of groundwater discharge to the stream. Two experiments using chloride as a tracer and having rainfall rates of 4.3 and 1.9 cm h−1 showed that the discharge of preevent water to the stream preceded event water and that at early times, preevent water was the predominant component of streamflow. In addition, the results of the two tracer experiments show that the significance of preevent water increases with decreasing rainfall rate and that for the 1.9 cm h−1 rainfall rate preevent water was the main component of the stream hydrograph. The proportions of preevent and event water in the streamflow after steady conditions were reached were determined largely by the extent of the seepage face. This in turn would be determined by the hydraulic conductivity of the medium, the surface slope, and the rainfall intensity.
Effects of Urbanization on Frequencies of Overflows and Pollutant Loadings From Storm Sewer Overflows: A Derived Distribution Approach
Authors: Loganathan G. V. , Delleur J. W.
Published: February 2008

On the basis of exponential density functions for volume of runoff, interevent time, and duration of runoff event and beta density for the rescaled pollutant (biochemical oxygen demand) concentration, and gamma density for river flow volumes during a critical period, new distributions are derived for overflow volumes and for quality of pollutant in the river after mixing with the untreated overflows of the overtaxed system. This is accomplished by means of hydrological relationships between different variables. The current data on runoff volume, duration of runoff events, etc., are transformed to account for future urbanization activities. The newly formed variables are used in the derivation of probability distributions for overflows and receiving body pollutant concentration after urbanization. The analytical model is compared with the simulation model “STORM.”
A Physically Based Flood Frequency Distribution
Authors: Díaz‐Granados M. A. , Valdes J. B. , Bras R. L.
Published: February 2008

The geomorphoclimatic instantaneous unit Hydrograph theory, the joint probability density function of storm duration and intensity, and Philip's representation of the infiltration process are used to derive a flood frequency distribution that could be used in regions with no streamflow records. The resulting flood frequency distribution is in analytical form containing only few climatologic and physiographic parameters of the catchment. This frequency distribution was tested against frequency distributions calculated from historic records for arid and wet climates, with good and reasonable results, respectively.
Hydrothermal Processes Beneath Arctic River Channels
Authors: Wankiewicz Anthony
Published: February 2008

Perennially unfrozen ground (river talik) exists beneath Rengleng River and Caribou Creek near Inuvik, Northwest Territories. Subchannel ground temperature observations to 13 meters depth were obtained in April, August, and November of 1977–1978. River talik thermal diffusion parameters were determined from heat transfer simulations of the summer and autumn profiles. It was found that while conduction is the dominant heat transfer process in the talik beneath Caribou Creek, macrodispersion of heat by flowing ground water is the dominant process beneath Rengleng River. The latter increases apparent conductivity by an order of magnitude over simple conduction and resulted in 14°C of summer heating 3 meters beneath the channel. Ground water flow along a talik is shown by flow net analysis to vary periodically in both time and space when the surface water profile in the channel follows a pool‐and‐riffle sequence. After the streams cease flowing in midwinter, a frost layer up to 2 meters thick develops beneath the center of the channels. Temperature recordings in 1978 showed that frost did not begin to thaw until the runoff peak of June 8, 1978, remaining partially frozen at deeper levels over 16 additional days.
The Krafla Geothermal Field, Iceland: 3. The generating capacity of the field
Authors: Bodvarsson G. S. , Pruess K. , Stefansson V. , Eliasson E. T.
Published: February 2008

This paper presents analytical and numerical studies of the generating capacity of the Krafla field. A general lumped parameter model is developed which can be used to obtain rough estimates of the generating capacity of a geothermal field based on the size of the wellfield, the average formation porosity, and the amount of recharge to the system. The model is applied to the old wellfield at Krafla. More sophisticated calculations of the generating capacity of the Krafla field are also performed using distributed‐parameter models. Two‐dimensional areal models of the various reservoir regions at Krafla are developed and their generating capacities (MWe) evaluated. The results obtained indicate that the old wellfield can sustain steam production of 30 MWe for 30 years. The estimated power potential of the new wellfield is 20 MWe for 30 years. To obtain the required steam production several additional wells may be drilled in the old and new wellfields.
A hydrologically useful station precipitation model: 1. Formulation
Authors: Georgakakos Konstantine P. , Bras Rafael L.
Published: February 2008

A one‐dimensional, physically based precipitation model is formulated. Particular emphasis is placed on its utility for real‐time river flow forecasting. Thus, the model is in state‐space form, suitable for use with modern estimation theory techniques, and it uses only operationally readily available, meteorological variables as its input. Parameterization of the model components is based on well‐established observations and theories on water vapor condensation, precipitation mechanisms, and subcloud evaporation of falling hydrometeors. Model input consists of ground level station temperature, pressure, and dewpoint temperature observations. The model predicts the spatially averaged, ground surface precipitation rate in the characteristic area determined by the spatial scales of the input. The water equivalent mass condensed in a cloud column defined by the characteristic area is the model state. Key physical parameters in the formulation are the pressure at the cloud top, the height‐averaged updraft velocity, and the inverse of the average diameter of the hydrometeors at cloud base.
Wetting front advance and freezing of meltwater within a snow cover: 2. A simulation model
Authors: Marsh Philip , Woo M.‐K.
Published: February 2008

A simulation model is developed which incorporates the effect of flow fingers at the leading edge of the wetting front, ice layer growth within and at the base of the snow cover, and meltwater infiltration into the underlying frozen soils. The model results demonstrated that ice layers grow rapidly over a 24‐ to 36‐hour period due to the conduction of heat into the snow and underlying soil. Sufficient water is frozen as ice layers to slow the finger wetting front and to account for the rapid snow and soil warming. Wetting front advance and ice layer growth were found to be sensitive to snow temperature, thermal conductivity, volume of flow in the fingers, and irreducible water saturation. Simulation of a warm snow cover showed that with reduced ice layer growth the flow fingers were able to transmit rapidly water to the snow cover base before the entire snow cover was wet. In the arctic situation the soil was sufficiently cold to ensure basal ice growth throughout the melt period. Basal ice growth was found to be sensitive to soil infiltration, length of the growing period, and the snowmelt rate. As a result of the negative soil heat flux, all meltwater is not available for runoff until both the liquid and thermal requirements of the snow and soil have been satisfied.
A Field Method to Determine Unsaturated Hydraulic Conductivity Using Flow Nets
Authors: Stephens Daniel B.
Published: February 2008

A practical new field method is proposed to evaluate hydraulic conductivity in partially saturated media near a water impoundment. The new method is an inverse procedure which utilizes a flow net constructed from the steady state total hydraulic head distribution around the water source. In the vicinity of constant head sources and downstream along any stream tube, wetness and conductivity generally decrease. Knowing the stream tube geometry and hydraulic gradient from the flow net, Darcy's law is used to determine unsaturated hydraulic conductivities within the stream tube relative to some segment of the stream tube where conductivity is known. This approach was used successfully to predict the unsaturated hydraulic conductivity which was input to two variably saturated numerical models, utilizing total hydraulic head fields generated by the models. This procedure is also applied to pressure head and water content data collected in the field surrounding a constant head borehole infiltration test originally designed to determine only saturated hydraulic conductivity above the water table. For practical purposes the new procedure compares very favorably with (1) results of a field experiment to obtain unsaturated hydraulic conductivity in situ using the instantaneous profile method and (2) values of unsaturated conductivity calculated from field and laboratory measurements of water content and pressure head.
Markov Flow Models and the Flood Warning Problem
Authors: Yakowitz Sidney
Published: February 2008

Let {Yj} represent periodically sampled river discharge values. For simplicity, say that a flood occurs at epoch n + 1 if, for some fixed T, Yn+1 > T. Assume that at epoch n, the decision maker must decide whether or not to issue a flood warning, this decision being based on the past flow record {Yj} j≤n. Finally, assume that costs have been assigned to the two types of mistakes: the “false alarm” event, and the event that a flood occurs when no warning was issued. It is argued that outside the Gaussian assumption, standard time series methodology is inappropriate for the flood warning problem. The purpose of this paper is to relate recent progress based on alternate principles. A nonparametric inference procedure is described which converges to the optimal decision function for the flood warning problem as the length of the historical record increases for any stationary G2‐ergodic Markov process. Under additional assumptions, rates can be established and shown to be optimal in a certain sense. The new methodology is compared with autoregressive moving average predictors on simulated and river flow data.
Exploration of a Rigid Ice Model of Frost Heave
Authors: O'Neill Kevin , Miller Robert D.
Published: February 2008

A numerical model is explored which simulates frost heave in saturated, granular, air‐free, solute‐free soil. It is based on equations developed from fundamental thermomechanical considerations and previous laboratory investigations. Although adequate data are lacking for strict experimental verification of the model, we note that simulations produce an overall course of events together with significant specific features which are familiar from laboratory experience. Simulated heave histories show proper sensitivities in the shapes and orders of magnitude of output responses and in the relations between crucial factors such as heave rate, freezing rate, and overburden.
Municipal Demand for Water in Kuwait: Methodological Issues and Empirical Results
Authors: Al‐Qunaibet Mohammad H. , Johnston Richard S.
Published: February 2008

This study utilized, for the first time, a demand function for municipal water derived from the Stone‐Geary utility function, thereby permitting explicit consideration of the minimum amount of water necessary for daily needs. Using monthly data from Kuwait, this demand function gave greater price elasticity estimates but smaller income elasticity estimates than those of other countries. It was estimated that the “subsistence” water use level in Kuwait is about 42 L per capita per day and the results suggest that at least in that wealthy country, people do respond to changes in the prices of public services.
Effects of Instream Flow Requirements on Water Supply Reliability
Authors: Palmer Richard N. , Snyder Regina M.
Published: February 2008

Increasing water demands have directed new interest toward methods for defining water supply system performance. These demands include not only traditional municipal, industrial, and agricutural demands, but instream flow uses such as power production and fish flow maintenance. This paper suggests procedures for evaluating water supply performance when instream flows for fish are required of a municipal water supply. A computer simulation model is used with synthetic inflow sequences to investigate indices of system performance for the Seattle, Washington water supply system. A review of techniques used to establish instream flow requirements is presented with a history of instream flow requirements established for the Seattle supply. The trade‐offs between values of instream flows and municipal water supply performance are presented to quantitatively illustrate the impacts of instream requirements.
The Automatic Calibration of Conceptual Catchment Models Using Derivative‐Based Optimization Algorithms
Authors: Gupta Vijai Kumar , Sorooshian Soroosh
Published: February 2008

This paper examines the possibility of using derivative‐based optimization algorithms for automatic calibration of conceptual rainfall‐runoff models with threshold structures. A method is discussed for explicit computation of the derivatives based on an analysis of the modality of behavior present in such models. In the method the threshold structures are not replaced by smoothing functions, thereby preserving the conceptual integrity of these models. The discussion includes a theoretical analysis of a single linear reservoir (with threshold) model which provides some insights into the issue of threshold parameter identifiability. Simulation study comparisons of the Newton (derivative based) and the Simplex (direct search) optimization algorithms indicate that the former is more efficient, especially when the number of parameters to be optimized is large. However, the results indicate that careful study of the issues related to model identifiability is required if any significant progress is to be achieved in the area of automatic calibration of conceptual rainfall‐runoff models.
Municipal Water Demand Study, Oklahoma City and Tulsa, Oklahoma
Authors: Cochran Richard , Cotton Arthur W.
Published: February 2008

By using a multiple regression model, this longitudinal study analyzes the methods and results of the factors which influence water consumption in Oklahoma City and Tulsa, Oklahoma during the 20‐year period of 1961 through 1980. The explanatory variables utilized in the model include the average price of water per thousand liters (X1); constant per capita income (X2); average monthly precipitation measured in millimeters (X3); average monthly temperatures in °C(X4); and number of households per thousand population (X5). The results indicate that average price and per capita income were predictive variables for Oklahoma City's water demand, while only per capita income was found to be a predictor for consumption in Tulsa.
Generalized Scale Invariance in the Atmosphere and Fractal Models of Rain
Authors: Lovejoy S. , Schertzer D.
Published: February 2008

In recent years there has been considerable interest in stochastic rain models. By developing new ideas about scale invariance and intermittency we argue that the scope of such models can be greatly extended. The notions of scale invariance, intermittency, and the associated idea of fractal dimension have lately gained considerable ground, particularly in the context of extremely variable phenomena such as those found in the mesoscale and in hydrodynamic turbulence. We review some relevant work and argue that the atmosphere respects a symmetry principle that we call generalized scale invariance in which the statistical properties of the small and large scale are related to each other by a magnification coupled with a differential stratification (due to gravity) and differential rotation (due to the Coriolis force). We further argue that the extremely erratic (intermittent) nature of the atmosphere is characterized by scale invariant (fractal) measures leading to hyperbolic (fat‐tailed) probability distributions of the fluctuations. The standard statistical methods based on exponential fall offs in both correlations and probability distributions are inappropriate when the variability is of this type. We show how both the scaling and intermittency may be exploited to develop extremely variable stochastic models of rain. Although the models examined here are the simplest of a family of extremely variable processes (depending on only two radar‐determined parameters), they lead to realizations possessing many realistic features of the rainfield including complexity of form, clustering and bands at all scales, as well as differential stratification and rotation. Finally, we point to weaknesses in the models (in particular, their monodimensional nature) and suggest possible improvements.
An Approach to Parameter Estimation and Stochastic Control in Water Resources With an Application to Reservoir Operation
Authors: Loaiciga Hugo A. , Mariño Miguel A.
Published: February 2008

This paper presents an algorithm for the estimation of parameters in state‐space models that represent hydrologic processes in which the state variables are observed with error. The algorithm is based on the maximization of the conditional expectation of the likelihood function of the state equation. The estimation algorithm is numerically stable and guarantees local convergence under mild conditions. It is also shown that the estimation algorithm can be coupled with an optimal control method to yield a combined control estimation technique that can be easily implemented. An application of the theory and methods developed herein is given for flood routing via reservoir operation.
Current Issues in the Quantification of Federal Reserved Water Rights
Authors: Brookshire David S. , Watts Gary L. , Merrill James L.
Published: February 2008

This paper examines the quantification of federal reserved water rights from legal, institutional, and economic perspectives. Special attention is directed toward Indian reserved water rights and the concept of practicably irrigable acreage. We conclude by examining current trends and exploring alternative approaches to the dilemma of quantifying Indian reserved water rights.
Computationally Efficient Algorithms for Parameter Estimation and Uncertainty Propagation in Numerical Models of Groundwater Flow
Authors: Townley Lloyd R. , Wilson John L.
Published: February 2008

Finite difference and finite element methods are frequently used to study aquifer flow; however, additional analysis is required when model parameters, and hence predicted heads are uncertain. Computational algorithms are presented for steady and transient models in which aquifer storage coefficients, transmissivities, distributed inputs, and boundary values may all be simultaneously uncertain. Innovative aspects of these algorithms include a new form of generalized boundary condition; a concise discrete derivation of the adjoint problem for transient models with variable time steps; an efficient technique for calculating the approximate second derivative during line searches in weighted least squares estimation; and a new efficient first‐order second‐moment algorithm for calculating the covariance of predicted heads due to a large number of uncertain parameter values. The techniques are presented in matrix form, and their efficiency depends on the structure of sparse matrices which occur repeatedly throughout the calculations. Details of matrix structures are provided for a two‐dimensional linear triangular finite element model.
Testing Flood Frequency Estimation Methods Using a Regional Flood Generation Model
Authors: Lettenmaier Dennis P. , Potter Kenneth W.
Published: February 2008

A regional flood generation model is proposed, wherein the logarithms of the first two moments of the annual flood distribution at each site depend on the logarithm of the drainage area. This model is parameterized in terms of the regional mean coefficient of variation,
, and the site‐to‐site coefficient of variation of the coefficient of variation, Cc. Eight flood frequency estimation methods, including two at‐site and six regional estimators, were tested. Generated floods were drawn from three parent distributions: extreme value l, lognormal, and Pearson 3. The regional estimators had lower root mean square errors than the at‐site estimators, even when the region was moderately heterogeneous (high Cc), except when the parent was extreme value 1. However, the regional estimators were not always robust with respect to the parent flood distribution. The flood index method, which was based on regional probability weighted moments, performed quite well when
and Cc were both low. As
and Cc, increased, however, its performance degraded markedly, primarily due to dominance of the quantile estimation variance by the variance in the at‐site mean estimator. This result suggests that for high
and/or Cc, improvements in regional flood estimation will come from improved estimators of the at‐site mean annual flood, rather than the regional (normalized) flood frequency distribution.
On the Variation of Infiltration Into a Homogeneous Soil Matrix Containing a Population of Macropores
Authors: Beven Keith J. , Clarke Robin T.
Published: February 2008

A population of channels penetrates a soil matrix that is otherwise homogeneous. The channels are assumed to be vertical and of circular cross section with constant diameter, but channel depths and radii are allowed to vary over the population. This paper uses a model based on the Green‐Ampt assumptions to predict infiltration rates through the walls and bases of channels, resulting in a mathematical description of the way in which infiltration develops in the soil and in which channels fill with water until eventually overland flow is initiated. This model takes account of the fact that there may be a random distribution of channels in space. Expressions for the expected mean and variance of infiltration volumes are derived. Some example results are given and show that below the matrix wetting front the variance of the change in water content with 30 and 50 channels per square meter may be of the same order as the mean change in water content. The presence of channels can lead to significant increases in predicted channel volumes.
Gamma Ray Attenuation Studies of Interception From Sitka Spruce: Some Evidence for an Additional Transport Mechanism
Authors: Calder I. R. , Wright I. R.
Published: February 2008

Various forest canopy characteristics of stands of Sitka spruce (Picea sitchensis (Bong.) Carr.), including canopy density, the aerodynamic resistance to the transfer of water vapor, and the rates of change of drainage and evaporation of water with respect to canopy storage, were investigated using direct measurements of canopy mass and water storage. The measurements, made at sites located in Wales and Scotland, utilized the attenuation of a horizontal beam of gamma rays which was arranged to scan through the canopy at different levels. The aerodynamic resistance to the transport of water vapor from the canopy to a reference level 5 m above mean tree height was found to be consistent with the value of 3.5 s m−1, determined from earlier modeling studies (I. R. Calder, 1977). This value is, however, lower and shows less wind speed dependence than would be expected from conventional formulae which are based on eddy diffusion theory and tree height. The possibility of explaining these discrepancies in terms of an additional transport mechanism involving large‐scale eddies is discussed.
A Second‐Order Approach for the Modeling of Dispersive Transport in Porous Media: 2. Application to Solute Motion in Pipes and Capillary Tubes
Authors: Tompson Andrew F. B. , Gray William G.
Published: February 2008

The second‐order dispersion model developed by Tompson and Gray (this issue) is reduced to a one‐dimensional form in terms of dimensionless variables and is applied to the simple problem of solute transport in pipes and capillaries. Numerical experiments allow the dimensionless constitutive coefficients appearing in the model to be evaluated under several flow regimes. Simple functional relationships for these coefficients in terms of the Peclet number are developed. The model performs well using these scale independent coefficients, even at early times and short travel distances, when the traditional first‐order Fickian model is inadequate.
Sources and Sinks of Ions in a Soft Water, Acidic Lake in Florida
Authors: Baker Lawrence A. , Brezonik Patrick L. , Edgerton Eric S.
Published: February 2008

Fluxes and storage of water and major ions were measured for McCloud Lake, a small, acidic soft water lake in north central Florida that receives 90% of its water input from direct precipitation. Wet precipitation had a volume‐weighted pH of 4.5 and accounted for a H+ flux of 420 eq/ha yr; deposition of SO2, NO2, and HNO3 contributed an additional 150–300 eq H+/ha yr. Although precipitation passing through the sandy soils and littoral sediment was neutralized by mineral weathering, sulfate reduction or adsorption, and nitrate immobilization, ground water was only 10% of the total water input to the lake and neutralized only about 30% of precipitation H+ input. Compared to atmospheric deposition, lake water shows little enrichment of cations but is depleted in SO42−, NO3− and NH4+, while >80% of precipitation H+ is neutralized. The major H+ neutralization processes within the lake are sulfate reduction (26–34 meq SO42−/m2 yr) and NO3− immobilization (17–20 meq NO3−/m2 yr), while NH4+ immobilization is a small internal source of H + . Sinks and sources of cations could not reliably be calculated because of uncertainties in groundwater inputs. Internal H+‐consuming processes are important in lakes with no surface inlets or outlets and which receive most of their water from direct precipitation. For these lakes, the rate and extent of acidification is largely determined by a balance between H+ inputs and H+ consumption by internal processes.
Dispersion in Fractal Fracture Networks
Authors: Ross Benjamin
Published: February 2008

The solute transport equation describes dispersion as a diffusion‐like process characterized by a constant dispersivity, implying that small pulses of contaminant grow as the square root of distance traveled. Measured dispersivities tend to be proportional to the scale of the measurement, suggesting that the pulses grow in linear proportion to distance. An exponent r, defined by the relationship d∼Lr where d is the standard deviation of position of a contaminant particle and L is the distance traversed, may be used to characterize dispersion. It takes a value ½ in the first case and 1 in the second. The movement of a contaminant particle is analyzed here as a random walk through a fracture network composed of fissures of varying transmissivity. If large‐transmissivity fractures are sufficiently few, then one calculates r = ½. If large‐transmissivity fractures are numerous, one obtains 2r = q + 1, where q is an exponent that describes the relationship between fracture spacing and transmissivity. Inserting the reasonable value q= 1 gives r = 1. This theory thus provides a physical basis for the observed scale‐dependence of dispersivity.
Flood Frequency Analysis Using the Cox Regression Model
Authors: Smith James A. , Karr Alan F.
Published: February 2008

Procedures for incorporating time‐varying exogenous information into flood frequency analyses are developed using the Cox regression model for counting processes. In this statistical model the probability of occurrence of a flood peak in a short interval [t,t+dt) depends in an explicit manner on the values attofk“covariate” processesZ1, …,Zk. Specifically, lettingdN(t) be 1 if a flood peak occurs in [t,t+dt) and 0 otherwise,dN(t) =a(t) exp {∑j=1kbjZj(t)} +dM(t) wherea, the “baseline intensity,” is an unknown function,bis a vector of unknown “regression” parameters, and the errordM(t) is (conditionally) orthogonal to the past history. Two applications, assessment of relative importance of physical processes such as snow melt or soil moisture storage on flood frequency at a site and derivation of time‐varying flood frequency estimates, are considered.
Performance, Analysis, and Simulation of a Two‐Well Tracer Test at the Mobile Site
Authors: Molz Fred J. , Güven Oktay , Melville Joel G. , Crocker Ronald D. , Matteson Keith T.
Published: February 2008

During the late summer of 1984 a two‐well tracer test was performed which involved travel distances of 38.3 m to 90 m. A bromide tracer slug was injected at one well while groundwater was simultaneously pumped from the other well. The two‐well test, which required 32 days to complete, was then simulated by GeoTrans, Inc., using a three‐dimensional advection‐dispersion model with a longitudinal dispersivity of 0.15 m, a transverse dispersivity of 0.05 m, and the permeability distribution being measured independently in a single‐well test. (Single‐well test results, which involved a travel distance of 5.5 m, indicated that the hydraulic conductivity varied by about a factor of 4 throughout the aquifer thickness.) The two‐well test simulation, made without knowledge of the test results, and without any calibration, was remarkably good. Local hydrodynamic dispersion was negligible, so that the concentration versus time breakthrough at the withdrawal well could be simulated just as well with a quasi‐three‐dimensional advection model having zero hydrodynamic dispersion. This implies that over the travel distances applicable to the two‐well test the spreading of the slug in the aquifer depended mainly on macroscopic velocity variations that were quantifiable in terms of the inferred permeability distribution. This result, which pertains to an aquifer in a fluvial terrace deposit of Quaternary age, is similar to that observed by Pickens and Grisak in a sandy glaciofluvial aquifer near the Chalk River Nuclear Laboratories in Canada. Such flow systems can result in fully three‐dimensional plumes with high concentrations of contaminant moving over large horizontal distances in the higher‐permeability zones.
A Case Study of a Chemical Spill: Polychlorinated Biphenyls (PCBs): 3. PCB Sorption and Retardation in Soil Underlying the Site
Authors: Anderson Michael R. , Pankow James F.
Published: February 2008

Condie silt from near a polychlorinated biphenyls (PCBs) and chlorinated benzenes spill site was studied with respect to the sorption and predicted retardation of these compounds. The soil organic carbon fraction (foc) of the silt was measured to be 0.0036 ± 0.00088. The sorption partition coefficient (Kp′ milliliters/gram) values were: 2,2′,5,5′‐tefrachlorobiphenyl (4‐PCB), 5000; 2,2′,4,5,5′‐pentachlorobiphenyl (5‐PCB), 9400; and 2,2′,4,4′,5,5′‐hexachlorobiphenyl (6‐PCB), 26,000. The direct measurement of the Kp values allowed an improved estimation of sorption over that possible with the measured foc and the available literature Koc data. Mean transport retardation factors (R) for 4‐PCB, 5‐PCB, and 6‐PCB in saturated silt were calculated to be 2.7 E + 04, 5.0 E + 04, and 1.4 E + 05, respectively. This implies that dissolved PCBs will move only very slowly through unfractured Condie silt. Since the Kp values of the PCBs were not affected when 20 mg/L of 1,2,4‐trichlorobenzene was added to the aqueous phase, PCB transport at the site will not be accelerated by the presence of the chlorinated benzenes. Therefore if fractures are not present in the silt in its middle and lower levels, then there is little chance that the PCBs pose a threat to the underlying Regina aquifer system. R values predicted for 1,2,4‐trichlorobenzene and 1,2,4,5‐tetrachlorobenzene were 120 and 600, respectively; they may also not pose an immediate threat to the underlying aquifer if fractures are absent.