bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial variability of surface temperature along two transects of a bare soil
Authors: Vauclin M. , Vieira S. R. , Bernard R. , Hatfield J. L.
Published: February 2008

The spatial variability of surface temperature has been examined on a bare soil located at the University of California at Davis. Surface temperatures were measured between 1300–1400 hours three consecutive days after a sprinkler irrigation. Measurements were made at every meter along two transects with two infrared thermometers differing only by their field of view. In addition, soil samples were collected on the third day with the same pattern to determine the gravimetric water content between the soil surface and 5 cm of depth. All data were found to be normally distributed regardless of their position along the transects. Semivariograms and autocorrelation functions were determined and the measurements were found to be correlated over space. A first‐order autoregressive process with a white noise was found to describe the spatial structure of all the sets of data. Variances of sample means were calculated by taking into account the interdependence between observations and were compared to variances obtained by assuming uncorrelated observations.
Pricing as a policy to reduce sewage costs
Authors: Strudler Michael , Strand Ivar E.
Published: February 2008

Compliance in Maryland with the Federal Clean Water Act will cost an estimated $3 billion. By charging a modest water/sewage fee for residential water use ($2 per thousand gallons), it is shown that sewage flows could be reduced, resulting in a compliance cost savings of $21 million. The cost reduction occurred even though only one third of the municipalities (heavy per capita water users) had to bear the increased price. Pricing policies are suggested as a method of reducing the costs of environmental standards.
Simulation of salt water–fresh water interface motion
Authors: Polo Jose Ferrer , Ramis Franscisco J. Ramos
Published: February 2008

A mathematical model is presented which describes the salt water–fresh water motion with a sharp interface, assuming the validity of the Dupuit approximation. This model is used as a base to derive a numerical model (finite difference method) which is unconditionally convergent and stable. A method for solving the equations is selected together with a convergence accelerating procedure. The treatment of the boundary conditions in the interface is discussed, and a general and automatic solution for that problem is presented. Several tests with analytical solutions have been performed with good results.
Model of light penetration in a turbid lake
Authors: Stefan Heinz G. , Cardoni John J. , Schiebe Frank R. , Cooper Charles M.
Published: February 2008

The relationships governing the penetration and attenuation of light in natural water bodies are of great importance to studies and models of photosynthesis and water quality in general. Quantitative expressions which give the rate of reflection of incident light at a water surface and absorption and scattering of light by suspended inorganic (clay) particles and by suspended organic particles (phytoplankton and detritus) in the water are developed herein for Lake Chicot, a highly turbid lake in Arkansas. Differentiation between inorganic and organic types of particles reveals their respectively different effect on light penetration. In addition, light attenuation is also a function of wavelength. Therefore, three wave bands are distinguished. In addition, light as seen by flat plate sensors and spherically integrated light as experienced by an algal cell are distinguished. To facilitate modeling of planktonic photosynthesis, a relationship between incident total radiation measured above the water (as available from a weather station) to underwater photosynthetically active radiation has been developed for Lake Chicot. The work described was exploratory and relied exclusively on Lake Chicot data. The results were intended for use in a water quality simulation model.
A numerical procedure for the solution of the steady state variable density groundwater flow equation
Authors: Kuiper Logan K.
Published: February 2008

A numerical code is developed for the solution of the three‐dimensional steady state groundwater flow equation in which groundwater density varies with spatial position and is treated as known spatially dependent parameter. The integrated finite difference grid elements of the numerical code are rectangular when viewed along the vertical direction, but their top and bottom surfaces parallel or are coincident with the interfaces between the geologic strata within the solution region. Conditions that are sufficient for the accuracy of the code are derived. Approximate solutions for pressure head, as determined from the code, are compared for accuracy with several exact analytic test solutions.
Sensitivity to acidification of lakes in the flat tops wilderness area, Colorado
Authors: Turk John T. , Adams Dee Briane
Published: February 2008

Lakes of the Flat Tops Wilderness Area in northwestern Colorado are sensitive to acidification if precipitation in the area becomes as acidic as that of the northeastern United States. Alkalinity values as small as 70 µeq l−1 occur in the higher‐altitude lakes. Most lakes at altitudes of 3380 m or greater are predicted to have alkalinity values of 200 µeq l−1 or less. About 370 lakes having a total surface area of about 157 ha are calculated to be sensitive to acidification.
A soil and atmospheric boundary layer model for evapotranspiration and soil moisture studies
Authors: Camillo P. J. , Gurney R. J. , Schmugge T. J.
Published: February 2008

A computer model of the upper soil and lower atmosphere boundary layer has been developed for use with remotely sensed data. It includes both energy and moisture balances, and it uses a predictor/corrector integrator with an automatically changing time step; these two components make the model both stable and efficient. It is driven by surface heat and moisture fluxes computed from standard meteorological data. Remotely sensed surface temperature and soil moisture can be compared to model estimates for calibration. The model has been tested using 44 hours of data from a bare soil site. Using daily maximum surface temperatures for calibration, estimated hourly surface temperatures agreed with measurements to better than 1 K. The results are insensitive to the soil heat capacity and most sensitive to the thermal conductivity and aerodynamic roughness. By varying these within physically reasonable limits, bounds on daily evaporation of 3.2 mm and 3.8 mm were estimated.
Simulation of solute transport in a chemically reactive heterogeneous system: Model development and application
Authors: Miller C. W. , Benson L. V.
Published: February 2008

One‐dimensional transport of solutes in a saturated porous medium has been simulated using a numerical model CHEMTRN. This model includes dispersion/diffusion, advection, ion exchange, formation of complexes in the aqueous phase, and the dissociation of water. The mass action, transport, and site constraint equations are expressed in a differential/algebraic form and solved simultaneously. In the mass action equations describing complexation and sorption processes, the activities of the species in the aqueous phase are approximated using the Davies equation. A solubility constraint can be set at the inner boundary. The model was applied to a study of the migration of strontium in groundwater. Results show that surface site competition is important when the strontium concentration is comparable to the background electrolyte concentration, in which case a constant kD model does not simulate the transport of chemical species adequately. In addition, the pH level was buffered to a level of approximately 10 near the wasteform due to the incorporation of the solubility constraint. For the particular case studied, the incorporation of aqueous complexation did not significantly enhance strontium mobility.
Unsaturated flow in spatially variable fields: 3. Solute transport models and their application to two fields
Authors: Bresler Eshel , Dagan Gedeon
Published: February 2008

An approximate model of salt transport in a spatially variable field during infiltration and redistribution is presented. The water flow is assumed to be vertical, and both pore water velocity and depth of wetting front change in the horizontal plane due to the variability of soil hydraulic properties. These variables are computed with the aid of the model developed in part 1 (Dagan and Bresler, this issue) and part 2 (Bresler and Dagan, this issue) of the present study. The salt transport in the vertical profile is computed by using an approximate, closed form solution of the convection‐dispersion equation, with the value of the dispersivity increasing from zero to its maximum (3 cm) as the front propagates downward. The concentration profiles vary in the horizontal plane because of the aforementioned variation of water flow variables. The expectation value and the variance of the concentration are computed as function of depth and time for the two variable soils considered in part 2 (Panoche, with large variability, and Bet Dagan, with lesser variability). The results are compared with those based on a numerical simulation of the water flow and salt transport, as well as with those pertaining to an equivalent, deterministic, uniform soil (for the expected value). It is shown that the approximate model yields quite accurate results when compared with the numerical simulations for the field of large variability, while some differences are present for the more uniform one. In any case, the results for the expected value, based on the traditional approach of replacing the variable field by an equivalent uniform one, include a much larger error. It is suggested that the approximate, simplified model presented here may serve as a basis for simulation of additional effects not considered here, e.g., adsorption, root extraction, and change of soil properties due to salt content. The main conclusion is that in spite of the apparent complexity, the statistical moments of salt concentration in a spatially variable field can be determined by using simple flow models. Therefore further refinement of models of transport in homogeneous columns does not seem to be warranted, and the research effort should be concentrated on the study of field variability.
Estimating spatial variability in soil moisture with a simplified dynamic model
Authors: Clapp R. B. , Hornberger G. M. , Cosby B. J.
Published: February 2008

Observed spatial variability of soil moisture in the field may be due to several factors. Topographic effects, soil heterogeneity, and spatial variability in precipitation and vegetation may induce variability in measured soil moisture. Scaling theory has been suggested as a promising tool for describing soil heterogeneity and, consequently, a portion of spatial variability of measured soil moisture. We investigate the appropriateness of ascribing soil moisture variability to heterogeneity of soil properties through the use of a model of soil moisture dynamics and scaling theory. The model, termed a wetting front model, is a simplified representation of water movement in soils. The model conceptually depicts the moisture profile as discrete blocks of soil moisture separated by sharp fronts. Probabilistic simulations were run with input data appropriate to watersheds R‐5 and R‐7 at Chickasha, Oklahoma. Results from the simulations indicate that variability due to soil heterogeneity remains relatively constant through time with only slight increases during redistribution following infiltration. A comparison of simulated and observed soil moisture integrated from the surface to the 15‐cm depth shows that heterogeneity in soil hydraulic properties may account for approximately 75% of observed standard deviation.
Numerical studies of the heat and mass transport in the Cerro Prieto Geothermal Field, Mexico
Authors: Lippmann M. J. , Bodavarsson G. S.
Published: February 2008

Numerical simulation techniques are employed in studies of the natural flow of heat and mass through the Cerro Prieto reservoir, Mexico and of the effects of exploitation on the field's behavior. The reservoir model is a two‐dimensional vertical east to west‐southwest cross section, which is based on a recent hydrogeologic model of this geothermal system. The numerical code MULKOM is used in the simulation studies. The steady state pressure and temperature distributions are computed and compared against observed preproduction pressures and temperatures; a reasonable match is obtained. A natural hot water recharge rate of about 1×10−2 kg/s per meter of field length (measured in a north‐south direction) is obtained. The model is then used to simulate the behavior of the field during the 1973–1978 production period. The response of the model to fluid extraction agrees to what has been observed in the field or postulated by other authors. There is a decrease in temperatures and pressures in the produced region. No extensive two‐phase zone develops in the reservoir because of the strong fluid recharge. Most of the fluid recharging the system comes from colder regions located above and west of the produced reservoir.
Steady state fluid response in fractured rock: A boundary element solution for a coupled, discrete fracture continuum model
Authors: Shapiro Allen M. , Andersson Johan
Published: February 2008

A discrete fracture representation of a highly fractured groundwater aquifer is inappropriate as a modeling approach since the location of all fractures can never be explicitly specified. However, the alternative of exclusively employing a continuum description of the medium then neglects any geologic information that exists with regard to the location of specific fractures in such formations. In order to take better advantage of geologic information in highly fractured aquifers a model is proposed which couples the discrete fracture and continuum conceptualizations. In regions where discrete fractures are designated, an effecient means of computing the steady state fluid responses is formulated with the use of the boundary element method. This allows the consideration of highly complex fracture geometries, since fluid responses in the porous rock are described with a set of linear equations written only in terms of the hydraulic head and fluid mass flux at the boundaries the porous rock shares with the fractures. One‐dimensional equations of fluid movement in the fractures written in terms of the same variables make coupling of the two systems straight forward. In this technique, discretization only along the fractures is required. Thus the internal discretization of the host rock that would be characteristic in the use of finite difference and finite element methods is alleviated. At the boundary of the region where specific fractures are identified, a continuum conceptualization is coupled to the discrete fracture model. Steady state fluid responses in the continuum domain are defined using a semianalytic technique which is based on the discretization of Green's third identity. The resulting coupled model allows the discrete fracture and continuum conceptualizations to be employed in the modeling of those areas where they are judged to be most appropriate, based on the availability of physical information.
An estimate of the costs of liming to neutralize acidic Adirondack surface waters
Authors: Menz Fredric C. , Driscoll Charles T.
Published: February 2008

Chemical requirements and costs are presented for neutralization of 663 Adirondack lakes with acid neutralizing capacity (ANC) values of <200 μeq/l. Calculations were made using calcium carbonate (CaCO3) to achieve a range of target levels of ANC for 1‐, 5‐, and 10‐year periods of base application. Dose requirements included both aqueous and sediment demand. The estimated costs for a 5‐year base addition program range from $40 to $75 per surface hectare for accessible lakes and from $450 to $675 per hectare for remote lakes (in 1982 dollars). The relative cost‐effectiveness of neutralizing lakes for different time periods was evaluated by the uniform annual cost method. The cost estimates do not include administrative costs, costs of limnological studies to determine base dosages, possible adverse effects of chemical treatment of acidic waters, or other costs to restore lakes to their conditions prior to acidification.
An efficient finite element technique for modeling transport in fractured porous media: 2. Nuclide decay chain transport
Authors: Huyakorn Peter S. , Lester Barry H. , Mercer James W.
Published: February 2008

A finite element model is presented for simulation of nuclide decay chain transport in a naturally fractured porous medium system. The model is capable of representing the physical system using a dual‐porosity approach, a discrete fracture approach, or a combination of these two approaches. Advection and hydrodynamic dispersion in the fractures, as well as diffusion in the porous matrix and chain reactions of solute species, can be taken into account simultaneously. An efficient finite element solution technique has been developed to solve a coupled system of governing partial differential equations. Via this technique, spatial discretizations and solutions of systems of algebraic equations for nodal concentration values in fracture and porous matrix domains can be performed separately. The present finite element model has been verified against analytical solutions. Two test problems involving transport of a chain of three components in unfractured and fractured porous media are presented to demonstrate the accuracy and efficiency of the proposed finite element technique. Results indicate that the present numerical model is capable of producing good predictions of breakthrough curves using relatively coarse spatial and temporal discretizations. A major advantage of the present transport model over previous transport models is that the latter are based on a numerical approach that employs overall discretization and simultaneous solution of the entire set of algebraic equations for concentration values in the fracture and porous matrix block domains. Such an approach is not computationally efficient when compared with the present numerical approach, which employs not only separate discretizations of the fracture and porous matrix domains but also direct sequential solutions of much smaller subsets of algebraic equations. Another important practical aspect is that the present model enables more complex problems, involving transverse diffusion into porous matrix and two‐dimensional transport in the fracture flow plane, to be handled without resorting to a fully three‐dimensional grid. In practical applications, CPU time and cost involved in performing a fully three‐dimensional analysis of multiple species transport may be prohibitive.
A methodology for evaluation of flood forecast‐response systems: 1. Analyses and concepts
Authors: Krzysztofowicz Roman , Davis Donald R.
Published: February 2008

Determination of the value of flood forecasts at a microeconomic level necessitates the consideration of numerous hydrologic, organizational, behavioral, and economic factors. These factors and their interactions are captured in a concept of a flood forecast‐response (FFR) system. The forecast system extends from the collection of data through the forecasting of floods to the dissemination of warnings. The response system encompasses decision making by the floodplain dweller and the protective actions he takes. A methodology for evaluation of the performance of FFR systems is presented. It concerns specifically the economic evaluation of the effectiveness of riverine flood forecasts as a means of reducing property damage. The methodology is built of (1) a model of the FFR process and (2) a performance theory. The first element provides a comprehensive mathematical description of the physical FFR process which takes place during floodings; it outputs the expected annual losses (cost of protective action plus flood damage) incurred by the floodplain dweller under several scenarios. The second element establishes the performance measures and expresses them in terms of the outputs of the FFR model; the measures consist of values (expected annual reductions of the loss), efficiencies, and expected opportunity losses. This part presents a system analysis of the FFR process, describes the general structure of the methodology, and introduces the performance theory. The second part details the theory, and the third part reports three case studies.
A Case Study of a Chemical Spill: Polychlorinated Biphenyls (PCBs) Revisited
Authors: Atwater James W.
Published: February 2008

Remedial and monitoring efforts at the site of a polychlorinated biphenyl (PCB) spill in Regina, Saskatchewan, Canada, has produced information in addition to that found in the original investigation and reported in this journal. Additional pathways exist for horizontal movement of PCB within the underlying clays and silts. The PCB has moved horizontal at depth apparently under its own head resulting in deep contamination that does not have a surface expression.
A Descriptive Decision Process Model for Hierarchical Management of Interconnected Reservoir Systems
Authors: Adigüzel R. İlker , Coşkunoğlu Osman
Published: February 2008

A significant limitation of prescriptive optimization models is that their formulation is disassociated from the behavioral and organizational attributes of the problem addressed. In an attempt to alleviate this limitation a decision process model is formulated directly within a framework of decision agents involved in integrated long‐ and short‐term planning and management of multipurpose and multireservoir system operations. The resulting model is ierarchical, multilevel, multilayer, and decentralized. As such it is descriptive of a reservoir system managed and operated by geographically separated multiple agents with different authorities and responsibilities. Robustness and performance of the model is investigated by using the Shasta‐Trinity system of California as an example. Results are encouraging for the descriptive as well as prescriptive relevance of the model.
Darcy's Flow With Variable Permeability: A Boundary Integral Solution
Authors: Cheng Alexander H.‐D.
Published: February 2008

A boundary integral equation method (BIEM) for Darcy's flow with spatially varied permeability is developed. The formulation requires that Green's function be found for each given permeability variation. For a few permeability functions in one and two dimensions, which can be used to fit field permeability data, closed‐form Green's functions are obtained. Numerical examples are solved and verified.
Additional Tests on the Effect of Rainfall Intensity on Storm Flow and Peak Flow From Wild‐Land Basins
Authors: Hewlett J. D. , Fortson J. C. , Cunningham G. B.
Published: February 2008

Further evidence that hourly rainfall intensity has no appreciable effect on storm flows, and only a small effect on peak flows, was adduced from statistical analysis of 4094 storm events on 15 drainage basins ranging from 13 to 760 ha in area. The basins range from humid to semiarid climates and from flat to steep topography and contain various covers (forest, brush, grass, and swamp). The marginal coefficient of determination accounted for by maximum hourly rain intensity averaged about 1% for storm flows and about 10% for peak flows. The dependence of storm flows on rain intensity did not increase in larger storms or on more responsive basins, but rather the opposite. Similar analyses so far published by others show similar effects.
The Krafla Geothermal Field, Iceland: 4. History match and prediction of individual well performance
Authors: Pruess K. , Bodvarsson G. S. , Stefansson V. , Eliasson E. T.
Published: February 2008

A detailed distributed parameter model, in which all wells are represented individually, is reported for the Krafla geothermal system. The model is based on a synthesis of geological, geophysical, geochemical, and reservoir engineering data from the field. Numerical simulations achieve an approximate match for production rates and flowing enthalpies for 10 wells during the period 1976–1982. Predictions of future field performance on a well‐by‐well basis are presented for alternative field development plans, including additional production wells and reinjection of waste fluids.
In situ estimation of hydraulic conductivity using simplified methods
Authors: Jones A. J. , Wagenet R. J.
Published: February 2008

Five simplified methods of estimating the relationship between hydraulic conductivity K and water content θ were compared in this study. Redistribution of water following constant rate infiltration (steady state) was monitored for a 10‐day period at 100 locations and seven depths at each location within a 5000‐m2 fallow sandy loam field. All the methods assumed a unit hydraulic gradient during redistribution and an exponential relationship between k and θ of the form K(θ) = k0 exp [β(θ − θ0)]. The five methods were the θ, flux, and CGA methods (Libardi et al., 1980) and two methods based on a Lax solution of the Richards’ equation (Sisson et al., 1980). Water content data were used to calculate K0 and β by each method at each depth and location. Soil water flux was estimated for selected depths using appropriate mean and variance values of K0 and β for the field. Relative differences between the methods are briefly discussed.
Precipitation chemistry at Turrialba, Costa Rica
Authors: Hendry Charles D. , Berish Cory W. , Edgerton Eric S.
Published: February 2008

Bulk precipitation samples were collected weekly at Turrialba, Costa Rica, from March 1979 through March 1981 and analyzed for pH, conductivity, major cations and anions, nutrient (N and P) species, and 12 trace metals. Results indicated that Costa Rican precipitation contains relatively low levels of acidity, nutrients, and minerals. For example, during the precipitation years March 1979 to March 1980 and April 1980 to April 1981, volume‐weighted mean specific conductances were 4.88 and 4.82 μS/cm, respectively. Precipitation pH values ranged from 4.81 to 6.35 and the volume‐weighted mean pH was 5.34 over the 2‐year study. On the basis of equivalent ratios, excess [SO42−] was found to be the principal acidic anion, with only small possible contributions from excess [Cl−] or NO3−. Marine‐ derived aerosol accounted for virtually all of the Na+, Mg2− and Cl− deposited in Turrialba rain and was a minor contributor (3–15%) to the K+, Ca2+, and SO42− loadings. Excess [SO42−] comprised 85% of the total SO42− and may arise in Costa Rican precipitation due to long‐range transport, biogenic sources, or local volcanic emissions. Highest concentrations of minerals and nutrients were observed during the low rainfall period of early spring, which coincided with increased agricultural activities. Very low levels of trace metals were observed in the precipitation.
A Green‐Ampt Model of infiltration in a cracked soil
Authors: Davidson Malcolm R.
Published: February 2008

The motion of the wetting front in a two‐dimensional Green‐Ampt model of infiltration into a soil containing regularly spaced water‐filled vertical cracks is traced using a stepwise numerical procedure which progressively solves an integral equation for the velocity at points on the front at each time step. Initially, the calculated front exhibits a mushrooming effect at its base which diminishes both with time and as moisture potential becomes more negative. The shape of the front is independent of crack spacing/depth ratio until the interaction of wetted tongues emanating from adjacent cracks. Thereafter the front becomes flatter and advances further (cumulative infiltration is greater) relative to the crack depth, with decreasing crack spacing and increasingly negative moisture potential.
Chemical patterns of bulk atmospheric deposition in the state of Colorado
Authors: Lewis William M. , Grant Michael C. , Saunders James F.
Published: February 2008

Samples of bulk deposition from the atmosphere were taken over a 1‐year interval between May 1982 and May 1983 at 42 sites distributed over the state of Colorado. Collections were complete for the entire year at 36 of these sites. The collections were made biweekly and were analyzed for major cations, major anions, total particulate material, and the hydrogen ion (pH). A pH below 5.6 was characteristic of the annual precipitation over two thirds of the state, including all of the high‐elevation areas in central Colorado as well as substantial portions of the plains. The lowest pH values (average below 5.0) were found near the Continental Divide in the northern third and southern third of the state. Emissions of NOx and SO2 from power plants within or near the borders of the state are of a magnitude similar to that of the total deposition of SO4 = and NO3− N within the state. Gradients of acidity within the state are to a large degree explained by three factors: (1) location of power plants and urban areas with respect to prevailing winds, (2) differential transport of strong acids and alkalis, and (3) amount of wet precipitation. At lower elevations, carbonates neutralize strong mineral acids, as shown by the distributions of strong acid anions and divalent cations. Because of their association with terrestrial particulate materials, alkalis are transported over shorter distances than the gaseous precursors of mineral acids. Thus air masses moving over the mountains, which lack large sources of either alkalis or acids, show an increasing bias toward acidifying substances at higher elevations. This causes a statewide negative relation between pH and elevation. Superimposed on the elevation effect is a moisture effect caused by a strong relationship between strong acid deposition and amount of wet precipitation.
Groundwater contamination from an inactive uranium mill tailings pile: 1. Application of a chemical mixing model
Authors: White A. F. , Delany J. M. , Narasimhan T. N. , Smith A.
Published: February 2008

Low‐pH process waters contained in a number of inactive and abandoned uranium mill tailings in the United States represent potential sources of radionuclide and trace metal contamination of groundwater. Detailed investigations at a typical site at Riverton, Wyoming, indicate that chemical transport occurs from initial dewatering of the tailings, downward infiltration due to precipitation, and groundwater intrusion into the base of the tailings pile. Except for elevated uranium and molybdenum concentrations, current radionuclide and trace metal transport is limited by the near‐neutral pH conditions of the groundwater. Significant reactions include the dissolution of calcite, production of CO2, and precipitation of gypsum and the hydroxides of iron and aluminum. A geochemical mixing model employing the PHREEQE computer code is used to estimate current rates of the groundwater contamination by tailings water. A maximum mixing of 1.7% of pore water is a factor of 2 less than steady state estimates based on hydraulic parameters.
Solute travel times during trickle irrigation
Authors: Clothier B. E.
Published: February 2008

A theory of solute transport from drip (trickle) emitters is developed. The model of solute flow is based on piston displacement travel times and steady three‐dimensional water flow from a surface point source. Experimental evidence is presented to justify the omission of the solute diffusion‐dispersion term in the flow equation. Laboratory experiments are described to demonstrate the rapid onset of steady state water flow, especially near the emitter. Bromide tracer experiments were carried out in the laboratory using Manawatu fine sand with constant flux infiltration into a small surface cavity. The isochrones predicted from the theory were in accord with the measured bromide fronts.
Meandering channel response to altered flow regime: Milk River, Alberta and Montana
Authors: Bradley Cheryl , Smith Derald G.
Published: February 2008

Mean and peak flows, channel width, and rates of meander migration are examined for two sandy meandering reaches of the Milk River in south Alberta and north Montana. One reach, upstream of the international boundary near Onefour, Alberta, is affected by the St. Mary diversion. The other reach near Havre, Montana is below the Fresno Dam and reservoir. Comparisons are possible because of the ample and long‐term availability of maps, air photos, and hydrometric records preceding and succeeding the two altered flows for both reaches. Understanding the natural river regime and effects of diversion and dam storage are critical for predicting channel responses to a proposed additional dam on the Milk River. Results indicate that increased discharge due to a diversion has increased channel width 5.5 m and increased the rate of meander migration by 0.85 m/year. Downriver, reservoir storage has decreased channel width 16.8 m and the rate of meander migration by 1.3 m/year and caused channel bed degradation up to 1.5 m near the dam.
Interactive Water Resources Modeling and Model Use: An Overview
Authors: Loucks Daniel P. , Kindler Janusz , Fedra Kurt
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.
Interactive Computer Modeling for Policy Analysis: The Flood Hazard Problem
Authors: Kunreuther Howard , Miller Louis
Published: February 2008

This paper discusses an interactive modeling system to support policy analysis for dealing with flood hazards. Policy analysis in this area is complex due to numerous stakeholders with varying concerns, the variety of scenarios that might be considered, and alternative policy options. These conditions require that a modeling system be flexible and support users in a variety of ways. The system should be viewed as a decision aid rather than a burden. The modeling system described in this paper attempts to achieve these goals for microanalytic models that deal with samples of homeowners in a flood‐prone community.
Interactive Computer Modeling, Monitoring, and Control of Melbourne's Water Supply System
Authors: Cosgriff G. O. , Forte P. E. , Kennedy M. A. , Russell J. V. , Smith R. D. , West A. K.
Published: February 2008

The Melbourne and Metropolitan Board of Works in Melbourne, Australia operates two principle models of its water supply system. The first of these is a headworks model that simulates the major reservoirs and transfer mains of Melbourne's water supply system. This model uses monthly data for both the long‐term planning of the water supply system and in assisting in operational decisions regarding transfers of water between headworks storages. The second model is a network model that solves for heads and flows within Melbourne's water supply distribution system. The model can be run over a 24‐hour period and is used for investigating ways of improving the distribution of water within the system and for assisting and training operational staff. This paper describes the application of this network model to Melbourne's water supply system, including the implementation of computer graphics techniques. Examples demonstrating the application of color graphics to different parts of the system are given together with a discussion of the present integrated modeling, operation, and telemetry capability. The models will be continually modified and improved as both new systems are added to Melbourne's water supply system and greater knowledge of the existing system is ained. The implementation and use of the 24‐hour network simulation program by the Board has already resulted in a current savings in excess of $30 million. This is more than six times the total cost of the modeling and telemetry system. Future benefits are expected to add to this savings.
Applicability of Effective Parameters for Unsteady Flow in Nonuniform Aquifers
Authors: El‐Kadi Aly I. , Brutsaert Wilfried
Published: February 2008

As a rule, a groundwater aquifer consists of materials whose characteristics vary in space. On account of the uncertainty in determining these characteristics and their variation in the field and also for the sake of parsimony, it is often desirable to assume that the aquifer may be considered homogeneous and uniform; in other words, the prototype is modeled by an equivalent homogeneous and uniform aquifer with a set of effective parameters, which displays the same flow characteristics. To study the applicability of this concept, a Monte Carlo technique was used in the simulation of unsteady gravity drainage from a large unconfined aquifer. For given criteria of hydraulic equivalence applied to the outflow rate, effective parameters (hydraulic conductivity and drainable porosity) were obtained, hose variation was studied. It was found that only under certain conditions is it possible to define a single set of effective parameters to reproduce the median outflow hydrograph. The effective parameters were found to depend on both the distribution of the hydraulic conductivity and its spatial correlation.
Finite Element Matrix and Mass Balance Computational Schemes for Transport in Variably Saturated Porous Media
Authors: Huyakorn Peter S. , Mercer James W. , Ward David S.
Published: February 2008

An upstream‐weighted residual finite element formulation is developed for the numerical simulation of solute transport in variably saturated porous media. Included in this formulation is an influence coefficient scheme for element matrix evaluation and a mass balance computation scheme. These schemes are not only simple to implement but also cost effective. Three examples are provided to verify the numerical techniques and demonstrate the utility of the computer model. These examples indicate that mass balance information serves a useful purpose as a screening device for examining the numerical solution. They also show certain behavior of the mass balance error as well as numerical difficulties associated with the manner in which the finite element formulation of the transport equation is performed. Finally, information on the CPU time and cost required to solve the three example problems is provided to show the cost effectiveness of the present transport model. Although the present analysis considers only two dimensions, the schemes described can be extended to three dimensions, where the time and cost savings are more significant.
Interpretation of Pressure‐Depth Data From Confined Underpressured Aquifers Exemplified by the Deep‐Basin Brine Aquifer, Palo Duro Basin, Texas
Authors: Orr Elizabeth D. , Kreitler Charles W.
Published: February 2008

Investigations of underpressured aquifers can be improved by accounting for factors that impede accurate interpretation of pressure‐depth plots. Poor data quality and distribution obscure true pressure‐depth trends. Plotted data may also be distorted by the hydrogeologic setting, i.e., the surface topography, the structural dip of the aquifer, and the potentiometric surface. In the Palo Duro Basin in the Texas Panhandle, distortions caused by the hydrogeologic setting are reduced by delineating regions having little variation in surface topography and in structural dip of the aquifer. Pressure‐depth plots for these regions vary considerably. The effects of the hydrogeologic setting on these plots were evaluated by computing pressure‐depth data for flow parallel to the structural dip of the aquifer in each region. By comparing regression lines through real pressure‐depth data with those through computed data, true hydrologic conditions could be distinguished from the misleading effects of the hydrogeologic setting on pressure‐depth plots.
A condensed disaggregation model for incorporating parameter uncertainty into monthly reservoir simulations
Authors: Stedinger Jery R. , Pei Daniel , Cohn Timothy A.
Published: February 2008

A condensed version of the Valencia‐Schaake disaggregation model is developed which describes the distribution of monthly streamflow sequences using a set of coupled univariate regression models rather than a multivariate time series formulation. The condensed model has fewer parameters and is convenient for generating flow sequences which incorporate the intrinsic variability of streamflows and the uncertainty in the parameters of the annual and monthly streamflow models. The impact of parameter uncertainty on derived relationships between reservoir capacity and reservoir performance statistics is illustrated using required reservoir capacity (calculated with the sequent peak algorithm), system reliability, and the average total shortfall. Modeled sequences describe flows in the Rappahannock River in Virginia and the Boise River in Idaho. For high‐reliability systems the results show that streamflow generation procedures which ignore model parameter uncertainty can grossly underestimate reservoir system failure rates and the severity of likely shortages, even if based on a 50‐year record.
Optimization of a Spatially Variable Resource: An Illustration for Irrigated Crops
Authors: Feinerman E. , Bresler E. , Dagan G.
Published: February 2008

Economic optimization of a resource which is space dependent and displays irregular spatial variation was investigated. The resource (yield) of an entire field is regarded as a random variable which depends on a random function on the one hand, and a control variable on the other hand. The study focuses on the question of how economically efficient levels of relevant control variables may vary as a function of random spatial variability of resources, taking into account the decision maker's attitude to risk. A general approach to cope with the above question is developed, and the effects of uncertainty on the levels of the optimal control variables are investigated by comparing a deterministic case with two uncertainty levels of decision making: risk neutral and risk averse. Following the general methodology, expectation value and variance of average yield are first approximated by Taylor series expansion and then closed‐form solutions are obtained for a specific, exponential, yield production function. Subsequently, we illustrate the general analysis for the example of irrigated corn, the only control variable being water quantity, and with corp yield a spatial random function in the plane. The results suggest that the impact of random soil properties on optimum level of water application might be substantial. Hence it is generally worthwhile to account for spatial variability in optimizing level of irrigation or similar control variables.
Volumetric Pricing of Agricultural Water Supplies: A Case Study
Authors: Griffin Ronald C. , Perry Gregory M.
Published: February 2008

Models of water consumption by rice producers are conceptualized and then estimated using cross‐sectional time series data obtained from 16 Texas canal operators for the years 1977–1982. Two alternative econometric models demonstrate that both volumetric and flat rate water charges are strongly and inversely related to agricultural water consumption. Nonprice conservation incentives accompanying flat rates are hypothesized to explain the negative correlation of flat rate charges and water consumption. Application of these results suggests that water supply organizations in the sample population converting to volumetric pricing will generally reduce water consumption.
Mixing of a Stratified River by Barge Tows
Authors: Stefan Heinz G. , Riley Michael J.
Published: February 2008

The effect of commercial navigation (barge tows) on the mixing and the reestablishment of a stratified river has been measured in the upper Mississippi River downstream from a major wastewater effluent site. Observations have also been made in a laboratory flume. Mixing effectiveness increases from single towboats to unloaded barges to loaded barge tows. Energy expenditure by barge tows per foot of river length traveled is much larger than work done by gravity forces of the free‐flowing river to overcome bottom shear. The displacement of water by loaded barge tows appears to be more significant than the jet effect of the towboat propellers. One passage usually produces complete vertical mixing in the path of the tow; an entire cross section (700 feet × 11 feet (213.4 m × 3.4 m)) will be fully mixed by two or three passages. Surface waves and internal waves generated by a towboat passage cause surging of the effluent for up to 30 min after passage. Reestablishment of a stratified river is controlled by mean river velocity and the frontal velocity of the density current (underflow or overflow) resulting from the discharge. Calculated and observed reestablishment times depend on distance from the outlet and strength of the stratification. Order of magnitude comparisons of calculated and observed reestablishment times were in good agreement. Reestablishment of stratification may take from 15 to 45 min at a distance of only 1000 feet (304.8 m) from an outfall. Water quality models and field studies in impounded rivers with high navigation frequency must account for mixing and transport effects of towboats, particularly under low flow conditions.
Steady State Infiltration: Consequences of α Dependent on Moisture Content
Authors: Parlange J.‐Y. , Hogarth W. L.
Published: February 2008

It is shown from the examples of a clay and a sand that the α parameter, in the steady state infiltration equation, is usually far from constant over the whole range of moisture content. Thus the linearized form of the steady state infiltration equation does not give, in general, an accurate description of the flow of water in a soil if it has both dry and saturated regions. When α is dependent on moisture content, the limit of α small may represent either a saturated soil or a soil of low water content. The former is more readily achieved in a coarse‐textured soil and the latter in a fine‐textured soil.
Geometry‐Imbedded Darcy's Law and Transient Subsurface Flow
Authors: Narasimhan T. N.
Published: February 2008

The traditional interpretation of Darcy's experiment views it as a valuable means for setting up the partial differential equation of transient or steady state subsurface fluid flow. In the present work, Darcy's observations are viewed from a different perspective, enabling the statement of transient subsurface fluid flow in terms of an equation defined over finite domains of space and time. Two new notions, namely, geometry imbedding and location of average, are introduced. The equation describes transient flow along a flow tube with arbitrarily varying cross section, consisting of materials with properties dependent on fluid potential. This equation, based on its own postulates, is fully consistent within itself and exists independently of the classical partial differential equation. This technical note presents preliminary ideas on what appears to be a promising new line of inquiry that departs from the traditional approach based on continuum mechanics. Further work is in progress.