bluuebunny/crossref_metadata_2025 huggingface dataset:
E‐type asteroid spectroscopy and compositional modeling
Authors: Clark Beth Ellen , Bus Schelte J. , Rivkin Andrew S. , McConnochie Timothy , Sanders Josh , Shah Sweta , Hiroi Takahiro , Shepard Michael
Published: February 2004

We present near‐infrared spectroscopic observations (0.8–2.5 μm) of E‐type asteroids. We combine these observations with visible wavelength spectra obtained by other researchers and perform Hapke theory mixing model simulations of E‐type asteroid spectra in order to constrain possible compositions. Aubrites were originally suggested as the meteorite analog for the E‐type asteroids because of their similar visible wavelength colors and high albedos. The designation “E” was originally linked with the mineral enstatite, common in aubrite meteorites. More recently, the sulfides troilite and oldhamite have been suggested as possible components of E‐type asteroids. We tested the suggested compositional interpretations of aubrite meteorites and/or aubrites enhanced with sulfides. We also tested compositions of aubrites mixed with low‐iron silicate minerals. We find that E types can be separated into three groups on the basis of inferred composition: “Nysa‐like” E types are consistent with silicate mineralogy higher in iron than the mineral enstatite; “Angelina‐like” asteroids are consistent with silicate mineralogy, including a sulfide such as oldhamite; and “Hungaria‐like” E types are not inconsistent with aubrites. Our results indicate that some E‐type asteroids may be composed of materials that are not sampled by meteorites.
Runoff contamination by soil chemicals: Time scale approach
Authors: Wallach Rony
Published: February 2004

Two mass balance equations were used to model the transfer of dissolved chemicals from the soil solution to the surface runoff water and transport of these chemicals to the field outlet end. One mass balance equation is written for the chemicals dissolved in the overland water, and the other for the chemicals within the soil profile. The chemical input into the surface runoff water is by the rate‐limited convective mass transfer process. Two time scales are isolated: the slow time scale represents the diffusion‐based mass transfer process and the fast time scale represents the convective transport of dissolved chemicals by overland flow. Scaling the mass balance equations for the slow time scale yields a small parameter, which multiplies the time derivative of the mass balance equation written for the overland flow, providing a singular perturbation problem. By using the method of matched asymptotic expansion, an inner and outer problem is formulated and solved for each order of approximation. A single composite expansion, uniformly valid over the entire domain, is derived analytically. This approximated solution was compared with an exact analytical solution for the case in which chemicals are initially uniformly distributed throughout a semi‐infinite soil profile. The time scale method was then used to solve a more complicated problem in which chemicals are initially distributed within a certain soil surface layer of a semi‐infinite soil profile.
Laboratory analysis of fluid flow and solute transport through a fracture embedded in porous tuff
Authors: Haldeman W. R. , Chuang Y. , Rasmussen T. C. , Evans D. D.
Published: February 2004

Laboratory experiments were conducted to determine the flow and transport properties of a fractured porous tuff block measuring 20 × 20 × 50 cm. One porous ceramic plate was placed immediately above a fracture and two other plates were placed on either side of the fracture above the rock matrix. The plates control the pressure head applied to the upper surface of the fractured rock block. Laboratory results are simulated using the boundary integral method for a single saturated fracture with an assumed uniform transmissivity embedded within a porous tuff block. The simulation is used to identify the saturated hydraulic properties of the fracture. Matrix hydraulic conductivity is estimated as 50 × 10−9 m s−1 and the fracture transmissivity is estimated as 5.0 × 10 −9 m2 s−1. Much of the flow which exits the fracture at the lower surface first passes through the rock matrix even though a direct contact with a porous plate is present. Travel times and breakthrough curves are calculated by integrating the inverse velocity along a streamline, and then summing over all streamlines. Observed breakthrough curves were used to estimate fracture dispersivities which ranged from 0.0207 to 8.01 m. Breakthrough curves deviated from simulation results due to significant channeling of fracture flow.
Valuing potential groundwater protection benefits
Authors: Crocker Thomas D. , Forster Bruce A. , Shogren Jason F.
Published: February 2004

This paper explores the implications of endogenous risk for the economic value of preventing groundwater contamination. We consider the analytical implications of endogenous risk for five key building blocks frequently used to structure studies of groundwater valuation: the probability and the location of contamination, the exposed population, risk perceptions, and intertemporal issues.
Spatial rainfall distribution at a storm event in mountainous regions, estimated by orography and wind direction
Authors: Oki T. , Musiake K. , Koike T.
Published: February 2004

In this paper the orographical effect for rainfall distribution at a storm event is discussed. The main effect is represented by the ground‐forced ascending current of air. A three‐dimensional numerical model of the hydrostatic atmosphere, including basin orography, is used to estimate the ascending current area for any wind direction. The authors also propose a new concept named directional probability of storm event (DiPoSE). A severe storm is more likely to occur when the wind blows from a high DiPoSE direction rather than from a low DiPoSE direction. The wind direction at a storm event is determined from a DiPoSE analysis and is used in the numerical model. The calculated ascending air region is regarded as a severe rainfall area in mountainous river basins. The results are examined and compared with observations.
Residential water usage: A case study of the major cities of the western region of Saudi Arabia
Authors: Abu Rizaiza Omar S.
Published: February 2004

Socioeconomic and climatological data of the major cities of the western region of Saudi Arabia have been used to develop several models to estimate the residential water usage for different kinds of houses. The developed models correlate the residential water usages with temperature, income, family size, price of water, and availability of a garden within the house. The study shows that the residential water uses in houses supplied by a public pipe network are 1.4–2 times greater than the residential water uses in houses supplied by tankers. It also shows that the price elasticities are very similar to those estimated in the United States. Income elasticities, on the other hand, are lower than those typically found in more industrialized countries.
Geostatistical characterization of groundwater flow parameters in a simulated aquifer
Authors: Desbarats A. J. , Srivastava R. M.
Published: February 2004

An analog method is used to simulate a discrete transmissivity field free of the artifacts inherent in conventional multivariate Gaussian statistical generation methods. The simulated field provides a realistic model of a formation exhibiting the spatial continuity of extreme transmissivities which gives rise to barriers and preferential channels for flow. The heterogeneous transmissivity field and the corresponding steady‐state head and discharge fields are characterized in a geostatistical framework and observed spatial statistics are compared with theoretical results from the stochastic hydrogeology literature. The simulated transmissivity field exhibits a bimodal distribution and strong directional anisotropy with nested scales of heterogeneity. Despite these significant departures from standard models, the observed head covariance and head‐log‐transmissivity cross‐covariance agree well with theory. The spatial covariance of specific discharge is highly anisotropic reflecting preferential channeling in the mean direction of flow and the conservation of flux along streamlines. The effective transmissivity of the field is predicted more accurately by the spatial geometric average than by theoretical models despite the flow channeling and the anisotropy of heterogeneity. Tracer spreading, modeled by particle tracking, is non‐Fickian at displacements of up to 13.4 times the log‐transmissivity integral range because transport behavior is dominated by convection along a small number of preferential channels. The observed scale dependence of apparent longitudinal dispersivity is predicted generally well by theory. Results of this study suggest that ensemble theoretical models based on perturbation approaches can provide reasonable estimates of general flow and transport properties of single field realizations under moderate conditions of heterogeneity.
On the concept of evaporation from fresh and saline water bodies
Authors: Steinhorn Ilana
Published: February 2004

The use of several different concepts interchangeably as a measure of evaporation rate may result in up to 50% error in evaporation estimates.
Velocity distribution and bed roughness in high‐gradient streams
Authors: Wiberg Patricia L. , Smith J. Dungan
Published: February 2004

A model for the velocity field over a poorly sorted bed is derived herein and applied to flow in steep streams with coarse gravel beds. In such streams, large clasts often are comparable in size to stream depth and act as obstacles to the flow. The effect of these obstacles on a flow is estimated by partitioning total stress, proportional to the depth‐slope product, into a purely fluid component and a form‐drag component associated with flow around the obstacles. An eddy viscosity closure is used, with a length scale dependent on both distance from the boundary and wake dimension. Resulting velocity profiles agree well with profiles measured by Marchand et al. (1984) in nine mountain streams in Colorado. Model runs for a range of conditions reveal that the velocity distribution depends primarily on D84z and flow depth h; D84z is the length of the vertically oriented axis of clasts at the 84th percentile of the grain size distribution. Calculated values of mean velocity, normalized by shear velocity, are well represented by a simple log linear relationship in terms of relative roughness D84/h.
An evaluation of analytical solutions to estimate drawdowns and stream depletions by wells
Authors: Spalding Charles P. , Khaleel Raziuddin
Published: February 2004

Analytical solutions for computing drawdowns and streamflow depletion rates often neglect conditions that exist in typical stream‐aquifer systems. These conditions can include (1) partial penetration of the aquifer by the stream, (2) presence of a streambed clogging layer, (3) aquifer storage available to the pumping well from areas beyond the stream, and (4) hydraulic disconnection between the stream and the well. A methodology is presented for estimating extended flow lengths and other parameters used to approximate the increased head losses created by partially penetrating streams and clogging layer resistance effects. The computed stream depletion rates and drawdown distributions from several analytical solutions (Theis, 1941; Glover and Balmer, 1954; Jacob, 1950; Hantush, 1965) were compared to those obtained using a two‐dimensional groundwater flow model. The stream geometry was approximated as a semicircle. Numerical simulation results indicate that, because of the use of simplifying assumptions, the analytical solutions can misrepresent aquifer drawdown distributions and overestimate stream depletion rates. Assuming that a correct simulation of the stream depletion phenomenon is provided by the numerical model, the error associated with each of the simplifying assumptions was determined. At a time of 58.5 days after pumping began, errors in computed stream depletion rates due to neglect of partial penetration were 20%, those due to neglect of clogging layer resistance were 45%, and those due to neglect of storage in areas beyond the stream were 21%. Neglecting hydraulic disconnection had only a minor effect (i.e., an error of 1% only at a time of 58.5 days after pumping began) on computed stream depletion rates and a noticeable effect on aquifer drawdown distributions.
A semiempirical model of bare soil evaporation for crop simulation models
Authors: Brisson Nadine , Perrier Alain
Published: February 2004

In crop simulation models the water subroutine computes evaporation and transpiration separately. This property allows a greater confidence in the simulation of the early crop stages in terms of water requirements. In the present article the authors suggest a semiempirical model of the drying stage of soil evaporation that can be easily integrated into various crop models. The model is based on a physical approach, yet it depends solely on permanent soil properties and on some key data on the local climate. The basic theory relies upon the mass balance of a dry surface layer of varying thickness. After successive assumptions on the main limiting factors of the drying process, the authors demonstrate that this process can be described by one equation relating actual to potential evaporation. The advantage of this formula comes from its introducing just one synthetic parameter that can be expressed as the product of two components: a climatic one and a pedological one. When compared with experimental data, the results of the model show that the order of magnitude of the evaporative process is respected, which is required for crop models.
Convective accelerations and boundary shear stress over a Channel Bar
Authors: Whiting Peter J. , Dietrich William E.
Published: February 2004

Alternate bars are important features in alluvial channels as they determine flow and transport patterns. They appear fundamental to selection of meander wavelengths and the geometry of bends. Bend flow has been studied extensively: far less study has been made of flow over alternate bars. Field results from Solfatara Creek, a 5.2‐m‐wide, 0.2–0.7‐m‐deep gravel bed channel where flow exits an upstream bend and shoals over a bar in a straight reach, are used to examine patterns of flow and the fluid forces determining the flow field. Large cross‐sectional area changes, tied primarily to variation in depth, force large stream‐wise accelerations and substantial cross‐stream flow off the central bar. The topographically driven downstream and cross‐stream accelerations are sufficiently large that their influence upon the balance of forces is of the same order as the pressure gradient and the boundary shear stress. The importance of convective accelerations in the downstream flow equation in this straight reach concurs with bend flow results, but the similar importance of convective accelerations in the cross‐stream equation contrasts with results from bend flow. While part of the difference may be attributed to the lower stage conditions herein, in the absence of significant curvature change the cross‐stream force balance depends upon the flow going over and around the bar. Local boundary shear stress estimated from the law‐of‐the‐wall and a roughness algorithm decreases out of the upstream bend, increases over the bar top to values approaching the threshold for motion, and then decreases in deeper flow. Strong bed surface coarsening maintains the topography in a stress field that would otherwise lead to planation of the bar top and filling of the deeper regions.
Impact of Vapor Sorption on the Subsurface Transport of Volatile Organic Compounds: A Numerical Model and Analysis
Authors: Culver Teresa B. , Shoemaker Christine A. , Lion Leonard W.
Published: February 2004

A flexible finite element transport model, which includes the impact of vapor sorption, is developed to simulate the movement of volatile organic compounds (VOCs) in variably saturated porous media. The two‐dimensional numerical model predicts contaminant transport by aqueous advection, aqueous dispersion, aqueous and vapor diffusion, and surface volatilization. For a soil with increasing water contents with depth, one‐dimensional simulations demonstrate that strong vapor sorption may reduce the total amount of VOC that volatilizes in 100 days from 84.6% of the initial mass volatilized without vapor sorption to 73.2%. Yet, for a soil with low water contents at depth, such as in an area with limited recharge, vapor sorption enhanced the rate of volatilization in 100 days from 72.4% without vapor sorption to a peak of 90.3%. When low soil moisture was combined with a soil type that has strong vapor sorption characteristics, VOC transport was significantly retarded.
Snow hydrology of a headwater Arctic basin: 2. Conceptual analysis and computer modeling
Authors: Hinzman Larry D. , Kane Douglas L.
Published: February 2004

Lack of hydrologic data in the Arctic, particularly during snowmelt, severely limits modeling strategy. Spring snowmelt in Imnavait watershed is a very brief event, usually lasting about 10 days. Peak flow normally occurs within 36 hours of the beginning of streamflow. All downslope movement of water occurs within the top 10 cm of the highly organic soil mat or on the surface. Snow damming of snowmelt runoff is an important mechanism which must be considered in the modeling process of small watersheds. These unique characteristics of Arctic hydrology will affect the methodology and performance of a hydrologic model. The HBV model was used in an investigation of the hydrologic regime of an Arctic watershed during the spring snowmelt period. From the analysis of five spring melt events we found that HBV can adequately predict soil moisture, evaporation, snow ablation and accumulation, and runoff. It models the volumes of snowmelt runoff well, but more data are needed to improve the determination of snowmelt initiation. Use of HBV as a predictive tool is dependent upon the quality of the meteorologic forecast data.
Groundwater contamination at the Kesterson Reservoir, California: 2. Geochemical parameters influencing selenium mobility
Authors: White Art F. , Benson Sally M. , Yee Andrew W. , Wollenberg Harold A. , Flexser Steven
Published: February 2004

Transport of selenium in groundwater at the Kesterson Reservoir in the Central Valley of California was strongly retarded because of chemical reduction and precipitation mediated by microbial activity. Under such conditions, negative correlations were documented between aqueous Se and Fe2+, Mn, and H2S. Locally, the presence of oxidizing species, notably O2 and NO3, suppressed this reduction, permitting Se mobilization in the shallow aquifer. Selenate, the dominant and most oxidized form of Se, was in electrochemical disequilibrium with subordinate concentrations of selenite. Normally slow inorganic reduction rates were accelerated by microbial activity which utilizes oxidized chemical species including selenate as electron donors during the oxidation of organic matter. Two stratified redox barriers to selenium migration were documented beneath Kesterson: an underlying shallow anoxic zone underlying most of the pond bottom, characterized by high organic content and sulfate reduction, and a deeper dynamic front established by localized O2 infiltration from the overlying ponds and Fe2+ release from aquifer materials. The reducing nature of this deeper aquifer ultimately precludes Se transport to regional groundwater.
Pore scale spatial analysis of two immiscible fluids in porous media
Authors: Gvirtzman Haim , Roberts Paul V.
Published: February 2004

A conceptual model is introduced describing the spatial distribution of two immiscible fluids in the pore space of sphere packings. The model is based on the ideal soil concept of homogeneous arrangement of identical spheres but is generalized to include random packing. It quantitatively analyzes the interfacial area between wetting and nonwetting fluids and between the fluids and the solid spheres, as a function of the saturation degree. These relationships depend on the packing arrangement of the spheres, the sphere radius, and the fluid‐solid contact angle. The model focuses on the region of low saturation of the wetting phase, where the wetting phase is comprised of pendular rings. When the nonwetting phase appears as ganglia, the model assumes single‐chamber ganglia. Three‐dimensional graphical illustrations are provided. Three potential applications are pointed out: (1) to quantify the water‐air interface in the unsaturated zone; (2) to analyze connate water interfacial area in petroleum reservoirs and to assess the effect of surfactants during enhanced oil recovery; and (3) to estimate the interface between groundwater and floating nonaqueous phase liquids above the water table.
An analytical solution to Richards' equation for time‐varying infiltration
Authors: Warrick A. W. , Islas A. , Lomen D. O.
Published: February 2004

An analytical solution is developed for Richards equation for time‐varying infiltration. The infiltration rates must be specified as piecewise constants with time. The answer is expressed as a sum of two terms, the first is a function of the instantaneous infiltration and the second an integral which accounts for the water distribution within the profile for the previous infiltration history. The solutions assume specific forms for the soil water diffusivity and hydraulic functions used earlier by Broadbridge and White (1988).
New water transfer restrictions: The West returns to riparianism
Authors: Tarlock A. Dan
Published: February 2004

Fundamental shifts in water allocation and management are occurring throughout the West. Changing public values have reversed our historic preference for supply augmentation through the construction of new storage systems and replaced it with one for the reallocation of existing supplies. The emerging reallocation era will be characterized by the better management of existing supplies to serve both traditional and new user communities. Reallocation can be accomplished in three ways: (1) the rededication of unallocated or unused blocks of stored water on federal and state reservoirs, (2) the voluntary transfer of existing water rights, and (3) the redefinition of existing rights by judicial decisions and legislation which trim consumptive entitlements. We currently lack a coherent water allocation principle to replace the equation of conservation with storage and maximum consumption, but we are simultaneously trying to reduce the transaction costs of transfers and to impose a number of ad hoc state and federal restraints on water transfers to accommodate the previously neglected claims of nontraditional water users and other interested parties. These new laws can greatly increase the costs of transfers and make them politically unattractive. The expanded recognition of traditional and new third party rights could produce a new riparianism in the West. This would overturn the law of prior appropriation which has thrived because it was premised on the severance of the right to use water from its source and allowed water to be allocated to new demands. In contrast, the common law of riparian rights confines water rights to landowners in the watershed of a stream. From the beginning, western courts rejected the watershed limitation, but many recent transfer restraints modify the law of prior appropriation and reintroduce the principle of watershed protection rule in the form of a premise that river systems should be managed on an ecosystem basis. Emerging new watershed rules could make all transfers presumptively suspect.
Radiocarbon in Dissolved Organic Carbon, A Possible Groundwater Dating Method: Case Studies From Western Canada
Authors: Wassenaar Leonard , Aravena Ramon , Hendry Jim , Fritz Peter
Published: February 2004

This paper explores the feasibility of using 14C in dissolved organic carbon (DOC) as an alternative isotopic ground water dating method. Two hydrogeologically contrasting groundwater systems were tested; the Cretaceous age Milk River aquifer, and low‐permeability, organic rich, Wisconsinan age Prairie tills in southern Alberta, Canada. Comparisons of radiocarbon data were made between DOC fractions, dissolved inorganic carbon (DIC), and several DIC geochemical age correction models along well defined flow paths. The data presented demonstrate that 14C dating of DOC fractions can indeed provide an alternative method for determining isotopic groundwater ages, under suitable conditions. However, detailed information may be required regarding (1) the geologic nature of the aquifer and its flow system, (2) the isotopically conservative behavior of DOC, (3) the initial 14C activity of DOC in recharge, and (4) the effect of bacterial redox processes on the 14C activity of DOC. In the Milk River aquifer, DOC 14C ages were successfully used to estimate groundwater residence times, as well as to further refine input parameter assumptions for the DIC method. In the Prairie tills, DOC 14C ages were used to establish a maximum age for the pore waters in an environment where the DIC method is especially problematic.
Snow accumulation and distribution in an Alpine Watershed
Authors: Elder Kelly , Dozier Jeff , Michaelsen Joel
Published: February 2004

Distribution of snow water equivalence (SWE) was measured in the Emerald Lake watershed located in Sequoia National Park, California, by taking hundreds of depth measurements and density profiles at six locations during the 1986, 1987 and 1988 water years. A stratified sampling scheme was evaluated by identifying and mapping zones of similar snow properties on the basis of topographic parameters that account for variations in both accumulation and ablation. Elevation, slope, and radiation values calculated from a digital elevation model were used to determine the zones. Of the variables studied, net radiation was of primary importance. Field measurements of SWE were combined with the physical attributes of the watershed and clustered to identify similar classes of SWE. The entire basin was then partitioned into zones for each survey date. Statistical analysis showed that partitioning the watershed on the basis of topographic and radiation variables does produce superior results over a simple random sample.
Using Kalman Filtering to Improve and Quantify the Uncertainty of Numerical Groundwater Simulations: 1. The Role of System Noise and Its Calibration
Authors: Van Geer Frans C. , Te Stroet Chris B. M. , Yangxiao Zhou
Published: February 2004

Deterministic models are widely used to describe the behavior of the hydraulic head in time and space. It would be useful to know the uncertainty of these approximations of reality, what data on groundwater head they require and whether these data can be used to improve the model's performance after calibration/validation. Therefore the use of a Kalman filter algorithm for assessing the uncertainty of a deterministic groundwater model is described. It is suggested that the strength of the Kalman filter is that it makes good use of the available information to assess uncertainty and to improve model performance. This has implications for applications such as the analysis and design of groundwater networks and on‐line groundwater management. After briefly describing how to combine a Kalman filter with a deterministic groundwater model, some important aspects like quantifying the system noise statistics and calibrating these values are emphasized. These aspects are illustrated using a one‐dimensional hypothetical example of a groundwater system.
Comparable estimates of the recreational value of rivers
Authors: Sanders Larry D. , Walsh Richard G. , McKean John R.
Published: February 2004

The contingent valuation method (CVM) and travel cost method (TCM), recommended by the federal guidelines, are applied to the problem of estimating recreational benefits in a case study of rivers in the Colorado Rocky Mountains. The primary purpose is to assess the validity of the behavioral intentions reported in CVM surveys compared to actual behavior‐based TCM analysis. Comparison of the two approaches has been limited by potential measurement problems including variation in the valuation question and model specification. This study evaluates CVM questions asking for both trip and annual values, versus TCM models of the number of trips per participant with and without adjustment for the probability of participation. Based on this case study, we cannot reject the hypothesis that recreation benefits estimated by the alternative methods are equal. Apparently, the ordinary CVM and individual TCM can provide as useful an approximation of the recreational economic welfare effects of river protection as the alternative procedures.
Dynamics of Moving Boundary Overland Flows Over Infiltrating Surfaces at Hillslopes
Authors: Govindaraju Rao S. , Kavvas M. Levent
Published: February 2004

The three flow processes occurring on hillslopes (overland flows, streamflows, and subsurface saturated‐unsaturated flows) are in dynamic equilibrium and interact continuously through their common boundaries. A physics‐based, deterministic, distributed model incorporating internal coupling of the three components is developed to study the extent and location of saturated regions neighboring the streams. These saturated zones develop overland flow and are very responsive to rainfall and are therefore important contributors to the hillslope hydrograph. Using a wide channel which drains the water from the side hillslopes (resembling an open book) for a physical section, we study the response of these variable source areas (VSAs) to various hydrologic and topographic parameters. An infiltrating boundary condition, which allows for both the Horton and Dunne mechanisms of overland flow generation, is incorporated in the analysis. It is observed that the dynamic modeling of the VSAs is useful for determining the hillslope hydrograph properties.
Efficient and accurate front tracking for two‐dimensional groundwater flow models
Authors: Schafer‐Perini Annette L. , Wilson John L.
Published: February 2004

Four new algorithms are presented to cost‐effectively delineate displacement fronts and capture zones via particle tracking in complex flow fields. These algorithms include methods of (1) defining path lines using “mixed distance and time particle tracking”; (2) computing displacement fronts and capture zones using “dynamic particle allocation front tracking” allowing insertion/deletion of particles to optimize front definition; (3) obtaining accurate breakthrough curves by using simultaneous “mass redistribution,” reallocating particle mass among particles defining the displacement front; and (4) determining production well breakthrough curves using “optimized sorting algorithms” when backward tracking to map capture zones. Examples are shown for capture zones and aquifer remediation applications. Comparisons are made to conventional algorithms. Results show that the number of particles required to define displacement fronts and breakthrough curve is a function of time, position, and How field complexity. Dynamic front tracking results in significant savings of storage and computational expense, even for relatively simple velocity fields. A corresponding increase in the accuracy of breakthrough curves is obtained.
Horizontal redistribution with capillary hysteresis
Authors: Philip J. R.
Published: February 2004

Exact and relatively simple analysis is possible for one hysteretic redistribution process, that in long horizontal columns with the two parts, x < 0 and x > 0, at different uniform moisture contents θ1 and θ2 (θ1 > θ2) at time t = 0. We formulate and solve this problem. The key to its simplicity is its similarity character, with moisture profile x(θ) proportional to t1/2. At the interface x = 0 there is, for t > 0, a permanent and constant moisture content jump θ3 to θ4 (θ3 > θ4). The operative moisture potential is the primary drying potential for x < 0, θ1 ≥ θ ≥ θ3 and the primary wetting potential for x > 0, θ4 ≥ θ ≥ θ2. The operative moisture diffusivity is the primary drying diffusivity for x < 0 and the primary wetting diffusivity for x > 0. The drying diffusivity is greater than the wetting diffusivity near θ = θ1 and less near θ = θ2 Solutions are found for illustrative examples corresponding to four values of H, the relative magnitude of the hysteresis loop. The resorptivity R, the total wet‐to‐dry exchange of water across x = 0 in reduced form, is analogous to the sorptivity S in absorption and infiltration. For the calculated examples, R is about one third of S for the corresponding absorption process and varies only mildly with H. Nonhysteretic calculations may thus give reasonable estimates of R for horizontal hysteretic redistribution, though they cannot give details such as the moisture jump at x = 0, Desorption moisture profiles for x < 0 are very gradual, with a large depth of penetration. Absorption profiles for x > 0 are relatively steep, and the penetration depth small. It follows that in experiments the initially wet section of the column should be made some 5–10 times longer than the initially dry sector.
A coupled channel network growth and hillslope evolution model: 2. Nondimensionalization and applications
Authors: Willgoose Garry , Bras Rafael L. , Rodriguez‐Iturbe Ignacio
Published: February 2004

This paper explores the scaling and similitude properties of the system of governing equations for a catchment evolution model that was presented in an accompanying paper (Willgoose et al., this issue). Similitude is an important concept that allows the quantification of the similarities of, and differences between, two catchments. Through the use of a small number of nondimensional numbers the governing physics of the channel network and surrounding hillslopes in a catchment may be summarized. These nondimensional numbers lead to similarity conditions that allow for the quantitative comparison of data between field catchments and between the field scale and the controlled experimental scale. Derived relationships are presented for the drainage density of the channel network and the rate at which the network grows, parameterized using the nondimensional numbers. Drainage density is shown to be mostly a function of the hillslope channel initiation number that relates the slopes and lengths of hillslopes in a very simple fashion. Finally, it is shown that the form of a channel network is very sensitive to initial conditions. Though the exact form of the network and the hillslopes may vary greatly, along with their topological statistics, physical statistics such as drainage density are only slightly affected.
A physical explanation of an observed link area‐slope relationship
Authors: Willgoose Garry , Bras Rafael L. , Rodriguez‐Iturbe Ignacio
Published: February 2004

An observed log‐log linear relationship between channel slope and contributing area is explained by the erosional physics that lead to catchment form. It is postulated that tectonic uplift is in balance with the fluvial erosion down wasting that dominates catchment erosion, and it is shown that this relationship results in the observed log‐log linear relationship at dynamic equilibrium. In addition, it has been observed that there are deviations from this log‐log linear relationship near the catchment divide, with observed slopes being lower than those predicted from the relationship. This is explained by noting that for small areas, fluvial erosion effects are dominated by soil creep and rain splash, modeled by diffusive physics. The area at which this deviation from log‐log linearity occurs is that point on the hillslope at which diffusive physics, like soil creep and rain splash, begin to dominate fluvial erosion. These predictions are confirmed by numerical simulations using a catchment evolution model.
Landscape Aesthetics of Riparian Environments: Relationship of Flow Quantity to Scenic Quality Along a Wild and Scenic River
Authors: Brown Thomas C. , Daniel Terry C.
Published: February 2004

The relationship between flow quantity and scenic quality was measured for a “wild and scenic” river in Colorado. Respondents' scenic beauty judgments of video sequences depicting the river at flow rates from 120 to 2650 cfs (3.40 to 75.0 m3/s) were scaled to an interval scale measure of perceived scenic beauty following psychophysical scaling procedures. Regressions of scenic beauty on variables describing flow and other site characteristics showed scenic beauty to increase as flow increased up to about 1100–1500 cfs (31–42 m3/s) and then fall as flow continued to increase. Optimum flows for scenic beauty typically occur for two short periods each year, during the ascending and descending portions of the annual late spring peak runoff season. Flow explained from 10 to 25% of the variance in scenic beauty, depending on how much emphasis the scenic beauty judgment format tended to place on flow.
A daily hydroclimatological data set for the continental United States
Authors: Wallis James R. , Lettenmaier Dennis P. , Wood Eric F.
Published: February 2004

Previous attempts to validate general circulation model simulations of land surface hydrology have often been limited by the absence of systematic historical data, especially for runoff, precipitation, and temperature. Because hydrological response times for unregulated watersheds in the United States vary from a few hours to a few days at most, climatological studies dealing with land surface hydrology require data at relatively short time intervals. We describe a set of 1009 U.S. Geological Survey streamflow stations, and 1036 National Oceanic and Atmospheric Administration climatological stations, for which long‐term (1948–1988) observations have been assembled into a consistent daily data base with missing observations estimated using a simple closest‐station prorating rule. Care was taken in selection of the streamflow stations to assure that the records were essentially free from regulation. The climatological stations are a subset of the historical climatology network for which monthly data are described by Quinlan et al. (1987). The data format is provided to facilitate development of alternative data retrieval algorithms, Estimated values for missing data, as well as suspicious observations, are flagged. The data are retrievable by station list, state, latitude‐longitude range, and hydrologic unit code from compact digital read‐only memory (CD ROM). CD‐ROM copies are available from the second author.
Numerical Study of the Maximum Boundary Shear Stress Induced by Raindrop Impact
Authors: Hartley D. M. , Alonso C. V.
Published: February 2004

The magnitude, position, and timing of the instantaneous maximum boundary shear stress caused by a raindrop on a shallow pool of water are investigated using a series of computer simulation experiments in which the Navier‐Stokes equations are solved numerically. A dimensional analysis defines a set of parameters involving fluid properties and initial conditions relevant to the problem. Numerical simulations are performed over ranges of these parameters using a generic, two‐dimensional, incompressible, free surface flow model. Results of the simulations are summarized in simple algebraic relationships which serve to clarify the relative importance of the parameters. The algebraic relationships also serve as an efficient substitute for the numerical model in the estimation of the magnitude, position, and timing of the maximum boundary shear stress. Laboratory measurements of water‐droplet‐induced shear stress are used to demonstrate the validity of the algebraic relationships.
Pressure transients in a double‐porosity medium
Authors: Young Roger
Published: February 2004

Pressure transients associated with a constant‐rate pumping test in a double‐porosity (fissured or multilayered) reservoir may exhibit, in succession, several periods of characteristic log linear dependence on time. If the flow in the matrix blocks is primarily vertical then slope halving of the semilog gradient may be observed, but if the radial component of block flow becomes significant then pressure stabilization can occur. During the final period of formation flow an increase in gradient is associated with a dominant vertical component of block flow, but if the radial component is significant then a decrease in gradient will be observed.
A Large‐Scale Flow and Tracer Experiment in Granite: 2. Results and Interpretation
Authors: Abelin Harald , Birgersson Lars , Moreno Luis , Widén Hans , Ågren Thomas , Neretnieks Ivars
Published: February 2004

Water and tracer flow has been monitored in a specially excavated drift in the Stripa mine. Several new experimental techniques and equipment were developed and used. The whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected. Eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift. The flow rate and tracer monitoring was kept up for more than 2 years. The tracer breakthrough curves and flow rate distributions were used to study the flow paths, velocities, hydraulic conductivities, dispersivities and channeling effects in the rock. In a companion paper the experimental design and performed experiments are described. The present paper describes the interpretation of flow and tracer movement in the rock outside the drift. The tracer movement was measured by the more than 160 individual tracer curves. The tracer experiments have permitted the flow porosity and dispersion to be studied. The possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed.
A Large‐Scale Flow and Tracer Experiment in Granite: 1. Experimental Design and Flow Distribution
Authors: Abelin Harald , Birgersson Lars , Gidlund Jard , Neretnieks Ivars
Published: February 2004

This paper describes the Stripa three‐dimensional experiment where water and tracer flow has been monitored in a specially excavated drift in the Stripa mine. Several new experimental techniques and equipment were developed and used. The experiment was performed in a specially excavated drift, 100 m long, at the 360 m level in granite. The whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected. Eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift. The flow rate and tracer monitoring was kept up for more than 2 years. The tracer breakthrough curves and flow rate distributions were used to study the flow paths, velocities, hydraulic conductivities, dispersivities and channeling effects in the rock. This paper describes the experimental techniques, the fracture mapping, the tracer and flow rate measurements and the results of the flow rate measurements. The detailed observations made possible by the plastic sheeting technique have given some qualitative as well as quantitative information on flow rate distribution in fractured rock which previously has not been available. These observations may be of importance for assessing the transport of dissolved species such as radionuclides through fractured rock.
Tritium and Helium 3 Isotope Ratios for Direct Estimation of Spatial Variations in Groundwater Recharge
Authors: Solomon D. K. , Sudicky E. A.
Published: February 2004

In the absence of strong dispersion the ratio of atmospherically derived tritium (3H) and its stable daughter, helium 3 (3He), can be used to accurately date shallow groundwater with ages ranging from 0 to about 50 years. The effects of dispersion on 3H/3He ages are examined by numerical simulation in simple one‐ and two‐dimensional flow systems. For a 3H input function that is relatively constant in time the difference between 3H/3He ages and purely advective groundwater travel times is controlled by the relative magnitude of the groundwater velocity, the 3H decay constant, and the dispersivity of the porous media. In many shallow sandy aquifers the groundwater velocity is sufficiently large and the dispersivity sufficiently small that the difference between the true groundwater travel time and the 3H/3He age near the water table can be neglected (<10% difference). This suggests that measurements of the 3H/3He age gradient near the water table can be used to estimate recharge rates and vertical velocity values with a high degree of spatial resolution. In contrast to 3H activities, modeled 3H/3He ages are relatively insensitive to uncertainties with respect to the 3H input function. Thus combined measurements of 3H and 3He offer considerable advantage over measurements of 3H alone. The ability to obtain reliable estimates of spatial variations in recharge rates combined with accurate groundwater ages in shallow unconfined aquifers will undoubtedly provide valuable constraints when calibrating models of groundwater flow and solute transport in such systems.
A Numerical Model for Calculating the Distributions of Velocity and Boundary Shear Stress Across Irregular Straight Open Channels
Authors: Pizzuto James E.
Published: February 2004

A model is presented for calculating the distributions of velocity and boundary shear stress across irregular straight open channels. A turbulent kinetic energy transport equation and a two‐dimensional ramp function for the turbulent length scale provide turbulence closure. A modified sigma transformation maps the channel cross section onto a rectangular domain; the transformed equations are solved by a simple finite difference algorithm. Velocity profiles generated by the model are logarithmic close to the bed, but in the core of the flow, predicted velocities follow a wake profile similar to that observed experimentally. The boundary shear stresses calculated by the model for smooth one‐dimensional flows are accurate to within 0.02%. The model also reproduces flow and boundary shear stress data for smooth rectangular and trapezoidal laboratory channels; the average boundary shear stress is calculated to within about 1%, and the distributions of velocity and shear stress are similar to those obtained from laboratory measurements. Local errors are caused by ignoring weak secondary currents and by using a simplistic symmetry assumption for the boundary condition at the water's surface. The model overestimates the discharge by an average of 8%; this error probably occurs because the model ignores the resistance due to secondary currents.