bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of the western United States snowpack from snowpack telemetry (SNOTEL) data
Authors: Serreze Mark C. , Clark Martyn P. , Armstrong Richard L. , McGinnis David A. , Pulwarty Roger S.
Published: September 2002

Daily station data from U.S. Department of Agriculture snowpack telemetry (SNOTEL) archives through the 1995/1996 season are used to examine the climatic characteristics of snow water equivalent (SWE) for the mountainous western United States and linkages with precipitation (PRE) and temperature. Quality control procedures were developed to screen outliers in each variable. SWE for April 1 at the SNOTEL sites compares favorably with colocated snow course values. Regional differences in the seasonal cycle of SWE are discussed in terms of winter‐half precipitation, temperature, and the corresponding SWE/PRE ratio. The percentage of annual precipitation represented by snowfall is highest for the Sierra Nevada (67%), northwestern Wyoming (64%), Colorado (63%), and Idaho/western Montana (62%) sectors, manifesting high SWE/PRE ratios and winter‐half precipitation maxima. Lower percentages for the Pacific Northwest (50%) and Arizona/New Mexico (39%) reflect lower ratios and, especially for the latter region, a larger fraction of PRE falling outside of the accumulation season. Interannual variability in SWE in the colder inland regions is primarily controlled by available precipitation. For the warmer Pacific coast regions and Arizona/New Mexico the more important factor is the SWE/PRE ratio, illustrating the sensitivity of these areas to climate change.
Surface length scales and shear stress: Implications for land‐atmosphere interaction over complex terrain
Authors: Albertson John D. , Parlange Marc B.
Published: September 2002

A large eddy simulation (LES) code of the atmospheric boundary layer (ABL) has been developed and applied to study the effect of spatially variable surface properties on the areally averaged surface shear stress at the land‐atmosphere interface. The LES code simulates the space and time evolution of the large‐scale turbulent eddies and their transport effects in the ABL. We report here on simulations of flow over spatially variable roughness fields. The dynamics are simulated, and the resulting space‐time fields are averaged to explore the effects of the surface variability length scales on the average surface shear stress, as used in large‐scale models to estimate scalar fluxes, such as evaporation. We observe asymmetrical response of the smooth‐to‐rough and rough‐to‐smooth transitions, such that the effects of the transitions accumulate rather than cancel. It is shown that the presence of abrupt changes in surface roughness and the atmosphere's response to these patches create a marked dependence of the statistical structure of surface shear stress on the length scale of the surface patches. An increase in regionally averaged surface stress for decreasing horizontal patch length scale is found.
Field test of high molecular weight alcohol flushing for subsurface nonaqueous phase liquid remediation
Authors: Falta Ronald W. , Lee Cindy M. , Brame Scott E. , Roeder Eberhard , Coates John T. , Wright Charles , Wood A. Lynn , Enfield Carl G.
Published: September 2002

A pilot scale field test of non‐aqueous phase liquid (NAPL) removal using high molecular weight alcohols was conducted at Operable Unit 1, Hill Air Force Base, Utah. Petroleum hydrocarbons and spent solvents were disposed of in chemical disposal pits at this site, and these materials are now present in the subsurface in the form of a light non‐aqueous phase liquid (LNAPL). This LNAPL is a complex mixture of aromatic and aliphatic hydrocarbons, chlorinated solvents, and other compounds. The field experiment was performed in a 5 m by 3 m confined test cell, formed by driving interlocking sheet pile walls through the contaminated zone into an underlying clay. The test involved the injection and extraction of about four pore volumes (1 pore volume=7000 L) of a mixture of 80% tert‐butanol and 15% n‐hexanol. The contaminants were removed by a combination of NAPL mobilization and enhanced dissolution, and the results of postflood soil coring indicate better than 90% removal of the more soluble contaminants (trichloroethane, toluene, ethylbenzene, xylenes, trimethylbenzene, naphthalene) and 70–80% removal of less soluble compounds (decane and undecane). The results of preflood and postflood NAPL partitioning tracer tests show nearly 80% removal of the total NAPL content from the test cell. The field data suggest that a somewhat higher level of removal could be achieved with a longer alcohol injection.
Nonwetting phase retention and mobilization in rock fractures
Authors: Longino Bettina L. , Kueper Bernard H.
Published: September 2002

Perchloroethylene (PCE) was injected into fractured limestone samples (approximately 0.3 m × 0.3 m square) under controlled conditions to assess nonwetting phase fracture retention capacity. Testing was performed using two rock samples containing a single fracture in each, one fractured along a bedding plane and the other fractured along a prominent stylolitic joint. Residual PCE saturation decreased from 21% of the fracture volume at horizontal to 3% at completely vertical in the bedding plane fracture and decreased from 27% to 10% of the fracture volume under the same conditions in the stylolitic fracture. A portion of the retained residual was removed by waterflooding the fractures. The PCE retention capacity of both fractures exhibited a strong correlation with combined capillary and Bond number (Nc + krWNB) provided that initial residual saturation
was defined in the absence of both buoyant and viscous forces. Residual PCE saturation decreased as the magnitude of NC + krWNB increased; however, even at Nc + krWNB values approaching 10−2, all residual PCE was not completely removed from the fractures.
Soil water retention and maximum capillary drive from saturation to oven dryness
Authors: Morel‐Seytoux Hubert J. , Nimmo John R.
Published: September 2002

This paper provides an alternative method to describe the water retention curve over a range of water contents from saturation to oven dryness. It makes two modifications to the standard Brooks and Corey [1964] (B‐C) description, one at each end of the suction range. One expression proposed by Rossi and Nimmo [1994] is used in the high‐suction range to a zero residual water content. (This Rossi‐Nimmo modification to the Brooks‐Corey model provides a more realistic description of the retention curve at low water contents.) Near zero suction the second modification eliminates the region where there is a change in suction with no change in water content. Tests on seven soil data sets, using three distinct analytical expressions for the high‐, medium‐, and low‐suction ranges, show that the experimental water retention curves are well fitted by this composite procedure. The high‐suction range of saturation contributes little to the maximum capillary drive, defined with a good approximation for a soil water and air system as
, where krw is relative permeability (or conductivity) to water and hc is capillary suction, a positive quantity in unsaturated soils. As a result, the modification suggested to describe the high‐suction range does not significantly affect the equivalence between Brooks‐Corey (B‐C) and van Genuchten [1980] parameters presented earlier. However, the shape of the retention curve near “natural saturation” has a significant impact on the value of the capillary drive. The estimate using the Brooks‐Corey power law, extended to zero suction, will exceed that obtained with the new procedure by 25 to 30%. It is not possible to tell which procedure is appropriate. Tests on another data set, for which relative conductivity data are available, support the view of the authors that measurements of a retention curve coupled with a speculative curve of relative permeability as from a capillary model are not sufficient to accurately determine the (maximum) capillary drive. The capillary drive is a dynamic scalar, whereas the retention curve is of a static character. Only measurements of infiltration rates with time can determine the capillary drive with precision for a given soil.
Soil water flow dynamics in a managed cutover peat field, Quebec: Field and laboratory investigations
Authors: Schlotzhauer Susanne M. , Price Jonathan S.
Published: September 2002

In this paper concerned with soil water dynamics in a managed cutover peat field, the microscale hydrological processes and parameters governing water flow and storage through variably saturated peat are investigated. An open water ditch‐reservoir enhanced wetting of adjacent cutover peat, maintaining the water table depth above 43 cm during the summer, surface soil moisture above 45%, and water tension in the surface layer above −45 mbar. Desaturation of pores was noted in the −2 and −10 cm depths, but at −30 and −50 cm a decrease in moisture content of several percent was associated with compression of the peat as the water table dropped. Air entry occurred only at pressures below −15 mbar. Seasonal subsidence resulted in cumulative vertical displacement in excess of 10 cm during the study period. Typical settlements in the peat ranged between 11 and 23% of the lowering of the water table. Considerable hysteresis was observed, and vertical displacement was 5 times greater in response to water loss, compared to rewetting. The specific storage (Ss) in the 180 cm thick deposit averaged 9.4 × 10−4 cm−1 during drying periods but averaged only 2.6 × 10−4 cm−1 on rewetting.Ss was more important than specific yield (Sy) in the overall aquifer storativity. Transient hydraulic properties resulted from the shifting soil structure. The increase in peat bulk density caused by drying increased the water retention capacity and decreased hydraulic conductivity. Mean saturated hydraulic conductivity was 15 cm d−1 and decreased 2 orders of magnitude as the degree of saturation dropped from 1 to 0.4. The horizontal/vertical anisotropy ratio was 4. The changing surface elevation in response to seasonal subsidence had a profound influence on the nature of the storage changes and hydraulic parameters of the peat soil.
Analysis of long‐term land subsidence near Mexico City: Field investigations and predictive modeling
Authors: Ortega‐Guerrero Adrian , Rudolph David L. , Cherry John A.
Published: September 2002

The Mexico City region has several flat plains formed on exceptionally porous (60–90%) lacustrine deposits overlying a highly productive regional aquifer. Severe land subsidence due to consolidation of the lacustrine aquitard caused by aquifer exploitation has resulted in restrictions on pumping in the core of Mexico City. This has led to large increases in aquifer pumping in the outlying lacustrine plains where satellite communities are rapidly expanding. The Chalco Basin is one of these lacustrine areas where pumping began in the 1950s and greatly increased in the 1980s. The lacustrine sequence in the Chalco area is significantly thicker than anywhere else in the Basin of Mexico averaging 100 m and reaching a maximum thickness of 300 m. Consequently, this area is susceptible to the highest potential land subsidence effects as a result of groundwater extraction of anywhere in the basin. Land subsidence in the central part of the Chalco Basin has increased to 0.4 m/yr since 1984 and by 1991 total subsidence had reached 8 m. The rapid land subsidence in this area is causing the accumulation of meteoric waters during the rainy season resulting in extensive flooding of farmland. This study first demonstrates a methodology for combining hydraulic data from a network of monitoring wells, geotechnical data from core samples, and a compilation of historical information on land surface elevation to quantify groundwater flow and land subsidence phenomena within the rapidly subsiding Chalco Basin. Then a one‐dimensional mathematical model is employed to develop predictions of future land subsidence under a range of pumping conditions. The model permits the hydraulic properties of the aquitard to vary as transient functions of hydraulic head and porosity. Simulations suggest that under current pumping rates, total land subsidence in the area of thickest lacustrine sediment will reach 15 m by the year 2010. If pumping is reduced to the extent that further decline in the potentiometric surface is prevented, total maximum subsidence would be significantly less, ∼10 m, and the rate would nearly cease by 2010.
Linking observed and general circulation model upper air circulation patterns to current and future snow runoff for the Rocky Mountains
Authors: Byrne J. M. , Berg A. , Townshend I.
Published: September 2002

Snowmelt runoff from alpine areas is the primary source of streamflow and water supply in western North America. Increasingly, questions about the impacts of global climate change on watershed yield are being asked. This paper is a forecast of expected changes to runoff for two key rivers in western North America. The paper develops and applies linkages between historical and general circulation model (GCM) upper air circulation patterns deemed to control winter precipitation in the northern Rocky Mountain states and southern Alberta. Historical and 1 × CO2 GCM upper airflow conditions are quite similar, but there are substantive variations in the GCM 2 × CO2 upper airflows. Relative occurrence (dominance) of historical synoptic patterns is statistically linked to historical spring runoff for the Oldman and Colorado Rivers. These linkages are used to forecast variation in the future runoff on the basis of variations in synoptic pattern statistics for the 2 × CO2 GCM upper airflow patterns.
Determining soil hydraulic functions from evaporation experiments by a parameter estimation Approach: Experimental verifications and numerical studies
Authors: Romano Nunzio , Santini Alessandro
Published: September 2002

A parameter estimation method is developed for the determination of unsaturated soil hydraulic properties from evaporation experiments under laboratory conditions. Variables used in the inversion procedure are soil water pressure heads at various positions and total soil weights, both measured as a function of time during the experiment. Unknown parameters of different analytical expressions used to describe the soil hydraulic properties are estimated by coupling a finite difference solution of the Richards equation with a nonlinear optimization problem. This problem is formulated by minimizing the deviations between the numerical solution of the transient flow process and the real system response measured during the experiment. Minimization of the objective function is performed using a version of the Levenberg‐Marquardt's method; the procedure also provides information about the uncertainty in parameter estimates. The performance of the selected parametric relationships is evaluated, and the applicability and accuracy of the proposed inverse method are shown by comparing estimated water retention and hydraulic conductivity functions with experimental results obtained via the instantaneous profile method. Parameter sensitivity analyses and stability of the inverse solutions are discussed with reference to the originally designed evaporation experiment and to an evaporation method that is developed with a view to reducing experimental efforts. Further insights into the properties of existence and uniqueness of inverse solutions are gained by examining contour plots of the objective functions under varying experimental conditions. The results confirm the reliability and flexibility of the proposed method and suggest that the evaporation flux imposed at the upper soil surface may determine the well posedness of the optimization problem.
Effects of logging and fire on runoff and erosion on highly erodible granitic soils in Tasmania
Authors: Wilson Cathy J.
Published: September 2002

A set of rainfall simulator experiments was carried out in a logged forest in Tasmania, Australia, to quantify the impact of logging and fire on runoff and soil loss. A large, portable rainfall simulator was developed for the experiments to help overcome problems associated with spatially varying hydraulic and erosion properties of the soil. Simulated rainfall events with intensities of approximately 35, 75, and 150 mm h−1 were applied to four 300 m2 plots with different levels of surface disturbance: severely burnt, logged and burnt with high mechanical disturbance, logged with low mechanical disturbance, and undisturbed. The experiments indicated that the amount of runoff and soil loss from the plots depended on the type and degree of disturbance to the natural biotic crust developed on this soil. Erodibility per unit runoff was greatest on the severely burnt plot; but runoff on the mechanically disturbed site was so great that it produced the highest total sediment yield on an event basis. Runoff production was similar on the three plots where the natural biotic crust was largely intact and was low relative to the plot with high mechanical disturbance. Total sediment yield was typically higher on logged plots than on unlogged plots.
Variability of wetting front velocities during a field‐scale infiltration experiment
Authors: Young M. H. , Wierenga P. J. , Warrick A. W. , Hofmann L. L. , Musil S. A.
Published: September 2002

Strategies for characterizing subsurface hydraulic properties often lack observations on actual water movement in soil. The goals of this study were to investigate the variability of wetting front velocities during a field‐scale infiltration experiment at the Maricopa Environmental Monitoring site, Maricopa, Arizona (surface area: 50 by 50 m). Wetting front velocities and soil textural components were analyzed as local and effective parameters. Local representation was done by measuring the wetting front travel time through specific depth increments (normally 0.5 m) to a depth of 3 m. Effective representation was done by measuring travel time from ground surface to the depth of interest in 0.5‐m increments from the 1‐m to 3‐m depths. Textural components were represented similarly. One‐way analysis of variance (ANOVA) tests were run on wetting front velocities and soil textural components, with spatial location of neutron probe access tubes and soil sampling points classified as replicates and depth intervals classified as independent treatments. The results showed that mean local velocities varied significantly with depth (range = 20–44 cm d−1). Effective front velocities varied much less (range = 22–25 cm d−1) and were found to be statistically the same, even though differences in soil texture and strong layering were observed. As the total wetting depth increased, variance in effective wetting front velocity decreased, with a coefficient of variation of wetting front arrival of only 9% at the 3‐m depth. The decline in the variance of the front velocity is consistent with previous findings that the variance of effective parameters reduces as the measurement scale increases.
Sensitivity of stream temperatures in the United States to air temperatures projected under a global warming scenario
Authors: Mohseni Omid , Erickson Troy R. , Stefan Heinz G.
Published: September 2002

To project mean weekly stream temperature changes in response to global climate warming and for studies of freshwater ecosystems, a four‐parameter nonlinear function of weekly air temperatures was used. One parameter, the upper bound stream temperature, was obtained by extreme value analysis from stream temperature data, and the other three parameters were obtained by least squares regression analysis. The least squares regression function was developed separately for the warming season and the cooling season (hysteresis) to take heat storage due to snowmelt or reservoir operations into account. There were very weak correlations between model parameters and annual or seasonal air temperatures. To project weekly stream temperatures under a 2 × CO2 climate scenario, weekly air temperature data from 166 weather stations, incremented by the output of the Canadian Center of Climate Modelling (CCC) general circulation model (GCM), were applied to nonlinear stream temperature models developed for 803 stream gaging stations. An error analysis indicated that only 39 stream gaging stations would not exhibit a significant change under the CCC‐GCM 2 × CO2 climate scenario. The projections at the remaining 764 stream gaging stations showed that mean annual stream temperatures in the contiguous United States would increase by 2°–5°C, least near the West Coast and most in the Missouri River and Ohio River basins. On average, there would be a 1°–3°C increase in the maximum and minimum weekly stream temperatures under the 2 × CO2 climate scenario, most in the central United States. It was also found that most streams would experience the maximum change in weekly stream temperatures in spring (March–June). The minimum changes in stream temperatures are projected to occur in winter (December and January) and summer (July and August) throughout the United States.
Approximate analytical solution of the Boussinesq equation with numerical validation
Authors: Hogarth W. L. , Parlange J. Y. , Parlange M. B. , Lockington D.
Published: September 2002

A new approximate solution of the one‐dimensional Boussinesq equation is presented for a semi‐infinite aquifer when the hydraulic head at the source is an arbitrary function of time. Estimates for recharge, discharge, and elevation of the water table are given. The simplicity and accuracy of the approximation are compared with “exact” numerical and analytical solutions. The method of solution is illustrated with several examples including the commonly treated case of a constant boundary head and a nonmonotonically varying boundary head.
Field observation of flow in a fracture intersecting unsaturated chalk
Authors: Dahan Ofer , Nativ Ronit , Adar Eilon M. , Berkowitz Brian , Ronen Zeev
Published: September 2002

Flow through a natural fracture crossing unsaturated chalk in an arid region was investigated in a field experiment using a specially designed experimental setup. The setup allowed complete control of the flow domain inlet and outlet. Water flux into and out of the fracture was measured in small segments of the fracture openings, and flow trajectories were identified using seven fluorobenzoic acid tracers. A 5 day percolation experiment on a 5.3 m long fracture showed significant spatial and temporal variability of the flow regime. Flow through fracture openings did not reach a steady state either in individual segments or across the entire flow domain, although the boundary conditions were kept relatively steady for the entire duration of the experiment. Flow trajectories within the fracture plane varied over time; however, most of the flow was confined to small sections of the fracture. Over 70% of the flux was transmitted through <20% of the studied fracture openings. Observations from the tracer tests suggest that flow paths can coexist near each other without water mixing, probably because the fracture fill generates unconnected flow paths across the main fracture void.
Three‐dimensional flow measurements in rock fractures
Authors: Dijk Peter E. , Berkowitz Brian
Published: September 2002

Nuclear magnetic resonance imaging is applied to measure flow patterns in natural, water‐saturated, rough‐walled rock fractures. From three‐dimensional water density and velocity vector images the fracture morphology and flow patterns are determined. The parabolic nature and asymmetry of the velocity profiles, and thus the accuracy of local cubic law flow rate predictions, vary greatly. This depends on the degree of wall roughness. Particularly complex flow patterns are found in one sample which contains a sharp fracture wall discontinuity. A power law for the flow rate versus aperture for the low‐flow region was found without considering the hydraulic gradients.
Advective mass transfer from stationary sources in porous media
Authors: Jia C. , Shing K. , Yortsos Y. C.
Published: September 2002

We study mass transfer to a flowing fluid in porous media from stationary sources of various geometries. Effects of the porous medium and the source geometry are explored using a modification of the local mass transfer coefficients. We develop exact solutions for mass transfer in flow over a flat plate and asymptotic and numerical solutions in flow over sources of various geometries, including self‐similar surfaces, such as a Koch surface and a percolation cluster. For the latter, as well as for sources distributed at the pore‐network scale, a pore‐network representation of the porous medium is used. The dependence of the overall mass transfer rates on various parameters, and particularly on the flow rate, is analyzed. The analysis allows for macroscopic coefficients in equations, which lump the process in terms of an effective, first‐order reaction, to be interpreted in terms of the microstructure of the porous medium and the source geometry.
Forecasting river flow rate during low‐flow periods using neural networks
Authors: Campolo Marina , Soldati Alfredo , Andreussi Paolo
Published: September 2002

The pollution in the river Arno downstream of the city of Florence is a severe environmental problem during low‐flow periods when the river flow rate is insufficient to support the natural waste assimilation mechanisms which include degradation, transport, and mixing. Forecasting the river flow rate during these low‐flow periods is crucial for water quality management. In this paper a neural network model is presented for forecasting river flow for up to 6 days. The model uses basin‐averaged rainfall measurements, water level, and hydropower production data. It is necessary to use hydropower production data since during low‐flow periods the water discharged into the river from reservoirs can be a major fraction of total flow rate. Model predictions were found to be accurate with root‐mean‐square error on the predicted river flow rate less then 8% over the entire time horizon of prediction. This model will be useful for managing the water quality in the river when employed with river quality models.
Temporal and spatial variability of North American prairie snow cover (1988–1995) inferred from passive microwave‐ derived snow water equivalent imagery
Authors: Derksen C. , LeDrew E. , Goodison B.
Published: September 2002

Estimates of regional snow water equivalent (SWE) are essential for hydrological prediction, climatological analysis, and meteorological forecasting. Passive microwave‐derived estimates of snow cover have unique benefits such as all‐weather imaging, rapid scene revisit capabilities, and the ability to provide these quantitative SWE data. For this study the available time series of special sensor microwave/imager (SSM/)) brightness temperatures in the equal area SSM/I Earth grid projection were processed with the Canadian Atmospheric Environment Service dual‐channel SWE algorithm for a ground‐validated North American prairie region. Seven winter seasons (December, January, and February) of SWE imagery spanning 1988–1995 and averaged for 5 day intervals were subjected to a rotated principal components analysis (PCA) performed individually for each season. A final PCA considering all 7 winter seasons was performed in order to investigate the degree to which snow cover patterns reappear from one season to the next. Results indicate that modes of snow cover in the North American prairies are most persistent during the late winter (February) and exhibit a greater degree of variability during December than the other winter months. Two snow cover regimes are identified for the study region, with the winters of 1988/1989–1991/1992 characterized in a manner that is unique in both temporal and spatial aspects from the winters of 1992/1993–1994/1995.
Ecohydrology: A hydrologic perspective of climate‐soil‐vegetation dynamies
Authors: Rodriguez‐Iturbe I.
Published: September 2002

The hydrologic mechanisms underlying the climate‐soil‐vegetation dynamics and thus controlling the most basic ecologic patterns and processes are described as one very exciting research frontier for the years to come. In this personal opinion I have concentrated on those processes where soil moisture is the key link between climate fluctuations and vegetation dynamics in space and time. The soil moisture balance equation at a site is shown to be the keystone of numerous fundamental questions which may be instrumental in the quantitative linkage between hydrologic dynamics and ecological patterns and processes. Some of those questions are outlined here, and possible avenues of attack are suggested. The space‐time links between climate, soil, and vegetation are also explored from the hydrologic perspective, and some exciting research perspectives are outlined.
Trichloroethene DNAPL flow and mass distribution in naturally fractured clay: Evidence of aperture variability
Authors: O'Hara S. K. , Parker B. L. , Jørgensen P. R. , Cherry J. A.
Published: September 2002

A cylindrical sample, 0.5 m in diameter and length, was obtained by excavation from 3.7–4.2 m depth below ground surface in a surficial deposit of fractured glaciolacustrine clay. The sample was enclosed in a triaxial cell in a cold room to impose conditions close to field temperature and stress. Hydraulic testing using a hydraulic gradient of 2 provided a saturated hydraulic conductivity of 7 × 10−10 m/s, which is only slightly larger than the matrix hydraulic conductivity. The cubic law provided a mean hydraulic aperture of 5–6 μm for the four continuous vertical fractures in the sample. A column of immiscible‐phase trichloroethene (TCE) imposed incrementally at the top of the sample provided an entry‐pressure‐derived aperture equal to 17 μm for a parallel‐plate fracture. TCE dense nonaqueous phase liquid (DNAPL) that flowed through the sample produced dissolved‐phase diffusion haloes in the matrix that indicated the preferential fracture pathways. These haloes indicated that DNAPL flowed through only 5–15% of the visible, oxidation‐stained fractures; hence natural fractures had variable apertures along their length, and the larger aperture regions provided channels for fluid flow. Using the hydraulic test results and applying the cubic law only to the aperture segments of confirmed DNAPL flow, an equivalent hydraulic aperture of 8–11 μm was obtained, which is greater than the conventional mean hydraulic aperture and smaller than the local aperture determined from the DNAPL entry pressure. These differences are large in the context of fluid flux, which is proportional to the aperture cubed.
Implications of sorption kinetics to radionuclide migration in fractured rock
Authors: Xu Shulan , Wörman Anders
Published: September 2002

A new model framework for transport of radionuclides in fractured rock, which includes sorption kinetics and surface diffusion, is developed and verified experimentally. Interpretations of two types of complementary batch tests indicate that sorption kinetics in the rock matrix is governed by migration phenomena along intragranular microfissures. About 40% of the matrix pore volume consists of such pores not active in the main matrix diffusion process along the intergranular fissures. The adsorption rate coefficient obtained for the surface sorption kinetics on small granite particles is 2 or 3 orders of magnitude larger than that obtained for intact rock. The studied rock material was diorite collected in a typical Swedish crystalline bedrock at the Äspö Hard Rock Laboratory. An exact solution is derived in a form that expresses the relative error in the temporal variance of a pulse travelling in a fracture resulting if sorption kinetics is omitted. The relative error of the peak value of the pulse increases with distance and can be several hundred percent in cases typical of performance assessment analyses of a nuclear waste repository.
Perceptions of flood risk: A case study of the Red River Flood of 1997
Authors: Burn Donald H.
Published: September 2002

Risk perception is examined in the context of the Red River flood of 1997. The role that experience with prior flood events plays in risk perception is highlighted as well as the impacts of experience on the mitigation actions selected by individuals. The Red River flood of 1997 demonstrated that individuals with different prior flood experience could be expected to behave differently during a flood event. This implies that flood warnings should be tailored to the characteristics of the target audience.
A hydrometeorological model for basin‐wide seasonal evapotranspiration
Authors: Dias Nelson Luís , Kan Akemi
Published: September 2002

A new methodology is proposed to capture the seasonal behavior of evapotranspiration from precipitation and streamflow data and to develop hydrometeorological evapotranspiration models tailored for each basin. The water budget method for determining evapotranspiration is downscaled to periods between 15 and 160 days that occur between well‐marked hydrological recessions. Using these uneven time periods, the error associated with the unknown soil moisture storage is minimized, whereas groundwater storage changes are estimated by means of a classical linear groundwater reservoir whose time constant is obtained by recession analysis. This seasonal water budget (SWB) method is able to reproduce the seasonal signal of evapotranspiration even when it is absent from the precipitation and streamflow records. The estimates are also compatible with calculated monthly net radiation. By selecting short enough water budget periods it is possible to check the relationship between SWB evapotranspiration estimates and net radiation, Penman and Priestley‐Taylor potential evaporation, precipitation minus outflow, water vapor deficit, and basin storage. The ratio of SWB evapotranspiration to an upper limit value represented by either net radiation or potential evaporation is well correlated with precipitation minus outflow, water vapor deficit, or both but is very poorly related to basin storage. The calculated regressions lead to a family of hydrometeorological evapotranspiration monthly (HEM) models fitted to the basins in question, in a way analogous to the calibration of rainfall‐runoff models. In the two watersheds where the methodology was applied the HEM models were able to preserve mass, with total accumulated differences no larger than 0.25 mm d−1 and root‐mean‐square errors of the order of 0.7 mm d−1.
Tidal networks: 2. Watershed delineation and comparative network morphology
Authors: Rinaldo Andrea , Fagherazzi Sergio , Lanzoni Stefano , Marani Marco , Dietrich William E.
Published: September 2002

Through the new method for automatic extraction of a tidal network from topographic or bathymetric fields described in a companion paper [Fagherazzi et al., this issue], we analyze the morphology of aggregated patterns that we observe in nature in different tidal environments. Specifically, we define, on the basis of a hydrodynamic analysis, a procedure for watershed delineation and for the identification of the “divides” for every subnetwork and look at the resulting drainage density and its related scaling properties. From the systematic, large‐scale plots of drainage density and channel width versus watershed area we address the issue of a possible geomorphic criterion that corresponds to the parts of the tidal landscape that are characterized by river‐like features. We also analyze the relationship of total contributing tidal basin area to channel widths and to mainstream lengths (Hack's law). We study comparatively probability distributions of total drainage areas and of “botanical” mass (the area of the channelized landscape upstream of a given section) for tidal and fluvial patterns and find altered scaling features of tidal landforms that reflect the complex interactions of different mechanisms that shape their geometry. Simple geomorphic relationships of the types observed in the fluvial basin (e.g., power laws in the watershed area versus drainage density, mainstream length, or channel width relationships) do not hold throughout the range of scales investigated and are site‐specific. We conclude that tidal networks unlike rivers exhibit great diversity in their geometrical and topological forms. This diversity is suggested to stem from the pronounced spatial gradients of landscape‐forming flow rates and from the imprinting of several crossovers from competing dynamic processes.
Estimating root zone soil moisture from surface soil moisture data and soil‐vegetation‐atmosphere transfer modeling
Authors: Wigneron Jean‐Pierre , Olioso Albert , Calvet Jean‐Christophe , Bertuzzi Patrick
Published: September 2002

We studied the possibility of estimating root zone soil moisture through the combined use of a time series of observed surface soil moisture data and soil‐vegetation‐atmosphere transfer modeling. The analysis was based on the interactions between soil‐ biosphere‐atmosphere surface scheme and two data sets obtained from soybean crops in 1989 and 1990. These data sets included detailed measurements of soil and vegetation characteristics and mass and energy transfer in the soil‐plant‐atmosphere system. The data measured during the 3‐month experiment in 1989 are used to investigate the accuracy of soil reservoir retrievals, as a function of the time period and frequency of measurements of surface soil moisture involved in the retrieval process. This study contributes to better defining the requirements for the use of remotely sensed microwave measurements of surface soil moisture.
Seasonal volume forecast of the Diamante River, Argentina, based on El Niño observations and predictions
Authors: Berri Guillermo J. , Flamenco Eduardo A.
Published: September 2002

A statistically significant relationship is found between the seasonal volume October–March of the Diamante River (central Andes mountains of Argentina) and the sea surface temperature (SST) in the Niño3 region of the Pacific Ocean (5°S‐5°N, 9O°W‐150°W), during the previous March–April and simultaneous November–December. The Niño3 SST anomalies are positively correlated with seasonal volume anomalies. A multiple linear regression model for October–March water volume predictions is developed, making use of Niño3 anomalies observed during March–April and six‐month November–December Niño3 forecast produced in May. A cross‐validation analysis of three‐category (tercile) forecasts for the period 1980–1994 reveals a 73% model skill, equal to that of the snowpack thickness model in use. The results of this study are of practical application to hydrologic forecast for water resources management and hydroelectricity generation. This methodology would allow the water resources administrator to have available every year in May a forecast of the water available in the system during the following melting period October–March, before the wintertime snowfalls.
Liquid retention and interfacial area in variably saturated porous media: Upscaling from single‐pore to sample‐scale model
Authors: Or Dani , Tuller Markus
Published: September 2002

A new model for liquid configuration in angular pore space considering both capillary and adsorptive contributions was proposed as an alternative to the conventional bundle of capillaries representation. In this study we develop a statistical framework for upscaling pore‐scale processes to represent a sample‐scale response of variably saturated porous medium. The representation of pore size distribution by the gamma distribution enables derivation of closed‐form expressions for sample‐scale liquid retention and liquid‐vapor interfacial area. The statistical framework calculates the expected values of liquid configuration as a function of pore geometry and chemical potential considerations. Media properties are used to estimate upscaling parameters by matching model predictions with measured retention data subject to specific surface area constraint. Additionally, a method for estimating liquid‐solid adsorption behavior for the medium is proposed. Model predictions compare favorably with measured retention data, yielding a similar close fit as obtained with the van Genuchten parametric model. Liquid‐vapor interfacial area as a function of chemical potential is readily calculated using the estimated retention parameters. Model calculations of liquid‐vapor interfacial area for sand show reasonable agreement with measurements obtained with surface‐active tracers. The contribution of liquid films dominates the total liquid‐vapor interfacial area and often surpasses the capillary contribution (curved menisci) by several orders of magnitude. This illustrates potential limitations in using cylindrical pore network modeling of interfacial area for multiphase flow predictions. The detailed picture of liquid vapor interfaces provides a sound basis for unsaturated hydraulic conductivity calculations in the sample cross section (i.e., neglecting network effects) and offers insights into microbial habitats and related exchange processes in partially saturated porous media.
Colorado River sediment transport: 1. Natural sediment supply limitation and the influence of Glen Canyon Dam
Authors: Topping David J. , Rubin David M. , Vierra L. E.
Published: September 2002

Analyses of flow, sediment‐transport, bed‐topographic, and sedimentologic data suggest that before the closure of Glen Canyon Dam in 1963, the Colorado River in Marble and Grand Canyons was annually supply‐limited with respect to fine sediment (i.e., sand and finer material). Furthermore, these analyses suggest that the predam river in Glen Canyon was not supply‐limited to the same degree and that the degree of annual supply limitation increased near the head of Marble Canyon. The predam Colorado River in Grand Canyon displays evidence of four effects of supply limitation: (1) seasonal hysteresis in sediment concentration, (2) seasonal hysteresis in sediment grain size coupled to the seasonal hysteresis in sediment concentration, (3) production of inversely graded flood deposits, and (4∥ development or modification of a lag between the time of a flood peak and the time of either maximum or minimum (depending on reach geometry) bed elevation. Analyses of sediment budgets provide additional support for the interpretation that the predam river was annually supply‐limited with respect to fine sediment, but it was not supply‐limited with respect to fine sediment during all seasons. In the average predam year, sand would accumulate and be stored in Marble Canyon and upper Grand Canyon for 9 months of the year (from July through March) when flows were dominantly below 200–300 m3/s; this stored sand was then eroded during April through June when flows were typically higher. After closure of Glen Canyon Dam, because of the large magnitudes of the uncertainties in the sediment budget, no season of substantial sand accumulation is evident. Because most flows in the postdam river exceed 200–300 m3/s, substantial sand accumulation in the postdam river is unlikely.
The size of the freshwater zone below an elongated island with infiltration
Authors: Bakker Mark
Published: September 2002

An exact solution is derived for two‐dimensional, steady interface flow below an elongated island with infiltration. The exact solution is obtained with the hodograph method in combination with conformal mapping; the complex specific discharge function and the reference function are used as auxiliary functions. A new procedure is presented for the solution of the parameter problem in the conformal map of the upper half plane onto the domain in the specific discharge plane. The exact solution is used to compute the depth of the interface for both isotropic and anisotropic aquifers. The depth of the interface at the center of the island is independent of the vertical hydraulic conductivity; the length of the outflow face at the beach is independent of the horizontal hydraulic conductivity. The exact solution can only be evaluated numerically for values of the infiltration rate that are at least an order of magnitude larger than may be expected realistically. For practical problems it is proposed to approximate the shape of the interface with a semiellipse; explicit equations are given for the size of the ellipse in terms of the aquifer parameters. The approximate solution is compared to the exact solution for a number of cases with large infiltration rates (so that the exact solution could be evaluated). The approximate and exact solutions produce results that are identical for at least six significant digits for all cases investigated, which suggests that it may be reasonable to use the approximate formulas outside the range of comparison. Solutions for isotropic and anisotropic aquifers obtained with the approximate formulas are compared to results obtained with a Dupuit solution for a set of realistic aquifer parameters; the interface is approximated well with the Dupuit solution.
Development of a pore network simulation model to study nonaqueous phase liquid dissolution
Authors: Dillard Leslie A. , Blunt Martin J.
Published: September 2002

A pore network simulation model was developed to investigate the fundamental physics of nonequilibrium nonaqueous phase liquid (NAPL) dissolution. The network model is a lattice of cubic chambers and rectangular tubes that represent pore bodies and pore throats, respectively. Experimental data obtained by Powers [1992] were used to develop and validate the model. To ensure the network model was representative of a real porous medium, the pore size distribution of the network was calibrated by matching simulated and experimental drainage and imbibition capillary pressure‐saturation curves. The predicted network residual styrene blob‐size distribution was nearly identical to the observed distribution. The network model reproduced the observed hydraulic conductivity and produced relative permeability curves that were representative of a poorly consolidated sand. Aqueous‐phase transport was represented by applying the equation for solute flux to the network tubes and solving for solute concentrations in the network chambers. Complete mixing was found to be an appropriate approximation for calculation of chamber concentrations. Mass transfer from NAPL blobs was represented using a corner diffusion model. Predicted results of solute concentration versus Peclet number and of modified Sherwood number versus Peclet number for the network model compare favorably with experimental data for the case in which NAPL blob dissolution was negligible. Predicted results of normalized effluent concentration versus pore volume for the network were similar to the experimental data for the case in which NAPL blob dissolution occurred with time.
Some analytical solutions of the linearized Boussinesq equation with recharge for a sloping aquifer
Authors: Verhoest Niko E. C. , Troch Peter A.
Published: September 2002

Subsurface flow from a hillslope can be described by the hydraulic groundwater theory as formulated by the Boussinesq equation. Several attempts have been made to solve this partial differential equation, and exact solutions have been found for specific situations. In the case of a sloping aquifer, Brutsaert [1994] suggested linearizing the equation to calculate the unit response of the hillslope. In this paper we first apply the work of Brutsaert by assuming a constant recharge to the groundwater table. The solution describes the groundwater table levels and the outflow in function of time. Then, an analytical expression is derived for the steady state solution by allowing time to approach infinity. This steady state water table is used as an initial condition to derive another analytical solution of the Boussinesq equation. This can then be used in a quasi steady state approach to compute outflow under changing recharge conditions.