bluuebunny/crossref_metadata_2025_split huggingface dataset:
Velocity profiles measured on the windward slope of a transverse dune
Authors: Mulligan Kevin R. 
Published: February 2007

AbstractVelocity gradients measured on the windward slope of a transverse dune show that flow acceleration strongly affects the turbulence structure of wind. Wind profiles measured below a height of 1.6m are nonlogarithmic and the altered nature of velocity profiles varies over the windward slope of a dune. These findings suggest that calculated values of shear velocity are largely dependent upon the height and location of wind speed measurements, as well as the strength of the prevailing wind. Moreover, if Bagnold‐type transport equations are used to calculate rates of sand transport on a dune, wind speeds must be measured within 0.2 m of the dune surface. If wind speeds are measured above this height, the resulting errors in calculated shear velocity will manifest themselves as errors in calculated rates of sand transport. If rates of sand transport are derived from wind speeds measured above 0.2 m the calculated rates may underestimate sand transport on the windward face of a dune as a result of flow acceleration. In contrast, if a dune has a separate crest upwind of the brink, the expansion and subsequent deceleration of flow downwind from the crest may result in an overestimation of sand transport.
Chemical textures on quartz grains: An experimental approach using salts
Authors: Magee A. W. , Bull P. A. , Goudie A. S. 
Published: February 2007

AbstractTwo groups of fresh crushed Brazilian quartz grains (0.4–0.6 mm) were placed in 10 ml of various saturated salt solutions (sodium sulphate, sodium chloride, magnesium sulphate, sodium carbonate, and sodium carbonate and soil). One group was placed in an environmental cabinet programmed to simulate summer diurnal temperature and relative humidity values recorded in Wheeler Valley, a dry valley in southern Victoria Land, Antarctica. The other group was allowed to remain at normal laboratory conditions. Quartz grains from both groups were removed at pre‐selected intervals for examination using the scanning electron microscope. After 50 hours chemical surface textures were formed on the quartz grains in all but the sodium sulphate solution. At the 140 hour interval all the salt solutions used were producing chemical surface textures on the quartz grains. This paper demonstrates that chemical surface textures can be produced on quartz grain surfaces by saturated salt solutions in a short period of time and may prove to be representative of chemical surface textures produced in a saturated saline environment.
The significance of scarp retreat for cenozoic landform evolution on the Colorado Plateau, U.S.A.
Authors: Schmidt Karl‐Heinz 
Published: February 2007

AbstractSince the beginning of the Cenozoic period several hundreds of metres of the sedimentary cover have been removed from the Colorado Plateau. Palaeoclimatic considerations show that the Colorado Plateau has been dominated by dry climates throughout the Cenozoic with the possible exception of the early Palaeocene. Today in the still prevailing arid climate, which strongly accentuates differences in rock resistance, the relief shows a structurally controlled cuesta scarp topography in the slightly deformed strata of alternating resistance.In examining whether the denudational efficiency of scarp retreat was sufficient to account for the wide erosional gaps in the sedimentary cover, rates of scarp retreat were determined by using the information of dated volcanic material and by applying a new method, which calculates the amount of retreat from the width of beheaded valleys of known age. Rates of retreat range from 0·5 to 6·7 km my−1. The results show that the rates of retreat are controlled by the thickness and resistance of the caprocks.A model of Cenozoic scarp retreat demonstrates that the rates of recession calculated for the scarps in Upper Cretaceous rocks were sufficient to bring them into their present positions from the centre of the Monument Uplift on the central Colorado Plateau. The late Eocene positions of the cliffs in the Early Tertiary formations give an indication of their maximal extent. After the Upper Cretaceous sediments had been removed from the uplifts, erosion cut through successively older rocks, and activated scarps in stratigraphically lower positions. Scarp retreat can operate simultaneously and independently at different levels, which enabled this erosional mechanism to remove great proportions of the sedimentary cover of the Colorado Plateau during the Cenozoic.
An assessment of surface‐mine reclamation based upon sheetwash erosion rates at the Glenrock coal company, Glenrock, Wyoming
Authors: Toy Terrence J. 
Published: February 2007

AbstractComparative erosion rates provide a rational basis for evaluating reclamation success because the work performed by erosion processes is a function of both forces and resistances operating on a surface. Sheetwash erosion data collected by the LEMI technique over several years at the Dave Johnston Mine in east‐central Wyoming show that, based upon average values, there is generally little difference between the erosion rates of natural and reclaimed hillslopes at this locale. Therefore, it is permissible to infer that the reclamation programme has been successful from a geomorphic perspective. However, there is considerable variation in erosion rates about the average for individual hillslopes in both the natural and reclaimed groups.Examination of these data by hillslope element and segment show that, based upon average values, the concave elements of natural and reclaimed hillslopes experience the highest rate of sheetwash erosion. Again, however, there is considerable variation about the average and considerable erosion can occur in any element or segment of particular hillslopes.Lastly, there are seasonal oscillations of hillslope surface elevation with frost‐heaving prevalent during the late autumn to early spring months and erosion prevalent during the late spring to early autumn months.
Longitudinal dunes can move sideways
Authors: Hesp Patrick , Hyde Robert , Hesp Virginia , Zhengyu Qian 
Published: February 2007

AbstractLongitudinal dunes occur in all major sand areas in the world. Their dominant mode of migration or extension is considered to be either prevailing‐ or resultant wind‐parallel, the dunes extending downwind via accretion of the terminal nose. In the Qaidam Pendi in Northwest China a series of active longitudinal dunes extend downwind at 5–10 m yr−1. Internal sedimentary structures examined in the dunes, however, display beds dipping in one direction rather than two opposed directions as is expected. Analysis of aerial photographs confirms that these dunes migrate laterally up to three metres per year, whilst maintaining a symmetrical longitudinal dune morphology.
A distinction between ice‐pushed and ice‐lifted landforms on lacustrine and marine coasts
Authors: Gilbert Robert 
Published: February 2007

AbstractStudy of a small lake, Second Roach Pond, in Maine, U.S.A. clarifies the distinction between shoreline features created by ice push which occurs on both lacustrine and marine coasts, and those created by ice lift related to tidal action in the marine environment. Ice lifting occurred as littoral sediments were frozen into the lake ice, followed by a rise in water level due to damming of the lake before the nival melt each spring. In the period 1905 to 1969 prominent barricades were constructed by this means. A classification based on this distinction is proposed. Ice‐pushed landforms include ramparts, ridges in coarse and fine sediments, stone pavements, ice keel grooves, pushed boulder grooves, and tails off promontories. Ice‐lift features include boulder barricades, perched stones, stone garlands, and ice keel depressions.
The rate of bedrock weathering by frost action: Field measurements and a predictive model
Authors: Matsuoka Norikazu 
Published: February 2007

AbstractShattering rate, surface temperature, moisture content, and the physical and strength properties of bedrock were measured in four rockwall sites of the Japanese Alps. Five‐year observations revealed that the bedrock shattering rate was usually much higher in the freeze‐thaw period from October to next May than in the frost‐free period from June to September. This indicates that frost action is the most important shattering process, although unusual heavy rainstorms in summer are also responsible for the shattering. A combination of some empirical relationships derived from recent laboratory experiments leads to a predictive model of the frost shattering rate. This model shows that the annual shattering rate is dependent on the annual freeze‐thaw frequency on the rock surface, and the degree of saturation and tensile strength of the rock masses. The coefficients involved in the model were determined using the field data.
Coarse woody debris and channel morphology interactions for undisturbed streams in southeast Alaska, U.S.A.
Authors: George Robison E. , Beschta Robert L. 
Published: February 2007

AbstractCoarse woody debris and channel morphology were evaluated for five low‐gradient streams that ranged from first to fourth order (0.7 to 55 km2 watershed area). Debris volumes were directly related to variations in bankfull width. Woody debris was associated with 65 to 75 per cent of all pools and the relative proportion of types of pools (i.e. plunge, lateral scour, etc.) varied with stream size. High variability in channel depths and widths was common. The results provide benchmark values of woody debris loadings and channel morphology for undisturbed coastal Alaskan stream systems.
A long flume study of the dynamic factors affecting the resistance of a loamy soil to concentrated flow erosion
Authors: Govers G. , Everaert W. , Poesen J. , Rauws G. , De Ploey J. , Lautridou J. P. 
Published: February 2007

AbstractExperiments were carried out in a 20 m long flume to assess the variation of the runoff erosion resistance of a loamy soil as a function of initial moisture content and compaction. The results of seven experimental runs show that the runoff erosion resistance of a loamy material is extremely sensitive to variations in initial moisture content and, to a somewhat lesser extent, in bulk density. The very low resistance to runoff erosion of initially dry material is explained by structural changes which take place at the time of wetting: slaking and microfissuration cause a considerable decrease of the soil's shear strength and therefore of its resistance to runoff erosion. A first analysis shows that, during a given rainfall event, initially dry soils may well show significantly more erosion than initially wet soils, despite the increase of infiltration with decreasing initial moisture content.
An estimator for the density of a sediment‐induced stratified fluid
Authors: Shiati K. 
Published: February 2007

AbstractThe contribution of dissolved salts and/or sediment particles in altering the fluid density cannot be neglected in studying density stratified flows. In this paper equations are presented to evaluate the density of water as a function of temperature, salt content, and sediment load. A nomograph based on these equations is constructed. The nomograph is applied to estimating the density variations of the Shapur River, a sediment‐laden stratified river in Southern Iran. It is illustrated that sediment gives rise to large peaks in density of the river. Such variations are known to be an important factor in geomorphology.
Differential bedload transport rates in a gravel‐bed stream: A grain‐size distribution approach
Authors: Shih Shyuer‐Ming , Komar Paul D. 
Published: February 2007

AbstractThe grain‐size distributions of bedload gravels in Oak Creek, Oregon, follow the ideal Rosin distribution at flow stages which exceed that necessary to initiate breakup of the pavement in the bed material. The distributions systematically vary with flow discharge and bed stress, such that at higher flow stages the grain sizes are coarser while the spread of the distribution decreases. A differential bedload transport function for individual grain‐size fractions is formulated utilizing the dependence of the two parameters in the Rosin distribution on the flow stress. The total transport rate, which is also a function of the flow stress, is apportioned within the Rosin grain‐size distribution to yield the fractional transport rates. The derived bedload function has the advantage of yielding smooth, continuous frequency distributions of transport rates for the grain‐size fractions, in contrast to the discrete transport functions which predict rates for specified sieve fractions. Successful reproduction of the measured fractional transport rates and bedload grain‐size distributions in Oak Creek by this approach demonstrates its potential for evaluations of transport rates of size fractions in gravel‐bed streams. The approach will be useful in investigations of downstream changes in bed material grain‐size distributions.
The hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer
Authors: Poesen J. , Ingelmo‐Sanchez F. , Mucher H. 
Published: February 2007

AbstractRainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface. For a given cover level, rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation. Compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface. For the same cover level, rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer. The effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage. Micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by Poesen (1986): i.e. runoff generated as rock flow or as Horton overland flow can (partly) infiltrate into the unsealed soil surface under the rock fragments, provided that they are not completely embedded in the top layer. Hence, rock fragment position, beside other rock fragment properties, should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers. A simple model, based on the proportions of bare soil surface, soil surface occupied by embedded rock fragments, and soil surface covered with rock fragments resting on the soil surface, describes the runoff coefficient data relatively well.
Distributions of horizon‐limited direct beam potential radiation in steep pastures
Authors: Boyer Douglas G. , Feldhake Charles M. 
Published: February 2007

AbstractAgricultural production from steep terrain is frequently limited to pasture systems, where forage harvesting is done by grazing animals. Intercepted solar radiation determines the energy available for forage production. A model was developed for estimating potential direct beam radiation in areas with a wide range of aspects, landscape positions, and various shadow sources. The model was applied to a small, steep pasture watershed in central Appalachia to determine the spatial distribution of potential direct beam radiation. Effective horizon was an important parameter affecting the energy budget of the study watershed. A simple means for estimating global radiation from the modelled potential direct beam radiation, given atmospheric transmissivity and cloudiness, was presented. When the proportion of global radiation that was diffuse radiation was increased the effective horizon was less important and the spatial variability of modelled radiation decreased.
Trapping of airborne dust by mosses in the Negev Desert, Israel
Authors: Danin Avinoam , Ganor Eliezer 
Published: February 2007

AbstractAirborne silt and clay containing calcium carbonate, quartz, clays, marine nannoplankton, and aquatic diatoms are trapped among stems of mosses in the Negev Highlands Desert. The mosses were studied in an area with 70 mm mean annual rainfall. They grow over the particles covering them and trap additional dust as it comes, resulting in the accumulation of loess sediments. The mosses protect the accumulated soil from erosion by wind or water. Remnants of the moss leaves and stems were found at a depth of 15 mm and more. No particles or minerals typical to basalt were found in the moss‐trapped soil. The function of cushiony mosses may be used to explain the processes of loess trapping and protection in larger areas in moister areas such as the Northern Negev. Microscopic fossils in the dust may be used as guides to the origin of the (aeolian) sediments.
Hydrological mapping from SPOT imagery
Authors: Ali Abdalla Elsadig 
Published: February 2007

AbstractFour SPOT images, one panchromatic and three multispectral, were studied to evaluate their usefulness for hydrological mapping in an arid environment. Simple visual methods of interpretation were used to plot the drainage network independently from each test image. The results were compared with the drainage network shown on the topographic map of the area. Results show that with the panchromatic image, over 90 per cent of the map content could be discerned, identified, and plotted. The accuracy of plotting the drainage system from the multispectral images seems to depend on the season in which data had been acquired. However, in all cases, the success rate is not less than 70 per cent. Comparison with Landsat Thematic Mapper (TM) imagery showed that SPOT system is superior in hydrological mapping.
Geochemical equilibria of iron in sediments of the roaring river alluvial fan, Rocky Mountain National Park, Colorado
Authors: Litaor M. Iggy , Keigley R. B. 
Published: February 2007

AbstractIron geochemistry of the sediments and interstitial waters of the Roaring River alluvial fan in the Rocky Mountain National Park, Colorado was studied using a chemical equilibria approach. Large concentrations of colloidal Fe in the filterable Fe of the interstitial waters results in considerable overestimation of Fe2 + activity. The overestimation of Fe(II) seriously hampered the usefulness of chemical equilibria approach in the study of Fe geochemistry. Buried soil organic matter and a high water table within the alluvial fan has produced a highly reduced environment which results in elevated colloidal and filterable iron concentrations in the interstitial waters. The source of the iron is probably iron oxides within the buried soil and primary iron‐bearing minerals in the sediments. When the iron‐rich solutions reach the surface, the water rapidly oxidizes and amorphous ferric hydroxides precipitate. Between 190 to 370 mmol of iron per kg of surficial material were precipitated at the surface within two months. Noticeable decreases in the total amount of C and extractable iron (20 per cent and 30 per cent respectively) in the buried soil were observed during the study period (1985‐1987) which implies a significant reduction in iron dissolution and subsequent deposition across the alluvial fan.
Climatic effects on the runoff conditions in Hungary
Authors: Nováaky Béla 
Published: February 2007

AbstractUsing runoff and climatic observations from 37 small watersheds in Hungary a regional climate‐runoff relationship has been established. This non‐linear relationship is a modification of Budiko's similar equation and can be used to estimate the effect of climate changes on long‐term average runoff. The degree of change in runoff depends not only on changes in precipitation and temperature, but also on the present climate characteristics. The regional relationship is verified only within a relatively narrow range of precipitation and temperature and this fact limits its use in climate impact assessment. Model calculations show that a relatively slight shift in climate, an increase in annual temperature by 0.5°C, and a decrease of annual rainfall by 0.08 mm d−1 may lead to a decrease of runoff by 25‐30 per cent in small watersheds of Hungary.
Landscape ecological and spatial impacts of climatic change in two areas in the Netherlands
Authors: Jongman Rob H. G. , Souer Martin A. 
Published: February 2007

AbstractThe possible impact of climatic change on the water balance is analysed for the River Dommel and the Veluwe, an area drained by many very small brooks. A water balance is calculated for the winter and the summer period. With the help of four scenarios, based on GCMs, climate data from the dry year 1976 and land use scenarios the impact of climatic change and a possible superposed effect of acid precipitation is analysed. The results show that although the yearly changes in the water balance are small in some cases, in all cases the fluctuations in the water balance between winter and summer period increase. Changes in precipitation and evapotranspiration are multiplied in water storage and runoff. This will have consequences for water use planning and management.
Superposition of aeolian dust ripple patterns as a result of changing wind directions
Authors: Goossens Dirk 
Published: February 2007

AbstractThe effect of a change of wind direction on the orientation (and some other morphometric characteristics) of aeolian dust ripples is investigated. Ripple formation is simulated in a wind tunnel on surfaces that are already characterized by a previously established rippling. The effect of a wind rotation of 45 degrees, 90 degrees, and 180 degrees is examined. It is found that wind rotations of 45 and 180 degrees will lead towards a ripple alignment perpendicular to the last air flow. A wind rotation of 90 degrees, however, leads towards a ripple alignment perpendicular to the resultant wind direction. The faster the wind blows, the more this effect is expressed. No distinct relationship exists between the asymmetry of a dust ripple (and a dust ripple field) and the direction of the wind blowing as the ripples formed. As the orientation and asymmetry of aeolian dust ripples do not necessarily reflect the air flow direction during which the ripples formed, great care should be taken when reconstructing wind directions from such aeolian ripples.
Coarse cliff‐top aeolian sedimentation in northern Gaspésie, Québec (Canada)
Authors: Hétu Bernard 
Published: February 2007

AbstractThis paper deals with the effects of wind on rockwall dynamics. On 5 and 6 January, 1988 very strong northwest winds (blizzard) were blowing onto the rockwall of Mount Saint‐Pierre (alt.: 424 m), Gaspésie, Québec (Canada). The most violent recorded squall reached 99·4 km h−1. During this event, the summit plateau received a large amount of aeolian sediments originating from the shale rockwall that forms the mountain's northwest side. In the 15 to 20 m wide by 75 m long belt located along the top of the rockwall, over a 1200 m2 area, a continuous layer of debris completely covered the snow. This layer of debris had a mean thickness of 11·4 mm, which represents an accumulated volume in the order of 13 m3. Largely dominated by sand and granules (2–4 mm), the 28 samples collected for grain‐size analysis also contained numerous thin shale flakes, many of which were longer than 10 mm. The largest flake measured had a width of 134 mm and a weight of 164·3 g. Six available 14C dates provide information concerning mean cliff‐top aeolian sedimentation rate for the last thousand years (c. 1·8 mmyr−1).