bluuebunny/crossref_metadata_2025_split huggingface dataset:
The incidence and nature of bedload transport during flood flows in coarse‐grained alluvial channels
Authors: Reid Ian , Frostick Lynne E , Layman John T 
Published: February 2007

AbstractA continuous record reveals that the incidence of bedload in a coarse‐grained river channel changes from flood to flood. Long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood‐wave. But when floods follow each other closely, the bed material is comparatively loose and offers less resistance to entrainment. In this case, substantial amounts of bedload are generated on the rising limb. This is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season. This produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse‐grained channels. Besides this, the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion. This adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory. Bedload is shown to be characterized by a series of pulses with a mean periodicity of 1.7 hours. In the absence of migrating bedforms, it is speculated that this well‐documented pattern reflects the passage of kinematic waves of particles in a slow‐moving traction carpet. The general pattern of bedload, including pulsations, is shown to occur more or less synchronously at different points across the stream channel.
Lake catchment based studies of erosion and denudation in the merevale catchment, Warwickshire, U.K.
Authors: Foster I. D. L. , Dearing J. A. , Simpson A. , Carter A. D. , Appleby P. G. 
Published: February 2007

AbstractSediment yields estimated from contemporary stream monitoring of suspended sediment in the Merevale forested catchment, North Warwickshire, were compared with the sediment yield record obtained from analysis of lake sediment in the downstream reservoir. Total sediment volume and mass for nine periods since 1861 were calculated by extrapolation of synchronous levels in 54 cores, identified from magnetic susceptibility and other magnetic measurements, and by using 210Pb and 137Cs analysis to provide an absolute sediment chronology. Sediment yield estimated from the two methods show comparable but low (50‐200 kg ha−1 yr−1) levels of sediment loss. While suggesting that lake sediments can be a useful means for extending the period over which contemporary monitoring exists, the study stresses the need for detailed historical records of land use and climate against which long term sediment yield records can be evaluated.
Salt marsh cliff stability in the oosterschelde
Authors: Van Eerdt Martha M. 
Published: February 2007

AbstractSalt marsh cliff erosion in the Oosterschelde, due to basal scour and small‐scale failure, was monitored during a two‐year period using reference stakes. The composite marsh cliffs have a cantilever profile. Their stability is evaluated from beam failure analysis. A model is proposed, in which the cantilever weight is taken as the motive force; the major resistive force is the tensile strength. By substituting height, undermining width and soil mechanical properties of the cliff in the model, one can identify the cliffs that are likely to fail. Salt marsh cliffs, which combine a large tensile strength due to roots at the top of the profile with a large compressive stress at the cliff base due to the sandy texture of the subsoil, display the highest resistance to beam failure. The critical cliff dimensions, observed in the field, correspond with the values calculated from the proposed model of beam failure.
Thermal properties as controls on rock surface temperature maxima, and possible implications for rock weathering
Authors: McGreevy J. P. 
Published: February 2007

AbstractFour rock types (basalt, sandstone, granite, and chalk) are examined with respect to the maximum surface temperatures which they experience when subjected to similar conditions of exposure. Rock temperature measurements are reported for an urban environment and for two experimental situations in which an infrared lamp is used to simulate heating under cold and hot conditions. Differences in rock temperatures are discussed with reference to thermal rock properties (albedo, specific heat capacity, and thermal conductivity). Some natural situations are suggested in which thermal rock properties could conceivably play a role in determining the extent to which rocks would be affected by particular weathering processes.
Holocene alluviation in Southeast England and some implications for palaeohydrological studies
Authors: Burrin P. J. 
Published: February 2007

AbstractImplicit in models of palaeohydrological reconstruction is the assumption that a close relationship exists between climate, hydrological regime, and fluvial systems. Unfortunately, there can be a number of complicating factors involved, some of which are becoming increasingly well known. Research into Holocene alluviation in southeast England has demonstrated some associated difficulties which range from the problem of relating anthropogenically modified drainage networks to an understanding of contemporary rates of floodplain development to the impact of prehistoric societies on valley sedimentation. A theoretical model is presented whereby varying geomorphic domains contributing to floodplain and valley fill construction can be recognized. It is suggested that attempts to apply this framework to palaeohydrological studies may assist in the realization of a more accurate reconstruction in which former hydrological responses are integrated within a broader palaeoenvironmental context.
Trace elements in alluvia of the upper Vistula as indicators of palaeohydrology
Authors: Klimek Kazimierz , Zawilinska Lucyna 
Published: February 2007

AbstractIn the Vistula valley near Góra, at the northern foreland of the Carpathians Mountains, there are young alluvia deposited in the historical period. These alluvia are difficult to date precisely because of the lack of organic interbedded material. In the Vistula drainage basin upstream of Góra since the second half of 18th century small centres of metal, textile, motor, and petrochemical industries have been developed. Concentrations of trace elements such as: Cr, Mn, Co, Ni, Cu, Zn, Cd, Pb, and of some macroelements were used as indicators of the age of different alluvial fills. The main part of the Vistula valley floor was built up by sediment accumulation before the development of industry but after the medieval phase of rural colonization of the Carpathians. Deposits filling the abandoned channels dissecting the valley floor have an increased content of some trace elements and deposits date from the second half of the 18th century, when the first foundries and blacksmith's shops were developed. A drastic increase of concentration of the most abundant trace elements in the youngest alluvial fill indicates that the fill dates from the last decade of rapid industrial development.
A preliminary scanning electron microscope study of honeycomb weathering of sandstone in a coastal environment
Authors: McGreevy J. P. 
Published: February 2007

AbstractHoneycomb weathering has been observed in a Carboniferous sandstone at a coastal location near Ballycastle on the north coast of Northern Ireland. Specimens of this sandstone have been analysed by X‐ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. Results reveal that calcium sulphate (gypsum) is the only salt present and is found only at and immediately below the rock surface. SEM observations suggest that crystallization of salts in pores could easily dislodge quartz grains to promote granular disintegration, whilst etching of quartz grain surfaces attests to chemical weathering activity within the rock However, the reason for the development of the honeycomb pattern is not known.
Laboratory simulation of rock weathering by salt crystallization and hydration processes in hot, arid environments
Authors: Sperling C. H. B. , Cooke R. U. 
Published: February 2007

AbstractThe results of a series of experiments are reported in this paper which were designed to differentiate between the forces of crystal growth and hydration in salt weathering, using a single salt‐hydrate system (sodium sulphate), five contrasting rock types, and several diurnal temperature‐relative humidity cycles which permitted or inhibited these processes and simulated ground surface climates in hot, arid environments. It was shown that hydration of sodium sulphate is an effective mechanism of rock disintegration but that it is significantly less destructive than crystal growth pressure. Crystallization of thenardite (Na2SO4) is, in turn, more effective in rock weathering than the crystal growth of mirabilite (Na2SO4.10H2O). In general, rates of disintegration were most rapid where the diurnal temperature range was extreme and relative humidity lowest.
Surface sealing as influenced by slope angle and position of simulated stones in the top layer of loose sediments
Authors: Poesen Jean 
Published: February 2007

AbstractThe influence of five different slope angles and two different positions of simulated stones in the top layer of a sandy and a silty sediment on surface sealing intensity is examined in the laboratory. Sealing intensity is assessed by studying changes of percolation rate through a sediment layer with simulated rainfall duration and by measuring cohesion of the 5 mm thick upper sediment layer, a measure of seal strength, by means of a torvane. Slope has a negative influence on sealing intensity. For a constant per cent of simulated stone cover, sealing intensity is lowest in the case of stones placed on the sediment surface compared to the case of stones pushed into the surface layer. Explanations for these findings are given and some implications are further discussed.
An investigation into the relationship between salt weathering debris production and temperature
Authors: Davison Alan Paul 
Published: February 2007

AbstractAn investigation using laboratory simulation has been made using air temperature data for Tunisia, Antarctica, and southwest England. An experiment with a 50 cycle run produced results which showed significantly greater debris production in the Antarctica and Tunisian simulations than in the southwest England simulation.Using X‐ray analysts to determine salt penetration, an inverse relationship between salt penetration and debris production was seen to exist. This could be the result of evaporation in the Tunisian simulation and rapid freezing in the Antarctic simulation, concentrating salts in the upper layers of the rock samples. In the southwest England simulation, no freezing, and relatively high humidities allowed greater penetration, thus distributing an equal input of salt over a greater area.The author tentatively suggests the possible existence of a parabolic relationship between salt weathering and temperature.
Transporting capacity of overland flow on plane and on irregular beds
Authors: Govers G. , Rauws G 
Published: February 2007

AbstractIn this paper the transporting capacity of thin flows, in the laminar and transitional flow regime, is studied. Experiments were carried out on irregular as well as on plane beds, using two totally different set‐ups. The results of these two types of experiment were convergent. In both cases, sediment concentration was clearly related to grain shear velocity and unit stream power, expressed as the product of mean velocity and slope (Yang, 1973). The data agreed with those of Kramer and Meyer (1969). For a sandy bed, the unit stream power relationship was able to predict reasonably well the sediment concentrations measured on a mulched surface. For laminar and transitional flows, both the unit stream power and the shear velocity are related in the same way to slope and unit discharge. The unit stream power is a parameter which in particular can be very easily measured and might therefore become useful in obtaining a quick estimate of the transporting capacity of a thin flow. However, before a sediment transport equation for thin flows can be developed, more information is needed about the influence of the flow regime and grain size and density.
A sediment budget for a forested catchment in Luxembourg and its implications for channel development
Authors: Duijsings J. J. H. M. 
Published: February 2007

AbstractIn the forested catchments of the Luxembourg Keuper area, deeply‐incised valleys have developed in which streambank erosion is a widespread phenomenon. For one of the catchments in this area, the Schrondweilerbaach catchment, a sediment budget was constructed in order to determine the relative contributions of the various channel and valley slope processes to sediment output.Streambanks contributed 53 percent of the output with bank scour and subsoil fall being the main processes while to a lesser extent bank material was supplied by bank failures, splash erosion, and soil creep. The remaining 47 per cent of the sediment was derived from the valley slopes mainly through the combined action of rainsplash detachment and overland flow transport. During the two years of investigations sediment output from the drainage basin almost equalled sediment input from streambanks and valley slopes. The results of the measurements of the various streambank processes are integrated in a descriptive model for the present‐day widening of valley incisions in the study area and used to hypothesize the palaeohydrological development of the basin. Special attention is paid to the (in)direct effects of the forest vegetation on streambank erosion and sediment transport through the stream channel.
Fractals in Karst
Authors: Laverty Martin 
Published: February 2007

AbstractThe analysis of cave survey data is used to establish that cave length exhibits fractal (self‐similar) behaviour, with dimensions in the range 1–1·5, over a range of measurement resolutions from 1 to 100 m. It is suggested that fractal dimensions, together with their range of applicability, will prove to be useful parameters for the study of caves.
A model of the redistribution of disaggregated soil particles by rainsplash
Authors: Wright Andrew C. 
Published: February 2007

AbstractA model of the dispersion of splash droplets from a single raindrop impact on a sloping soil surface is combined with a theory of the entrainment of mineral particles from a disaggregated mixture in splash droplets to obtain a model of the dispersion of such particles by a raindrop impact. Stochastic modelling techniques extend this further to a model of the spatial redistribution of soil on a plot after a period of rainfall.Since the model is probabilistic and physically based it enables the incorporation of further advances in the understanding of splash erosion at all stages and can simulate the effect of the stochastic nature of rainfall and soil properties on the process. Several different situations are simulated. These include the movement of marked soil particles from point sources and the spatial patterns of erosion on a sloping plot. The model can also simulate the differential erosion of different soil particle size fractions.
Intermittent surging movements of a coastal landslide
Authors: Grainger P. , Kalaugher P. G. 
Published: February 2007

AbstractSince the late 1960s there has been a large mudslide in coastal cliffs of Permo‐Triassic strata (conglomerate overlying mudstone) at West Down Beacon, 2 km west of Budleigh Salterton, Devon. A total displacement of 100 m was achieved between 1981 and 1985 as the lobate toe of the mudslide pushed forward across the beach in eleven surges of movement. Each surge involved a displacement of between 5 and 15 m and was completed within a few hours. The toe moved by planar sliding, possibly on more than one seaward‐dipping shear surface or zone. Occasionally there were additional relatively minor displacements (less than 1 m), but normally the mudslide was stationary between the major surges. After each surge high‐oblique aerial photographs were obtained for stereoscopic interpretation. Debris falls from the cliff appear to have triggered some of the mudslide surges. A displacement recording of one surge has indicated that the rate of movement of the mudslide may have been partly controlled by variations in sea level during the tidal cycle.
Bedload transport and sediment yield in the Onyx River, Antarctica
Authors: Mosley M. P. 
Published: February 2007

AbstractBedload transport measurements were made in a braided reach of the Onyx River, Wright Valley, Antarctica, during summer 1984/85. Transport was predominantly of sand in the form of dunes, which moved in a band down the centre of the channels, the perimeters of which were composed of a gravel pavement created during short duration high flows in earlier years. Transport rates at‐a‐point and past‐a‐cross‐section were highly variable in space and time, even under conditions of constant discharge, and it was inferred that many factors other than hydraulic conditions—particularly sediment supply—control transport rates.An empirical power function relationship between sediment discharge and water discharge was used to predict an average annual total sediment discharge of 3400 t y−1 past the study reach. This gives a specific sediment yield of 5.9 t km−2 · y−1, which is two orders of magnitude less than values for Arctic and Alpine proglacial rivers, and confirms earlier conclusions that sedimentation rates on Antarctic sandur are much lower than in the arctic.
Late quaternary monsoon patterns on the Loess Plateau of China
Authors: And Li Jijun , Zhaodon Feng , Lingyu Tang 
Published: February 2007

AbstractChina's Loess Plateau was formed under special conditions. The tectonic movement, topographical characteristics, and monsoon patterns combined to create a favourable environment for the accumulation of thick loessic deposits. The Loess Plateau itself is part of the ‘Monsoon Triangle’ of China, a region very susceptible to climatic changes. Throughout the Upper Pleistocene the palaeoenvironment on the Loess Plateau alternated from steppe, to deciduous forest and coniferous forest, in response to shifts in the atmospheric circulation. Three monsoon patterns appear to be indicated: (1) a full glacial monsoon pattern (18000–15000 yr BP) which induced a cold and dry climate favouring loess accumulation in steppe conditions; (2) an interglacial monsoon pattern (last interglacial and Holocene) in which a warm humid climate prevailed with deciduous forests, leaving palaeosols interbedded within the loess sequence; and (3) a transitional or interstadial monsoon pattern (50 000–23 000 yr BP) in which the climate was cold and humid in the Loess Plateau, encouraging the development of coniferous forest.
A preliminary electron probe study of microchemical variations in desert varnish in Western New South Wales, Australia
Authors: Dragovich D. 
Published: February 2007

AbstractExamination of desert varnish samples from Australia by electron microprobe and energy dispersive spectrometry has shown that gross layering of iron‐ and manganese‐enrichments is variable. Surface (upper) varnish may be similar to lower varnish, or be relatively enriched in either iron or manganese. When viewed in sections cut parallel to the varnished surface, microlaminations with high manganese content (up to 30 per cent) were sometimes found in concentrically zoned patterns around grains.Dorn et al. (1986) have proposed that chemical changes occur with increasing varnish age. In this study, the possibility of such changes was examined at the within‐varnish scale by comparing near‐surface and deeper (upper and lower) portions of the same varnishes. Variations in elemental ratios (K + Ca:Ti) at this scale were shown to be largely unsystematic, suggesting either that samples were unrepresentative; that element inputs to varnish have varied over time; that the varnish was too young for differentiation by weathering into an upper and lower layer; that varnish cover formed rapidly and at one time; or that existing varnish cover represents the coalescence of numerous individual patches of varnish, each of which formed over a relatively short period.
A contour‐based topographic model for hydrological and ecological applications
Authors: Moore I. D. , O'Loughlin E. M. , Burch G. J. 
Published: February 2007

AbstractA digital model for discretizing three‐dimensional terrain into small irregularly shaped polygons or elements based on contour lines and their orthogonals is described. From this subdivision the model estimates a number of topographic attributes for each element including the total upslope contributing area, element area, slope, and aspect. This form of discretization of a catchment produces natural units for problems involving water flow as either a surface or subsurface flow phenomenon. The model therefore has wide potential application for representing the three‐dimensionality of natural terrain and water flow processes in the fields of hydrology, sedimentology, and geomorphology. Three example applications are presented and discussed. They are the prediction of zones of surface saturation, the prediction of the distribution of potential daily solar radiation, and the prediction of zones of erosion and deposition in a catchment.
A laboratory simulation of rock breakdown due to freeze‐thaw in a maritime Antarctic environment
Authors: Hall Kevin 
Published: February 2007

AbstractResults of freeze‐thaw simulations on three large blocks of quartz‐micaschist are presented. Three types of water to ice phase change were identified from temperature and ultrasonic measurements. It is suggested that the type of phase change results from a particular combination of rock moisture content, solute concentration, freeze amplitude, and rate of fall of temperature. The temperature at which ice thawed inside the rock (−0.7 to −1.9°C) was also found, and this indicates the possibility of freeze‐thaw effects without positive temperatures. Approximately 80 per cent of the water that will freeze under natural conditions, in the Maritime Antarctic environment under study, appears to have done so by −6°.