bluuebunny/crossref_metadata_2025_split huggingface dataset:
On using the effective contact angle and the water drop penetration time for classification of water repellency in dune soils
Authors: Wessel A. T. 
Published: February 2007

AbstractSandy soils are often water repellent when dry. In sloping areas this may result in surface runoff and erosion. Water repellency in soils can be classified with the solid‐liquid contact angle which is difficult to determine. Another method is the water drop penetration time. This method is not only easier to apply but provides a more useful scale for classifying water repellent soils. Moreover, it is directly related to erosion hazard because runoff depends on the time required for the infiltration of rain drops. A close relationship was found between the contact angle and the water drop penetration time in dune soils along the coast of the Netherlands.
Contour scaling of a sandstone by salt weathering under simulated hot desert conditions
Authors: Smith B. J. , McGreevy J. P. 
Published: February 2007

AbstractA laboratory study has been used to investigate relationships between salts and contour scaling—a weathering feature commonly observed on rock surfaces in salt‐rich environments. Surface disaggregation and essentially surface‐parallel cracks were produced in sandstone blocks using 10 per cent solutions of sodium sulphate and magnesium sulphate applied daily to single exposed surfaces for sixty days. A control block soaked once in saturated magnesium sulphate and subsequently wetted daily with distilled water showed extensive surface disaggregation, but no cracking. Both surface disaggregation and subsurface cracking were associated with relative concentrations of microcrystalline salt. A tentative model of contour scaling is proposed, which involves linking together potential cracks by salt‐induced fracturing of intervening, crack‐stopping grains. Further control blocks treated respectively with 10 per cent and saturated sodium chloride showed no evidence of subsurface cracking and only limited surface disaggregation of the ‘saturated’ block.
A model of channel response in disturbed alluvial channels
Authors: Simon Andrew 
Published: February 2007

AbstractDredging and straightening of alluvial channels between 1959 and 1978 in West Tennessee caused a series of morphologic changes along modified reaches and tributary streams. Degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed‐levels by as much as 6·1 m. Following degradation, reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction. Aggradation downstream of the area of maximum disturbance reached 0·12 m per year with the greatest rates occurring near the stream mouths.The adjustment of channel geometry and phases of channel evolution are characterized by six process‐oriented stages of morphologic development—premodified, constructed, degradation, threshold, aggradation, and restabilization. Down‐cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded (threshold stage). Channel widening continues through the aggradation stage as the ‘slough line’ develops as an initial site of lower‐bank stability. The bank profile develops three dynamic elements (1) vertical face (70° to 90°), (2) upper bank (25° to 50°), and (3) slough line (20° to 25°). Alternate channel bars form during the restabilization stage and represent incipient meandering of the channel.
Evolution of salt‐marsh cliffs in muddy and sandy systems: A qualitative comparison of British West‐Coast estuaries
Authors: Allen J. R. L. 
Published: February 2007

AbstractSalt‐marsh cliffs in the muddy Severn Estuary are mostly strong and tall. They are retreating in response to the erosive attack of wave and tidal currents chiefly through toppling failures and rotational slips. In the sandy Solway Firth and Morecambe Bay systems, marsh cliffs are strong only in their upper parts, where a dense root‐mat of marsh grasses binds the sediments. Here cantilever and toppling failures are the main response of the cliffs to tidal and wave erosion The differences between the three estuarine systems in the mechanisms of marsh‐cliff erosion are partly reflected in the mode of preservation of the cliffs on the restoration of the conditions leading to renewal of marsh growth.
Structure and stability of the former subglacial drainage system of the glacier De Tsanfleuron, Switzerland
Authors: Sharp Martin , Gemmell J. Campbell , Tison Jean‐Louis 
Published: February 2007

AbstractA well‐developed subglacial drainage system consisting of large cavities developed in the lee of bedrock steps connected together by a network of Nye channels is exposed on an area of recently deglaciated limestone bedrock in front of Glacier de Tsanfleuron, Switzerland. This system covers some 51 per cent of the bedrock surface area, and is believed to have transported the bulk of supraglacially‐derived meltwaters through the glacier. Using the cavity hydraulics model of Kamb (1987), it is shown that the geometry of the system rendered it stable against collapse by meltback of channel roofs into a tunnel‐dominated system. For likely combinations of glacier geometry and meltwater discharge, the steady state water pressure in this system would have been only a small fraction of that required for flotation, and for discharges of less than about 0·5–5 m3 s−1 water would have flowed at atmospheric pressure. The system appears to have adjusted to varying discharges by a combination of varying water pressure and changing the total cross‐sectional area of flow by altering the number of active channels connecting cavities. Glacier sliding velocity would have been independent of meltwater discharge for discharges at which water flowed at atmospheric pressure, but would have risen with increasing discharge for higher flows. Velocities on the order of 0·1 m d−1 are predicted for a realistic range of discharges and effective pressures, and these are believed to be plausible. Episodes of enhanced sliding in glaciers with similar drainage systems could be triggered by a rise in meltwater discharge across the threshold between flows at atmospheric pressure and flow under pressure from the glacier.
Temporal variations in bedload transport rates associated with the migration of bedforms
Authors: Gomez Basil , Naff Richard L. , Hubbell David W. 
Published: February 2007

AbstractTemporal variations in bedload transport rates that occur at a variety of timescales, even under steady flow conditions, are accepted as an inherent component of the bedload transport process. Rarely, however, has the cause of such variations been explained clearly. We consider three data sets, obtained from laboratory experiments, that refer to measurements of bedload transport made with continuously recording bedload traps. Each data set is characterized by a predominant low‐frequency oscillation, on which additional higher‐frequency oscillations generally are superimposed. The period of these oscillations, as isolated through the use of spectral analysts, ranged between 0·47 and 168 minutes, and was associated unequivocally with the migration of bedforms such as ripples, dunes, and bars. The extent to which such oscillatory behaviour may be recognized in a data set depends on the duration of sampling and the length of the sampling time, with respect to the period of a given bedform.Several theoretical probability distribution functions have been developed to describe the frequency distributions of (relative) bedload transport rates that are associated with the migration of bedforms (Einstein, 1937b; Hamamori, 1962; Carey and Hubbell, 1986). These distribution functions were derived without reference to a sampling interval. We present a modification of Hamamori's (1962) probability distribution function, generated by Monte Carlo simulation, which permits one to specify the sampling interval, in relation to the length of a bedform. Comparisons between the simulated and observed frequency distributions, that were undertaken on the basis of the data described herein, are good (significant at the 90 per cent confidence level). Finally, the implications that temporal variability, which is associated with the migration of bedforms, have for the accurate determination of bedload transport rates are considered.
Laboratory experiments on the influence of slope length on runoff, percolation and rill development
Authors: Bryan R. B. , Poesen J. 
Published: February 2007

AbstractExperiments to test relationships between slope length, percolation, and runoff were carried out in a laboratory flume under simulated rainfall at intensities from 24·2‐26 mm h−1. A composite soil subject to sealing was mixed from a clay and a sand and tested on 2·39 m, 7·18 m, and 17 m slopes for a minimum of 200 min. Runoff discharge is not a simple function of rainfall excess and slope length but shows a complex pattern dominated by surface sealing, rill development and headcut incision. Rill development by concentrated surface wash conformed to established threshold hydraulic conditions, but subsequent headcut incision was necessary to breach the seal and significantly affect percolation/runoff ratios. Headcut evolution is complex, apparently reflecting hydraulic instability and possibly different stages in seal development. Headcut and rill incision shows a cyclic pattern interspersed with broad areas of sheetwash and colluvial deposition where percolation rates are very low.
Sediment transfer and transformation of an alluvial valley floor: The river South Tyne, Northumbria, U.K.
Authors: Macklin Mark G. , Lewin John 
Published: February 2007

AbstractThe amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the River South Tyne, northern England. Analysis of lateral and vertical channel change over this period, the extent of actively reworked gravels, and identification of metals in alluvial units, show five ‘sedimentation zones’ separated by more stable reaches. Aggradation in the late nineteenth century was followed by a period of storage and local reworking, and then incision. Some reaches show short‐term storage of sediment injected from tributaries which may be dispersed by floods. There is some evidence of transfer of sediment bodies downvalley within sedimentation zones, and of a sediment ‘wave’ movement between zones in lower parts of the South Tyne investigated. Present‐day incision, the variation in the area of actively reworked gravel spreads, and the widespread dispersal of fine‐grained toxic metal mining wastes all have practical implications. The intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave.
Morphology of Red Creek, Wyoming, an arid‐region anastomosing channel system
Authors: Schumann R. Randall 
Published: February 2007

AbstractRed Creek, in the Red Desert area of the Great Divide Basin, Wyoming, is an arid‐region anastomosing stream. The narrow, deep, and sinuous main channel is flanked by anastomosing flood channels, or anabranches. Most anabranches are initiated at meander bends. The primary mechanism of anabranch initiation is avulsion during overbank floods. Anabranch enlargement occurs by headward erosion. Anabranches act as distributary channels during floods, when water and sediment from overbank flows are transported to and deposited on the floodplain via the anabranches. During periods of low discharges, the anabranches act as tributaries to the main channel, transporting runoff from the floodplain and surrounding hillslopes to the main channel of Red Creek.Aggradation is occurring in the main channel and on the floodplain throughout the study reach. Infilling of the main channel occurs primarily by lateral accretion, while the floodplain accretes vertically through deposition of overbank sediment from the main channel and anabranches. Infilling of the main channel may cause avulsion of the main channel into an anabranch. The abandoned main channel segment may then fill completely or act as an anabranch. Because lateral migration of channels is inhibited by the high cohesion of the silt and clay channel sediment, periodic avulsion is the primary form of lateral mobility in the system.
Enhanced boulder weathering under late‐lying snowpatches
Authors: Ballantyne Colin K. , Black Nicola M. , Finlay Donna P. 
Published: February 2007

AbstractA Schmidt test hammer was employed to assess the aggregate surface hardness of samples of boulders dug out from under late‐lying snowpatches at sites in Switzerland, Scotland and Norway. The results were compared with an equivalent set of readings made on boulders at nearby snow‐free control sites. The results in every case reveal that the aggregate surface hardness of boulders buried by late‐lying snow is significantly less (at the 0·001 level) than that of boulders at the corresponding control sites. This result indicates that late‐lying snow significantly enhances rock weathering, probably because boulder and rock surfaces are exposed to prolonged wetting by percolating meltwater under late‐lying snowbeds.
Channel sediment variability along a river: A case study of the Siret River (Romania)
Authors: Ichim I. , Radoane M. 
Published: February 2007

AbstractThe Siret River has the largest drainage basin (42 274 km2) in Romania. It gathers all the rivers from the eastern part of the Eastern Carpathians, a fact that causes marked asymmetry of the basin. This study is principally concerned with changes in the form of the longitudinal profile and the grain size variability introduced by the Carpathian tributaries. Channel sediment analyses considered the petrography, granulometry, and morphometry of the pebbles, relating these to the river bed and floodplain geometry and to some properties of the drainage basin.The following conclusions arise. The Siret River undergoes an intense regrading of its longitudinal profile, with marked aggradation between transects 24 and 26 (see Figures 1 and 2). This reflects selective accumulation of coarse material due to the massive contribution of the Carpathian tributaries. This phenomenon has been continuous throughout the Holocene, resulting in the gravel sheet formation of the Pericarpathian piedmont.
Solution‐collapse depressions and suspensates in the limnocrenic lake of banyoles (ne Spain)
Authors: Canals M. , Got H. , Julia R. , Serra J. 
Published: February 2007

AbstractA high resolution seismic reflection survey in the Banyoles limnocrenic solution lake allowed penetration of dense suspensates occupying cone‐like bottom depressions of different size. The depressions result from the dissolution and collapse of underlying Eocene calcareous and gypsiferous materials over which lacustrine sediments of varying thicknesses have accumulated.The suspensates occupying the depressions present three main types of seismic signatures: stratified, semistratified, and transparent. The densities of the suspensates and the water depths of their tops, which fluctuate continuously, vary from one depression to another. The maximum seismically recorded suspensate thickness is 44 m.Morphological and structural features, seismic characters, and variable degrees of hydraulic activity, point to the existence of different stages of maturity in the lake bottom depressions. This work brings new insight on the dynamics and evolution of limnocrenic solution lakes.
Some mudslide movement patterns
Authors: Allison Robert J. , Brunsden Denys 
Published: February 2007

AbstractA study has been made of the mechanisms of movement in a mudslide and the interrelationships between the controlling variables. Detailed monitoring has been conducted on a mudslide developed in the Wealden Beds, a Cretaceous mudrock. The parameters which govern mudslide instability have been continuously monitored using electronic datalogging techniques. Slip can be divided into four components: small ‘multiple’ (stick slip) movements which are grouped temporally; gradual or ‘graded’ slip within defined temporal limits; rapid ‘surge’ events which occur over a short time interval and involve large displacements and unexplained ‘random’ movements. Each of these four components occurs with varying frequency and at different times in the seasonal record. Slip is usually separated by periods of little or no change. Each component of mudslide movement displays characteristic patterns of pore water pressure change.
Scour, fill, and burial depth of coarse material in gravel bed streams
Authors: Hassan Marwan A. 
Published: February 2007

AbstractScour, fill, and burial depths of coarse particles were examined in two ephemeral streams using magnetically‐tagged particles and scour chains. The burial depth varied within a bedform and from one bedform to another. The maximum burial depth was recorded in bars, but differences in the mean burial depth in the pools, bar, and thalweg were insignificant. Mean burial depth was three to six times the median size of material on bar surfaces and ten to thirty times that in the pools and thalweg. More than eighty per cent of the tagged particles which were located on, or close to, the bed surface moved in each event. Although previously buried particles were moved by flood events, others which were initially exposed remained stationary on the surface or were buried in situ. The data indicate that the mean burial depth was intermediate between the mean depths of scour and fill. Deeply buried particles probably reflect the development of scour holes during flood flows. Aggradation and degradation changed the recorded burial depth, relative to the local bed surface, of stationary tracer particles. These observations indicate that scour and fill processes during a flow event are sporadic and change with water discharge.
Large‐scale floodplain modelling
Authors: Gee D. Michael , Anderson Malcolm G. , Baird Laura 
Published: February 2007

AbstractA two‐dimensional horizontal finite element numerical model (RMA‐2) was applied to a 24 km river channel‐floodplain reach in West Germany. Initial results indicate that finite element schemes may successfully estimate inundation in large‐scale floodplain applications. Potentially, the resulting detailed velocity vector distributions and identification of inundation zones throughout storm events could provide an insight into the present day sedimentary environment on the floodplain.
Runoff generation in a sandy area—the nizzana sands, Western Negev, Israel
Authors: Yair A. 
Published: February 2007

AbstractThis paper presents the results of sprinkling experiments conducted over the lower part of vegetated and crusted linear dunes as well as over flat playa surfaces that appear in the interdune corridors. Data obtained show that these two surface units respond quickly to rainstorms. Runoff generation can be expected for any storm exceeding 2‐3 mm and runoff coefficients are high. When the topsoil algal crust, 1 to 2 mm thick, is removed from the surface of the dune, infiltration increases drastically and eliminates any possibility of runoff generation under present‐day rainfall conditions. This data may be of great help in the understanding of the geomorphology and sedimentary sequence of the corridors separting linear dunes.
Experimental frost and salt weathering of chalk—I
Authors: Jerwood L. C. , Robinson D. A. , Williams R. B. G. 
Published: February 2007

AbstractTo try to resolve the conflicts surrounding the influence of salts on frost weathering, chalk cubes were immersed, separately, in solutions of sodium chloride, sodium sulphate, and magnesium sulphate at concentrations of 5·5 per cent and 12·5 per cent, in a mixed solution of sodium chloride and sodium sulphate, and in distilled water. The cubes were subjected to six freeze‐thaw cycles with temperatures ranging from either +15 to — 10°C or + 15 to — 30°C. The results confirm that frost weathering can be enhanced by the presence of certain salts, but the degree of enhancement depends both on the concentration and type of salt and on the intensity of the freeze‐thaw regime. Some, but not all, of the results can be explained by the phase changes that occur during the freezing of the salt solutions.
Slope‐induced changes in channel character along a gravel‐bed stream: The Allt Dubhaig, Scotland
Authors: Ferguson Rob , Ashworth Phil 
Published: February 2007

AbstractChanges in channel character along a small river in the Scottish Highlands are described using measurements in seven reaches over a 3 km length with no significant tributaries but a decline in slope from 0.02 to 0.00015 because of local baselevel control. This decline in slope is associated with rapid downstream fining of the gravel bed followed by an abrupt transition to a sand bed. The channel pattern alters progressively rather than abruptly, in the sequence (1) near‐braided, (2) meandering with active point‐bar chutes, (3) meandering with active outer‐bank talweg, (4) stable equiwidth sinuous. The changes in channel pattern and hydraulic geometry are predicted better by rational approaches based on critical shear stress or other physical concepts than by purely empirical discriminant or trend equations. Measurements in five reaches confirm a downstream decrease in shear stress and the amount and calibre of bedload. It is argued that the downstream changes in channel character in this stream are induced by profile concavity inherited from deglacial conditions, are typical of many streams in mountainous areas and can be understood in terms of slope‐induced changes in hydraulic properties.
Neotectonic effects on sinuosity and channel migration, Belle Fourche River, Western South Dakota
Authors: Gomez Basil , Marron Donna C. 
Published: February 2007

AbstractShort‐term instability in the behaviour of a small, meandering alluvial channel is identified from the relation between sinuosity and either floodplain slope or channel slope within 17 reaches along an 81‐kilometre section of the Belle Fourche River in western South Dakota. In reaches 1 to 4 and 11 to 17 the channel is relatively stable and sinuosity varies inversely with channel slope. In reaches 5 to 10, sinuosity is positively related to floodplain slope. Sinuosity increases markedly in reaches 5, 6, and 7 (which are immediately downstream from a discontinuity in the long profile of the floodplain) in association with an increase in floodplain slope. Immediately upstream from the discontinuity, bankfull channel depth and sinuosity decrease and the area of the floodplain reworked by meander migration between 1939 and 1981 increases, in association with a decrease in floodplain slope. Channel behaviour in reaches 5 to 10 is best explained as a consequence of neotectonic activity, as indicated by changes in elevation recorded along geodetic survey lines that cross lineaments that may delimit the eastern boundary of the Black Hills uplift. Sinuosity acts as a barometer of the effects of neotectonic activity on alluvial channels. Initial indications of channel and floodplain instability due to neotectonic activity may be derived from evidence of anomalously active channel migration, as documented from photographic or topographic sources.