bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Piedmont landscape of Maryland: A new look at an old problem
Authors: Costa John E. , Cleaves Emery T. 
Published: February 2007

AbstractThe Piedmont upland of Maryland has been variously interpreted as a peneplain, a series of peneplains, a surface of marine planation, and a landscape in dynamic equilibrium. These different perspectives of landform evolution are related to different scales of time and space. Both equilibrium and episodic erosion features can be recognized in the modern landscape. An equilibrium condition is suggested by adjustment of first and second order streams to rock structure and lithology, entrenchment of some streams against gneiss domes, altitudinal zonation of rock types around gneiss domes, correlation of lithology with overburden thickness on uplands, decreasing overburden thickness on uplands related to decreasing degree of metamorphism of crystalline rocks, and correlation of secondary mineral assemblages with subsurface drainage and slope. The long‐term episodic character of erosion is suggested by clastic wedges on the adjacent Coastal Plain, an upland of low relief that truncates non‐carbonate rocks of different lithologies, isovolumetric chemical weathering of alumino‐silicate rocks, clastic deposition in marble valleys, and weathering profile truncation by modern drainage.The Maryland Piedmont may have been an area of positive relief subject to subaerial erosion since Triassic and possibly Permian time. The upland surface preserved in the eastern Piedmont developed by the Late Cretaceous. In the interval from the Late Cretaceous to the Late Miocene, low input of terrigenous sediments to the Coastal Plain, dominance of marine sedimentation, and spotty evidence of saprolite formation on crystalline rocks, suggest that the Maryland Piedmont was an area of low relief undergoing intense weathering. Incised valleys were formed during a cycle of erosion probably initiated in the Late Miocene and extensive colluvial sediments were deposited on hillslopes by periglacial processes during the Pleistocene.
Bank erodibility of shallow sandbed streams
Authors: Pizzuto James E. 
Published: February 2007

AbstractCross‐sections were surveyed at straight reaches of 16 sandbed streams in the midwestern U.S. Two stratigraphic horizons are found in the banks at each site, an upper cohesive unit usually composed of silt and clay, and a lower unit composed of sand.Bank erosion on these rivers occurs when the upper cohesive unit is undercut by scour at bends. The overhanging cohesive block fails by toppling forward into the channel. During failure, the soil is primarily in tension rather than compression or shear. Analysis of this failure mechanism leads to a field method for measuring the tensile strength of riverbanks. Measured values of the tensile strength are not correlated with the channel geometry. Thus, the erodibility of the cohesive bank sediments does not influence the geometry of the rivers studied.
Sedimentation within a regulated river
Authors: Petts Geoffrey E. 
Published: February 2007

AbstractChannel change induced by tributary sediment injection to a regulated, gravel‐bed river is described for the River Rheidol, U.K., eighteen years after dam closure. Morphological and sedimentological data are presented for an aggrading reach. A primary lobate bar appears to have initiated flow separation and the subsequent construction of channel‐side berms. Hydraulic sorting has operated to produce both longitudinal and lateral particle‐size reduction, and selective particle‐size dispersal appears to be an important process influencing channel change. The channel is adjusting to a lower width‐depth ratio form, of smaller capacity, and with a steeper slope.
Isovolumetric weathering and silcrete formation, southern Cape Province, South Africa
Authors: Summerfield M. A. 
Published: February 2007

AbstractCalculations of absolute elemental gains and losses based on isovolumetric bedrock alteration are applied to deep weathering profiles and silcrete developed on Dwyka Tillite and Bokkeveld Shale. Bedrock weathering to kaolinite and illite yields sufficient SiO2 to account for observed thicknesses of associated silcrete. Absolute accumulation of SiO2 in silcrete is complemented by substantial absolute depletion of Al2O3. Absolute accumulation of TiO2 in both silcrete and associated weathered material together with authigenic anatase concentrations in silctete recorded during micromorphological investigations indicate TiO2 mobilization in a low pH environment (pH < 3·75) during silcrete formation. Under these low pH conditions increased Al2O3 solubility led to replacement of kaolinite and illite by a proportion of SiO2 retained in the weathering profile through restricted drainage.
River channel change: Problems of interpretation illustrated by the river derwent, north Yorkshire
Authors: Richards K. , Greenhalgh C. 
Published: February 2007

AbstractSome inherent limitations of the spatial interpolation method of identifying and interpreting channel adjustment are illustrated by a study of the River Derwent in Yorkshire. Here, cross‐sections downstream from a river diversion appear to have contracted in size when compared with predictions based on upstream relationships between channel form variables and basin area. However, these sections are slightly larger than expected for their diminished discharge, suggesting that they have not fully adjusted to altered environmental conditions and are still in a transient state.
Stone movement on hillslopes in the Mojave Desert, California: A 16‐year record
Authors: Abrahams Athol D. , Parsons Anthony J. , Cooke Ronald U. , Reeves Richard W. 
Published: February 2007

AbstractPrevious research has shown that either hydraulic action or creep may be the dominant process transporting coarse debris down hillslopes in the American Southwest. This study analyses the movement over 16 years of painted stones on two hillslopes in the central Mojave Desert to ascertain which of these two processes dominate in this region. The distance moved (M) is found to be directly related to length of overland flow (X) and hillslope gradient (S), and inversely related to particle size (D). The fact that M is more highly correlated with X than with S suggests that hydraulic action rather than creep is the dominant process. It is concluded that this is probably the case over most of the Mojave and Sonoran Deserts on slopes up to at least 24°, and that it is only at higher elevations where winters are more severe that creep may become dominant.
Surface runoff and sediment yield in the Ardèche rangelands
Authors: Roels J. M. 
Published: February 2007

AbstractThis paper presents a case study of runoff and sediment generation under Submediterranean rangeland conditions (Ardèche drainage basin, France). Measurements indicate that on a rough hillslope interrill runoff and sediment are not produced uniformly over the slope surface. It is observed that runoff concentrates immediately in non‐permanent interrill flow paths, which under average storm conditions vary in length from 1.0 to 12.5 m. Long interrill flow paths may eventually become permanent. These permanent flow paths, called pre‐rills, are introduced as a new source area, and are considered to be the initial stage in the development of rills. Along pre‐rills considerable quantities of runoff and sediment are carried away.This study also shows that calculations based on interrill, pre‐rill, and rill runoff will only have significance if storm and soil conditions are specified in detail. It is concluded from a correlation analysis between the runoff volume and the amount of soil loss on a storm‐by‐storm basis that the runoff volume alone cannot explain the amount of sediment that is generated in each source area; soil availability is an additional factor that must be taken into account.
Flow and grainsize pattern in a sharply curved river bend
Authors: Van Alphen J. S. L. J. , Bloks P. M. , Hoekstra P. 
Published: February 2007

AbstractThe main characteristics of river flow and grainsize in a bend of the sand bedded meandering river Dommel, The Netherlands, are presented. Measurements were carried out at a relatively low discharge in a sharply curved bend following a long straight reach. In the studied bend, secondary circulation is restricted to the thalweg area; only in the downstream part of the bend it exists over the entire cross‐section. Therefore, on the entire pointbar platform, which comprises the larger part of the bend, the median sedimentation diameter of the bedload material is governed by the distribution of the longitudinal components of the bed shear stress only.
Ventifacts distribution in Qatar
Authors: Babikir A. A. A. , Jackson C. C. E. 
Published: February 2007

AbstractThis study attempts to investigate the distribution of ventifacts in Qatar. It is believed that ventifacts are confined to the areas within about 5 km of the Miocene or Mio‐Pliocene Hofuf formations and the spreads of continental gravels derived from them. Three hypotheses were formulated: (1) Ventifacts in Qatar are confined to areas within about 5 km of the Hofuf formations and the spreads of continental gravels derived from them. The distribution of ventifacts within these areas varies according to the nature of the ground surface; (2) The most active ventifaction areas are where the continental gravels merge with the Eocene limestone because of the increase in saltation particle speed in these areas where bedrock or bare limestone is exposed; (3) The unit area ratio of ventifact to non‐ventifact pebbles varies inversely with the total amount of pebbles. To test these hypotheses, nine land class categories were identified in the three major Hofuf formations. Line transects were carried out from randomly selected stations near the middle of the Hofuf formations. Along each transect systematic sampling was carried out at 200 m intervals. The data were processed using a WANG MVP 2200 computer with software developed for the project. It was found that ventifacts tend to concentrate on the outer edges of the continental gravels in areas of limestone outcrop and limestone pavement. Higher areas have big gravel counts and a low ratio of ventifacts while the low‐lying plains have small gravel counts and a higher ratio of ventifacts. In certain areas ‘ventifact fields’ were found where the density of ventifacts was as high as 30 per m2. Many of the ventifacts in these fields were buried beneath the surface suggesting that the ventifaction predates the present site conditions. Other high ventifact density areas were discovered where the ventifacts have collected in shallow depressions or hollows on the limestone plateaux. Water action has washed these ventifacts, a high proportion of which are dreikanters, into the hollows, where they have been partially buried in fine alluvial silts. These ‘ventifact graveyards’ are generally only a few metres wide but contain large numbers of fine specimens.
Drop shape and erosivity part II: Splash detachment, transport and erosivity indices
Authors: Riezebos Hans Th. , Epema Gerrit F. 
Published: February 2007

AbstractThe relevance of drop shape for erosivity was tested for different combinations of drop sizes and fall heights. For all test combinations together the introduction of the observed drop shape in erosivity parameters only produces minor improvements in the relation between erosivity and detachment and transport by splash. This result is attributed to the dominance of oblate shapes in high velocity conditions. Using small fall heights and low fall velocities as in many rainfall simulators and drop tests it is shown that prolate drops produce a splash detachment which is 2 to 3 times higher than that produced by drops with an oblate shape at impact. As drop production in rainulators or for aggregate stability drop tests may result in more or less uncontrolled variations of drop shape, it is concluded that in addition to other test conditions drop shape should be specified. Moreover it is noted that the erosive capability of prolate drops can explain partly the high splash erosion amounts below vegetation.
Changes in river regime after the construction of upstream reservoirs
Authors: Chien Ning 
Published: February 2007

AbstractThis article presents and analyses many years of investigations in China on the fluvial processes downstream of impounding and detention reservoirs. The study covers the change in hydrograph, the recovering of sediment concentration along the river course, the degradation of stream bed, the adjustment of longitudinal profile, the coarsening of bed material, the change in channel width, and the trend of channel pattern variation for alluvial streams downstream of impounding reservoirs. Without confluence of major tributaries, the degradation may extend to a great distance below the dam. In the process of reducing the sediment carrying capacity of the flow to match the diminished sediment supply, the coarsening of bed material is a factor of equal, if not greater, importance as compared with the flattening of channel gradient. In places where the flow has not been sufficiently cut down and the bank is erosive non‐resistant, a receding of banklines may take place in concurrence with the deepening of the river bed. Below detention reservoirs, even if the total runoff and sediment supply remain essentially unchanged, the modification of the hydrograph is sufficient to enhance the deterioration of the downstream channel.
A palaeovalley system in the floodplain of the Mark River (Central Belgium)
Authors: Huybrechts Willy 
Published: February 2007

AbstractA borehole programme on the floodplain of the River Mark has revealed an important fossilized fluvial system, now invisible in the present landscape. The palaeovalley meanders gently and is up to 200 m wide and 8 m deep. It is eroded in older fluvial sands, probably of Pleniglacial age, overlain by an aeolian cover of varying thickness. As indicated by several radiocarbon dates of the valley fill deposits, the erosion of the system took place in the pre‐Holocene period. The filling proceeded in three phases. The morphological implications of each phase and their spatial extension are demonstrated. Most of the vertical fill consists of a sandy loam to loam. Around 9000 yr BP, the accumulation of an organic facies (mainly woodpeat) started, followed by the deposition of a weak fluvial clay. At 1400 yr BP the filling of the palaeovalley was complete.
Chemical denudation on a magnesian limestone hillslope, field evidence and implications for modelling
Authors: Crabtree R. W. , Trudgill S. T. 
Published: February 2007

AbstractThe pattern of relative denudation at the soil‐bedrock interface over a wooded Magnesian Limestone hillslope was investigated using micro‐weight loss bedrock tablets. The resulting pattern of weight loss after emplacement for one year indicated a consistent upslope increase in solutional denudation. Results from tablets emplaced for two years confirmed this. Dye tracing and gypsum sphere weight loss results showed that water movement over the slope was by vertical percolation and not by throughflow. The pattern of solutional denudation was related to changes in soil type and associated changes in soil pH. Continued slope development by solutional denudation will ultimately lead to slope decline. Comparison with a similar study suggests that a general soil chemistry based model of hillslope solutional denudation can be proposed.
Turbidity and suspended solids variations downstream of a regulating reservoir
Authors: Gilvear D. J. , Petts G. E. 
Published: February 2007

AbstractA controlled reservoir release from Llyn Celyn to the Afon Tryweryn, Wales, U.K., has been used to study suspended load and turbidity variations. Turbidity was monitored continuously at two sites and 235 suspended solids samples were obtained at these and three additional sites during the passage of the release wave. The results are compared with data for a natural tributary flood event. The reservoir release data relate to sediment source depletion and reflects changing sources along the channel. Close to the dam, fine organic matter dominates the seston which scanning electron microscopy revealed to be predominantly allochthonous organic matter, with algal fragments and inorganic diatom frustules, derived from the periphyton of the channel bed. Coulter Counter analysis showed the seston to be relatively coarse with a median particle‐size of 20 μm. Within 3 km of the dam, however, minerogenic particles dominate the sediment load of which more than 90 per cent is finer than 10 μm. This represents the flushing of channel‐bed accumulations derived from tributary sources. The relationships between suspended sediment concentration and turbidity during the release are characterized by a marked, anticlockwise hysteresis. This contrasts with the clockwise hysteresis for the tributary flood event, but the different relationships cannot be explained by particle‐size variations alone; seston composition also appears to be an important control.
Application of photogeological mapping to studies of glacial history of south spitsbergen
Authors: Lindner Leszek , Marks Leszek , Ostaficzuk Stanisław , Pękala Kazimierz , Szczęsny Ryszard 
Published: February 2007

AbstractThe aim of this paper is to describe a study of Quaternary landforms and sediments of selected areas in South Spitsbergen by means of field observations supplemented by photogeological mapping from air photos. The results of these investigations are presented in the form of four geological‐geomorphological maps at a scale of 1:10000. These maps are also analysed in terms of the glacial history of South Spitsbergen.
The effect of road construction on sediment deposition in Loch Earn, Scotland
Authors: Duck Robert W. 
Published: February 2007

AbstractIn 1982 an unmetalled road was constructed in a Scottish Highland glen, Glen Ogle, crossing several left bank tributaries of the Ogle Burn, one of the main influents to Loch Earn. As a result, at least 1824 tonnes of sediment were deposited over an area of 4‐6 ha of loch bed in less than 2 months. This was over 20 times as much material by weight than had passed a temporary gauging station, near the confluence with the loch, during an earlier 12 month monitoring period. The mean thickness of the resultant deposit should, under normal circumstances, have taken some 20 to 25 years to accumulate. Thus, this study provides a quantified illustration of the potential impact of a specific human activity on the acceleration of erosion and deposition rates.
A medium‐term estimate of bedload yield in allt A'Mhuillin, Ben Nevis, Scotland
Authors: Richards Keith , McCaig Mike 
Published: February 2007

AbstractThe 13‐year average bedload yield of Allt a'Mhuillin is estimated from accumulations in boulder traps to be about 261 km−2 yr−1. This represents a minimum estimate of the highest average bedload yields likely to be generated from natural British catchments of the order of 10 km2 in area.
Regional variation of mechanical and chemical denudation, upper Colorado River Basin, U.S.A.
Authors: Schmidt Karl‐Heinz 
Published: February 2007

AbstractThe variation of mechanical and chemical denudation is investigated using discharge and sediment yield data from the Upper Colorado River System. Annual precipitation ranges from approximately 150 mm to 1500 mm. Mean specific yield ranges from 0‐2 1/s km2 ( = 6 mm p a) to 151/s km2 ( = 475 mm p a). The hydrological‐geomorphological system adjusts itself to these varying climatic conditions; in some areas, however, the effects of lithology or land use seem to override the climatic controls. It is demonstrated that the increase in the absolute and particularly the relative amount of suspended sediment is closely related to a decrease in annual runoff and to an increase in the importance of high magnitude/low frequency events. This indicates that in areas of low annual runoff and high runoff variability, soluble rocks are more resistant than in more humid areas. During high magnitude/low frequency events, suspended sediment concentrations and loads are very high in semiarid areas due to sparse vegetation cover and dominance of direct runoff. Events of moderate magnitude and frequency, which in more humid areas transport most of the dissolved load, seldom occur. The trend towards increasing mechanical denudation is even observed in areas of very low runoff (0‐221/s km2 = 7 mm p a). The peak of sediment yield in dry areas seems to approximate the point of no runoff very closely. Mechanical and chemical denudation are of equal importance at a runoff of about 300 mm per year.
The adjustment of the meandering pattern of the lower Jordan River to change in water discharge
Authors: Klein Micha 
Published: February 2007

AbstractThe annual discharge of the Lower Jordan River has decreased from about 1250 × 106 m3 y−1 to about 300 × 106 m3 y−1 due to water exploitation. The decrease in water discharge was not followed by a similar decrease in the suspended sediment. Evidence from air photographs and maps from 1920s to early 1970s show that the river is adjusting itself by shortening its course. The shortening is not distributed uniformly along the valley length. Local effects obscure the effect of decreasing discharge. Since the early 1970s the channel is becoming longer again due to a change in the dominant flow.
World patterns and amounts of detrital soil carbon
Authors: Meentemeyer Vernon , Gardner John , Box Elgene O. 
Published: February 2007

AbstractSoil carbon data were collected from published sources for 50 measurement sites spanning the globe's major climate and vegetation types. For each site, climate, vegetation, and land‐use variables were determined and entered into a multiple curvilinear regression program to predict soil carbon. The best model incorporates an estimate of site disturbance, annual actual evapotranspiration, and annual soil moisture deficit, and yields an R = 0‐803. The curvilinear regression equation was coupled with a large climatic database and computer cartography programs to produce first‐generation maps of estimated soil carbon. These maps correctly portray soil carbon as high in boreal and cool temperate zones and low in deserts and tropical zones.Computer planimetry of maps of soil carbon for an ‘undisturbed’ world and for a ‘disturbed’ world resulted in estimates of 1457 × 109 mtC and 504 × 109 mtC respectively. These estimates compare favourably with recent estimates using other approaches. Clearly, the disturbance factor is critical to future refinements in estimates, suggesting the need for detailed studies of the relationship between land‐use history and the creation and destruction of this important carbon pool.
Climatic control of the assemblages of secondary clay minerals in the A‐horizon of United States soils
Authors: Folkoff Michael E. , Meentemeyer Vernon 
Published: February 2007

AbstractThe concentrations (per cent) of secondary clay minerals (mica, vermiculite, montmorillonite, chlorite and kaolinite) in the A‐horizon of 99 soil sample sites were entered into a cluster program to determine the common clay mineral assemblages found in U.S. soils. Five major assemblages were identified with the most common assemblage consisting of mica, montmorillonite and kaolinite. A suite of climatic variables was determined for each of the 99 sites, including the water balance variables and Arkley's leaching index. A discriminant analysis was then used to predict the occurrence of a clay assemblage from the climate data. Sixty per cent of the sites could be correctly predicted, although not all assemblages could be predicted equally well; two assemblages could be predicted with 88 and 82 per cent accuracy. The precipitation of the wettest month and Arkley's leaching index accounted for most of the predictive power. Thus this study supports theoretical models which suggest that seasonal moisture supply is an important control of clay genesis and persistence. A residuals analysis indicated that many of the palaeosols in the data set and many of the soils from glacial parent materials possessed clay mineral assemblages not expected on the basis of modern climate.