bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative analysis of land surface topography
Authors: Zevenbergen Lyle W. , Thorne Colin R. 
Published: February 2007

AbstractLand surface topography significantly affects the processes of runoff and erosion. A system which determines slope, aspect, and curvature in both the down‐slope and across‐slope directions is developed for an altitude matrix. Also, the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix. A FORTRAN 66 program performs the analysis.
The old alluvium of Singapore and the extinct drainage system to the South China Sea
Authors: Gupta Avijit , Rahman Ausafur , Poh Wong Poh , Pitts John 
Published: February 2007

AbstractIn both sand quarry faces and boreholes the Old Alluvium of Singapore is a matrix supported pebbly sand with minor beds of better sorted sands and clays. The beds can be grouped into four textural classes (pebbles, coarse sand with fine pebbles, medium to coarse sand, clay, and silt), each with characteristic sedimentary structures. The deposit appears to be the proximal facies of an ancient braided river alluvium of possible Pleistocene age.This widespread but scattered alluvium is found both on land and offshore on the Sunda Shelf in Southeast Asia. It is believed to have been deposited during low sea levels. In Singapore, the mineralogy of the grains forming the Old Alluvium suggests a mixed provenance of granitic and low‐grade metamorphic origin. The volume and freshness of the deposited material indicate an environment of considerable relief, seasonal rainfall, and extremely active erosional processes, conditions considerably different from the current ones. The Old Alluvium was probably deposited by seasonal rivers which experienced periodic large floods. Such regional conditions could have prevailed over much of Southeast Asia at the time of deposition of the Old Alluvium.
Modelling gravel‐bed topography from sediment transport
Authors: Naden Pamela 
Published: February 2007

AbstractA simple queueing model which generates bed topography consistent with the mechanics of gravel motion is presented. The equations on which it is based are derived from the application of simple theoretical ideas and an analysis of published flume data (Meland and Norrman, 1966; Francis, 1973; Abbott and Francis, 1977). The simulation produces an extremely variable bed topography in which at least two scales of bedform may be identified. Features of 5–10 grain wavelengths, similar to pebble clusters, are superimposed on other forms whose wavelength is up to 30–40 grains and which resemble step‐pools systems and antidunes. Sediment transport shows many of the characteristics found in the field and the model is, therefore, thought to provide a useful starting point from which to examine the interaction between flow, sediment transport, and bedforms in gravel‐bed and cobble streams.
Raindrop impact and water flow on the vegetative surfaces of trees and the effects on stemflow and throughfall generation
Authors: Herwitz Stanley R. 
Published: February 2007

AbstractThe physical processes of raindrop impact and water flow on the leaves and branches of selected tropical tree species were examined under laboratory conditions using simulated rainfall. Inclined branches were found to be particularly efficient in detaining impacting water droplets. This efficiency in raindrop detention increases linearly as a function of branch inclination on branches that are initially dry. On branches that have been thoroughly wetted, this increase in raindrop detention with branch inclination is best expressed as a logarithmic function. At branch inclinations of 60° above the horizontal, the quantity of branchflow was found to be > 80 per cent of the total quantity of impacting rainfall, indicating that < 20 per cent was lost to rainsplash. The strong positive relationship between branchflow and branch inclination explains why trees with large projected areas of steeply inclined upthrust branches have significant quantities of intercepted water draining from their branches and trunks under heavy rainfall conditions. This drainage from the woody frame of trees influences surficial processes by generating both stemflow and large throughfall droplets.
Morphology and sedimentology of a tributary confluence bar in a regulated river: North Tyne, U.K.
Authors: Petts Geoffrey E. , Thoms Martin C. 
Published: February 2007

AbstractThe form and structure of a tributary confluence bar in a regulated channel are analysed and related to channel adjustment to the imposed flow regime. The bar is characterized by a tripartite structure with two facies, and by marked lateral coarsening, characteristics which relate to the changing hydraulic conditions within the narrowing channel form.
Geomorphic inheritance and the development of tower karst
Authors: Williams Paul W. 
Published: February 2007

AbstractFour genetic types of tower karst are identified, the most typical consisting of residual hills protruding from a planed carbonate surface veneered by alluvium. Two extreme possibilities for tower karst evolution are recognized: a direct development that is independent of any previous morphology and a sequential development that depends explicitly on the morphological characteristics of a previous cockpit karst phase. Examples of both are described, although the latter appears the more common. South China tower karst is examined in this light. Palaeomagnetic analysis of cave deposits in a tower near Guilin indicate the feature to be a time‐transgressive landform. Four principal controls of tower development are discussed and a model of tower evolution is presented.
Effects of glaciations and permafrost upon the development of karst in Canada
Authors: Ford Derek 
Published: February 2007

AbstractCanadian examples suggest that karst landforms may be divided into eight types in terms of their temporal relationships to the record of repeated Quaternary glaciations. Two types are postglacial, two are subglacial, one type occurs where glacial features are adapted to karstic drainage, and three types display sequences of karstic and glacial action. Glacier effects upon karst landforms and their underlying aquifers display the gamut of possibilities. They may destroy, inhibit, preserve, or stimulate karst development. Where continuous permafrost is maintained when covered by glacier ice, postglacial karst is limited to the active layer epikarst. Where permafrost is thawed beneath ice or during deglaciation there are a variety of postglacial karst developments, depending in part upon climate and in part upon local lithologic and relief conditions.
Impact of forest clearance on the soils of tropical cone karst
Authors: Furley Peter A. 
Published: February 2007

AbstractThe precise nature and effects of forest clearance, followed by a two to three year cycle of shifting cultivation and subsequent secondary re‐growth, was observed in an area of lowland evergreen forest over cone karst topography in central Belize. The surface soil properties varied in their response to disturbance but a number of significant changes were measured by comparing the pre‐clearance and post‐cultivation soil analyses. Four groups of soil properties were identified: (1) organic properties which suffered a marked decrease over the summit and upper slope areas and which showed a tendency to increase towards the foot, (2) alkaline status which demonstrated an increase on the upper slopes, (3) nutrient cations whose levels, from more limited evidence, were generally lower after clearance, particularly in the summit and upper slope areas, and (4) soil physical properties, where both the fine fraction and soil depth were drastically affected by clearance; the proportion of clay diminished on the upper slopes and increased at the footslope zone whilst soil depth thinned at the summit and increased markedly over the foreland. The scale of disturbance is so considerable that it has led to recommendations to limit cultivation and clearance pressure in these vulnerable environments.
Overwash occurrence consequent on morphodynamic changes following lagoon outlet closure on a coarse clastic barrier
Authors: Orford J. D. , Carter R. W. G. , Forbes D. L. , Taylor R. B. 
Published: February 2007

AbstractThe reduction in sediment volume of an ebb‐tide delta, as a consequence of lagoon outlet closure on a coarse clastic barrier in southeast Ireland, initiated a sequence of beachface and barrier changes downdrift. Elimination of sediment supply to the ebb‐delta caused a cessation of downdrift longshore swash bar welding, and led to beach volume reductions which in turn allowed a temporal sequence of beach and nearshore morphodynamic domains to develop. These domains then controlled the sedimentation regime of the barrier adjacent to the old outlet. A temporal sequence of (a) dissipative barrier; (b) reflective barrier; and (c) inner reflective (barrier face)/outer dissipative (subtidal) wave regimes match respectively periods of (a) barrier crest build up by crestal dune development; (b) barrier crest instability (barrier width increasing, barrier height decreasing) due to rhythmic overwash; and (c) a return to barrier crest stability with limited aeolian accretion. Two barriers at different stages in this sequence are discussed.
Slope failures in the Ochil Hills, Scotland, November 1984
Authors: Jenkins A. , Ashworth P. J. , Ferguson R. I. , Grieve I. C. , Rowling P. , Stott T. A. 
Published: February 2007

AbstractIntense rainfall in November 1984 caused several slope failures on the steep slopes of the Ochil Hills. Each failure was of soil and till, no more than 2 m thick over bedrock, in a steep bowl. From 30–350 m3 of sediment was removed. Failure seems to have been by shallow sliding triggered by saturation, but each slide became a debris flow, the largest one (Menstrie) filling a house with mud which was at twice the liquid limit two days after the event. The storm which caused the failures had an estimated recurrence interval of 50 years but the frequency of heavy rain is increasing and similar failures occurred nearby the following year.
Stratigraphy, geochemistry, and thermoluminescence ages of lower Mississippi Valley loess
Authors: Pye K. , Johnson R. 
Published: February 2007

AbstractFour periods of loess deposition in the Lower Mississippi Valley can be identified on the basis of geochemical and mineralogical criteria, radiocarbon dating, and thermoluminescence dating. These are designated Loess Units 1,2,3, and 4 in order of increasing age. Carbonate‐rich Unit 1 loess comprises more than 70 per cent of the thickness of the loess profiles. 14C and TL dates indicate this loess was deposited between 9 000 and 20 000 years ago. A maximum sedimentation rate of 2.17 mm yr−1 has been recorded near Vicksburg just after the last Laurentide glacial maximum, between 17 190 and 15 580 years ago. The Unit 2 loess, which is thin and partly decalcified, was deposited slowly between about 25 000 and 20 000 years ago. The Unit 3 and Unit 4 loess formations, which are both highly weathered, have yielded TL ages of 76 000–85 000 years and 119 000‐ > 132 000 years, suggesting they were deposited during the Altonian Substage of the early Wisconsinan and the Illinoian glacial stage respectively. The four loess units are stratigraphically equivalent to the Peoria, Farmdale, Roxana, and Loveland loess formations previously recognized in Illinois. The source of dust in both areas was glacial outwash in the Mississippi Valley. During interglacials and interstadials, when the supply of glacial debris was reduced and the Mississippi River changed from a braided to a meandering regime, dust sedimentation in southern Mississippi virtually ceased, allowing weathering and pedogenesis to proceed.
Niveo‐aeolian deposits and denivation forms, with special reference to the great Kobuk Sand Dunes, Northwestern Alaska
Authors: Koster Eduard A. , Dijkmans Jos W. A. 
Published: February 2007

AbstractThe geomorphology, lithology and chronostratigraphy of extensive, late Pleistocene inland and river dune sands, aeolian sand sheets (‘cover sands’) and loess deposits of periglacial origin in northwestern Europe are well known. However, the idea that some of these aeolian sediments result from niveo‐aeolian processes is still an open question, as no diagnostic sedimentary features have yet been reported. Moreover, actual niveo‐aeolian sediments and related denivation forms, reported from various cold‐climate regions, are not suitable analogues. Recent observations in active dune fields in northwestern Alaska indicate that interstratification of wind‐driven snow and sand preferentially occurs on slip faces of transverse, barchanoid or parabolic dune ridges. Annual denivation forms develop: e.g. snow ramparts, sinkholes, snow hummocks, snow meltwater fans and tensional cracks. The surface consists of a cracked wet sand layer with a dimpled surface and spongy structure. Although the preservation potential of these features is low in this specific case, similar features may be observed in ancient sediments elsewhere and provide useful palaeoclimatic indicators. The niveo‐aeolian concept should therefore not specifically be related to late Pleistocene cover sand deposition in northwestern Europe, as previously assumed.
Channel change, fluvial geomorphology and river engineering: The case of the Afon Trannon, Mid‐Wales
Authors: Leeks G. J. , Lewin J. , Newson M. D. 
Published: February 2007

AbstractThe Afon Trannon, a gravel‐bed river in mid‐Wales with a catchment area of 72 km2, has recently been the subject of an engineering flood protection scheme. Following the enlargement and grading of the channel, lateral instability has produced considerable problems of maintenance. Geomorphological investigations are described which attempt to pinpoint the lessons of the scheme. Historical studies of floodplain sediments and channel change indicate firstly, an initially rather stable channel, but secondly a considerable, early history of channelization which may still have repercussions for system stability. This early channelization has now been modified in the recent scheme. Contemporary field study by survey and sediment tracing using the magnetic technique indicates the present instability of the sediments in a meandering channel given a trapezoidal cross‐section and varied banks. Low‐flow adjustments are as important as flood adjustments in the lower, straightened reach. Lessons for engineering schemes include the desirability of assessing erosion risk by rapid, cheap field techniques and historical investigations, and the consideration of more ecologically acceptable channel designs.
A hydrogeochemical model for stream chemistry, Cascade range, Washington, U.S.A.
Authors: Dethier David P. 
Published: February 2007

AbstractA simple mixing model demonstrates that chemical variations in Cascade surface waters reflect flow from three general zones: alpine areas, forested colluvial slopes, and seasonally saturated areas. The chemistry of weathering solutions in alpine portions of the Williamson Creek catchment (North Cascade Range) results from alteration of plagioclase, hornblende, and biotite to kaolinitic material and vermiculite. Surface and shallow groundwater in forested portions of the catchment reflect these reactions, dissolution of small quantities of carbonate, and biologic activity. Both at‐a‐point and downstream chemical variations are explained quantitatively by the volume of water that originates in each of the hydrogeochemical source areas. Water from the forested colluvial slopes is most significant on an annual basis. However, summer low‐flow is a mixture of colluvial waters and dilute solutions from the alpine zone, whereas 10 to 30 per cent of peak flow in snowmelt and rainstorms is produced from seasonally saturated areas. Poor concentration/discharge (C/Q) correlations, typical of Cascade rivers, result from mixing of significant C/Q relations for water leaving each source area. Model predictions could be substantially improved by better data for the effects of temperature, water‐contact time, and biologic cycling on the chemistry of soil water from forested zones.
The concept of dominant discharge applied to two gravel‐bed streams in relation to channel stability thresholds
Authors: Carling Paul 
Published: February 2007

AbstractDominant discharge may be defined as that discharge which transports most bed sediment in a stream that is close to steady‐state conditions. The concept is examined in relation to two single thread gravel‐bedded streams. One stream is alluvial and free to adjust its geometry whilst in the other, channel capacity and form are partially constrained by cohesive till‐banks and a heavily compacted bed.The total quantity of bedload and its calibre were measured for every flood over a six year period, so that the relationship between the grain‐size of bedload and the most effective discharge could be examined in the context of thresholds for channel change.The dominant discharge concept was applicable to the alluvial stream in that the bankfull value is an effective discharge for maintaining channel capacity. The concept applied less well to the ‘non‐alluvial’ stream. Although in both streams the bankfull value was exceeded for less than 0.34 per cent of the time, overbank flows are important in instigating channel change. It is only during overbank flows that the largest bed material is entrained in quantity. For within‐channel flows a threshold separates flows which winnow fine matrix from those which entrain the finer bed gravels. This threshold occurred at 60 per cent bankfull.It was concluded that the dominant discharge concept can be applied to streams close to steady‐state which are alluvial, competent, and free to adjust their boundaries. An important proviso is that two channel‐stability domains can be recognized. These domains represent channel maintenance and channel adjustment and are defined by intrinsic thresholds in the bed material entrainment function.
Using geostatistics and spectral analysis to study spatial patterns in the topography of southeastern Washington State, U.S.A.
Authors: Mulla David J. 
Published: February 2007

AbstractTopography for four areas in the Palouse region of southeastern Washington State having different patterns and encompassing areas of about 900 ha each were quantitatively compared and described using two‐dimensional semi‐variograms and periodograms. The four areas studied were from the Garfield, La Crosse, Thornton, and Wilcox quadrangle topographic maps.Semivariance of elevation residuals were modelled using a combination of spherical, periodic, or linear semivariogram models. The range of the spherical component was interpreted as a relatively short‐range scale of correlation which was not periodic. For each of the study areas a model was developed to describe the variation in range with orientation. Values for the range from this model reached maximum values of from about 700 m to 800 m at an orientation of from 35° to 55° (approximately northeast) in each study area. This orientation was interpreted as the dominant direction of non‐periodic small‐scale landscape features. The wavelength and amplitude of the periodic semivariogram component, which were highly correlated, were interpreted in terms of parallel northeast‐trending ridges having relatively long scales of periodic correlation varying in size from about 1350 m to 2100 m. This attempt to identify the dominant orientation of periodic landscape features using models for the wavelength and amplitude was, however, not completely definitive.Two‐dimensional spectral analysis provided significantly more detail concerning orientation and wavelengths of the periodic topographic patterns than the semivariogram analysis. In the Garfield study area, spectral analysis identified north‐trending ridge systems separated by a wavelength of 1494 m and northeast‐trending systems with a wavelength of 747 m. In the La Crosse study area, both north and northeast‐trending patterns were identified having periodic spacings of 980 and 735 m. North‐trending ridges separated by wavelengths of 996 m and northeast‐trending ridges separated by wavelengths of 747 or 996 m were the predominant periodic features of topography in the Thornton study area. In the Wilcox study area, northeast‐trending ridge systems separated by wavelengths of 373, 498, or 996 m were detected.A comparison of the results from geostatistical and spectral analysis of these complex topographic surfaces shows that each approach had significant strengths and weaknesses. Two‐dimensional analysis with semivariograms was the only method which could be used for identifying the correlation scale and orientation of relatively small non‐periodic landscape features. Two‐dimensional spectral analysis accurately identified the predominant orientation of relatively large periodic features in topography, whereas semivariogram analysis was somewhat inconclusive. Also, semivariograms were generally unable to detect the presence of multiple or harmonic periodicities operating at different wavelengths along a given orientation.
Analysis of linear dune sediment‐form relationships in the Kalahari dune desert
Authors: Thomas David S. G. 
Published: February 2007

AbstractWilson's (1972a, b) hypothesis of grain size control of dune spacing is tested using data from linear dunes in the Kalahari dune desert. The results confirm Wasson and Hyde's (1983b) rejection of the universal applicability of the theory, though this does not discount relevance to other dune types. Factors pertaining to the rejection of the grain size theory in the Kalahari are considered. Results also demonstrated that the height and spacing of linear dunes are related, but only when values are grouped for blocks of dunes. The gradient of the h/S relationship differs between dunefields, possibly because sand supply differences have an effect upon dune geometry.
Buttresses of tropical rainforest trees influence hillslope processes
Authors: Herwitz Stanley R. 
Published: February 2007

AbstractDuring heavy rainfall events, the buttresses of tropical rainforest trees limit the occurrence of stemflow‐generated overland flow and soil erosion on hillslopes. Buttresses promote infiltration by causing stemflow to diverge into separate flow paths on the trunk and by increasing the stemflow contact area at the ground surface. Buttresses oriented normal to hillslopes function as barriers that further promote infiltration and limit the downslope transport of sediments and chemically‐enriched stemflow water. These relationships between buttressing, stemflow, and hillslope processes have not been previously noted in the literature. Buttresses are generally regarded as mechanically efficient support structures that increase the resistance of trees to windthrow and uprooting; however, this also has an inhibiting effect on hillslope processes because the mounds of bare soil uprooted by tree falls are particularly vulnerable to rainsplash erosion.