bluuebunny/crossref_metadata_2025 huggingface dataset:
Eolian deposition determined by the oxygen plasma furnace
Authors: Jones P. S. A.
Published: February 2007

The oxygen plasma furnace enables small samples of clastic sediment to be separated from filter papers at low temperatures without physical or chemical alteration of the sediment. This technique provides a suitable treatment for processing very small samples of alpine eolian sediment, enabling their grain size distribution, mineralogy, and origin to be determined.
Drop shape and erosivity part I: Experimental set up, theory, and measurements of drop shape
Authors: Epema Gerrit F. , Riezebos Hans Th.
Published: February 2007

Simulated raindrops falling in still air have a shape that is mainly determined by surface tension and hydrostatic pressure. Drops released from capillary tips show an initial shape variation ranging from prolate to oblate but eventually this oscillation is damped. At terminal velocity drops have attained equilibrium and have an oblate shape. Measurements of the shape of simulated rain drops produced by capillary tubes were made using a simple, newly‐developed photographic set up. The measurements showed that models describing the oscillation frequency and amplitude of drops falling at terminal velocity can also be applied to the simulated drops. A comparison is made between the shape of raindrops in natural storms and simulated drops. Recommendations are given regarding fall heights in simulation in relation to the drop shape in nature.
The stratigraphy of flandrian relative sea‐level changes at a site in tayside, Scotland
Authors: Smith D. E. , Dawson A. G. , Culungford R. A. , Harkness D. D.
Published: February 2007

Peat deposits in a gully at the inland margin of the Firth of Tay carselands contain a transgressive wedge of estuarine sediments laid down at the culmination of the Main Postglacial Transgression. In previous work, the sequence of deposits in the gully and their age have been examined at one location. The present study both extends and evaluates that previous work, employing further field work and laboratory analyses. The detailed stratigraphy of the deposits is identified, whilst from a borehole close to the limit of the transgressive deposit, diatom analysis and geochemical analyses, involving the determination of Al, Mg, C, and δ 13CPDB are outlined. Eight 14C assays from peat at the transgressive and regressive contacts in four boreholes along the wedge of estuarine sediments are described. Whilst the results of diatom analysis are inconclusive, the geochemical analyses indicate that the sediment accumulated broadly continuously without major changes in the depositional environment. It is concluded that the Main Postglacial Transgression in the gully was at first rapid, then slowed and culminated between 6240 ± 80 and 6030 ± 80 (or 6170 ± 90) radiocarbon years, B.P. It is subsequently maintained that the geochemical analyses described here may be of value in determining the continuity of transgressive deposits, whilst the practice of obtaining multiple radiocarbon assays at such locations should enable assessment of age to be refined. This may in turn assist in testing the hypothesis of shoreline diachroneity in glacioisostatically affected areas.
210Pb dating of scottish lake sediments, afforestation and accelerated soil erosion
Authors: Battarbee Richard W. , Appleby Peter G. , Odell Kevin , Flower Roger J.
Published: February 2007

Changes in the rate of soil erosion in lake catchments can be identified from changes in the rate of sediment accumulation in lakes. Here we compare recently afforested sites with non‐afforested sites in the Galloway area of Southwest Scotland. We show that lakes with non‐afforested catchments have slow, constant sediment accumulation rates, whereas lakes with recently afforested catchments have changes in accumulation that parallel the known history of afforestation. For Loch Grannoch the sediment accumulation rate increases from 0.1 cm yr−1 to over 2 cm yr−2 during the disturbance period. Data from L. Skerrow, however, suggest that the rate might decline to predisturbance levels after approximately 10 years as the forest canopy closes and drainage channels stabilize.
Human influence upon sedimentation in Llangorse Lake, Wales
Authors: Jones R , Benson‐Evans K. , Chambers F. M.
Published: February 2007

Palaeolimnological studies at Llangorse Lake, Wales, constitute part of the British contribution to IGCP Project 158 (The Palaeohydrology of the Temperate Zone in the Last 15000 Years). The lake has been adopted as the Reference Site for the South Wales region under Subproject 158B (Lake and Mire Environments) and is located in the Reference Area for Britain: the Severn Basin.

Results of biological, physical, and multielement chemical analyses on a 12.35 m Livingstone core are presented and compared with previous analyses on short Mackereth cores taken from two troughs in the lake basin. Human impact upon post‐glacial sedimentation is assessed with reference to sediment chemistry, physical properties, and sedimentation rates, based on relative pollen,14C, and210Pb dating. Vegetational history of the catchment is inferred from a pollen diagram for a section of the core fromc. 8 to 6.75 m depth in which evidence for human impact is first apparent. Water content, loss on ignition, and carbonate content are presented for the whole core; density, water content, loss on ignition, carbonates, and elemental analyses of P, Ca, Mg, K, Ti, Al, Fe, and Mn for the interval 6 75 and 8.25 m depth.

Sedimentation rates were low during Boreal and Atlantic times (c. 9000‐ 5000 BP), rose significantly from the time of the elm decline (estimated at 5000 BP) and increased further atc. 1800 BP when nekron muds were succeeded by deposition of silty clay. Inferred rates of erosion of soils from the catchment are discussed and related to sediment chemistry.
An improved method of aggregate stability measurement
Authors: Farres P. J. , Cousen S. M.
Published: February 2007

The stability of individual soil aggregates to impacting water drops is now regarded as a fundamental parameter required in any soil erodibility assessment. This stability has been measured by the use of single drop rainfall simulators, the characteristics and operation of which have, in the past, shown considerable variation. The drop sizes, impact frequency, drop fall height, chemistry of drop‐forming liquid, aggregate pretreatment, and definition of breakdown affect the way in which the apparatus can be used to define stability. Within this paper each one of these characteristics is considered and a piece of apparatus proposed which is believed to give results with increased consistency and replicability. The described apparatus can be readily reproduced in any laboratory situation, and has the added advantage of being not only appropriate for the measurement of indices of stability, but also of providing an environment in which the mechanisms of aggregate breakdown can be investigated.
Detrended correspondence analysis of heathland vegetation: The identification of runoff contributing areas
Authors: Gurnell A. M. , Gregory K. J. , Holus S. , Hill C. T.
Published: February 2007

Detrended correspondence analysis is applied to information on vegetation composition for the heathland zone of a New Forest catchment. A map of runoff contributing areas is constructed from a soil moisture related gradient in the vegetation data and the resulting map compares favourably with other information on runoff contributing areas in a subcatchment.
Spatial variability and variations in bedload transport direction in a subtidal channel as indicated by sonographs
Authors: Goedheer G. J. , Misdorp R.
Published: February 2007

Three sonographs of a part of a subtidal channel, located in the Oosterschelde, are described and interpreted. The sonographs are used to determine the asymmetry of the bedforms. Current profiles and directions are used to explain differences in dimensions and characteristics of the bedforms. The relations between current velocity parameters and bedform characteristics in intertidal zones do not apply to subtidal forms. The division in the depth‐velocity diagrams between the types of 2d and 3d bedforms of Dalrymple et al. (1978) is not valid.
Sediment variability and bed material sampling in gravel‐bed rivers
Authors: Mosley M. P. , Tindale D. S.
Published: February 2007

In a 350 m wide reach of the braided, gravel‐bed Ashley River, the surface layer of the bed material was sampled in 141 areas of homogeneous graded sediment along seven cross‐sections, and 30 kg bulk samples were collected at 86 randomly selected locations along the cross‐sections. At one location, a single 854 kg sample composed of 28 subsamples was also collected.

Analysis of the single large sample indicate that accurate determination of mean grain size D at that site requires, desirably, a sample of ∼ 100 kg, but that samples in which the weight of the largest stone is less than 5 per cent of the total weight have unbiased estimates of D. Spatial variability of bulk material is such that 228 and 50 samples are needed to estimate D to ± 10 and ± 20 per cent respectively of the true value; requirements for estimating inclusive graphic standard duration are only 11 and 3 respectively.

The grain‐size distribution of the surface layer is only weakly related to the bulk material beneath. The results of ‘Wolman sampling’ along 12 cross‐sections at two pace intervals (average 120 stones per cross‐section) indicate that estimation of overall surface D to ±10 and ±20 per cent would require sampling along 64 and 14 cross‐sections respectively.

It is concluded that accurate characterization of bed sediment in gravel‐bed rivers is very demanding of labour and resources, and that careful planning is needed to ensure efficiency and meaningful results.
Estimation of soil loss at a regional scale based on plot measurements—some critical considerations
Authors: Roels J. M.
Published: February 2007

The paper is prompted by apparent deficiencies in the design of plot studies in regional erosion surveys. The principal shortcomings of observational erosion research have been poor sampling design and inadequate analyses of data. The paper identifies various sources of bias which must be taken into account before plot data can be extrapolated to land units in a regional survey. Judging from soil loss data of a case‐study in the Ardèche rangelands one may conclude that even accurate plot measurements can still be rather a rough basis for regional erosion assessment. Finally, the paper highlights strategies that might be used to improve erosion sampling.
The downstream gradation of particle sizes in the Squamish river, British Columbia
Authors: Brierley Gary J. , Hickin Edward J
Published: February 2007

The exponential downstream decline in particle size predicted by Sternberg (1875) is examined within a highly active alpine fluvial environment, the gravel‐bed Squamish River in southwestern British Columbia. Transect survey procedures for sampling within the coarse alluvial gravels are described in detail. Downstream trends for various particle size statistics, plotted with distance from a major sediment source, are considered according to two scenarios. Evaluation of overall trends indicates that the downstream expression derived by Sternberg (1875) is not the most appropriate; rather, curves are better described by power functions. This reflects a very rapid decline in particle size immediately downstream of the major sediment source. Secondly, evaluation of downstream trends in relation to channel planform determines that exponential functions with different coefficients describe adequately relations within individual planform reaches. There is insufficient evidence to suggest which of these two scenarios may be appropriate. Several lines of evidence suggest that the trends found are more the result of selective sediment transport phenomena than of abrasion, a condition attributed to channel competence within a system dominated by sediment‐supply conditions.
A study of dells in the new forest, Hampshire, England
Authors: Tuckfield Cyril G.
Published: February 2007

Dells in the New Forest are described as amphitheatre‐shaped hollows, perched on valley sides, sometimes singly, in other places in groups tributary to small dry valleys. They have steep rear walls and sides, flatfish floors, and convex lips, usually without any water‐worn channels. The slopes on which they occur, cut in Eocene sands and clays, have been subjected to solifluction, and this has produced wide gently sloping terraces at the foot of the hillside. Superficial deposits within the New Forest dells are divided into two groups by process: a lower head of fragmented flints in a sandy or clayey matrix, assigned to Zone III; overlying colluvial deposits including slumped material and slope wash, dated by reference to a buried soil to Zone VIIa. Although scoured by solifluction, other processes probably account for the initial formation of the hollows, and nivation is suggested. The dells are compared with the chalk coombes of southern England and the dellen of European and other writers. A possible chronology is suggested for the New Forest dells.
Arsenic in the Yellow river, China
Authors: Runhua Huang
Published: February 2007

Data collected since 1973 show high levels of arsenic in the Yellow River, very largely from natural sources. Average and peak concentrations, and the downstream distribution of the arsenic suggest the most likely source as the loess which provides 90 per cent of the river's suspended load. Arsenic is strongly absorbed by the silt and clay in the river: some of it is deposited in reservoirs and delta sediments but most is carried out to sea.
Timing the transport of water through the upper vadose zone in a Karstic system above a cave in Israel
Authors: Even H. , Carmi I. , Magaritz M. , Gerson R.
Published: February 2007

Chemical and isotopic analysis of karst water dripping over a one year period from seeps in a cave above the Cenomanian aquifer in the Judea hills of Israel lead to several conclusions: (i) The tritium ages and the chemical composition of water from different seeps in a karstic cave vary greatly, (ii) The reservoirs in the upper part of the vadose zone hold water for up to several decades, (iii) Some of the cave seeps are mixtures of the old and more recent meteoric water from paths of different length, (iv) The history of storm events can only be traced in some of the seeps, (v) For most dripping seeps there is no immediate response of seepage discharge to the rainfall intensity and quantity—i.e. the seepage discharge is fairly constant.
Peat slides in Teesdale and Weardale, northern pennines, july 1983: Description and failure mechanisms
Authors: Carling P. A.
Published: February 2007

Peat landslides that occurred in Upper Teesdale and Weardale in 1983 are described. The slides occurred after thunderstorm rainfall of a very rare intensity and return period. The slope geomorphological features and the vegetation associated with the slide areas are detailed.

Baseline geotechnical data are used in a simple retrospective stability analysis, treating the peat slides as shallow translational slips. The analysis demonstrates the probable important role played by open moor drains, natural soil pipes, and prior cracking of the peat (owing to dessication or slow mass movement) in the rapid transfer of water to the failure zone within an impervious sensitive clay beneath the peat.

The frequency of peat landslides and the visual persistence of sites is considered briefly in relation to substratum and peat stability within a context of climatic change. It is suggested that there may be a gradation of type from the classic Irish bog‐burst, through failures of intermediate character, to peat slips involving rigid peat blocks. Antecedent conditions and the mechanism of failure need not be similar for mass movements at either end of this spectrum.
A re‐examination of the evidence for a Plio‐Pleistocene marine transgression on the Chiltern Hills. III. deposits
Authors: Moffat A. J. , Catt J. A.
Published: February 2007

A petrological re‐examination of the deposits that Wooldridge and Linton used as evidence for a Plio‐Pleistocene marine transgression on the Chiltern Hills indicates that many are fluvial and some have been reworked in a periglacial climate. However, those from Little Heath and Rothamsted, Hertfordshire and Lane End, Buckinghamshire are confirmed as marine and Plio‐Pleistocene. Subsidence during the Pleistocene is suggested by the northeasterly decline in height of the few truly marine deposits.
The occurrence on carboniferous coal of anthropogenic origin in the contemporaneous Vistula river sediments near Cracow (Southern Poland)
Authors: Rutkowski J.
Published: February 2007

Carboniferous pit coal is the most important anthropogenic component of the contemporaneous Vistula river gravels and sands with individual fractions containing from 10 to 98 per cent coal fragments. Coal concentration is connected with differences in the bulk density between coal and other gravel components. The lower sediments date from the first half of the nineteenth century when the coal began to appear in large quantities in the Vistula channel. The presence of coal is also an indicator of the depth of channel sediment reworking during floods in the nineteenth and twentieth centuries.
A physically‐based model of the dispersion of splash droplets ejected from a water drop impact
Authors: Wright Andrew C
Published: February 2007

A model has been developed which predicts the dispersion of splash droplets produced by the impact of a water drop on a sloping soil surface.

Experimental results of the ejection velocities and ejection angles of the splash droplets are generalized to a planar slope and the resulting splash distances are calculated taking into account the effects of air resistance. The predictions are presented in terms of the numbers of splash droplets from the impact point to surrounding squares arranged in a grid on the slope.

The model explains many experimentally observed features of raindrop splash in terms of the mechanics of the processes involved and can make predictions of the effects of slope, wind, raindrop size, and soil properties on droplet dispersion. The component of the raindrop velocity parallel to the surface of the slope is identified as the main factor determining the degree and the direction of the asymmetry in the splash droplet dispersion.

By combining the model with a theory of the entrapment of soil in the splash droplets it is possible to extend it to predict the dispersion of soil particles by raindrop impact, which is the basis of a model of soil erosion by rainsplash.
14C dating and palaeoenvironment of the historic ‘little ice age’ glacier advance of Nigardsbreen Southwest Norway
Authors: Matthews John A. , Innes John L. , Caseldine Christopher J.
Published: February 2007

Moss and grass remains associated with a well‐developed in situ palaeosol buried beneath a moraine ridge in front of Nigardsbreen (Jostedalsbreen ice cap, southern Norway) have been 14C‐dated. Pollen preserved with the plant remains suggests the existence of an agricultural landscape prior to the deposition of the moraine. The calibrated dates and the pollen spectra are in close accord with historically‐documented evidence for the timing and palaeoenvironment of the ‘Little Ice Age’ advance of the glacier. Considerable potential is indicated for estimating the maximum ages of moraine ridges and for palaeoenvironmental reconstruction where such documentary evidence does not exist.
Infiltration‐excess caused by Stemflow in a cyclone‐prone tropical rainforest
Authors: Herwitz Stanley R.
Published: February 2007

Tropical rainforest canopy trees that have large projected areas of upwardly inclined branches are capable of funnelling large volumes of rainwater down their trunks. During periods of prolonged heavy rainfall on Mount Bellenden Ker in northeast Queensland, Australia, stemflow volumes were found to be as much as two orders of magnitude greater than the volume of incident rainfall expected in a rain gauge occupying an area equal to the trunk basal area. Stemflow totals ranging from 6000 to 70000 litres were generated by individual trees from 7800 mm of rainfall over two successive wet seasons.

The combination of high intensity rainfall and the funnelling effect results in significant quantities of infiltration‐excess at the ground surface. Stemflow fluxes as high as 31.4 cm3 min−1 per cm2 of basal area (i.e. the equivalent of 314 mm min−1) were recorded when rainfall intensity was only 2 mm min−1. The mean infiltration capacity of the topsoil was determined to be 6.2 mm min−1. The areas over which the stemflow would have had to spread in order to infiltrate were computed to be as much as 3 m2 around the bases of individual canopy trees. Approximations of the distances that the infiltration‐excess would have travelled away from the tree bases were calculated by assuming that the infiltration area either expands radially outward in the form of an annulus or extends straight downslope from the tree base.
Determination of dissolved organic matter in streamwater using visible spectrophotometry: A comment
Authors: Finlayson Brian
Published: February 2007

A discussion querying the need (Grieve, 1985) for further studies on the use of the technique, which is already well established. The use of chemical oxygen demand is also questioned.
Contemporary and palaeo channel patterns and the late quaternary stratigraphy of Cooper Creek, Southwest Queensland, Australia
Authors: Rust Brian R. , Nanson Gerald C.
Published: February 2007

Braided and anastomosing channels make up two major coexistent networks in the mud‐dominated fluvial system of Cooper Creek, Southwest Queensland. The floodplain is characterized by a system of mud braids operative when floods inundate the whole alluvial surface. Anastomosing channels are inset deeper into the floodplain, operate at modern flows, and transport a traction load of sand.

Shallow stratigraphic data show that an underlying sand sheet is unrelated to surface channel patterns and was formed by a system of meandering streams. According to preliminary dates based on thermoluminescence, the change from a sand‐ to mud‐dominated fluvial regime took place between 50 000 and 200 000 years B.P., and probably reflects increasing aridity.
A quantitative soil‐stratigraphic approach to the correlation and dating of post‐glacial river terraces in Glen Feshie, western Cairngorms
Authors: Robertson‐Rintoul M. S. E.
Published: February 2007

Little is known about Holocene river terrace development in upland Scottish valleys. Interpretation of many of the terrace sequences, previously suggested to have been formed by meltwaters either from the last Scottish ice sheet or the Loch Lomond Advance, has generally been based on morphological data. In this paper an alternative approach to the traditional height‐based method of terrace correlation and dating is presented using data from Glen Feshie, western Cairngorms. Terrace fragments are numerically classified and objectively grouped using quantitative soil‐stratigraphic data. Principal Components Analysis is used to both quantify pedological data and separate temporal trends in the data from variance due to local site factors. The scores on the temporal component are used to derive soil‐stratigraphic units developed on the surficial sediments of the Glen Feshie terraces by grouping soil sites using a hierarchical clustering technique. This provides evidence for at least five soil‐stratigraphic units developed on the fluvial surfaces. Various methods of absolute dating control permits association of these surfaces with five phases of terrace development. These are placed tentatively at 13 000, 10 000, 3600, 1000, and 80 radiocarbon years B.P., suggesting at least three phases of valley floor incision in Glen Feshie during the late Holocene.
Quantitative analysis of land surface topography
Authors: Zevenbergen Lyle W. , Thorne Colin R.
Published: February 2007

Land 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

In 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

A 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

The 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

The 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

Four 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

Canadian 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

The 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

The 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

Intense 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

Four 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

The 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

The 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

A 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

Dominant 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

Topography 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

Wilson'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

During 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.
Velocity profiles measured on the windward slope of a transverse dune
Authors: Mulligan Kevin R.
Published: February 2007

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