bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stability of composite river banks
Authors: Thorne Colin R. , Tovey N. Keith 
Published: February 2007

AbstractThe stability of a river bank depends on the balance of forces, motive and resistive, associated with the most critical mechanism of failure. Many mechanisms are possible and the likelihood of failure occurring by any particular one depends on the size, geometry and structure of the bank, the engineering properties of the bank material, the hydraulics of flow in the adjacent channel and climatic conditions.Rivers flowing through alluvial deposits often have a composite structure of cohesionless sand and gravel overlain by cohesive silt/clay. Bank erosion occurs by fluvial entrainment of material from the lower, cohesionless bank at a much higher rate than material from the upper, cohesive bank. This leads to undermining that produces cantilevers of cohesive material. Upper bank retreat takes place predominantly by the failure of these cantilevers. Three mechanisms of failure have been identified: shear, beam and tensile failure.The stability of a cantilever may be analysed using static equilibrium and beam theory, and dimensionless charts for cantilever stability constructed. Application of the charts requires only a few simple measurements of cantilever geometry and soil properties. In this analysis the effects of cracks and fissures in the soil must be taken into account. These cracks seriously weaken the soil and can invalidate a stability analysis by affecting the shape of the failure surface.Following mechanical failure, blocks of soil must be removed from the basal area by fluvial entrainment if rapid undermining and cantilever generation are to continue. Hence, the rate of bank retreat is fluvially controlled, even though the mechanism of failure of the upper bank is not directly fluvial in nature.This cycle of bank erosion: undermining, cantilever failure and fluvial scour of the toe, operates over several flood events and has important implications for river engineering, channel changes, and the movement of sediment through fluvial systems.
Asymmetry of river channel cross‐sections: Part I. Quantitative indices
Authors: Knighton A. D. 
Published: February 2007

AbstractMost river cross‐sections display some degree of asymmetry for which there is no adequate quantitative definition. Indices of asymmetry are derived using two principles based on areal differences and maximum depth displacement relative to the channel centreline. The indices are assessed firstly by comparing values for a set of constructed channel shapes which are ranked in order of increasing visual asymmetry, and secondly by analysing a series of 50 cross‐sections from a small mountain stream. Two indices, A* and A2, are probably the most valuable, and could be used to test and generate hypotheses regarding the related changes to cross‐sectional and planimetric form which occur during the transition from a straight to a meandering channel, particularly if parallel measures of flow asymmetry are defined.Part II of this paper, concerned with ‘Mode of Development and Local Variation’ will be published in a subsequent issue of this journal.
Drainage area and the variation of channel geometry downstream
Authors: Klein Micha 
Published: February 2007

AbstractRecent geomorphological studies tend to deal with small basins. The understanding of small basin dynamics provides important information for the understanding of large basin dynamics assuming that the extrapolation of small basin data to larger basins is valid. This work tests the validity of this extrapolation of data with reference to channel geometry.An analysis of the variation of channel width downstream reveals that the value b =0.5 (W = aQb) is a ‘good’ average. However, the use of a one‐line model consisting of a simple power function incurs a loss of a considerable amount of relevant information concerning the channel form and hence the channel processes. It has been shown that the –b– value for small basins and very big basins is lower than the one for the intermediate basins.
Prediction of limestone solution rates from rainfall and runoff data: Some comments
Authors: Gunn John 
Published: February 2007

AbstractRecent work by Láng (1977) on solutional erosion rates in limestone drainage basins in relation to rainfall contains serious errors and has a questionable logical basis. Although much sounder, Smith and Atkinson's (1976) work on erosion rates in relation to runoff also requires modification as it greatly overestimates erosion rates in two areas of New Zealand. Greater resolution could probably be obtained by relating autogenic runoff to the rate of solution by autogenic waters and by computing separate relationships for areas where solution takes place under open and closed system equilibrium conditions. These factors should be taken into account in the experimental design of future studies.
Observations in a cavity beneath grinnell glacier
Authors: Anderson R. S. , Hallet B. , Walder J. , Aubry B. F. 
Published: February 2007

AbstractDuring a 3‐year period, several aspects of the glacier‐rock interface were studied in a cavity beneath 5–8 m of ice near the terminus of Grinnell Glacier, Montana, U.S.A. Continuous week‐long records of the summer sliding rate revealed a very uniform speed of about 12 m a−1 during the summer, a value about 20 per cent higher than the average annual sliding rate. Several decimetre‐sized rock fragments were broken from the glacier bed near the lee sides of bedrock ledges and transported down‐glacier. In the course of a two‐week long experiment, the glacier abraded its bed significantly and non‐uniformly. It is of interest that significant quarrying and abrasion occurred under thin ice with relatively little entrained debris.
Slope profile variability in first‐order drainage basins
Authors: Parsons A. J. 
Published: February 2007

AbstractIf the three‐dimensional form of a hillslope is regarded as an infinite population of two‐dimensional slope profiles, values for attributes of the form of the hillslope can be determined by sampling and estimating the means of the attributes of the population of slope profiles. Twelve attributes are examined in seven first‐order drainage basins located on the South Downs in East Sussex to determine necessary sample sizes. Results show that if spatial randomness is assumed the size of sample required varies considerably from one attribute to another but is commonly very large. Of four alternatives to spatial randomness that are tested, consideration of both hillslope plan form and valley asymmetry are shown not to lead to reduction in sample size. However, results do suggest that maximum slope, percentage of profile length in the range 5° to < 10°, and mean angular difference between adjacent slope segments may all be dependent upon distance of the slope profile down valley. Furthermore, initial tests of the effect of spatial autocorrelation suggest that for some attributes consideration needs to be given to this factor when determining sampling strategies.
Sediment yields from a laboratory catchment and their relationship to rilling and surface armouring
Authors: Rowntree K. M. 
Published: February 2007

AbstractThe development and testing of sediment simulation models require continuous monitoring of erosion processes and sediment yields from catchment areas at a wide range of scales. A series of experiments are described in which runoff and sediment yields from a small laboratory catchment were monitored through six consecutive storms applied to each of three soil types. Slope microtopography and the surface particle‐size distribution were surveyed between storms. Pronounced peaks in sediment concentration at the start of each storm were not observed for these conditions, but significant variation in yield through a series of storms was shown to result from the interaction of rilling and armouring processes as the source of sediment shifted from the rills to interrill areas. In view of the experimental findings the validity of experiments reporting average or ‘stable’ erosion rates is questioned. The need for dynamic models capable of simulating rill development and changes in sediment availability is emphasized.
Circular meander pools
Authors: Alford John J. , Baumann Robert H. , Lewis Anthony J. 
Published: February 2007

AbstractAerial photographs led to the detection of a previously undescribed type of river meander. These features are characterized by nearly circular pools located at the apex of the bend and are widely distributed on small to medium sized coastal plain streams in the southeastern United States. Bathymetric evidence shows that the structure of meanders containing circular pools is distinctive. Field and laboratory evidence suggests that these features are formed by a short‐lived countercurrent that develops during the flood cycle.
Hydrothermal alteration and earth surface rock weathering: A basalt example
Authors: McGreevy J. P. 
Published: February 2007

AbstractGeomorphologists have not devoted sufficient attention to the formation of clay minerals by hydrothermal activity. This paper describes the breakdown of freshly‐quarried basalt by cyclic wetting and drying. Breakdown is attributed to the swelling of hydrothermally‐derived smectite, and it is argued that the effects of endogenic processes can exert a significant control upon weathering behaviour under earth surface conditions.
Structure, composition and bulk properties of upland stream gravels
Authors: Carling Paul A. , Reader Nigel A. 
Published: February 2007

AbstractUpland gravel‐bedded streams in the U.K. have received only scant attention from both hydrologists and sedimentologists, but are worthy of further investigation. The sedimentology of three small streams in Teesdale in the Pennines has been examined in detail. Grain‐size characteristics, bedforms, structure, composition and packing characteristics of these deposits are described, and compared where appropriate with published information.It is argued that a fuller appreciation of gravel bed composition and morphology should eventually contribute to an improved understanding of sediment transport and deposition mechanisms, and, hence, to improved accuracy in sediment transport and deposition estimates.
Lias clay slope sections and their implications for the prediction of limiting or threshold slope angles
Authors: Chandler R. J. 
Published: February 2007

AbstractA series of previously published engineering studies of Lias clay slopes in the East Midlands is summarized, along with the description of some further slope sections. All the slopes studied show evidence of landsliding, though some of it may be of periglacial origin. The very disparate nature of the different landslides suggest that various different erosion regimes were responsible for the original slope formation; it is believed that the smaller landslides are more typical of the area. Piezometric observations show that at the present day maximum pore pressures are proportionately less in the larger landslides, the average value of the pore pressure parameter ru varying between 0.48 for shallow landslides to 0.32 in the largest. Stability analyses show that the residual strength is strongly stress dependent, Φr', (c'r = 0) varying from > 16° in shallow landslides to 10° in the case of the largest. These and other factors have important implications for the often used practice of combining laboratory measurements of residual strength with the Infinite Slope method of stability analysis to predict threshold slope inclinations for landsliding.
Storm runoff processes and subcatchment characteristics in a new zealand hill country catchment
Authors: Taylor Colin H. , Pearce Andrew J. 
Published: February 2007

AbstractThe quickflow responses of six subcatchment areas in a small hill country catchment in the Craigieburn Range, South Island, New Zealand, were compared for a range of storm sizes, rainfall intensities and antecedent wetness conditions. Topography and soil characteristics suggested that all subcatchments would receive subsurface stormflow input, but that some would receive larger saturation overland flow inputs than others. Quickflow yields and response ratios were positively correlated with storm size and antecedent wetness conditions in the subcatchment most suited to producing saturation overland flow. In subcatchments more likely to be dominated by subsurface flow, quickflow yields and response ratios were positively correlated with storm size, but were either not correlated, or negatively correlated, with antecedent wetness. Quickflow responses were either not significantly or negatively correlated with rainfall intensity variables. Quickflow from the subcatchment most suited to produce saturation overland flow providing an increasing proportion of total catchment quickflow in larger storms and as antecedent conditions became wetter. Subcatchment responses varied greatly in space and time and there was less pattern to the variation than had been expected. Where topographic and pedologic conditions permit substantial responses to storm rainfall by both saturation overland flow and subsurface stormflow, simple topographic and soil indicators may not be useful guides to the relative importance of runoff mechanisms, or to the identification of runoff‐source areas.
Rock mass strength and the form of some inselbergs in the central namib desert
Authors: Selby M. J. 
Published: February 2007

AbstractA rock mass strength classification, involving eight parameters, has been applied to selected inselbergs in the Namib Desert. The inselbergs are formed of schists, gneiss, granite and marble. Their slope inclinations are in a strength equilibrium with their rocks. The study suggests that the strength classification is consistent and has a general validity, and that rock slopes, undergoing uniform weathering, retreat to form slopes which are adjusted to their rock mass strength: this is a more general statement than the common hypothesis of parallel retreat. The favoured hypothesis of slope evolution in the Namib is one of retreat rather than downwearing.
Comments on: Experimental test of autosuspension
Authors: Pantin H. M. 
Published: February 2007

AbstractThe experiments of Southard and Mackintosh prove only that autosuspension did not occur under the tested conditions; these were based on the Bagnold (1963) criterion, which is unsound. An alternative criterion is re‐emphasized, and a method for testing its validity suggested. Two separate derivations are given for the power required for sediment suspension.
Concave‐bank benches and associated floodplain formation
Authors: Page Kenneth , Nanson Gerald 
Published: February 2007

AbstractThis paper describes the morphology, sequential development and general sedimentology of concave‐bank benches on the Murrumbidgee River of southeastern Australia, and also notes their important role in floodplain formation on certain meandering rivers in western Canada. Benches form against the concave bank (cut‐bank) of abruptly curving bends immediately upstream of the point of maximum curvature. As a result of flow deflection against the upstream limb of the convex bank, the channel widens here and produces a zone of expanded flow facilitating flow separation near the upstream limb of the concave bank. Sedimentation within this zone starts with a longitudinal‐shaped bar of medium sand forming a platform isolated even at low flow by a narrow secondary channel against the concave bank. Aggradation of the longitudinal‐shaped bar with fine sand, mud and organic matter permits the establishment of trees. Further sedimentation, particularly around the young trees, results in the formation of a fully developed bench isolated by the secondary channel from the remainder of the floodplain only during high flows. Observations on confined meandering rivers in western Canada provide evidence of substantial floodplain formation by concave‐bank bench accretion, a process distinctly different in character to the more familiar mechanism of lateral point‐bar accretion. Furthermore, the preservation of abundant organic debris means that extensive bench deposits may be a source of locally useful natural gas from within floodplain sediments.
Long‐term erosion on granitic roadcuts based on exposed tree roots
Authors: Megahan Walter F. , Seyedbagheri Kathleen A. , Dodson Patrick C. 
Published: February 2007

AbstractExposed roots were used to estimate soil and bedrock erosion on the cut slopes of a 45‐year‐old road constructed in granitic soils of the Idaho Batholith. The original roadcut surface was defined by projecting a straight line from the toe of the cut past the end of the exposed root to the intersection of a straight line projected along the surface of the hillslope. A cross‐sectioning technique was then used to determine erosion to the present roadcut surface. A total of 41 exposed root sites were used to estimate erosion on a 1350 m‐long section of road. Average erosion was 1·0 and 1·1 cm/year for soil and bedrock respectively. Buttressing by tree roots caused lower erosion rates for soil as compared to bedrock. Both soil and bedrock erosion rates showed statistically significant correlations with the gradients of the original cut slope. The bedrock erosion data provide a reasonable estimate of the disintegration rate of exposed granitic bedrock exhibiting the weathering and fracturing properties common to this area. The road is located in a study watershed where long‐term sediment yield data are available. Sediment data from adjacent study watersheds with no roads were compared to sediment data from the roaded watershed to estimate the long‐term increase in sediment yield caused by the road. The increase amounts to about 2·4 m3/year. This figure, compared to the average annual on‐site road erosion, provides an erosion to sediment delivery ratio of less than 10 per cent. Based on study results, road construction and maintenance practices are suggested for helping reduce roadcut erosion.
Geomorphic effects of a 10‐year storm on a small drainage Basin in the Texas Panhandle
Authors: Finley Robert J. , Gustavson Thomas C. 
Published: February 2007

AbstractBedded Permian salt in the Palo Duro Basin of the Texas Panhandle is being considered for isolation of nuclear waste. Studies underway to evaluate the geomorphic processes affecting any waste repository that may be sited in the region include studies of the geomorphic events associated with individual storms. On 26 May, 1978, thunderstorms occurred near Canyon, Texas, which received 130mm of rain, and on a small instrumented watershed at Buffalo Lake, 16 km to the southwest, which received 71 mm of rain. Rainfall at Buffalo Lake was concentrated in a period of 3 hours, representing a return period of approximately 10 years and a maximum 30‐minute intensity of 64 mm/hour.Erosion‐pin fields, topographic surveys, and stakes for headcut monitoring had been established 2 to 3 months before the storm in a 640‐m long tributary canyon to Tierra Blanca Creek downstream of Buffalo Lake. Canyon slopes of moderately to slightly calichified sands and gravels of the Ogallala Formation are capped by well‐indurated caliche on the canyon rim. Erosion‐pin fields showed average net erosion of 2·4 cm (0° to 9° slope) to 2·7 cm (10° to 19° slope) and a single‐pin maximum value of 6·2 cm in the 20° to 29° slope class. Headcuts 1 to 2 m deep in alluvial‐colluvial material on the floor of the canyon migrated as much as 12 m upstream. Canyon floor deposition occurred as a series of elongate bars, 16m long and longer, located at the mouth of tributary gullies, downstream from scours, and at slope breaks. Grain sizes ranged from boulders up to 70cm in intermediate axis deposited in the upper canyon to fine to very fine sand deposited as a sheet up to 25cm thick beyond the mouth of the canyon at Tierra Blanca Creek.In an adjacent canyon a sequence of irregular beds of caliche gravel, mixed sand and gravel, and fine sand up to 3 m thick is exposed. Comparison of this sequence with deposits resulting from the 26 May, 1978, storm suggests that the coarse fraction of the alluvial sequence is deposited by repetitive major storm events. Cobble and boulder units 30 to 70cm thick can evidently be deposited in a few hours. Under the continental climate of the Texas Panhandle, erosion, deposition, and stream incision are taking place primarily in discrete steps related to episodes of intense rainfall.
A world model of soil carbon dioxide
Authors: Brook George A. , Folkoff Michael E. , Box Elgene O. 
Published: February 2007

AbstractMean growing season soil PCO2 data were obtained for 19 regions of the world in nine countries. Bivariate and multiple linear regression analysis with soil log(PCO2) as the dependent variable and TEMP, PRECIP, log(AET), and log(PET) as the four climatic independent variables demonstrated that AET was the best independent predictor of soil PCO2. An improved soil PCO2‐AET model was developed by assuming (1) that as AET approaches zero, soil PCO2 approaches the atmospheric value and (2) that there is an upper limit to soil PCO2 at very high AET. This model has the form log(PCO2) = −3·47 + 2·09 (1 −e−0·0172 AET) where AET is in mm. It explains 67 per cent of the initial variation in the soil PCO2 data, predicts a soil log(PCO2) of − 3·47 at AET = 0, and an upper limit of 3·5 per cent (log(PCO2) = − 1·45) for mean growing season soil PCO2 at AET values of 2000 mm and above. The results of this study suggest that soil PCO2 levels in tropical areas are, on average, higher than those in temperate, alpine, and arctic regions.
Soil water residence times and solute uptake on a dolomite bedrock—preliminary results
Authors: Trudgill Stephen T. , Laidlaw Ian M. S. , Smart Peter L. 
Published: February 2007

AbstractCalcium and magnesium levels have been monitored in slope foot drainage waters on a dolomite bedrock. Both calcium and magnesium rich pulses occur. Short term dissolution experiments demonstrate high calcium levels in solution while other authors have suggested that long residence time groundwater has relatively high levels of magnesium due to calcite precipitation. Patterns of field fluctuations in Ca: Mg ratios can thus be tentatively interpreted in terms of short residence time water of high calcium content mixing with long residence time water of high magnesium content. Fluorometric dye tracing has been used to indicate the orders of magnitude of soil water residence times, suggesting that quickflow components are resident in the system for a few hours to a few days. Further work is in progress.
Resistance to flow in rough supercritical sheet flow
Authors: Savat Jan 
Published: February 2007

AbstractShallow water depths on steep slopes of as much as fifty per cent can be measured easily by weighing a light flume and the water it contains. Because water accelerates along the flume, a good approximation of the steady state depth is obtained when the recording balance is fixed to its bottom end.From the unit discharge and the depth, and not from measurements of the surface velocity, the Darcy‐Weisbach friction coefficient can be calculated. The present results show that this friction coefficient is larger in thin sheet flows than that calculated from the equation for rough turbulent flow. This latter could fit at a Reynolds Number of 50,000. When the regime is laminar (Re < 2,440) the Darcy‐Weisbach friction coefficient always exceeds the theoretical value of 96/Re. The great relative depth of standing and travelling waves could account for this discrepancy together with turbulence and wake formation around bottom grains.Herein it is assumed that a regime can prevail where a laminar superlayer glides over a turbulent sublayer in the vicinity of bottom grains, because the ratio of the surface velocity to the mean velocity can greatly exceed 1.5, especially on steep slopes.Until photographs of the streamlines are taken, no statement about flow regimes in supercritical sheet flow can be made.