bluuebunny/crossref_metadata_2025_split huggingface dataset:
Contributions to storm quickflow in a small headwater catchment—the role of natural pipes and soil macropores
Authors: McCaig Michael 
Published: February 2007

AbstractAnalysis of hydrographs from a 4·3 hectare stream head catchment indicates that storm runoff is generated from dynamic source areas. The volume and timing of contributions from different parts of the catchment show, when compared with the extent of surface saturation, that pipeflow generated from areas not saturated at the soil surface is a significant component of the quickflow hydrograph. A simple model of pipeflow generation and contribution is discussed in the light of field results.
Dune formation on the humid tropical sector of the North Queensland Coast, Australia
Authors: Pye K. 
Published: February 2007

AbstractSeveral previous attempts have been made to explain the apparent poor development of coastal dunes in the humid tropics in terms of lack of wind energy, failure of sand supply to the shoreline, excessive climatic wetness, salt crust formation on beaches, and the character of tropical back‐beach vegetation. However, recent published reports indicate that coastal dune occurrences are more common in the humid tropics than was formerly thought, throwing suspicion on the idea that environmental conditions militate against dune formation in these areas as a whole. Evidence from the humid tropical sector of the North Queensland coast suggests that the poor development of dunes in this area primarily reflects poor sediment sorting in the beach and nearshore zone and low wind energy at the shoreline due to the nature of the coastal orientation and physiography in relation to the prevailing southeasterly winds. These limiting factors are not unique to humid tropical climates.
Cavernous weathering in the Capitol Reef Desert, Utah
Authors: Mustoe G. E. 
Published: February 2007

AbstractTafoni and honeycomb weathering are abundant in sandstones at Capitol Reef National Park. Cavities are particularly common in talus blocks resting on alkali‐rich soil, in vertical walls of desert washes, and in sandstones containing calcareous cement. Chemical analyses, X‐ray diffraction data, and field observations suggest that salt weathering is the most important cause of disintegration, but dissolution of calcite cement also occurs in calcareous sandstones. Cavernous weathering at Capitol Reef produces cavities similar in appearance to features found in arkose outcrops along the coast of northwest Washington, even though the environmental conditions at these two locations are very different.
Equilibrium bank geometry and the width of shallow sandbed streams
Authors: Pizzuto James E. 
Published: February 2007

AbstractCross‐sections of 16 straight sandbed streams in Minnesota, Iowa, and Nebraska were surveyed. Two stratigraphic horizons were found in the banks at each site, an upper cohesive unit usually composed of silt and clay and a lower unit composed of sand.Bank erosion on these rivers occurs when the upper cohesive unit is undercut by scour at bends. The overhanging cohesive block fails by beam or cantilever failure. As upper bank failure is a direct result of undercutting, the stability and rate of retreat of the bank are largely determined by erosion of the sandy part of the bank. The cohesive layer has little influence on bank retreat and width adjustment on the rivers studied here.A quantitative lateral sediment transport model developed by Parker (1978a) is used to calculate the steady‐state geometry of the sandy part of the bank. Results are obtained for the shape, length, and height of the sandy part of the bank. The model predicts the length of the bank fairly well, and the theoretical equation for the height of the bank is of the correct form. The model, however, overestimates the slope of the bank.The height of the sandy part of the bank (Db) is approximately equal to the depth of the mean annual flow. Since Db is determined by the lateral sediment transport model, the width (W) may be obtained from the equation of continuity (Q = WDbV), published flow (Q) data, and a resistance equation for the mean velocity, V. The calculated widths are similar to those measured in the field.
Characteristics and occurrence of wind erosion features in the Namib Desert
Authors: Lancaster N. 
Published: February 2007

AbstractSmall scale features resulting from wind erosion are widespread in the Namib Desert. They include selective erosion of lithological variations (etching), flutes and grooves, facetting of clasts and residual boulders, and smoothing and polishing of rock surfaces. Large scale features are tentatively identified and are restricted to the southern Namib, with its high energy, unidirectional wind regime.Wind erosion features are best developed on fine‐grained rocks of intermediate hardness. They are oriented towards or parallel to modern strong winds.The turbulent flow of wind armed only with dust particles is probably more important than wind driven sand in creating smooth polished rock surfaces, flutes, and grooves. Wind driven sand appears to be significant only in facetting rock masses.
The identification of four stages during micro‐rill development
Authors: Merritt Elaine 
Published: February 2007

AbstractSeparation of rill and inter‐rill erosion is required in many of the soil erosion models currently being developed. The feasibility of basing the separation on the hydraulic properties of the flow and resultant sediment production is examined in a laboratory simulation of rill initiation and development. Four stages are identified in the process of rill formation; these are sheetflow, flowline development, micro‐rills, and micro‐rills with headcuts. There are significant differences in terms of flow characteristics between the stages, especially between sheetflow and flowlines, indicating the promise of this method for making a more precise distinction between rill and inter‐rill erosion.
Holderness coast erosion and the significance of ords
Authors: Pringle (Nee Phillips) Ada W. 
Published: February 2007

AbstractA sample ord, a low section of beach characteristic of the Holderness coast, is examined as it moved southwards between 1977 and 1983 and its significant role in coast erosion is demonstrated. The reduction in beach level at the cliff foot by up to 3.9 m enabled most HWN tides to reach it, as compared with only some HWS tides along the inter‐ord beach, and the volume of till eroded from the cliffs increased by eight times to an annual mean of 72m3m−1. The Holderness tills are shown to be composed of 31 per cent sand and coarser sediment which is the sediment range of the beaches. Where an ord is sited the massive injection of beach sediment goes to form the ord's most prominent constructional feature, the lower beach ridge which extends southwards from the centre of the ord. Analysis of 12 months' observer wave data collected at Withernsea in 1969/70 indicates that a net southward sand movement of 144 000 m3 occurred. Comparison of this rate with beach sediment input rates along the whole coast backed by till cliffs suggests a sediment deficit at the northern end and a surplus towards the southern end. This conclusion is supported by an overall increase in beach sediment volume southwards from Barmston. Within this longshore sediment transport system, the ords migrate southwards from their point of origin in the Barmston‐Skipsea area, without losing their identity until reaching the tip of Spurn Head.
Traditional and multivariate techniques in the interpretation of floodplain sediment grain size variations
Authors: Brown A. G. 
Published: February 2007

AbstractThe vertical and horizontal variation of sedimentary fades is the raw data for the interpretation of flood plain history from which palaeohydrological inferences are frequently drawn. Mixed and fine floodplain sediments present problems of interpretation because of a large grain size range and frequent polymodality caused by the mixing of process‐associated grain size components. This paper discusses the use of traditional grain size statistics and the use of the mode and multivariate statistics. The mode, although much neglected, is indicative of up‐profile grain size changes and has practical advantages over the mean for mixed and fine floodplain sediments. Constrained cluster analysis and principal components analysis are used directly on Coulter counter results. These techniques can rapidly divide a floodplain profile into grain size units and indicate the principal vectors of grain size variation which will be related to the changing processes of deposition. Principal components analysis reveals the importance of the medium to fine silt category in accounting for grain size variations, suggesting that a critical factor in determining the type of alluvial unit deposited is the degree to which it has received fine suspended material. Grain size data from the Lower Severn are used to construct a CM diagram which is compared with a texture triangle. From both the CM and multivariate analysis a generalized backswamp profile is constructed which shows the existence of a coarser top unit caused by the addition of a fine to medium sand component to the underlying sediment during the Late Holocene.
Winds and sand movements in the Namib Sand Sea
Authors: Lancaster N. 
Published: February 2007

AbstractWind regimes in the vicinity of the Namib Sand Sea are high energy unimodal near the coast, becoming bimodal or complex inland. There is an overall decrease in wind energy and sand transport rates from south to north and west to east, such that sand moves from coastal and southern source areas to accumulate in the northern and central parts of the sand sea. Such a pattern can explain much of the observed spatial variability in dune types, sizes, and sediment characteristics and lends support to a climatic model of sand sea formation in this region.Seasonal and daily cycles of wind velocity and direction give rise to episodic sand transport, most of which is generated by winds of moderate velocity and frequency.
Approaches to dynamic equilibrium in theoretical simulations of slope development
Authors: Ahnert Frank 
Published: February 2007

AbstractThe model SLOP3D is used to identify characteristic aspects of slope development under different conditions. A series of slopes along the Kall valley in the northern Eifel is reproduced by a developmental sequence of model slopes. The spatial and temporal variations of the components of slope development systems (relief, slope form, weathering rates, denudation rates) are discussed by means of mass movement and wash denudation models. The negative feedbacks between system components create a tendency towards the establishment of a dynamic equilibrium which is reached, however, only if the endogenic and exogenic conditions remain constant for the required relaxation time. The latter is shown to be a function of slope length, of the rate of uplift, of the denudational process type, and of the intensity of exogenic inputs (e.g. precipitation). Varying rock resistance leads to the development of shield inselbergs only if the rate of denudation becomes higher than the maximum possible weathering rate of the resistant bedrock.
Slopes, boundary conditions, and the development of convexo‐concave forms—some numerical experiments
Authors: Armstrong Adrian C. 
Published: February 2007

AbstractSlope profile sequences are as much influenced by their boundary conditions as they are by the processes operating. The development of a simple slope under a single process can adopt a variety of forms depending on initial and boundary conditions, and a given form can be derived from several different processes. For example, convexo‐concave forms develop under soil creep with basal accumulation, under wash with an initial step form, and under mixed wash and creep processes.
Accuracy and precision of methods for estimating river loads
Authors: Ferguson R. I. 
Published: February 2007

AbstractRiver loads often have to be estimated from continuous discharge data but relatively infrequent sampling of sediment, solute, or pollutant concentrations. Two standard ways of doing this are to multiply mean concentration by mean discharge, and to use a rating curve to predict unmeasured concentrations. Both methods are known from previous empirical studies to underestimate true load. Statistical considerations explain these biases and yield correction factors which can be used to obtain unbiased estimates of load. Simulation experiments with normally‐distributed scatter about log‐linear trends, and sampling experiments using a natural data set, show that the corrected rating curve method has lower sampling variability than other unbiased methods based on average instantaneous load and is thus the recommended procedure when the rating plot is of the assumed form. The precision of all methods increases with sample size and decreases with increasing rating‐curve slope and scatter.
The effects of soil piping on contributing areas and erosion patterns
Authors: Jones J. A. A. 
Published: February 2007

AbstractNatural piping doubles the dynamic contributing area on the upper Maesnant stream in mid‐Wales, mainly through linking points well beyond the riparian zones of seepage to the stream. Both discharge and sediment transport rates in the major pipes are closely related to the size of shallow surface microtopographic hollows in which they lie, and which themselves are largely created by piping erosion. However, pipe dischrges are frequently generated by contributing areas larger than these surface depressions and some pipes run counter to the surface topography. The redistribution and acceleration of hillslope drainage processes by piping has implications for theories of hillslope development, especially through plan‐form modifications, and also for channel discharge and erosion.
Holocene alluvial fan and terrace formation in the Bowland Fells, Northwest England
Authors: Harvey A. M. , Renwick W. H. 
Published: February 2007

AbstractIn the Bowland Fells, Lancashire, northwest England, in the headwater valleys of the Hodder river system, is a suite of Holocene fluvial landforms. Debris cones and alluvial fans at tributary junctions, and river terraces along the main valleys post‐date late Pleistocene forms and pre‐date the modern valley floor alluvial forms. Eight 14C dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of Holocene erosion to be identified with debris cone/fan deposition taking place after c. 5400 BP but before c. 1900 BP and again at c. 900 BP. Some of the fans and cones are complex with deposits attributable to both phases; others are simple and attributable only to the later phase. In the headwaters an upper terrace at c. 5400 BP pre‐dates the cones and a lower terrace is contemporaneous with the first debris cone phase. Lower downvalley the youngest of three terraces date from c. 5000 BP or earlier indicating that the sequence is less complex downstream.
Manganese‐rich rock coatings from Iceland
Authors: Douglas G. R. 
Published: February 2007

AbstractManganese‐rich rock coatings are widespread in Iceland, especially in fractures in basalt lavas. Three common types of coating are described. A thick subsurface coating is found on whaleback forms on high plateaux. The most common type is thinner and occurs in hydrothermal clay‐filled fracture systems which are especially well developed in tholeiite lavas. A third type occurs in younger rocks and is associated with tephra‐rich, loessic sediment which fills open fractures and vesicles. There are differences in the chemistry, morphology, and mineralogy of these coatings which are interpreted as being due to the different microenvironments in which they form. The fracture microenvironment is regarded as being of much more importance to coating thickness and chemistry than simple age and in this respect the hydrothermal clays seem to favour rapid manganese concentration. On the other hand, there are variations in coating type, both laterally and vertically through the lava succession, which are related to regional distribution of hydrothermal alteration and rock type. The regional patterns are the result of Iceland's lateral drift and as a result there is an incidental connection between coating type and rock age. There is some evidence to suggest that the manganese coatings may be both forming and being degraded rapidly in the present environment.
Blue‐green algae and terrestrial limestone weathering on Aldabra Atoll: An S.E.M. and light microscope study
Authors: Viles H. A. 
Published: February 2007

AbstractBlue‐green algae have been observed to affect limestone weathering on Aldabra Atoll, Indian Ocean. Three different habitats can be identified on the rock surface, i.e. epilithic, chasmolithic, and endolithic. Algae in each habitat may affect weathering in various ways. Samples of blue‐green algae and rock were taken from various terrestrial and coastal environments on Aldabra Atoll. Samples of limestone tablets and calcite crystals after one year in situ were also studied. Light and S.E.M. microscopy revealed that endolithic boreholes were present on many samples, especially those from frequently wetted sites, to a maximum depth of 800 μm. An ‘altered zone’ of micrite and algal filaments was also discovered in many samples. From morphological and petrographical evidence blue‐green algal influences on weathering on Aldabra Atoll seem to be very complex and cannot easily be related to small scale landforms.
Sampling for isotopic responses in surface waters
Authors: Lawler H. A. 
Published: February 2007

AbstractThis paper considers situations in which stable isotopes may be used as natural tracers of precipitation through to surface waters. Two aspects affecting the applicability of the technique are highlighted: first, the variance through time of isotope concentrations in precipitation, i.e. the isotope input signal, and second, the attenuation or damping of this signal during the transmission of water downwards through the hydrological system. Both factors affect the likelihood of obtaining an isotope response, i.e. a variation of isotope concentrations in a surface water which may be related to variations in the precipitation input.Analysis of precipitation over the Malham area, U.K., reveals large isotopic variations through time. These variations, however, are only poorly correlated with meteorological variables (temperature, precipitation amount, and air mass type). Snowmelt and occluded frontal rainfall are suggested as providing the most reliable ‘spikes’ for an isotopic response at the output in tracing studies. In most hydrological systems, a high degree of signal attenuation is noted. In the Malham area of karst, 57 per cent of the total range of input variation was lost in surface waters, whilst 74 per cent was lost in mobile soil moisture. An isotopic response can only reasonably be expected in a system with rapid throughput, where there is little opportunity for mixing and storage of waters.
Soil pipes and their role in runoff generation and chemical denudation in a humid tropical catchment in dominica
Authors: Walsh R. P. D. , Howells K. A. 
Published: February 2007

AbstractNumerous soil pipes are reported from a small catchment in an area of kandoid (kaolin‐rich) soils and 2375 mm annual rainfall in the humid tropical volcanic island of Dominica, West Indies. Two spot surveys in August 1982 at baseflow during the wet season indicated that pipes contributed at least 14–16 per cent of streamflow. Sampled pipeflow was of similar chemical composition to the baseflow‐dominated streamwater. Specific conductance (249–420 μS cm−1) and silica (75 mg l−1) levels of pipeflow were high and suggested that the pipes tapped solute‐rich water close to the soil‐rock interface. The principal pipes flow perennially and showed little response to daily rainfalls of up to 43 mm during the monitoring period.
Incipient motion conditions for single rock fragments in simulated rill flow
Authors: Torri D. , Poesen J. 
Published: February 2007

AbstractLaboratory experiments using simulated tilting rill channels with different bed roughnesses have been conducted to determine hydraulic conditions for incipient motion of single rock fragments lying on rill beds. These threshold conditions can be described by a modified Shields' entrainment parameter (θm) and relative depth (Z), adjusted for rill conditions. The negative relation found between θm and Z also fits steep (stream) channel data collected by other investigators. Plots of the classical Shields' entrainment parameter (θ) versus both relative depth and relative particle size also showed clear negative trends. Special care has been taken to avoid false relations that can arise between compound parameters. This occurs when the latter are not independent from each other because of their definitions.
On the modelling of sand bedforms using the semivariogram
Authors: Robert André , Richards Keith S. 
Published: February 2007

AbstractThis study shows the usefulness of the semivariogram for modelling sand ripples created by water flows of varied flow intensity. A combination of two mathematical functions is fitted to each sample semivariogram, that is an exponential (or stochastic) component and a periodic component. The parameters of each of these components have direct physical meaning. A non‐dimensional ratio combining the two parameters of the exponential model is interpreted as a regularity index (which increases with the degree of regularity of bedform arrangement). This regularity index is inversely related to the Froude number of the flow. The non‐dimensional wavelength, estimated from the dominant periodic function, is also inversely and closely related to the Froude number. The wave height, accurately estimated from properties of the two fitted components, is a direct function of flow velocity and is also proportional to the standard deviation of bed elevations. The bedform shape introduces a considerable discrepancy between the generally assumed normal frequency distribution and the empirical distributions of bed height. The series of bed elevations are generally characterized by a mixture of normal distributions having the same variance but different means. The calculation of a covariance assuming a constant and single mean (as in spectral analysis) can therefore be misleading and the problem may be avoided by using the semivariogram.
Neoglacial gelifluction in the Jostedalsbreen Region, Western Norway: Evidence from dated buried palaeopodsols
Authors: Nesje Atle , Kvamme Mons , Rye Noralf 
Published: February 2007

AbstractRadiocarbon dating of thin palaeopodsols buried beneath turf‐banked gelifluction lobes at four localities in the low alpine mountain zone in the Jostedalsbreen region, western Norway, show that gelifluction processes were initiated subsequent to the late Subboreal Chronozone. Although large age‐depth gradients have been demonstrated from buried palaeosols in southern Norway, evidence is presented that the palaeosols in this study show only moderate age‐depth gradients. The age estimates from these buried palaeosols give maximum dates of burial, but the error is not thought to be large. Gelifluction processes were probably initiated close to the time of the climatic deterioration, which led to the formation of the present glaciers during the Subatlantic Chronozone. The processes may have been most active during the peak of the Little Ice Age, during which a periglacial climate was established to low levels in this mountainous region.