bluuebunny/crossref_metadata_2025_split huggingface dataset:
Suspended solids concentrations and river water chemistry
Authors: Imeson A. C. , Verstraten J. M. 
Published: February 2007

AbstractIn some rivers concentrations of suspended solids are influenced to a large degree by the chemistry of the river water. This is particularly true for rivers with fine sediments draining areas where soils have high percentages of exchangeable sodium and where changes in the electrolyte concentrations during hydrologic events result in an alternation between conditions favouring dispersion and those favouring flocculation. This relationship is illustrated for low flow conditions by data from a small river in Eastern Australia.At high flows, variations in suspended solids concentrations independent of those resulting from changes in discharge and erosion are difficult to establish. However, in semi‐arid regions high concentrations of clay and silt may sometimes be transported. The way such concentrations reflect changes in water chemistry is illustrated by a flash flood from Morocco and by data from the Moreau River in South Dakota. A contrasting example from Northern England describes conditions where the water chemistry produces dispersion and high suspended solids concentrations.The relationship between electrolyte concentration, exchangeable sodium percentage and suspended solids concentrations is described for each drainage basin. Such relationships provide an insight into the nature of erosion processes in a catchment and help to explain why suspended solids concentrations at low flows may be so variable.
Rainwash experiments on the erodibility of loose sediments
Authors: Poesen J. 
Published: February 2007

AbstractLaboratory experiments using simulated rainfall, splash boards and trays were conducted in order to obtain information on the erodibility of loose sediments as a time‐dependent phenomenon. In all, ten different sediments ranging from silt (D50= 24μm) to coarse sand (D50= 593 μm) were studied. The effect of three different initial states of the sediments, namely the air dry state T1, the field capacity state T2, and the desiccated state T3, on the erodibility was also assessed.Variations in detachability during a rain erosion experiment can be explained by change in water content (including liquefaction and the development of a water layer on the surface), cohesion, and granulometric composition of the top layer. The coarsest sandy sediments almost always yielded the highest detachability when starting from an initial field capacity state, T2. For the finer sediments, the highest detachability was found for the homogeneous and not yet compacted initial air dry state, T1. The effect of the initial desiccated state T3 on the detachability of the finer sediments was also a function of the rainfall duration.The relationship between detachability and median grain size of the sediments was very similar to the relation between grain size and the susceptibility to runoff and wind erosion established by other investigators. The highest detachability was found for a fine very well sorted sand with a median grain size of 96 μm.
The assessment of chemical weathering rates within an upland catchment in north‐east Scotland
Authors: Reid J. M. , Macleod D. A. , Cresser M. S. 
Published: February 2007

AbstractA study has been made of weathering in Glendye, an upland catchement of heather moorland underlain mainly by granite with some gneiss in north‐east Scotland. The concentrations of a range of elements and ions in precipitation and river water were measured over a twelve‐month period. The total input and output of each element or ion was calculated. The resulting balances show net outputs of all species except hydrogen ion. Large net outputs of silicon (38.5 kg ha−1 a−1) and bicarbonate (48 kg ha−1 a−1) indicate considerable chemical weathering. A large net output of chloride (32 kg ha−1 a−1) indicates the importance of dry deposition of oceanic aerosols. When this is allowed for the rate of output of elements due to weathering is.Si>Ca>Na>Mg>K>Fe>Al.These results were compared with the abundance of elements in bedrock and differential weathering ratios calculated. These are compared with data from the Hubbard Brook study in New Hampshire. In both cases calcium is by far the most mobile element. The relative importance of the atmosphere and of chemical weathering as sources of each element was calculated, and the results compared with those of a study at Wet Sleddale in the Lake District. Similar patterns emerge in both cases.
Sediment yield studies of headwater catchments in Sussex, S.E. England
Authors: Collins M. B. 
Published: February 2007

AbstractThe transport of sediment from six small (0.2 to 17.6 km2) headwater catchments is described. The catchments under investigation were located in relation to predominant lithological deposits within the Cretaceous rock succession; two of the areas were underlain by (Weald) clay, two by sandstone (Ashdown Sand and Tunbridge Wells Sand) and two by chalk. The climate of the region under investigation is temperate, with an average annual precipitation (850 mm) in excess of potential evapotranspiration (450 mm).The transport of suspended material from within the catchments was examined by collecting samples of the water‐sediment mixture draining the areas, using hand held depth‐integrating and permanently installed stage sampling systems. The results of the regularly maintained sampling programme, over a two‐year period, are described. Attempts were made to both measure and compute bed load transport.Suspended sediment concentrations are compared between catchments and related to hydrological characteristics. The nature of the material in transit is examined.Sediment rating curves are derived for each of the headwater catchments, defining the relationship in the form y = Axb (where y = suspended sediment concentration (mg/1) and x = water discharge (m3/s)). Annual rating curves are used to derive annual suspended sediment loads by combination with water discharge data, using a log‐incremental computerized approach. Multiple regression techniques have been used to examine annual loads in terms of hydrological and morphological characteristics of the headwater catchments.Based on the field information available, a generalized model for the relationship between suspended sediment concentration and water discharge is described.Finally, the derived annual loads from the headwater catchments are combined with both limited observations from the larger Sussex rivers and data available for other catchment investigations in the British Isles, to produce a series of prediction equations for catchment yield under temperate climatic conditions.
Mangos shale‐associated alluvium
Authors: Laronne Jonathan B. 
Published: February 2007

AbstractInquiry into the dissolution kinetics of naturally occurring geologic materials, rather than individual mineral species, has been relatively neglected. This is especially true of surface processes, the realm of surface water hydrology and geomorphology. This paper focuses attention at a laboratory study of the rate of such complex reactions.Functions defining the dissolution rates of saline (0.1–20 per cent salt content) Mancos Shale‐associated alluvium in distilled water follow varying patterns. Dissolution is characterized by an initial (<5 min) high rate constant, by a following phase (20 min‐57 h) where rates are reduced drastically, and by a final period of encroachment to equilibrium. Initial dissolution rates increase with increase in salt content and sediment: water ratio. The time necessary to approach equilibrium is, however, found to be directly proportional to the sediment; water ratio. The concentration of Na+, Mg2+, Ca2+, SC2−4 and HCO−3, and the relative abundance of Ca2+ and HCO−3 increase continuously with contact time, indicating that the hydrated sodium and magnesium sulphate minerals provide most of the initial solutes, though not necessarily most of the total solute bulk.The results obtained in this study indicate that the high initial dissolution rate of soluble minerals from alluvium, and particularly from shales in contact with aqueous solutions, is too short‐lived to account for most of the solutes occurring in heavily sediment‐laden surface flow. Excluding input from slower, usually supersaturated subsurface flow, dissolution from sediment in transport should be a major source of solutes in originally undersaturated and kinetically unequilibrated surface water in semiarid and arid regions.
The effect of a new zealand beech forest canopy on the kinetic energy of water drops and on surface erosion
Authors: Mosley M. P. 
Published: February 2007

AbstractRain and throughfall drops were sampled during rain events in a New Zealand beech forest and the frequency distributions of drop mass and kinetic energy calculated. The kinetic energy of throughfall under the canopy was always greater than that of rainfall in the open, notwithstanding interception losses. During a typical rain event in which 51 mm fell in 36 h, the total kinetic energy of throughfail was 1.5 times greater than that of rainfall, and the mean amount of sand splashed from sample cups was 3.1 times greater under the canopy than in the open. It appears that where mineral soil is exposed at the surface, by animal trampling or burrowing for example, rates of soil detachment by splash under a forest canopy will probably exceed those in the open.
The geormorphology of subalpine snow avalanche runout zones: San juan mountains, colorado
Authors: Huber Thomas P. 
Published: February 2007

AbstractA comparison was made between the distal ends of twenty‐two avalanche and fifteen non‐avalanche slopes in the San Juan Mountains of Colorado, U.S.A. All slopes occurred in the subalpine zone. Six characteristics were used for analysis: type of slope, surface material, longitudinal profile, perched debris or debris tails, avalanche impact on opposite valley wall, and transverse profile. Both fan and roadbank avalanche slope types were found along with the non‐avalanche slopes. Almost all slopes were turf covered rather than talus since the work was done below treeline. Twenty avalanche slopes had a distinctive concave longitudinal profile. Little debris of any kind was found since the slopes were in an area of insignificant amounts of detritus. Many of the larger and two of the smaller avalanche slopes showed evidence of impact upon the opposite slope. Eighteen of the avalanche slopes had convex transverse profiles.
Asymmetry of river channel cross‐sections: Part II. mode of development and local variation
Authors: Knighton A. D. 
Published: February 2007

AbstractA five‐stage model of the development of cross‐sectional asymmetry is proposed in which alternating bar deposition and bed scour are important elements. Quasi‐periodic reversals in the sense of asymmetry and a progressive increase in the magnitude of asymmetry at sections which develop an asymmetry initially are major features of the model. Application of Bridge's (1977) model confirms several features of the model and suggests that the degree of asymmetry is directly related to bend curvature. After the initial stages, subsequent changes to the cross‐sectional and planimetric form of the channel may be intensified by the developing asymmetry through a system of positive feedbacks in which the levels of form and flow distortion are interrelated. Asymmetry appears to provide an important link between cross‐sectional and plan form adjustment.Spatial series of asymmetry obtained for three lengths along a mountain stream contain features predicted by the model. In particular, the dominant peak in spectral density functions occurs at a frequency with a corresponding wavelength close to 4πw which has significance in terms of the meander wavelength‐width relationship (Richards, 1976a). This consistency is remarkable considering local differences. In addition, sections in curved reaches tend to be more asymmetric, especially when sited at pools. However, contrary to expectation, channel width is not significantly correlated with asymmetry.
Aspect‐induced differences in hillslope processes
Authors: Churchill Robert R. 
Published: February 2007

AbstractThe type and relative rate of geomorphic process activity on residual hillslopes in the White River Badlands of South Dakota were found to vary as a function of aspect‐induced differences in topoclimate. Drainage densities on north‐facing slopes several orders of magnitude greater than those on slopes facing south indicate that north‐facing slopes experience greater fluvial erosion. Comparative analysis of mass movement features suggests that north‐facing slopes are prone to relatively high‐magnitude, low‐frequency failures, whereas south‐facing slopes experience far more frequent but much smaller movements.Variations in process activity can be explained in large part by aspect‐induced differences in moisture regime. Field monitoring of moisture conditions indicates that north‐facing slopes maintain higher and less variable moisture levels. South‐facing slopes are not only drier in‐ general but are subject to more frequent and intense episodes of wetting and drying. Differences in moisture conditions promote differences in weathering activity as evidenced by thicknesses of slope regoliths. Higher moisture levels on north‐facing slopes lead to more rapid dissolution of binding cements and consequently, thicker regolith covers. On south‐facing slopes, however, regolith covers are virtually non‐existent due to both drier conditions and episodic desiccation, which triggers small rockfalls. Greater fluvial erosion on north‐facing slopes is a consequence of higher antecedent moisture levels, which retard infiltration. Further, the unconsolidated regolith cover is more erodible than the relatively unweathered materials exposed on the surfaces of south‐facing slopes. Resistance to slumps and mudflows is lower on north‐facing slopes because the weathered regolith is less cohesive than the unweathered parent material and also because the regoliths are periodically saturated.
A wave tank experiment on the erosional mechanism at a cliff base
Authors: Sunamura Tsuguo 
Published: February 2007

AbstractA laboratory experiment using a two‐dimensional wave tank was designed to investigate the mechanism of erosion at a cliff base by waves armed with rock fragments. The experiment was performed under constant wave conditions by systematically changing the amount of beach sand at the foot of steep model cliffs of the same slope and strength. Cliff erosion occurred when the beach material at the cliff/beach junction was moved by waves. Turbulence created by bores rushing up on the beach mobilized the sand and exerted a mechanical shearing force on the cliff face using the sand as an abrasive. The analysis of results indicated that the effect of the abrasive doubled when the cliff/beach junction was located above Still Water Level (SWL) as compared to when it was below SWL. The assailing force of the sediment‐laden water masses was proportional to the square of the bore speed immediately in front of the cliff face. The factor of proportionality is related to the quantity of beach sand entrapped in the turbulent fluid.
Small channels: Their experimental formation, nature, and significance
Authors: Moss A. J. , Green Patricia , Hutka J. 
Published: February 2007

AbstractThe manner in which small channels are generated, from plane beds beneath sheet flows, has been experimentally elucidated. On plane, erodible, sand beds, the transition from thin, supercritical sheet flows to the channelled condition was studied over ranges of discharge, slope, and temperature. Secondary flow of the second kind, its action facilitated by steep vertical velocity gradients in the primary flows, caused sheet‐flow instability. Along junctions between neighbouring secondary cells, both either raised or lowered elements of the primary flow. In the latter case, fast surface water was lowered to the bed, causing relatively intense, local, longitudinal scour. Dislodged grains were moved divergently to either side, leaving straight, central trenches. Development of positive feedback between cells and trenches led to rapid enlargement of the latter and concomitant growth of paired levees. The resulting structures, ‘protochannels’, were themselves ephemeral, developing two types of instability associated with secondary flow of the first kind. Firstly, small deviations from bilateral symmetry were enhanced, causing evolution into meandering channels. Secondly, headcutting led to multiple tributary development and, at resulting confluences, the action of strong pairs of secondary cells led to the development of braiding channels. Because they are shortlived, protochannels are but rarely seen in nature. Their seeding is markedly temperature‐sensitive, reflecting their frictional origin.The erosive power of shallow overland flow largely depends on flow‐energy concentration by secondary flow, firstly into channels, then within the channels themselves. Suppression of secondary flow, as by intense raindrop bombardment, can stabilize sheet flows.In deeper water, the effects of secondary flow appear relatively less dramatic. However, even if such motion is weak, bedload divergence from attachment lines can favour entrainment locally and thus affect bed geometry. Analogy between our results and river behaviour appears close and. on continental shelves where water must often flow as sheets, structures resembling giant protochannels evidently persist.
The relation of chain length to chain curvature in natural channel networks
Authors: Abrahams Athol D. 
Published: February 2007

AbstractAnalyses of three different areas indicate that chain curvature controls chain length indirectly through valley‐side plan form. It follows that, since concave chains on one side of a stream are usually matched by convex chains on the other side, tributary development and abstraction do not occur independently along either side of a stream, as has hitherto been assumed.
The contribution of throughflow to storm runoff: An evaluation of a chemical mixing model
Authors: Anderson M. G. , Burt T. P. 
Published: February 2007

AbstractThe contribution of throughflow to storm runoff is examined using a chemical mixing model. The results predict that throughflow is an important component of storm runoff particularly during the period of stream recession. Supporting hydrological data suggests that a major throughflow input occurs coincident with the stream discharge peak. The two sets of results therefore conflict in the predicted timing of the throughflow response.
Dunes on the skeleton coast, Namibia (South West Africa): Geomorphology and grain size relationships
Authors: Lancaster N. 
Published: February 2007

AbstractSimple, and locally compound, transverse and barchanoid dunes dominate the 2000 km2 Skeleton Coast dunefield in northwestern Namibia/South West Africa. Dune height and spacing are closely correlated (r = 0‐89) and decrease across the dunefield from southwest to northeast, with an accompanying change from transverse to barchanoid ridges and ultimately barchans.The dunes are aligned transverse to the dominant strong south and south southwest onshore winds. Alignment patterns indicate that surface roughness changes between coastal plain and dunes cause dune‐forming winds to swing to the right over the dunes, but resume their original direction beyond.Grain size and sorting vary at three scales: the dune, the dune landscape and through the dunefield. Overall the sands, derived from three localities by deflation from beaches supplied by vigorous longshore drift, become progressively finer and better sorted across the dunefield paralleling changes in dune height and spacing.A statistically significant relationship (r = −0−65) was established between dune spacing and the phi grain size of the coarser fraction of the dune sands, demonstrating the importance of the protective effects of coarse grains, and suggesting that the morphometry of simple transverse dunes may be controlled by the scale of turbulence associated with the threshold wind speed required to move the coarsest fraction of the dune sand.
Grand canyon—a quantitative approach to the erosion and weathering of a stratified bedrock
Authors: Aronsson Gunnar , Linde Krister 
Published: February 2007

AbstractA new method is proposed for solving a differential equation arising from weathering‐limited development of a valley. Allowance is made for horizontal stratification and overhang can be allowed to develop. The model is applied to the Grand Canyon and comments are included on its relevance.
Threshold of coarse sediment transport in broad and narrow natural streams
Authors: Carling P. A. 
Published: February 2007

AbstractThe threshold of coarse sediment transport has been examined in natural streambeds in an upland Pennine (U.K.) area. Threshold values of the total boundary shear stress (T0) (for a given grain size), in a narrow natural stream (W/D < 11) are considerably higher than values of T0 in a broad stream (W/D > 11). Efficiency in the entrainment process is related not only to the overall channel geometry, but also varies as a function of discharge in channels characterized by compound roughness.Empirical curves relating T0 and a mean grain size (d5) are presented, but are limited in application to streams of similar physical and hydraulic characteristics as the ones examined in this investigation. Considerable divergence is noted between these empirical functions and a summary empirical function for general application obtained from a published source. The reasons for this divergence are discussed.The influence of grain shape was found not to be important in the initiation of motion criterion. This conclusion may reflect the limited range of natural grain shapes in the study streams, but might reasonably apply to other field investigations of similar streams.Modifications of the Shields' and Yalin diagrams are suggested for practical applications in shallow streams with poorly‐graded bed material. The Shields' parameter may be regarded as an inverse function of the relative protrusion of individual grains in the shallow flow depth (d5/D). The increased importance of augmented drag forces, in the entrainment process in shallow flows, is suggested as the physical explanation for the reduced values of the Shields' parameter. However, the relationships presented should not be applied to laboratory experiments concerned with well‐graded sediments (therefore beds with little deviation in level), in which the Shields' parameter may be regarded as constant at high Reynolds' grain numbers.Consistent estimated field values of ϵ, a threshold sediment transport parameter, might be used to compare field data to threshold values derived from statistical arguments and laboratory experiments reported in the literature.