摘要:

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 evidentl

ISSN:0197-9337    

DOI:10.1002/esp.3290070502

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractDissolved organic matter (DOM) concentrations in throughfall, throughflow, and runoff were recorded in a small (95 ha) woodland catchment in North Warwickshire for a period of eight weeks following a prolonged dry spell. DOM is shown to be positively related to stream discharge over the sampling period, although distinctive flushing effects were identified. The net contribution of DOM to total dissolved solids load carried in the river was only 2.4 per cent, and represented significantly less than published carbon losses by mineralization of soil organic matter. Throughfall inputs were some 100 times higher than streamflow outputs from the catchment.

ISSN:0197-9337    

DOI:10.1002/esp.3290070503

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

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 parameterruvarying 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 landslidi

ISSN:0197-9337    

DOI:10.1002/esp.3290070504

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

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 area

ISSN:0197-9337    

DOI:10.1002/esp.3290070505

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractIn identifying controls on rock slope form a distinction is made between: (1) rock slopes with joints which dip steeply out of a cliff and hence are subject to mass failure of the rock mass above a critical joint; and (2) rock slopes with inclinations which are either in equilibrium with the mass strength of their rocks, or have profiles which will develop towards strength equilibrium as cross joints open. In the first class of slope, stability results not just from the basic frictional resistance of the rock but also from the frictional roughness along the critical joint and from the normal stress acting across that joint. Stability may be reduced by weathering and loss of strength of the joint wall rock. As a result of normal stress variations with depth, induced by overburdens, high cliffs which are not undercut have a concave profile. The second group of slopes includes those with inclinations controlled at the scale of individual joint blocks, buttressed slopes and those on unjointed rock masses. Buttressed and unjointed rock masses develop towards a condition of mass strength equilibrium as cross joints open. Strength equilibrium slopes may be recognized by application of a rock mass strength classification proposed for geomorphic purposes. Eleven propositions are formulated which identify controls on rock slope development and some consequences of these controls.

ISSN:0197-9337    

DOI:10.1002/esp.3290070506

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

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 assume

ISSN:0197-9337    

DOI:10.1002/esp.3290070507

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractA laboratory experiment has been conducted to examine the effects of ‘frost and salt’ weathering (i.e. physical breakdown by the freezing of salt solutions) on a limestone. Results show that the presence of certain salts in solution can inhibit frost damage. These findings are in direct conflict with those presented by Goudie (1974) and, more recently, Williams and Robinson (1981).Comparison of the experimental methods used in each of these three studies suggests that opposing results can be explained in terms of the different experimental procedures which were employed. If salt supply is frequent and plentiful then it seems likely that rock breakdown will be enhanced‐this is the case represented by the experiment of Williams and Robinson. Conversely if the salt supply is limited and the amounts of salt remain more or less constant then rock breakdown will be inhibited‐the case of the present experimental study. Caution is therefore advocated when attempting to extrapolate laboratory‐derived results to infer on the behaviour of rocks under natural conditions.Several environmental situations in which ‘frost and salt’ weathering may be a possibility are dsiscussed, but it is concluded that further field data, especially concerning temperature regimes and salt availability at and below rock surfaces in cold regions, would be necessary before more definite statements could be made about the efficacy of

ISSN:0197-9337    

DOI:10.1002/esp.3290070508

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

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.

ISSN:0197-9337    

DOI:10.1002/esp.3290070509

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractRainfall drop‐size distributions were measured at a site in northern England using the ‘oflour‐pellet’ technique. A relationship between intensity and kinetic energy is presented. Even at the low rainfall intensities observed (<5 mm h−1average over an hour) measureable amounts of rainsplash movement took place, and these movements have been related to rainfall p

ISSN:0197-9337    

DOI:10.1002/esp.3290070510

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY

摘要:

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 suspensio

ISSN:0197-9337    

DOI:10.1002/esp.3290070511

出版商:John Wiley&Sons, Ltd    

年代:1982

数据来源: WILEY