ISSN:0197-9337    

DOI:10.1002/esp.3290060302

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractExperimental geomorphology is a part of functional geomorphology. It tries to reach an exact analysis of the processes and to give statements on their importance for the recent relief forming. In all cautiousness the results may be transformed into more extensive areas and other time periods. Experimental geomorphology plays a differing role within the geomorphological research of the European countries. Most of the investigations deal with process studies and the quantification of weathering, mass movement, deflation, surface runoff, sediment transport in stream channels and denudation of watersheds. Experimental geomorphology should not be a goal in itself, but should be used as an applied geomorphology and for the examination of geomorphological theories as well.

ISSN:0197-9337    

DOI:10.1002/esp.3290060303

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA recent study conducted in the Sde Boqer experimental site drew the attention to the possible influence of the burrowing and digging activity of some desert animals on the spatial variation of erosion rates over arid limestone slopes. Such activity provides loose soil aggregates which are easier to remove by shallow overland flows, than is the compacted and crusted loessial soil.In order to study the regional extent of available sediment amounts produced by the biological activity, six plots were selected in the northern Negev in the range of 65 mm to 310 mm average annual rainfall amount. All plots had the same, north facing, aspect and the same lithologic composition. Their size varied from 1110 m2to 5470 m2. Available sediment produced was found to vary from 3 g to 70 g/m2, increasing with rainfall amount. The distribution of available sediment within each plot was not spatially uniform depending greatly on the spatial distribution of bedrock surfaces and soil cover. The overall possible influence of the biotic activity on short term cycles of soil erosion over limestone arid slopes in the Negev is discussed.

ISSN:0197-9337    

DOI:10.1002/esp.3290060304

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractIn mixed oak‐beech forests in the undulating Keuper region of Luxembourg extensive areas of the forest floor are litter‐free or covered with worm casts during many months of the year. This creates an opportunity for splash erosion or erosion by (saturation) overland flow. A systematic investigation of the occurrence and seasonality of the litter‐free areas resulting from the action of the earthworm speciesLumbricus terrestris, L. was undertaken in a forest with poorly to imperfectly drained, silty clay loam soils. This forest exhibits microtopographic depressions of a few hundred square metres which are damper than the immediate surroundings and which seem to favour the activity ofL. terrestris.A vegetation survey showed that the depressions also have a slightly different vegetation from the immediate surroundings. The activity ofL. terrestris, which pulls leaves from the surface into its hole, was followed by establishing 11 plots, 5 × 5 m in size, and surveying these with monthly intervals during a year. The percentage of bare soil ranged from zero during the winter for all plots to a maximum of 60 per cent in July and August for some plots. Rates of leaf removal were found to follow trends in soil moisture content. The relationship observed between the occurrence of bare soil and composition of the understorey vegetation allowed the vegetation map of the forest to be used to estimate the area of exposed soil.The effects of the cast producing speciesAllolobophora nocturna, Sav. andA. longa, Ude. were studied in a mixed oak‐beech forest with sandy loam to sandy clay loam soils. These soils are moderately well drained. Cast production was measured within a fenced‐off area of 50 × 45 m, in which 10 plots of 1 m2each were located at random. A fine nylon netting 30 cm above the soil surface prevented splash erosion of the newly formed casts between the monthly visits. The cast material was collected, dried and weighed. Splash erosion of the casts was investigated with 50cm high splash collectors. The percentage of bare soil in front of the splash boards was estimated from photographs. From the limited data available the yearly rate of cast production appears to be approximately 1.5 kg/m2(15 ton/ha). No significant correlations were obtained so far in most cases between amount of soil caught in the splash traps and percentage of soil covered with

ISSN:0197-9337    

DOI:10.1002/esp.3290060305

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

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 variabl

ISSN:0197-9337    

DOI:10.1002/esp.3290060306

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractFied observations on Rwaza Hill near Butare (Rwanda) revealed the nearly omnipresence of small natural terracettes, developing as a result of superficial slips and accelerated creep movements. On the steepest slope under study, the humic A‐horizon of the soil profile migrated downslope over a mean distance of 14.5 cm from October 1977 till October 1978.A high hydraulic conductivity horizon, displaying low cohesion and consistency characteristics as compared with overlying and underlying material, is developed at the base of the sliding soil.Planar slides, as well as rotational slips occur, the location of failures being determined by the presence of this plane of weakness.Generation of basal interflow in an artificial soil column showed that the state of failure is preceded by localized rheological creep of a plastic viscous soil material, undergoing seepage pressur

ISSN:0197-9337    

DOI:10.1002/esp.3290060307

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractLaboratory experiments, based on the theory proposed by van Heerden (1967) that net splash discharge equals the difference betweenyMiViandmiyi, whereMandYdenote downslope masses and projected distances andmupslope projected distances and masses, demonstrate that the work done by splash is a function of the slope angle to (sin a)1.9.Net discharge of sediment (q) therefore increases to (sina)0.9, It is equally a function of the susceptibility to splash erosionK, which is a complex function of the moisture content of the sands and their grain size distribution.The technique proposed for the assessment of the mean projected splash distances is rapid and gives very accurate results. When carefully applied, it can also be used for fine material like, for example, loess.The splash board technique which is currently used for many field experiments, provides none of the basic information necessary for establishing a discharge‐slope relationshi

ISSN:0197-9337    

DOI:10.1002/esp.3290060308

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

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

ISSN:0197-9337    

DOI:10.1002/esp.3290060309

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThe drop test for aggregate stability results in a distribution of destroyed aggregates with increasing drop number. The influence of prewetting time on drop test results is considered. Secondly new indices to describe the drop test results and modifications of the drop test are suggested to avoid undue influence of small numbers of very stable aggregates, and to shorten the test procedure.

ISSN:0197-9337    

DOI:10.1002/esp.3290060310

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThe effects of soil crusting in Belgium are particularly conspicuous on the loamy plateaus and hill‐regions of southern Flanders, Brabant and Hesbaye. Field observations, made at the end of rainy winter seasons, permitted the making of a simple distinction between: (a) ‘stable’ soils showing crusting on less than 50 per cent of their total surface, without any evident slope wash, and (b) ‘unstable’ soils, crusting over more than 50 per cent of the total surface, with evident rainwash and basal colluviation.The Atterberg limits have been examined for both soil types. It was found that the upslope part of the liquid limit curves, in the range of low consistencies (high water contents), is steeper for stable than for unstable soils. So a distinctive consistency index C2–10was deduced from the liquid limit curves, which may be used for prediction of the relative sensitivity of topsoils for crusting. Stable, well‐structured clods are more hydrophobic than unstable material. This was made clear by wettability tests under a rain simulator. Therefore more water must be added to remolded, stable material to lower its consistency, as is shown by the liquid limit curves.Crustability decreases and C5–10values increase with increasing clay and organic matter contents, as one would expect. Stable soils are well aggregated. But rain simulator tests also showed that the detachment of this material by raindrop impact is high. Therefore, crumbs and clods of stable soils are relatively more sensitive to splash erosion. Their erosion results from the ejection of stable aggregates. Clods of unstable topsoils are compacted and flattened by raindrop impact, which causes internal liquefaction.Micromorphological analysis indicates that typical stable topsoils originate from well‐structured Ap‐horizons and from Bt‐horizons of grey‐brown podzolic soils (Alfisols). Laminated silt and mudcrust fragments characterize unstable topsoils which originate, at least partly, from slopewash deposits. The external stability of both stable and unstable clods is increased by compaction and by surficial concentration of gravel, coarse sands, root and other plant fragments. Thin sections of unstable material show the internal collapse of structures, due to liquefaction.A clear distinction must be made between the structural stability and the

ISSN:0197-9337    

DOI:10.1002/esp.3290060311

出版商:John Wiley&Sons, Ltd    

年代:1981

数据来源: WILEY