ISSN:0197-9337    

DOI:10.1002/esp.3290090602

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractTwenty soils from the Leuven region were tested in the laboratory with a rainfall simulator. Their texture varied from loam to loamy sand. On the basis of the results obtained, they were classified as a function of the runoff and splash erodibility. For every soil, several properties were determined and tentatively used to explain the classifications based on the runoff and splash erodibility.Significant negative correlations were found between silt content, aggregate stability, C5–10index, water content at saturation, and cohesion on the one side and erodibility on the other; a positive correlation was found between sand content and erodibilit

ISSN:0197-9337    

DOI:10.1002/esp.3290090603

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractBlowouts are the main feature of wind erosion in the dunes along the Dutch coast. A number of characteristics, such as their growth against the prevailing wind and the spontaneous stabilization when certain dimensions are reached, are believed to be caused by a prominent quality of the southwest wind,viz.its gustiness. This hypothesis is tested in a two‐dimensional computer model which simulates the effect of wind gusts on a sandy surface along the main axis of the blowout. A number of constraints based on field observations are built into the model. The results closely resemble the longitudinal section of the blowou

ISSN:0197-9337    

DOI:10.1002/esp.3290090604

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractThe main characteristics of river flow and grainsize in a bend of the sand bedded meandering river Dommel, The Netherlands, are presented. Measurements were carried out at a relatively low discharge in a sharply curved bend following a long straight reach. In the studied bend, secondary circulation is restricted to the thalweg area; only in the downstream part of the bend it exists over the entire cross‐section. Therefore, on the entire pointbar platform, which comprises the larger part of the bend, the median sedimentation diameter of the bedload material is governed by the distribution of the longitudinal components of the bed shear stress onl

ISSN:0197-9337    

DOI:10.1002/esp.3290090605

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractIn earlier papers the authors discussed several micromorphological and textural characteristics of loamy afterflow deposits derived from loess material and formed during overland flow without splash. This discussion is completed by considering the critical load concentrationsccrfor the start of sedimentation, taking into account the hydraulic properties of laminar flow. Furthermore, a remarkable combination of clayey and medium coarse, sandy laminae was observed in the deposits produced under laboratory conditions. Mechanisms are proposed to explain the affinity of these fractions for simultaneous deposition.When laminated silt loam deposits are found in the Pleniglacial Middle loess deposits in the southern part of The Netherlands or in the Belgian Hesbayan loess, showing structural modifications, for example cracks formed after sedimentation, it is not always clear whether these modifications were the results of cold or relatively warm conditions. This paper describes micromorphological and laboratory investigations aimed at identifying criteria representative of warm conditions. The experiments examined the effect of drying on the structure of laminated silt loam deposits produced by afterflow and enabled the characterization of the modifications formed.Drying could be done at room temperature, with circulating warm air, or at temperatures below 0°C. Elsewhere (see Coutard and Mücher, 1985), the influence of drying at temperatures below 0°C on the structures of an afterflow silt loam deposit will be discussed.In comparison with the deformation in laminated silt loam deposits due to freeze‐drying, these new formations are small and have only locally influenced the sedimentary structures. These structure modifications are:formations of cracks dominantly in clay layers and less (about 25 per cent of the cracks) in very fine silt layers, consisting of grains smaller than 10 μm in diameter, with only very locally deformations of the laminated structure;only incidentally the cracks are partly refilled by a subsequent overland flow deposit, mostly only followed by sealing of cracks;only incidentally the cracks are partly refilled by a subsequent overland flow deposit, mostly only followed by sealing of cracks;curling or argillaceous laminae, maximum 5 mm in upward direction;only very locally, formations of the tiny waved laminae, with a vertical amplitude between 100 and 400 μm, in combination with the occurrence of ve

ISSN:0197-9337    

DOI:10.1002/esp.3290090606

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractOn many more or less loamy soils, rill erosion is reported to start on slopes that are equal to or steeper than 2–3°; critical Froude numbers for the start of rill wash on these slopes vary between 2·0 and 3·0. This explains why colluvial deposition often occurs on slopes below 2–3°, when water spreads out at the downslope extremities of the rills.The critical hydraulic conditions for loess loam deposition were tested in the laboratory for slopes of 0·5° and 2°, applying unit‐discharges (q) up to 10 cm2/s. It appeared from these experiments that for afterflow, without raindrop impact, deposition starts for critical load concentrations (ccr) varying between several g/1 and about 60 g/l. Under rainccramounts to a minimum value of 100–125 g/l and it increases when the runoff film becomes thinner. Nevertheless, deposition in pluvial runoff is also possible, as was the case during the Weichselian, according to data from quarries in Belgium and in The Netherlands.A modified Kalinske equation is proposed forccrprediction, with the introduction of a typical empirical coefficientCrand considering such factors as shear stress and mean particle size. Massive sedimentation may occur when it stops raining and afterflow starts, sinceccrvalues are then much lower. It is shown from the Shields' diagram that loamy suspensions are more sensitive to sedimentation than sands

ISSN:0197-9337    

DOI:10.1002/esp.3290090607

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractField experiments have been done on simulated flows over different rough pre‐rill and rill bed surfaces. The purpose of the experiments was to evaluate the hydraulic roughness properties of these bed surfaces. Conventional equations describing the relation of the resistance coefficient to the Reynolds number for flow in closed conduits or open channels can also be applied to shallow flows provided the boundary values of the Reynolds number, which discriminate between the various flow regimes, are adapted. When the Reynolds number is less than 100 the flow regime is laminar. Above this figure the flow is either transitional or turbulent, depending on the roughness of the bed surface. The degree of turbulence can be deduced from a morphological description of the pre‐rill and rill bed surface roughn

ISSN:0197-9337    

DOI:10.1002/esp.3290090608

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractIn this paper, the authors present the results of both macroscopic and microscopic investigations on structure development created by repeated ice lensing in various loamy experiments. Experimental data are compared with observations performed on active forms in High Arctic and Alpine Mountain environments. Those observations are also compared with phenomena observed in fossil periglacial formations of Western Europe.Platy and short prismatic structure formation is bonded to the hydraulic and thermal conditions during ice segregation. When a long series of alternating freezing and thawing affects platy structures, the fabric evolves, also being influenced by slope and drainage conditions: cryoturbations, frostcreep, and gelifluction can appear. They are characterized by specific microfabrics which are better developed with an increasing number of cycles: this is clear in experiments where hydraulic and thermal parameters are better controlled.Vesicles are also a prominent characteristic of the surface horizon in experiments and arctic soils. The genesis of vesicles is discussed on the basis of new observations and is related to the mechanical collapse of frost‐created aggregates under the mechanical work of soil air escape during soil saturation by water at tha

ISSN:0197-9337    

DOI:10.1002/esp.3290090609

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractSimulated raindrops falling in still air have a shape that is mainly determined by surface tension and hydrostatic pressure. Drops released from capillary tips show an initial shape variation ranging from prolate to oblate but eventually this oscillation is damped. At terminal velocity drops have attained equilibrium and have an oblate shape. Measurements of the shape of simulated rain drops produced by capillary tubes were made using a simple, newly‐developed photographic set up. The measurements showed that models describing the oscillation frequency and amplitude of drops falling at terminal velocity can also be applied to the simulated drops. A comparison is made between the shape of raindrops in natural storms and simulated drops. Recommendations are given regarding fall heights in simulation in relation to the drop shape in natur

ISSN:0197-9337    

DOI:10.1002/esp.3290090610

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY

摘要:

AbstractDisplacement of landslide blocks after initial slope failure can be very slow. In most cases movement of the blocks is attributed to sliding along a well‐defined slip surface. It is discussed here whether, in addition to these so‐called plastic movements, (continuous) creep processes are involved in the slow displacement. The study was carried out in the downstream part of the Bonne valley in the French Alps, where landslide complexes have developed in varved clay material. Displacements of landslide blocks were measured during a period of three years. Inclinometer measurements in flexible tubes showed that a creep zone developed above the slip surface in a zone about 1 m thick. These field observations on creep processes were supported by soil mechanical analysis. Threshold values for creep found in the laboratory nearly coincide with threshold values calculated from a field creep model developed by Ter‐Stepanian. During the measuring period ±15 per cent of the displacement of the blocks possibly occurred via continuous

ISSN:0197-9337    

DOI:10.1002/esp.3290090611

出版商:John Wiley&Sons, Ltd    

年代:1984

数据来源: WILEY