ISSN:0360-1269    

DOI:10.1002/esp.3290020202

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractThis paper discusses field observations, field measurements, field and laboratory experiments concerning the physical weathering and the erodibility of sandy Tertiary rocks and loess mantles in Belgium. The observed phenomena and the experimental data have been discussed in terms of soil mechanics. Special attention has been paid to crack sets and desquamation in consolidated Tertiary sands resulting from lateral offloading, to the relative high erodibility of glauconiferous sands, and to the sensitivity of loess and loamy soils for solifluction, rainwash and colluviation. A stability index E has been proposed for loamy soils based upon the characteristics of the liquid limit curve. Two‐year observations and measurements at the dune station of Kalmthout have shown how the loess fraction can be transported in a basal drift near the ground, and how rainstorms provoke deflation and rainwash on dunes where gravel is moving in saltation during heavy storms. Litter flow has been found to occur on all actual forested slopes. All these data on morphogenetic processes have led to some considerations of the Quaternary morphological evolution of Lower and Middle Belgium: the modelling mainly by sheetwash of periglacial glacis, the evolution of the Hageland hills and of the Plateau of Brabant, the morphodynamics of loamy slopes, Late Glacial and Holocene dune building, and finally the Holocene evolution of forested slope

ISSN:0360-1269    

DOI:10.1002/esp.3290020203

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractIn the Laboratory of Experimental Geomorphology experiments were carried out on loess from the Pleniglacial A of the Weichselian. Most of the experiments had as their objective determination of the effect of slope angle, rainfall intensity, raindrop impact, added overland flow and concentrations of suspended material, on the erosion and redeposition of loess.At various stages during the experiments, as well as at the beginning and end, undisturbed samples of loess were collected for micromorphological investigation.—Pluvial runoff (overland flow with raindrop impact) supplied with or without terminal runoff, gave rise to laminated deposits, tightly packed and moderately differentiated in size and mineral species.—After flow (the flow that occurs in the field during a short period after rainfall has ceased) and meltwater flow were simulated by terminal runoff. If the discharge and suspended load were moderate (respectively 0.81/min/dm and 20,000 mg/l), the sediments produced were very well laminated, well sorted and minerally differentiated, and loosely packed. In an exceptional case, with a very high discharge (81/min/dm) and suspended solid load (150,000 mg/l), the sediments were virtually unlaminated, and consisted of very loosely packed aggregates, which must have been formed during transport.—Splash (material transported exclusively under raindrop impact) was applied successively to: calcium carbonate rich loess, decalcified loess and Ap‐material from a loess soil profile. In these three sediments no lamination, sorting and practically no mineral differentiation were produced that could be observed in the thin sections. Comparing the laboratory results with the situation in two loess quarries, one near Leuven and one near Tongrinne (both in Belgium), the micromorphological interpretation of the sediments in the field ranged from the very simple to the very complex.—The small quarry near Leuven contained a cross‐section through a gully filled with laminated calcareous loess. This sediment could be interpreted as having probably been formed by pluvial runoff alternating with after flow.—The large quarry near Tongrinne was more complicated. The several deposits here could have been formed under conditions ranging from pluvial runoff alternating with after flow, to splash and/or meltwater flow with high wash‐load concentrations.The micromorphological research suggested that the loess was not only reworked by meltwater but also by pluvial runoff; the latter being probably the most important process, at least during Early We

ISSN:0360-1269    

DOI:10.1002/esp.3290020204

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractIf the hydraulics of a flow is to be understood, then at least a few parameters must be known accurately. When the depth and the unit discharge are measured correctly, many other parameters can be calculated, e.g. the mean velocity of the flow, the friction, the Reynolds Number, the Froude Number, and, if the study is to be connected with erosion measurements, the shear stress. A method is therefore developed for the direct measurement of the depth of disturbed water films, by weighing the entire run; the depth of the flow is thus equal to the weight of the water contained in it, one gram being the equivalent of one cm3, divided by the area of the run. Corrections to the measurement are, however, necessary because the water accelerates along the run to a steady state velocity, because the weight drops due to an acceleration in the gravity field, because the weight of the spattered drops has to be known if simulated rainfall is applied, and because the impact of the drops causes a weight. The accuracy of the method is 10 μ if the flow conditions are not to be studied on too steep slopes and if the discharge used is not too great. The main results are plotted in Figure 6 which combines the formulas for laminar, transitional and turbulent flow that are obtained. A comparison with available literature suggests mat sheet flow can either be laminar or purely turbulent, but that mixed flows prevail on low slopes, under 0.5 per cent combined with greater water depths. Since the flow equations on steep slopes obey physical laws, sin S is to be used instead of S, which stands for tan S.The experiments have shown that the effect of the rainfall impact on the Darcy‐Weisbachfdoes not exceed 20 per cent in the case of laminar flow on gentle slopes. This influence diminishes when the discharge increases, or when the Reynolds Number increases, as well as when the slope angle increas

ISSN:0360-1269    

DOI:10.1002/esp.3290020205

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractIn the gently undulating Keuper region of Luxembourg valley incisions in mixed oak‐beech forests are being widened by a process of soil fall. This process is optimized by a number of ecological conditions. Soil profiles examined in the Deifebaach catchment, located between Larochette and Ettelbruck, generally have an abrupt boundary between the silty surface soil (A2 horizon) and the dense clayey subsoil (B horizon). This boundary is marked by the formation of a dense root mat. The subsoil contains a large proportion of oriented clay and is subject to swelling and also to dispersion. Clay particles translocated downwards increase the density of the subsoil and decrease its permeability. The soils are very poorly drained, being waterlogged for much of the year, and have experienced some fragipan development.When the subsoil is exposed it disintegrates into an incoherent mass of aggregates and recedes beneath the root mat which supports the overlying material until it eventually collapses. The nature and amount of soil fall recession is examined along a 320 m reach of die Deifebaach. It was found that at least 30 per cent of the right bank and 40 per cent of the left bank are subject to recession by soil fal

ISSN:0360-1269    

DOI:10.1002/esp.3290020206

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractThe sediment supply of a first‐order catchment in the Luxembourg Ardennes is considered. In the absence of overland flow the most important process of sediment supply is splash erosion. This is confined to areas of exposed mineral soil produced mainly by the burrowing activity of animals. The amount of splash erosion reflects not only burrowing but also the yearly cycle of litter‐fall and decay. The concentration of suspended material in the catchment river is not related to the discharge but in most cases to rainfall intensity. Turbidity measurements made at 1‐minute intervals showed a considerable degree of detail which illustrated the role of splash in supplying sediment to the river, although other processes can be important. The difficulty of estimating the output of material from a small catchment by means of a simple rating curve is stressed as is the need to consider slope and sediment supply processes in an ecological co

ISSN:0360-1269    

DOI:10.1002/esp.3290020207

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractIn wooded dry valleys in the Luxembourg Ardennes a gravelly and slightly organic colluvial deposit occurs. The depositionary nature of the material is ascertained by its micromorphological characteristics and its position on top of a truncated argillic horizon of an older soil. Pollen analysis revealed the colluvium to have been formed in the last 500 years, the lower 37 cm in the Haarts valley under non‐forest (presumably arable land) conditions and the upper 10 cm under today's oak woodland. A formation of the colluvium by Horton overland flow is ruled out by permeability and infiltration capacity measurements of the forest soil. The importance of rainsplash erosion for the formation of the upper part of the colluvium is demonstrated with simplified Ellison type splash boards. Two modes of transport, induced by raindrop impact, may be distinguished, one through the air (particles up to 6.3 mm) and one across the soil surface (particles up to and above 1 cm). The overall grain size distribution of the trapped soil strongly resembles that of the colluvium, and the gravel sized rock fragments in the colluvium certainly do not exclude an origin by rainsplash erosio

ISSN:0360-1269    

DOI:10.1002/esp.3290020208

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractHydro‐pedological investigations were carried out in a small forested watershed on the Lower Emsian formations of the Lower Devonian in the Luxembourg Ardennes. These rocks consist of weakly metamorphosed shales and quartzites, of which only the shales are undergoing appreciable weathering, and are composed of quartz, sericite, albite and chlorite, with minor amounts of haematite (goethite) and traces of pyrite, rutile and apatite. The alumino‐silicates react with CO2charged water, forming kaolinite, with vermiculite and smectite as intermediate phases and releasing cations and silica for solution. From a hydrological study and a detailed programme of soil, spring and river water sampling the year could be subdivided into three characteristic hydrological periods. The runoff during these periods could be separated into various components, some of which have a characteristic water chemistry. The amount of material removed in solution was 7,448 kg for the years 1973/1974 and 1974/1975 (220 kg/ha/year). The output of material in solution is probably much greater than the output of material in suspension and as bedload. The chemical erosion rate could be calculated with these output data, after making allowance for atmospherically supplied materials and biomass recycling; it amounts to 4,435 kg (131 kg/ha/year), which is 59.5 per cent of the total solutional out

ISSN:0360-1269    

DOI:10.1002/esp.3290020209

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractRainfall simulation is a technique which aids, under controlled conditions, the understanding of a part of the processes involved in water erosion. Simulation requires, that the relevant characteristics of natural rainfall be closely reproduced. Physical limitations and conflicting conditions obstruct the realization of a correct reproduction of all characteristics belonging to different kinds of natural storms.A laboratory rainfall simulator, EROS MII, of the tubing type is under construction. The simulator is composed of 8 plexiglass boxes (50 × 50 × 5 cm) producing rainfall intensities between 1 cm/h and 15 cm/

ISSN:0360-1269    

DOI:10.1002/esp.3290020210

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY

摘要:

AbstractQuantitative procedures are discussed for the simulation of baselevel lowering, weathering, and several denudation processes within the framework of a three‐dimensional model of landform development Net baselevel lowering is modelled as the outcome of the mass balance at the slope foot Bedrock weathering is seen as a function of waste thickness; a distinction is made between mechanical weathering, with maximum intensity on bare bedrock, and chemical weathering, with maximum intensity under a waste cover thick enough to retain sufficient moisture. Denudation processes considered are splash, viscous flow, plastic flow, and wash‐the latter with a submodel for generating a characteristic spatial distribution of relative runoff discharge. Despite the different empirical results and theoretical considerations that influenced the design of the model equations for these denudation processes, all except suspended load wash denudation produce very similar slope forms. It is shown that these seemingly different equations can be interpreted as special cases of a single general denudation equat

ISSN:0360-1269    

DOI:10.1002/esp.3290020211

出版商:John Wiley&Sons, Ltd    

年代:1977

数据来源: WILEY