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Infiltration is a very complex process. Rock fragments affect infiltration by their presence in the soil matrix and on the soil surface. Procedures for quantifying soil and surface rock fragments are reviewed. Within the soil the physical properties and hydraulic properties that affect infiltration are shown to be influenced by rock fragments. Physical properties discussed are bulk density, porosity...
Field studies on the influence of rock fragments on surface sealing, hence infiltration, remain scarce and contradictory. To document this issue, rainfall simulation experiments were carried out on 37 undisturbed 1-m 2 plots located along a pedo-climatic transect across West Africa. An important part of the variability of infiltration coefficient (R 2 = 0.71) could be explained by...
This introductory paper reviews various aspects of rock fragments in top soils. Such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils. Particular attention is paid to the definition and measurement of rock fragment content in top soils, the density of soils containing rock fragments, the spatial...
The effect of rock fragment content on fine soil bulk density is investigated and a relation is proposed. Such a relation is an extension of an algorithm that allows the estimate of soil bulk density when rock fragments are not present. A comparison between measured and predicted data has been made using the equation proposed here and Rawls' algorithm that calculates fine earth bulk density.A nomogram...
Physical and hydric characteristics of the upper three horizons (average depth of sampling: 0-0.25; 0.25-0.60 and 0.60-1.20 m) of 92 soil profiles of Spain, grouped according to the geological nature of the rock fragments on the soil surface, or in the soil profile, were studied. Mathematical relations were developed to separate the contributions of the fine earth fraction and of the fraction above...
The effects of soil properties that affect water availability to plants such as soil depth, rock fragments, parent material and degree of erosion on biomass production of rainfed wheat were studied on hilly soils under different weather conditions. Total above ground biomass production (TAGBP) of wheat was measured along catenas of marl and shale-sandstone formations in two successive growing periods...
Improved techniques for estimating soil erosion by water have shown that soil surface cover is a major component in the estimate of soil loss. Erosion prediction models require the user to input slope gradient and soil profile descriptions. If equations expressing the relations between slope gradient, soil profile rock fragment content, and surface rock fragment cover were embedded in these models,...
The effect of rock fragments and rock fragment cover on the deposition of airborne dust was examined in a wind tunnel. Four parameters were studied: pebble size, pebble flattening, cover density and wind speed. The effect of these parameters on the deposition of dust on the pebbles, on the deposition of dust between and underneath the pebbles, and on total dust deposition (pebbles + interpebble...
The hydraulics of interrill overland flow on stone-covered desert surfaces depend on the resistance to flow, which may be partitioned into grain resistance, form resistance, wave resistance, and rain resistance. Efforts to model large-scale roughness in open channels suggest that resistance to overland flow on such surfaces is a function of grain Reynolds number, Froude number, flow depth, and the...
This paper reviews the various effects of rock fragments on soil erosion by water. Since these effects are scale dependent, they are investigated at three different nested spatial scales: the microplot (4 x 10 -6 -10 0 m 2 ), the mesoplot (10 -2 -10 2 m 2 ) and the macroplot (10 1 -10 4 m 2 ). For each scale the corresponding...
Theoretical model experiments demonstrate that non-periglacial sorted nets can develop on any piece of unobstructed ground surface that has little or no gradient, if it bears a loose, discontinuous cover of pebble-sized stones and if these particles are moved on the surface in small steps in any direction of the compass with equal probability. The physical causes of these movements are not important...
Rock-fragment covers veneer hillslopes in many parts of the world and influence the operation of hydrologic and geomorphic processes on those surfaces. The purpose of this investigation was to examine the spatial variability of rock-fragment cover on morphological units of hillslopes in southeastern Arizona, U.S.A. Simple statistical models, based upon hillslope gradient as well as a soil-slope...
Eight xeralfs from the province of Jaen in the region of Andalusia (southern Spain) were studied. The micromorphology and mineralogy of the clay and sand fractions from the Bt horizon, among other characteristics, were investigated, and indices of pedogenic evolution, including relative redness index, relative development index of color and the relative development index of color + structure, clay...
As a result of the sea-level drop at the last glacial maximum (about 100-120 m in the South China Sea, and 130-150 m in the East China Sea), the size and configurations of the China Seas changed greatly. The East China Sea with the Yellow Sea and Bohai Gulf was reduced into an elongated trough, while the South China Sea became a semi-enclosed gulf. Due to the southern shift of the polar front in...
Italian badlands are present along the Appennini mountains, with an annual precipitation which ranges from 400 to 1200 mm. The genesis of these badlands has often been studied, whereas current processes and erosion rates have only rarely been examined and measured. This paper describes a preliminary study on a badland developed in temperate mediterranean climate and located in SW Tuscany (Italy)...
Hillslope deposits in northern KwaZulu-Natal, South Africa are incised by gullies (dongas) which expose sequences of buried palaeosols developed within a succession of discontinuity-bounded colluvial sedimentary units. Infilled and buried palaeogully topography attests to at least four geomorphic cycles, comprising gully cut-and-fill and palaeosol formation, on hillslopes in the region during the...
In 1985 a plot study was started on sloping cultivated loess soils in South-Limbourg (The Netherlands) to evaluate the effects of various cropping systems of fodder maize on runoff, soil loss and crop yield under natural rainfall. To monitor degradation of soil structure including crust formation, undisturbed vertical samples (15 7 cm) for soil micromorphological analysis were taken of the top...
Stratigraphic differentiation of Quaternary coastal sedimentary sequences is frequently based upon the recognition of individual palaeosols. A number of assumptions are commonly made in the compilation of such lithostratigraphies; first, that the development of soil profiles (spodosols) within coastal sedimentary sequences occur within stable sedimentary units and second, that one soil profile equals...
We have determined both morphological and analytical soil profile and horizon development indices for seven fluvial terrace soils of Holocene to Middle Pleistocene age in relation to the sandy gravel parent material. The relationship between age of fluvial terrace soils and morphological and chemical indices of horizons and their depth indicates two main trends: (i) as soil age increases, index values...
Surface runoff and sediment yield in the grey dunes along the Dutch coast are rare events restricted to conditions of water repellency in summer. The sediment moves in mudflow-like tongues. From March 1989 to December 1990, weekly surface runoff and sediment yield have been measured on an experimental plot, along with a number of meteorological parameters. Rainfall intensity is more important than...
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