Incipient motion conditions for single rockfragments in simulated rill flow
This paper examines incipient motion conditions for single rockfragments in simulated rill channels : threshold conditions for rockfragments in rill flow will be compared with existing theory (Shields) for channels and rivers.
Soil containing rockfragments: effects on infiltration
Rockfragments in soil: surface dynamics
Infiltration ; Model ; Rock ; Soil ; Soil properties
Procedures for quantifying soil and surface rockfragments are reviewed. Within the soil the physical properties and hydraulic properties that affect infiltration are shown to be influenced by rockfragments. Physical properties discussed are bulk
density, porosity and water content. Hydraulic properties that affect infiltration are water retention, saturated conductivity and unsaturated conductivity. Rockfragments on the soil surface have been reported to both increase or decrease infiltration
Rockfragments in top soils: significance and processes
Rockfragments in soil: surface dynamics
Climatic variation ; Grain size distribution ; Hydrology ; Land use ; Rock ; Soil ; Soil erosion ; Soil properties ; Spatial variation
This introductory paper reviews various aspects of rockfragments in top soils. Such information is required 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 rockfragment content in top soils, the density of soils containing rockfragments, the spatial distribution and movement of rockfragments in top soils, the effects of rockfragments on some key hydrological processes, thermal
Surface sealing as affected by various rockfragment covers in West Africa
Rockfragments in soil: surface dynamics
Africa ; Arid area ; Infiltration ; Model ; Porosity ; Rill wash ; Rock ; Semi-arid area ; Soil ; Soil properties ; West Africa
This paper has two main objectives: to analyse the relations between rockfragment parameters (ground cover, position, size) and sealing for a large range of soils of West Africa which is a region where soils containing rockfragments commonly occur
The effect of rockfragment 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 rockfragments 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 has been constructed for transforming rockfragment content from a by-mass to a by-volume basis
and vice versa. Such a nomogram allows the comparison of data on rockfrragment content expressed in different units.
The relation between surface rock-fragment cover and semiarid hillslope profile morphology
Rock-fragment cover on hillslope surfaces profoundly influences 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. Simple statistical models, based upon hillslope gradient as well as a soil-slope factor were developed and validated for the estimation of percent rock-fragment covers on these units.
Spatial distribution of surface rockfragments along catenas in semiarid Arizona and Nevada, USA
Rockfragments in soil: surface dynamics
Arizona ; Bassin-versant ; Catena ; Domaine semi-aride ; Erosion des sols ; Etats-Unis ; Fragment de roche ; Modèle ; Nevada ; Pente de versant ; Prévision ; Roche ; Sol
Arizona ; Catena ; Forecast ; Model ; Nevada ; Rock ; Semi-arid area ; Slope gradient ; Soil ; Soil erosion ; United States ; Watershed
The major objectives of this study are to determine if a slope gradient-surface rockfragment cover relation exists on various catenas of semiarid Arizona and develop an equation to describe this relation.
The hydrological response of soil surfaces to rainfall as affected by cover and position of rockfragments in the top layer
Rainfall experiments have been conducted in laboratory in order to assess the hydrological of top soils very susceptible to surface sealing and containing rockfragments in different positions with respect to the soil surface. For a given cover
level, rockfragment position in the top soil has an ambivalent effect on water intake and runoff generation. The effects of rockfragment position on infiltration rate and runoff generation are proportional to cover percentage. A simple model, based
on the proportions of bare soil surface, soil surface occupied by embedded rockfragments, and soil surface covered with rockfragments resting on the soil surface, describes the runoff coefficient data relatively well.
Belgique ; Erosion des sols ; Erosion hydrique ; Expérimentation ; Fragment lithique ; Infiltration ; Propriétés du sol ; Ruissellement ; Simulation de pluie ; Sol cultivé ; Splash ; Vitesse d'érosion
In this study interrill laboratory experiments with simulated rainfall for 60 min were conducted to assess the influence of subsurface rockfragments incorporated in a disturbed silt loam soil at different depths below the soil surface
, on infiltration, surface runoff and interrill erosion processes for small and large rockfragment sizes. Although only small differences in infiltration rate and runoff volume are observed between the soil without rockfragments (control) and the one
with subsurface rockfragments, considerable differences in total interrill soil loss are observed between the control treatment and both contrasting rockfragments sizes. This is explained by a rapid increase in soil moisture in the areas above the rockfragments
and therefore a decrease in topsoil cohesion compared with the control soil profile. The results highlight the impacts and complexity of subsurface rockfragments on the production of runoff volume and soil loss and requires their inclusion in process-based
This paper reviews the various effects of rockfragments on soil erosion by water. Since these effects are scale dependent, they are investigated at three different nested spatial scales: the micro-, the meso- and the macroplot. For each scale
the corresponding process mechanism are discussed. Particular attention is paid to the effects of rockfragment cover on the intensity of soil erosion processes. The scatter of the data indicates that a given rockfragment cover can have different efficiencies
The effect of rockfragments on wheat biomass production under highly variable moisture conditions in Mediterranean environments
Rockfragments in soil: surface dynamics
Agropedology ; Biomass ; Catena ; Mediterranean area ; Rock ; Slope ; Soil ; Soil properties ; Soil water ; Wheat
The objective of this study was to document the relationships among biomass production of rainfed wheat and those soil properties that affect water availability such as soil depth, rockfragments, parent material and degree of erosion along
Hydric properties of some spanish soils in relation to their rockfragment content: implications for runoff and vegetation
Rockfragments in soil: surface dynamics
Castilla-León ; Grain size distribution ; Rock ; Runoff ; Soil ; Soil properties ; Soil water ; Spain ; Valencia ; Vegetation
This paper examines the influence of rockfragments on the hydric properties of some Spanish soils and, as far as the present knowledge allows, to draw conclusions on the development of vegetation and on the production of surface runoff.
Element-pool balances in soils containing rockfragments
The quantification of element pools and their changes in time is an important part of the analysis of ecosystems. This quantification is more difficult in soils with rockfragments. Repeated sampling and geostatistical analysis were used to quantify
spatial heterogeneity in rockfragment content. Cs 137 measurements were used to quantify fine-earth contamination of dry-sieved and washed rockfragments because they are nondestructive and allowed for repeated analysis of the same sample. The Cs 137
technique therefore allows an easy and less laborious estimation of the part of other element pools associated with rockfragments than direct measurements.
Effect of rockfragment eccentricity on eolian deposition of atmospheric dust
The aim of this study is to investigate the physical effects of rockfragment eccentricity on the dust deposition mechanism. This was examined in a wind tunnel. All data in this study refer to intial dust deposition (not accumulation), since only
The goal of this paper is to determine the processes and/or environmental controls responsible for the distribution of rockfragments in soils and weathering mantles in the Ouachita Mountains, and the implications for regolith evolution
. The regolith is a dynamic feature, reflecting the influences of vertical and horizontal processes, of active weathering at the bedrock interface, and of surficial sediment movements. The role of trees in redistributingrock fragments suggests that significant
Field-scale estimation of the volume percentage of rockfragments in stony soils by electrical resistivity
Bassin parisien ; Beauce ; Electrical resistivity ; France ; Geophysics ; Model ; Quantitative analysis ; Rockfragment ; Soil ; Soil properties ; Soil water ; Stony soil
Analyse quantitative ; Bassin parisien ; Beauce ; Eau du sol ; Fragment de roche ; France ; Géophysique ; Modèle ; Propriétés du sol ; Résistivité électrique ; Sol ; Sol pierreux
This paper presents a method that uses field spatial electrical resistivity measurements to determine the volume proportion of rockfragments. Based on the hypothesis that the electrical resistivity signal noise increases as the proportion of rock
fragments increases, a model was developed that uses the standard deviation of the apparent electrical resistivity measurements over a small area as an indicator of rockfragment contents. The model was tested on 3 study areas of several hectares containing
soil units with varying quantities of rockfragments in the Beauce region (Villamblain, France). The developed model strongly depends on the water content in the soil and the rock type and must be calibrated in each context. Nevertheless, estimations
of the rockfragment content in stony soils can be performed efficiently in the surface horizon as well as all along the soil profile.
Spatial distribution of rockfragments in cultivated soils in northern Ethiopia as affected by lateral and vertical displacement processes
Distribution spatiale ; Domaine aride ; Domaine semi-aride ; Désertification ; Ethiopie ; Fragment de roche ; Pente de versant ; Pratique culturale ; Ruissellement ; Sol ; Sol cultivé
Although, in semi-arid environments, rockfragments at the soil surface and within the topsoil play an important role in desertification control, little is known about their spatial distribution. Therefore, this study analyses spatial patterns
of rockfragment cover along catenas, and the vertical variations in volumetric rockfragment content in soil profiles in the highlands of Tigray, northern Ethiopia. Natural and anthropogenic processes inducing these patterns are assessed.
Effect of rockfragments on eolian deposition of atmospheric dust
Rockfragments in soil: surface dynamics
Aeolian dust ; Aeolian features ; Experimentation ; Rock ; Spatial variation ; Wind speed
The effect of rockfragment 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 was measured separately. Air flow separation seems to play a primary role in the spatial distribution of dust deposition within a rockfragment field
This paper reports the results of a series of experiments on the downslope movement of rockfragments due to trampling by sheep and goats on a scree slope near Aglasun, Turkey. The experimental results are used to obtain a first estimate
on the intensity of the process which can then be compared to the reported intensity of other processes causing the movement of rockfragments on steep slopes. Furthermore, the effect of rockfragment movement on downslope and vertical sorting are analysed.
The relationship between gradient and the size of rockfragments on debris slopes on dolerite-capped inselbergs in the southern Orange Free State
A low correlation was found between slope angle and size of rockfragments on dolerite capped inselbergs, due to the slow rate of creep and rapid mass movement of larger fragments. - (AJC)