Soil Erosion Studies Research Articles

Rates and predictability of ephemeral gully erosion in two contrasting environments

Summary Ephemeral gully erosion in agricultural land is an important source of sediment that is frequently being overlooked and not accounted for in soil erosion studies. However, there is field evidence that ephemeral gully erosion is responsible for significant soil losses. On the other hand, little is known about the factors controlling ephemeral gully erosion. In addition, the relative contribution of ephemeral gully erosion to total sediment production in agricultural catchments has not been assessed. The aim of this study is to assess the relative importance of ephemeral gully erosion in two different environments. In this study we use aerial photographs to estimate the relative importance of ephemeral gully erosion in topographically defined flow paths in the sediment budget of some study catchments. These study catchments are located in Southern Portugal with a dominance of lithosols and Central Belgium where loam and sandy loam soils prevail. The field data indicate that erosion in topographically defined drainage lines is the dominant sediment source and causes the major erosion threat in the loam belt of Belgium and for the stony soils in the Alentejo region of south Portugal ; the ratio between the soil loss due to ephemeral gully erosion and rill- interill erosion ranges between 0.4 and 2.3 for the Belgian study sites and between 4.5 and 5.2 for the Portugese catchments. Therefore, the importance of erosion in drainage lines has to be taken into account when planning erosion control measures at the catchment scale. The observed pattern of ephemeral gully erosion can not be explained by using the available rill erosion equations. However, in the loamy region of Belgium the pattern of ephemeral gully erosion can be predicted by using the product of upslope contributing area (A) and the slope gradient (S) which is a measure for the erosi vity of the concentrated flow. In Portugal however, the pattern of ephemeral gullies can be predicted by a combination of A. S (measure for the erosivity of the overland flow) and a measure of soil saturation (ln(A/S)). The soil profile is not very deep and is overlaying an impermeable rock layer. These results indicate that erosion in topographically defined concentration lines in Belgium is mainly the result of Hortonian overland flow while in Portugal soil saturation and related seepage forces seem to be the dominant incision mechanism.

Modelling overland flow with seepage

The hydraulics of flow in thin sheets on the soil surface during rainfall is an essential component in the study of soil erosion and conservation, design of surface drainage systems and in the solution of sedimentation problems. Overland flow conditions are significantly affected by infiltration (exfiltration) and percolation through the soil, both varying in time and space. A time-dependent model developed for analyzing the problem of overland flow on infiltrating surfaces is the subject matter of this paper. Infiltration (exfiltration) is computed using a finite element submodel for Darcian flow through porous media. The computed flux across the soil surface becomes input to an overland flow submodel which uses a combination of the finite element and finite difference techniques. The computed depths of overland flow and water table positions in the soil layer are compared with experimental results.

Soil erosion in developing countries: where geomorphology fears to tread!

Geomorphology claims an expertise in the study of soil erosion and the development of conservation solutions. Yet what are presented as “facts” about erosion, especially in developing countries where the need for conservation is greatest, is usually unhelpful and sometimes wrong. To understand why the scientific message becomes distorted, geomorphologists should see themselves as actors on a political economic stage, constrained in their role by ideological modes of analysis which themselves shift as science adopts particular ways of promoting itself. The answers given by geomorphological analysis are as much a product of ideology as they are of the process being studied. As applied scientists, geomorphologists could assist their cause greatly by providing quality information on erosion process rates and their impact in a timely and applicable way. Descriptive and predictive models hold scope for extending geomorphological information beyond empirical confines. Examples throughout the paper are drawn from projects in South Asia, South America and southern Africa.

A review of physical management for crusting control in Australian cropping systems - Research opportunities

Soil surface crusting has severe agricultural and environmental effects. In Australian cropping areas, many studies have dealt with chemical treatments (as reviewed by Chartres 1992) but less emphasis has been focussed on physical management practices. The present review deals initially with 30 papers which involve reduced tillage, stubble retention and seedbed formation. Conservation practices have usually been analysed by their effects on soil properties, soil erosion and crop yield rather than by their specific impact on crust development. Moreover, the effects of reduced tillage and stubble retention on crusting have not been determined in most studies. Seedbed formation (e.g. the Tatura system), however, has been shown to be an effective physical management practice for crusting control. Many stability tests have been developed in Australia and used worldwide. Choice of the most relevant predictive test, as well as selection of the most suitable control technique, actually requires a good knowledge of the processes which can be involved in crust formation according to the soil, climatic and management conditions. The results of this review, which deals with 95 papers, suggest a few research opportunities, i.e. (i) furthering of knowledge about the different processes involved in crust formation under various cropping environments, (ii) monitoring soil strength according to crust development, (iii) development of field methods for the assessment of crust development, (iv) development of quantitative models consistent with recent qualitative crusting models, (v) development of methods for the determination of crust development at the field scale rather than small plot scale. Finally, this review recommends to integrate soil surface crusting studies and soil erosion studies.

A erosão dos solos no contexto social

This paper aims to outline the need to include the social, economic and political issues on soil erosion studies. Therefore, the adoption of soil conservation strategies should take into consideration these issues. The paper also outlines the soil erosion problem, the political components of soil erosion, soil conservation policies, and finally shows why most soil conservation policies have failed, in developing countries, due to the traditional approaches used in most soil erosion and conservation programmes. Some alternative approaches are proposed, to deal with the problem, in order to reach sucess.

Application of the Caesium-137 Technique in a Study of Soil Erosion on Gully Slopes in a Yuan Area of the Loess Plateau Near Xifeng, Gansu Province, China

The caesium-137 technique has been used to derive hitherto unavailable information concerning erosion rates on gully slopes in a yuan area of the Loess Plateau in Gansu Province, China. The patterns shown by the caesium- 137 inventories were used to interpret the dominant erosion processes operating on cultivated and uncultivated land. These patterns demonstrate the importance of tillage redistribution and water erosion on cultivated terraces and suggest that both wind and water erosion processes operate on grassland areas. Rates of erosion derived from the caesium-137 inventories for the sites on uncultivated land indicate that the estimate of 61 km-2 year-1 provided by the local soil conservation station may be a serious underestimate, although the data do confirm the importance of full vegetation cover in controlling erosion. The erosion rates derived for terraced cultivated sites are in line with published estimates. Two terrace types were examined and these were characterized by widely divergent net erosion rates, indicating that narrow-strip terraces cultivated parallel to the contour should be used where possible, because these offer a clear soil conservation benefit.

Application of the Caesium-137 Technique in a Study of Soil Erosion on Gully Slopes in a Yuan Area of the Loess Plateau near Xifeng, Gansu Province, China

Application of the Caesium-137 Technique in a Study of Soil Erosion on Gully Slopes in a Yuan Area of the Loess Plateau near Xifeng, Gansu Province, China

CONTRIBUTIONS ON THE PHYSICAL GEOGRAPHY OF TROPICAL AFRICA

ABSTRACTOf the various aspects of physical geography on tropical Africa, geomorphology appears to have received the greatest attention both in depth and spread of research efforts. Several themes have been developed, among which are individual landform studies with emphasis on the description and explanation of the origin of several landforms, the most important being inselbergs. Applied geomorphology with emphasis on accelerated soil erosion is also an important theme. Up to the 1960s research was generally descriptive and speculative, but with the advances in soil erosion studies in the USA and South Africa, researchers have embarked on programmes involving the measurement of runoff, soil loss, and the determination of several indices of rainfall erosivity and soil erodibility. Coastal studies have also received considerable attention. While earlier studies were largely descriptive, recent studies involve the application of sedimentological principles. Wave parameters and beach profiles are being quantified to facilitate the quantitative study of coastal processes. Palaeogeomorphology was largely focused on the study of the morphology of old sand dunes in the current Sahel zone, on past lake levels and on the formation of stonelines. However, current efforts have moved on to the significance of palaeo deposits for purposes of mineral exploitation. Possibly the most significant new theme relates to hydrology and fluvial studies. Current research efforts in these areas include detailed morphometric analyses of small drainage basins, instrumentation and measurement of stream and sediment discharge, and detailed studies of basin topographic attributes. The paper concludes that future efforts should focus more on empirical studies so that physical geographers can make a fundamental impact on the development of the discipline in tropical Africa.

Use of fallout radionuclides as indicators of erosion processes

AbstractThe different depth penetration characteristics of 137Cs, 7Be and 210Pb excess in undisturbed soils can be used to identify erosion processes by analysis of sediments derived from surface erosion. Caesium‐137 concentrations (half‐life 30 years) typically decrease to half the surface value at between 30 and 50 mm. Beryllium‐7 (half‐life 53 days) has half‐penetration depths of between 0.7 and 10 mm, whereas 210Pb excess (half‐life 20.2 years) has half‐penetration depths between 10 and 30 mm. Experiments designed to determine the applicability of these depth penetration characteristics to soil erosion studies are reported. Surface runoff was artificially generated at two locations in a grazed paddock using a rainfall simulator. Suspended sediment was extracted from runoff and analysed for natural and artificial gamma emitting radio‐nuclides. Suspended sediment derived from sheet flow contained initially high values of 137Cs, 7Be and 210Pb excess. As the experiment continued 137Cs concentrations remained high, but 7Be and 210Pb excess value decreased with time. This is interpreted as indicating a change from sheet dominated erosion to rill dominated erosion. During a second experiment artificial rain was allowed to fall onto an eroded gully wall. The derived suspended sediment contained no detectable 137Cs, 7Be or 210Pb excess. Overland flow from above the gully wall was then allowed to run down the gully face and mix with the water falling directly onto the gully wall. There was no detectable change in the radionuclide signature, showing that the gully wall was the predominant source of sediment. This was tested independently by mass balance and 226Ra to 232Th ratios. The good correlation between 210Pb excess and 7Be at this site suggests that the differential technique described here may be applicable over time‐scales longer than are possible with 7Be. It may therefore be practical to examine catchment erosion history through analysis of 210Pb excess and 137Cs in sediment cores.

Application of GIS methods in soil erosion modelling

Soil erosion studies are of great importance, not only from a scientific, but also from a practical point of view. The most widely used assessment method is the application of the Universal Soil Loss Equation (USLE). Three calculation methods are shown in the paper. The first method is only based on the USLE, whereas the two other calculation methods represent different estimations of soil loss by the USLE. In each case, soil loss assessment was carried out by GIS methods. ARC-INFO is used for the storage of the data layers on each factor controlling soil erosion. The main advantage of the GIS methodology is in providing quick information on the estimated value of soil loss for any part of the investigated area. The results obtained by the different calculations are slightly different. An evaluation of the results and of the methods is given in the discussion.

Comparison of major and trace components of Chinese and Canadian soils

INAA was used to determine 32 major and trace elements in 21 soil samples collected from the Loess Plateau, China, and Ontario, Canada. The elemental concentrations determined in different layers of each soil, have been used for comparison in order to find out the general characteristics and any significant differences between Canadian and Chinese soils which developed from similar parent materials. This data can be useful to pedologists and geochemists to study the elemental behaviours and the influences of climate and environment on soil formation. Effort is directed to applying a statistical factor pattern recognition method to these soils for possible use in future soil erosion and transport studies in China. From this study, four soil factors were resolved each for the Chinese and Canadian soils.

L'érosion des sols cultivés dans la région de La Flèche. Le rôle de l'évolution du paysage rural et des façons culturales (Soil erosion near La Flèche, Sarthe, France)

Abstract. - A study of soil erosion near La Flèche (Sarthe, France) reveals that the processes of ablation (rill-interril, gully erosion) and accumulation, are located in a way governed by topography. But, the present increase in activity of erosion is linked to restructuring of the farmland and changes in land use and practices, motivated by economical reasons. This paper contents a case study of a catastrophic event.

A case study of soil erosion on frozen ground in the river Lärjeån valley, NE Göteborg, SW Sweden

A case study of soil erosion on frozen ground in the river Lärjeån valley, NE Göteborg, SW Sweden

Probing the environment with accelerator-based techniques

Natural and anthropogenic events are changing atmosphere, water, soil and other parts of our planet. Advanced analytical techniques based on particle accelerators can provide useful tools to characterize samples of environmental interest. For example, accelerator mass spectrometry (AMS) is used to detect geological tracers and chronometers, such as 14C, 10Be, 36Cl and 129I, present at ultratrace levels in the environment. These long-lived isotopes are useful for the study of soil erosion and salinization, ground water management and nuclear waste disposal. Another accelerator-based analytical technique, synchrotron-radiation-induced X-ray emission (SRIXE), can be used to study the microscopic distribution of heavy metals and other trace elements in the environment. SRIXE microprobes are being developed to map trace elements in individual micron-size particles and micro-organisms.

Design and operation of a rainfall simulator for field studies of runoff and soil erosion

The present paper describes the design, construction, calibration and operation of a spray rainfall simulator, and the plot equipment for field studies of soil erosion processes generating solutes and sediments subsequently transported by runoff. Selected rainfall intensities of 48 and 58 mmh −1 are representative of storm events of 15 minutes duration and of the maximum intensity encountered in the middle section of the Ebro valley. The drop size distribution of the simulated rainfall is close to that recomended by BUBENZER (1979). For D 50, fall velocities obtained by operating pressures of 29.4 and 58.8 kPa represent between 85 and 97% (rainfall of 48 mmh −1) and between 86 and 98% (rainfall of 58 mmh −1) of their terminal velocity. According to the sprinkling height, average kinetic values are 13.10 Jm −2mm −1 for rainfall of 48 mmh −1, and 13.00 Jm −2mm −1 for rainfall of 58 mmh −1. Application of simulated rainfall for 15 minutes proved sufficient to obtain directly applicable data.

New Technique for Measuring Volumetric Shrinkage in Soils

AbstractVolumetric shrinkage in soils is an important physical parameter used in soil erosion and soil mechanics studies. The American Society for Testing Materials D427 method for determining volumetric shrinkage was modified using a less toxic silicone‐mineral spirits mixture instead of liquid Hg. The silicone‐mineral spirits method yielded the same results in shrinkage as measured by the Hg method for a wide range of soils containing between 22 and 48% clay. Use of the silicone‐mineral spirits mixture decreases safety hazards associated with liquid Hg and is more economical.

Application of a low‐cost database to soil erosion and soil conservation studies in the Awash Basin, Ethiopia

AbstractIn large‐scale land resource planning exercises, Geographical Information Systems (GIS) form a valuable means of storing, retrieving, displaying, and analysing spatially‐referenced data, as well as enabling the simulation of the consequences of various alternative development options. However, at this scale only generalized policies for the allocation of finance can be made, and the implementation of those policies will invariably require detailed evaluation at the local level. This suggests that expenditure on the central planning process itself should be limited, with funds reserved for later site studies. The form of GIS adopted centrally should also lend itself to easy use and interpretation by policymakers and planners. These requirements suggest that GIS development using proprietary off‐the‐shelf database management software may be preferable to high‐technology GIS software. This paper outlines the development of such a GIS, based on dBase‐III‐plus and its internal programming language, in the analysis of problems of soil erosion and soil conservation in the large (110,000 km2) drainage basin of the Awash River in Ethiopia. The methodology employed involves the FAO modification of the Universal Soil Loss Equation, which clearly lacks a secure process basis, but is appropriate for the scale of planning involved and the quality of calibration data available. The GIS is used to map patterns of soil erosion, to identify target areas for conservation on the basis of criteria of sensitivity to land use change, and to assess the costs and benefits of conservation work in those areas. It is suggested that the simple form of GIS involved in this study has much to offer environmental managers in developing countries in the rapid development of plans for soil conservation.

Shallow soil monoliths for laboratory studies on soil erosion from undisturbed soil surfaces

Details of a sampling frame for obtaining 500 mm long, 250 mm wide and 100 mm high soil monoliths for soil erosion studies under laboratory conditions are given. A procedure for obtaining and transporting the monoliths intact to the laboratory is outlined. Preliminary results from tests on the susceptibility of a few soil surfaces to erosion by rain-impacted flow are presented.

A Geomorphological Approach to Soil Erosion Studies in Lesotho

This paper presents, in brief, the research into runoff and soil erosion presently being carried out in the Maphutseng area in Lesotho, Southern Africa. The research has a multilevel approach, i.e....

Rainfall and Runoff Erosion Indices for Eastern Canada

ABSTRACT RAINFALL and runoff erosivity indices for the eastern Canadian provinces of Quebec and Ontario were calculated from the once-in-2 year, 6 h rainfalls. Isoerodent maps were then plotted. Annual erosivity indices which account for winter and snowmelt conditions are also included. A monthly distribution of the erosivity index is presented. Design personnel now have access to more precise erosivity indices, covering a wider geographical location. The availability of the isoerodent maps will enhance the quality of soil erosion and conservation studies in eastern Canada.