High Erosion Risk Research Articles

Soil changes and tree growth in intensively managed Pinus radiata in northern Spain

In intensively managed forest plantations, clear-cutting and intensive site preparation may have negative effects on fundamental soil processes that determine the sustainability of these systems. This study was conducted to evaluate the effects of highly mechanized site preparation—involving the removal of organic residues (humus layer and slash)—on soil properties and tree growth in radiata pine plantations growing on steep forest land in northern Spain. In spite of the high risk of erosion, this type of management is carried out without any consideration for soil conservation. These plantations are growing on acidic soils with low reserves of available nutrients and therefore nutrient deficiencies may occur in the medium or long term. Site preparation caused moderate to considerable soil compaction and the effects were still pronounced after 9 years. As a consequence of accelerated erosion and soil disturbance, significant depletion of soil organic matter, Ca and Mg available nutrients, cation exchange capacity and base saturation were observed after removal of logging residues; in the most severe cases the effects were still detected 9 years after site preparation. Availability of Ca to trees was also reduced. Nine years after site preparation, scalped and ploughed soils also showed decreased microbial biomass, lower microbial activity, and less aerobic and anaerobic mineralizable N. Tree growth was significantly reduced where the logging residues and humus layer were removed, especially when this was followed by deep ploughing. During the 9 years of the study, the mean annual increment of timber volume decreased from 8.4 to 2.4 m 3 ha −1. We conclude that leaving logging residues on site avoids soil compaction, favours nutrient uptake in trees and maintains soil biological properties. On the basis of these results, the retention of logging residues and reduction of soil perturbation during site preparation are highly recommended.

Erosion risk levels at the NW Portuguese coast: The Douro mouth - Cape Mondego stretch

The entire northwestern coast of Portugal is undergoing severe erosion and there are several areas at high risk of erosion. Commonly considered as a problem—because it jeopardizes human development along the coast—erosion is indeed a natural process of sediment redistribution. This paper presents a brief analysis of erosion driving forces and the subsequent state of vulnerability that coastal segments between the mouth of the River Douro and Cape Mondego are facing. The paper also discusses erosion risk levels, low or high, and the subsequent questions whether there are populations, economical assets or natural habitats at risk and/or areas prone to coastal flooding. Main challenges and future trends along the study area are identified in the light of understanding the underlying causes of conflicts and what realistically can be achieved given the morphodynamics and hydrodynamic processes, human development established along this coastal segment and the existing policies.

Expectativa de degradação dos recursos hídricos em microbacias hidrográficas com auxílio de sistemas de informação geográfica

The present work evaluated the expectation of water-courses degradation in Areas of Permanent Preservation (APP), a watershed situated at Jundiaí/SP county. A data base of environmental aspects was elaborated using factors and calculations from the Universal Soil Loss Equation (USLE), in a Geographical Information System (GIS), which allowed the obtaintion of information plans about soil losses and erosion risk. A correlation matrix of the factors of erosion risk, was elaborated accounting for soil use and steepness-slope present in the APP, to evaluate degradation expectation. According to the resulty, 32% of the total area showed high erosion risk, and the APP showed high expectation of water-course degradation. The proposed methodology provided important aid to identify areas with expectation of water-course degradation, being an adequated tool for environmental analysis of watersheds.

Potential impacts of petroleum exploration and exploitation on biodiversity in a Patagonian Nature Reserve, Argentina

Petroleum exploration and extraction are common on the Patagonian steppe, but their impacts on the native biodiversity have not been properly evaluated. We describe both activities in a Patagonian nature reserve and consider their potential impacts on biodiversity. More than 2025 km of seismic lines inside the reserve resulted in 87.21 m2/ha (0.9%) of directly affected land, and 793 fragments of native habitats were defined with a mean area of 1.26 ± 0.74 km2. Vegetation recovery on seismic lines is extremely poor. We discuss the role of seismic lines as barriers to native species, and their significance in encouraging poaching and the expansion of exotic invasive plants. There is a high degree of overlap between current petroleum activities and areas of special conservation concern (high erosion risk, vegetation diversity, abundance of endemic plant species, and habitat quality for native vertebrates). All these have a significant impact on the efficiency of the conservation area and highlight the urgent need to implement appropriate mitigating actions.

The impact of soil properties and topography on drought vulnerability of rainfed cropping systems in southern Spain

The acreage of rainfed almond plantations ( Prunus dulcis (Miller)) in Spain has rapidly increased during the last 30 years, reflecting a tendency towards specialisation in perennial, rainfed crops in many Mediterranean regions. Seminatural vegetation and diverse cropping systems have been converted into monocultures with low tree densities leaving the soil unprotected. This paper illustrates the contrast in water conservation strategies between traditional and modern almond plantations in the Murcia region (Spain), and highlights the impacts of intensification on soil degradation. The role of lateral and vertical redistribution of soil moisture in water conservation will be discussed based on the analysis of soil moisture retention characteristics, temporal variation in soil moisture content and soil moisture patterns. A traditional cereal/almond cropping system typical for marl areas with a subdued relief will be compared to a modern almond monoculture in a highly dissected landscape on slate bedrock. The low water holding capacity of the stony soil in the slate area caused rainfall to penetrate deep in the profile and thus soil moisture fluxes were mainly vertical. Semivariograms of topsoil moisture content after an isolated rain day (19 and 27 mm for the nearest raingauges) demonstrated the differences in lateral redistribution of soil moisture between the cropping systems. A spatial pattern in the marl soil with a range of 69 m was observed, whereas soil moisture in the slate area showed no spatial pattern except for higher values in the narrow valley bottom. The scarcity of rainfall producing lateral redistribution of soil moisture explained the lack of reliable moisture supply in the marl area. This led to very low overall plant densities at 16 trees ha −1, restricted to wetter zones upstream of retention dams. The redistribution of soil moisture by vertical fluxes in the stony soils of the slate area explained the uniform, widely spaced trees at densities of 204 trees ha −1. This study has highlighted the need for rainfall to penetrate deep into the soil to sustain almond monocultures in semiarid climates. However, this requires a loose, bare topsoil between the trees and thus large areas of bare soil are exposed on hillslopes resulting in high erosion risks.

Rill and gully development during an extreme winter runoff event in Norway

Erosion on agricultural fields in Norway has earlier been reported to be mainly sheet and minor rill erosion. Exceptional rainfall events during January and February (230% of 30 years monthly mean) in 1990 led to extreme runoff and widespread erosion also on areas normally not considered to have a high erosion risk. This study presents the results of a field survey in three counties where rills and ephemeral gullies were measured after this event. Shifting weather conditions with freezing and thawing had given frozen subsoil. Topsoil conditions varied from ice- and snow-covered surface to thawed surface with frozen subsoil. In one of the areas with a high clay content, only the upper topsoil layer was unfrozen during this event. Extended sheet erosion and smaller rills occurred. In the southernmost locations, more of the topsoil profile was unfrozen. Combined with a high silt/sand content, more severe rilling and ephemeral gullies developed. Gullies developed down to the depth of the drainpipes in all locations. This erosion equals soil losses of more than 100 tons ha −1 or 8–9 mm soil lost from the entire field area. Different mechanisms for gully development were registered. Gullies developed as enlarged rills with headward migration and sidewall sloughing. Knickpoints in the slope could also lead to gully development. Concentrated water flow entering the field from farmyards, roads, neighbouring fields and woods could be the starting point for uncontrolled rilling and ephemeral gullying. The combination of frozen subsoil, saturated soil with low strength and intense rainfall led to gully development also on areas with gentle slopes, especially sandy soils. Management practices like crop cover, tillage and lack of surface water control highly influenced the development of gullies.

Soil conservation effectiveness and energy efficiency of alternative rotations and continuous wheat cropping in the Loess Plateau of northwest China

Winter wheat ( Triticum aestivum L.) monoculture is common in wheat-growing areas of the Loess Plateau of northwest China. This system is characterized by nearly 3-month summer fallow from wheat harvest at the end of June or early July to sowing in late September. It not only lowers the overall precipitation-use efficiency because of the large amount of evaporation from the bare soil surface during the fallow period but also entails high risk of erosion by summer rainstorms. There is a need to develop more effective cropping systems to replace the current production system. Seven alternative rotations, mainly using wheat, rapeseed, corn, potato, pearl millet, linseed, alfalfa and sweetclover, were established and their use of environmental resources, production performance, energy efficiency, soil fertility sustainability, and soil conservation effectiveness were compared with continuous wheat cropping. The rotations had greater potential use of environmental resources. Despite showing no clear advantage in grain yields, all rotations were significantly higher in total above-ground biomass production and more efficient in energy transformation compared with continuous wheat cropping. After a 3-year cycle, the rotations did not adversely affect soil bulk density but some rotations significantly increased soil water-stable aggregates compared with the initial measurement. For the rotations based on the inclusion of legumes, the availability of N was apparently improved but the total P was substantially reduced compared with the initial measurement and continuous wheat cropping. An assessment of soil conservation effectiveness with a weighted soil conservation effectiveness index (WSCEI) indicated that the rotations performed much better than continuous wheat cropping in conserving soil and water resources. This study also strongly recommend that it is feasible to cultivate winter wheat followed by a 3-month legume fallow crop in year 1 and then a summer crop cultivation in the next. This system provides a soil cover during both erosion-prone rainy periods while leaving the soil bare for about 7 months (October–April) every 2 years. Another alternative is to cultivate winter wheat followed by a 15-month legume crop cultivation in years 1 and 2 and then a summer crop in year 3. This system allows the soil to be covered during three rainy periods while leaving the soil bare for about 7 months every 3 years. As most of this 7-month period is winter with low rainfall (snow) and temperatures below 0 °C, not only is soil evaporation very low but the risk of erosion is also low.

Geomorphological observations and related natural hazards using merged remotely sensed data: a case study in the corinthos area (ne peloponnese, s. greece)

Natural hazards are mostly related to the activation of combined geomorphological and geological processes that control landform development. The study area is located in the NE part of Peloponnese (Corinthos prefecture). It is a typical agricultural area with intense relief, the result of active tectonics and important human intervention. This study demonstrates the benefits from the synergism of SAR data (ERS‐2) and optical data (SPOT2‐XS) in order to highlight the possible natural‐hazardprone areas. These data give different and complementary information since the radar signal depends mostly on topography, surface roughness and soil moisture, whereas the visible/infrared channels provide spectral information mostly on vegetation and land use/cover. The application presented here was focused on the enhancement of the high erosion risk areas, the improvement of the terrain interpretation, the mapping and highlighting of the landform morphology, and a more accurate determination of the main factors that control the flooding risk of Corinthos town.

Lake Toba: Need for an integrated management system

AbstractLake Toba is the largest year‐round lake in South‐East Asia and the largest volcanic lake in the world. The Lake Toba catchment area faces an environmental crisis characterized by widespread deforestation, drought, decline of the water level, water quality degradation, invasive species and loss of biological diversity. More than half of the Lake Toba catchment area is classified as land at high erosion risk. Widespread poverty gives people little room to think beyond day‐to‐day needs and is an instrument for unsustainable methods of fishing and growing food. The Lake Toba catchment area is not managed as an integrated whole, but rather as four separate districts. Guidelines and orders tend to come from the government in Jakarta rather than being developed locally with stakeholder involvement. Differences in approach between government and non‐governmental organizations (NGOs) have resulted in friction and mistrust between the two. Local, national and international NGOs have been the biggest contributors to increasing the awareness of the need for an integrated approach to managing the lake. Technical exchanges with Lake Champlain have facilitated an exchange of experience of managing a large lake watershed, the transfer of low‐cost alternative technologies for managing waste water in small communities and development of new approaches to pulp and paper mills on both lakes. The Lake Toba Heritage Foundation’s priorities include establishing a research and monitoring programme, creating a science and education centre, and developing better coordination among central, provincial and district levels of government.

Modelling soil erosion in tropical environments using remote sensing and geographical information systems

Soil erosion probability maps were produced under various case scenarios by accounting for uncertainties in the data and in the decision rule, using the Universal Soil Loss Equation (USLE), remote sensing and geographical information systems (GIS). This objective was realized by applying the Bayesian Probability Theory within IDRISI, a raster based GIS. The outcomes were two continuous probability soil erosion maps ranging from zero to 1. Comparing these maps with an earlier study indicates that accounting for the uncertainties has, in general, decreased the probability of soil erosion. Based on average readings for specific sites on the maps, increases in erosion risk under the second case scenario have had the highest impact on the highlands that is in the central, eastern, and northern regions of Langkawi Island, Malaysia. Assuming a 10% risk, this impact has increased by 11.98, 11.83 and 5.741% for high, medium and low soil erosion risk areas on the island respectively.

Modelling of vegetative filter strips in catchment scale erosion control

The efficiency of vegetative filter strips to reduce erosion was assessed by simulation modelling in two catchments located in different parts of Finland. The areas of high erosion risk were identified by a Geographical Information System (GIS) combining digital spatial data of soil type, land use and field slopes. The efficiency of vegetative filter strips (VFS) was assessed by the ICECREAM model, a derivative of the CREAMS model which has been modified and adapted for Finnish conditions. The simulation runs were performed without the filter strips and with strips of 1 m, 3 m and 15 m width. Four soil types and two crops (spring barley, winter wheat) were studied. The model assessments for fields without VFS showed that the amount of erosion is clearly dominated by slope gradient. The soil texture had a greater impact on erosion than the crop. The impact of the VFS on erosion reduction was highly variable. These model results were scaled up by combining them to the digital spatial data. The simulated efficiency of the VFS in erosion control in the whole catchment varied from 50 to 89%. A GIS-based erosion risk map of the other study catchment and an identification carried out by manual study using topographical paper maps were evaluated and validated by ground truthing. Both methods were able to identify major erosion risk areas, i.e areas where VFS are particularly necessary. A combination of the GIS and the field method gives the best outcome.

Prioritizing erosion-prone areas in hills using remote sensing and GIS — a case study of the Sukhna Lake catchment, Northern India

Traditionally, assessment of productivity of land took priority over all other aspects of evaluating land use performance. Presently, the effects of land use on the quality of the environment and environmental sustainability of production systems have become the major issues. In hills, the terrain conditions aggravate erosion-induced land degradation. Judicious allocation of available resources for sustainable production requires mapping, monitoring and prioritizing the areas based on their susceptibility to degradation. Remote sensing and Geographic Information Systems are effective tools for inventory, monitoring and management of spatially distributed resources. This paper presents a case study of the 42 km2 Sukhna Lake catchment in the Shiwalik hills conducted for the delineation and prioritization of erosion-prone areas using RS and Geographic Information Systems. Multi-spectral IRS ID-LISS III data acquired in March 1998 was used for the supervised digital classification of the land use/land cover type. The catchment was classified in six land use classes: forest, agriculture, scrub, barren hills, streambed and settlements. These classes were divided into sub-classes based on the cover characteristics. Using the U.S. Soil Conservation Service curve number method, runoff potential of each delineated hydrologic unit was computed in a grid-based analysis using an ARC/INFO GIS. Erosion-prone areas were classified further by integration of a digital elevation model or DEM-derived slope, aspect and flow length. To get an ordered priority of the erosion-prone areas, a cumulative erosion index was computed from the rating given to the three main causative factors, ie, slope, soil erodibility, and land cover, on a scale of 1–7 for each grid. The cumulative index was further classified in four classes for spatial representation of the erosion-prone areas on the catchment map. The study revealed that 32.9 percent of the catchment area is susceptible to high or very high erosion risk and thus has to be managed with appropriate conservation strategies.

Land Use Mapping And Geographic InformationAnalysis Of The Genil-Cordobilla Sub-basin(Mediterranean Area) Of Spain From ThematicMapper Satellite Imagery

Soil erosion is a complex phenomenon of land degradation that is highly significant in a Mediterranean type environment (Lopez Bermudez 1996). Thus, the different characteristics of the physical environment and especially the historic soil and vegetation uses, are considered by the FAO (1977), to be the most relevant factors to be taken into account in this sort of study. Spain's case is especially worrying given that it ranks fourth on the list of European countries with the highest levels of surface erosion, with around 1000 million metric tons, Corine-Cec (1992). Of this, 49% of the country's surfaces shows a high risk of potential erosion, Andalucia being one of the most sensitive regions, Moreira (1987), Bergsma (1980), ICONA-LUCDEME (1988-1989), Albadalejo (1994) amongst others. The area covers approximately 750,794 knf, constitutes part of a Genii river sub-basin in the province of Cordoba (Spain). The present study utilizes highly important up-to-date tools and techniques: Geographic Information Systems and remotely sensed data, which aim to evaluate the changes that occurred in soil use between 1975, 1995 and 1998. The factor of soil protection through vegetation will be monitored from spectral parameters taken into account in this research are the ranges: TM1 to TM7. The changes of land use can be especially observed in olive groves. Management Information Systems, C.A. Brebbia & P. Pascolo (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-815-5

Classification from Landsat TM of Indurated Volcanic Materials (tepetates) of the Mexican Neo‐volcanique Belt

Tepetates, altered indurated and sterile volcanic tuffs, are located among the neo‐volcanic belt in central Mexico. They are divided into three classes according to the erosion level: outcrop tepetates, discontinuous tepetates (in process of erosion), and underlying tepetates (related to fragile areas with high erosion risk). For local communities and peasants, the existence of tepetates is a heavy constraint, with the impossibility to cultivate the land as it is. In order to know the localization and extension of tepetates, we experimented with various classification techniques of a Landsat Thematic Mapper satellite image. Masking techniques were used, assisted both by a DEM and photo interpretation, in addition to radiometric segmentation to obtain a map of tepetates in a study area. The resulting map showed the location of outcrop tepetates well, in agreement with existing soil maps, but underestimated underlying tepetates and high‐risk erosion localities, due mainly to the heterogeneity of the classes at the scale used (30 m pixel).

Assessment of erosion hazard with the USLE and GIS: A case study of the Upper Ewaso Ng'iro North basin of Kenya

The Universal Soil Loss Equation (USLE) was used to predict soil erosion hazard in the Upper Ewaso Ng’iro North basin of Kenya using data from erosion plots and reconnaissance surveys. The R-factor (rainfall erosivity) was determined by extrapolation from the rainfall amount-erosivity relationship, using data from autographic records. The K-factor (soil erodibility) was determined using data obtained by laboratory analysis of soil samples collected from 83 test sites in the basin. The LS-factors (slope length and steepness) were determined from a digital elevation model (DEM) of the basin, while the C-factor (crop and management) was determined from vegetation cover data, obtained from SPOT imagery and field surveys. The P-factor (conservation practice) was estimated from maps of soil conservation, obtained from the Ministry of Agriculture. A raster-based Geographic Information System (GIS) was used to interactively calculate soil loss and map erosion hazard. The results obtained were comparable to measured soil loss values from erosion plots. About 36 percent of the Upper Ewaso Ng’iro basin was predicted to have high risk of erosion, most of this land being in the overgrazed rangelands. Land use and management were the major factors associated with soil erosion, and — to a lesser extent — the topography. Due to the reconnaissance scale of this study there were limitations in determining reliable LS, C and P factors for the USLE. In addition, there is a need for research to determine appropriate P-factors for local soil conservation practices, such as trash lines, fanya-juu terraces and stone lines.

Erosion risk assessment and sediment yield production of the King Talal Watershed, Jordan

King Talal Dam (KTD) watershed is the most important one in Jordan. At its outlet lies the KTD (80 MCM capacity) which serves irrigation purposes in the Jordan Valley. However, the dam suffers from accelerated annual sedimentation. Therefore, this study is directed to assess the erosion risk over the watershed, and to simulate actual annual sediment yield at the dam in order to devise the appropriate conservation practices. Generalized assessment was first conducted over the watershed on the basis of drainage texture, rainfall erosion index (R), and the ratio p2/P. As a result, the watershed is divided into zones of severe, high (gullying), high (overland flow) and low erosion risk. Sediment yield at the dam was evaluated by a simulation model. For model validation the simulation results were compared to the measured values over 12 years period, and a good agreement was obtained in some of the years. The simulation results allow us to assess the application of two practical conservation practices: terracing and plantation of trees.

Soil erosion under different harvesting managements in steep forestlands from northern Spain

In spite of the high risk of erosion, highly mechanized operations, in which humus layer removal and down-slope ploughing are practised, are often employed to prepare steep forestlands for planting. The purpose of this study was to evaluate the effect on soil loss of three post-harvesting management systems usually used in a mountainous region of northern Spain. The techniques evaluated were (a) conventional stem-only harvesting, (b) whole-tree harvesting and humus layer removal and (c) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. Soil erosion was measured in a total of 39 recently clear-felled Pinus radiata plantations over the period between the stand harvesting and establishment of understorey vegetation. They were located on slopes with gradients of between 40 and 50 per cent. For all treatments the associated runoff–rainfall ratios were high, indicating inherent low permeability of the soil. Intense site preparation resulted in considerable decreases in soil organic matter and increases in bulk density, which decreased the hydraulic conductivity and subsequently produced higher runoff. These deteriorations of soil properties delayed the establishment of pioneer vegetation thus extending the period of high erosion. In the ploughed soils, the higher soil erodibility and the removal of slash and vegetation cover resulted in a four-fold increase of soil losses when compared with no mechanical site preparation. The results indicate that, in order to maintain the soil productivity, and for conservation purposes, harvesting management should minimize the soil disturbances and maintain the slash and vegetation cover. Copyright © 1999 John Wiley & Sons, Ltd.

Soil erosion under different harvesting managements in steep forestlands from northern Spain

In spite of the high risk of erosion, highly mechanized operations, in which humus layer removal and down-slope ploughing are practised, are often employed to prepare steep forestlands for planting. The purpose of this study was to evaluate the effect on soil loss of three post-harvesting management systems usually used in a mountainous region of northern Spain. The techniques evaluated were (a) conventional stem-only harvesting, (b) whole-tree harvesting and humus layer removal and (c) whole-tree harvesting and humus layer removal followed by down-slope deep ploughing. Soil erosion was measured in a total of 39 recently clear-felled Pinus radiata plantations over the period between the stand harvesting and establishment of understorey vegetation. They were located on slopes with gradients of between 40 and 50 per cent. For all treatments the associated runoff–rainfall ratios were high, indicating inherent low permeability of the soil. Intense site preparation resulted in considerable decreases in soil organic matter and increases in bulk density, which decreased the hydraulic conductivity and subsequently produced higher runoff. These deteriorations of soil properties delayed the establishment of pioneer vegetation thus extending the period of high erosion. In the ploughed soils, the higher soil erodibility and the removal of slash and vegetation cover resulted in a four-fold increase of soil losses when compared with no mechanical site preparation. The results indicate that, in order to maintain the soil productivity, and for conservation purposes, harvesting management should minimize the soil disturbances and maintain the slash and vegetation cover. Copyright © 1999 John Wiley & Sons, Ltd.

Reduction in soil loss from erosion-susceptible soils amended with humic substances from oxidized coal

Soils that pose high risk of erosion require amendment with either natural or synthetic soil conditioners to reduce soil loss hazards. The objective of this study was to evaluate the potential of using coal-derived humic substances (as soil conditioners) to reduce runoff erosion on erosion-susceptible soils. Surface (0–20 cm) samples of severely degraded soils from Principina in Tuscany (Orthic Xerofluvent) and Bovolone in Venice (Udic Ustochrept) in Italy were used to assess the effects of five rates (0, 0.05, 0.10, 0.50 and 1.00 g/kg) of humic acids (HA) on soil loss and other hydrological parameters. A rainfall simulator was used to apply approximately 40 mm/h intensity rain for 1 h on soil beds of dimensions 2 m × 0.5 m × 0.01 m, packed at a bulk density of 1.20 Mg/m 3 and inclined at a slope of 15%. The amount of soil eroded ( E) and the time to initiate runoff (Rt) and drainage (Dt) were related to changes in the water-holding capacity and aggregate stability of the soils following the HA treatments. In the control treatments, the values of E, Rt and Dt were higher in the Principina than Bovolone soil. Increasing HA rates generally delayed Rt, accelerated Dt and reduced E substantially on both soils. On the Principina soil a reduction of about 36% in soil loss was obtained by adding only 0.05 g/kg of HA (equivalent to 100 kg/ha). On the sandier Bovolone soil, the same magnitude of reduction was achieved with 0.10 g/kg (200 kg/ha) of HA. Improvements in Rt and Dt from the HA amendments explained between 58 and 81% of the variation in E from both soils. Furthermore, improvements in the water retention capacity more than in the aggregate stability of these soils accounted for the reduced runoff erosion. These results show that amending erosion-susceptible soils with low rates of coal-derived humic substances is a potentially effective soil management practice for reducing erosion rates.

Soil erosion from a single rainstorm over an area in East Lothian, Scotland

Abstract. An area of about 24 km2 in arable East Lothian, Scotland, was examined for soil erosion by water following a severe rainstorm in October 1990. Significant erosion was found in only 10 fields out of 26.5 in an area where topography, soils and cropping suggest a high erosion risk. Doubt is cast on some assessments of the widespread risk of significant soil erosion by water in arable areas of the UK.