Fluvial and slope‐wash erosion of soil‐mantled landscapes: detachment‐ or transport‐limited?

Many numerical landform evolution models assume that soil erosion by flowing water is either purely detachment‐limited (i.e. erosion rate is related to the shear stress, power, or velocity of the flow) or purely transport‐limited (i.e. erosion/deposition rate is related to the divergence of shear stress, power, or velocity). This paper reviews available data on the relative importance of detachment‐limited versus transport‐limited erosion by flowing water on soil‐mantled hillslopes and low‐order valleys. Field measurements indicate that fluvial and slope‐wash modification of soil‐mantled landscapes is best represented by a combination of transport‐limited and detachment‐limited conditions with the relative importance of each approximately equal to the ratio of sand and rock fragments to silt and clay in the eroding soil. Available data also indicate that detachment/entrainment thresholds are highly variable in space and time in many landscapes, with local threshold values dependent on vegetation cover, rock‐fragment armoring, surface roughness, soil texture and cohesion. This heterogeneity is significant for determining the form of the fluvial/slope‐wash erosion or transport law because spatial and/or temporal variations in detachment/entrainment thresholds can effectively increase the nonlinearity of the relationship between sediment transport and stream power. Results from landform evolution modeling also suggest that, aside from the presence of distributary channel networks and autogenic cut‐and‐fill cycles in non‐steady‐state transport‐limited landscapes, it is difficult to infer the relative importance of transport‐limited versus detachment‐limited conditions using topography alone. Copyright © 2011 John Wiley & Sons, Ltd.     

Sediment detachment and transport processes associated with internal erosion of soil pipes

Subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping. The development of perched water tables fosters lateral flow that can result in seepage at the surface and/or formation of soil pipes by internal erosion of preferential flow paths. Continued internal erosion of soil pipes can lead to gullies, dam and levee failures. However, the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented. This paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes. Knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes. Copyright © 2017 John Wiley & Sons, Ltd.     

Soil erosion by surface water flow on a stony,semiarid hillslope

Soil erosion on hillslopes occurs by processes of soil splash from raindrop impacts and sediment entrainment by surface water flows. This study investigates the process of soil erosion by surface water flow on a stony soil in a semiarid environment. A field experimental method was developed whereby erosion by concentrated flow could be measured in predefined flow areas without disturbing the soil surface. The method allowed for measurements in this study of flow erosion at a much wider range of slopes (2·6 to 30·1 per cent) and unit discharge rates (0·0007 to 0·007 m2 s−1) than have been previously feasible. Flow velocities were correlated to discharge and hydraulic radius, but not to slope. The lack of correlation between velocity and slope might have been due to the greater rock cover on the steeper slopes which caused the surface to be hydraulically rougher and thus counteract the expected effect of slope on flow velocity. The detachment data illustrated limitations in applying a linear hydraulic shear stress model over the entire range of the data collected. Flow detachment rates were better correlated to a power function of either shear stress (r2 = 0·51) or stream power (r2 = 0·59). Published in 1999 by John Wiley & Sons, Ltd.     

Downslope soil detachment–transport on steep slopes via rain splash

This study developed a one‐dimensional model of downslope rain splash transport based on field experiments and previous studies. The developed model considers soil detachment processes, ground cover, probability densities, and the effect of overland run‐off in preventing detachment. Field monitoring was conducted to observe precipitation run‐off, ground cover, and sediment production on steep hillslopes. Field‐observed data were used to develop the splash detachment rate equation, probability densities for splash transport, and the maximum splash transport distance. Observed and estimated splash transport showed overall agreement, with some differences for small storm events or events with relatively low intensity, probably caused by variation of overland run‐off depth and connectivity as well as differences in soil surface cohesion at various degrees of wetness. Our model can provide insights on the interactions among rainfall intensity, soil surface condition, soil wetness, and splash transport on forested hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.     

Modelling the process of soil detachment by rill flow on steep loessial hillslopes

Soil detachment by rill flow is a key process of rill erosion, modelling this process can help in understanding rill erosion mechanisms. However, many soil detachment models are established on conceptual assumptions rather than experimental data. The objectives of this study were to establish a model of soil detachment by rill flow based on flume experimental data and to quantitatively verify the model. We simulated the process of soil detachment by rill flow in flume experiments with a soil-feeding hopper using loessial soil on steep slopes. Seven flow discharges, six slopes and five sediment loads were combined. Soil detachment capacity, sediment transport capacity, and soil detachment rate by rill flow under different sediment loads were measured. The process of soil detachment by rill flow can be modelled by a dual power function based on soil detachment capacity and transport capacity deficit as variables. The established model exhibited high credibility (NSE=0.97; R²=0.97). The contributions of soil detachment capacity and transport capacity deficit to soil detachment rate by rill flow reached 60% and 36%, respectively. Soil detachment capacity exerted more influence on soil detachment rate than did transport capacity deficit. The performance of the WEPP rill erosion equation is also favourable (NSE=0.95; R²=0.97). The two power exponents in the model we established strengthen the role of soil detachment capacity in soil detachment rate and weaken that for transport capacity deficit. Soil detachment capacity and transport capacity deficit played important roles in the determination of soil detachment rate by rill flow. The results can be applied to implement the numerical modeling and prediction of rill erosion processes on steep loessial hillslopes. © 2019 John Wiley & Sons, Ltd.     

Modelling increased soil cohesion due to roots with EUROSEM

As organic root exudates cause soil particles to adhere firmly to root surfaces, roots significantly increase soil strength and therefore also increase the resistance of the topsoil to erosion by concentrated flow. This paper aims at contributing to a better prediction of the root effects on soil erosion rates in the EUROSEM model, as the input values accounting for roots, presented in the user manual, do not account for differences in root density or root architecture. Recent research indicates that small changes in root density or differences in root architecture considerably influence soil erosion rates during concentrated flow. The approach for incorporating the root effects into this model is based on a comparison of measured soil detachment rates for bare and for root‐permeated topsoil samples with predicted erosion rates under the same flow conditions using the erosion equation of EUROSEM. Through backwards calculation, transport capacity efficiencies and corresponding soil cohesion values can be assessed for bare and root‐permeated topsoils respectively. The results are promising and present soil cohesion values that are in accordance with reported values in the literature for the same soil type (silt loam). The results show that grass roots provide a larger increase in soil cohesion as compared with tap‐rooted species and that the increase in soil cohesion is not significantly different under wet and dry soil conditions, either for fibrous root systems or for tap root systems. Power and exponential relationships are established between measured root density values and the corresponding calculated soil cohesion values, reflecting the effects of roots on the resistance of the topsoil to concentrated flow incision. These relationships enable one to incorporate the root effect into the soil erosion model EUROSEM, through adapting the soil cohesion input value. A scenario analysis shows that the contribution of roots to soil cohesion is very important for preventing soil loss and reducing runoff volume. The increase in soil shear strength due to the binding effect of roots on soil particles is two orders of magnitude lower as compared with soil reinforcement achieved when roots mobilize their tensile strength during soil shearing and root breakage. Copyright © 2008 John Wiley & Sons, Ltd.     

Temporal variation in soil detachment under different land uses in the Loess Plateau of China

Measurements of temporal variations in soil detachability under different land uses are badly needed to develop new algorithms or evaluate the existing ones for temporal adjustment of soil detachability in continuous soil erosion models. Few studies have been conducted in the Loess Plateau to quantify temporal variations in detachment rate of runoff under different land uses. The objectives of this study were to investigate the temporal variations of soil detachment rate under different land uses and to further identify the potential factors causing the change in detachment rate in the Loess Plateau. Undisturbed soil samples were collected in the fields of arable land (millet, soybean, corn, and potato), grassland, shrub land, wasteland, and woodland and tested in a laboratory flume under a constant hydraulic condition. The measurements started in mid‐April and ended in early October, 2006. The results showed that soil detachment rate of each land use fluctuated considerably over time. Distinctive temporal variation in detachment rate was found throughout the summer growing season of measurement in each land use. The maximum detachment rates of different land uses varied from 0·019 to 0·490 kg m^–2 s^–1 and the minimum detachment rates ranged from 0·004 to 0·092 kg m^–2 s^–1. Statistical analysis using a paired‐samples t‐test indicated that variations in soil detachment rate differed significantly at the 0·05 level between land uses in most cases. The major factors responsible for the temporal variation of soil detachment were tillage operations (such as planting, ploughing, weeding, harvesting), soil consolidation, and root growth. The influence of tillage operations on soil detachment depended on the degree of soil disturbance caused by the operations. The consolidation of the topsoil over time after tillage was reflected by increases in soil bulk density and soil cohesion. As soil bulk density and cohesion increased, detachment rate decreased. The impact of root density was inconclusive in this study. Further studies are needed to quantify the effects of root density on temporal variations of soil detachment. This work provides useful information for developing temporal adjustments to soil detachment rate in continuous soil erosion models in the Loess Plateau. Copyright © 2009 John Wiley & Sons, Ltd.     

Raindrop‐impact‐induced erosion processes and prediction: a review

Raindrop‐impact‐induced erosion is initiated when detachment of soil particles from the surface of the soil results from an expenditure of raindrop energy. Once detachment by raindrop impact has taken place, particles are transported away from the site of the impact by one or more of the following transport processes: drop splash, raindrop‐induced flow transport, or transport by flow without stimulation by drop impact. These transport processes exhibit varying efficiencies. Particles that fall back to the surface as a result of gravity produce a layer of pre‐detached particles that provides a degree of protection against the detachment of particles from the underlying soil. This, in turn, influences the erodibility of the eroding surface. Good understanding of rainfall erosion processes is necessary if the results of erosion experiments are to be properly interpreted. Current process‐based erosion prediction models do not deal with the issue of temporal variations in erodibility during a rainfall event or variabilities in erodibility associated with spatial changes in dominance of the transport processes that follow detachment by drop impact. Although more complex erosion models may deal with issues like this, their complexity and high data requirement may make them unsuitable for use as general prediction tools. Copyright © 2005 John Wiley & Sons, Ltd.     

Soil detachment by overland flow on steep cropland in the subtropical region of China

Accurate prediction of soil detachment capacity is fundamental to establish process-based erosion models and improve soil loss assessment. Few studies were conducted to reveal the mechanism of detachment process for yellow soil on steep cropland in the subtropical region of China using field experiments. This study was performed to determine soil detachment characteristics and explore the relationships between soil detachment capacity (D _c) and flow rate, slope gradient, mean velocity, shear stress, stream power and unit stream power. Field experiments were conducted on intact soil with flow rates ranging from 0.2 × 10⁻³ to 0.5 × 10⁻³ m⁻³ s⁻¹ and slope gradients varying from 8.8 to 42.4%. The results showed the following. (a) D _c of yellow soil was smaller than other soils because of its high clay content. (b) D _c was more susceptible to flow than to slope gradient. Power functions were derived to depict the relationship between D _c and the flow rate and slope gradient (R² = 0.91). (c) D _c was better simulated by power functions of the stream power (R² = 0.83) than functions of the shear stress or the unit stream power. (d) Considering its accuracy, simplicity and accessibility, the power function based on flow rate and slope gradient is recommended to predict D _c of yellow soil in the field. The results of this study provide useful support for revealing soil detachment mechanism and developing process-based soil erosion models for the subtropical region of China.     

Response of soil detachment rate to the hydraulic parameters of concentrated flow on steep loessial slopes on the Loess Plateau of China

Using hydraulic parameters is essential for describing soil detachment and developing physically based erosion prediction models. Many hydraulic parameters have been used, but the one that performs the best for describing soil detachment on steep slopes when the lateral expansion (widening) of rills is not limited has not been identified. An indoor concentrated flow scouring experiment was performed on steep loessial slopes to investigate soil detachment rates for different flow rates and slope gradients. The experiments were conducted on a slope‐adjustable plot (5 m length, 1 m width, 0.5 m depth). Sixteen combinations of 4 flow rates (10, 15, 20, and 25 L/min) and 4 slope gradients (17.6%, 26.8%, 36.4%, and 46.6%) were investigated. The individual and combined effects of slope gradient and flow hydraulic parameters on soil detachment rate were analysed. The results indicated that soil detachment rate increased with flow rate and slope gradient. Soil detachment rate varied linearly and exponentially with flow rate and slope gradient, respectively. Multivariate, nonlinear regression analysis indicated that flow depth exerted the greatest influence on the soil detachment rate, followed by unit discharge per unit width, slope gradient, and flow rate in this study. Shear stress and stream power could efficiently describe the soil detachment rate using a power equation. However, the unit stream power and unit energy of the water‐carrying section changed linearly with soil detachment rate. Stream power was an optimal hydraulic parameter for describing soil detachment. These findings improve our understanding of concentrated flow erosion on steep loessial slopes.     

An experimental investigation of the effects of thawed soil depth on rill flow velocity

Water flow velocity is an important hydraulic variable in hydrological and soil erosion models, and is greatly affected by freezing and thawing of the surface soil layer in cold high-altitude regions. The accurate measurement of rill flow velocity when impacted by the thawing process is critical to simulate runoff and sediment transport processes. In this study, an electrolyte tracer modelling method was used to measure rill flow velocity along a meadow soil slope at different thaw depths under simulated rainfall. Rill flow velocity was measured using four thawed soil depths (0, 1, 2 and 10 cm), four slope gradients (5°, 10°, 15° and 20°) and four rainfall intensities (30, 60, 90 and 120 mm·h⁻¹). The results showed that the increase in thawed soil depth caused a decrease in rill flow velocity, whereby the rate of this decrease was also diminishing. Whilst the rill flow velocity was positively correlated with slope gradient and rainfall intensity, the response of rill flow velocity to these influencing factors varied with thawed soil depth. The mechanism by which thawed soil depth influenced rill flow velocity was attributed to the consumption of runoff energy, slope surface roughness, and the headcut effect. Rill flow velocity was modelled by thawed soil depth, slope gradient and rainfall intensity using an empirical function. This function predicted values that were in good agreement with the measured data. These results provide the foundation for a better understanding of the effect of thawed soil depth on slope hydrology, erosion and the parameterization scheme for hydrological and soil erosion models.     

Predicting physical equations of soil detachment by simulated concentrated flow in Ultisols (subtropical China)

Soil detachment in concentrated flow is due to the dislodging of soil particles from the soil matrix by surface runoff. Both aggregate stability and shear strength of the topsoil reflect the erosion resistance of soil to concentrated runoff, and are important input parameters in predicting soil detachment models. This study was conducted to develop a formula to predict soil detachment rate in concentrated flow by using the aggregate stability index (As), root density (R_d) and saturated soil strength (σ_s) in the subtropical Ultisols region of China. The detachment rates of undisturbed topsoil samples collected from eight cultivated soil plots were measured in a 3.8 m long, 0.2 m wide hydraulic flume under five different flow shear stresses (τ = 4.54, 9.38, 15.01, 17.49 and 22.54 Pa). The results indicated that the stability index (As) was well related with soil detachment rate, particularly for results obtained with high flow shear stress (22.54 Pa), and the stability index (As) has a good linear relationship with concentrated flow erodibility factors (K_c). There was a positive linear relationship between saturated soil strength (σ_s) and critical flow shear stress (τ_c) for different soils. A significant negative exponential relationship between erodibility factors (K_c) and root density (R_d) was detected. This study yielded two prediction equations that allowed comparison of their efficiency in assessing soil detachment rate in concentrated flow. The equation including the root density (R_d) may have a better correlation coefficient (R² = 0.95). It was concluded that the formula based on the stability index (As), saturated soil strength (σ_s) and root density (R_d) has the potential to improve methodology for assessing soil detachment rate in concentrated flow for the subtropical Chinese Ultisols. Copyright © 2012 John Wiley & Sons, Ltd.     

A comparison of the effectiveness of the roots of two grass species in reducing soil erosion on alluvial fans in south-east China

The effects of root systems on soil detachment by overland flow are closely related to vegetation types. The objective of this study was to quantify the effects of two gramineous roots (Paspalum mandiocanum with shallow roots and Pennisetum giganteum with deep roots) on soil detachment capacity, rill erodibility, and critical shear stress on alluvial fans of benggang in south-east China. A 4-m-long and 0.12-m-wide flume was used. Slope steepness ranged from 9% to 27%, and unit flow discharge ranged from 1.39 × 10⁻³ to 4.19 × 10⁻³ m² s⁻¹. The mean detachment capacities of P. mandiocanum and P. giganteum lands were 18% and 38% lower than that of bare land, respectively, and the effects of root on reducing soil detachment were mainly reflected in the 0- to 5-cm soil layer. The most important factors in characterizing soil detachment capacity were root length density and soil cohesion, and soil detachment capacity of the two grass lands could be estimated using flow shear stress, soil cohesion, and root length density (NSE = 0.90). With the increase in soil depth, rill erodibility increased, whereas shear stress decreased. The mean rill erodibilities of P. mandiocanum and P. giganteum lands were 81% and 61% as much as that of bare land, respectively. Additionally, rill erodibilities of the two grass lands could be estimated as an exponential function by root length density and soil cohesion (NSE = 0.88). The mean critical shear stress of P. mandiocanum and P. giganteum lands was 1.29 and 1.39 times that of bare land, respectively, and it could be estimated with a linear function by root length density (NSE = 0.76). This study demonstrated that planting of the two grasses P. mandiocanum and P. giganteum could effectively reduce soil detachment and enhance soil resistance to erosion on alluvial fans, with the deep roots of P. giganteum being more effective than the shallow roots of P. mandiocanum. The results are helpful for understanding the influencing mechanism of root systems on soil detachment process.     

Sediment detachment in piping-prone soils: Cohesion sources and potential weakening mechanisms

Soil piping is a widespread land degradation process that may lead to gully formation. However, the processes involved in sediment detachment from soil pipe walls have not been well studied, although their recognition is a crucial step to protect soils from piping erosion. This study aims to recognize the factors affecting cohesion and to identify the mechanisms which are likely to be responsible for the disintegration of soil. The study has been conducted in mid-altitude mountains under a temperate climate (the Bieszczady Mountains, the Carpathians, SE Poland). The research was based on the detailed field and laboratory analyses of morphology, and the physical and chemical properties of soil profiles with and without soil pipes. Moreover, experiments with flooding the undisturbed soil samples using different solutions (deionized water, ammonium oxalate, dithionate citrate, 35% hydrochloric acid and 30% hydrogen peroxide) were conducted in order to check the role of air slaking, the removal of soil organic carbon (SOC), and Fe and Al oxides on sediment detachment. The obtained results have confirmed that soil pipes develop in quite cohesive soils (silt loams), which allow the formation and maintenance of pipes with a diameter up to 30 cm. Soil cohesion, and thus susceptibility to piping, are impacted by the content of major oxides, soil particle size distribution, biological activity and porosity. The tested soils affected by piping erosion have a lower content of Al₂O₃ and Fe₂O₃, and free Fe (Fe_(DCB)), lower clay content, higher biological activity (more roots and animal burrows), higher porosity, and more and larger pores than the profile without soil pipes. The experiments have indicated that especially SOC along with Fe and Al oxides are an important cohesion source in the study area. This suggests that the removal of SOC, and Fe and Al oxides may weaken and disintegrate aggregates in soil pipes. Further study of soil leaching and tensile strength will broaden understanding of which chemical processes control where pipes will develop in other cohesive piping-prone soils. © 2020 John Wiley & Sons, Ltd.     

Characterizing incipient motion of low fines content soils with varying compositions,water contents,and relative densities

Laboratory flume experiments were conducted to quantify the effects of the soil characteristics on the critical shear stress of low fines content soil samples collected from the Montauk shores in New York. The collected soils were reconstituted at five different fines contents, ranging between 0 and 20%. These soil mixtures were composed of two initial water contents, dry of optimum and optimum moistures, and two relative densities, one moderate dense and the other dense. The strength indices of...     

Concentrated flow erosion rates reduced through biological geotextiles

Soil erosion by concentrated flow can cause serious environmental damage. Erosion‐control geotextiles have considerable potential for reducing concentrated flow erosion. However, limited data are available on the erosion‐reducing potential of geotextiles. In this study, the effectiveness of three biological geotextiles in reducing soil losses during concentrated flow is investigated. Hereto, runoff was simulated in a concentrated flow flume, filled with an erodible sandy loam on three slope gradients (13·5, 27·0 and 41·5%). Treatments included three biological geotextiles (borassus, buriti and bamboo) and one bare soil surface. Darcy–Weisbach friction coefficients ranged from 0·01 to 2·84. The highest values are observed for borassus covered soil surfaces, followed by buriti, bamboo and bare soil, respectively. The friction coefficients are linearly correlated with geotextile thickness. For the specific experimental conditions of this study, borassus geotextiles reduced soil detachment rate on average to 56%, buriti geotextiles to 59% and bamboo geotextiles to 66% of the soil detachment rate for bare soil surfaces. Total flow shear stress was the hydraulic parameter best predicting soil detachment rate for bare and geotextile covered surfaces (R² = 0·75–0·84, p <0·001, n = 12–15). The highest resistance against soil detachment was observed for the borassus covered soil surfaces, followed by buriti, bamboo and bare soil surfaces, respectively. Overall, biological geotextiles are less effective in controlling concentrated flow erosion compared with interrill erosion. Copyright © 2009 John Wiley & Sons, Ltd.     

LISEM: A SINGLE-EVENT,PHYSICALLY BASED HYDROLOGICAL AND SOIL EROSION MODEL FOR DRAINAGE BASINS. II: SENSITIVITY ANALYSIS,VALIDATION AND APPLICATION

A new hydrological and soil erosion model has been developed and tested: LISEM, the Limburg soil erosion model. The model uses physically based equations to describe interception, infiltration and soil water transport, storage in surface depressions, splash and flow detachment, transport capacity and overland and channel flow. From the validation results it is clear that, although the model has several advantages over other models, the results of LISEM 1.0 are far from perfect. Based on the sensitivity analysis and field observations, the main reasons for these differences seems to be the spatial and temporal variability of the soil hydraulic conductivity and the initial pressure head at the basin scale. Another reason for the differences between measured and simulated results is our lack or understanding of the theory of hydrological and soil erosion processes.     

The effect of conservation tillage on runoff erosivity and soil erodibility during concentrated flow

Crop residues in conservation tillage systems are known to cause both a reduction in the erosive runoff power and an increase in the topsoil erosion resistance. In this study, the relative importance of both mechanisms in reducing soil loss by concentrated flow erosion is examined. Therefore, a method to calculate the effective flow shear stress responsible for soil detachment in the presence of a residue cover is applied. The determination of effective flow shear stress is based on the recalculation of the hydraulic radius for residue treatments. The method was tested in a laboratory flume by comparing soil detachment rates of identical pairs of soil samples that only differ in the presence or absence of crop residues. This shear stress partitioning approach and a soil detachment correction were then applied to a dataset of soil detachment measurements on undisturbed topsoil samples from a no‐till field plot on a loess‐derived soil, sampled during one growing season. Results indicate that only a small fraction (10% on average) of the difference in soil detachment rate between conventional and conservation tillage can be attributed to the dissipation of shear forces on the residues. The remaining decrease in soil detachment during concentrated runoff after a two‐year application of conservation tillage can be explained by the increased dry bulk density and root and crop residue content in the topsoil that reduces soil erodibility. After correcting for the presence of residues, the temporal variability in soil detachment rates (D_r) during concentrated flow for a given flow shear stress (τ) for both treatments can be predicted fairly well (R² = 0·87) from dry soil bulk density (DBD, representing consolidation effects), soil moisture content (SMC, representing antecedent rainfall conditions), the dry mass of organic material (OM, representing root growth and residue decomposition) and saturated soil shear strength σ_{s, sat} using an equation of the form: This study is the first to show that the effect of conservation tillage on soil detachment rates is a result of soil property modifications affecting soil erodibility, rather than a result of the surface residue decreasing flow erosivity. Copyright © 2007 John Wiley & Sons, Ltd.     

PHYSICAL PROCESS BASED SOIL EROSION MODEL IN A SMALL WATERSHED IN THE HILLY LOESS REGION

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Modified MMF (Morgan–Morgan–Finney) model for evaluating effects of crops and vegetation cover on soil erosion

Modifications are made to the revised Morgan–Morgan–Finney erosion prediction model to enable the effects of vegetation cover to be expressed through measurable plant parameters. Given the potential role of vegetation in controlling water pollution by trapping clay particles in the landscape, changes are also made to the way the model deals with sediment deposition and to allow the model to incorporate particle‐size selectivity in the processes of erosion, transport and deposition. Vegetation effects are described in relation to percentage canopy cover, percentage ground cover, plant height, effective hydrological depth, density of plant stems and stem diameter. Deposition is modelled through a particle fall number, which takes account of particle settling velocity, flow velocity, flow depth and slope length. The detachment, transport and deposition of soil particles are simulated separately for clay, silt and sand. Average linear sensitivity analysis shows that the revised model behaves rationally. For bare soil conditions soil loss predictions are most sensitive to changes in rainfall and soil parameters, but with a vegetation cover plant parameters become more important than soil parameters. Tests with the model using field measurements under a range of slope, soil and crop covers from Bedfordshire and Cambridgeshire, UK, give good predictions of mean annual soil loss. Regression analysis of predicted against observed values yields an intercept value close to zero and a line slope close to 1·0, with a coefficient of efficiency of 0·81 over a range of values from zero to 38·6 t ha^?1. Copyright © 2007 John Wiley & Sons, Ltd.