Soil erosion resistance effects on rill and gully initiation points and dimensions

Recent research has indicated the large spatial and temporal variation in soil erosion resistance against concentrated flow (SER). This study analyzes this variability in relation to rill and gully initiation locations on slopes and the downslope eroded volumes. The soil erodibility (Kc) and critical flow shear stress (τ_cr), were estimated from topsoil properties and correlated to eroded rill and gully volumes and their initiation points on slopes in the Belgian loess belt. Therefore, concentrated flow paths and topsoil properties were measured in their vicinity. The results show that rill and gully initiation points, and hence the lengths of concentrated flow paths, depend on τ_cr, which is controlled by soil surface conditions and can be predicted from saturated soil shear strength. Soil erosion control measures that increase soil shear strength (e.g. thalweg compaction), can therefore decrease rill and gully lengths. Once a rill or an ephemeral gully is initiated, its cross‐section was found to depend on Kc, which can be estimated from the soil water content, dry bulk density, and the dry density of roots and crop residues incorporated in the topsoil. 74% of the variation in the channel cross‐sectional area measured in the study area could be predicted from the combined effect of flow intensity and these three soil properties, whereas flow intensity alone could only account for 31% of the variation. Soil conservation measures affecting one of the soil properties that control Kc (e.g. double drilling of the thalweg, conservation tillage) can therefore decrease the cross‐sections of the concentrated flow paths. These findings also indicate that rill and gully initiation points are not only topographically controlled but also depend on the SER, which in turn determines the dimensions of these concentrated flow paths. Hence, knowledge of the variability in SER is indispensable. Copyright © 2009 John Wiley & Sons, Ltd.     

A simulation model for unified interrill erosion and rill erosion on hillslopes

A mathematical model was developed for simulating runoff generation and soil erosion on hillslopes. The model is comprised of three modules: one for overland flow, one for soil infiltration, and one for soil erosion including rill erosion and interrill erosion. Rainfall and slope characteristics affecting soil erosion on hillslopes were analysed. The model results show that the slope length and gradient, time distribution rainfall, and distribution of rills have varying influence on soil erosion. Erosion rate increases nonlinearly with increase in the slope length; a long slope length leads to more serious erosion. The effect of the slope gradient on soil erosion can be both positive and negative. Thus, there exists a critical slope gradient for soil erosion, which is about 45° for the rate of erosion at the end of the slope and about 25° for the accumulated erosion. Copyright © 2005 John Wiley & Sons, Ltd.     

Plant root traits affecting the resistance of soils to concentrated flow erosion

The effect of plant species on erosion processes may be decisive for long‐term soil protection in degraded ecosystems. The identification of functional effect traits that predict species ability for erosion control would be of great interest for ecological restoration purposes. Flume experiments were carried out to investigate the effect of the root systems of three species having contrasted ecological requirements from eroded marly lands of the French Southern Alps [i.e. Robinia pseudo acacia (tree), Pinus nigra austriaca (tree) and Achnatherum calamagrostis (grass)], on concentrated flow erosion rates. Ten functional traits, describing plant morphological and biomechanical features, were measured on each tested sample. Analyses were performed to identify traits that determine plant root effects on erosion control. Erosion rates were lowest for samples of Robinia pseudo acacia, intermediate in Achnatherum calamagrostis and highest in Pinus nigra austriaca. The three species also differed strongly in their traits. Principal components analysis showed that the erosion‐reducing potential of plant species was negatively correlated to root diameter and positively correlated to the percentage of fine roots. The results highlighted the role of small flexible roots in root reinforcement processes, and suggested the importance of high root surface and higher tensile strength for soil stabilization. By combining flume experiment to plant functional traits measurements, we identified root system features influencing plant species performance for soil protection against concentrated flow erosion. Plant functional traits related to species efficiency for erosion control represent useful tools to improve the diagnosis of land vulnerability to erosion, plant community resistance and the prediction of ecosystem functioning after ecological restoration. Copyright © 2012 John Wiley & Sons, Ltd.     

Rill and ephemeral gully erosion in a small olive grove catchment in Spain: Interactions between management and conservation measures

Concentrated flow erosion in Mediterranean cultivated areas is considered a major process of land degradation. Rills and ephemeral gullies in a 6.4 ha olive orchard catchment located in an intensive commercial farm, which could represent a common degradation scenario in hilly areas, were measured and compared with the sediment loads at the outlet. Four GPS survey campaigns were carried out between March 2009 and March 2014, for periods with cumulative precipitation ranging between 728 and 121 mm. Chopped pruning residues were kept on the lanes during campaigns 2–4, whereas a grass cover crop was seeded in campaign 4. Rainfall, runoff and sediment loads were measured in a flume gauge station at the catchment outlet. The ratio of concentrated flow erosion to catchment sediment load varied between 1.0 and 35.0. Total concentrated flow erosion ranged between 25.0 and 0.1 t ha⁻¹. Rill erosion was the dominant process on ephemeral gullies for three campaigns, with a mean contribution to the total concentrated flow erosion of 55%. Rills clearly followed tractor tracks along the most parallel lanes to the maximum slope. Therefore, a change in traffic direction would be helpful to reduce the connectivity, controlled by the spatial distribution of rows and lanes in the farm. Olive plantation distributions should prioritize hydrological criteria to adapt traffic patterns in olive farms, as long as the tractor manoeuvrability and risk of overturning are not adversely affected. Although the farmer only kept the cover crop for one campaign, it proved to be an efficient measure for interrupting rills along the lanes, whereas pruning residues were effective for the control of interrill erosion. On-site application of pruning residues reduced their handling and transport costs, while increasing the soil fertility and soil cover. However, guidelines for the efficient application of pruning residues are still necessary in terms of residue rates and orientation.     

Rehabilitation effects on gully sediment yields and vegetation in a savanna rangeland

Gully rehabilitation can contribute to catchment management by stabilizing erosion and reducing downstream sediment yields, yet the globally observed responses are variable. Developing the technical basis for gully rehabilitation and establishing guidelines for application requires studies that evaluate individual rehabilitation measures in specific environments. An eight-year field experiment was undertaken to evaluate sediment yield and vegetation responses to several gully rehabilitation measures. The rehabilitation measures aimed to reduce surface runoff into gully head cuts, trap sediment on gully floors and increase vegetation cover on gully walls and floors. The study occurred in a savanna rangeland in northeast Australia. Two gullies were subject to treatments while four gullies were monitored as untreated controls. A runoff diversion structure reduced headcut erosion from 4.3 to 1.2 m² yr⁻¹. Small porous check dams and cattle exclusion reduced gully total sediment yields by more than 80%, equivalent to a reduction of 0.3 to 2.4 t ha⁻¹ yr⁻¹, but only at catchment areas less than 10 ha. Fine sediment yields (silt and clay) were reduced by 7 and 19% from the two treated gullies, respectively. The porous check dam deposits contained a lower percentage of the fine fraction than the parent soil. Significant regeneration of gully floor vegetation occurred, associated with trapping of organic litter and fine sediment. Increases in vegetation cover and biomass were comprised of native perennial grasses, trees and shrubs. In variable climates, long-term gully rehabilitation will progress during wetter periods, and regress during droughts. Understanding linkages between rehabilitation measures, their hydrologic, hydraulic and vegetation effects and gully sediment yields is important to defining the conditions for their success.     

An investigation of soil erosion and redistribution in a Mediterranean lowland agricultural catchment using caesium-137

This study sought to contribute to an improved understanding of soil erosion and redistribution on Mediterranean agricultural land, where traditional soil conservation practices have been applied over millennia to provide effective protection of cultivated land. The study was undertaken in the Na Borges catchment, a groundwater-dominated lowland limestone basin (319 km2), located in the northeastern part of Mallorca, Spain. The average sediment yield from the basin, based on river sediment load data, is 1 t/km2·yr. The 137Cs technique was used to quantify soil redistribution rates over the past 40 years and to identify the key factors involved in soil erosion and redistribution processes. To estimate erosion and deposition rates and to elucidate the main factors affecting soil redistribution, samples were collected from six slope transects representative of the local land use and slope gradients and the presence or absence of soil conservation practices. A mass balance and a profile distribution conversion model were used for cultivated areas and areas of natural vegetation, respectively, to derive point estimates of the soil redistribution rates from the 137Cs inventories measured for individual soil bulk cores. In areas without soil conservation practices, the estimated mean soil erosion rates ranged from 12.7 to 26.4 t/ha·yr, which correspond to the slight and moderate erosion classes. The erosivity of Mediterranean climatic conditions combined with the influence of agricultural practices and slope gradient on soil erosion, represent the main factors responsible for the variation of soil losses documented for the cultivated land located in downslope areas, in the absence of soil conservation practices. Deposition dominated for those transects affected by soil conservation practices, with rates ranging between 18.8 and 96.6 t/ha·yr. However, this situation does not mean that soil conservation measures retain all the sediment, but rather that agriculture and urbanization (i.e. new rural paths and stone boundaries) modified the micro-topography and diverted sediment from other upslope zones towards the slopes where sampling transects were located.     

Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands – towards a sediment budget

This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100–2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area‐weighted average rate of soil erosion by water in the catchment, measured over four years (1998–2001), is 14·8 t ha^?1 y^?1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha^?1 y^?1. Calculated sediment yield (5·6 t ha^?1 y^?1) is similar to sediment yield measured in nearby catchments. Seventy‐four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present‐day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd.     

Assessment of magnetite as a magnetic tracer for sediments in the study of ephemeral gully erosion: Conditioning factors of magnetic susceptibility

In gully erosion, the detached soil can be transported over long distances along the landscape. The eroded material can be redistributed and/or deposited on the soil surface along the landscape and then eventually be buried by newly eroded and deposited sediment. There can be significant variability of the soil conditions (e.g., texture and moisture content) over which the eroded material travels. The eroded material can be detected through the use of magnetic tracers attached to or mixed with the eroded soil. In this study we evaluated the degree to which the magnetic signal of the magnetite is conditioned by (i) burial depth of tracer, (ii) condition of soil covering the tracer and (iii) tracer concentration. In the laboratory containers were filled with a specific soil. In the filling process, a 0.5-cm layer of a soil–magnetite mixture was interspersed in the soil profile at a certain depth. Experiments encompassed three different soil–tracer concentrations (1000:1, 200:1, 100:1), four burial depths of tracer (0 cm, 3 cm, 5 cm and 10 cm from soil surface), and two different soils. In each case, the magnetic susceptibility was measured with a susceptometer. Experiments were repeated with different soil moisture contents. If the tracer is located under the soil surface, a minimum soil–tracer concentration of 200:1 is required for its correct detection. The intensity of the magnetic signal decreases dramatically with the vertical distance of the tracer from the soil surface. The maximum detection depth for the tracer's magnetic signal is strongly dependent on the natural magnetic susceptibility of the soil, which masks the tracer's signal. Variation in soil moisture content does not significantly affect the magnetic signal. For extensive field studies, the soil–tracer volume to be handled would be very high and therefore, it is necessary to explore new tracer application techniques.     

Changes in hydrology and erosion over a transition from grassland to shrubland

The degradation of grasslands is a common problem across semi‐arid areas worldwide. Over the last 150 years, much of the south‐western United States has experienced significant land degradation, with desert grasslands becoming dominated by shrubs and concurrent changes in runoff and erosion which are thought to propagate further the process of degradation. Plot‐based experiments to determine how spatio‐temporal characteristics of soil moisture, runoff and erosion change over a transition from grassland to shrubland were carried out at four sites over a transition from black grama (Bouteloua eriopoda) grassland to creosotebush (Larrea tridentata) shrubland at the Sevilleta NWR LTER site in New Mexico. Each site consisted of a 10 × 30 m bounded runoff plot and adjacent characterization plots with nested sampling points where soil moisture content was measured. Results show distinct spatio‐temporal variations in soil moisture content, which are due to the net effect of processes operating at multiple spatial and temporal scales, such as plant uptake of water at local scales versus the redistribution of water during runoff events at the hillslope scale. There is an overall increase in runoff and erosion over the transition from grassland to shrubland, which is likely to be associated with an increase in connectivity of bare, runoff‐generating areas, although these increases do not appear to follow a linear trajectory. Erosion rates increased over the transition from grassland to shrubland, likely related in part to changes in runoff characteristics and the increased capacity of the runoff to detach, entrain and transport sediment. Over all plots, fine material was preferentially eroded which has potential implications for nutrient cycling since nutrients tend to be associated with fine sediment. Copyright © 2009 John Wiley & Sons, Ltd.     

Sensitivity of runoff and soil erosion to climate change in two Mediterranean watersheds. Part I: model parameterization and evaluation

Climate change is expected to effect storm runoff and erosion processes in Mediterranean watersheds at multiple spatial scales. Models are typically applied to estimate these impacts; however, the scarcity of spatially distributed data for parameterization, calibration and validation often prevents application of these models, particularly for larger catchments. This report, the first part of a two‐part article, presents an application and evaluation of the MEFIDIS model for two Mediterranean meso‐scale watersheds (115 and 290 km²) in a data‐scarce environment. A multi‐scale assessment method was used that combines quantitative validation and qualitative evaluation, consisting of three steps: (1) calibration at the small (field) scale using results from rainfall simulation experiments; (2) calibration and validation for catchment‐scale results while changing catchment‐scale parameters only (channel roughness and a parameter controlling the distribution of saturated areas); and (3) qualitative evaluation of within‐watershed erosion processes using empirical estimates of sediment delivery ratio and gully location. The results indicate that calibrating MEFIDIS at the field scale can provide reasonable results for catchment runoff and sediment export and for within‐watershed erosion processes. Copyright © 2009 John Wiley & Sons, Ltd.     

Soil erosion and overland flow in Japanese cypress plantations: spatio-temporal variations and a sampling strategy

ABSTRACT

Many studies have focused on soil erosion in unmanaged Japanese cypress plantations because the sparse understory vegetation and litter covering the forest ground enhance soil erosion. In this study, soil erosion, litter, and overland flow measurements were conducted over 14 months to identify the spatio-temporal variation and examine the optimal sample size. Fifteen traps (each 0.25 m wide) were installed in line along the bottom of a 15-m-wide slope. Soil erosion and overland flow had large spatial variations as compared to litter. The temporal coefficient of variation of soil erosion and overland flow was highest during dry seasons, while smaller during wet seasons. The random sampling analysis showed that the rate of decrease in spatio-temporal variation became moderate as the sample size increased beyond six. This result indicated that the optimal sample size was five, the total width of which was equivalent to about 8% of the monitored slope width.     

Using GIS and a digital elevation model to assess the effectiveness of variable grade flow diversion terraces in reducing soil erosion in northwestern New Brunswick,Canada

Flow diversion terraces (FDT) are commonly used beneficial management practice (BMP) for soil conservation on sloped terrain susceptible to water erosion. A simple GIS‐based soil erosion model was designed to assess the effectiveness of the FDT system under different climatic, topographic, and soil conditions at a sub‐basin level. The model was used to estimate the soil conservation support practice factor (P‐factor), which inherently considered two major outcomes with its implementation, namely (1) reduced slope length, and (2) sediment deposition in terraced channels. A benchmark site, the agriculture‐dominated watershed in northwestern New Brunswick (NB), was selected to test the performance of the model and estimated P‐factors. The estimated P‐factors ranged from 0·38–1·0 for soil conservation planning objectives and ranged from 0·001 to 0·45 in sediment yield calculations for water‐quality assessment. The model estimated that the average annual sediment yield was 773 kg ha^?1 yr ^?1 compared with a measured value of 641 kg ha^?1 yr^?1. The P‐factors estimated in this study were comparable with predicted values obtained with the revised universal soil loss equation (RUSLE2). The P‐factors from this study have the potential to be directly used as input in hydrological models, such as the soil and water assessment tool (SWAT), or in soil conservation planning where only conventional digital elevation models (DEMs) are available. Copyright © 2009 John Wiley & Sons, Ltd.     

Laboratory soil piping and internal erosion experiments: evaluation of a soil piping model for low‐compacted soils

Mechanistic models have been proposed for soil piping and internal erosion on well‐compacted levees and dams, but limited research has evaluated these models in less compacted (more erodible) soils typical of hillslopes and streambanks. This study utilized a soil box (50 cm long, 50 cm wide and 20 cm tall) to conduct constant‐head, soil pipe and internal erosion experiments for two soils (clay loam from Dry Creek and sandy loam from Cow Creek streambanks) packed at uniform bulk densities. Initial gravimetric moisture contents prior to packing were 10, 12 and 14% for Dry Creek soil and 8, 12, and 14% for Cow Creek soil. A 1‐cm diameter rod was placed horizontally along the length of the soil bed during packing and carefully removed after packing to create a continuous soil pipe. A constant head was maintained at the inflow end. Flow rates and sediment concentrations were measured from the pipe outlet. Replicate submerged jet erosion tests (JETs) were conducted to derive erodibility parameters for repacked samples at the same moisture contents. Flow rates from the box experiments were used to calibrate the mechanistic model. The influence of the initial moisture content was apparent, with some pipes (8% moisture content) expanding so fast that limited data was collected. The mechanistic model was able to estimate equivalent flow rates to those observed in the experiments, but had difficulty matching observed sediment concentrations when the pipes rapidly expanded. The JETs predicted similar erodibility coefficients compared to the mechanistic model for the more erodible cases but not for the less erodible cases (14% moisture content). Improved models are needed that better define the changing soil pipe cross‐section during supply‐ and transport‐limited internal erosion, especially for piping through lower compacted (more erodible) soils as opposed to more well‐compacted soils resulting from constructing levees and dams. Copyright © 2013 John Wiley & Sons, Ltd.     

Equifinality and uncertainty in physically based soil erosion models: application of the GLUE methodology to WEPP–the Water Erosion Prediction Project–for sites in the UK and USA

Despite the wealth of soil erosion models available for the prediction of both runoff and soil loss at a variety of scales, little quantification is made of uncertainty and error associated with model output. This in part reflects the need to produce unequivocal or optimal results for the end user, which will often be an unrealistic goal. This paper presents a conceptually simple methodology, Generalized Likelihood Uncertainty Estimation (GLUE), for assessing the degree of uncertainty surrounding output from a physically based soil erosion model, the Water Erosion Prediction Project (WEPP). The ability not only to be explicit about model error but also to evaluate future improvements in parameter estimation, observed data or scientific understanding is demonstrated. This approach is applied to two sets of soil loss/runoff plot replicates, one in the UK and one in the USA. Although it is demonstrated that observations can be largely captured within uncertainty bounds, results indicate that these uncertainty bounds are often wide, reflecting the need to qualify results that derive from ‘optimum’ parameter sets, and to accept the concept of equifinality within soil erosion models. Attention is brought to the problem of under‐prediction of large events/over‐prediction of small events, as an area where model improvements could be made, specifically in the case of relatively dry years. Finally it is proposed that such a technique of model evaluation be employed more widely within the discipline so as to aid the interpretation and understanding of complex model output. Copyright © 2000 John Wiley & Sons, Ltd.     

Sensitivity of runoff and soil erosion to climate change in two Mediterranean watersheds. Part II: assessing impacts from changes in storm rainfall,soil moisture and vegetation cover

The impacts of climate change on storm runoff and erosion in Mediterranean watersheds are difficult to assess due to the expected increase in storm frequency coupled with a decrease in total rainfall and soil moisture, added to positive or negative changes to different types of vegetation cover. This report, the second part of a two‐part article, addresses this issue by analysing the sensitivity of runoff and erosion to incremental degrees of change (from ? 20 to + 20%) to storm rainfall, pre‐storm soil moisture, and vegetation cover, in two Mediterranean watersheds, using the MEFIDIS model. The main results point to the high sensitivity of storm runoff and peak runoff rates to changes in storm rainfall (2·2% per 1% change) and, to a lesser degree, to soil water content (?1·2% per 1% change). Catchment sediment yield shows a greater sensitivity than within‐watershed erosion rates to both parameters: 7·8 versus 4·0% per 1% change for storm rainfall, and ? 4·9 versus ? 2·3% per 1% change for soil water content, indicating an increase in sensitivity with spatial scale due to changes to sediment connectivity within the catchment. Runoff and erosion showed a relatively low sensitivity to changes in vegetation cover. Finally, the shallow soils in one of the catchments led to a greater sensitivity to changes in storm rainfall and soil moisture. Overall, the results indicate that decreasing soil moisture levels caused by climate change could be sufficient to offset the impact of greater storm intensity in Mediterranean watersheds. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance of the LandSoil expert-based model to map erosion and sedimentation: application to a cultivated catchment in central Belgium

Intensive agricultural practices on sensitive soils induce high erosion rates in central Belgium. Expert-rules models quantify runoff and erosion at catchment scale, avoiding over-parameterization, and can include some direct or indirect connectivity features. The aim of this article is to test the ability of an expert-based model, LandSoil, to quantify runoff and to locate erosion and sedimentation areas in a small cultivated loamy catchment in Belgium during the years 2014, 2015 and 2016. Spatialized data are important for assessing model outputs and the erosive response. Measurements of runoff and observation of spatial erosion/deposition patterns, especially around major connectivity points, permitted an assessment of the reliability of the model results. Runoff modelling gave contrasting results (good linear adjustment at the outlet of the 83 ha sub-catchment (point 1): r² of 0.96, Nash–Sutcliffe criterion of 0.95; less good at the outlet of the 3.9 ha sub-catchment (point 2): r² of 0.28, Nash–Sutcliffe criterion of –0.47). For point 2 the poor results are explained by the very few runoff events observed, a scaling effect and the small area with a single land use. Graduated rulers demonstrate that the model is able to provide a coherent pattern of erosion/deposition. The study highlights great sensitivity to the effect of land use, land allocation, landscape design and slope gradients. Grass strips induce deposition of eroded particles when slopes are gentle (< 2%). Woodland strips decrease connectivity by being in the stream but deposit thinner sediment layers. Field boundaries have a role in the transport, but not really the quantity, of sediments. This model validation in the Belgian loess context allows us to use LandSoil in other similar environments in order to estimate the effects of landscape management scenarios. © 2020 John Wiley & Sons, Ltd.     

Seasonal patterns of runoff and erosion responses to simulated rainfall in a badland area in Mediterranean mountain conditions (Vallcebre,southeastern Pyrenees)

Regolith surface characteristics and response were examined over a three‐year period in a badland area in a Mediterranean middle‐mountain zone near Vallcebre (Eastern Pyrenees). Preliminary work carried out in this area indicated clear seasonal patterns of regolith properties driven by frost heaving in winter and crusting and erosion in the rest of the year. Rainfall simulations were performed with a small portable nozzle simulator in order to study seasonal changes in runoff generation, erosion rates and raindrop effect on bulk density changes. The results showed large seasonal variations in runoff and erosion responses. In?ltration rates after runoff start were correlated with precipitation depth before runoff start; runoff generation was therefore related to regolith saturation only to a very limited extent. Erosion rates were more controlled by runoff rates than by the weakness of regolith against raindrop splash, and sediment grain size increased with concentration. The combined role of antecedent regolith moisture and bulk density explained most of the seasonal variability in in?ltration, bulk density changes during rainfall and erosion rates, but some seasonal differences in sediment detachability were not explained by these variables and may be attributed to changes in roughness. Overall, runoff and erosion responses were relatively stable during spring and autumn, whereas wide variations in in?ltration rates and sediment detachment occurred in winter and summer respectively. Experiments conducted in a single season would have produced poorly representative, if not erroneous, results. Copyright © 2004 John Wiley & Sons, Ltd.     

Operational performance of current synthetic aperture radar sensors in mapping soil surface characteristics in agricultural environments: application to hydrological and erosion modelling

Synthetic aperture radar (SAR) sensors are often used to characterize the surface of bare soils in agricultural environments. They enable the soil moisture and roughness to be estimated with constraints linked to the configurations of the sensors (polarization, incidence angle and radar wavelength). These key soil characteristics are necessary for different applications, such as hydrology and risk prediction. This article reviews the potential of currently operational SAR sensors and those planned for the near future to characterize soil surface as a function of users' needs. It details what it is possible to achieve in terms of mapping soil moisture and roughness by specifying optimal radar configurations and the precision associated with the estimation of soil surface characteristics. The summary carried out for the present article shows that mapping soil moisture is optimal with SAR sensors at low incidence angles (<35 ). This configuration, which enables an estimated moisture accuracy greater than 6% is possible several times a month taking into account all the current and future sensors. Concerning soil roughness, it is best mapped using three classes (smooth, moderately rough, and rough). Such mapping requires high‐incidence data, which is possible with certain current sensors (RADARSAT‐1 and ASAR both in band C). When L‐band sensors (ALOS) become available, this mapping accuracy should improve because the sensitivity of the radar signal to Soil Surface Characteristics (SSC) increases with wavelength. Finally, the polarimetric mode of certain imminent sensors (ALOS, RADARSAT‐2, TerraSAR‐X, etc.), and the possibility of acquiring data at very high spatial resolution (metre scale), offer great potential in terms of improving the quality of SSC mapping. Copyright © 2007 John Wiley & Sons, Ltd.