ASSESSING THE PERFORMANCE OF A SPATIALLY DISTRIBUTED SOIL EROSION AND SEDIMENT DELIVERY MODEL (WATEM/SEDEM) IN NORTHERN ETHIOPIA

Most regional‐scale soil erosion models are spatially lumped and hence have limited application to practical problems such as the evaluation of the spatial variability of soil erosion and sediment delivery within a catchment. Therefore, the objectives of this study were as follows: (i) to calibrate and assess the performance of a spatially distributed WATEM/SEDEM model in predicting absolute sediment yield and specific sediment yield from 12 catchments in Tigray (Ethiopia) by using two different sediment transport capacity equations (original and modified) and (ii) to assess the performance of WATEM/SEDEM for the identification of critical sediment source areas needed for targeting catchment management. The performance of the two model versions for sediment yield was found promising for the 12 catchments. For both versions, model performance for the nine catchments with limited gully erosion was clearly better than the performance obtained when including the three catchments with significant gully erosion. Moreover, there is no significant difference (alpha 5 per cent) between the performances of the two model versions. Cultivated lands were found to be on average five times more prone to erosion than bush–shrub lands. The predicted soil loss values in most parts of Gindae catchment are generally high as compared with the soil formation rates. This emphasises the importance of implementing appropriate soil and water conservation measures in critical sediment source areas prioritising the steepest part of the catchment (i.e. areas with slope >50 per cent). The applicability of the WATEM/SEDEM model to environments where gully erosion is important requires the incorporation of permanent gully and bank gully erosion in the model structure. Copyright © 2011 John Wiley & Sons, Ltd.     

Relative Contribution of Rill/Interrill and Gully/Channel Erosion to Small Reservoir Siltation in Mediterranean Environments

Reservoir siltation because of water erosion is an important environmental issue in Mediterranean countries where storage of clear surface water is crucial for their economic and agricultural development. The high density of gully systems observed in Mediterranean regions raises the question of their contribution to reservoir siltation. In this context, this study quantified the absolute and relative contributions of rill/interrill and gully/channel erosion in sediment accumulation at the outlet of small Tunisian catchments (0·1–10 km²) during the last 15 years (1995–2010). To this end, a fingerprinting method based on measurements of caesium‐137 and total organic carbon combined with long‐term field monitoring of catchment sediment yield was applied to five catchments in order to cover the diversity of environmental conditions found along the Tunisian Ridge and in the Cape Bon region. Results showed the very large variability of erosion processes among the selected catchments, with rill/interrill erosion contributions to sediment accumulated in outlet reservoirs ranging from 20 to 80%. Overall, rill/interrill erosion was the dominant process controlling reservoir siltation in three catchments whereas gully/channel erosion dominated in the other two catchments. We identified the presence of marly gypsum substrates and the proportion of catchment surface covered by soil management/conservation measures as the main drivers of erosion process variability at the catchment scale. These results provided a sound basis to propose guidelines for erosion mitigation in these Mediterranean environments and suggested to apply models simulating both rill/interrill and gully/channel erosion in catchments of the region. Copyright © 2015 John Wiley & Sons, Ltd.     

基于GPS与GIS 技术的长江上游山地冲沟的分布特征研究

长江上游山地生态环境十分脆弱，冲沟系统广泛分布，但对该区冲沟的发生演变一直缺乏定量研究数据。以西昌长山岭地区为对象，应用RTK-GPS对该区冲沟系统进行测量，建立数字高程模型（DEM）；同时基于GIS技术，探讨了从DEM上提取冲沟系统的方法，并以实测冲沟系统为依据，对所提取的冲沟系统的精度进行了对比分析。结果表明，利用DEM提取冲沟系统是一种快速、有效的方法。与此同时，分析了长江上游地区山地冲沟系统的分布特征，结果表明，小流域的沟壑密度为46．7m／hm^2，冲沟侵蚀速率高达191．9t／（hm^2．a），小流域内的土壤侵蚀为极强度土壤侵蚀，以控制冲沟侵蚀为主的水土保持措施，是该地区生态环境建设中值得重视的关键问题。     

Monitoring of soil erosion and assessment for contribution of sediments to rivers in a typical watershed of the Upper Yangtze River Basin

An assessment of the effectiveness of soil conservation practices is very important for watershed management, but the measurement over a small area does not necessarily represent the truth over a large area. Monitoring of soil erosion and analysis of sediment delivery were carried out in the Lizixi watershed (which is typical of the Upper Yangtze Basin, China), using remote sensing and a geographic information system (GIS). Land‐use and land‐cover maps were prepared by an interpretation of 1986 and 1999 images from SPOT and Landsat TM. Slope‐gradient maps were created from digital elevation model (DEM), while merged images of SPOT and Landsat TM were used to obtain land‐use information. The area of soil erosion was classified by an integration of slope gradients, land‐use types and vegetation cover rates, and soil erosion rates and their changes were calculated in a grid‐based analysis using an Erdas GIS. The change in sediment delivery ratio was estimated based on the changes in soil erosion rates from both monitoring and the truth survey. There was a reduction in soil erosion rate of 4·22 per cent during a 13‐year period after soil conservation practices were adopted in the Lizixi watershed. The amount of sediments transported into rivers has decreased by 51·08 per cent during the same period due to an integrated application of biological and engineering measures. The comparison of soil erosion severity between pre‐conservation and post‐conservation revealed that soil loss has been obviously diminished and the measures were quite effective. Copyright © 2004 John Wiley & Sons, Ltd.     

Assessing and mitigating the effects of agricultural soil erosion on roadside ditches

Purpose

Roadside ditches line more than 6.3 million km of roadways in the USA, dissecting the natural topography and altering the flow of runoff from the catchments that drain into them. In agricultural regions, more than 30% of a watershed may directly drain into the roadside ditch system. Quantifying soil erosion and sediment export from agricultural watersheds is a crucial component when considering long-term soil sustainability.

Materials and methods

Our study evaluated the relation of catchment soil erosion and ditch sedimentation at six representative roadside ditches in Lime Creek watershed (eastern Iowa) and quantified the effectiveness of possible catchment conservation practices to reduce soil erosion and ditch sedimentation.

Results and discussion

Study results provide clear evidence linking roadside ditches to the agricultural catchments that drain into them. Among the six ditch sites, catchment erosion was found to be inversely related to sediment storage within the ditch due to erosive power of water entering the ditches from their basins. Of four catchment scenarios to reduce soil erosion, no-till with cover and graded terrace did not require land to be taken out of production and provided the most significant reductions in catchment erosion rates.

Conclusions

Results indicated that reducing nutrient and sediment loads to ditches by incorporating in-field conservation practices in ditch catchments may be more economical and environmentally sustainable than current management practices for both farmers and roadway managers because they trap detached soil sediments before they enter the ditch.

     

黄土丘陵沟壑区不同土地利用方式下小流域侵蚀产沙特征

为进一步优化和合理配置水土保持措施,以黄土丘陵沟壑区3个不同土地利用方式下的坝控小流域为例,基于人工探槽取样、淤积层次甄别及与产流降雨事件的对应关系,结合1∶10 000早期地形图与全站仪测量,拟合库容曲线来估算淤地坝泥沙淤积量,进而反演坝控流域的产沙模数变化特征。结果表明:(1)延河马家沟3个不同土地利用方式下的洞儿沟、阎桥和芦渠坝控小流域,自建坝至2016年的多年平均淤积量分别为2 748.80,4 634.31,3 141.17 t;(2)洞儿沟、阎桥和芦渠流域多年平均产沙模数分别为2 432.56,3 131.29,1 794.95 t/(km~2·a),依次属于轻度、中度和轻度侵蚀;不同土地利用方式下坝控小流域的最小产沙降雨量均20 mm以上;(3)不同的土地利用方式对小流域侵蚀产沙影响显著,人类活动明显的阎桥流域多年平均产沙模数大于以林草地为主的洞儿沟流域,而以林地和梯田为主的芦渠流域多年平均产沙模数最小。由此可见,在黄土丘陵沟壑区合理配置不同的水土保持措施,是减少小流域侵蚀产沙的有效途径。     

黄土高原沟沿线的廊道防蚀效应探析

在分析黄土高原地区的沟沿线、沟沿线上下沟间地和沟谷地土壤侵蚀特征、小流域泥沙来源、坡沟侵蚀产沙关系的基础上，结合廊道的生态功能和以往的研究结果，认为在沟沿线的上部建立草灌与整地工程措施相结合的植物廊道，来拦蓄阻截沟间地的来水来沙，可使流域的土壤侵蚀量减少54．5％～77、0％。     

Assessment of soil erosion hazard in Kilie catchment,East Shoa,Ethiopia

This paper reports on a field study conducted in Kilie catchment, East Shoa Zone, Ethiopia to assess the rate of soil erosion by employing a soil loss prediction model (Universal Soil Loss Equation) integrated with in remote sensing and geographical information systems (RS/GIS), environment and gully measurement techniques. The final soil erosion risk map was produced after multiplication of the six factors involved in the USLE and RS/GIS. Gully measurement showed that the erosion rate is higher for the upland areas than the lowlands due to inappropriate soil and water conservation measures, free grazing by animals and conversion of hillside areas into farmlands. About 97·04 per cent of the study catchment falls within a range of 0–10 t ha⁻¹ yr⁻¹ sheet/rill erosion rate. We found that 2·17 per cent of the study area in the uplands has a soil erosion rate falling between 10 and 20 t ha⁻¹ yr⁻¹. About 0·8 per cent of the study area in the uplands is hit by severe sheet/rill erosion rate within the range of 20–60 t ha⁻¹ yr⁻¹. Gully erosion extent in the study area was evaluated through gully measurement and quantification methods. Gully density of 67 m ha⁻¹ was recorded in the catchment. The gully to plot area ratio was found to be 0·14 on average. Hence, in the upland areas, sustainable land management practices are required in order to reduce the rate of soil erosion. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of the Effectiveness of Forest Restoration and Check‐Dams to Reduce Catchment Sediment Yield

Reforestations and check‐dams are two commonly used measures to reduce soil erosion rates and sediment export from highly eroding catchments. Here, we evaluated the impact of the construction of 94 check‐dams and land use changes (caused by agricultural abandonment and reforestations) on sediment yield in the Upper Taibilla catchment (320 km², SE Spain) from 1956 to 2000. We combined land use change analysis, field surveys, and application of the WaTEM‐SEDEM erosion and sediment yield prediction model for nine scenarios combining land use maps (1956, 1987, and 2000) and different numbers of check‐dams throughout the catchment. Land use changes alone reduced sediment yield up to 14%, but in combination with check‐dams, the reduction in sediment yield reached 44 ± 6%. Sediment yield reduction was higher in smaller sub‐catchments, with, on average, a higher transport capacity than larger catchments, illustrating the scale dependency of human impacts on sediment fluxes and the buffer capacity of larger catchments. From an economical perspective, the construction of check‐dams was estimated to be more expensive than reforestation programs in the studied catchment, while adding more check‐dams did not always result in a proportional reduction of sediment yield. This indicates that optimizing check‐dam distribution relative to land use patterns is crucial to decrease catchment sediment yield. Check‐dams have a large and instantaneous impact on sediment yield over a restricted time period, while reforestations have important sustained effects at a lower economic cost. These contrasting effects require a careful evaluation for optimal effective catchment management. Copyright © 2014 John Wiley & Sons, Ltd.     

Flow and Sediment Connectivity in Semi‐arid Landscapes in SE Spain: Patterns and Controls

Much of the water and sediment fluxes in semi‐arid catchments are found to be highly concentrated in localized pathways. Identifying the location of these pathways in the landscape is important for management and restoration. Measures can then be targeted so as to minimize the potential for erosion and sediment flux along these pathways. A method of repeat field mapping of flow and sediment pathways suitable for Mediterranean catchments is presented. Several small catchments in Cárcavo basin, SE Spain, differing in topographic and land use characteristics, were monitored under several events. Morphometric properties of pathways were analysed and compared with rainfall characteristics. Number and length of pathways varied with rainfall characteristics and also antecedent conditions. In low rainfall events, runoff sources and main pathways were disconnected, but in a larger event, the network of pathways became fully connected. The pathway patterns showed that man‐made lines such as terrace embankments and tracks have a major influence on sediment connectivity. Micro‐topographic factors, soil moisture and the presence of vegetation are highly influential on pathways and the frequency of water and sediment fluxes. Runoff and erosion hotpots for the development of pathways were identified, which should be targeted for mitigation and restoration measures using vegetation. The relevance of local scale factors emphasizes the importance of repeat field observations to understand connectivity and pathways development in the landscape. Copyright © 2015 John Wiley & Sons, Ltd.     

Gully Head Retreat in the Sub‐Humid Ethiopian Highlands: The Ene‐Chilala Catchment

In the northern highlands of Ethiopia, gully erosion is severe. Despite many efforts to implement gully prevention measures, controlling gully erosion remains a challenge. The objective is to better understand the regional gully erosion processes and to prevent gully head retreat. The study was conducted in the Ene‐Chilala catchment in the sub‐humid headwaters of the Birr River located southwest of Bahir Dar, Ethiopia. Twelve gully heads were monitored during the 2014 and 2015 rainy monsoon phase. We measured gully head morphology and retreat length, soil shear strength, ground water table levels, and catchment physical characteristics. Two active gully head cuts were treated in 2014 and an additional three head cuts in 2015 by regrading their slope to 45° and covering them with stone riprap. These treatments halted the gully head advance. The untreated gullies were actively eroding due to groundwater at shallow depths. The largest head retreat was 22.5 m, of which about half occurred in August of the first year when the surrounding soil was fully saturated. Lowering both the water table and protecting the gully heads can play a key role in reducing gully expansion and soil loss due to gully erosion in the Ethiopian highlands. Copyright © 2016 John Wiley & Sons, Ltd.     

降水和土地利用变化对罗玉沟流域水沙关系的影响

为探讨降水和土地利用变化对流域水沙关系的影响,以黄土高原丘陵沟壑区罗玉沟流域为研究区域,利用流域25年(1986—2010年)的年降水量、年径流量和年输沙量以及土地利用变化资料,分析罗玉沟流域水沙演变规律和水沙关系变化。结果表明:在1986—2010年罗玉沟流域年降水量和汛期降水量基本保持平稳,无明显的增减趋势,而流域年径流量和年输沙量整体呈波动递减的变化趋势,降水与径流相关分析得出,汛期产流产沙对流域年径流量和年输沙量影响最显著。对不同时期流域水沙变化分析,土地利用方式改变,主要是梯田、林草等水土保持措施,对于流域减水减沙作用有限,梯田和林草面积的增加并未明显改变流域水沙关系,淤地坝等工程措施对黄土高原丘陵沟壑区流域减水减沙具有重要作用。研究结果可为黄土丘陵沟壑区水土流失治理及水土保持措施布设提供理论依据。     

Soil erosion assessment of Lake Alemaya catchment,Ethiopia

Land degradation due to soil erosion is the major problem facing Ethiopia today. In the Lake Alemaya catchment soil erosion is caused by the intense rainfall, steep topography, and poor vegetation cover coupled with cultivation of steep lands, and inadequate conservation practices. Sediment from the catchment has affected the storage capacity of Lake Alemaya. This study has integrated the Agricultural Non‐point Source Pollution Model (AGNPS) and the technique of the Gographic Information System (GIS) to quantify soil erosion in the Lake Alemaya catchment. After application of the AGNPS, it appears that 66 per cent of the catchment has a soil erosion rate of 10 to more than 80 t ha⁻¹ y⁻¹. The annual soil loss is estimated at 31 t ha⁻¹, which is more than the permissible value of 1–16 t ha⁻¹ for different agro‐ecological zones of Ethiopia. The sediment yield of the catchment is about 10 148 ton with a delivery ratio of 6·82 per cent. Therefore, an effective management plan is needed for the conservation and rehabilitation of the catchment and to maintain the storage capacity of Lake Alemaya. Copyright © 2006 John Wiley & Sons, Ltd.     

Gully erosion: Impacts, factors and control

Gully erosion attracts increasing attention from scientists as reflected by two recent international meetings [Poesen and Valentin (Eds.), Catena 50 (2–4), 87–564; Li et al., 2004. Gully Erosion Under Global Change. Sichuan Science Technology Press, Chengu, China, 354 pp.]. This growing interest is associated with the increasing concern over off-site impacts caused by soil erosion at larger spatial scales than the cultivated plots. The objective of this paper is to review recent studies on impacts, factors and control of gully erosion and update the review on ‘gully erosion and environmental change: importance and research needs’ [Poesen et al., 2003. Catena 50 (2–4), 91–134.]. For the farmers, the development of gullies leads to a loss of crop yields and available land as well as an increase of workload (i.e. labour necessary to cultivate the land). Gullies can also change the mosaic patterns between fallow and cultivated fields, enhancing hillslope erosion in a feedback loop. In addition, gullies tend to enhance drainage and accelerate aridification processes in the semi-arid zones. Fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion. In this respect, tracers such as carbon, nitrogen, the nuclear bomb-derived radionuclide 137 Cs, magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment. Recent studies conducted in Australia, China, Ethiopia and USA showed that the major part of the sediment in reservoirs might have come from gully erosion.Gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess (European belt, Chinese Loess Plateau, North America) and sandy soils (Sahelian zone, north-east Thailand) or in soils prone to piping and tunnelling such as dispersive soils. Most of the time, the gullying processes are triggered by inappropriate cultivation and irrigation systems, overgrazing, log haulage tracks, road building and urbanization. As exemplified by recent examples from all over the world, land use change is expected to have a greater impact on gully erosion than climate change. Yet, reconstructions of historical causes of gully erosion, using high-resolution stratigraphy, archaeological dating of pottery and ¹⁴C dating of wood and charcoal, show that the main gully erosion periods identified in Europe correspond to a combination not only of deforestation and overuse of the land but also to periods with high frequency of extreme rainfall events.Many techniques have proved to be effective for gully prevention and control, including vegetation cover, zero or reduced tillage, stone bunds, exclosures, terracing and check dams. However, these techniques are rarely adopted by farmers in the long run and at a larger spatial scale because their introduction is rarely associated with a rapid benefit for the farmers in terms of an increase in land or labour productivity and is often contingent upon incentives.     

安塞县侯沟门村新农村建设与水土保持措施配置研究

根据野外天然降雨定位监测试验、野外人工模拟降雨与放水冲刷试验、土壤侵蚀类型遥感监测资料及附近纸坊沟小流域泥沙监测资料等.对安塞侯沟门村不同小流域土壤侵蚀类型及其分布规律和水土保持措施配置进行系统研究,特别是对村庄、道路、裸露坡面硬地面产流产沙规律进行了研究.明确了水土保持综合治理思路和重点及存在的问题,为今后评价土壤侵蚀变化、水土保持规划和综合治理提供科学依据.     

Derivation of site-related measures to minimise soil erosion on the watershed scale in the Saxonian loess belt using the model EROSION 3D

The Saxonian loess belt is one of the areas in Germany most endangered by water erosion. As consequence of extreme rainstorms, farmland and adjacent areas, e.g. villages, roads, biotopes and watercourses, are repeatedly damaged. Estimating soil loss is a crucial factor for sustainable land use planning in this region. Since soil erosion measurements are usually conducted at the scale of plots, thereby being both costly as well as time-consuming, erosion models are substantial tools for soil protection policies. This paper summarises and integrates the results of a research project aimed at assessing the present situation as well as that of future landscape planning alternatives, using the physically based EROSION 3D simulation model on a catchment scale. EROSION 3D can estimate the yields of sediment for small watersheds and enables environmental researchers and planners to locate the main areas of soil loss and deposition. Five different scenarios based on past and present land use information as well as future landscape 2 planning alternatives were simulated.The modelling results showed that scenarios based on only one option for minimising soil loss were not sufficiently effective in reducing sediment production. However, the combination of active soil protection measures such as conservation tillage with passive measures like grassed waterways or buffer strips resulted in an adequate soil protection. In contrast to passive protection measures, best management practices like non-tillage systems are commonly used in the Saxonian loess belt already. Thus, the implementation of passive measures is an important future task in land use planning. Simulation models like EROSION 3D can provide the information needed for the adequate localisation and the dimensioning of site-specific measures.     

The onsite cost of gully erosion and cost‐benefit of gully rehabilitation: A case study in Ethiopia

Gully erosion often indicates extreme land degradation. In the highlands of Ethiopia, wide and deep gullies are common features, significantly affecting land used for agriculture. However, little action is being taken to address the problem. Where rehabilitation actions in Ethiopia are taking place, they are rarely studied by financially quantifying their costs and benefits. Therefore, this study developed methods of quantifying gully erosion costs and rehabilitation costs and benefits by considering the soil components of four model rehabilitated gullies in Ethiopia. Data were obtained from a physical survey supported by secondary information from relevant agricultural offices. Quantification was achieved by monetizing gully erosion cost through yield loss and gully rehabilitation calculations according to expenditure, while rehabilitation benefits were obtained by monetizing estimated deposited soil nutrients using fertilizer prices. Cost‐benefit values show that investment in gully rehabilitation can be an economically viable proposition in some instances. Stakeholders involved in gully rehabilitation should continue to invest in appropriate techniques of gully rehabilitation and management to ensure continued benefits from rehabilitated gullies and use of surrounding farmlands. Copyright © 2010 John Wiley & Sons, Ltd.     

Soil Conservation Through Sediment Trapping: A Review

Preventing the off‐site effects of soil erosion is an essential part of good catchment management. Most efforts are in the form of on‐site soil and water conservation measures. However, sediment trapping can be an alternative (additional) measure to prevent the negative off‐site effects of soil erosion. Therefore, not all efforts should focus solely on on‐site soil conservation but also on the safe routing of sediment‐laden flows and on creating sites and conditions where sediment can be trapped. Sediment trapping can be applied on‐site and off‐site and involves both vegetative and structural measures. This paper provides an extensive review of scientific journal articles, case studies and other reports that have assessed soil conservation efforts and the sediment trapping efficacy (STE) of vegetative and structural measures. The review is further illustrated through participatory field observation and stakeholders' interview. Vegetation type and integration of two or more measures are important factors influencing STE. In this review, the STE of most measures was evaluated either individually or in such combinations. In real landscape situations, it is not only important to select the most efficient erosion control measures but also to determine their optimum location in the catchment. Hence, there is a need for research that shows a more integrated determination of STE at catchment scale. If integrated measures are implemented at the most appropriate spatial locations within a catchment where they can disconnect landscape units from each other, they will decrease runoff velocity and sediment transport and, subsequently, reduce downstream flooding and sedimentation problems. Copyright © 2014 John Wiley & Sons, Ltd.     

Erosion modelling approach to simulate the effect of land management options on soil loss by considering catenary soil development and farmers perception

The prevention of soil erosion is one of the most essential requirements for sustainable agriculture in developing countries. In recent years it is widely recognized that more site‐specific approaches are needed to assess variations in erosion susceptibility in order to select the most suitable land management methods for individual hillslope sections. This study quantifies the influence of different land management methods on soil erosion by modelling soil loss for individual soil‐landscape units on a hillslope in Southern Uganda. The research combines a soil erosion modelling approach using the physically based Water Erosion Prediction Project (WEPP)‐model with catenary soil development along hillslopes. Additionally, farmers' perceptions of soil erosion and sedimentation are considered in a hillslope mapping approach. The detailed soil survey confirmed a well‐developed catenary soil sequence along the hillslope and the participatory hillslope mapping exercise proved that farmers can distinguish natural soil property changes using their local knowledge. WEPP‐model simulations show that differences in soil properties, related to the topography along the hillslope, have a significant impact on total soil loss. Shoulder and backslope positions with steeper slope gradients were most sensitive to changes in land management. Furthermore, soil conservation techniques such as residue management and contouring could reduce soil erosion by up to 70 percent on erosion‐sensitive slope sections compared to that under tillage practices presently used at the study site. The calibrated model may be used as a tool to provide quantitative information to farmers regarding more site‐specific land management options. Copyright © 2008 John Wiley & Sons, Ltd.     

Slope and rainfall effects on the volume of sediment yield by gully erosion in the Souar lithologic formation (Tunisia)

The Souar lithologic formation in semi-arid Tunisia is undergoing severe gully erosion which is threatening soil and water resources. Soil conservation strategies have focused more on terracing than on gully control techniques, since the contribution of gully sediment yield in the overall soil loss from watersheds is unknown. The paper reports investigations into the sediment yield provided by head-cut as well as sidewall–floor erosion of first order gullies on gentle and steep slope catchments underlined by the Souar lithologic formation. We measured mean field sediment volumes evacuated by different headward reaches of 10 and 9 gullies located on gentle and steep slope catchments, respectively. Two equations between the length of the gully head cutting and the corresponding volume of evacuated sediment were established. The treatment with a Geographic Information System (Arc View) of air photographs of six flights from 1952 to 2000 allowed the calculation of the volume of sediment provided both by head cutting and gully sidewalls–floor erosion through the following up of gully extension in eight catchments during the five periods separating the dates of these flights. Total gully erosion was on average 1.66 m³ ha^− 1 year^− 1 for the gentle slopes and 5.603 m³ ha^− 1 year^− 1 for the steep slopes. Sidewalls–floor contribution in total erosion was on average 81.5% for the gentle slopes and 77.8% for the steep slopes. We found out that the mean annual rainfall resulting from 40 mm daily rainfall threshold explained better the variation of annual head cutting sediment yield for these five periods than any other annual rainfall resulting from lower daily rainfall thresholds. Two equations between these two variables were established both for gentle and steep slope catchments.