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There is a knowledge gap concerning the identification and quantification of transported soil particles in subsurface flows. If these soil particles reach relevant amounts, protective measures against soil erosion applied on the surface may be partially ineffective, and the soil may degrade further and unnoticed. In consequence, there is a need to develop a method to determine this subsurface particle transport in situ. A laboratory flume experiment was developed to examine the processes of fine soil material transport as well as the development of sediment traps for in situ measurements. Since, steep-slope vineyard soils are especially prone to subsurface flows they were subject of first investigations: The shallow steep-slope vineyard soils of the Mosel wine region are mainly developed from Devonian argillaceous schists and Pleistocene terrace sediments. Among the main physical characteristics are a very high rock fragment content and a loose surface layer over a strongly compacted layer caused by the combined action of tillage and weathering. This structure is presumably prone to subsurface flows within the upper horizon, especially in periods of very high soil moisture. The results of this laboratory experiment clearly confirm the presence of subsurface particle transport and the applicability of a sediment trap prototype consisting of a relatively simple and low-cost drain structure.

Rain driven flash floods have severe impacts on society and landscape functions. The July 2021 flood in the Eifel region, west Germany, was one drastic example of such impact. While media and scientists rightfully highlighted the meteorological and hydrological aspects of this flood, it was the concurrent reorganisation of important landscape conditions and the debris carried by the fast flowing water that made this flood so devastating and unpredictable.Here, we take a process-based impact perspective and systematically ask, which were the specific roles of non-hydraulic but geomorphic dynamics that implemented the damage, caused flood non-linearities and amplified the landscape deterioration. We combine insights from field mapping campaigns during, right after and within the relaxation phase of the flood with high resolution geophysical and LiDAR surveys to discuss the role of hillslopes, vegetation, fluvial sediment mobilisation and the legacy of anthropogenic landscape reorganisation. We conclude that some of these elements emerged as the flood event evolved, causing either transient effects or persistent landscape features, thus modifying the response of the landscape to future events, also to less intense precipitation events.Our findings not only support more tailored recovery efforts for the flood affected Eifel catchments, but should also inform landscape development trajectories and potentially crucial factors in other Central European regions.

Rainfall simulators represent often-used equipment for soil research. Depending on their performance, they could be appropriate for some soil research or not. The aim of this research is to provide insight into the capabilities of existing dripping rainfall simulators (DRS) to mimic natural rainfall and the frequency of simulated rainfalls of certain characteristics, facilitate the selection of rain simulators that would best meet the needs of soil research and to reach a step closer to the standardization of rainfall simulators. DRS performance was analyzed integrally, for simulators with more than one dripper (DRS>1) and with one dripper (DRS=1). A statistical analysis was performed for the performance of the DRS, wetted area, drop size, rainfall intensity, duration and kinetic energy. The analysis showed that DRS can provide rainfall that corresponds to natural rainfall, except in terms of the drop size distribution and wetted area. However, usually there are more factors that do not correspond to natural rainfall, such as the median drop size, volume and kinetic energy. Metal and plastic tubes (MT and PT) as the most present dripper types showed a strong relation between the outer diameter (OD) and drop size, while the inner diameter (ID) relation was moderate-to-weak. However, when increasing the range of MT drippers, for diameter size, the relation significance becomes very strong for bouts ID and OD. With the increase in the ID of PT, the relation deviates from the logarithmic curve that represents all drippers together. The sizes of the drops generated by the drippers are mostly in the range between 2 and 6 mm, while the number of drops smaller than 2 mm is relatively small. The intensity and duration of the simulated rain can be successfully produced to match natural values, with the most frequently simulated short-term rainfall of a high intensity. Most simulations were conducted at a fall height of up to 2 m, and then their number gradually decreases as the height gets closer to 5 m. Most simulations (58.6%) occur in the range between 20-90% KE, then 33.0% in a range of 90-100%, with only 8.4% lower than 20% KE.

In the context of the Sustainable Development Goals (SDG), understanding landscape evolution is essential to design long-term management plans. In agricultural fields, such as the vineyards on steep slopes, the terraces offer one of the most important morphological changes. However, it is not clear if the poorly managed agricultural terraces are optimal to reduce soil erosion and overland flow, although the trafficability is improved. Therefore, the main aim of this research is to compare the differences between initial soil erosion processes on poorly managed terraced vineyards and sloping vineyards at the pedon scale, considering the key role of the SSC (Soil Surface Components). To achieve this goal, twenty-six rainfall simulations were performed, considering the inclination, vegetation and stone covers, and surface roughness. Our research was carried out in the sloping vineyards (>20°) of the Almachar municipality, in the Montes de Malaga (Spain). Those vineyards are characterized by bare soils, low organic matter and high rock fragment contents. Our results showed that higher soil losses (42.2 g m−2 vs 9.4 g m−2) and runoff (4.9 l m−2 vs 1.6 l m−2) were detected in the plots of the poorly managed terraced vineyard than in the sloping one. Moreover, the time to runoff generation was lower in the poorly conserved terraces (232 s) than in the sloping vineyard (679 s), showing a faster saturation capacity. The SSC considered as the key factors were the reduction of the stone cover and an increase of roughness. As a conclusion, we confirm that the imminent transformation from sloping vineyards into terraced fields could lead several land degradation processes if a poor management is carried out, and no control measures are applied during the process, such as the conservation of stone walls or vegetation cover above the embankment, which is not in compliance with the SDG.

Rainfall simulation experiments are widely used in soil science, geomorphology and hydrology research and teaching. Such experimental setups are particularly important in the study of rainfall-runoff, erosion and pollutant transport processes. Rainfall simulators have been applied within laboratory- and field-based studies and have the advantage of enabling controlled and reproducible rainfall events of varying intensity, duration and drop spectra. The flexibility and adaptability of rainfall simulators to examine diverse research applications of varying temporal and spatial scales means that hundreds of tailor-made rainfall simulator setups can be identified across the literature. Although it is beneficial for researchers to adapt their experimental designs to suit their specific research objectives, the diversity in the type, sizing, form, operation and methodologies of rainfall simulators ultimately results in complications when comparing results and outputs obtained between studies.Currently, comparisons between studies can be very difficult, if not impossible, as the different measurement methods, artificial rainfall event characteristics and test conditions result in considerable difficulties when benchmarking results and findings obtained from rainfall simulation experiments. We recommend that the scientific community should establish a set of methodological procedures aimed at harmonising basic procedures in rainfall simulator-based studies in the fields of hydrological and geomorphological sciences. This would ensure that results obtained from different rainfall simulator studies and setups are harmonised, regulated and comparable. On the one hand, this process involves harmonising rainfall simulators design characteristics, whereas further steps should focus on measurement methods and metrics so results can be more readily compared.This presentation highlights the inherit problems in benchmarking and comparing studies at present due to large variations in the way that researchers and institutions assess and quantify rainfall simulator performance and present results. Some degree of ‘standardisation’ of rainfall simulator approaches is needed. However, standardising approaches used within rainfall simulation does not allow researchers to adapt their experimental setups to suit their specific research needs, which is one of the key benefits of using rainfall simulators. Instead, ‘harmonisation’ (i.e. ensuring that the scientific community develop a set of regulated and comparable methodological procedures and best practices for use in rainfall simulator studies whilst still allowing some degree of adaptability for specific research practices) is required. Here we present a series of harmonisation procedures, which should be developed to ensure that rainfall simulators are designed and constructed to allow for harmonisation, as well as suggesting a series of steps towards harmonising the methods and metrics used to quantify and compare experimental results.With these objectives in mind, we aim to stimulate the discussion and enhance understanding of the difficulties and requirements of rainfall simulator based experimental research, namely by creating a platform that embraces and consults the International research community across multiple research facilities and institutes. This presentation will kick-start discussions (via web seminar sessions beginning in Summer 2021) leading up to a future international symposium addressing and acting upon these issues and disseminating the findings of this consultation period (Spring/Summer 2022 in Coimbra, Portugal). Everyone is invited to join this step towards harmonisation in rainfall simulation.

Within the European project Diverfarming (Horizon 2020, no 728003), which investigates crop diversification and low-input farming across Europe, we study the aggregate stability variability of soils with high rock fragment content on steep sloping vineyards in the upper Saar valley of the Mosel area (Wawern, Rhineland-Palatinate, Germany).In the framework of the case study researched by Trier University and their partners, aromatic herbs (Oregano and Thyme) are planted in rows underneath the grapevines to minimize soil erosion, suppress unwanted weeds and to be harvested for further use. Additionally, this cultivation affects different soil characteristics such as aggregate stability.We analyse the aggregate stability using and comparing three different methods:wet sieving which is executed in two different ways – slaked and rewetted treatment, percolation method and single drop technique. Aim of the study is to understand the effect of soil treatments underneath the grapevines, and to identify the method(s) being able to quantify the differences best.Regarding the different methods, first results indicate that the quantified aggregate stabilities of each method are comparable. With this, we could identify differences between uncultivated rows (control areas), and the rows intercropped with aromatic herbs. In the latter ones, the aggregate stability underneath the grapevines is affected positively. Furthermore, there is a clear difference between slaked and rewetted treatment within the wet sieving method, where less stable aggregates are isolated.The results indicate that the accomplished management (vine intercropped with Oregano and Thyme) improves the aggregate stability and therefore it improves the soil quality in general.

Mechanized vineyard floor tillage aims at minimizing negative impact of weeds on water competition and spread of pests and diseases without herbicide application. It includes tillage between vines, in the vine row, and in headlands around vineyard blocks. While there is an increased awareness from vine growers and scientists concerning water erosion, wind erosion and dust emission are largely unnoticed processes that have not been investigated yet. The emission of soil particles seems to be strongly associated to the working of the soil surface by means of (tracked) tractor. This impact may be particularly important on surfaces considered erosion stable due to vegetation or stone cover preventing soil from direct detachment by wind.The row-tillage only underneath the vines is an important management practice in modern and in organic viticulture because of the strongly reduced soil disturbance compared with clearing of the complete vineyard floor area. We investigated tillage as a trigger for wind erosion and dust production on particularly inclined vineyards in this study.Three different tillage tools in three combinations were tested on two different steep-slope vineyards by means of modified Wilson and Cook Sampler (MWACS): rotary hoe, disc plow, and finger weeder.We measured eroded material on both sites for different states of soil moisture and wind intensity. The results suggest a relationship between particular tillage tool combinations and airborne substrate particles that correspond to the general mechanical procedure.These first results for measurement of tillage-induced wind erosion and dust emission indicate a considerable potential of vineyards to release dust that is related to specific management device needs to be investigated by means of qualitative analysis, flux measurements and monitoring.

The Mosel wine region (Rhineland-Palatinate, Germany) is the largest steep vineyard region in the world. Due to extreme slopes, tillage with heavy machinery, increase in extreme precipitation events, and new planting of vines, these vineyards are among the agricultural systems most affected by soil erosion.As a result of viticulture since the Roman period and their special characteristics, almost all vineyard soils in the Mosel region are classified as Terric Anthrosols. These soils are characterized by a very high rock fragment content (mainly Devonian argillaceous schists and fluvial sediments) and a loose surface horizon over a compact one due to tillage or weathered parent material. This structure enables subsurface flows within the upper horizon, especially in periods of very high soil moisture.There is a knowledge gap concerning the identification and quantification of transported soil particles in this subsurface flow. If these soil particles reach relevant amounts, superficial protective measures against soil erosion may be partially ineffective, and the soil degrades due to substantial loss of fine material. In consequence, there is a need to develop a method to determine this subsurface particle transport in situ.In this study, a first experimental approach for assessing the occurrence of subsurface erosion of fine-grained soil particles within soils is presented. Using this experimental set-up, it is possible to prove the process of fine soil material transport as well as the development of sediment traps for in situ measurements.The experimental approach consists of a sediment trap prototype, based on a drainage pipe, which is positioned into a test flume. The dimensions of this flume are 2.7 m x 0.9 m x 0.2 m (L x W x H). It is filled with material from a vineyard soil of the Mosel valley flanks. Water enters the flume from the upper end with the help of an 0.11 m high overflow. The sediment trap is 0.86 m long and has an 0.855 m x 0.4 m long side-cut-out where a mesh (mesh aperture 3 mm x 6 mm) is installed. It is connected to a separate drain where the water and eroded sediment are collected. This is analysed in the laboratory to quantify the amount and characteristics of the eroded material. Additionally, the total subsurface flow is measured by a drain at the lower end of the soil body for having a total mass budget of runoff and erosion.The preliminary results show a clear correlation between the measured total subsurface flow and sediment transport with the ones collected with the sediment trap. The results suggest that this sediment trap prototype is clearly suitable to quantify the subsurface soil erosion. In the further course of the work, the sediment trap will be installed in situ in the vineyards to test its field applicability to determine valid subsurface erosion rates in vineyard soils.

The effects of intercropping grapevine with aromatic plants are investigated using a multi-disciplinary approach. Selected results are presented that address the extent to which crop diversification by intercropping impacts grapevine yield and must quality, as well as soil water and mineral nutrients (NO3-N, NH4-N, plant-available K and P). The experimental field was a commercial steep-slope vineyard with shallow soils characterized by a high presence of coarse rock fragments in the Mosel area of Germany. The field experiment was set up as randomized block design. Rows were either cultivated with Riesling (Vitis vinifera L.) as a monocrop or intercropped with Origanum vulgare or Thymus vulgaris. Regarding soil moisture and nutrient levels, the topsoil (0&ndash, 0.1 m) was more affected by intercropping than the subsoil (0.1&ndash, 0.3 m). Gravimetric moisture was consistently lower in the intercropped topsoil. While NO3-N was almost unaffected by crop diversification, NH4-N, K, and P were uniformly reduced in topsoil. Significant differences in grapevine yield and must quality were dominantly attributable to climate variables, rather than to the treatments. Yield stabilization due to intercropping with thyme and oregano seems possible with sufficient rainfall or by irrigation. The long-term effects of intercropping on grapevine growth need further monitoring.

Raindrop splash describes processes related to a raindrop impacting a soil surface. Splash erosion is the initial phase of soil erosion by rain and dominates particle erosion and redistribution prior to the generation of overland flow, and its impact on splash rates has not been fully understood yet. The extent of splash erosion is determined by drop-surface interactions with major influencing factors related to drop characteristics and soil surface properties. Effects of raindrop splash are diffusion of surface material, supply with easily erodible sediments, compaction, and sealing, thus directly and indirectly affecting subsequent hillslope processes on various spatio-temporal scales. The geomorphological relevance of raindrop splash ranges on micro- to macrotopographic scale and influences source and sink dynamics concerning sediment transport and flow path development in the context of connectivity research and may be a landscape factor in ranges particularly in the case of wind-driven raindrops.

Rainfall simulators are one of the most popular research devices for studying the impacts of rainfall on activation of runoff, infiltration, and sediment transport mobilization in the landscape. The research covers also related processes such as generation mechanisms of overland flow, interrail and rill erosion, soil compaction, soil surface changes, sealing, crusting, solutes transport, and others. Regarding the high number of research goals, different fields of application, and, finally, also due to the technical creativity of the research staff, several different rainfall simulator types are available and the standardization is not in sight. In this chapter, the differences in the existing devices with their pros and cons, the different research applications as well as the constraints, needs, and challenges for a future use are explained and some application examples included.

Rainfall simulation is widely used within hydrological and geomorphological sciences and is particularly important in the study of rainfall-runoff, erosion and pollutant transport processes. Rainfall simulators have been applied within laboratory- and field-based studies and have the advantages of enabling controlled and reproducible rainfall event characteristics in relation to rainfall intensity, duration, and drop spectra. The flexibility and advantages of using rainfall simulators to study a wide range of research objectives has resulted in significant diversity in the type, sizing, form, operation and methodologies of rainfall simulators, and an extensive review of rainfall simulator research has led to more than 250 different rainfall simulator setups being identified in the literature. Rainfall simulators come in all different shapes and sizes!The adaptability of rainfall simulators to study a wide range of research areas of varying scale ultimately results in several issues when comparing results and outputs obtained from different simulator setups. In fact, comparisons between studies can be very difficult, if not impossible, as the different measurement methods, artificial rainfall event characteristics and test conditions result in considerable difficulties when benchmarking results and findings obtained from rainfall simulation experiments. Thus, the scientific community should establish set methodological procedures to allow comparisons between results obtained from different rainfall simulator setups. Harmonization of basic procedures in rainfall simulator based studies in the fields of hydrological and geomorphological sciences would ensure that results between different rainfall simulator studies are comparable, standardised and regulated. The first step in this process involves standardising rainfall simulators design characteristics, whereas further steps should focus on measurement methods and metrics so results can be compared.This paper aims to bring together current understanding on the use of rainfall simulators within hydrological and geomorphological research, and provide a platform to discuss and enhance understanding of the requirements on the standardisation of rainfall simulator based experimental research. This paper also aims to establish an international research community focused on advancing standardisation in rainfall simulation based at different research facilities and institutes, and will kick-start discussions leading up to a future international symposium dealing with these issues (date TBC). Everyone is invited to join this (small) step towards standardisation in rainfall simulation!

The Mosel wine region (Rhineland-Palatinate, Germany) is the largest steep vineyard region in the world. Due to extreme slopes (>17°), tillage with heavy machinery, increase in extreme precipitation events and new planting of vines, these vineyards are among the agricultural systems most affected by soil erosion.Due to viticulture since the Roman period and their special characteristics, almost all vineyard soils in the Mosel region are classified as Terric Anthrosols. Soils are characterized by a very high rock fragment content (schists and fluvial sediments) and a loose surface layer over a compact layer due to tillage or weathered parent material. This structure enables subsurface flows between these two layers, especially in periods of very high soil moisture.There is a knowledge gap in the identification and quantification of transported soil particles in this subsurface flow. If these soil particles reach relevant amounts, superficial protective measures may be partially ineffective and the soil degrades despite the existing protection. In consequence, there is a need to develop a method to determine this subsurface particle transport in situ.Here, we present a first experimental approach for assessing the occurrence of sub surface erosion of fine-grained soil particles within soils. With this, it is possible to prove this process and the development of a sediment trap prototype, based on a drainage pipe, for in situ measurements of subsurface soil erosion.

The intensification of European agriculture leads to soil degradation, reduction of biodiversity and an increased economic risk for the farmers. An approach towards solving this problem is crop diversification and the optimized use of resources. Increasing agricultural efficiency/resilience through diversification and the associated falling environmental costs could contribute to the growth of the European agricultural sector by adapting the entire value chain.The EU-funded project DIVERFARMING (Horizon 2020 no 728003) aims to develop and deploy innovative farming and agribusiness models based on crop diversification. Germany is involved with a broad-based study in organic steep slope viticulture in Wawern (Saar Valley).A fundamental issue of steep slope viticulture is related to vegetation management below the vines. In order to overcome problems of soil erosion and soil organic matter depletion, an increasing number of winemakers is establishing cover crops such as grasses and legumes in driving lanes. On the contrary, the area underneath the vines is typically kept free of vegetation to avoid fungal diseases and competition on water. As cover crops do not benefit to the value chain and may compete with vines on water or have other adverse effects on vine performance, an alternative strategy for vegetation management underneath vines in steep slope viticulture is required.Therefore, intercropping vines with perennial herbs like Thyme and Oregano growing underneath is a promising cropping practice to address the abovementioned issues. Both herbs are economically valuable and originate from dry and warm environments, which are typical for most viticultural areas. Furthermore, their relatively low need for water and flat-growing habitus is assumed to be suitable to cover the soil underneath the vines in order to protect against erosion and suppress weeds without having adverse effects on vine growth and -health. They can be marketed directly or indirectly as a concentrate for cosmetics, perfumes, nutritional supplements and food.During the 5-year project, we will investigate impacts on and interactions between crops, soil ecological and physicochemical properties as well as erosion and emission of greenhouse gases to evaluate ecological benefits of crop diversification. Selected results obtained within the first two years of investigation will be presented.

Viticulture is a land use system with a high impact on the environment and the landscape due to the high input of energy and material for soil and plant management. Reducing the input would help to reduce both, the environmental and economic costs, and consequently, increase the sustainability of this crop production. In Germany, especially in the Mosel area, vineyards are also part of the cultural heritage and substantial part of the touristic appeal, especially those located on steep slopes with shallow soils developed on Devonian slate. Within the last decades, the economic sustainability of the vineyards and cellars have been on the focus, by applying land consolidation, increasing the use of machinery and rationalisation of plant protection by e.g. spraying pesticides with helicopters. However, the awareness of the consequences of this kind of high intensive viticulture has also lead to changes in some paradigms, especially regarding soil protection: greening of the lane and selective traffic of machines is becoming more and more widespread, and there is a slowly growing community of wine cellars applying organic production. A careful management of the vegetation within the traffic lanes, and recently the implementation of plants underneath the grapevines is meant to increase soil quality and to reduce the risk of erosion. Here, we will present the concept developed within the EU-H2020 project Diverfarming (H2020-RUR-2016-2/728003), where aromatic herbs (Thymus vulgaris, Origanum vulgare) have been planted underneath grapevines. The purpose is to suppress the growth of plants fostering diseases, to reduce soil disturbance and thus, to increase soil quality as well as to stabilize it against soil erosion. A holistic approach is adopted, as the analysis and monitoring covers plant growth, soil parameters up to product quality and a value chain analysis.

It is well known that rainfall causes soil erosion in sloping German vineyards, but little is known about the effect of age of plantation on soil erosion, which is relevant to understand and design sustainable management systems. In the Ruwer-Mosel valley, young (1- to 4-years) and old (35- to 38-years after the plantation) vineyards were selected to assess soil and water losses by using two-paired Gerlach troughs over three years (2013-2015). In the young vineyard, the overland flow was 107 L m-1 and soil loss 1000 g m-1 in the year of the plantation, and decreased drastically over the two subsequent years (19 L m-1; 428 g m-1). In the old vineyard, soil (from 1081 g m-1 to 1308 g m-1) and water (from 67 L m-1 to 102 L m-1) losses were 1.2 and 1.63 times higher, respectively, than in the young vineyard.

Las unidades geomorfologicas estan relacionadas con ciertos procesos y con la historia de su formacion. Ademas, se definen por sus formas y materiales. En este estudio se investigan los procesos de erosion en diferentes unidades de relieve. Simulaciones de lluvia, experimentos en rigolas y seguimientos a traves de fotografia aerea se llevaron a cabo en dunas, glacis, rellenos holocenos, taludes y terrazas franco-arcillosos de origen cuaternario, con el objeto de conocer la variacion en la intensidad de los procesos. Para ello, se evaluaron el impacto de las gotas de lluvia, la generacion de escorrentia, la erosion en inter-rigolas y rigolas durante varios anos. Las areas de estudio se situaron en el NE y SE de Espana, sur de Marruecos y norte de Burkina Faso. Los resultados muestras claramente que los procesos medidos son muy diferentes entre si segun la formacion de las propias unidades de relieve. Las dunas y los rellenos holocenos en los valles son altamente susceptibles a la erosion por el impacto de las gotas de lluvia y la formacion de regueros. Por el contrario, las terrazas sobre materiales franco-arcillosos muestran baja susceptibilidad a los procesos de erosion. Por lo tanto, se puede concluir que las distintas unidades de relieve muestran diferentes dominancia e intensidad de procesos. Las diferencias son mas significativas con el incremento de la escala y la complejidad del proceso erosivo: el crecimiento de las carcavas varia mucho mas entre diferentes unidades que los efectos del impacto de la gota de lluvia y la formacion de rigolas.

Transport of soil particles prior to the occurrence of overland flow is one of the big question marks in soil erosion studies. The exact measurement of short-distance transported soil particles is a challenge to soil erosion science due to the particular requirements of the experimental design and test procedure. To quantify amount and distance of each type of transport, we developed an experimental laboratory setup including a multiple-gutter system and the Trier Portable Wind and Rainfall Simulator (PWRS). Measured were amount and travel distance of soil particles detached and transported by raindrops (splash-creep and splash), wind-driven rain (splash-creep, splash-saltation and splash-drift) and wind (reptation and saltation). The test setup included three different agents of erosion (rain solely, wind-driven rain and wind solely), two substrates (sandy and loamy), three surface structures (smooth/ grain roughness, rills lengthwise and rills transversal) and three slope angles (0°/horizontal, 7° downslope and 7° upslope). The results give detailed transport patterns of the three erosion agents under the varying substrates and surface conditions up to a distance of 1.6 m. Influence of the surface factors varies, whereas the factor “agent of erosion” seems to be the most crucial one. Under the applied rain intensity and wind velocity, wind-driven rain splash generates the highest erosion and a further travel distance of the particles due to the combined action of wind and rain. The impact of all three agents of erosion implicates considerable redistribution processes and is a crucial factor for investigation of source- and sink dynamics, field scale sediment budgets and connectivity.

The movement of stones is important in a variety of disciplines such as geomorphology or hydraulic engineering. Plenty of different sensors, visual, active or passive tracers exist to capture movements in various ways. However, none of them is sufficiently small to be implanted in pebbles with a longest axis of approx. 60 mm. In this article, a sufficiently small probe is introduced: the Smartstone probe. It consists of a metal cylinder (diameter 8 mm, length 55 mm) with a flexible antenna and contains a Bosch BMX055 sensor composed of a triaxial accelerometer, magnetometer and gyroscope, respectively. Additional components inside the probe are memory to store data, active RFID (Radio-frequency identification) technique to transmit data and two button cells as power supply. Mounted into a pebble, the applicability of this probe was tested in laboratory flume experiments by determining the pebble movement using the Smartstone measurements and comparing them to the movement pattern captured by a high-speed camera. The derived orientations and positions in these test experiments resulted in deviations of 32.4% compared to the visual footage. The different reasons for deviations are noise, quantization error, integration error, orientation error and clipping. The error sources were divided with supplementary experiments resulting in mean absolute deviation (MAE) of 3.3% due to noise, quantization, and integration errors; orientation errors result in an increased MAE of 13.7% in natural environment and 21.7% in laboratory. The MAE of all experiments containing clipping was 63.2%. These deviations will be reduced in future by application of methods like Kalman filtering or Markov models, which are established in other disciplines like computer science, robotics or (pedestrian) navigation.

Abandonment of agricultural land results in on- and off-site consequences for the ecosystem. In this study, 105 rainfall simulations were carried out in agriculture lands of the Mediterranean belt in Spain (vineyards in Malaga, almond orchards in Murcia, and orange and olive orchards in Valencia) and in paired abandoned lands to assess the impact of land abandonment on soil and water losses. After abandonment, soil detachment decreased drastically in the olive and orange orchards, while vineyards did not show any difference and almond orchards registered higher erosion rates after the abandonment. Terraced orchards of oranges and olives recovered a dense vegetation cover after the abandonment, while the sloping terrain of almond orchards and vineyards enhanced the development of crusts and rills and a negligible vegetation cover resulted in high erosion rates. The contrasted responses to land abandonment in Mediterranean agricultural lands suggest that land abandonment should be programmed and managed with soil erosion control strategies for some years to avoid land degradation.

A surface-hitting raindrop transfers a part of its kinetic energy onto the surface and thereby destroys aggregates and moves soil particles. The magnitude of interrill processes is largely determined by the intensity and kinetic energy of rainfall. Wind alters all erosion-relevant characteristics of a falling raindrop such as velocity, impact angle and kinetic energy. It also might capture and drag an airborne soil particle. To quantify the amount of raindrop erosion with and without the influence of wind, an experimental setting within the Portable Wind and Rainfall Simulator was developed and applied. The results on cohesionless sandy substrate suggest that wind considerably increases raindrop-erosion: 1. The mean amount of detached substrate is increased by the factor 50. 2. The covered distance is greater. 3. The process splash-creep is intensified. The study highlights a potentially very strong impact of wind-driven rain on soil erosion. The evaluation of splash and splash-saltation is one important step towards the general understanding and realistic assessment of regional and global soil erosion rates and application in soil erosion models.

For a long time, studies concerning erosion caused by concentrated overland flow mainly dealt with the erosion and the transport of fine material. More recent studies have shown that rock fragments reduce the intensity of soil erosion processes on the one hand, but on the other hand rock fragment movements also have been observed both in the rill- and interrill erosion processes. However, there is little knowledge about the movement process of rock fragments in shallow channel flow. Are certain movement patterns typical for different shapes? Are there relationships between movement patterns and slope and flow velocity? Are all these patterns and relationships reproducible? To answer these questions, we performed laboratory channel experiments. With these experiments, we could obtain information about movement patterns of pebbles, by varying the following parameters: shape (flat, ellipsoidal, nearly spherical), size (diameter between 1.97 and 4.0 cm) and channel slope (5°, 10°). During the experiments, a high-speed camera was used to capture the motion of eight specially painted pebbles. The resulting image sequences were processed using both automatic image processing and manual visual inspection. Besides the movement patterns, the pebbles velocity, the water velocity and the water depth were estimated. We could show that there were different movement patterns depending on the shape and the slope. For the 5° experiments, the big, flat pebbles lie at the beginning of the tests. After the following yawing, the pebbles mainly showed the movement form rolling around the longest axis. For the 10° experiments the big, flat pebbles showed the same movement pattern firstly, but later in the sequence, they started to roll around their shortest axis and in the end this movement form was combined with saltation. These patterns are described using a simple symbolic language: sequences of pictograms describe the consecutive movement forms. Furthermore, we detected five different velocity groups of the pebbles for each slope: different cross-section shapes of the pebbles result in different acceleration behavior. The methodology is limited to clear water in laboratory use. Even a larger water depth restricts the image processing. Thus, in the future the experiments will be combined with a small sensor that is implanted in the pebbles and measures forces (acceleration), compass (magnetic flux density) and rotations (gyroscope).

Prediction and risk assessment of hydrological extremes are great challenges. Following climate predictions, frequent and violent rainstorms will become a new hazard to several regions in the medium term. Particularly agricultural soils will be severely threatened due to the combined action of heavy rainfall and accompanying winds on bare soil surfaces. Based on the general underestimation of the effect of wind on water erosion, conventional soil erosion measurements and modeling approaches lack related information to adequately calculate its impact. The presented experimental-empirical approach shows the strong impact of wind on the erosive potential of rain. The tested soils had properties that characterize three environments 1. Silty loam of semi-arid Mediterranean dryfarming and fallow, 2. clayey loam of humid agricultural sites and 3. cohesionless sandy substrates as found at coasts, dune fields and drift-sand areas. Total erosion was found to increase by a factor of 1.3 to 7.1, depending on site characteristics. A complementary laboratory procedure was applied to quantify explicitly the effect of wind on raindrop erosion as well as the influence of substrate, surface structure and slope on particle displacement. These tests confirmed the impact of wind-driven rain on total erosion rates to be of great importance when compared to all other tested factors. To successfully adapt soil erosion models to near-future challenges of climate change induced rain storms, wind-driven rain should be included into the hazard management agenda.

The influence of wind on raindrops and subsequent processes of soil detachment and transport on natural soil surfaces is an essential gap of knowledge. The urgently required data about reactions, interactions and actual impact on soil erosion rates are generally produced under laboratory conditions on highly disturbed substrates, which cannot reflect natural system responses. The Portable Wind and Rainfall Simulator was applied on autochthonous soils in semi-arid Spain to investigate and quantify the relative impact of wind-driven rain on total erosion. On highly degraded crusted soils and freshly ploughed orchard soils in semi-arid Spain, total erosion measured during experiments (30 min; 96 mm h −1 ) were 28.8–150.4 g m −2 and 29.5–30.7 g m −2 , respectively. Concerning the relative impact of wind-driven rain on total erosion, ambiguous results were obtained: the difference to erosion generated by windless rain ranged from +37.4 to −24.2%, to sediment concentration from +46.7 to −20.6% and to runoff coefficients from +18.8 to −7.4%. The study indicates a potentially very strong impact of wind-driven rain and underlines the paramount importance of experimental data derived on autochthonous soil surfaces for process understanding, realistic assessment of soil erosion rates and application in soil erosion models.

The Mosel Wine region has suffered during the last decades a decrease in productive area, mostly on steep sloping vineyards. To avoid the spread of diseases, the extraction of grapevines on abandoned vineyards is mandatory in Rhineland-Palatinate. At the same time, the organic production of wine is growing slowly, but well established in the area. We assess in this paper the degree of the land-use changes, as well as their effect on runoff generation and sediment production, depending on the age of the abandonment, as well as the type and age of the land management, whether organic or conventional. Land use data were obtained to identify land-use change dynamics. For assessment of runoff generation and soil erosion, we applied rainfall simulation experiments on the different types of vineyard management. These were organically managed, conventionally managed and abandoned ones, all of varying ages. During the last decades of the last century, a decrease of around 30% of vineyard surface could be observed in Germany&rsquo, s Mosel Wine Region, affecting mostly the steep sloping vineyards. Despite a high variability within the types of vineyard management, the results show higher runoff generation, and soil erosion associated with recently installed or abandoned vineyards when compared to organic management of the vineyards, where erosion reached only 12%. In organic management, runoff and erosion are also reduced considerably, less than 16%, after a decade or more. Thus, organic vineyard management practices show to be very efficient for reduction of runoff and erosion. Consequently, we recommend to adopt as far as possible these soil management practices for sustainable land management of steep sloping vineyards. In addition, soil protection measures are highly recommended for vineyard abandonment according to the law.

The relative impact of water and wind on total erosion was investigated by means of an experimental-empirical study. Wind erosion and water erosion were measured at five different sites: (1) Mediterranean fallow, (2) Mediterranean orchard, (3) wheat field, (4) vineyard and (5) sand substrate. Mean erosion rates ranged from 1.55 to 618 g&middot, m&minus, 2&middot, h&minus, 1 for wind and from 0.09 to 133.90 g&middot, 1 for rain eroded material over all tested sites. Percentages (%) of eroded sediment for wind and rain, respectively, were found to be 2:98 on Mediterranean fallow, 11:89 on Mediterranean orchard, 3:97 on wheat field, 98:2 on vineyard and 99:1 on sand substrate. For the special case of soil surface crust destroyed by goat trampling, the measured values emphasize a strong potential impact of herding on total soil erosion. All sites produced erosion by wind and rain, and relations show that both erosive forces may have an impact on total soil erosion depending on site characteristics. The results indicate a strong need to focus on both wind and water erosion particularly concerning soils and substrates in vulnerable environments. Measured rates show a general potential erosion depending on recent developments of land use and climate change and may raise awareness of scientist, farmers and decision makers about potential impact of both erosive forces. Knowledge about exact relationship is key for an adapted land use management, which has great potential to mitigate degradation processes related to climate change.

28 páginas, 6 figuras, 2 tablas.- The definitive version is available on: http://www.sciencedirect.com/science/article/pii/S0341816213001252, [EN] Small-scale portable rainfall simulators are an essential research tool for investigating the process dynamics of soil erosion and surface hydrology. There is no standardisation of rainfall simulation and such rainfall simulators differ in design, rainfall intensities, rain spectra and research questions, which impede drawing a meaningful comparison between results. Nevertheless, these data become progressively important for soil erosion assessment and therefore, the basis for decision-makers in application-oriented erosion protection. The artificially generated rainfall of the simulators used at the Universities Basel, La Rioja, Malaga, Trier, Tübingen, Valencia, Wageningen, Zaragoza, and at different CSIC (Spanish Scientific Research Council) institutes (Almeria, Cordoba, Granada, Murcia and Zaragoza) was measured with the same methods (Laser Precipitation Monitor for drop spectra and rain collectors for spatial distribution). Data are very beneficial for improvements of simulators and comparison of simulators and results. Furthermore, they can be used for comparative studies, e.g. with measured natural rainfall spectra. A broad range of rainfall data was measured (e.g. intensity: 37–360 mm h− 1; Christiansen Coefficient for spatial rainfall distribution: 61–98%; median volumetric drop diameter: 0.375–6.5 mm; mean kinetic energy expenditure: 25–1322 J m− 2 h− 1; mean kinetic energy per unit area and unit depth of rainfall: 0.77–50 J m− 2 mm− 1). Similarities among the simulators could be found e.g. concerning drop size distributions (maximum drop numbers are reached within the smallest drop classes < 1 mm) and low fall velocities of bigger drops due to a general physical restriction. The comparison represents a good data-base for improvements and provides a consistent picture of the different parameters of the simulators that were tested., The research for this study was funded by the Deutsche Forschungsgemeinschaft (DFG) project number Ri-835/6-1. We would like to thank the anonymous reviewers for their remarks.

The aim of this study was to enable a quantitative comparison of initial soil erosion processes in European vineyards using the same methodology and equipment. The study was conducted in four viticultural areas with different characteristics (Valencia and Málaga in Spain, Ruwer-Mosel valley and Saar-Mosel valley in Germany). Old and young vineyards, with conventional and ecological planting and management systems were compared. The same portable rainfall simulator with identical rainfall intensity (40 mm h− 1) and sampling intervals (30 min of test duration, collecting the samples at 5-min-intervals) was used over a circular test plot with 0.28 m2. The results of 83 simulations have been analysed and correlation coefficients were calculated for each study area to identify the relationship between environmental plot characteristics, soil texture, soil erosion, runoff and infiltration. The results allow for identification of the main factors related to soil properties, topography and management, which control soil erosion processes in vineyards. The most important factors influencing soil erosion and runoff were the vegetation cover for the ecological German vineyards (with 97.6 ± 8% infiltration coefficients) and stone cover, soil moisture and slope steepness for the conventional land uses.

Small portable rainfall simulators are considered a useful tool to analyze soil erosion processes in cultivated lands. European research groups in Spain (Valencia, Málaga, Lleida, Madrid and La Rioja), France (Reims) and Germany (Trier) have used different rainfall simulators (varying in drop size distribution and fall velocities, kinetic energy, plot forms and sizes, and field of application) to study soil loss, surface flow, runoff and infiltration coefficients in different experimental plots (Valencia, Montes de Málaga, Penedès, Campo Real and La Rioja in Spain, Champagne in France and Mosel-Ruwer valley in Germany). The measurements and experiments developed by these research teams give an overview of the variety of methodologies used in rainfall simulations to study the problem of soil erosion and describe the erosion features in different climatic environments, management practices and soil types. The aims of this study are: (i) to investigate where, how and why researchers from different wine-growing regions applied rainfall simulations with successful results as a tool to measure soil erosion processes; (ii) to make a qualitative comparison about the general soil erosion processes in European terroirs; (iii) to demonstrate the importance of the development of standard method for measurement of soil erosion processes in vineyards, using rainfall simulators; and (iv) and to analyze the key factors that should be taken into account to carry out rainfall simulations. The rainfall simulations in all cases allowed infiltration capacity, susceptibility of the soil to detachment and generation of sediment loads to runoff to be determined. Despite using small plots, the experiments were useful to analyze the influence of soil cover to reduce soil erosion, to make comparisons between different locations, and to evaluate the influence of different soil characteristics. The comparative analysis of the studies performed in different study areas points out the need to define an operational methodology to carry out rainfall simulations, which allows us to obtain representative and comparable results and to avoid errors in the interpretation in order to achieve comparable information about runoff and soil loss., We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)., We acknowledge all the co-authors for the fast and friendly response to take part in this paper and their useful suggestions and corrections. Furthermore, we also thank the Caixa-Bank and DAAD (Deutscher Akademischer Austauschdienst) for the Scholarship grant awarded to J. Rodrigo-Comino.

The present paper is based on several field investigations (monitoring soil and rill erosion by aerial photography, rainfall simulations with portable rainfall simulators, and manmade rill flooding) in southern Spain. Experiments lead now to a closer understanding of the dynamics and power of different soil erosion processes in a gully catchment area. The test site Freila (Andalusia, Spain) covers an area of 10.01 ha with a rill density of 169 m ha−1, corresponding to a total rill length of 1694 m. Assuming an average rill width of 0.15 m, the total rill surface can be calculated at 250 m2 (0.025 ha). Given that, the surface covered by rills makes up only 0.25% of the total test site. Since the rill network drains 1.98 ha, 20% of the total runoff comes from rills. The rills’ sediment erosion was measured and the total soil loss was then calculated for detachment rates between 1685 g m−2 and 3018 g m−2. The interrill areas (99.75% of the test site) show values between 29 and 143 g m−2. This suggests an important role of rill erosion concerning runoff and soil detachment.

The importance of distinguishing and discretely studying the subprocesses of runoff generation and erosion has led to the development of rainfall simulations on small plots. We methodically upgraded a small portable rainfall simulator with particular respect to (1) rainfall characteristics that include homogeneous spatial rainfall distribution and drop spectrum, (2) handling, and (3) control of test conditions. We measured simulator characteristics with rain gauges, calibration plate and Laser Precipitation Monitor by Thies (LPM). The upgraded small rainfall simulator, and measurements of the improved rainfall characteristics are presented in this paper.The upgraded configuration shows the desired improvements: regarding drop size distribution, a close relationship to natural rainfall (Marshall & Palmer Distribution) can be observed. Due to low fall heights, measured drop fall velocities are slow; maximum velocities range between 3.4 and 5 m s1. Mean kinetic energy expenditure, mean kinetic energy per unit area and unit depth of rainfall and mean momentum are 214 J m2 h1, 5.8 J m2 mm1 and 0.016 kg m s1, respectively. The spatial rainfall distribution of the upgraded simulator is homogenous with a Christiansen-Uniformity Coefficient of 91%. The measured variables show extremely low variation throughout all tests and should therefore be reproducible in field investigations at any time.

In this investigation two rainfall simulators have been compared, concerning drop size distribution, drop fall velocity, and spatial rainfall distribution. Additionally, the effect of wind onto rainfall characteristics is measured with the combined wind and rainfall simulator.The results indicate that the used nozzles in both simulators have very small water discharge fluctuations (< 2%). regarding drop size distribution a very close relation of both simulators and natural rainfall (marshall & palmer distribution) can be observed. owing to low fall heights, measured drop fall velocities are too slow ranging from 3.4 to 5 m s−1. The spatial rainfall distribution of the small rainfall simulator is very homogenous with a Chistiansen Coefficient (CU) of 91%. In contrast, the combined wind and rainfall simulator has CU values of 60%, which clearly improve with simultaneous simulation of wind (CU = 76%). The collected variables of both simulators show extremely low fluctuations throughout all tests and are therefore reproducible in field investigations at any time. In dieser Untersuchung geht es um den direkten Vergleich der Regeneigenschaften zweier Regensimulatoren, insbesondere hinsichtlich des Tropfengrosenspektrums, der Fallgeschwindigkeit und raumlichen Verteilung der Tropfen sowie der Reproduzierbarkeit der Ergebnisse. Mit der kombinierten Wind-/Beregnungsanlage wird zudem untersucht, welchen Ein fluss der zugeschaltete Wind auf die Regeneigenschaften dieser Anlage ausubt.Die Ergebnisse der Kalibrierungen belegen, dass die eingesetzten Dusen beider Regensimulatoren eine auserst geringe Mengenabweichung pro Zeiteinheit aufweisen (< 2%). bezuglich der tropfengrosenverteilung wurde eine sehr gute Ubereinstimmung beider anlagen mit dem naturlichen niederschlagsspektrum (marshall & palmer-verteilung) festgestellt. im gegensatz dazu sind die tropfenfallgeschwindigkeiten entsprechend der geringen fallhohe zu niedrig (3.4-5 m s−1). Die raumliche Verteilung des Niederschlags der Kleinberegnungsanlage ist sehr homogen (Cu = 91%); im Gegensatz dazu weist die Wind-/Beregnungsanlage in Simulationen ohne Wind Inhomogenitaten (Cu = 60%) auf, wahrend mit Wind diese deutlich ausgeglichen werden (Cu = 76%). Alle genannten Messgrosen weisen uber alle Versuche beider Anlagen auserst geringe Schwankungen auf und sind damit im Gelande jederzeit sicher reproduzierbar.

Vineyards are one of the most German conditioned eco-geomorphological systems by human activity. Precisely, the vineyards of the Ruwer Valley (Germany) is characterized by high soil erosion rates and rill problems on steep slopes (between 23–26°) caused by the increasingly frequent heavy rainfall events, what is sometimes enhanced by incorrect land use managements. Soil tillage before and after vintage, application of vine training systems and anthropic rills generated by wheel tracks and footsteps are observed along these cultivated area. The objective of this paper is to determine and to quantify the hydrological and erosive phenomena in two chosen vineyards, during diverse seasons and under different management conditions (before, during and after vintage). For this purpose, a combined methodology was applied. Investigating climatic, pedological, geomorphological and botanic-marks variables was suggested on the two experimental plot in the village of Waldrach (Trier, region of Rhineland-Palatinate). First, high infiltration rates (near 100%) and subsurface flow was detected by rainfall simulations performed at different times of the year. The second method to investigate the geomorphological response of slope inclination, two 10 m and one 30 m long rills were measured using geometrical channel cross-section index, depth and width. The highest variations (lateral and frontal movements) were noted before and during vintage, when footsteps occurred in a concentrated short time. Finally, two maps were generated of soil loss, indicated by the botanic marks on the graft union of the vines. As results 62.5 t−1 ha−1 yr−1 soil loss rate was registered (one year) on the experimental plots of the new vineyards, while 4.3 t−1 ha−1 yr−1 on the old one.

Recent research has shown that wind can have a signififi cant inflfl uence on velocity, impact angle and kinetic energy of raindrops, and subsequently increases soil erosion. The aims of this study were to 1) quantify the inflfl uence of wind on water erosion, 2) specififi cally observe the difference in processes betweenwindless rain (WLR) and wind-driven rain (WDR) simulations and 3) test the device’s and test sequence’s practicability. The Portable Wind and Rainfall Simulator (PWRS), recently developed at Trier University for plot-scale in situ assessment of differences in soil erosion with and without the inflfl uence of wind on raindrops, wasused. To facilitate extraction of the inflfl uences of WDR on soil erosion, to avoid systematic errors, and to reduce variability between test plots, a defifi ned order of four consecutive test runs was established: 0) wind simulation, 1) WLR simulation on dry soil, 2) WLR simulation on moist soil, 3) WDR simulation. The tests were conducted on homogenous sandy substrate deposited on an area of 15.2 m 60 m with uniform and smooth surface and low inclination (1°) in the Willem Genet Tunnel of Wageningen University. The results show an increase of eroded sediment ranging from 113 % up to 1108 % for WDR simulations in comparisonto WLR simulations. The increase in runoff was considerably lower (15 % to 71 %), resulting in an increase of sediment concentration between 56 % and 894 %. The results indicate an immense impact of WDR on soil erosion of sandy cohesionless substrate. The experimental setting and measurement proved reliable and reproducible and enables a clear process observation and quantififi cation in the fifi eld.

To assess the inflfl uence of rainfall simulator type and plot dimensions on runoff and erosion, seven small portable rainfall simulators from Freiberg, Tubingen, Trier (all Germany), Valencia, Zaragoza (both Spain), Basel (Switzerland) and Wageningen (the Netherlands) were compared on a prepared bare fallow fifi eld. The experiments were carried out during an international rainfall simulator workshop, organized at Trier University (Germany) from 30th of June to 1st of July 2011.The tested rainfall simulators differ in design, rainfall intensities, rain spectra, etc. and represent most of the devices which have been used over the last decade in Europe. The plots for the different rainfall simulators were selected as similar as possible concerning soil physical and chemical properties, aspect and inclination and were chosen to be placed side by side in horizontal direction. Test procedure was standardized in order to examine the inflfl uence of the rainfall simulator andplot dimension only. The results show a clear and consistent relationship in runoff, erosion and infifi ltration behaviour of the different used rainfall simulators. With all the devices total soil loss is measurable, but different plot sizes, intensities and kinetic energies of the simulated rainfall caused differences in soil loss and runoff quantities per unit of area. Regarding course characteristics over runs, similarities could be observed especially in runoff behaviour. The rainfall simulators (> 1 m² plot size) are able to reproduce infifi ltration and interrillerosion processes. With an increase of plot size (≥ 1 m²), rill-erosion will be also reflfl ected. Therefore it can be concluded that up to a certain plot size, the results of the different simulators are comparable and depend in their magnitude on the properties of the applied rainfall. The increase in process complexity with increasing plot size shows, that the scale of the simulation is one of the most important parameters to be taken intoaccount when comparing values of erosion and runoff.

Rainfall simulation is a widely used method for soil erosion studies on agricultural land. Major problem of this experimental research method is the comparability between different simulators due to differences in simulated rainfall. Therefore the purpose of this study is to characterize the rainfall produced by a rainfall simulator which was widely used during the last decades. Four different calibration methods were used to assess the drop size distribution: (1) Indication Paper, (2) Plaster Micro Plot, (3) Joss–Waldvogel Disdrometer and (4) Laser Distrometer (Thies). Additionally, the latter one was used to measure drop fall velocity in combination with drop diameter. The spatial rainfall distribution pattern on the plot was measured with 100 rainfall gauges. The spatial rainfall distribution pattern clearly shows a heterogeneity, which is caused by the used nozzle configuration. Considerable differences in drop-size distribution can be observed depending on the used measurement technique. Laser Disdrometer and Plaster Micro Plot cover the whole produced drop size spectrum ranging from 3.0 mm, whereas Indication Paper as well as the Joss–Waldvogel Disdrometer primarily show drops smaller than 2.0 mm. Characterisation of rainfall is therefore strongly dependent on the used method and if different methods are used, may lead to contradictory results. The volume drop size distribution reflected by the Laser Distrometer is very similar to that one produced by rain with an intensity of 40 mm h −1 . Nevertheless, with maximum velocities above 10 m s −1 small drops are by far too fast and large drops with velocities dominantly below 5 m s −1 are too slow compared to natural rainfall. As an overall result, the simulator can be characterised as suitable for runoff and infiltration measurements, but with constraints due to the low reproducibility of the spatial rain distribution. As a consequence of the produced drop spectrum and fall velocity the erosion quantities may be underestimated systematically. For this, methodological development has to be focussed on homogeneous spatial rainfall distributions and on increasing the amount of large drops with higher fall velocities.

Aggregation is a major feature of soil structure. It affects transfer of water and gas through the soil and at the soil surface, plant growth, etc. Under rainfall, seedbed structure evolves, leading to crust development, which affects overland flow and erosion. This evolution depends on both rainfall properties (intensity, drop size distribution, initial wetness) and soil properties (aggregate size distribution, stability). Four major disaggregation processes have been identified : (1) slaking due to air entrapment, (2) micro-cracking due to differential clay swelling, (3) mechanical breakdown due to kinetic energy and (4) clay dispersion. Clay dispersion occurs under sodic conditions. It was previously shown that mechanical breakdown and micro-cracking can actually take place under rainfall. However, slaking has only been demonstrated for aggregate stability tests. To test the occurrence of slaking under rainfall, a experiment was conducted under controlled conditions. It used the rainfall simulation facility of the soil science laboratory (INRA, Orléans. France). Two soils with different textures (a clay loam and a silt loam) were used because of their known difference in sensitivity to slaking, as shown by aggregate stability tests. Initially dry aggregates (1-3 mm and 3-5 mm size ranges) were placed under rainfall (deionized water) for various durations, allowing the measurement of disaggregation through time using a laser diffraction sizer. Four rains with different kinetic energy and rainfall intensity were used. Results allow to distinguish between disaggregation processes and to specifically identify slaking. Using complementary studies from the literature, their conditions of occurrence under rainfall are outlined.