7 research outputs found
Recherche dâindicateurs de ruissellement et des risques dâĂ©rosion au moyen de tests dâinfiltromĂ©trie dans le bassin versant du RhĂ©raya (Haut-Atlas occidental, Maroc)
Lâobjectif de ce travail est dâĂ©tudier les risques de ruissellement et dâĂ©rosion dans le bassin versant du RhĂ©raya (Haut-Atlas du Maroc) au moyen dâun irrigateur manuel Ă rampe sur 1 m2. Nous recherchons des indicateurs faciles Ă dĂ©terminer directement sur le terrain (Ă©tats de surface du sol) ou Ă partir des tests en laboratoire (stabilitĂ© des agrĂ©gats, texture, matiĂšre organique), qui soient bien corrĂ©lĂ©s avec lâinfiltrabilitĂ© et la turbiditĂ© issues des tests dâinfiltromĂ©trie. Pour les diffĂ©rents sols affleurant dans le bassin, les rĂ©sultats ont mis en Ă©vidence une grande variabilitĂ© de lâinfiltrabilitĂ© (de 1 à  70 mm.hâ1) et de turbiditĂ© des eaux de ruissellement (de 1,5 à  325 g.Lâ1). La turbiditĂ© a pu ĂȘtre mesurĂ©e correctement grĂące Ă la mise au point dâun nouveau dispositif de collecte des eaux de ruissellement de lâirrigateur. Bien que lâinfiltrabilitĂ© et le ruissellement soient la rĂ©sultante dâinteractions entre toutes les caractĂ©ristiques physiques du sol, certaines apparaissent dominantes dans notre contexte. Nous montrons ainsi que lâinfiltrabilitĂ© est dĂ©terminĂ©e principalement par la texture et lâouverture de la surface du sol et que la turbiditĂ© est due essentiellement Ă la surface de sol nu exposĂ©e au ruissellement. Ces indicateurs cartographiables offrent la possibilitĂ© dâune spatialisation des risques dâĂ©rosion au niveau du bassin versant.The objective of this study was to investigate the risks of runoff and erosion of soils in the Rheraya catchment (High Atlas, Morocco) using infiltrometer tests on 1 m2 plots. We were looking for indicators that are easily obtained directly from field observations (ground surface features) or by laboratory tests (aggregate stability, soil texture and organic matter), and are well correlated with infiltrability and turbidity measurements from the infiltrometer tests. For the various soils present in the study area, the results show a large variability of infiltrability values (from 1 to 70 mm·h-1) and turbidity (from 1.5 to 325 g·L-1). The turbidity was correctly measured thanks to the development of a new runoff collector that doesnât disturb the soil. Although runoff and erosion are the result of interactions among many parameters, some of these appear to be dominant in our case. The measurements show that the infiltrability was correlated mainly with texture and soil surface opening, whereas turbidity was related to the surface of bare soil that was exposed to runoff. These indicators may be used to determine the spatialization of potential erosion in the Rheraya catchment
Numerical analysis of a model for Nickel-Iron alloy electrodeposition on rotating disk electrode
International audienceTo better understand the nickel-iron electrodeposition process, we have developed one-dimensional numerical model. This model addresses dissociation, diffusion, electromigration, convection and deposition of multiple ion species.\ The reaction mechanism in this model differs in that and are the electroactive species and and are not involved whatsover.\ To take account of the anisot-ropic behaviour of the solution we introduce a domain decomposition numerical method. Simulations with experimental data shows that our model can predict characteristic features of the nickel-iron system
Effets des plantations forestiĂšres sur banquettes sur le ruissellement et l'Ă©rosion par rapport aux parcours dans les montagnes semi arides du Haut-Atlas de Marrakech (Maroc)
LâĂ©rosion hydrique est un phĂ©nomĂšne qui porte prĂ©judice aux ressources en eau et en sol des bassins versants du Maroc. Lâobjectif de ce travail est de quantifier lâeffet des amĂ©nagements (replantations forestiĂšres de pins essentiellement, associĂ©es Ă la crĂ©ation de banquettes) Ă partir de mesures rĂ©alisĂ©es sur parcelles dâĂ©rosion (150 mÂČ) sous pluies naturelles installĂ©es sur deux types de sols contrastĂ©s et importants dans le bassin versant de lâoued RhĂ©raya (argilites permo-triasiques et substrat magmatique), situĂ© dans le Haut Atlas Occidental du Maroc.Cinq annĂ©es dâobservations ont montrĂ© que dans la majoritĂ© du bassin les Ă©vĂšnements provoquant du ruissellement sont rares et ne produisent que peu de sĂ©diments (entre 0.03 et 1.1 t. ha-1. an-1). Par contre, le ruissellement est plus frĂ©quent et lâĂ©rosion nettement plus importante sur le sol nu des ravines argileuses (340 t. ha-1. an-1). Les plantations de pins sur banquettes sur argilites rouges ont montrĂ© leur efficacitĂ© pour le blocage du ruissellement et de lâĂ©rosion lorsquâelles sont encore fonctionnelles. Inversement, les banquettes non entretenues (banquettes comblĂ©es de sĂ©diments et sol sans vĂ©gĂ©tation observĂ©es sur substrat magmatique) augmentent le ruissellement et lâĂ©rosion.Water erosion has a strong negative impact on soil and water resources in Morocco. The objective of this work is to quantify effect of management (Pine Plantation associated with the creation of graded terrasses) from measurements on erosion plots (150 mÂČ) with natural rainfall installed on two contrasting soil types in the Rheraya watershed (red clay Permo-Triassic and magmatics rocks) in the Western High Atlas of Morocco.Five years of observation have shown that on the majority of the catchment, rainfall events causing runoff are rare and produce little sediments (between 0.03 and 1.1 t. ha-1. an-1). Conversely, runoff is more frequent and erosion much higher in gullies on red clay (340 t. ha-1. an-1). The pine plantations associated with embankments and ditches showed their strong effectiveness for blocking runoff and erosion when they are still functional. Conversely, those that were not maintained, with ditches filled with sediments, have no more or even a strong negative effect
Variabilité spatio-temporelle de la teneur en carbone du sol en milieu agricole carbonaté : exemples d'apports de la spectroscopie proche infrarouge
Effective protection of environmental resources requires an understanding of spatial and temporalvariation of soil properties, and its causes and its consequences. However, the acquisition of data on thisvariability requires datasets whose achievement is limited by the cost of physico-chemical analyses, and also insome cases by the amount of material available. For studies related to carbon sequestration in soils and theirvulnerability to land use and climate changes, additional limitations appear in carbonate soils as organic formsand inorganic carbon must be distinguished. Assuming that the near-infrared spectroscopy (NIRS) could helpovercome these limitations, this paper presents some results obtained with NIRS through two examples ofstudies in carbonate environment, one in the watershed the Rheraya (High Atlas of Morocco) and the other inthe plain of Languedoc (France). These examples show that depending on the particular case studied andphysicochemical methods implemented a procedure for prediction by NIRS may be efficient to predict the Corgand inefficient for predicting carbonates or moderately efficient in predicting the Corg and very efficient to predictthe carbonates.La protection efficace des ressources environnementales nĂ©cessite une bonne connaissancedes variations spatiales et temporelles des propriĂ©tĂ©s des sols, ainsi que de ses causes et de sesconsĂ©quences. Cependant, l'acquisition de donnĂ©es sur cette variabilitĂ© nĂ©cessite des jeux dedonnĂ©es dont l'obtention est limitĂ©e par le coĂ»t des analyses physico-chimiques, mais aussi, danscertains cas, par la quantitĂ© de matĂ©riau disponible. Pour les Ă©tudes liĂ©es Ă la sĂ©questration ducarbone dans les sols et Ă leur vulnĂ©rabilitĂ© aux changements dâusage et aux changementsclimatiques, des limites supplĂ©mentaires apparaissent dans les sols carbonatĂ©s, car les formesorganiques et inorganiques du carbone doivent ĂȘtre distinguĂ©es. Partant de lâhypothĂšse que laspectroscopie proche infrarouge (SPIR) pourrait permettre de dĂ©passer ces limites, cettecommunication prĂ©sente quelques rĂ©sultats obtenus avec la SPIR Ă travers deux exemples d'Ă©tudesen milieu agricole carbonatĂ©, lâun dans le bassin versant de la RhĂ©raya (Haut-Atlas du Maroc) etlâautre dans la plaine languedocienne (France). Ces exemples montrent notamment que selon le casĂ©tudiĂ© et les mĂ©thodes physico-chimiques mises en Ćuvre, une procĂ©dure de prĂ©diction par SPIRpeut ĂȘtre soit efficiente pour prĂ©dire le Corg et non efficiente pour prĂ©dire les carbonates, soitmoyennement efficiente pour prĂ©dire le Corg et trĂšs efficiente pour prĂ©dire les carbonate
An integrated modelling and remote sensing approach for hydrological study in arid and semi-arid regions : the SUDMED programme
Recent efforts have been concentrated in the development of models to understand and predict the impact of environmental changes on hydrological cycle and water resources in arid and semi-arid regions. In this context, remote sensing data have been widely used to initialize, to force, or to control the simulations of these models. However, for several reasons, including the difficulty in establishing relationships between observational and model variables, the potential offered by satellite data has not been fully used. As a matter of fact, a few hydrological studies that use remote sensing data emanating from different sources (sensors, platforms) have been performed. In this context, the SUDMED programme has been designed in 2002 to address the issue of improving our understanding about the hydrological functioning of the Tensift basin, which is a semi-arid basin situated in central Morocco. The first goal is model development and/or refinement, for investigating the hydrological responses to future scenario about climate change and human pressure. The second aim is the effective use of remote sensing observations in conjunction with process models, to provide operational prognostics for improving water-resource management. The objective of this paper is to present the SUDMED programme, its objectives, and its thrust areas, and to provide an overview of the results obtained in the first phase of the programme (2002-2006). Finally, the lessons learned, future objectives, and unsolved issues are presented
Lutte antiérosive
Face Ă la pression dĂ©mographique et fonciĂšre dans les pays en dĂ©veloppement, la productivitĂ© des terres connaĂźt actuellement une forte baisse dans de nombreuses rĂ©gions tropicales. Par ailleurs, la succession rapprochĂ©e des tempĂȘtes cycloniques entraĂźne l'appauvrissement extrĂȘme de certaines populations du fait de la dĂ©gradation des terres et des inondations des plaines oĂč se dĂ©veloppent les principales agglomĂ©rations. Telles sont les problĂ©matiques Ă©tudiĂ©es par l'IRD et le rĂ©seau Ărosion de l'AUF dont ce CD prĂ©sente les derniers travaux. Initialement rĂ©unies dans la perspective d'un colloque Ă HaĂŻti (annulĂ© suite au sĂ©isme de 2010), les contributions publiĂ©es ici portent sur des Ă©tudes de cas Ă HaĂŻti, mais aussi Ă Madagascar, au Maghreb ou au Vietnam, soit au total une soixantaine de communications et une sĂ©rie de documents rĂ©cents issus des rĂ©flexions des experts. StructurĂ© en six thĂšmes, ce CD constitue ainsi une source bibliographique prĂ©cieuse pour les dĂ©cideurs, les experts, les ONG, les acteurs de la sociĂ©tĂ© civile et les chercheurs concernĂ©s par la gestion durable de l'eau et la restauration de la productivitĂ© des sols (GCES)
Spatial variability of the relationships of runoff and sediment yield with weather types throughout the Mediterranean basin
Summarization: Soil degradation by water is a serious environmental problem worldwide, with specific climatic factors being the major causes. We investigated the relationships between synoptic atmospheric patterns (i.e. weather types, WTs) and runoff, erosion and sediment yield throughout the Mediterranean basin by analyzing a large database of natural rainfall events at 68 research sites in 9 countries. Principal Component Analysis (PCA) was used to identify spatial relationships of the different WTs including three hydro-sedimentary variables: rainfall, runoff, and sediment yield (SY, used to refer to both soil erosion measured at plot scale and sediment yield registered at catchment scale). The results indicated 4 spatial classes of rainfall and runoff: (a) northern sites dependent on North (N) and North West (NW) flows; (b) eastern sites dependent on E and NE flows; (c) southern sites dependent on S and SE flows; and, finally, (d) western sites dependent on W and SW flows. Conversely, three spatial classes are identified for SY characterized by: (a) N and NE flows in northern sites (b) E flows in eastern sites, and (c) W and SW flows in western sites. Most of the rainfall, runoff and SY occurred during a small number of daily events, and just a few WTs accounted for large percentages of the total. Our results confirm that characterization by WT improves understanding of the general conditions under which runoff and SY occur, and provides useful information for understanding the spatial variability of runoff, and SY throughout the Mediterranean basin. The approach used here could be useful to aid of the design of regional water management and soil conservation measures.ΠαÏÎżÏ
ÏÎčÎŹÏÏηÎșΔ ÏÏÎż: Journal of Hydrolog