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National audience; De la mise en place d’indicateurs pour la planification urbaine à la mesure des stocks de carbone, en passant par les instruments juridiques et économiques pour la protection des sols, cet ouvrage, issu du programme Gessol, synthétise les dernières connaissances biotechniques et sociétales sur le sujet. Il souligne l’importance d’une gestion durable des sols dans les enjeux globaux et identifie les leviers d’actions possibles.

Le sol, régulateur de la quantité et de la qualité de l’eauLa gestion des sols agricoles pour réduire la contamination des milieux aquatiquesLa gestion des sols urbains et péri-urbains pour réguler les flux et épurer les eauxConclusionBibliographie

International audience; Soil surface characteristics (SSC) constitute an important land surface property that drives the partitioning between infiltration and runoff. Therefore, knowledge of SSC is crucial for runoff-forecasting in hydrology. However, the difficulties in measuring spatial variabilities and temporal dynamics of SSC have limited the use of this property in operational hydrology at the catchment extent. Recent progresses have permitted to characterize hydrological SSC classes (H-SSC) with distinct infiltration rates, by implementing monotemporal classifications along with aerial photos. However, when dealing with Mediterranean vineyards, some classes still are difficult to discriminate on the basis of remotely sensed spectral and spatial information only. The objective of the current study was to propose a multitemporal classification that integrates a priori information about possible H-SSC evolutions, such as it is possible improving their characterization. H-SSC evolutions could be either natural, depending on rainfall events, or anthropogenic, driven by soil management practices. Knowledge of possible H-SSC evolutions was translated in the form of decision rules. It was applied to a time series of H-SSC class maps derived from a monotemporal classification of monthly aerial photos. As compared to the monotemporal classification, the multitemporal classification had two advantages for the identification of H-SSC classes. First, it allowed improving the discrimination of classes related to crusting processes, with increased performances between 35 and 48% relative. Second, it was able to detect H-SSC temporal evolutions in relation to soil management practices. (C) 2012 Elsevier B.V. All rights reserved.

Contact: pare@supagro.inra.fr; International audience; Soil surface characteristics (SSC) influence strongly hydrological processes and are known to vary largely in space and time according to soil characteristics and soil management. Because tillage is a main source of variation, the goal of this study was to present and evaluate a prediction model of the temporal variation of the SSC after tillage at the catchment level. The study focused on bare soils prevailing in spring and summer. A logistic regression approach was used to predict the evolution along three stages, starting from the fresh tillage stage to the crusted soil stage. This method provides the probabilities of occurrence of each stage. The predictor candidates tested were a rainfall characteristic, namely cumulative rainfall depth or cumulative kinetic energy, basic soil properties and tillage features. The results showed that a model based on cumulative kinetic energy since tillage and soil stoniness accurately predicts the dynamics of SSC: the rate of well classified SSC was 91%. However, no significant difference in the prediction performance was found using as predictor either cumulative kinetic energy or cumulative rainfall amount since tillage. In the prediction model, the rainfall characteristic was the most significant predictor for the SSC evolution and the only one during the first stages of crust development since tillage. Stoniness was also shown to influence SSC evolution but only during the last stages of crust development: high stone cover speeds up soil surface evolution. The same approach using logistic regression can be applied elsewhere but will require a re-examination of the most relevant predicting variables. Finally, to be able to predict the soil surface characteristic evolution on an annual scale, weed growth characteristics must be considered in the list of predictor candidates.

Correspondance auteur: Raclot D. raclot@supagro.inra.fr; International audience; Soil erosion surveys and modeling approaches often rely on datasets collected from small experimental plots or fields. Therefore, one important issue is to assess to what extent reference data collected on small areas can be affected by soil tillage practices and extrapolated to larger areas. The objectives of this paper are to discuss: (i) the impact of superficial tillage on the erosion rates at field scale and (ii) the impact of the scale on the erosion rates for areas ranging from small fields to 1 km(2) catchments. We analyzed a dataset of 18 rainfall events including runoff and erosion data from fields of approximately 1200 m(2) and 3200 m(2) consisting of vineyards with two contrasting weeding practices - either superficial tillage or notillage with chemical weeding - and from the outlet of a 0.91 km(2) catchment that was 70% vineyard. Results showed that superficial tillage significantly reduced (4.5 times) soil losses as compared to notillage, with a large event-to-event variability. Considering the natural conditions studied by the authors, no-tillage with chemical weeding is not recommended for the study area. Erosion rates observed at catchment scale were significantly lower than those observed at the scale of individual fields. This trend, which has already been observed by many researchers, confirms that catchment soil loss cannot be estimated by the sum of individual field soil losses. In this context, the scaling transition between the field and the 1 km(2) catchment can be analyzed in terms of the spatial variability of soil management and connectivity between the sediment-producing and deposition areas

International audience; During the last decades, the European loess belt has been confronted with a significant increase in environmental problems due to erosion on agricultural land. Spatially distributed runoff and erosion models operating at the catchment scale are therefore needed to evaluate the impact of potential mitigation measures. Expert-based models offer an alternative solution to process-based and empiricalmodels, but their decision rules are only valid for the local conditions forwhich they have beenderived. The STREAMmodel,whichwas developed inNormandy (France), has been applied in two Belgian catchments having a similar soil texture, as well as in a catchment of southern France differing by soil, land use and climate characteristics. The performance of hydrological models can be assessed for instance by calculating the Nash–Sutcliffe efficiency criterion (ENS).When applied to Belgium, the model results are satisfactory to good after an adaptation of the decision rules (0.90bENSb0.93 for runoff predictions and 0.85bENSb0.89 for erosionpredictions).Given the important environmental differences between Normandy and southern France, the model rules were also adapted for application in the latter environment. Unfortunately, the quality of runoff predictions was insufficient to simulate erosion in southern France. In conclusion, STREAMis a reliablemodel providing satisfactory runoff and erosion predictions in the regionswhere hortonian overland flowdominates.Nevertheless, an adaptation of decision rules based on localmulti-scale (plot, field, catchment) data is needed, before running themodel. STREAMcan then serve as a decision support tool to design for instance flood control measures.

Chapitre 2.3; International audience

Correspondance: fax: +33 4 6763 2614. E-mail address: moussa@ensam.inra.fr; International audience; Tillage operations are known to greatly influence local overland flow, infiltration and depressional storage by altering soil hydraulic properties and soil surface roughness. The calibration of runoff models for tilled fields is not identical to that of unfilled fields, as it has to take into consideration the temporal variability of parameters due to the transient nature of surface crusts. In this paper, we seek the application of a rainfall-runoff model and the development of a calibration methodology to take into account the impact of tillage on overland flow simulation at the scale of a tilled plot (3240 m(2)) located in southern France. The selected model couples the (Morel-Seytoux, H.J., 1978. Derivation of equations for variable rainfall infiltration. Water Resources Research. 14(4), 561-568). Infiltration equation to a transfer function based on the diffusive wave equation. The parameters to be calibrated are the hydraulic conductivity at natural saturation K-s, the surface detention S-d and the lag time omega. A two-step calibration procedure is presented. First, eleven rainfall-runoff events are calibrated individually and the variability of the calibrated parameters are analysed. The individually calibrated K-s values decrease monotonously according to the total amount of rainfall since tillage. No clear relationship is observed between the two parameters S-d and omega, and the date of tillage. However, the lag time omega increases inversely with the peakflow of the events. Fairly good agreement is observed between the simulated and measured hydrographs of the calibration set. Simple mathematical laws describing the evolution of K-s and omega are selected, while S-d is considered constant. The second step involves the collective calibration of the law of evolution of each parameter on the whole calibration set. This procedure is calibrated on 11 events and validated on ten runoff inducing and four non-runoff inducing rainfall events. The suggested calibration methodology seems robust and can be transposed to other gauged sites.

Correspondance: voltz@ensam.inra.fr; International audience; Observation and interpretation of spatial soil surface moisture patterns are fundamental to spatially distributed modelling of runoff generation, soil evaporation, and plant transpiration. Compared to natural basins, man-made managements in farmed basins, such as field limits, agricultural practices and the networks of ditches, Lead to great spatial heterogeneity in hydrological processes at the catchment scale. The aim of this study was to identify the factors controlling the spatio-temporal variability of the surface soil moisture in the farmed Mediterranean catchment of Roujan (0.91 km(2)) located in southern France. Intensive measurements of soil moisture patterns were recorded during two drying sequences, respectively, in dry and wet seasons. Results show that the soil surface characteristics (SSC), which result in part from the agricultural practices such as soil tillage, chemical weed control or grass covering, are the main factors controlling the spatio-temporal distribution of the soil surface moisture during both the wet and dry drying sequences. However, in this study, none of the local factors such as the soil insolation (sunlight reaching soil surface through the plant canopy if there is one), the slope, the aspect and the soil texture is correlated to the soil moisture spatial variability. Only local factors control the spatio-temporal variability of soil surface moisture because agricultural operations like tillage influence greatly the local surface runoff by altering soil hydrologic properties. Also, the ditch networks influence the water transfer from the fields to the catchment outlet by routing runoff directly to the catchment outlet without modifying the soil surface moistures of downslope fields. Consequently, in farmed catchments the agricultural managements and practices strongly modify the spatio-temporal soil moisture distribution and must be taken into account in the understanding and in the modelling of hydrological processes

Most runoff simulation and infiltration models have been developed at the global-catchment scale or the local-soil column scale. Few models have been specifically developed at the scale of agricultural fields and there are no guidelines to help modellers choose an adequate model to simulate overland flow and hence analyse the impact of different soil management practices on flood generation. A comparison is undertaken to select and calibrate models that simulate Hortonian overland flow at the field or small plot scale. The proposed methodology couples a runoff production model to a unit hydrograph transfer function. Four different models were tested: Philip, Morel-Seytoux, Horton and SCS. These models differ by their mathematical structure and the parameters to be calibrated while input hydrologic data are the same site data: rainfall/runoff and initial water content. The models are calibrated on 14 events and validated on 14 others. The results of both the calibration and validation phases are compared on the basis of their performance with regards to six objective criteria, three global criteria and three relative criteria representing volume, peakflow, and the root mean square error. The first type of criteria gives more weight to strong events whereas the second considers all events to be of equal weight. The results show that the calibrated parameter values are dependent on the type of objective criteria used. Furthermore, when analysing the performance of the six objective criteria used, it can be seen that the global volume, global RMSE and relative peakflow criteria give the best compromise between bias and precision. Within the selected modelling framework, Morel-Seytoux's model performed better than the other three and the SCS gave the worst results. Horton's model showed to be more consistent in overall performance than Philip's model. Results also highlight problems related to the simulation of low flow events and intermittent rainfall events.

Field limits, tillage practices and ditch networks constitute man-made hydrological discontinuities in farmed catchments, and are expected to influence hydrological response during flood events. The purpose of this study is to assess the role of human impact, especially the existence of tillage practices and ditch network, on flood events. The study area is the farmed catchment of Roujan (0.91 km 2 ) located in Southern France for which a spatially distributed hydrological model, MHYDAS, was developed and tested. The model considers the catchment as a series of interconnected field parts linked to the ditch network. Descriptions are provided for the main model procedures: computation of Hortonian excess rainfall on fields using the Green and Ampt approach, conversion of excess rainfall to surface runoff, interaction between ditch network and groundwater using a simple Darcian model and flood routing through the ditch network using the diffusive wave model. To analyse the role of both tillage practices and the ditch network, two sets of sensitivity analysis of the model were applied. The first set studied the role of tillage practices by comparing the actual spatial distribution of tillage practices on the catchment with three hypothetical scenarios. The second set studied the role of the ditch network by comparing the actual man-made ditch network with a hypothetical drainage network automatically extracted from a digital elevation model. Results show the importance of the role of tillage and the ditch network on the form of the hydrograph, the lag time, the runoff volume and the peak discharge. This technique could also be applied to study the impact of land use change on the hydrological behaviour of the catchment.

International audience; In the Mediterranean wine producing region, soil surface remote sensing for hydrological modelling is hampered by the discontinuous canopy of the perennial vine stocks. Very high spatial resolution imagery allows the recording of ground resolution elements that comprise only soil in between vine stocks. To enable the comparison of the resolution element's spectral properties with known bi-directional properties of different types of soil surface, pixels representing the pure and sunlit soil surface have first to be extracted from the imagery. Multi-scale analysis proved to provide a robust and satisfactory segmentation method. Conditional per-field adjustment of a multi-scale image mask allows the extraction of the image segments corresponding to the sunlit soil surface, whatever its state or composition. Moreover, the vegetation cover can be estimated with an error of at most 10% if the geometric configuration is taken into account.; Extraction de la surface du sol éclairée dans des images de télédétection de cultures pérennes et discontinues ; le cas du vignoble méditerranéen. En région méditerranéenne viticole, l'estimation des états de surface du sol par télédétection est perturbée par la présence d'un couvert végétal pérenne et discontinu. L'imagerie à très haute résolution spatiale permet d'obtenir des pixels constitués uniquement de la surface du sol. Pour comparer la radiométrie de ces pixels aux propriétés bidirectionnelles connues de différents types de surface, on cherche à isoler les pixels correspondant à la surface du sol éclairée. L'analyse multi-échelle fournit une approche de segmentation robuste et satisfaisante. L'ajustement conditionnel par parcelle d'un masque obtenu par analyse multi-échelle permet d'accéder à la surface du sol éclairée, indépendamment de son état ou de sa composition. De plus on peut estimer le couvert végétal de la vigne avec une marge d'erreur de 10 % si la configuration géométrique est prise en compte.

Little work has up to now been done on the mechanisms of storm flow generation in Mediterranean cultivated environments. The present work analysed such mechanisms by natural chemical tracing in a small Mediterranean wine-growing catchment (0.91 km 2 ): Roujan, Herault, France. Two autumn runoff events with very different characteristics were studied. The first, a minor one (specific peak flow=28 l/s/km 2 ), was used to evaluate the sensitivity of the environment to low intensity rainfall. The second was significantly larger (specific peak flow=944 l/s/km 2 ) and was used to analyse the response of the catchment to heavy downpours. Tracer concentrations at the catchment outlet, for the groundwater of two distinct geomorphological units (depression and plateau) and in an experimental plot are presented. A mixing model involving three reservoirs and two tracers (chloride and nitrate) is then used to estimate the contributions of the three main storm flow components: (a) the pre-event water deriving from the depression groundwater; (b) the event water of the precipitations; and (c) the pre-event water of the plateau groundwater. The event water end member basically corresponds to infiltration-excess overland flow plus direct precipitation on saturated areas. The imprecision of the calculations was estimated by the Monte Carlo method. During both runoff events, there was little variation in the rate at which the stream was fed by pre-existing water deriving from the groundwater, although the water tables rose rapidly. Overland flow dominated in the rapid storm flow. Its contribution varied between 12 and 82% according to the importance of the event. When the water level rose, particularly in the case of the heavy runoff event, the overland flows concentrated in the man-made network of ditches running down towards the main ditch. This wave of overland flow spread, expelling the pre-event water into the ditches located downstream, which were initially fed by the groundwater. With the rapid rise in the level of water in the ditches, ditchwater infiltrated into the groundwater, and the latter then ceased to contribute to the flow in the ditch network.

The variation in the availability of diuron to transport by overland flow was studied in a vineyard field under a Mediterranean climate during three years. The availability of diuron decreased with time due to the dissipation of diuron in the topsoil and the decrease of its accessibility by runoff water, which is not represented in pesticide transfer modelling. Thus, calculated concentrations of diuron with simple and actual relations are always greater than those measured in the overland flow.

The Mediterranean climate is characterized by a hot and dry summer where occasional storm events induce erosion and runoff. The high leaching potential of pesticides to surface waters under such climate conditions are not in relation to the main body of data that originated from summer-rain row-crop scenarios. In this 2-yr study we monitored runoff discharge and concentrations of the two soil applied herbicides diuron [3-(3,4-dichlorphenyl)-1,1-dimethylureal and simazine [6-chloro-N 2 ,N 4 -diethyl-1,3,5-triazine-2,4-diamine] from two field sites-one tilled and one no-till-cropped with grapevine (Vitis vinifera L.; Cinsault and Aramon, respectively). Despite a time lag of 140 d in 1994 between chemical application and first runoff event, diuron concentrations in overland flow exceeded 200 μg L -1 at the no-till site. In 1995 the first strong rainfall-runoff event following application carried >87 and 60% of the respective seasonal simazine and diuron loss at both sites, although it accounted for

National audience