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International audience; A C++-Python package is proposed for 3D mechanical simulations of granular geomaterials, seen as a collection of particles being in contact interaction one with another while showing complex grain shapes. Following the socalled Level Set-Discrete Element Method (LS-DEM), the simulation workflow stems from a discrete field for the signed distance function to every particle, with its zero-level set corresponding to a particle’s surface. A Fast Marching Method is proposed to construct such a distance field for a wide class of surfaces. In connection with dedicated contact algorithms and Paraview visualization procedures, this shape description eventually extends the YADE platform for discrete simulations. Its versatility is illustrated on superquadric particles i.e. superellipsoids. On computational aspects, memoryrequirements possibly exceed one megabyte (MB) per particle when using a double numeric precision, and time costs, though also significant, appear to be lighter than the use of convex polyhedra and can be drastically reducedusing a simple, OpenMP, parallel execution.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; In civil engineering, the utilisation of expert judgement is important for evaluating the reliability of structures whose failure behaviour is little known and difficult to quantify. This article presents the application of the approaches of elicitation, calibration and aggregation of expert opinions to evaluate the reliability of river levees. These approaches have seldom been used in the field of French hydraulic structures whereas there is growing interest for them in other countries, concerning structures reliability and other fields such as aerospace industry, nuclear industry, hydrology, statistics, economics, psychology etc. This article proposes a quantitative approach to the use of expert judgement for evaluating river levee failure probability. An application to the case of an existing river levee is presented. The approach developed assesses the expert opinions according to their calibration (statistical accuracy) and their informativeness, then aggregates them in a single calibrated opinion. Applying the proposed weighting and aggregation procedure reduces variability in the probability of failure estimate, then it provides a better probabilistic distribution of aggregated expert opinion than of individual expert opinions. The results allow identifying a trend of aggregated expert opinions that point towards over- or lack of confidence.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; This assesses features of otoliths from laboratory-reared embryos, larvae and juvenile European chub Squalius cephalus from hatching to 180 days post-hatching (dph). We observed the development of the three pairs of otoliths (lapilli, sagittae and asterisci) and more precisely shape changes, as well as timing and deposition rate of increments of the lapilli. The lapilli and the sagittae were present at hatching, whereas the asterisci formed between 20 and 30 dph. The lapillus and sagitta shapes were round until 20 dph. From 60 dph the anterior and the posterior rostra of the sagittae were well developed, but very thin, making this otolith too fragile to manipulate for further studies of shape and validation of otolith increment deposition rate. The lapilli provided reliable age estimates for free embryos, larvae and juveniles up to 120 dph. However, caution should be taken when ageing fish older than 150 dph as an underestimation was noticeable. The regression of the number of otolith increments on age showed a slope and an intercept not significantly different from 1 and 0, respectively , which indicated that otolith growth increments were deposited on a daily basis, with the first microincrement occurring at hatching. Increment counts were consistent between three interpreters, indicating a consistent and reliable age estimate. This study validates that the otolith increment deposition rate can be used to assess hatching dates and daily growth of wild S. cephalus under 150 dph and in environments similar to the conditions used in this study.

[Departement_IRSTEA]Territoires [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; Large wildfires across parts of France can cause devastating damage which puts lives, infrastructure, and the natural ecosystem at risk. In the climate change context, it is essential to better understand how these large wildfires relate to weather and climate and how they might change in a warmer world. Such projections rely on the development of a robust modelling framework linking large wildfires to present-day atmospheric variability. Drawing from a MODIS product and a gridded meteorological dataset, we derived a suite of biophysical and fire danger indices and developed generalized linear models simulating the probability of large wildfires ( > 100 ha) at 8 km spatial and daily temporal resolutions across the entire country over the last two decades. The models were able to reproduce large-wildfire activity across a range of spatial and temporal scales. Different sensitivities to weather and climate were detected across different environmental regions. Long-term drought was found to be a significant predictor of large wildfires in flammability-limited systems such as the Alpine and south-western regions. In the Mediterranean, large wildfires were found to be associated with both short-term fire weather conditions and longer-term soil moisture deficits, collectively facilitating the occurrence of large wildfires. Simulated probabilities on days with large wildfires were on average 2-3 times higher than normal with respect to the mean seasonal cycle, highlighting the key role of atmospheric variability in wildfire spread. The model has wide applications, including improving our understanding of the drivers of large wildfires over the historical period and providing a basis on which to estimate future changes to large wildfires from climate scenarios.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; The paper offers an analytical determination of the hydraulic properties of an unsaturated soil with reference to its retention curve, which describes the relationship between the volumetric water content and capillarity through matric suction. The analysis combines a particulate approach focused on the physics at the pore scale, including microstructural aspects, with a probabilistic approach where the void space and grain size are considered as random variables. In the end, the soil water characteristic curve of an unsaturated granular medium along a drying path can be derived analytically based on the sole information of particle size distribution. The analysis hinges on the tessellation of a wet granular system into an assemblage of tetrahedral unit cells revealing a pore network upon which capillary physics are computed with respect to pore throat invasion by a non-wetting fluid with evolving pendular capillary bridges. The crux of the paper is to pass from particle size probability distribution to a matching void space distribution to eventually reveal key information such as void cell and solid volume statistics. Making reasonable statistically based assumptions to render calculations tractable, the water retention curve can be readily constructed. Model predictions compare quite favourably with experimental data available for actual soils, especially in the high saturation range. Having a sound scientific basis, the model can be made amenable to address a variety of soils with a wider range of particle sizes.

International audience; The Level Set-Discrete Element Method (LS-DEM) extends DEM towards arbitrary grain shapes by storing distance-to-surface values on a grid for each Discrete Element (DE), together with considering boundary nodes located onto the DE's surface. Both these ingredients are shown to affect the precision and computational costs of LS-DEM, considering various numerical simulations at the contact-and packing-scales for ideal spherical and superellipsoid shapes. In the case of a triaxial compression for spherical particles, approaching with a reasonable precision the reference result obtained in classical DEM requires the grid spacing to be smaller than one tenth of particle size, as well as using a couple thousands of boundary nodes. Computational costs in terms of memory (RAM) or evaluation time then increase in LS-DEM by two or three orders of magnitude. Simple OpenMP parallel simulations nevertheless significantly reduce the increase in time cost, possibly dividing the latter by 20.

International audience; Numerous freshwater acanthocephalans are able to alter the behaviour of their intermediate hosts to increase their predation risk by final hosts, thereby enhancing trophic transmission between their two hosts. Because temperature is widely expected to impact freshwater host-parasite interactions, we investigated how it can affect movements of both uninfected and Pomphorhynchus laevis-infected Gammarus pulex in an artificial stream in 5 cm/s water flow. We found that P. laevis infection of G. pulex induced both higher frequency and higher amplitude of movements along the artificial stream. Moreover, at warmer temperature (21°C), uninfected and P. laevis-infected G. pulex moved more in the artificial stream than at 15°C. In this regard, warmer temperature could then impact gammarids distribution and increase P. laevis transmission rate toward their definitive host in freshwater ecosystems. Firstly, this study provides new insights into how the key temperature factor influences gammarids species movements in the stream. Secondly, elevated temperature did not influence the intensity of P. laevis manipulation in G. pulex intermediate host. This work highlights that warmer temperature might affect the distribution and the behaviour of infected or uninfected freshwater gammarids with no direct effect on acanthocephalan trophic transmission through manipulation.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; This study investigates how the shear rate can affect the geomembrane - protective geotextile friction angle. Four types of geomembranes (GMB) were considered (EPDM, HPDE, PP, and PVC) and a single nonwoven needle-punched geotextile (GTXnw) was used to make the interfaces with the geomembrane. Three shear devices were used: a large-scale inclined plane (IP), a shear box (SB), and a small-scale shear device (ssSD). The ssSD allows two shear modes to be compared: one mode involves incrementally increasing the shear stress, and the other involves imposing a constant tangential velocity at the interface. Only the PP GMB- GTXnw was tested with the SB and the ssSD. Inclined plane standardised tests show that for the three interfaces that undergoes gradual sliding (EPDM, PP and PVC GMB- GTXnw), it is shown that a step-by-step experimental procedure gives significantly lower interface friction angle than that given by the procedure from the current international standard, which is explained by the increase of interface shear stress with sliding speed. These observations are confirmed by shear box tests. One major practical result is that, following the nature of geosynthetics, the shear rate applied in large-scale shear box tests should be adapted to assess a safety value of a geosynthetic - geosynthetic interface friction angle.

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; To understand the effects of environmental changes on ecosystems, it is important to determine the factors and mechanisms influencing the strength of species interactions in food webs. However, joint effects of predation risk and additional environmental factors on species interaction strengths in multitrophic systems remain largely unexplored, leaving a substantial gap in our understanding of the links between local environmental characteristics and food web properties. To fill this gap, we investigated the effects of habitat complexity and predation risk by top predatory dragonfly larvae (Aeshna cyanea) on feeding rates and energetic efficiency (i.e. the ratio of acquired and expended energy) of the larvae of three intermediate predatory odonate species (Libellula quadrimaculata, Sympetrum sanguineum, and Ischnura elegans) preying on cladocerans. We hypothesised that predation risk would decrease the feeding rate, especially in the structurally simple habitat, and increase the metabolic rate of all intermediate predators. We also expected higher feeding rates of intermediate predators using aquatic vegetation as a perching site (i.e. Sympetrum and Ischnura) in the structurally complex habitat. Finally, we expected to observe habitat- and predation risk-dependent energetic efficiencies of the intermediate predators driven by changes in feeding and metabolic rates. The effect of predation risk on feeding rates was species specific and differed between the structurally simple and complex habitat. Habitat complexity increased feeding rates but only in the absence of predation risk. Moreover, predation risk signalled by chemical cues significantly increased Sympetrum vulgatum feeding rates but did not influence the feeding rates of the two other intermediate predators. Metabolic rates varied among the three intermediate predators but were not affected by predation risk. Estimated energetic efficiency decreased with intermediate predator body mass and depended, to a lesser extent, on the interactive effect of habitat complexity and predation risk. Our results imply that the effects of habitat complexity and predation risk on trophic interactions are likely to be determined by traits related to foraging and defence of the intermediate predators and their habitat domains, and that energetic efficiency is mainly determined by predator mass. Given that habitat complexity and predation risk can vary substantially across habitats, we conclude that it is important to consider habitat complexity and predation risk to better understand and predict the effects of environmentally driven variations on trophic interaction strength and metabolic rates that underlie the energetic efficiency of individual consumers. This has important implications for population and community dynamics as well as ecosystem functioning.

[Notes_IRSTEA]article n° 117877; International audience; The frequency, duration, and severity of drought events are expected to increase in the Mediterranean area as a result of climate change, with strong impacts on forest ecosystems and in particular individual tree growth. Tree growth response to drought is strongly influenced by local site and stand characteristics that can be quantified using competition indices (CIs) and water stress indices (WSIs). These indices have been widely used to predict tree growth; however, they are numerous, and few studies have investigated them jointly. In this context, we investigated the potential of using CIs and WSIs to investigate tree behaviour under drought. The main objective of this study was to quantify P. halepensis Mill. annual radial growth using tree size from the previous year, CIs and WSIs. We studied twelve 50-year-old Pinus halepensis plots located in the South-East of France distributed in different density treatments (light, medium and dense). At each plot, all trees were measured (height, circumference), spatialized and the ring-widths were measured for ~15 trees. We also developed a two-strata (over- and understorey) forest water balance model to simulate soil water content at a daily resolution based on stand characteristics (LAI values in particular) and soil properties. A mixed modelling approach was eventually used to investigate the drivers of P. halepensis annual radial growth and to test the performance of five CIs and four WSIs. The best growth model included tree size, the sum of Basal Area of Larger trees in a 5 m-radius (BAL; as CI), and the number of days that trees experienced water stress in a year (as WSI) as predictors. This model explained up to 56% of the variance in observed pine tree growth, which increased up to 77% when the individual tree was included as a random effect on the intercept. We found that distance-independent CIs can perform as well as distance-dependent CIs in our study site. The duration of drought alone appeared to better predict tree growth than drought intensity and duration, or drought timing. The selected model led us to reaffirm the positive effect of thinning on tree secondary growth when facing long and intense drought.

Aucun "Copyright Transfer Agreement" n'a été signé ici par les auteurs en faveur d'un éditeur commercial (qui n'existe pas ici); International audience; The Discrete Element Method (DEM) is an efficient tool for modelling granular materials, usually approaching them by spherical particles. Aiming for a better description of grain shapes, the present work first illustrates the Level Set (LS) description of arbitrary surfaces in a DEM extension coined as LS-DEM. LS-DEM logically results in a massive increase in the simulation storage requirements and evaluation time, which is here illustrated with reference to DEM for the ideal case of spherical particles. Then, Level Set Quadtree/Octree data structures are proposed as algorithm improvements to alleviate the computational costs of LS-DEM.

post-print; International audience; Microbial endosymbiontsalter the phenotype of their host which may have cascading effects at both population and community levels. However, we currently lack information on whether the effects of viruses on both host phenotypic traits and host population demography can modify interactions with upper trophic levels. To fill this gap, we investigated whether a prevalent densovirus infecting the aphid Myzus persicae(i.e. MpDNV) can modify trophic interactions between host aphids and their natural enemies (i.e. predators and parasitoids) by influencing aphid phenotypic traits (i.e. body mass and defensive behaviours), population demography (i.e. density and age-structure) and susceptibility towards both predation and parasitism. We found that the virus decreased aphid body mass but did not influence their behavioural defences. At the population level,the virus had a minor effect on aphid adult mortality whereas it strongly reduced the density of nymphs and influenced the stage structure of aphid populations. In addition, the virusenhanced the susceptibility of aphids to parasitism regardless of the parasitoid species. Predation rate on adult aphids was not influenced by the virus but ladybeetle predators strongly decreased the number of aphid nymphs, especially for uninfected ones compared to infected ones. As a result, the virus decreased predator effect on aphid populations. By reducing both aphid quality and availability, increasing their susceptibility to parasitism, and modulating predator effect on aphid populations, we highlighted that viral endosymbionts can be prevalent drivers of their host ecology as they modify their phenotypes and interspecific interactions. These virus-mediated ecological effects may have consequences on enemies foraging strategies as well as trophic webs dynamics and structure.

International audience; Warming and disturbance of precipitation dynamics are expected in the Mediterranean basin, resulting in longer, more intense drought and heat waves. Here we investigated how litter microbial functioning and responses to stress may be shaped by coastal environmental conditions, and whether this depends on litter type (Pinus halepensis, Pistacia lentiscus and their admixture). Mesocosms of monospecific and mixed litters collected from both inland and coastal areas were subjected to either control (25 C, 60% water holding capacity [WHC]) or stress conditions (five drying-rewetting [D/rW] cycles: 1 week of drying at 35 C, 1 week at 25 C, 60% WHC). Litters were characterised using chemical analyses (C/N ratio and solid-state 13 C nuclear magnetic resonance [NMR] spectroscopy) and indicators of microbial activity (lignocellulolytic activities, basal respiration [BR], active microbial biomass [MB], fungal and bacterial catabolic profiles). Litter type controlled cellulases and basal respiration in litters from the inland area (e.g. positive correlations between these microbial indicators and di-O-alkyl C + O-alkyl C and %N), whereas the litter-type effect was smoothed for the coastal area. Fungal and bacterial catabolic profiles were mainly shaped by the coastal conditions and litter type, respectively, indicating that fungi were more sensitive to coast-specific conditions and bacteria more sensitive to their immediate surrounding (i.e. litter type). After D/rW cycles, microbial catabolic profiles showed: (a) a stronger stress impact on microbial communities from the inland area and (b) pre-exposure to coastal constraints limited the drought effect on decomposers from the coastal area. Our findings reveal that coastal environmental conditions and litter type are major drivers of microbial functioning and responses to drought stress.

International audience; Inter-individual variability of tree drought responses within a stand has received little attention. Here we explore whether the spatial variations in soil/subsoil properties assessed through electrical resistivity tomography (ERT) could explain variations in drought response traits among trees.We used ERT to compute the percent variation in resistivity (PVR) between dry and wet conditions as an indicator of spatial variability in total available water content. PVR was computed in two different depth ranges (0-2 and 2-5 m) for eleven Quercus ilex stools in a Mediterranean forest stand. PVR values were compared to biological traits, including tree water status (predawn water potential (Ψ)), leaf traits (δ 13 C, leaf mass area (LMA)), and canopy defoliation measured after intense drought.We found significant correlations between PVR and biological variables. For Ψ , the nature and strength of the correlations vary according to the level of drought intensity. The correlation between Ψ and PVR was positive during well-watered conditions in the upper layer (0-2 m) and during water-limited conditions in the deeper layer (2-5 m). During most severe droughts, however, the Ψ was negatively correlated with PVR in the upper layer. Trees with lower PVR in the upper layer were also associated with water use efficiency (higher δ 13 C), higher LMA, and a lower level of defoliation after extreme drought.Overall, our results indicate that local differences in soil/subsoil properties affect tree response to drought and suggest that less favorable soil/subsoil conditions (lower PVR) can lead to lower water stress during the driest period and to lower defoliation after extreme drought. Plausible explanations for this better acclimation include higher stomatal regulation and improved deep soil and subsoil water exploration by trees located in more adverse conditions. We encourage the development of ERT in ecological studies to further explore the interrelated relationships between soil/subsoil, climate, and tree functioning.

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; The surface erosion of soil samples caused by an impinging jet can be analysed using the jet erosion test (JET), a standard experimental test to characterize the erosion resistance of soils. This paper specifically addresses the flow characteristics of a laminar impinging jet over the irregular surface of granular beds to discuss the pertinence and relevance of commonly used empirical estimations based on a selfsimilar model of a free jet. The JET is here investigated at the microscale with a coupled fluid-particle flow numerical model featuring the lattice Boltzmann method (LBM) for the fluid phase combined with the discrete element method (DEM) for the mechanical behaviour of the solid particles. The hydrodynamics of a laminar plane free jet are confronted with the results from a parametric study of jet impingement, both on solid smooth and fixed granular surfaces, that take into account variations in particle size, distance from jet origin, and jet Reynolds number. The flow characteristics at the bed surface are here quantified, including the maximal values in tangential velocity and wall shear stress, which can be regarded as the major cause of particle detachments under hydrodynamic solicitation. It is shown that the maximal velocity at the impinged surface can be described by the free jet self-similar model, provided that a simple empirical coefficient is introduced. Further, an expression is proposed for the maximal shear stress in laminar conditions, including a Blasius-like friction coefficient that is inversely proportional to the square root of the jet Reynolds number. To conclude, finally, the JET erosion of different cohesionless granular samples is analysed, confirming that the threshold condition at the onset of granular motion is consistent with the Shields diagram and in close agreement with previous experimental results.

International audience; Each year, wildfires spreading in wildland-urban interfaces (WUI) damage or destroy homes and other important assets, threatening residents and firefighters and sometimes resulting in loss of lives. In most cases, the vegetation located in the area comprised between wildland vegetation and housing is responsible for this fire propagation. This ornamental vegetation can be composed of native or exotic species, but also of landscaping dead fuel materials such as mulches that also sustain fire propagation and present a more heterogeneous structure compared to wildland vegetation. Correctly assessing the flammability of these ornamental species in order to properly choose, locate and maintain them when landscaping is necessary to reduce wildfire risk and prevent fire propagation in WUI. Likewise, an adapted modelling of fire propagation in this type of vegetation is needed.

In this report, we present a new case of mosaic trisomy 13 with prolonged survival, firstly detected by array-CGH analysis which was carried out because of moderate intellectual disability with postaxial hexadactyly, dermatologic features, ventricular septal defect, bicuspid aortic valve, and aortic dystrophy in a 19-year-old male patient. In a subset of 15% of the cells, the patient carried a derivative chromosome 10 generated by a nonreciprocal (10;13) translocation inherited from his healthy mother who carried the translocation in a balanced and homogeneous state. FISH analyses showed interstitial telomeric sequences at the breakpoints. To our knowledge, this is the second report of a patient with trisomy 13 mosaicism displaying a severe aortic root dilatation. We also discuss the mechanisms which could explain the mosaic state, the most likely one being related to the instability of the interstitial telomere.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; La politique Trame verte et bleue (TVB) repose au niveau national sur un document cadre, appelé « Orientations nationales » (ON TVB), dont l'objectif est d'assurer une cohérence nationale de la TVB, tout en laissant un libre choix de méthode à chaque échelle territoriale. À la demande du ministère chargé de l'écologie, le Centre de ressources TVB a effectué depuis 2010 un suivi technique de l'élaboration des Schémas régionaux de cohérence écologique, afin de connaître les choix méthodologiques des régions et la façon dont elles appréhendaient les ON TVB. En 2017, les informations récoltées dans le cadre de ce suivi ont fait l'objet d'un bilan dont cet article retranscrit les principaux résultats et en tire des premières leçons sur la mise en oeuvre des ON TVB.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels [Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; This report presents a new large-scale test apparatus (LSTA) developed to assess the efficiency of a geosynthetic reinforcement for the limitation of deformations of a geosynthetic lining system (GLS) over a 0.5 m wide cavity. Two experiments were conducted. The first one involved a geosynthetic clay liner, a nonwoven needle-punched geotextile and a high-density polyethylene geomembrane. For the second experiment, a 50 kN/m polyvinyl alcohol geogrid was embedded within the sand layer below the geosynthetic clay liner to provide reinforcement above the cavity. An overburden pressure varying from 10 to 100 kPa was applied to the top of the GLS. Strain gauges were used to measure the strain within the geogrid and the geomembrane. The results proved that the 50 kN/m geogrid reinforcement beneath the geomembrane reduced the maximum strain within the geomembrane, compared to the case where the geomembrane was unreinforced, by 25% on average. The results showed that the overall strain within the geomembrane was 31% to 42% less than that of the geogrid above the cavity. Finally, the results showed that the spatial distribution of the strain within the geomembrane and that of the geogrid differed because of a conical shape of the collapsed zone.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; The establishment and development of oak (Quercus spp.) seedlings are frequently impaired by siteheterogeneity resulting from historical anthropogenic disturbances in Mediterranean basin woodlands.In particular, the alteration of forest structure and soil biotic and abiotic components can compromise the natural regeneration of Persian oak (Quercus brantii Lindl.) in western Iran. This study aimed to investigate how soil properties, soil mesofauna diversity and stand structural indices differ between welland poorly regenerated areas. We sampled 105 plots in an oak woodland subjected to past disturbances but protected from human activities for the last 20 years. These 100-m2plots were distributed into two groups: i) poorly regenerated plots (PRP) with only 0 or 1 newly established oak seedling, and ii) well regenerated plots (WRP) with ≥3 seedlings. In each plot, we characterized the forest structure using three structural indices, and determined the soil properties and mesofauna diversity. Structural indices were higher in WRP than in PRP for height (0.83 and 0.23), diameter differentiation (0.74 and 0.36) and species mixture (0.90 and 0.21). Also, richness and diversity of soil mesofauna were lower in PRP than in WRP. Acanonical correspondence analysis (CCA) ordination clearly separated WRP, which were characterized by a clumped spatial distribution of mature oak trees on fertile soils, from PRP that exhibited a uniform spatial distribution of trees established on soils with a higher sand content (63 and 59%) and a higher bulk density (1.7 and 1.3). The uniform spatial distribution of trees, which was less favourable to oak seedling establishment, was inherited from intensive past human disturbances. To favour oak regeneration, we recommend applying management actions in cooperation with land-users, in particular the conservation of small patches of tree clumps to act as islands of fertility and seed sources.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Capacity matrices are widely used for assessment of ecosystems services, especially when based on participatory approaches. A capacity matrix is basically a look-up table that links land cover types to ecosystem services potentially provided. The method introduced by Burkhard et al. in 2009 has since been developed and applied in an array of case studies. Here we adress some of the criticisms on the use of capacity matrices such as expert panel size, expert confidence, and scoring variability. Based on three case-study capacity matrices derived from expert participatory scoring, we used three different approaches to estimate the score means and standard errors: usual statistics, bootstrapping, and Bayesian models. Based on a resampling of the three capacity matrices, we show that central score stabilizes very quickly but that intersample variability shrinks after 10-15 experts while standard error of the scores continues to decrease as sample size increases. Compared to usual statistics, bootstrapping methods only reduce the estimated standard errors for small samples. The use of confidence scores expressed by experts and associated with their scores on ecosystem services does not change the mean scores but slightly increases the standard errors associated with the scores on ecosystem services. Here, computations considering the confidence scores marginally changed the final scores. Nevertheless, many participants felt it important to have a confidence score in the capacity matrix to let them express uncertainties on their own knowledge. This means that confidence scores could be considered as supplementary materials in a participatory approach but should not necessarily be used to compute final scores. We compared usual statistics, bootstrapping and Bayesian models to estimate central scores and standard errors for a capacity matrix based on a panel of 30 experts, and found that the three methods give very similar results. This was interpreted as a consequence of having a panel size that counted twice the minimal number of experts needed. Bayesian models provided the lowest standard errors, whereas bootrapping with confidence scores provided the largest standard errors. These conclusions prompt us to advocate when the panel size is small (less than 10 experts), to use bootstrapping to estimate final scores and their variability. If more than 15 experts are involved, the usual statistics are appropriate. Bayesian models are more complex to implement but can also provide more informative outputs to help analyze results.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; This study assesses the effects of vegetation patterns and environmental factors on the abundance of natural tree and shrub regeneration in semi-arid forests of the Zagros Mountains, western Iran. We sampled 120 releves at different topographic positions in a protected area of the studied region. Floristic composition, slope, elevation and soil properties were recorded at each releve, and woody seedling density was measured. We have first discerned five floristic groups using two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA) and then explored the relationships among the floristic group compositions, environmental factors and seedling densities. The indicator species of the 5 groups were Quercus brantii, Acer monspessulanum, Cerasus microcarpa, Rhamnus arvensis and Astragalus licyoides. Our results indicated that these groups were significantly affected by elevation and soil properties and the soil properties refer to: EC (electrical conductivity), N (nitrogen), K (potassium), OM (organic matter), and bulk density. Woody regeneration was composed of Q. brantii, A. monspessulanum, C. microcarpa, Amygdalus scoparia and Crataegus pontica seedlings. The highest density of seedlings was found for Q. brantii (97.14 (±48.00)/hm2) and the lowest for A. scoparia (2.28 (±1.50)/hm2). Quercus brantii was the dominant species and the seedling density was positively correlated with soil pH and P (phosphorus) values. A. scoparia regeneration was negatively correlated with elevation, and the seedling density peaked in C. microcarpa group. There was no significant variation in distribution of C. pontica seedlings among the groups, but the seedling density of this species was positively correlated with slope and potassium. Cerasus microcarpa seedlings were more abundant in the Q. brantii group than in other groups. This study showed that the regeneration of trees and shrub species was unequally distributed in different floristic groups for some species (A. scoparia and C. microcarpa) but not for other (Q. brantii and C. pontica) and was generally correlated with some environmental factors, particularly elevation, slope and soil nutrients (P and K). These results are a first step to implement future management and restoration strategies for promoting forest regeneration.

1. In-stream nitrate removal capacity may be used as a proxy for the ecosystem service of water quality regulation. It is well known that this natural function is driven by abiotic and biotic factors in running water environments. With regard to biotic drivers, most of the literature focuses on the microbial community influences, but there has been very little emphasis on the relationship with the benthic macroinvertebrate community. Since this community feeds on microbial assemblages (autotrophic and/or heterotrophic biofilms) that live on the streambed and in the hyporheic zone of the river, macroinvertebrates also have the potential to influence nitrate removal via its influences on microbiological processes. 2. The objective of this study was to examine the potential relationship between the macroinvertebrate communities and nitrate removal. A dataset of in-stream nitrate removal rates measured in nine-third-order streams was analysed. The simultaneous influences of abiotic (hydromorphological, physical and chemical characteristics) and biotic (biofilm and macroinvertebrate) drivers were examined and together explained 56% of the in-stream nitrate removal variance. An analysis of the independent contributions of each driver showed that abiotic drivers (e.g. ammonium, dissolved organic carbon, temperature and transient zone) contributed 40% of this nitrate removal variance, whereas the macroinvertebrate community contributed 39%. 3. The potential relationship between macroinvertebrates and nitrate removal was subsequently explored using trait-based approaches of the macroinvertebrate community. This method allows for the selection of trait modalities assuming a top-down control of microbial communities by macroinvertebrates, with in-stream abiotic conditions correlated with nitrate removal (assuming that environmental conditions affect macroinvertebrate community composition). 4. The main trait modalities positively correlated with nitrate removal were scraper (feeding habit), flagstones/boulders/cobbles/pebbles (substrate preference), crawler and interstitial (locomotion) and detritus (food). The main modalities negatively correlated with nitrate removal were silt and mud with microphytes (as substrate preference), and with fine sediment with microorganisms, and dead animals (as food sources). These results agreed with the hypothesis of top-down control and enhanced understanding of the influence of hydromorphological factors on nitrate removal. 5. This study highlights the involvement of the macroinvertebrate community in in-stream nitrate processing, and demonstrates the usefulness of applying a functional approach to explain relationships between biodiversity and ecosystem function., This study was supported by funding from the STREAMES European project (EVK1-CT-2000-00081) in the 5th Framework Programme.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE; International audience; The current study presents experiments for the initial stages of fluidization induced by a localized fluid injection. The process was studied by recording high-speed videos in a 2-D-region far from the boundaries using Planar Laser Induced Fluorescence and Refractive Index Matching. The experimental setup allowed for several parameters to be systematically studied including particle sizes, initial bed heights, and injection port diameters. The results show that the critical flow rate required for fluidization is primarily dependent on the initial height of the granular bed. However, this dependence is not a linear relation but progressively plateaus for larger heights. Conversely, the diameter of the chimney relates only slightly to the injection port diameter and significantly more to the diameter of the particles.

[Departement_IRSTEA]Territoires [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; In recent years, numerous studies have investigated the relationship of extreme precipitation intensities with temperature derived from a binning method using present-day weather data. The aim of this approach is that these dependencies, or so-called apparent scaling rates, provide insights on how precipitation extremes could evolve in the future climate. In a recent paper, Bao et al. showed that there is a large discrepancy between the present-day apparent scaling rates

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; The role of terpenes on flammability is not clearly determined, especially for species used in wildland-urban interfaces (WUI) where the fire risk is high. This work aims at checking if the leaf flammability of different WUI species (Pinus halepensis, Cupressus sempervirens, C. leylandii, and C. arizonica) varied across seasons possibly highlighting the role of leaf moisture content (FMC) and terpene content (investigated at three levels: total, family and compounds). All year round, P. halepensis presented the highest flammability related to high content in sesquiterpenes, mostly caryophyllene and α-humulene, and low FMC in contrast to C. arizonica. Species presented different seasonal flammability and terpene patterns. Diterpene totarol, sesquiterpene germacrene, and monoterpene myrcene increased flammability (in C. sempervirens, C. arizonica, and P. halepensis, respectively) while monoterpene α-pinene (in P. halepensis) and several other diterpene compounds, especially manool oxyde-13-epi, decreased it (in C. leylandii). Terpene compounds linked to flammability seasonally varied only in C. leylandii, the species showing the highest diversity of compounds. FMC did not affect flammability, except time-to-ignition in C. sempervirens. Regardless of season, the highly flammable species should be avoided close to housing, especially when they form horizontal fuel continuity (as in ornamental hedge) that can easily propagate the fire.

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; Assessing whether trait variations among individuals are consistent over time and among environmental conditions is crucial to understand evolutionary responses to new selective pressures such as climate change. According to the universal thermal dependence hypothesis, thermal sensitivity of metabolic rate should not vary strongly and consistently among organisms, implying limited evolutionary response for metabolic traits under climate change. However, this hypothesis has been rarely tested at an individual level, leaving a gap in our understanding of climate change impacts on metabolic responses and their potential evolution. Using the amphipod Gammarus fossarum, we investigated the variability and repeatability of individual metabolic thermal reaction norms over time. We found large variations in both the thermal sensitivity (i.e. slope) and expression level (i.e. intercept) of individual metabolic reaction norms. Moreover, differences among individuals were consistent over time, and therefore repeatable. Inter-individual variations in body mass resulted in a high repeatability of metabolic expression level but had no significant effect on the repeatability of thermal sensitivity. Overall, our results highlight that inter-individual variability and repeatability of thermal reaction norms can be substantial. We conclude that these consistent differences among individuals should not be overlooked when apprehending the ecological and evolutionary effects of climate change.

[Departement_IRSTEA]Eaux [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; Abiotic and biotic factors affect plants in various ways which in turn affect associated arthropod communities through direct and/or indirect bottom-up interactions. Several review articles have synthesized studies examining the indirect effects of abiotic factors on plant-arthropod interactions, mainly focusing on soil nitrogen, soil water status, and climate change. However, these studies have mostly focused on bitrophic interactions, whereas most ecological systems are composed of at least three trophic levels. Lately, research on plant-mediated multitrophic interactions in plant-arthropod food web has received increasing interest. Both the intensification of agriculture and the global climate change have the potential to trigger bottom-up effects that cascade through trophic links. In this review article, we synthesize the most recent studies describing how abiotic changes could modulate plant-mediated bottom-up forces and how it could affect arthropod communities and associated biocontrol services. We discuss potential for increasing the sustainability of managed and natural ecosystems, and highlight road maps for future studies.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; To live at the closest of the Mediterranean forest to enjoy the benefits of Nature: an idea that reaches more and more city-dwellers... but it comes with its own set of risks. In south-eastern France, almost half of the total fire ignitions occurs in the areas where housing intermingles with wildland. In these areas, called wildland-urban interfaces, the fire risk is high, especially in summer because of the weather conditions conducive to fire and of the higher population density, most fires being human-caused. Moreover, the flammable vegetation surrounding housing makes the situation worse, forming a fuel continuity that allows the fire propagation from the forest to housing. With the on-going global change, the forest fire issue needs to be tackled with a higher efficiency than ever in order to strongly mitigate the occurrence of destructive fire events in these areas.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; Levees can fail because of different types of mechanisms: external erosions, internal erosions, instabilities. These mechanisms can act separately or in a more complex failure scenarios, leading to a breach, a failure of the levee system, and the flooding of inhabited areas. Usually, more than one mechanism can be involved in a breach. As an example, the collapse of a protection revetment can lead to external erosion of the impervious upstream slope of a levee, which can lead to seepage and internal erosion, which can then lead to the breach. In this paper we present methods used in France for failure mode analysis and performance assessment of levees in regard to the main failure scenarios. Our failure mode analysis is briefly presented, as well as three methods for estimating the safety of levees. One of these methods, based on the use of indexes is presented in detail. This index-based method allows to use many different type of data and to combine them in different steps using expert-knowledge based rules: raw data is combined into status indicators representative of geotechnical characteristics of levee segments components, status indicators are combined into functional criteria which represent the performance of a geotechnical function, functional criteria are combined into performance indicators which represent the safety of the levee relatively to a failure scenario.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; National audience; Le comportement mécanique des milieux granulaires triphasiques, tels que les sols partiellement saturés en eau, est étudié en combinant deux approches micro-mécaniques : une homogénéisation analytique avec des simulations numériques aux Éléments Discrets. Par homogénéisation, on exprime les contraintes macroscopiques de ces matériaux à partir des forces de contact inter-grains, des deux pressions différentes des fluides, et des efforts de tension superficielle, tous présents à l'échelle microscopique. L'expression µUNSAT ainsi obtenue associe de manière générale un caractère tensoriel (non-sphérique) aux différentes contributions, en accord avec la microstructure du matériau. Un modèle numérique aux Éléments Discrets permet ensuite de mesurer ces différentes contributions dans le cas d'un milieu granulaire idéal en conditions humides. Les résultats numériques démontrent l'anisotropie des contraintes capillaires dues aux phases fluides, et, dans une certaine mesure, le caractère effectif des contraintes dues aux forces de contact.

National audience; We present in this work a methodology for calculating capillary forces in grains assembly by minimizing the surface energy of water with the software Surface Evolver. The methodology is first validated on a capillary bridge between two grains. Then we compare numerical and experimental results in the case of the coalescence of bridges in an assembly of three grains. This method will permit to evaluate the capillary forces in a more complex assembly of grains, in order to improve a multi-scale model of soil.; On propose ici une méthode d'évaluation des forces capillaires dans des assemblages de grains, par minimisation de l'énergie de surface de l'eau à l'aide du logiciel Surface Evolver. La méthode est évaluée dans le cas simple d'un doublet capillaire entre deux grains. Elle est ensuite testée dans le cas de la coalescence de deux ponts dans un assemblage de trois grains. À terme, ces résultats permettront de calculer les forces capillaires dans un assemblage plus complexe afin d'enrichir un modèle multi-échelle de sol

International audience; Temperature is an important ecological driver modulating life history traits of organisms, such as growth and reproduction. With the ongoing global warming, understanding the mechanisms underlying the effect of temperature on size and resource allocation trade-off is crucial. The temperature-size rule (TSR) describes plastic growth patterns in populations of ectothermic species under different thermal environments, whereby warming results in faster initial growth but lower size at maturity. However, the evolution of the TSR remains poorly understood. Here we conducted an experiment with populations of the medaka fish Oryzias latipes maintained at two temperatures for successive generations to investigate changes in the growth pattern of the TSR. After rearing six generations at cold (20 degrees C) and warm (30 degrees C) temperature, we conducted common garden experiments on the seventh generation where we compare growth trajectories and reproduction patterns in four different groups of fish: (i) fish reared at cold temperature over all seven generations (cold past and present), (ii) fish reared at warm temperature over six generations and at cold temperature at the seventh generation (warm past and cold present), (iii) fish reared at warm temperature over all seven generations (warm past and present) and (iv) fish reared at cold temperature over six generations and at warm temperature at the seventh generation (cold past and warm present). For each treatment, we monitored growth curves and reproduction, and investigated changes in model parameters and reproduction up to 350 days after hatching. Our study showed changes in TSR patterns according to ancestral and developmental temperatures. Developmental temperature mainly impacted age at maturity and asymptotic size, whereas size at maturity was driven more by the dissimilarity between developmental and ancestral temperatures. Our results also highlight a loss of plasticity in temperature-size and reproductive patterns for the fish that were reared under warm condition over six generations.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; We herein present a recent micromechanical approach combining analytical homogenization with Discrete Element Method (DEM) simulations for a better understanding of the mechanical behaviour of granular soils in an intermediate state of water saturation. Analytical homogenization first leads to a so-called µUNSAT general expression for the macroscopic stress state, starting from micro-scale internal forces. The µUNSAT equations involve surface tension in addition to capillary pressure, and show a tensorial nature in accordance with preferential directions for the internal forces at the micro-scale. A DEM approach then enables one to access all stress quantities in the specific case of ideal wet granular materials. The results discuss the stress-strain-strength effective nature of the contact stresses stemming from contact forces, as well as the tensorial, anisotropic, character of fluid-induced capillary stresses.

International audience; This presentation covers more than 10 years of fruitful collaboration between Irphe, LMA and Irstea where our colleague and friend F. Anselmet played a central role. The presentation is organized in three parts. The first part deals with erosion of a cohesive soil by turbulent flow (F. Mercier PhD thesis). Work in progress concerning the acoustic emission of a turbulent flow in a soil is presented in a second part (C. Jeanniot PhD thesis). The last part is devoted to the interaction of a turbulent flow with acoustic sound wave inside a corrugated cylinder (G. Galeron PhD thesis) known as singing riser. Dikes and levees are prone to failure through two erosion processes [1]: i) internal erosion, induced by concentrated seepage that takes off and transports soil particles through the embankment and its foundation, ii) surface erosion induced by overflowing. Erosion of a cohesive soil by turbulent flow is studied with Computational Fluid Dynamics (CFD) numerical modelling, based on the adaptive remeshing of the water/soil interface to ensure the accurate description of the mechanical phenomena occurring near the soil/water interface [2,3,4]. The erosion law governing the interface motion is based on two erosion parameters: the critical shear stress and the erosion coefficient. The model is validated by comparison with closed-form solution of simple problems. The numerical results are then compared to laboratory test results: the Hole Erosion Test, which reproduces the mechanism of tangential erosion of a soil by turbulent flow in a circular pipe, and the Jet Erosion Test which reproduces the erosion of soil by a circular impinging turbulent jet. The shear stress at the wall appears to be well-described by the k- model while the pressure is better-described by the k- model. One means to monitor internal erosion is passive Acoustic Emission (AE) monitoring. This monitoring involves acoustic transducers to passively listen for acoustic energy released from internal sources. We study the potential of this approach at the laboratory, on the Hole Erosion Test [1]. Turbulent pipe flow in the hole generates acoustic waves that propagate in the soil sample. Acoustic sensors (accelerometers) installed on the equipment allow to measure these signals. The analysis sheds light on acoustic frequencies characteristic of the internal flow, between 0-10 kHz. The vibratory responses are analyzed from the acoustic signal using Fourier transforms and Lorenzian functions. The correlation of both frequency and intensity with flow velocity and hole diameter is studied [5]. Using a simplified model of the sound field generated inside the test sample by a wall turbulent pressure field inside a cylindrical hole, it is easy to determine, at least theoretically, the characteristics of the flow (convection velocity, diameter of the inner pipe, power spectral density of the flow) that play that contribute to the acoustic response of the test sample. The last part of this presentation is focused on a phenomenon often encountered in flow carrying pipes, since flow instabilities caused by geometric features may generate acoustic signals and thereafter interact with these signals in such a way that powerful pure tones are produced. A modern example is found in the so-called "singing risers", or the gas pipes connecting gas production platforms to the transport network. But the flow generated resonance in a fully corrugated circular pipe may be silenced by the addition of relatively low frequency flow oscillations induced by an acoustic generator.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; The Loire river levees are important and presently protect more than 300,000 inhabitants. During Loire levees hazards studies, a new methodology was developed by DREAL Centre - Val de Loire, Cerema and Irstea, for breaching probability assessment. The methodology is based on 5 scenarios initiated by overflow, internal erosion, slope sliding, external erosion (scour) and uplift mechanism. Specific fault tree and criteria were considered. This methodology was implemented in a spreadsheet tool called CARDigues. For several flood events and for each scenario, the tool calculates the breach hazard probability for every 50 m spaced profiles. The tool has been applied on 40 levee systems (500 km). CARDigues was also used to assess alluvial forest impact on levee breach probability. Indeed, for equivalent flow net in the channelized river, the rougher is the riverbed, the higher is the hydraulic level and then the breach hazard probability. CARDigues easily enables to identify the most impacted profiles by the last 20 years alluvial vegetation development. Other CARDigues developments and applications for levee management are currently tested. One deals with existing old levee system valorization. This article presents CARDigues methodology and tool and some applications on hydrographic Loire basin.; La Loire est un fleuve français dont les levées sont importantes en termes de dimension et de population protégée. Dans le cadre des études de dangers des digues du bassin de la Loire, une méthodologie a été mise au point pour l'estimation de leur probabilité de rupture. Elle fait intervenir 5 scenarios de rupture (surverse, érosion interne, glissement, érosion externe, soulèvement hydraulique) décomposés en arbres de défaillance simplifiés. Cette méthodologie est traduite et intégrée dans un outil de calcul appelé CARDigues. Il calcule la probabilité d'occurrence d'une rupture de digue sur des profils en travers espacés de 50 mètres et pour différentes crues. L'outil a été utilisé sur près de 40 systèmes d'endiguement (500 km). Cet outil a également été utilisé pour qualifier l'influence de la forêt alluviale sur le risque de rupture d'une digue. En effet, en augmentant la rugosité du lit, le développement de la forêt alluviale dans le lit mineur de la Loire augmente le niveau d'eau en crue le long de la digue, et, par conséquent, le risque de rupture de l'ouvrage. L'outil CARDigues a permis d'identifier les secteurs sur lesquels l'aléa de rupture de digue avait significativement augmenté ces 20 dernières années, du fait du développement de la forêt alluviale. D'autres applications, en lien avec la gestion des systèmes d'endiguement, sont en cours de test tels que la valorisation des ouvrages. L'objet de l'article est de présenter ces méthodes, l'outil et leurs applications à l'échelle d'un bassin hydrographique.

This paper presents an ongoing research about interfaces with earthen levees from a flood defence system. Interfaces or transitions zones can be found where there is a change in flood defence structure (e.g. earthen embankment to concrete flood wall), revetment protection (e.g. grass to riprap), cross section and in the construction or foundation materials. The investigation, supported by the Environment Agency in England, aims to consider the presence of transitions during flood defence condition assessment, quantify the effects of transitions on flood defence performance and manage the risk of transitions with improved design and retrofit solutions. The paper sets up an interface or transitions typology and discusses the main failure mechanisms at transitions. A framework to evaluate the performance of transitions in flood defence systems is also presented., Cet article présente une recherche en cours sur les interfaces dans les digues (ou levées) de terre d'un système de protection contre les inondations. Des interfaces ou des transitions peuvent être trouvées en cas de changement de la structure de la digue ou du type de revêtement de protection, de section transversale ou des matériaux de construction ou de fondation. Les travaux, financés par l'Environment Agency anglaise, vise à prendre en compte les transitions lors des diagnostics des ouvrages de protection contre les inondations, à quantifier les effets de ces transitions sur les performances de ces ouvrages et à gérer le risque posé par les transitions grâce à des solutions améliorées de conception et de confortement. La communication présente une typologie des interfaces ou des transitions et décrit les principaux mécanismes de défaillance liés aux transitions. Un cadre de méthodologie d'évaluation de la performance des transitions dans les systèmes de protection contre les inondations est également présenté.

International audience; 1. Ongoing global changes are causing major ecological shifts worldwide. Biological trends need to be assessed over long periods of time to better understand past and current community responses.2. The present study developed a methodological framework for meta-analyses to be conducted that account for the temporal and spatial autocorrelation of observational data. We provided the R code for processing this framework, which enables temporal trends to be tested through the analysis of long-term, spatially structured datasets. Taking both types of autocorrelation into account resulted in more conservative but arguably more reliable statistical outcomes.3. This meta-analysis framework was then applied to investigate long-term trends in environmental and fish-community time series in multiple stations in large French rivers over the past 4 decades.4. General significant upward and downward trends were highlighted in water temperature and flow discharge, respectively, over the study period. Concomitantly, the density of numerous species increased, resulting in large increases in both species richness (about + 50%) and total fish abundance (approximately four-fold), but with no significant trend in species evenness. Strong changes in species composition were observed during the study period, with an overall upward trend in the relative abundance of newcomers (i.e. species not sampled during the first years of the survey), while the trend in relative abundance of non-native species was non-significant. Moreover, the strongest signal underlying community changes was replacement of northern by southern species. 5. This study showed major changes in fish density and community structure in large rivers over the past 40 years and represents, to our knowledge, one of the first large-scale actual demonstrations (i.e. based on observations rather than predictions) of an overall poleward shift of freshwater fish communities in response to ongoing global changes. K E Y W O R D S global changes, long-term surveys, meta-analysis, poleward shift, spatio-temporal autocorrelation This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; An ongoing implementation of Level Set - Discrete Element Method in YADE is herein presented. We discuss the principles of the method, together with computational aspects.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [ADD1_IRSTEA]Adaptation des territoires au changement global; International audience; In the French Mediterranean, large fires have significant socio-economic and environmental impacts. The previous works dealing with fires in the French Mediterranean were based on gridded fire data commencing from the mid-1970s (e.g., Ruffault et al., 2016; Fréjaville and Curt, 2017; Ganteaume and Guerra, 2018; Lahaye et al., 2018). Working with longer time-series of georeferenced fires (extending back to 1958) would allow examining both spatial and temporal distributions of large fires (>100 ha) across the French Mediterranean. The objectives of this work were (i) to identify the locations associated with large fire recurrence and to quantify the spatial extent of the region with reburns, (ii) to establish the mean fire extent and the fire return level as well as the LF causes along a longitudinal transect spanning the study area (identifying possible roles of climate conditions and fuel continuity in shaping this longitudinal gradient), and (iii), building on previous research, to re-estimate trends in large fires across the region taking advantage of a fire record spanning almost six decades. A long-term geo-referenced fire time series (1958-2017) was used to analyse both spatial and temporal distributions of large fires (LF; ≥100 ha). Large fire causes were analysed according to the regional fire database Promethée that has recorded fires since 1973. The region was impacted in some locations up to 6 times by recurrent LF (Fig. 1) and 21% of the total area burned by LF occurred on a surface that previously burned in the past, with potential impact on forest resilience. We found contrasting patterns between the East and the West of the study area, the former experiencing fewer LF but of a larger extent compared to the latter, with an average time of occurrence between LF exceeding 4,000 ha 50 years in the West. This longitudinal gradient in LF return level contrasts with what we would expect from mean fire weather conditions strongly decreasing eastwards during the fire season but is consistent with larger fuel cover in the East, highlighting the strong role of fuel continuity in fire spread (Fig. 2). Figure 1: Fire recurrence on the 1961-2017 and 1958-2016 period in the western and eastern areas, respectively. Figure 2: Top) Longitudinal cross-section of mean LF extent computed over 30-km sliding windows. The 95% confidence intervals were estimated using a bootstrapping approach. Bottom) Same as top panel but for mean June-September FWI (in red) and the percent of biomass (in green). Additionally, our analysis confirms the sharp decrease in both LF frequency and burned area in the early 1990s, due to the efficiency of fire suppression and prevention reinforced at that time, thereby weakening the functional climate-fire relationship across the region. Regarding the causes of LF, the proportion of unknown cause was high throughout the region, varying from 74% to 77% from the West to the East. It is worth noting that the knowledge of smaller fires

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU [ADD1_IRSTEA]Hydrosystèmes et risques naturels; National audience; Le code ARFAN (« Areal RainFall ANalyses ») permet l'analyse multidurées de chroniques de pluie à pas de temps fixe. Il peut traiter les chroniques ponctuelles, ou des « pluies de bassin » qui en sont déduites (méthode des polygones de Thiessen 'dynamique' recalculant les coefficients de pondération en fonction des lacunes, calcul géostatistique par simulations conditionnelles, permettant d'estimer l'incertitude [code externe SAMPO]). L'échantillonnage est réalisé en maxima annuels et par dépassement de seuils (avec contrôle du choix du seuil et des critères d'indépendance, et validation de l'échantillon obtenu). L'ajustement des lois de probabilité reconnues donne les quantiles. Répéter sur la chronique moyennée sur plusieurs durées produit les courbes Intensité-durée-Fréquence décrivant le régime des pluies fortes (de bassin le cas échéant). Ces IdF sont classiquement utilisées pour construire des « pluies de projet probabilistes », moyennant le choix a priori d'une forme, symétrique ou non (triangle, double triangle, hyétogramme « moyen »). Cependant, cet objet est subjectif et très réducteur. La pluie « de bassin » suppose une hypothèse d'homogénéité spatiale des pluies ; or la variabilité temporelle et spatiale des phénomènes est considérable y compris au sein du bassin, et gouverne l'effet concret de tous dispositifs. Une stratégie de gestion des crues, basée ou non sur des ouvrages à dimensionner, doit considérer cette variabilité des phénomènes. Un progrès possible est de travailler par simulation continue : générer des chroniques de débit à partir de longues chroniques de champs de pluie stochastiques. La méthode est plus exigeante à mettre en oeuvre, mais restitue une variabilité riche et réaliste, nécessaire pour évaluer véritablement l'aléa d'inondation et l'effet d'ouvrages sur cet aléa. ARFAN est un outil de recherche ouvert et évolutif, destiné à tester des méthodes. Une version stable sera aussi disponible pour des utilisations pédagogiques et à l'attention des services de l'État et des bureaux d'étude. Ces travaux bénéficient du soutien du Ministère français chargé de l'Environnement (convention Multirisques) et de partenariats (PHC franco-algérien Tassili ; université autonome de Querétaro, Mexique). SAMPO a été soutenu par divers acteurs (ANR Floodscale, CCR, EdF, Sintef).

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; On December the 3rd and 4th of 2003, a huge flood occurred on the Rhone river, one of the greatest in France. As a consequence, more than 12 000 people and an important part of the economic activities of the area were impacted. Other inundations have occurred since the 1990s and a global public policy for flood management was introduced in 2009 through the "Plan Rhone". This flood management system is made with interrelated operations. This article deals with a part of the main one that consists on the creation of new overtoppable levee (by the SYMADREM) as a replacement of the actual one which is mainly a railway embankment owned by the SNCF. This new levee section is situated between the cities of Tarascon and bank Arles on the East of the Rhone river and aims to protect the two cities from flooding with a probability of occurrence up to 10-3. In order to obtain a consistent system of defence against floods, this embankment has to leave the water flowing over the future SYMADREM levee to pass through, that brought SNCF to design ten new flood discharge structures under the railway. Both parts of this operation will be done almost in the same time (between 2017 and 2020). French control authorities asked SNCF RESEAU to keep the same level of flood defence until the new levee is operational. In order to respect this policy, SNCF RESEAU proposed some actions that will help to provide work and levee safety all along the operation. The goal of this article is to present the work on the railway embankment and these actions.; Les 3 et 4 décembre 2003, une importante crue du Rhône a touché plus de 12 000 personnes et occasionné plus de 700 millions d'euros de dommages. Cette crue et plusieurs autres ayant touché la France au cours de la décennie, ont amené les pouvoirs publics à prendre conscience de la nécessité d'une stratégie globale de prévention des inondations. Sur le Rhône, cette stratégie se concrétise par le « Plan Rhône », regroupant plusieurs opérations interdépendantes. Parmi ces opérations pour lesquelles le SYMADREM vise la rénovation complète du système de digues de protection du Rhône, une des principales est la création d'une digue de 1er rang, en rive gauche du Rhône entre Arles et Tarascon. La digue étant conçue pour être déversante sur une partie de son linéaire, elle nécessite la mise en transparence hydraulique et le confortement du remblai ferroviaire qui assure actuellement la fonction de protection contre les inondations. Les travaux inclus dans l'opération sont réalisés de façon concomitante entre 2017 et 2020 mais le système de protection ne sera fonctionnel qu'une fois l'ensemble des travaux réalisés. D'ici-là, SNCF RESEAU a pour obligation de maintenir la continuité de protection des populations dans la plaine du Trébon. Afin de respecter cette obligation SNCF RESEAU a mis en place un ensemble d'actions, faisant l'objet de cette communication, permettant d'assurer la sécurité du chantier, composé de différentes phases aux enjeux biens définis, ainsi que du remblai ferroviaire en cas de crue.

The failure process of levees is based on assumptions of deterioration or partial breaking events series. These partial breaking events are caused by poor performance of one or several parts of the levee. Indeed, if one material properties or performance is under the required level, the levee stability can be no more guaranteed. The performance is the result of the initial condition and how it will evolve over time, what is called deterioration process. But deterioration process of natural material is not currently very well known. We propose in this article a discussion about aging of the material usually used for the watertightness function in a levee. We have based our discussion on an example of a silty soil deteriorated by a process of cyclic wetting and drying events. Cycles are supposed to represent the climatic environment of a levee with alternative of wet and dry seasons in one year. This kind of deterioration is not the only one and we propose a classification of degradation mechanisms that can affect the properties of natural properties. We discuss the quickness (fast, low, very low process) and the intensity (intense, intermediate or small process) of the deterioration processes. We also assume that these deterioration processes depend on the geographic localization of the levee and on the initial properties depending on the levee building quality., Les scénarios de rupture des digues sont basés sur des hypothèses d'enchaînement de dégradations ou de ruptures partielles de différentes parties des ouvrages. Ainsi, pour qu'une défaillance intervienne sur un tronçon de digue, il faut que certaines parties d'ouvrage arrivent à la limite de leur «bon» fonctionnement et que leurs propriétés passent en dessous d'un certain niveau de performance. L'évolution des propriétés et des performances n'est cependant pas toujours «binaire» : l'ouvrage semble être dans un état correct puis, instantanément, arrive à la rupture. Cet article propose une discussion sur les mécanismes de vieillissement des matériaux utilisés notamment pour leur fonction d'étanchéité, à partir d'exemples concrets. Le vieillissement est un phénomène normal qui apparaît soit par un usage répété de l'ouvrage soit par des phénomènes normaux de dégradation et d'usure par le temps et les conditions extérieures. Ce vieillissement normal peut être identifié au travers de mécanismes de dégradation qui seraient classés par type de dégradation (météorologique, interaction avec le vivant, interaction avec des masses d'eau), par intensité (fort, moyen, faible) et par cinétique (très long, rapide, instantané). Ces mécanismes de dégradations seraient dépendants de la localisation géographique de l'ouvrage, de la nature des composants et de la qualité initiale de la réalisation de l'ouvrage.

International audience; On December the 3rd and 4th of 2003, a huge flood occurred on the Rhone river, one of the greatest in France. As a consequence, more than 12 000 people and an important part of the economic activities of the area were impacted. Other inundations have occurred since the 1990s and a global public policy for flood management was introduced in 2009 through the "Plan Rhone". This flood management system is made with interrelated operations. This article deals with a part of the main one that consists on the creation of new overtoppable levee (by the SYMADREM) as a replacement of the actual one which is mainly a railway embankment owned by the SNCF. This new levee section is situated between the cities of Tarascon and bank Arles on the East of the Rhone river and aims to protect the two cities from flooding with a probability of occurrence up to 10-3. In order to obtain a consistent system of defence against floods, this embankment has to leave the water flowing over the future SYMADREM levee to pass through, that brought SNCF to design ten new flood discharge structures under the railway. Both parts of this operation will be done almost in the same time (between 2017 and 2020). French control authorities asked SNCF RESEAU to keep the same level of flood defence until the new levee is operational. In order to respect this policy, SNCF RESEAU proposed some actions that will help to provide work and levee safety all along the operation. The goal of this article is to present the work on the railway embankment and these actions.; Les 3 et 4 décembre 2003, une importante crue du Rhône a touché plus de 12 000 personnes et occasionné plus de 700 millions d'euros de dommages. Cette crue et plusieurs autres ayant touché la France au cours de la décennie, ont amené les pouvoirs publics à prendre conscience de la nécessité d'une stratégie globale de prévention des inondations. Sur le Rhône, cette stratégie se concrétise par le « Plan Rhône », regroupant plusieurs opérations interdépendantes. Parmi ces opérations pour lesquelles le SYMADREM vise la rénovation complète du système de digues de protection du Rhône, une des principales est la création d'une digue de 1er rang, en rive gauche du Rhône entre Arles et Tarascon. La digue étant conçue pour être déversante sur une partie de son linéaire, elle nécessite la mise en transparence hydraulique et le confortement du remblai ferroviaire qui assure actuellement la fonction de protection contre les inondations. Les travaux inclus dans l'opération sont réalisés de façon concomitante entre 2017 et 2020 mais le système de protection ne sera fonctionnel qu'une fois l'ensemble des travaux réalisés. D'ici-là, SNCF RESEAU a pour obligation de maintenir la continuité de protection des populations dans la plaine du Trébon. Afin de respecter cette obligation SNCF RESEAU a mis en place un ensemble d'actions, faisant l'objet de cette communication, permettant d'assurer la sécurité du chantier, composé de différentes phases aux enjeux biens définis, ainsi que du remblai ferroviaire en cas de crue.

International audience; Les ouvrages de protection contre la houle ou contre les submersions couvrent 17% des côtes françaises, soit 1210 km. Compte tenu du changement climatique, notamment l'élévation du niveau de la mer, et de la présence démographique importante, les enjeux sur le littoral sont considérables. Dans ce contexte, le projet de recherche collaborative DIGUE 2020 a été conçu de façon à construire une plateforme de recherche sur les digues maritimes en associant, en parallèle, des travaux de recherche sur l'auscultation et la durabilité de l'ouvrage, ainsi qu'une étude sur la perception du risque de submersion marine. Les connaissances développées et partagées au moyen de la plateforme de recherche envisagée ont pour objectif, à moyen terme, le développement de projets de confortement ou d'élaboration de nouvelles digues d'une conception durable et, sur le long terme, le développement d'une culture commune sur le risque de submersion marin

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; In 2016, Cerema (Centre for studies and expertise on Risks, Environment, Mobility and Urban and Country Planning) and Irstea (National Research Institute of Science and Technology for Environment and Agriculture), launched partnerships with local authorities, to provide assistance in carrying out their new missions in flood prevention and aquatic environment management. Nine of them applied as they needed technical support with the implementation of these new competences from January 1st, 2018. A few years before, in 2015, the regulation framework on hydraulic works had been reinforced. Local authorities now have to reach specific objectives on identification and supervision of flood defence systems. The new regulation framework on flood defence systems leads local authorities in charge of flood prevention to reconsider how their territories are protected, and how hydraulic structures take part into flood protection. Local authorities have thus to identify where flood defence systems are relevant and with which structures. They have to determine the level of protection and the limits of the protected areas. They also have to organize the surveillance and maintenance of the flood defence systems as well as fulfilling compulsory documents, such as risk analysis. This paper describes one example of methodology which has been developed to help a local authority in the identification of flood defence systems. It provides tools to characterize the protection with reference to the new regulation framework. It also highlights issues that are to be faced when applied on a complex territory, such as Troyes agglomeration.; En 2016, le Cerema (Centre d'Études et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement) et l'Irstea (Institut national de Recherche en Sciences et Technologies pour l'Environnement et l'Agriculture) ont lancé un appel à partenariat visant à accompagner les collectivités dans la prise de compétence GEMAPI (GEstion des Milieux Aquatiques et Prévention des Inondations). Plusieurs intercommunalités se sont portées candidates avec des questionnements très concrets liés à la mise en oeuvre de la compétence au 1er janvier 2018. Dans un contexte d'évolution récente de la réglementation sur les ouvrages hydrauliques, des besoins d'accompagnement dans l'identification des systèmes de protection contre les inondations sont très vite ressortis. La nouvelle réglementation sur les systèmes d'endiguement amène en effet le responsable de la prévention des inondations à repenser le mode de protection de son territoire et le rôle des nombreux ouvrages hydrauliques présents dans l'environnement du réseau hydrographique. Avec la prise de compétence GEMAPI, les collectivités sont confrontées à des problématiques liées à l'identification physique des systèmes d'endiguement, au niveau de protection apporté, à la définition de la zone protégée, à l'organisation de la surveillance à mettre en place, et à la réalisation des études réglementaires associées, notamment les études de dangers. Cet article décrit une méthodologie proposée pour accompagner une collectivité dans l'identification des systèmes de protection contre les inondations. Des outils sont proposés, qui permettent de caractériser la protection au regard des nouveaux objectifs réglementaires. Sont également exposés quelques questionnements soulevés dans le cas de la mise en oeuvre sur le territoire de l'agglomération troyenne.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; Levees hazard studies were introduced by the 2007 regulations on the safety of hydraulic structures. These studies are applied to levee systems since the publication of the decree of 12 May 2015. They are risk analyses in a particular format, defined by the regulations. The paper presents a method for carrying out hazard studies of levee systems based on risk analysis. It describes the specific risk analysis method developed for these systems and the associated method for analysing failure modes. Finally, it presents the interest of using risk analysis independently of a fluctuating regulatory framework, for the continuous improvement of protection structures, the systems they form and their management.; Les études de dangers de digues ont été introduites par la réglementation de 2007 sur la sécurité des ouvrages hydrauliques. Celles-ci s'appliquent aux systèmes d'endiguement depuis la publication du décret du 12 mai 2015. Ces études sont des analyses de risque dans un format particulier, défini par la réglementation. La communication présente une méthode de réalisation des études de dangers de systèmes d'endiguement basée sur une analyse de risque. Elle décrit la méthode spécifique d'analyse de risque développée pour ces systèmes et la méthode d'analyse des modes de défaillance associée. Enfin, elle présente l'intérêt de l'utilisation de l'analyse de risque indépendamment d'un cadre réglementaire fluctuant, pour l'amélioration continue des ouvrages de protection, des systèmes qu'ils forment et pour la gestion associée.

International audience; Much is known about levee from their design towards their decommissioning - including their construction, failure and degradation modes, diagnosis approaches, regulation of concern, etc. - though the information is scattered and sometimes lacks clarity. Some of the knowledge is not explicit but tacit. Knowledge exists in different formats such as texts, photographs and videos. New knowledge is generated over time. Consequently, it is interesting to develop tools that allow gathering, capitalizing, making explicit, disseminating current and future information. In this article, two tools aiming at disseminating knowledge on levees are presented. On the one hand, the article presents WikiBarDig (http://wikibardig.developpementdurable.gouv.fr/index.php/ Portail:Wikibardig), developed by Irstea and held by the French Ministry of Ecology (Ministère de la Transition Ecologique et Solidaire). This knowledge base aims at capitalizing and disseminating knowledge on hydraulic works (dams and levees). It is susceptible to interest a wide section of the public including students, teachers, and debutant and experienced engineers in the domain working for different organisations such as government inspection services, engineering offices, regional authorities, entities managing and owning structures. On the other hand, the article presents technical sessions managed by France Digues Association. These sessions provide forums for discussion, debate and meetings for levee managers. These two complementary tools currently present a specific interest due to the introduction of the GEMAPI (Aquatic Environment Management and Flood Prevention) competency since 2018/01/01, particularly for the section concerning protection against flood and sea. Indeed, these tools can support the communities or engineering during the implementation of this new competence.; Les connaissances sur la vie des ouvrages hydrauliques, de leur conception à leur démantèlement ou abandon - en passant par leur réalisation, leurs modes de rupture et dégradation, les méthodologies de reconnaissance et de diagnostic, la réglementation associée, etc. - sont nombreuses mais dispersées. Une partie de ces connaissances n'est pas explicite mais tacite. Elles présentent en outre des formats différents tels que, entre autres, textes, formules, photographies ou vidéos. De nouvelles connaissances sont créées au fil du temps. Il est donc intéressant de proposer des outils aptes à rassembler, capitaliser, expliciter et diffuser les connaissances actuelles et futures. Dans cet article sont présentées deux expériences visant à diffuser la connaissance sur les digues. Il s'agit d'une part, de l'outil WikiBarDig (http://wikibardig.developpement-durable.gouv.fr/index.php/Portail:Wikibardig), développé par Irstea et hébergé sur le site du Ministère de la Transition Écologique et Solidaire. Cette base de connaissance a pour objectif de capitaliser et diffuser les savoirs sur les ouvrages hydrauliques (barrages et digues). Il s'adresse à des publics pouvant être variés : étudiants, enseignants, ingénieurs débutants ou confirmés sur le domaine pouvant appartenir à différents organismes tels que services de contrôle de l'État, bureaux d'études, collectivités territoriales, gestionnaires et propriétaires d'ouvrages, établissements de recherche et d'enseignement. D'autre part, il s'agit des journées techniques organisées par l'association France Digues. Ces journées fournissent des lieux d'échanges, de débats et de rencontres des professionnels de la gestion des digues. Ces 2 outils complémentaires trouvent actuellement une résonance particulière avec l'instauration de la compétence GEMAPI (Gestion des Milieux Aquatiques et Prévention des Inondations) depuis le 1er janvier 2018, notamment pour le volet concernant la défense contre les inondations et contre la mer. Ils peuvent en effet constituer une aide auprès des collectivités ou des bureaux d'études en appui pour la mise en oeuvre de cette nouvelle compétence.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE [ADD1_IRSTEA]Hydrosystèmes et risques naturels; International audience; The hazard studies is the central statutory document presenting and justifying the performance levels of levee systems. It contributes to the legal security of the levee manager, then responsibility will be committed not for the damage which the levee systems did not allow to warn since it was designed, exploited and maintained according to the good engineering practice and to the legal and regulatory obligations. At the request of the French Ministry of Ecological and Solidarity Transition (MTES), Cerema oversaw the production of a technical document that aims to give explanation on how to carry out hazard studies of levee systems. This document is intended for the levee managers, which in many cases are new entities created by the new GEMAPI competence. In addition to this first document, a complementary handbook aims to help elaborate technical specifications for carrying out hazard studies. After outlining the objectives of the technical document and explaining briefly the regulatory context governing the risks studies of levee systems, the article develops the following topics: • what is levee system hazard study and what is it for?; L'étude de dangers est le document réglementaire central présentant et justifiant les niveaux de performance d'un système d'endiguement. Elle contribue