Modélisation pluie-débit à l’échelle annuelle en Algérie du nord

La modélisation du comportement hydrologique des bassins versants est incontournable dès lors que l'on s'intéresse à des problématiques relatives à l’évaluation et la gestion optimale des ressources en eau. Ceci s’illustre par un aspect quantitatif, dans les pays comme l’Algérie où l’alimentation en eau est un facteur limitant. L’objectif principal de cet article est d’expliciter les relations entre les conditions hydrologiques et la disponibilité en eau de surface. A cet effet, un modèle pluie-débit à l’échelle annuelle qui prend en compte les paramètres physiques et climatiques a été mis au point. L’application porte sur l’Algérie du Nord dont la superficie est de 325 000 km2.La mise au point de ce modèle nécessite au préalable une base de données qui a été acquise lors des travaux antérieurs incluant la carte des pluies médianes, la carte des perméabilités et le modèle numérique de terrain. Afin de compléter cette base de données, la cartographie des pluies des différentes années pour lesquelles on dispose des débits a été réalisée en utilisant une méthodologie intitulée "cartographie de la pluie centrée réduite". Ainsi, les données de 467 postes pluviométriques ont été traitées et ont permis de tracer les cartes des isohyètes annuelles.L’étude de la relation pluie-débit à l’échelle annuelle est basée sur les données de débits de 50 stations hydrométriques réparties à travers la zone d’étude. La démarche utilisée s’est inspirée de la fonction de production du S.C.S (Soil Conservation Service). Les résultats du modèle après calage ont permis d’obtenir un coefficient d’explication de 0,75, ce qui signifie que 75 % de la variance est expliquée par la pluie moyenne, la surface et un coefficient (a) qui correspond à la pente moyenne des bassins versants.Modelling the hydrological behaviour of drainage basins is very important for solving problems related to the evaluation and optimal management of water resources. This is illustrated quantitatively in countries such as Algeria where water supply is a limiting factor. The principal aim of this paper was to explain the relationship between hydrological conditions and the availability of surface water. A model of rainfall-discharge was developed on a yearly scale, taking into account physical and climatic parameters. The application was carried out in northern Algeria where the total land surface is about 325 000 km2.The development of this model required a database, which was acquired during previous studies where maps of median rainfall and permeability as well as the digital elevation model were developed. In order to complete this database, the cartography of rainfall for the years for which we have discharge data was carried out using a methodology entitled "mapping standardized rainfall". To estimate and map annual rainfall, the kriging method was used. Two problems were encountered:- The presence of a drift highly altered the variogram and made it very difficult to infer a sub- structure function;- The variogram is significant only if the hypothesis of ergodicity is valid, which was not easy to assume for any given year.In order to resolve these difficulties, a homogeneous random and secondary stationary order function (same mean at all points and same covariance function) must be calculated. A previous study by ANRH (1993) allowed us to know the statistical parameters of the distribution at each point. These parameters were mapped, taking into consideration the topographical relief and distance to the sea. For every year and at each rainfall measure point, the standardized rainfall could be deduced. The correlogram gave information about the spatial variability of the phenomenon and its range, and subsequently the standardized rainfall was then interpolated. Annual rainfall was calculated by combining the grids of the means, the variances and the centered reduced rainfall (TOUAZI and LABORDE, 2000). Thus, the data of 467 rainfall gauges were used in order to create maps of the yearly isohyets.The rainfall-discharge relationship on an annual scale was based on 50 hydrometric stations distributed throughout the study area. The methodology used was derived from the production function of the S.C.S (Soil Conservation Service). This production function was part of modelling, which transformed total rainfall to net rainfall. This method was very representative of the natural hydrological processes. Indeed, it takes into account rainfall and the maximum infiltration capacity (S), which depends on the nature of the soil (lithology), vegetation and soil moisture content. In the current study, the basin surface and a regional parameter (a) were introduced in order to calibrate the model. This production function was implemented by supplying different values for the parameter (S). The values (n+1) were obtained by increasing the previous value (n) by 10 %. We evaluated the different values of (S) in the same way to obtain the last value (i). We calculated for these different values of the parameter (S) the square of the difference between the measured and estimated discharges for each year by measuring the discharge at different stations. For each station, we calculated the sum of these values for all the years and we retained the value of (S) that gave the minimal value. The results demonstrated that the values of (S) obtained were not significant because they tend to the infinite. For this reason, (S) was considered as a constant. In order to improve the model, we repeated the same operation, but instead of (S), we used the parameter (a) and performed the same calculation. After calibration of the model the results gave a coefficient of determination of 0.75, which means that 75 % of the variance was explained by the mean rainfall, the surface and the parameter (a).To explain the parameter (a), we calculated the correlation between its value at each station with the corresponding geology. This latter variable was characterized by the average storage capacity, which corresponds to the weighted average of the surfaces of the basin assigned to each permeability category (TOUAZI, 2001). The results demonstrated a coefficient of determination of 0.1. The correlation with the topographical relief was not necessary because it was taken into account in the cartography of the rainfall. We then proceeded to the cartography of the parameter (a). The results demonstrated an east-west gradient that was constant and a north-south gradient that decreased from north to south. With the digital elevation model, we used a geographical information system to deduce the slopes. For each basin, the average slope was calculated by taking the average of the values of the slopes of all the pixels that constituted the individual basin. The correlation between slopes and corresponding values of the parameter (a) gave a coefficient of correlation of 0.6.The results obtained by this model after calibration gave a coefficient of determination of 0.75, which means that 75% of the variance was explained by the mean rainfall, the surface and a coefficient (a), which corresponds to the average slope of the drainage basins

Une méthode stochastique pour la prédétermination des fluctuations probables des durées de service des réservoirs collinaires en Tunisie

Un modèle de génération stochastique de pluies est couplé ˆ un modèle de calcul de l'index de leurs érosivités, dérivé de l'Equation Universelle de l'Erosion des Sols (USLE). Le premier fonctionne au pas de temps de 30mn, il est calé sur une série pluviographique de 15 ans de la Tunisie centrale. Le second modèle fonctionne par calcul automatique des cumuls et moyennes de l'érosivité des pluies générées.En mode opérationnel, ces deux modèles sont exploités pour simuler les aléas de l'envasement annuel des réservoirs collinaires de la zone aride et semi-aride de la Tunisie : le bassin versant est considéré comme une "boite noire" où l'agressivité climatique est la principale variable (quelques pluies extrêmes font l'essentiel de l'érosion), les autres facteurs sont considérés constants durant la durée de service du réservoir. Nous observons sur trois bassins versants répartis du nord au sud de la frange comprise entre 500mm et 250mm (de pluie moyenne annuelle), que la distribution annuelle des index d'érosivité des pluies peut être assimilée ˆ la distribution des transports solides.Sur l'un de ces bassins versants (OUED EL HISSIANE : 15,9 ) nous observons également que les valeurs extrêmes de l'érosion sont proportionnelles aux valeurs extrêmes de l'index d'érosivité des pluies. Seulement l'automne et le printemps sont des saisons érosives.Dans le cas de petits bassins versants non-jaugés, comme ceux pour l'aménagement de réservoirs collinaires, le générateur nous permet de constituer des chroniques d'érosivité de pluie. Si on considère que les autres paramètres sont constants, ce modèle nous aide à déterminer les intervalles de confiance de durées de service probables.Une analyse de sensibilité par la modification des paramètres du générateur (nombre d'épisodes, hauteur de pluie, maximum et durée d'averse etc ...) valide la méthodologie. De même une analyse régionale montre les faibles fluctuations des résultats sur l'étendue aride et semi-aride de la Tunisie.Ces deux résultats nous ont conduit à proposer un abaque régional de prédétermination des fluctuations probables des durées de service des réservoirs collinaires, compte tenu de la connaissance préalable de la durée de service moyenne probable.Cette méthode directement opérationnelle peut être utilisée pour l'aménagement, la planification, et la gestion des réservoirs collinaires. Elle améliore les études de faisabilité, notamment lorsqu'on la couple aux calculs économiques.A stochastic rainfall generator and a model for calculating the erosivity index of the Universal Soil Loss Equation (USLE) are coupled. The first one operates on a 30 min time step and it is calibrated on a 15 year historical pluviographic database for central Tunisia. The second model works like an automatic calculator, where the rain erosivity index can be averaged or summed. These two models are applied to simulate the annual siltation of hill reservoirs in arid and semi-arid areas of Tunisia. The catchment is considered as a "black-box" where mostly climatic aggressivity is varying (some extreme rainfall events cause most of the erosion) and the other erosion parameters are considered to remain constant over the lifetime of the reservoir. We know that the WISCHMEIER rain erosion index has no upper limit. When all the other factors are maintained constant, erosion is proportional to it. This climatic index is calculated for each rain event, but we can also calculate the annual average or sum it over many years. Soil losses (or solid transport) during a period are proportional to the value of this index summed over the same period.We demonstrate on three representative catchments lying from north to south (from 500 mm to 250 mm annual average rainfall) that the annual rain erosion index distribution can be considered comparable to the solid transport distribution (Galton distributions with equal statistical parameters).For the OUED EL HISSIANE catchment (15.9 km2), the annual extreme value of erosion is proportional to the annual extreme value of the rain erosion index. Only spring and autumn storms need be considered to calculate the annual sediment loss.On gauged small catchments like those of hill reservoirs, the rainfall generator can provide an erosivity rainfall record. Considering that the other erosion parameters are constant, this model allows one to calculate the confidence intervals of a reservoir's predicted durations. We equate the annual erosivity index distribution to the annual solid supplies distribution, and we generate and sum over several consecutive years many series of "solid supplies" to simulate the progressive silting up of the reservoirs (represented by the chosen period : sum over T=5 years, 10 years, 15 years ...). In the context of setting up hill reservoirs, this study concerns the potential duration and possible services of hydraulic structures (including the risk of rapid silting up of the reservoirs). This generator can be computed over many years and avoids the limitation due to the short observed time series.The methodological benefit of such an approach is therefore to avoid the difficulty of limited observed samples. It enlarges the data analysis of the series dispersal and residuals. This approach, based on observations and a statistical method, supports experimental analysis. It gives a clear idea of the rate of siltation, according to climatic hazards. A sensitivity analysis, where we modify the rainfall generator parameters (number of episodes and quantity of rain, peak and duration of storm...), is used to validate the methodology. A regional analysis shows a very low fluctuation considering the whole arid and semi-arid area of Tunisia. These two results led us to set up a regional abacus. This abacus reports the forecasts of the fluctuations of the time length service for hilly and small dams, including the probable average of their service duration. It allow a predetermination of the small dams' life time together with a confidence interval, and it can be used for small dam construction, planning and management. It improves the first feasibility study and can be included in economic calculations

Kinetic effects in stimulated Brillouin scattering

The role of ion and electron kinetic effects in the nonlinear evolution of stimulated Brillouin scattering (SBS) is investigated by means of particle-in-cell numerical simulations. The simulations were carried out in one and two spatial dimensions (1D and 2D), with a full PIC code, in which both ions and electrons are kinetic. The full PIC simulations are compared with those obtained from a hybrid PIC code (kinetic ions and Boltzmann electrons), making it possible to determine in which limit the electron kinetic effects are important. The simulation geometry corresponds to a coherent laser beam interacting with an expanding plasma slab. In the 1D simulations, the interaction becomes incoherent, as time goes on, in a domain that spatially begins in the plasma region close to the laser light entrance, and that ends within the plasma at a frontier which moves faster than the ion acoustic wave (IAW) velocity. The higher the laser intensity, the faster moves the frontier of this spatial domain. The SBS reflectivity drops at the very moment when this domain fills entirely the plasma. Two regimes have to be distinguished. In the regimes of low laser intensity, strong sub-harmonic generation of the excited IAW is observed to take place in this moving spatial domain, so that the SBS reflectivity drop is interpreted as being due to sub-harmonic generation. In the opposite regime of high laser intensity, there is no evidence of strong sub-harmonic generation, whereas a strong ion heating is observed, so that the reflectivity drop is interpreted as being due to enhanced ion damping. In the 1D simulations the electron kinetic effects are found to be able to smooth temporally the SBS reflectivity, although the overall picture remains the same when the electrons are taken as a Boltzmann fluid. In the 2D simulations, the SBS reflectivity is observed to drop rapidly in time because of the efficient nonlinear Landau damping on the ions, as previously reported by Cohen et al. [1]. In these 2D simulations, the electron kinetic effects are found to play a negligible role as compared with the ion kinetic effects

MODELISATION GEOSTATISTIQUE DE LA SALINITE DES EAUX SOUTERRAINES : CAS DE LA NAPPE DES SABLES DE BISKRA GEOSTATISTICAL MODELING OF GROUNDWATER SALINITY CASE STUDY: SAND BISKRA AQUIFER

La modélisation hydrogéologique (reconstruction des champs des écoulements et des champs de concentration) doit être effectuée à partir des données et informations de base recueillies sur le terrain. La densité limitée des réseaux de mesure, les lacunes fréquentes dans les séries statistiques font que l'estimation des différents paramètres hydrauliques par les modèles mathématiques est entachée d'erreurs. Le développement de la géostatistique dans les sciences de l'eau a permis de régionaliser des variables aussi bien spatiales que temporelles. Ces techniques permettent à l'hydrogéologue de disposer d'outils supplémentaires dans l'identification et la caractérisation des aquifères. Il est évident que l'identification et la détermination du mode de fonctionnement des systèmes aquifères conduit à comprendre les mécanismes de transfert de soluté et le degré de contamination des nappes. D’après les cartes piézométriques et de concentration en sel, il y’a une bonne concordance soit dans le sens d’écoulement et de déplacement de soluté, soit dans le gradient de la charge et de concentration. Cette nappe présente souvent des zones dont les concentrations en sels se situent à la limite des normes. Il existe des poches d’eau salée constituant des foyers de contamination en cas de modification des équilibres hydrodynamiques. The hydrogeologic modeling (rebuilding the fields of the flows and the fields of concentration) must be made from the data and the basic information collected. The limited networks of measurement, the frequent gaps in the statistical series have a negative effect to the prediction of different hydraulic parameters using such mathematical models. The development of geostatistic in sciences of the water allowed regionalizing spatial and temporal variables. These techniques allow the hydrogeologist to have supplementary tools in the identification and the characterization of aquifers. It is obvious that the identification and the determination of the operating process of the aquiferous systems lead to understand the transfer mechanisms of aqueous solution and the degree of aquifer contamination. According to the piezometric charts and salt concentration, there is a good agreement either in the direction of flow and displacement of aqueous solution, or in the gradient of the hydraulic head and concentration. This aquifer often presents zones whose salt concentrations are situated in norm limit. We notice there is existence of salt water pockets constituting of the hearts of contamination in case of modification of hydrodynamic balances

Anomalous asymmetry of magnetoresistance in NbSe3_3 single crystals

A pronounced asymmetry of magnetoresistance with respect to the magnetic field direction is observed for NbSe$_3$ crystals placed in a magnetic field perpendicular to their conducting planes. It is shown that the effect persists in a wide temperature range and manifests itself starting from a certain magnetic induction value $B_0$, which at $T=4.2$ K corresponds to the transition to the quantum limit, i.to the state where the Landay level splitting exceeds the temperature.Comment: 4 pages, 6 figures, to be appeared in JETP Let

Developement of real time diagnostics and feedback algorithms for JET in view of the next step

Real time control of many plasma parameters will be an essential aspect in the development of reliable high performance operation of Next Step Tokamaks. The main prerequisites for any feedback scheme are the precise real-time determination of the quantities to be controlled, requiring top quality and highly reliable diagnostics, and the availability of robust control algorithms. A new set of real time diagnostics was recently implemented on JET to prove the feasibility of determining, with high accuracy and time resolution, the most important plasma quantities. With regard to feedback algorithms, new model–based controllers were developed to allow a more robust control of several plasma parameters. Both diagnostics and algorithms were successfully used in several experiments, ranging from H-mode plasmas to configuration with ITBs. Since elaboration of computationally heavy measurements is often required, significant attention was devoted to non-algorithmic methods like Digital or Cellular Neural/Nonlinear Networks. The real time hardware and software adopted architectures are also described with particular attention to their relevance to ITER.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Integrating DGSs and GATPs in an Adaptative and Collaborative Blended-Learning Web-Environment

The area of geometry with its very strong and appealing visual contents and its also strong and appealing connection between the visual content and its formal specification, is an area where computational tools can enhance, in a significant way, the learning environments. The dynamic geometry software systems (DGSs) can be used to explore the visual contents of geometry. This already mature tools allows an easy construction of geometric figures build from free objects and elementary constructions. The geometric automated theorem provers (GATPs) allows formal deductive reasoning about geometric constructions, extending the reasoning via concrete instances in a given model to formal deductive reasoning in a geometric theory. An adaptative and collaborative blended-learning environment where the DGS and GATP features could be fully explored would be, in our opinion a very rich and challenging learning environment for teachers and students. In this text we will describe the Web Geometry Laboratory a Web environment incorporating a DGS and a repository of geometric problems, that can be used in a synchronous and asynchronous fashion and with some adaptative and collaborative features. As future work we want to enhance the adaptative and collaborative aspects of the environment and also to incorporate a GATP, constructing a dynamic and individualised learning environment for geometry.Comment: In Proceedings THedu'11, arXiv:1202.453

Multiplex polymerase chain reaction for simultaneous quantitation of human nuclear, mitochondrial, and male Y-chromosome DNA: Application in human identification

Human forensic casework requires sensitive quantitation of human nuclear (nDNA), mitochondrial (mtDNA), and male Y-chromosome DNA from complex biomaterials. Although many such systems are commercially available, no system is capable of simultaneously quantifying all three targets in a single reaction. Most available methods either are not multiplex compatible or lack human specificity. Here, we report the development of a comprehensive set of human-specific, target-specific multiplex polymerase chain reaction (PCR) assays for DNA quantitation. Using TaqMan-MGB probes, our duplex qPCR for nDNA/mtDNA had a linear quantitation range of 100 ng to 1 pg, and our triplex qPCR assay for nDNA/mtDNA/male Y DNA had a linear range of 100-0.1 ng. Human specificity was demonstrated by the accurate detection of 0.05 and 5% human DNA from a complex source of starting templates. Target specificity was confirmed by the lack of cross-amplification among targets. A high-throughput alternative for human gender determination was also developed by multiplexing the male Y primer/probe set with an X-chromosome-based system. Background cross-amplification with DNA templates derived from 14 other species was negligible aside from the male Y assay which produced spurious amplifications from other nonhuman primate templates. Mainstream application of these assays will undoubtedly benefit forensic genomics. © 2004 Elsevier Inc. All rights reserved

U-series and radiocarbon cross dating of speleothems from Nerja Cave (Spain): Evidence of open system behavior. Implication for the Spanish rock art chronology

Two stalagmites from Nerja cave (Andalusia, Spain) were studied. The cave is well known because of its long human occupation from the Upper Palaeolithic to the Chalcolithic and its abundant parietal prehistoric Art. The aims of this study were twofold: i) to compare uranium/thorium (Th/U) and Carbon-14 (C) ages obtained all along the growth axis of the stalagmites in order to understand the consequences of diagenetic processes on the validity of radiometric ages; ii) as one of the stalagmites contains black layers, attributed to combustion soot, to establish when these intense hearths were used and by which culture. Th/U and C ages were coupled with mineralogical studies using FTIR (Fourier-transform infrared spectroscopy) and thin section observations. The first stalagmite (GN16-9b) displays Th/U ages in stratigraphic order, and compatible with C ages corrected for a few percent of dead carbon. Homogeneous composition of aragonitic crystals characterized by their needle-like texture is observed throughout this speleothem. For the second stalagmite (GN16-7), in contrast, Th/U ages display large significant inversions and discordant results on the upper part and at the base of the stalagmite, suggesting a possible open system behavior for this chronometer. Interestingly, C ages are in stratigraphic order all along the stalagmite and are compatible with Th/U ages only in its central part. Mineralogical studies display evidence of aragonite to calcite transformation at the top and a complex mineralogical assemblage with interlayered silicates (possibly clays) and calcitic mineralogy for the base of GN16-7. In these parts, discordant Th/U ages were measured. In the middle part of the stalagmite, however, where the fibrous aragonite is well preserved, the C and Th/U ages agree. Our data suggest that in the case of aragonite to calcite transformation as shown here, Th/U ages are biased, but C ages seem to remain accurate, as already observed in aragonitic marine bio minerals. C ages obtained are used for the chronology of the soot layer, determined here between 7900 and 5500 years Cal BP, coherent with previous analysis of charcoals in the same sector of the cave. This study highlights the importance of working with at least two chronometers when stratigraphic age verification is not possible, as is the case of some parietal CaCO thin layers used for rock art dating. Recent Th/U ages published for carbonate deposits on Spanish parietal Art are discussed in light of this demonstration.This research was funded by ANR (grant number ANR-18-CE27- 0004, ApART project) and supported by the Paris Ile-de-France Region – DIM “matérieux Anciens et Patrimoniaux” for FTIR analysis. The authors thank LMC14 staff (Laboratoire de Mesure du Carbone-14), ARTEMIS national facility, for the results obtained with the Accelerator Mass Spectroscopy method, and the PANOPLY analytical platform. This research is part of the “Proyecto General de Investigación aplicada a la conservación de Cueva de Nerja” authorised by the Junta de Andalucía and financed by the Fundación de Servicios Cueva de Nerja. The authors also wish to thank the “Instituto de Investigación Cueva de Nerja” for supporting this research. M.A.Medina-Alcaide has a Postdoctoral Fyssen Grant; the results presented in this paper are included in the PID2019-107262GB-I00 and PDC2021-121501-I00 grants funded by MCIN/AEI/10.13039/501100011033