Ressources hydriques en Algérie du Nord

En Algérie, l'eau revêt un caractère stratégique du fait de sa rareté et d'un cycle naturellement perturbé et déséquilibré. Qu'il s'agisse de l'eau souterraine ou de l'eau de surface, les ressources sont limitées et, compte tenu des problèmes démographiques et de l'occupation de l'espace (sachant que près de 60% de la population algérienne sont concentrés dans la frange septentrionale du territoire qui ne représente que le dixième de la surface totale du pays), d'importants efforts sont nécessaires en matière d'urbanisation intégrée et de gestion rigoureuse dans l'exploitation des réserves, si on veut atteindre la satisfaction des besoins à l'horizon 2010. S'y ajoutent des problèmes de faible mobilisation et de mauvais recyclage par manque de maîtrise des stations d'épuration et l'envasement des retenues.Les 11 bassins versants exoréiques de l'Algérie du Nord couvrant une surface de 130 000 km2 présentent des potentialités en eaux de surface de 11.109 m3 dont seulement 2,13.109 sont mobilisés par les 98 barrages en fonctionnement en 1995. Les besoins estimés à l'horizon 2010 évalués à 9,384. 109 m3 se décomposent en 1,524.109 m3 pour l'eau potable (AEP), 0,23.109 m3 pour l'industrie (AEI) et 7,63.109 m3 pour l'agriculture (AEA) (tableau 6). Sachant que les réserves en eaux souterraines sont évaluées à 1,25.109 m3, le renforcement de la mobilisation des eaux de surface par 3,834. 109 m3 et des eaux souterraines par le captage de 0,33.109 m3 supplémentaires constituent la projection faite en 1995 pour l'horizon 2010 par les différentes institutions publiques intervenant dans la mobilisation et la gestion des ressources en eaux. Cet objectif est déjà fortement entamé en 2002 car fixé dans un contexte de cloisonnement des différentes structures (Hydraulique et Agriculture) et de difficile circulation de l'information entre elles. Il surévalue les capacités de réalisations des barrages, les surfaces à mettre en valeur dans le cadre du programme de développement agricole ainsi que les dotation par habitant en matière d'eau potable. Cette situation constitue un facteur aggravant la difficulté d'une appréhension correcte aussi bien des besoins que des différentes projections sur l'avenir. Les données présentées dans cette synthèse montrent qu'il est désormais impératif que l'aménagement du territoire tienne compte des quantités disponibles afin de rationaliser l'utilisation, la protection de la qualité et la récupération par le recyclage.La qualité chimique des eaux de l'Algérie du Nord est appréciée par les teneurs en nitrates et en chlorures des aquifères côtiers. Cependant, le développement économique et social conduit à une dégradation rapide de cette qualité des eaux, ce qui incite lourdement à œuvrer pour un meilleur recyclage et une meilleur protection des ressources. A défaut, la sanction serait la non satisfaction des besoins en eaux potable, d'irrigation et industrielle. Malheureusement, il semble que l'écart entre disponibilité et besoins soit difficile à réduire. Le but de cet article est de tenter une revue des causes du manque d'eau et des facteurs aggravants.In Algeria, water has a strategic place in economic development, because of its scarcity and a perturbed, non-equilibrated natural cycle. Because of the limited water resources, and the need to meet the demands for the desired quantity and quality of water by the year 2010, planners must develop reasonable alternatives that take into account multiple purposes and objectives. In addition to the growing demography, 60% of the population resides in the northern range of Algeria, which represents one tenth of the total area of the country. Furthermore, inadequate water treatment due to a lack of appropriate technology, siltation of existing dams and limited capacities for water storage hamper the decision-making process.The projected data for year 2010 show structural difficulties and organizational inadequacies that are linked to the multiple operating structures in charge of collecting and conveying the information. The other major difficulty is based on the quality of the information (e.g., empirical methods and a lack of data). For example, the evaporation rate is estimated by the traditional method of a Colorado pan in which the data are mostly discontinuous. The reservoir silt load is evaluated by irregular bathymetric measurements and the results are extrapolated over a year, sometimes from one year to the next. The volume of water losses during water transport and distribution is evaluated for only a very small portion of the network and is then generalized to the entire drinking water and irrigation system.The eleven watersheds of northern Algeria encompass an area of about 130,000 km2 and offer a surface water potential of approximately 11×109 cubic meters (m3) in which only 2.13×109 m3 were collected by 98 functional dams in 1995. According to the forecasts made in 1995, the creation of new reservoirs (17 dams are actually under construction, 25 are about to start construction, and 810 sites for small reservoirs are in the study phase) will increase the mobilized volume of water to about 5.89×109 m3. The silt load for 1995 as estimated by the National Dams Agency (ANB) for all the operational reservoirs corresponded to about 0.02×109 m3. Watershed erosion and the rapid degradation of the forest cover will raise this silt load to 0.482×109 m3. This situation is very alarming for the water resources and consequently in December 2001, the exploitation of major dams (Keddara, Fergoug, Oued Fodda, Ghrib, Beni Amrane, Ksob, Foum el Gherza, Foum el Gueiss) was temporary interrupted. Operations at the Ain Dalia and Hamman Grouz reservoirs were also interrupted in October 2002 due to silt load problems.The water losses from the distribution network, which were estimated around 1.193×109 m3 in 1995, will be reduced to about 0.532×109 m3 in the year 2010 by special renovation programs. The volume of water lost by evaporation represented 0.427×109 m3 in 1995 and will double for year 2010 to reach 0.883×109 m3, according to the ANB.In 1995, groundwater was pumped at a volume of about 0.849×109 m3 from an estimated total reserve of 1.256×109 m3. The urgent program of installing an additional 2000 wells will raise the extracted volume to 1.180×109 m3 by the year 2010. In the northern portion of the country, the water needs will evolve in the following manner : · from 0.791×109 to 1.524×109 m3 per year for drinking water ; · from 1.216×109 to 7.630×109 m3 per year for agricultural needs ; · from 0.120×109 to 0.230×109 m3 per year for industry.It seems clear that the forecast made in 1995 is infeasible and unrealistic. This prediction overevaluates the financial and technical capacities to carry out all the planned projects and also overestimates the land surface for the agricultural development program. The state of water resources and their distribution for the year 2002 already indicate depletion. Accordingly, the following incentive plans were proposed : · Urgent programs for providing potable drinking water from treated seawater for coastal big cities (Algers, Oran, Arzew, and Annaba). This alternative has been implemented starting September 2002 for Annaba and Arzew. · Encouraging and developing agricultural crops that consume less water and encouraging use of modern techniques for irrigation (drop irrigation). · Activating the construction of the 800 planned watershed reservoirs. · Implementing a program for treating and recycling waste waters. The groundwater quality analysis in the northern portion of Algeria, based on the nitrate and chloride concentrations, led to the following conclusion : · Increasing nitrate concentrations for groundwater samples (up to 175 mg×L-1 for Chlef, 200mg×L-1 for Sidi Bel Abbes, and values exceeding the permissible level of 45 mg×L-1 for over half of the sampling points throughout the Mitidja). · The dilution effect during flood events does not overcome the contamination of groundwater by the nitrates. · Most of the coastal aquifers are contaminated by seawater intrusion. The chloride concentration values are about 3,650 mg×L-1 for Algiers region (Mazafran) and sometimes exceed 4,000 mg×L-1 in the eastern portion of the country (Bourchaid, Kissir). · Water samples from dams and large reservoirs were not contaminated by nitrates because of the absence of agricultural activities in the watershed.The degraded water quality and its scarcity complicate the problem of water supply that is already critical in the region.In conclusion, the gap between water needs and the available water resource is very difficult to close. The goal of this article is to review some of the effects of water shortage and its components. The present article emphasizes the need to implement a change in the decision-making process for controlling and managing water. Improved management of water supplies must not only take into account the available water but also has to optimize and rationalize its use. An urgent planning program should also be developed for treating and recycling waste water and for protecting the environment

Electrical characteristics of a vertically integrated field-effect transistor using non-intentionally doped Si nanowires

International audienceIn this letter, we report the fabrication and the electrical characterization of Vertical Gate All Around Field-Effect Transistors (GAA-FET) using non intentionally doped Silicon NanoWires (SiNWs) grown by Chemical Vapor Deposition (CVD) using the Vapor-Liquid-Solid (VLS) mechanism as conduction channel. The SiNWs GAA-FET devices exhibited n-channel type semiconductor behavior with a threshold voltage at room temperature around-1.15 V, a high ION/IOFF ratio up to 10 6 with a low IOFF current about 1 pA, a maximum transconductance (gm,max ~ 0.9 µS at VGS =-0.65 V and VDS = 1 V) and a minimum inverse subthreshold slope around 145 mV/decade. In light of these characteristics, these devices can be suitable for high performance, low power consumption components and especially for high density integration in integrated circuits (ICs) interconnections regarding to their 3D architecture

Accurate strain measurements in highly strained Ge microbridges

Ge under high strain is predicted to become a direct bandgap semiconductor. Very large deformations can be introduced using microbridge devices. However, at the microscale, strain values are commonly deduced from Raman spectroscopy using empirical linear models only established up to 1.2% for uniaxial stress. In this work, we calibrate the Raman-strain relation at higher strain using synchrotron based microdiffraction. The Ge microbridges show unprecedented high tensile strain up to 4.9 % corresponding to an unexpected 9.9 cm-1 Raman shift. We demonstrate experimentally and theoretically that the Raman strain relation is not linear and we provide a more accurate expression.Comment: 10 pages, 4 figure

Effect of HCl on the doping and shape control of silicon nanowires

International audienceThe introduction of Hydrogen Chloride during the in-situ doping of Silicon Nanowires (SiNWs) grown using the Vapour Liquid Solid (VLS) mechanism was investigated. Compared with non-chlorinated atmospheres, the use of HCl with dopant gases considerably improves the surface morphology of the SiNWs, leading to extremely smooth surfaces and a greatly reduced tapering. The variations in the wire diameter are massively reduced for boron doping, and can not be measured at 600°C for phosphorous over several tens of micrometers. This remarkable feature is accompanied by a frozen gold migration from the catalyst, with no noticeable levels of gold clusters observed using scanning electron microscopy. A detailed study of the NWs apparent resistivity reveals that the dopant incorporation is effective for both types of doping. A graph linking the apparent resistivity to the dopant to silane dilution ratio is built for both types of doping and discussed in the frame of the previous results

Disproportionate Alterations in the Anterior and Posterior Insular Cortices in Obsessive–Compulsive Disorder

Recent studies have reported that the insular cortex is involved in the pathophysiology of obsessive–compulsive disorder (OCD). However, specific morphometric abnormalities of the insular subregions remain unclear. In this study, we examined insular cortical volume to determine whether the volume of the anterior and posterior insular cortices of unmedicated OCD patients differed according to different symptom dimensions.Using magnetic resonance imaging, we measured the gray matter volumes of the insular cortex and its subregions (anterior and posterior divisions) in 41 patients with OCD (31 drug-naïve and 10 non-medicated) and 53 healthy controls. Volumetric measures of the insular cortex were compared according to different OC symptoms. Enlarged anterior and reduced posterior insular cortices were observed in OCD patients. The insular volumetric alterations were more significant in OCD patients with predominant checking rather than cleaning symptoms when compared with healthy controls.Our results suggest the presence of unbalanced anterior and posterior insular volumetric abnormalities in unmedicated OCD patients and emphasize the distinct role of the insular cortex in different OC symptoms. We propose that the insular morphometric alterations may influence the modulation of interoceptive processing, the insular functional role, in OCD patients with different symptoms

Supportless Platinum Nanotubes Array by Atomic Layer Deposition as PEM Fuel Cell Electrode

International audienc