Search Results

The Kabyle ridge of Djurdjura (Algeria, DURAND-DELGA, 1969) is bordered by the basement to the north, which overthrusts it, and flyschs to the south which it overthrusts. Its structure corresponds to highly piled dipping thrust sheets. N140 transversal faults laterally cut them. The different structural units, mainly calcareous, which form the inner, central and southern ridge (FLANDRIN, 1952; FLANDRIN et al., 1952; COUTELLE, 1979; GELARD, 1979 and NAAK, 1988), isolated by low permeability layers, constitute independent drainage units (ABDESSELAM, 1995). The massive and thick lower Liassic and Eocene limestones are highly karstified and constitute the main aquifers (ABDESSELAM et al., 1990).FALLOT (1942) summarises the stratigraphy of the Djurdjura Triassic layers: conglomerates and red sandstones (Permo-Triassic), pale sandstones (Werfenian), dolomites and vermiculate limestones (Muschelkalk), variegated marls and cellular dolomites (Keuper), limestones (Rhetian).The lithostratigraphy of the Triassic of the Kabyle ridge is very differentiated from one unit to another (FLANDRIN, 1952; GELARD, 1979). This fact reflects an early sedimentary segmentation of the tethysian passive margin from the north to the south. The Kabylian Triassic (inner zones) contains gypsum and salty formations only very rarely. Thus, in the Djurdjura, evaporites are very rarely mentioned at the surface (LAMBERT, 1947; FLANDRIN,1952; COUTELLE, 1979; GELARD, 1979; NAAK, 1988; TEFIANI et al., 1991; DURAND-DELGA and TEFIANI, 1994), when the early authors (FALLOT, 1942; GIGNOUX, 1946) suspected the presence of a tectonised salty Triassic in the Djurdjura.Overall, the evaporitic outcrops are insignificant, compared to the Triassic ones of the Djurdjura. The Triassic layers however frequently bear vacuolar dolomites and cellular dolomites associated with variegated clays that can have been accompanied with gypsum and salt, which can have migrated with or without tectonic compressions.Water analysis is used to answer the question of the importance of gypsum and salty formations in the Kabylian Triassic.In an area where gypsum and salty layers rarely outcrop, chemical analyses of spring waters are used to demonstrate their importance in the Triassic of the Kabylian Dorsale of the Djurdjura. A hydrochemical study was carried out on the main perennial springs of the whole Djurdjura : chemical type, Sr content, Sr2+ /Ca2+ molar ratio.Strontium is a tracer bound to evaporites. High Sr2+ content in waters can only be explained by Celestite dissolution (SrSO4), a mineral that is associated with gypsum; Sr is thus a good tracer of the existence of evaporites. The Sr2+/Ca2+ ionic ratio (molar concentrations) is characteristic of an evaporitic origin if it equals or exceeds 1‰ (BAKALOWICZ 1988). It is higher than 5 ‰ in the Alpine Triassic layers (MEYBECK, 1984).A hydrochemical study enabled us to determine the water types: calcium bicarbonate for the most, with a second sulfate trend; Tinzert spring has a sodium chloride type (Fig. 2). It is situated at the lowest point to the west of the western Djurdjura, where the ridge is the widest (5 km). Its discharge ranges from 60 l·s-1 to 2 m3·s-1. Its water tastes very salty in the low water periods and the concentrations of evaporitic tracers are high: chlorides (> 1000 mg·l-1), sodium (> 500 mg·l-1), sulfates (> 200 mg·l-1) and potassium (> 25 mg·l-1).During flood periods, because of dilution and quick conduit flows in the upper calcareous zones, the water type becomes calcium bicarbonate. During this period, waters flowing out of the spring are traced by the limestone shallow waters (transit of epikarstic waters). On top and upstream from Tinzert, less than 20 metres to the South, Tala Agouni Lansar displays a very different chemical type, calcium bicarbonate. This fact demonstrates that Tinzert sodium chloride content is acquired by water which stays in the deep saturated zone (Figs. 3 et 4), and that longitudinal faults divide the lithological units into segments.Analyses of strontium in waters demonstrate that most of the springs (ABDESSELAM, 1995) have low Sr2+ contents (0.06-0.23 mg·l-1). Tinzert spring has a much higher content (0.35-1.83 mg·l-1 ; Table 1). The use of the Sr2+ /Ca2+ ratio (‰) enabled us to distinguish among aquifers completely developed in limestones, others related to Triassic sandstones and one related to salty layers. The map of Sr2+ /Ca2+ ratios indicates that the springs related to Triassic outcrops have the higher values (Fig. 3).According to the Sr2+ /Ca2+ ratio (‰), three groups can be distinguished:- springs related to limestones, with no relationship with Triassic formations, have a low Sr2+/Ca2+ ratio (< 1‰: Adarchi, Aghvaïlou-1 et 2, Tiksra, Thebout and Mendes; Table 1),outlets directly limited by red sandstones Triassic formations (Taliouine et Tabourt Lansar), have a Sr2+/Ca2+ ratio ranging between 1 and 1.5 ‰;Tinzert spring, with a Sr2+/Ca2++ ratio that ranges between 3 and 8.77 ‰. This Sr2+/Ca2+ ratio (> 5‰) classifies this water into the category of waters originating from the alpine Triassic evaporites (MEYBECK, 1984). This high ratio is coupled with the high sulfate, and especially the chloride and sodium content of these waters. This spring is situated on the trace of a north-east thrust sheet sole that probably includes Triassic in its lower part, which concerns the whole Haïzer massif of about 8 km. The water transit is probably either in the upper thrust sheet, or in the lower one, following the East-West axis lowering of the structure.The springs of the Djurdjura display well-differentiated hydrochemical responses. Several springs that only drain limestone have a standard calcium bicarbonate chemical type (Sr2+/Ca2+ < 1 ‰). Other springs (Sr2+/Ca2+ =1 - 1.5 ‰) are characteristic of waters that have flowed in the sandstone and dolomitic Triassic layers, which are observed on the outcrops. Tinzert spring at least, which drains the middle part of the limestone range (Fig. 4, Sr2+/Ca2+=3 - 8.77 ‰), is characterised by waters which have transited through the evaporitic Triassic. The waters of Tinzert spring have also high chloride, sodium and sulfate contents.In the Djurdjura, where evaporitic Triassic formations do not generally outcrop, except in very small lenses, an argument can be made for the existence of deep evaporitic Triassic deposits on the basis of the hydrochemical response of perennial springs.

Keywords: Djurdjura, Maghrebides, Evaporites, Trias, Hydrochimie, Source, Strontium, Djurdjura, Maghrebides, evaporites, Triassic system, hydrochemistry, spring, strontium

AbstractUnderstanding and predicting water temperatures is essential in order to help prevent or forecast high temperature problems. To attain this objective, we define in this work a model that predicts temperature variations in a small stream according to climatic variables, such as air temperature, water flow and quantity of rainfall in the river catchment. Static neural networks were used as a technique for evaluation of the relations among the various variables, with a mean error of 0.7°C.In addition, we developed a forecasting model able to estimate the short-term and mid-term variations of water temperature, i.e., to forecast the temperature of days (j+i , i=1,2…) from climatic parameters of day j. Two methods were used: the first one is iterative and uses the estimated value of day j to estimate the value of the water temperature for day j+1. The second method is much simpler, involving an estimate of the temperature of all days at once. The Levenberg-Marquardt algorithm implemented in the Matlab neural network toolbox allowed a marked improvement in the performance of the model. Very satisfactory results were then obtained by testing the validity by cross validation technique with a mean error of 1.5°C for long term prediction of 7 days.

Keywords: cours d'eau, réseaux de neurones, prédiction et prévision, température d'eau, validation croisée, stream, neural network, forecasting and prediction, water temperature, cross validation

AbstractThe Adra delta is located on the eastern limit of Almeria in South-East Spain. Entirely devoted to agriculture for many years, greenhouse crops now cover the entire delta. The intensive use of fertilizers and the recycling of irrigation water have resulted in an alarming increase in nitrate concentrations in the groundwater of the eastern part of the delta. Two wetlands located in this sector are protected as natural reserves and are included in the Ramsar Convention. These wetlands are discharge zones for the aquifer and have shown high nitrate concentrations for some years. The objective of this work was to study the effect of irrigation water recycling on nitrate contamination of groundwater and to highlight the effect of this contamination on the wetlands. A model simulating nitrogen transfer in the unsaturated soil was used to simulate nitrate concentrations in groundwater recharge. Considering the dilution of nitrate into the aquifer and the presence of denitrification processes in the eastern sector, measured nitrate concentrations in the aquifer were adequately reproduced, thus confirming the contribution of groundwater recycling through irrigation in aquifer contamination. Simulation of a hypothetical stop of irrigation water recycling showed that a period of ten years would be necessary for nitrate concentrations to reach levels measured before the start of greenhouse agriculture. Wetland efficiency in attenuating groundwater nitrate contamination has been stable at 92 to 94% from 1991 to 1997. Nitrate concentrations are nevertheless very high in the wetlands, threatening them with eutrophication.

Keywords: delta du rio Adra (Almérie, Espagne), eaux souterraines, nitrates, contamination, agriculture sous serre, lagunes, eutrophisation, Adra delta (Almeria, Spain), groundwater, nitrates, contamination, greenhouse agriculture, wetlands, eutrophication

AbstractThis article calls for increased cooperation and dialogue between born “Westerners” and born “Muslims” in the near future. It suggests human originality and individual creativity be valued when those cultures are encountering each other. A major challenge of our time is that of communication, including in religious matters. It is a test of human dignity with a far from certain outcome. Basically, Islam is a human faith, a way of life, and a kind of social order. For too long — notwithstanding the practice of Orientalist studies — the West has viewed Islam in the perspective of Western material, cultural and spiritual interests. In a period of Western hegemony it could hardly have been otherwise. Islam tended to be constructed as a radical alternative to the Western world. This dualist construction of the West and Islam, however, is not only untenable in scholarly terms but also implies political provincialism. Suggestions are made to create new kinds of relationships between Westerners and Muslims.

As Virginia Woolf said, our world is in the midst of childbirth. Multifaceted change is underway in cultural institutions, libraries, museums and, generally, in all places where knowledge is created. Change is transforming our work habits, practices and relationships with our users. How do we evaluate and highlight our place in the knowledge society? How do we reconcile change with the important notions of truth, cultural and social solidarity as well as sharing, that forceful catalyst of human dignity?Harnessing the mass of data to make them reliable and truthful and taking ownership of new technologies in order to build a free and open tender are part of the challenge to be met by those whose primary mission is to build a knowledge base, that is accessible, sincere, and altruistic for all.The change we are currently experiencing is the result of four major events in human history: the transformation of the financial, economic and commercial map of the world; the unfolding of a digital era that has forever changed the relationship of human beings to knowledge; the demographic expansions in Asia and Africa that will soon disrupt the distribution of the world's population; and, finally, the colossal environmental issues that our society must immediately face.Beginning with the first developments in Québec society and followed by an internationally renowned artificial intelligence laboratory, history is created with the information used by the human mind to which it imparts a vital energy. Change must be undertaken by sharing information in all its forms and with all, which means putting an end to the scandal that is illiteracy in our learned and connected societies. This also requires accelerating the transition to a digital civilisation, by establishing a digital legal deposit, the scanning of heritage collections and the creation of avant-garde libraries that provide a space for the innovative and creative laboratories such as the future Saint-Sulpice library.We also have to think about the future of creation. In an era of robotics, algorithms, artificial intelligence, and big data, what does the future hold for the safeguard, the production and the sharing of knowledge?

Political risks' market faced many changes during the last years. This is particularly true in the case of coverage on African risks. Paradoxically, only few countries from Africa are off cover. This situation is sometimes due to political, historical or economic reasons: some countries being hydrocarbons' exporters or under adjustment programs. But, more generally, banking and export-credits to Africa are decreasing. Insurers' behaviour is moving in the way of "disengagement". However, the management of political risks cannot be considered as unique. It depends on different factors like insurer's portfolio. This is why all attempt of harmonization will be difficult all the more as political risks is under de-politicization and criteria of underwriting are changing from risk-country to risk-project. But cooperation between export-credit insurers and between banks and insurers are highly desirable given decreasing capacities on insurance/reinsurance markets, marginalization of Africa in international trade and increasing difficulties of Africa in terms of access to private financing. In this context, it is worth to apply new approaches in terms of insurance even if the result will be new roles for banks, insurers and international organizations. This evolution will obviously not occur without African counterparts.