Impact des rejets urbains et industriels sur la qualité des eaux de la plaine de la Meboudja (Algérie)

Un site aquifère contaminé, situé en bordure de l’oued Meboudja (Annaba, Algérie), a été caractérisé en mettant en place une surveillance de la qualité des eaux de surface et souterraines affectées par les nombreux rejets industriels et urbains sur une période de 11 ans (1999?2009). Les déchets industriels sont déposés directement sur le sol et les effluents sont déversés dans l’oued Meboudja sans aucun traitement préalable. Les eaux souterraines présentent une conductivité électrique élevée (de 1000 à 6000 μS/cm), de fortes teneurs en chlorure et en sodium avec respectivement un maximum de 1400 et 730 mg/L. Partant des résultats de l’analyse en composantes principales effectuée sur 33 puits en juillet 2009, les trois principaux processus responsables de l’évolution chimique observée au niveau de l’aquifère ont été identifiés: (a) l’apport salifère du lac Fetzara et le lessivage des formations métamorphiques carbonatées (responsables de l’augmentation de la minéralisation) ; (b) l’alimentation de la nappe par les eaux de l’oued Meboudja, recevant de nombreux polluants industriels (responsable des fortes teneurs en fer et en manganèse) ; et (c) l’utilisation des produits chimiques dans l’agriculture (responsable de l’augmentation des teneurs en nitrates). Les fortes minéralisations sont enregistrées notamment dans les puits situés à proximité des rejets industriels. En outre, de fortes concentrations métalliques en fer et en manganèse sont observées dans les eaux de l’oued. L’évolution de ces deux éléments dans les eaux de la nappe au cours d’un cycle hydrologique montre que l’augmentation des teneurs est liée notamment à une réalimentation de la nappe par l’oued et à une mauvaise oxygénation de la nappe. L’existence de niveaux argileux peut en effet jouer le rôle d’écran en surface et favoriser les conditions réductrices dans la nappe. La Meboudja agit par conséquent comme une source diffuse de contaminants tout au long de son parcours. Les caractéristiques hydrodynamiques de l’aquifère ont été estimées à l’aide de l’interprétation des données des pompages d’essai effectués dans plus d’une dizaine de puits. Des modèles d’écoulement et de transport de polluants ont été élaborés en utilisant le code MODFLOW-MT3D. L’ampleur de la migration des contaminants a été évaluée pendant une période de 11 ans (1999?2009). L’interaction oued-nappe est considérée comme responsable de la migration des contaminants dans la plaine de la Meboudja.

EDITEUR Z. W. Kundzewicz

EDITEUR ASSOCIÉ C. Leduc     

Non‐linear stochastic inversion of gravity data via quantum‐behaved particle swarm optimisation: application to Eurasia–Arabia collision zone (Zagros,Iran)

Potential field data such as geoid and gravity anomalies are globally available and offer valuable information about the Earth's lithosphere especially in areas where seismic data coverage is sparse. For instance, non‐linear inversion of Bouguer anomalies could be used to estimate the crustal structures including variations of the crustal density and of the depth of the crust–mantle boundary, that is, Moho. However, due to non‐linearity of this inverse problem, classical inversion methods would fail whenever there is no reliable initial model. Swarm intelligence algorithms, such as particle swarm optimisation, are a promising alternative to classical inversion methods because the quality of their solutions does not depend on the initial model; they do not use the derivatives of the objective function, hence allowing the use of L₁ norm; and finally, they are global search methods, meaning, the problem could be non‐convex. In this paper, quantum‐behaved particle swarm, a probabilistic swarm intelligence‐like algorithm, is used to solve the non‐linear gravity inverse problem. The method is first successfully tested on a realistic synthetic crustal model with a linear vertical density gradient and lateral density and depth variations at the base of crust in the presence of white Gaussian noise. Then, it is applied to the EIGEN 6c4, a combined global gravity model, to estimate the depth to the base of the crust and the mean density contrast between the crust and the upper‐mantle lithosphere in the Eurasia–Arabia continental collision zone along a 400 km profile crossing the Zagros Mountains (Iran). The results agree well with previously published works including both seismic and potential field studies.     

Inland notches: lithological characteristics and climatic implications of subaerial cavernous landforms in Israel

Inland notches, are elongated concave‐shape indentations that develop on the carbonate rocky cliffs of mountainous zones, down to the desert fringe. These rock shelters form as a result of the interaction between specific petrologic characteristics and climatic controls, emphasizing the importance of environment upon rock decay. Inland notches are shaped due to slight differences (1–15%) in the porosity of the visor and cavity bed: the cavity bed is more porous, so more likely to erode by exfoliation and dissolution. Thus, the cavity bed retreats at a faster rate compared to the slower subaerial dissolution of the visor bed, until a critical point is reached where the visor collapses. In Israel, inland notches inhabit the same lithostratigraphic units as do large caves. The vast majority (71%) of inland notches are formed in hard, dense, and crystalline limestone deposited throughout the Turonian age. Another 27% are cut into the dolomitic sequence of the upper Albian and lower Cenomanian. The rest (2%) are dispersed in the various formations of the Cenomanian and Eocene eras. Notches are most common in semi‐arid and in Mediterranean climates but mainly in areas with annual rainfall of between 400 mm and 850 mm. In more humid areas (> 900 mm/yr) notches are negligible or completely absent, due to the rapid rate of chemical dissolution of carbonate rocks. In the desert fringe (200–300 mm/yr), mechanical decay is accelerated and notches exhibit disintegration processes, visor collapse, and rock falls. In the desert area (< 200 mm/yr), salt decay replaces the chemical decay characteristic of inland notches, encouraging tafoni formation. In addition, notches form through fluvial activity or on account of greater petrophysical differences between consecutive beds; i.e. elongated cavities may form in soft rocks, shaded by harder visors or crusts. Copyright © 2017 John Wiley & Sons, Ltd.     

Spatial rules that generate urban patterns: Emergence of the power law in the distribution of axial line length

This paper studies emergence/generation of power law in rank-order distribution of axial line length, which is a global pattern observed in real cities, due to interaction of a set of seven simple spatial rules at a local scale. These rules and their interactions form a model expected to simulate the morphological structure of free spaces in unplanned organic pedestrian small cities. Effects of each of the seven rules are discussed through repeated simulations of eight possible combinations of the rules, using a bottom-up process. The results show that the rules generate environments with statistically stable rank-order distribution of axial line length that follows the power law. It means that the axial maps of the simulated environments have a scale-free hierarchical structure such that their distributions lean toward short axial lines. It also represents dominance of local spatial structure, as the model renders a faster rate of growth at a local scale while allowing a steady growth at a global scale.     

Semi‐active neuro‐control for base‐isolation system using magnetorheological (MR) dampers

Vibration mitigation using smart, reliable and cost‐effective mechanisms that requires small activation power is the primary objective of this paper. A semi‐active controller‐based neural network for base‐isolation structure equipped with a magnetorheological (MR) damper is presented and evaluated. An inverse neural network model (INV‐MR) is constructed to replicate the inverse dynamics of the MR damper. Next, linear quadratic Gaussian (LQG) controller is designed to produce the optimal control force. Thereafter, the LQG controller and the INV‐MR models are linked to control the structure. The coupled LQG and INV‐MR system was used to train a semi‐active neuro‐controller, designated as SA‐NC, which produces the necessary control voltage that actuates the MR damper. To evaluate the proposed method, the SA‐NC is compared to passive lead–rubber bearing isolation systems (LRBs). Results revealed that the SA‐NC was quite effective in seismic response reduction for wide range of motions from moderate to severe seismic events compared to the passive systems. In addition, the semi‐active MR damper enjoys many desirable features, such as its inherent stability, practicality and small power requirements. The effectiveness of the SA‐NC is illustrated and verified using simulated response of a six‐degree‐of‐freedom model of a base‐isolated building excited by several historical earthquake records. Copyright © 2006 John Wiley & Sons, Ltd.     

The first large meteorite impact structure discovered in the Middle East: Jebel Waqf as Suwwan,Jordan

Abstract— Triggered by re‐evaluation of a 1960s report on the regional geology of the northeastern border region of Jordan and following Landsat satellite image investigation, a 5.5 km diameter, complex, circular structure was discovered in the central eastern region of the Kingdom of Jordan. Initial ground truthing revealed complex geological structures involving Upper Cretaceous and Paleogene strata, and including a prominent outer rim rising up to 60 m above the surrounding plain, an intermediate ring of up to 20 m elevation within a ring syncline, and a central zone of stratigraphically uplifted sedimentary strata characterized by intense macroscopic (folding and faulting, widespread cataclasis) and locally mesoscopic (cataclasis) deformation. Ten sites with shatter cone development in fine‐grained sandstone or limestone have been mapped to date, mostly in the outer parts of the central uplifted area. This finding confirms that the Jebel Waqf as Suwwan structure was formed as the result of the impact of an extraterrestrial projectile. Search for impact‐diagnostic micro‐deformation has been rather unsuccessful: only 1 quartz grain with both planar deformation features and planar fractures has been detected in a sandstone sample to date. The overall majority of the approximately 70 samples investigated by micropetrographic analysis consist of extremely fine‐grained chert, siltstone, or marly limestone. Cataclasis is widespread in chert and limestone, also on the micro‐scale. Considering the severely limited amount of characteristic impact microdeformation, and the stratigraphic situation within the central uplift, it is likely that a relatively deep level of the central uplift is currently exposed. The extensive drainage demonstrated for this region supports the conclusion that this impact structure could be quite deeply eroded‐especially as its geology involves some relatively soft lithologies (marls, limestones). The age of this impact event is at present poorly constrained at post‐Middle to Lower Eocene.     

Exploring the application of a flood risk management Serious Game platform

Based on the experience gained with SeCom2.0, we will explain the impact of game-based learning and provide an overview of the current use of Serious Games in teaching flood risk management in Germany. SeCom2.0 is a collaborative learning platform, which deals with a flood situation in Cologne. The use of Serious Games in flood risk management is still limited due to many factors. The article will give a deeper insight into the SeCom2.0 project, explaining the pedagogical design and the development. We will cover the pitfalls and possible suggestions for further development to facilitate wider use of such games by adapting the settings to local conditions. This article will also describe how a Serious Game can support lifelong learning for students and employees involved in flood risk management. The key components, design patterns and structure of or SeCom2.0 are described, along with ideas to implement selected topics in flood risk management in an engaging gaming environment.     

Surface soil assessment in the Ubhur area,north of Jeddah,western Saudi Arabia,using a multichannel analysis of surface waves method

Ten boreholes drilled in Ubhur area up to the depth of bedrock indicted the shallow depth of bedrock where the average depth ranges between 10 and 15 m. The standard penetration test N-values of these boreholes were measured and averaged. Based on N-values to the depth of bedrock, Ubhur area can be classified as site class C and D. Multichannel analysis of surface waves technique has been applied along seventy six profiles using 24-channel geophone array and 4.5Hz vertical geophones with 1m geophone spacing and sledgehammer and/or weight drop as seismic energy sources. Values of shear wave velocity to 30 m are calculated and then averaged (Vs30) where it ranges between 310.08 m/s and 1139.8 m/s. Therefore, Ubhur area can be classified into site class B, C and D based on site classification of the national earthquake hazards reduction program (NEHRP) recommendations. Accordingly, the greatest part of the study area falls in site class C while class B and D covered limited areas in the western and the eastern parts respectively. Depending on the shallow depth of bedrock in the study area, the Vs30 parameter is not applicable in the study area so the average values of Vs for the soil thickness, excluding the bedrock, have been calculated and mapped for site class C and D only. So Vs30 approach is not applicable for areas with shallow depth of bedrock which gives higher classification.     

Geoenvironmental studies on conservation of archaeological sites at Siwa oasis, Egypt

Siwa oasis is located in the extreme western part of the Egyptian western desert. There are several archaeological sites in the oasis; the most distinct ones are Alexander the Great temple at Aghormi hill and the Gebel El Mota tomb excavations. They have suffered due to deterioration and cracks of different kinds and some parts are getting worse as rock falls occur. From field inspection and lab analysis, it is clear that lithology plays an important role on the extent of damage. Alexander the Great temple was built over the northern edge of Aghormi hill, which consists of two distinct beds—an upper limestone bed and a lower shale one. From field survey and laboratory analysis, the shale is considered as a high expanded bed and weak in its bearing capacity, as its clay content (mainly smectite) experienced swelling due to wetting from the ground water spring underneath. Consequently, the upper limestone bed suffered from map cracking associated with rock falls due to the differential settlement of the swelled lower shale one. The temple was threatened by slope instability and had experienced many cracks. At Gabal El Mota tomb excavations, it was noticed that a comparison of tombs of the same opening size revealed that those that excavated on shale beds had cracked much more than those that excavated on limestone. This may be attributed to the low bearing capacity of excavated shale walls. The remedial measures suggested to overcome the stability problems on these archaeological sites are grouting or construction of retaining walls.