Etude des glissements de terrain dans la région d'Oued Athmania

Abstract

Northern Algeria presents a complex geology, structures and varied formations reflecting a geological history and palaeogeographic event. It is localized in a zone of convergence of plates and is characterized by a seismic activity important, result of an important internal geodynamics. The region of Oued Athmania, which is part of this active margin, has undergone a significant morpho-structural evolution during the Miocene and throughout the Quaternary. The relief has many deformations: some slopes have a chaotic and bloated appearance reflecting the fragility of the environment and its sensitivity to active morphogenesis manifested, inter alia, by different types of ground movements ranging from small stripping to large landslides, tipping crop fields and consequently reduced agricultural land, disruption of river dynamics and deposition of a considerable amount of materials at the wadi beds. These disturbances, in their size and scope, are beginning to pose serious problems for development and road infrastructure. This work is a contribution to the knowledge of these gravitational movements, to the identification of the major factors that are responsible for them, in particular those related to the morpho structural context and the mapping of the areas susceptible to landslides in the oued Athmania region. The methodology adopted was based on the analysis of the geological environment: it was to draw geomorphological and hydrographic features and to understand the history and evolution of the study area. Field observations, the deciphering of aerial photos, the analysis of the hydrographic network, geological and topographic maps, the hypsometric map and the digital terrain model were all steps that allowed us to make an assumption about the process of slope instability, thus highlighting the causal part of the faciological parameters such as the granulometric composition and the mineralogical procession of the affected formations and their properties, in order to map the potentially vulnerable zones with the help of a geographic information system that provides assured leadership to a real decision support system. This cartography exploits the functionalities offered by GIS for the structuring of data, the crossing of information layers and the spatial analysis of different themes. It also includes the AHP multicriteria hierarchical analysis approach which allowed us to assemble a multitude of decision criteria into a single model, to make a comparative evaluation of each pair of criteria and to calculate their weights for the assessment. Compared each pair of options against each subcriterion. The combination of these working techniques allowed us to reveal new morphostructures in the region and to identify a wide variety of terrain instabilities; this diversity is related to the geological complexity, mainly the tectonics and the mineralogical procession of the geological formations which seem to play the role of a catalyst in the acceleration and the development of the instabilities in the region.