Longitudinal Profile and Geomorphological Processes of the Oued Qarya in Relation to Lithology and Tectonics (Morocco)

Oued Qarya is a left-bank tributary of Oued Zloul (Sebou basin). Its basin drains an area of 323 km 2 from the northwestern slope of the Middle Atlas, folded in the province of Sefrou. These are heterogeneous geological terrains of the Lower and Middle Jurassic, dominated by the carbonate rocks of Lias (the mountain of the folded Middle Atlas). In a mountain area with relatively steep slopes, the organization of the hydrographic network and its hydrodynamic functioning are largely influenced by the inclination of the geological formations, the lithology of the terrain, and a dense network of tectonic accidents from the Alpine orogeny, some of which were reactivated during the Quaternary. This study presents the results of the analysis of the morphometry of the main watercourse, the concavity, and the slope breaks of the longitudinal profile of the Oued Qarya. It is essentially based on the determination of their morphometric characteristics, in particular the asymmetry factor (AF), the topographic asymmetry index (TTSI), as well as the concavity indices (IC) and (Er), the slope index (SL), and the index of the slope gradient (k). The results obtained highlight the relationship between the values of these indices and the arrangement of geological formations, the lithology of the terrain, and the influence of tectonics on the longitudinal profiles. The watercourse tends to deviate in the direction of the inclination of the geological formations. In addition, the concavity of the profile is stronger on less resistant geological formations (marl), compared to the sections developed on hard geological formations of limestone and liasic dolomites. In addition, the longitudinal slope of the profiles is generally accentuated on resistant soils, while the passage by ruptures coincides with more or less marked breaks in slopes.