Assessment of Torrential Correction Thresholds on Ourika Sub-Watershed of the Tensift Watershed (High Atlas of Marrakech, Morocco)

Abstract

The Ourika sub-watershed is composed of about twenty different watersheds with diverse lithology, slope, and structural organization. In order to better characterize the basin, we inventoried and extensively assessed the different types of thresholds implemented in each micro-watershed. The present study focused on the area located between Meltsen and Sidi Ali Oufarés faults, which includes several micro-watersheds that have been modified by the installation of structures. We selected 12 micro-watersheds from the main tributaries draining this zone, based on the level of risk: four micro-watersheds on the right bank from upstream to downstream (Wigrane and Walighane, Tachmacht, and Touggalkhir), and eight micro-watersheds on the left bank from upstream to down-stream (Imintaddarte, Oussane, Tikhfert, Tighazrit, Igri Foudene, Asni, Taljarft, and Tarzaza). The results of our study allowed us to detect and inventory 545 erosion protection structures made of masonry, gabions, and dry stone. However, the majority of these structures were damaged in several micro-watersheds due to steep slopes, torrential rainfall, and especially the solid sediment load resulting from the erosion of easily erodible old alluvial cones. This study serves as a warning to various stakeholders and decision-makers to ensure proper management in this mountainous system. The distribution of these thresholds is as follows: 62 masonry thresholds, accounting for 13.37%; 247 gabion thresholds, accounting for 45.32%; and 236 dry stone thresholds, accounting for 43.30%. The assessment of these structures revealed anomalies such as the loss of 17.43% of embankment structures and the destruction of certain thresholds.