Rockfalls in the Zireg watershed: factors of genesis and mapping of risk zones (Middle Atlas - Morocco)

Resumen

Rockfalls are characterized by the sudden separation of a rock mass from a slope, which rapidly descends downstream under the influence of gravity. These events represent one of the most common hazards in mountainous areas, potentially causing damage to people and property, as well as generating significant financial costs, especially when they affect homes and critical infrastructure (roads, railways, and power lines). Therefore, studying rockfall risk is crucial to improve their prevention and mitigate their impacts. It is also essential to assess how this risk is triggered, depending on geographical conditions. Estimating rockfall hazard levels requires access to accurate information and a detailed analysis method, combined with a sound geomorphological perspective, depending on the intended purpose. To this end, the method used takes into account the key factors that trigger the formation of falling blocks and their descent (lithology, slope, and land use) in the Zireg watershed (Middle Atlas, Morocco), relying on a model that quantifies the importance of each component. The geomorphological characteristics of the Zireg watershed are distinguished by its dynamic relief and irregular morphology, marked by steep, shaped slopes in carbonate and schistose material, sensitive to rockfall. It records active morphogenesis amplified by the aggressiveness of the Mediterranean climate. According to the descriptive study, we have shown that 4% of the total area is marked by high and very high degrees of risk, linked essentially to the presence of carbonate rock slopes, high to very high slopes and low or medium density plant cover.