The Development of Landslide Risk Maps in the Rif Mountains of Morocco: Between Al Hoceïma and El Jebha

Landslide Risk Maps in the Rif Mountains of Morocco

Abstract

The Central Rif region in Morocco, from Al Jebha to Al Hoceïma, has a rich history of landslides causing significant disruptions. The recent violent earthquake of Al-Hoceïma in 2003 led to a large land movement that caused the temporary closure of Regional Road N° 610 near Kassita. Besides, winter episodes with extreme rainfall, such as the record 136 mm in March 2020 near the El Jebha town, also caused an exorbitant slope sliding that interrupted traffic on National Road N° 16. These two examples of slope sliding, among others, demonstrate the interest in understanding and managing landslide risks in this region and constitute the background of the research. Thus, the purpose of this research is to identify the most vulnerable areas to landslides in the Al Jebha and Al Hoceïma regions to support their development. To conduct this study, we followed a methodology based on the inventory of dominant soils and rock formations with their geotechnical characteristics. Then, we proceeded with the presentation of their spatial distribution in geotechnical maps, constituting the first results. Subsequently, we discussed assumptions regarding the calculation of critical angles, such as the bishop method and the height of the studied slopes, alongside the definition of calculation cases considering the effects of rainfall and seismic activity on slope stability. We then calculated the critical angle for each soil in the fourth cases defined using the Talren tool, representing the second set of results. Furthermore, we assessed the natural dips of the study area based on a Digital Elevation Model using GIS tools to compute the quantity Δ, describing the difference between the critical angle and natural dips of each soil type. This led us to define landslide risk levels based on the range of the quantity Δ. Finally, using these results, we established landslide risk maps for the fourth cases, which constitute the main result of this paper. These risk maps serve as crucial tools for government decision-makers, guiding infrastructure investments like roads and tourism toward low-risk areas, optimizing fund allocation, and enhancing landslide hazard management effectively.