Landslide Hazard Assessment and Zonation by SSEP Rating Scheme – a Case From Debre Sina, Southwestern Margin of Afar Escarpment
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Date
2014-05-05
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Addis Ababa University
Abstract
The earth’s surface is always in a dynamic change. These changes are more pronounced in mountainous terrains as a result of different mass wasting processes. The hilly and mountainous terrains of the highlands of Ethiopia are frequently affected by rainfall-induced landslides of different types and sizes. The study area, Debre Sina, has experienced landslide hazard for a long period of time. The principal objective of the proposed research study was intended to prepare a landslide hazard zonation map of the area, particularly for hazardous zones.
To achieve this objective Slope Stability Suscebtibility Evaluation Prarameter (SSEP) rating scheme was adopted. Landslide hazard zonation is an integrated approach which considers cumulative effect of several triggering parameters of slope instability. As per the methodology of the present study, nine causative parameters have been dealt with which include relative relief, slope morphometry, slope materials, structures, groundwater, land use land cover, rain fall, seismicity and man-made activities. These all are considered to be responsible for inducing instability in slopes and thus, resulting into landslides.
Because of the fact that the study area is located in Main Ethiopian Rift, it has experienced/ experiencing landslide hazards which claimed the life of people and devastated both public as well as private properties. The geology of the area include quaternary sediments, ignimbrite, rhyolite, different kinds of basalts and tuff deposits which are highly weathered and changed in to unconsolidated sediments at some localities. Locally found geological structures like joints, dykes have considerable role in landslide hazard initiation.
As a general methodology, facet map was prepared from topographic map (1:50000) and rating values were assigned to each causative parameter based on its severity in triggering landslides to produce final landslide hazard zonation map. Accordingly, 25 % of the slopes fall in to moderate hazard where as 58 % and 17 % of the study area is found to be high and very high hazard zones, respectively. Validation of LHZ map with past landslide activities suggests rationality of considered governing parameters, the adopted SSEP technique, tools and procedures in developing the landslide hazard map of the study area.
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Keywords
Landslide Hazard Zonation, Slope Susceptibility, Landslide Hazard Evaluation, Landslide Hazard Mitigation, Debre Sina, Triggering Parameters