Landslide Hazard Evaluation and Zonation in Dilbe and its Surrounding Area Northwestern Central Ethiopia; an Integrated Gis Based Grid Overlay and Statistical Approach

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Date

2018-05-05

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Addis Ababa University

Abstract

The present study was carried out in Dilbe and its surrounding area around Northwestern Central Ethiopian, about 576 km from the capital city Addis Ababa. Due to landslides and related slope instability problems in the Dilbe area roads and agricultural plots are damaged and also local people are displaced from their residences. The main objective of the present study was to evaluate landslide hazard in the area and to produce landslide Hazard Zonation Map of the area. To achieve these objectives integrated GIS based grid overlay and statistical approach was followed. Six causative parameters: namely; slope-material, land use land cover, groundwater surface traces, slope, aspect and elevation were considered for hazard evaluation and zonation. A total of 30 past landslides in the study area were identified and recorded through field survey. An integration of Geographic Information Systems (GIS) based grid overlay and statistical approach was followed to rate the responsible factors for the landslide occurrence. As a part of methodology, a 10 x10 m polygon grid was prepared and overlaid over prepared causative factor maps in GIS environment. This overlay analysis was done to know the presence or absence of each causative factor sub-class within each polygon grid cell. For the purpose of rating of various causative parameters quantitative prediction was established using raster calculator in Arc-GIS, density ratio was made between total pixel count for landslide occur to total pixel count for landslide did not occurred. Later, hazard index ratio was calculated which was further utilized to deduce Landslide susceptibility index (LSI). Within each grid cell depending on presence of various factor classes LSI values were assigned. The sum total of LSI values for six parameters within each grid cell provided total landslide susceptibility index (TLSI), which finally formed the basis to produce LHZ map of the study area. The LHZ map shows that 11.64% (5.774km2) of the study area has a ‘very high landslide hazard’ (VHH) potential and 19.86% (9.91km2) area has ‘high landslide hazard’ (HH) potential. Whereas, the areas that account for ‘medium hazard’ (MH), ‘low hazard’ (LOH) and ‘very low hazard’ (VLH) are 14.3% (7.22km2), 38.2% (19.1km2) and 16% (8km2), respectively. Validation of the prepared hazard zone map revealed that 74% of past landslides fall within very high hazard and high hazard zone of the prepared LHZ map. Thus, the LHZ map validation provided satisfactory results and the various zones delineated can safely be applied for future developmental planning in the present study area.

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Keywords

Landslide, Landslide Hazard Zonation, Hazard Index, Landslide Susceptibility Value

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