**2.2 Materials**

The Ethiopia Mapping Agency's toposheet number (0637 D1) at a scale of 1:50,000 was used in the current study to demarcate the study area, and a land facet map was created using the topographic map. The slope morphometry and relative relief map were extracted using a DEM (digital elevation model) with a spatial resolution of 12.5 m from the Alaska Satellite Facility site. On January 10, 2019, cloud-free optical satellite data acquired by Landsat-8 Operational Land Imager (OLI) with path-row numbers 170-051 was also entered into the following portal (http://earthexplorer.usgs.gov/) and used to develop land use and land cover map of the current study area (**Figure 3**).

**Figure 2.** *Geological map of the study area.*

## **2.3 Methods**

The entire research area was initially divided into 106 slope land facets (**Figure 4**). In terms of slope inclination and slope direction, a land facet is defined as a land unit with more or less uniform slope geometry [4]. The slope facets were delineated using topographical maps. Facets were defined by major and minor hill ridges, primary and secondary streams, and other topographical undulations [4, 11]. The prepared facet map was then used as a base map for collecting data on the various causative factors. Lithology, structural discontinuity with slope, slope morphometry, relative relief, land use/land cover, groundwater-surface drops, rain-induced index, and human activities are among the factors that contribute to slope instability [4, 11, 12, 41]. As a result, the susceptibility evaluation parameter rating was assigned for each causative factor to get evaluated landslide hazard.

The total maximum susceptibility evaluation parameter rating for the various causative factors is 15. The maximum value was accounted for slope morphometry, groundwater situation, and seismicity 2.0. Land use land cover, rainfall-induced surface index, and human activity contributed to a maximum susceptibility evaluation parameter rate of 1.5. Furthermore, relative relief and slope geo-material each contribute at a rate of 1.0. Structured discontinuity, on the other hand, contributes a maximum susceptibility evaluation parameter rate of 2.50 (**Table 1**). The evaluated landslide hazard is the total sum of susceptibility evaluation parameter ratings for all causative factors; therefore, the greater the value of the susceptibility evaluation parameter, the greater the degree of hazard.

The slope susceptibility evaluation parameter was developed by [11] by taking intrinsic (inherent) and external landslide causative factors. Furthermore, the total prospect of instability was established by assessing landslide hazard, and it was determined facet-by-facet for which observations and investigations were made during

*Landslide Assessment and Hazard Zonation in the Birbir Mariam District, Gamo Highlands… DOI: http://dx.doi.org/10.5772/intechopen.108122*

#### **Figure 3.**

*General methodology flow chart for the study.*

#### **Figure 4.** *Land facet map of the study area.*

the fieldwork. As a result, ratings from **Table 1** have been assigned and evaluated landslide hazard is the total sum of susceptibility evaluation parameter ratings for the various causative factors for each facet. Each causative factor was assigned a rate


#### **Table 1.**

*Rating methods for both intrinsic, external causative factors and evaluated landslide hazard.*

based on subjective decisions attained from past research on intrinsic and external causing factors and their relative contribution to slope instability. Field and literature review data on intrinsic and extrinsic causative factors were incorporated. Finally, each causative parameter was rated on a facet-by-facet basis (**Figure 4**).
