Landslide susceptibility mapping and factor effect analysis using frequency ratio in a catchment scale: a case study fro
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ORIGINAL PAPER
Landslide susceptibility mapping and factor effect analysis using frequency ratio in a catchment scale: a case study from Garuwa sub-basin, East Nepal Prabin Kayastha
Received: 29 March 2014 / Accepted: 6 February 2015 # Saudi Society for Geosciences 2015
Abstract For assessing landslide susceptibility, the spatial distribution of landslides in the field is essential. The landslide inventory map is prepared on the basis of historical information of individual landslide events from different sources such as previously published reports, satellite imageries, aerial photographs and interview with local inhabitants. Then, the distribution of landslides in the study area is verified with field surveys. However, the selection of contributing factors for modelling landslide susceptibility is an inhibit task. The previous studies show that the factors are chosen as per availability of data. This paper documents the landslide susceptibility mapping in the Garuwa sub-basin, East Nepal using frequency ratio method. Nine different contributing factors are considered: slope aspect, slope angle, slope shape, relative relief, geology, distance from faults, land use, distance from drainage and annual rainfall. To analyse the effect of contributing factors, the landslide susceptibility index maps are generated four times using (a) topographical factors and geological factors, (b) topographical factors, geological factors and land use, (c) topographical factors, geological factors, land use and drainage and (d) all nine causative factors. By comparing with the pre-existing landslides, the fourth case (considering all nine causative factors) yields the best success rate accuracy, i.e. 81.19 %, which is then used to produce the final landslide susceptibility zonation map. Then, the final landslide susceptibility map is validated through chi-square test. The standard chi-square value with 3 degrees of freedom at P. Kayastha (*) Department of Hydrology and Hydraulic Engineering, Vrije Universiteit Brussel Pleinlaan 2, 1050 Brussels, Belgium e-mail: [email protected] P. Kayastha Mountain Risk Engineering Unit, Tribhuvan University Kirtipur, Kathmandu, Nepal P. Kayastha Attic Consulting Service Thamel, Kathmandu, Nepal
the 0.001 significance level is 16.3, whereas the calculated chisquare value is 7,125.79. Since the calculated chi-square value is greater than the standard chi-square value, it can be concluded that the landslide susceptibility map is considered as statistically significant. Moreover, the results show that the predicted susceptibility levels are found to be in good agreement with the past landslide occurrences. Keywords Landslide susceptibility . Frequency ratio . Factor effect . Garuwa sub-basin . Nepal
Introduction Extending from Afghanistan to Myanmar, the Himalaya region is inherently fragile and susceptible to landslides as a result of its rugged mountain topography, soft soil cover, high-intensity monsoon precipitation and weak nature of the geological structures (Upreti and Dhital 1996; Chalise
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