An Example for Preparation of GIS-Based Landslide Susceptibility Maps: Çayeli (Rize, NE Türkiye)
ABSTRACT: Landslides are leading natural disasters occurring in the Black Sea Region, which is one of the regions receiving a great deal of rain and which is the roughest one in our country, particularly the Eastern Black Sea. In the region, the damage caused by landslides is greater than that caused by earthquakes in the long term. In this study, the landslides that occurred in Çayeli in July 2002 as a result of heavy rain were investigated and the landslide susceptibility map was prepared for the study area. Initially, a landslide inventory map was created and 149 landslides in total were mapped. Based on field investigations, the factors of lithology-weathering, slope angle, slope aspect, landcover, elevation and proximity to river were evaluated as the parameters causing the landslides. Using topographical and thematic maps, the parameter maps were created in Geographical Information Systems (GIS) environment,. Associating the maps with the current landslides, their frequency ratio values were determined. In the light of these evaluations, it is thought that completely weathered dacite and pyroclastics, and completely weathered andesite-basalt and pyroclastics are effective in the landslide occurrence. The slope classes between 0º and 20º, northward-northeastward slopes and the elevation classes between 0 and 200 m were regarded as significant according to the obtained values. Similarly, landcover classes from agricultural and settlement area, and proximity to river classes between 0 - 100 m are parameter classes considered significant in paired comparisons. Then, weighted values were calculated and by taking these values in to account, a landslide susceptibility map was created. Finally, to analyse the performance of the map, the current landslides and the susceptibility map were compared and 81% of current landslides were determined to be situated in susceptible, highly susceptible and very highly susceptible areas.