Rockfall analysis based on UAV technology in Kazıklıali Gorge, Aladağlar (Taurus Mountains, Turkey)

Abstract

Rockfall is one of the most dangerous types of landslides and they take place in relation to slope instability. Dynamic processes such as freeze-thaw events, seismic activities and slope characteristics are the main control factors on rockfalls. Due to both topographic and climatic characteristics, many areas in Turkey have high rockfall risk and rockfall hazards correspond to 10-12% of the natural hazards in this country. In this study, rockfall characteristics of the Kazıklıali Gorge (0.25 km2) in the lower Emli River Basin located in the SW part of the Aladağlar Mts. was investigated using unmanned air vehicle (UAV) technology and rockfall modeling. Although there is no settlement in the gorge, it is one of the most attractive rock-climbing areas in Turkey; therefore, it is important to determine its rockfall characteristics and to make a risk assessment of the gorge. To determine its rockfall properties, an orthophoto and digital surface model with 3 cm resolution were created using UAV images. All rockfall blocks more than 0.5 m in diameter were digitized as polygons in GIS. Via these polygons, density maps were created and frequency distributions were calculated. As a result, 10,348 fallen rocks were determined in Kazıklıali Canyon. According to the diameter frequency, 75.7% of fallen rocks have a diameter of <2 meters, only 2.9% are ≥5 m in diameter, 78% of all fallen rocks are <2 m2, and only 10.2% have ≥5 m2 surface area. The topographical characteristics of the canyon affect the spatial distribution of rockfall density. The upper and middle parts of the canyon, which are the narrowest, have high density; while the lower valley, which is the largest part, has low density. Rockfall analysis shows that the areas with high rockfall probability are steep slopes where kinetic energy, jump height and rock velocity are very high. According to the results of 3D rockfall analysis, the maximum kinetic energy, maximum jump height and maximum velocity reaches 1400 kJ, 15 m and 32 m/s on the canyon walls, respectively. The upper and middle parts of the canyon walls which correspond to high rockfall density have maximum kinetic energy, rock jump height and rock velocity.