A comparative study on rockfall block motion characteristics using 3-D and 2-D rockfall simulations: a case study from Cappadocia (Mazı, Türkiye)

Within the scope of this research, rockfalls in Mazı village of Ürgüp (Türkiye) district were simulated on a digital surface model constructed using high resolution (2.9 cm) point cloud data retrieved from a real orthophoto mosaic gathered by an unmanned aerial vehicle in order to compare the results of 2-D and 3-D rockfall models. At the initial stage, 3-dimensional rockfall analyses were carried out using RocPro3D software and block dynamics such as trajectory, maximum runout distance, bounce height and total kinetic energy of the blocks were determined. Subsequently, a total of eight slope profiles were obtained from the point cloud data and 2-dimensional rockfall analyses were executed by means of RocFall 2-D software. Using a rockfall point source indicating the starting position of 2-D rockfall analysis, the rockfall analyses were repeated on 3-dimensional digital surface model and the block motion characteristics obtained from 2-D and 3-D analyses were compared. Eventually, it is revealed that block runout distances may differ in 3-D and 2-D rockfall analyses. Additionally, 3-D analyses reveal a significant advantage over 2-D analyses in terms of including topographic roughness, curves and obstacles in the model. On the other hand, one of the most significant variances between 2-D and 3-D rockfall analyses retrieved in this research is in the bounce height values. While the bounce height value in 2-D models may attain a maximum of 7 m, 3-D simulations point out that the detached blocks mostly roll over the slope with very low bouncing. When the simulation results are evaluated in terms of total kinetic energy, it is concluded that kinetic energy values are commonly higher in 2-D rockfall analyses than those of 3-D simulations. Conversely, block translational velocity values are typically comparable in both 2-D and 3-D rockfall models. Besides, considering the trajectories obtained via 3-D rockfall models for the study site, it is obvious that the settlement is under the risk of rockfall to a significant extent. Rockfall simulations highlight that the total kinetic energy values of the blocks are also quite high, which increase the destructive effect of rockfalls.