Rockfall susceptibility along Pasang Lhamu and Galchhi-Rasuwagadhi highways, Rasuwa, Central Nepal

The road network in Central Nepal suffered blockades and damage from numerous landslides and rockfalls due to the earthquake sequence in Gorkha, Nepal, in 2015. Additionally, frequent rainstorms in the area contributed to the recurrence of rockfalls and other types of landslides, hindering road infrastructure development and environmental management. Despite the several existing regional and local studies on landslide susceptibility in the area, rockfall-specific analysis is still lacking. In this paper, we assessed rockfall susceptibility in the sections of the Pasang Lhamu highway and the Galchhi-Rasuwagadhi highway in the Rasuwa district using a physically based model. We generated three-dimensional rockfall trajectories along the roads and used them to infer the rockfall susceptibility of the area. We selected potential locations for the initiation of rockfalls based on the optimization of the gridded slope angle, relief, and terrain ruggedness, validated the source map using statistical parameters, and compared them with a field-mapped rockfall source inventory. As a result, we identified which road sections in Ramche, Dandagaun, and Syaprubesi are highly susceptible to rockfalls. We published the field-based inventory of rockfall sources and segment-wise rockfall susceptibility of highways, where a rockfall susceptibility index of 5 indicated very high susceptibility and 1 very low susceptibility. Such findings and maps are helpful for researchers, land planners, developers, government bodies working on disaster risk reduction and policymakers to design a preliminary framework for rockfall mitigation and sustainable roads.