Modified “Rockfall Hazard Rating System for Pakistan (RHRSP)”: An Application for Hazard and Risk Assessment along the Karakoram Highway, Northwest Pakistan

Rockfall is a natural mountain hazard posing a severe threat to people, infrastructure, and vehicles along the transportation corridors. In this research, the standard Rockfall Hazard Rating System (RHRS) is slightly modified for the mountainous terrains of Pakistan through the quantification of animal activity along the highways. In the modified Rockfall Hazard and Rating System for Pakistan (RHRSP), animal activity is scored based on permanent and random animal tracks, shallow and higher altitudes, and shoulder width. The model is applied along the Karakoram Highway (KKH), which traverses a suture between Besham and Dasu (≈78 km), for Rockfall hazard and risk assessment mapping. An inventory of rockfalls, topples, and debris slides is compiled at 30 stations. Results show that rockfalls are mostly of the wedge and topple type failures. Fifty-seven percent of the area falls under the very-high to high hazard zone, 18% under moderate hazard, and 25% covers the low to very low hazard zone. Sixty-seven percent of the stretch is at very-high to high risk, distributed from Dubair to Dasu. The main reason for this risk is associated with narrow road width and limited shoulder width for vehicles. The RHRSP model is also applicable for other highways with the same geological and morphological settings.