Rockfall susceptibility assessment along M-2 Motorway in Salt Range, Pakistan

Rockfall is one of the recurrent geo-hazards in Pakistan and poses challenge not only to elements at risks but also to the infrastructure planners, engineers and government. In this study, rockfall susceptibility is spatially assessed in Salt Range along Motorway (M-2) within 500 m buffer zone. The events of rockfall become more frequent with damaging effect after the construction of M-2 even in the presence of certain structural measures like fences, protective walls, terraces and water diversion channels. Rockfall susceptibility was assessed using geological, meteorological, topographical, geo-morphometric conditions and rockfall events characteristics as input risk factors or spatial layers. Factor based ranking methodology was adopted in integration with geo-spatial tools for spatial assessment of rockfall risk. Similarly, importance of each risk factor is individually calculated and analysed in terms of cause and effect relation. Global Positioning System (GPS) based field measurements, landsat images, Shuttle Radar Topography Mission (SRTM) and Digital Elevation Model (DEM) is used as input data to map land cover conditions and carry out watershed analysis and slope-aspect analyses in ArcGIS10.2, respectively. The cumulative rockfall susceptibility assessment was finally done at 4-class ordinal scale (very high, high, moderate and low) by applying weighted overly analysis in GIS environment. Analysis revealed that very high susceptibility zone is in the lower southern part of the study area- attributed mainly to the fault, porous sedimentary rocks of laterite, sand stone and shale. This study carries great importance in rockfall risk reduction through structural and non-structural measures within Salt Range vis-`a-vis other mountainous regions in Pakistan. In addition, the current study approach can be utilized effectively to prioritize and geo-visualize the severity of potential future rockfall risk along other highways having similar geological and geomorphological settings.