Mountain highway stability threading on the fragile terrain of upper Ganga catchment (Uttarakhand Himalaya), India

Roads are the most critical means of connectivity in Himalayan villages. However, the terrain is inherently fragile with varied geological, geomorphological, ecological, and climate regimes, that result in frequent slope failure and disruption in connectivity. The risk is further to be increased by extreme events-generated hazards, which are expected to rise in frequency and magnitude with ongoing climate change. Critical scientific intervention, however, can improve the sustainability of road networks. The present study attempts to analyse and quantify the impacts of a major road widening project initiated in 2018 in the upper Ganga catchment, Uttarakhand Himalaya which has destabilised valley slopes along the widened segments. Also, a large quantity of excavated sediments is dumped down slopes, which is posing a threat to aquatic biodiversity. The estimates are based on Google Earth imagery of a few representative road segments recently widened in the upper Ganga catchment, which indicate a substantial increase in the landslide and unstable slope area following the road widening. The increase in unstable slope area is attributed to improper road widening approaches and poor slope management in seismically active Himalayan terrain. Further, the mean velocity plots of Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) indicate that the segments undergoing road widening are coherent with areas of significant earth surface change. A broad correlation between the road width and sediment yield indicates that even a slight increase in road width can result in a large-scale mass removal from the toe of the hillslope, inflicting cascading impact on hillslopes. The study recommends a more flexible road construction approach based on the environmental and geological aspects of the terrain for sustainable road networks. Further, the impact of climate change is looming over the Himalayas, and the relation between climate change and its potential effects on the stability of slopes remains an open issue.