Executive Summary : | The entire Himalayan region faces many extreme geohazards, due to endogenic or exogenic processes like neo-tectonic activities, earthquake activities, rainfall, or due to anthropogenic activities. Landslide is the most common hazard which is seen to cause great damage to life, homes, destruction to transportation, major developmental facilities like hydropower dams, and also loss of farming land. In an active orogenic belt like the Himalayas, recurrent or unmanageable landslide zones occur frequently along public and strategic locations. The most affected region due to landslide hazard is turning out to be the states of Uttarakhand, Himachal Pradesh and the Northeast of India. These states are also one of the most tourism dependent states, with Uttarakhand also being a major pilgrimage destination. The Char Dham Yatra, is often disrupted by landslides, especially triggered by excessive rainfall, which creates loss of life and blocking the movement of tourists. The Himalayan slopes are also marked by perpetually active rock fall zones which destroy crops and houses causing loss in property and economy. In the state where very less farming land is available, rock falls or debris slides completely damages the utility of the land. Over and above that, several regions like tribal areas need acute development and management systems. Developmental activities, like building of roads, however, also disturb the fragile Himalayan slopes and initiate slope failures. The biggest hurdle that lies in mitigation measures of a landslide zone is that, processes vary in magnitude, or repetivity, and the exposures are modified within a single event. Therefore, especially for a recurring zone where other conventional damage control measures fail to stabilise a slope, a comprehensive strategy is required to be adopted to reduce risks. For this the best management strategy is turning out to be a ‘Landslide Early Warning System' (LEWS). With the availability of continuous radar data from good satellites, Persistant-scatterer Synthetic Aperture Radar (PS-InSAR) can analyse data over a long period to understand slope motion, thereby generating areas which are likely to fail. Whereas, PS-InSAR can give continuous monitoring on a regional scale, a LEWS is a localized system which generates advance signal of an impending risk, in order that steps may be taken on time to reduce the impact of the threat. LEWS, therefore, can be the ultimate step after understanding the vulnerability through PS-InSAR. A LEWS is a system which generates advance signal of an impending risk, in order that steps may be taken on time to reduce the impact of the threat. LEWS is therefore seen to be adopted world-wide. Good meteorological/hydrological/geotechnical data acquisition and modelling can assist in fixing more precise threshold values for good early warning of an impending landslide. |