Prognosis and mitigation strategy for major landslide-prone areas A case study of Varunavat Parvat landslide in Uttarkashi township of Uttarakhand (India)
Introduction Himalaya isolates the Indian subcontinent from the rest of Asia. This highest and youngest mountain of the world was formed as a result of the coming together and eventual collision of India and mainland Asia. The people of Himalaya have borne the consequences of the quickened paces of the earth’s processes including the ever-threatening natural hazards (Valdiya, 2001). Major part of the state of Uttaranchal (now called as Uttarakhand) lies in the fragile mountain belt of Himalaya and has experienced tectonic turmoil several times in the distant past. During the last quarter of twentieth century there has been an increase in the frequency of natural disasters in this region. Major disasters in the last few years include Uttarkashi Earthquake of 1991, Chamoli Earthquake of 1999, infamous landslides of Okhimath and Malpa in the year 1998 and cloudbursts and flash floods in Khetgaon and Budakedar area during the monsoons of the year 2002. Sudden increase in anthropogenic activities like unplanned cutting of slope, blasting of highly jointed rock mass for road construction and unplanned disposal of the slope cut debris have further added to the fragility of Himalayan mountains and consequently there has been an increase in the vulnerability of this region to natural disasters (Uniyal and Prasad, 2006). In the first decade of the twenty-first century no other landslide in Himalayan region got more media attention than the landslide events from the hill called Varunavat Parvat in Uttarkashi township of Uttarakhand. Uttarkashi township in situated on the banks of Bhagirathi river (which is called Ganga in the downstream of Devprayag) at an elevation of 1,152 mts and is the district headquarters for the northern hill district of Uttarkashi named after this township (Figure 1). The township of Uttarkashi has a population of about 16,218 (Census of India, 2001, 2004) and is located on Rishikesh-Gangotri National Highway (NH-108) at a distance of about 200 km (approx.) from Dehradun, the capital of Uttarakhand state of India. This township lies in the fragile mountains of Himalaya and has a long history of natural disasters. Flash floods of Bhagirathi river in the late 1970s, Gyansu landslide more than two decades back in 1980, earthquake of the year 1991 have caused wide spread damage to life and property in Uttarkashi township and elsewhere in the district. The most recent disaster in this township has been large-scale landsliding from the hill called Varunavat Parvat, since Prognosis and mitigation strategy 623 Figure 1. Location map of study area
DPM 17,5 624 Plate 1. View of Varunavat Parvat on 1 October, 2003 with large active zone of Ramlila Ground slide and active zone of Horticulture Colony and Masjid Mohalla slide is also seen in the immediate east of the scarp of Ramlila Ground slide Plate 2. View of Varunavat Parvat in mid-October, 2003 September 23rd, 2003, which badly affected the commercial cum residential complexes, infrastructure facilities (a part of Rishikesh – Gangotri National Highway) in the upslope of Ramlila Ground in the heart of the township (Plates 1-4). Since 1 October, 2003 another slide was activated from Varunavat Parvat in the vicinity of Ramlila Ground slide and badly affected Masjid Mohalla and Horticulture colony localities (Plates 1, 2 and 5) of the township of Uttarkashi (Uniyal et al., 2004). NRSA (2001), in its Landslide Hazard Zonation Atlas has shown a part of Varunavat Parvat as high hazard zone.