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Prognosis and mitigation strategy for major landslide-prone areas Varunavat Parvat landslide in Uttarkashi

Prognosis and mitigation strategy for major landslide-prone areas A case study of Varunavat Parvat landslide in Uttarkashi township of Uttarakhand (India)


accumulated in the backyards of multi-storied Mandakni and Relax hotels at Uttarkashi Bus Stand area. District authorities promptly responded as they were aware of the uphill events and probable consequences in the form of large-scale landslides. Realizing the fact that emergency evacuation from the area was first and foremost task, the authorities launched a coordinated effort by involving different line departments (Police, Fire Brigade, Revenue, Irrigation Department etc.) and public representatives of local bodies for emergency evacuation from the bus stand and surrounding area of the township. In sharp contrast to the devastating landslide events of Okhimath and Malpa (Uttranchal) in the monsoon season of 1998, where hundreds of people lost their lives, the landslide events of Varunavat Parvat in Uttarkashi recorded zero casualty figures. This can be attributed to the slow and gradual movement of sliding mass from the hill (Varunavat Parvat) and awareness among masses about the onslaught of disaster and furthermore, preparedness and timely intervention by local people and administration. Damage assessment Devastating landslides in the Uttarkashi township during the months of September and October, 2003 have badly affected Bus Stand and surrounding area, part of Ramlila Ground, Masjid Mohalla and Horticulture Colony localities of the township. Consequently, about 81 buildings including 23 government buildings and 58 private buildings (multi-storied commercial complexes, residential cum commercial buildings) were damaged. According to initial estimates by district authorities a population of 2,911 from 362 families was affected. A segment of Rishikesh-Gangotri National Highway was also buried under the slide debris. The Central Technical Team has demarcated a buffer zone around landslide affected area of Uttarkashi and advised evacuation of the population of this zone in order to minimize the risk to the inhabitants in near future and to ensure the detailed investigations and treatment of hill slope (Central Technical Team, 2003). About 69 government buildings and 143 private buildings located in the buffer zone are to be reconstructed/relocated. According to local authorities the estimated cost of rehabilitation of affected population, relocation of government and commercial buildings and bridges, construction of alternate routes and hill slope stabilization is 2,552.1 million Indian Rupees (1US$ 47 Indian Rupees). Geology The rocks constituting Varunavat Parvat are mainly jointed and fractured phyllites and quartzites of Uttarkashi Formation of Garhwal Group of Lesser Himalayan sequence, dipping into the hill at an angle of about 35 o (Plate 6e). Agarwal and Kumar (1973) carried out detailed geological mapping of the area and recognized the lower part of Uttarkashi Formation as Netala Quartzite and upper part as Sartali Slates. Netala Quartizite is interbedded sequence of quartzite and slates exposed in the northern limb of NW-SE trending Baragadi Anticline (Jain, 1971), conformably underlying the slates. The quartzite of this sequence is white to buff coloured, fine grained and current bedded. Sartali Slates occur as banded grey, green, purple slate and interbedded quartzite and are conformably underlying limestone and dolomite of Syalna Formation. In Badethi-Boga section west of Uttarkashi township the Syalna Prognosis and mitigation strategy 627

DPM 17,5 628 Plate 6. Various natural and anthropogenic factors causing large scale slides on Varunavat Parvat Limestone occur as linear narrow and impersistent band but in the northeast of Uttarkashi township, immediate north of Mandwa and east of Kot they attain considerable thickness. Syalna Formation includes massive bluish grey to black light grey limestone and dolomite at places cherty and pelletal stromatolitic with subordinate slate and quartzite. Syalna Formation is overlain by Nagni Thank Formation. Kot Metavolcanics member consisting of green amygdaloidal schist with thin bands of ripple marked quartzite and arenaceous slates constitute the basal horizon of Nagni Tank Formation (Figure 2). Kot Volcanics are exposed around Sangrali area north of the active slide zones of Varunavat Parvat. The younger member of Gameri Quartzite is white to purple

Disaster management strategy for potential slide zones of Kumarkhera in Narendra Nagar township of Tehri Garhwal district, Uttarakhand, India