Prognosis and mitigation strategy for major landslide-prone areas A case study of Varunavat Parvat landslide in Uttarkashi township of Uttarakhand (India)
township but many other habitations in Himalayan region which are prone to landslides. On the basis of this case study of Varunavat Parvat landslide an attempt has been made for reading the signs of large scale landslides and preparedness, effective response and non structural mitigation are also discussed herein to minimize the impact of such disaster in the future. Prognosis for major landslide-prone areas and effective response Emergence of large cracks or sudden widening of existing cracks (from few centimeters to few meters) in the upper reaches of hill slope, particularly in the upslope or immediate down slope of habitation, infrastructure (road, water supply line, power line, telephone line or canal), agricultural land, wild life area and protected forest area indicate that the ground is witnessing rapid stretching and immediate measures are required to minimize the risk. Emergence of small slide zones (in the vicinity of a large active slide zone) and their head- ward shifting towards the neighboring large active slide zone is an indication of an impending disaster in the form of gradual or sudden triggering of large scale landslides in the area in near future. Best examples of this phenomenon are active slide zones of Ramlila Ground, Masjid Mohalla-Horticulture colony, which have developed in the year 2003 as a result of head-ward shifting of small slide zones and their subsequent merging with the large active zone of Tambakhani slide. Sudden disappearance of some seepage zones, fluctuation in the discharge of other such zones and emergence of new springs and seepage zones in the close vicinity of existing or abandoned seepage zones/springs are some other indications of gradual or sudden changes in the hydrology as a consequence to the imperceptible or perceptible slope movement. Few days or hours before a major slope failure (in the from of debris rock slide or subsidence) in an area of human habitation, the indications are sudden snapping of fencing wires, electricity and telephone wires between pillars/poles and sudden disruption of water supply due to breaking of pipe lines, displacement of canals (kools in local parlance) and sewer lines. Finally the sudden tilting of walls of houses coupled with the development of cracks on their roofs and walls and subsidence of floor and baranda imply that the slope failure may take place any time, may be in a few days or even few hours. Under the given circumstances the inhabitants of such localities should immediately evacuate children and old persons to safer location and domestic animals should be immediately untied and be allowed to go free. Furthermore, the locality should be abandoned as early as possible in an effort to minimize the loss of human and animal lives. Under given conditions, incessant rains for hours or continuous rains for days coupled with the flow of muddy water into the drains (gadera in local parlance) which otherwise have fresh water and rolling of boulders and small scale debris flows are strong indications that the area is at the verge of experiencing a major debris flow and inhabitants of the area should immediately abandon their houses. Preparedness and mitigation Participatory rural appraisal Local authorities should facilitate interactive sessions of NGOs with the villagers and (women in particular) of high-risk prone habitations in order to disseminate the Prognosis and mitigation strategy 641
DPM 17,5 642 information pertaining to the presence or emergence of cracks in the upslope of habitations/villages. It has been observed that the local villagers during day today collection of animal fodder sometimes notice newly emerging small slide zones, cracks and or sudden widening of existing cracks in the upslope areas of the village, but unfortunately this crucial information about the initiation of sliding activity often goes unnoticed by the Disaster Management Community due to lack of communication between villagers and Disaster Management community. Ban on construction activity in the vicinity of landslide zones Complete ban be imposed on new constructions in the immediate upslope of active or potential slide zones, as the active slide zones may cause gradual or rapid subsidence of upslope habitation. Similarly, the areas in the immediate down slope of landslide zone should also be avoided for construction activity as the debris flow and rock fall from upslope area might cause damage in the near future. Effective rehabilitation policy Construction of new houses (in the safer areas) for the affected population is a better option as compared to the distribution of money to the affected people for construction of new houses. It has been observed that in many cases this money is utilized by the affected people for repairing the same old houses which have already witnessed the damage due to landslides. In some cases even new houses are constructed in the close vicinity of landslide affected old houses or otherwise on an another unsafe site. Strict implementation of land use regulations Land use regulations should be strictly implemented to avoid unplanned cutting and overloading of fragile hill slope for construction activity. Furthermore, in high risk areas there should be complete ban on blasting for road construction or road widening, instead cut and fill method of road construction should be adopted. In view of the high cost of road construction through cut and fill method, restricted blasting can be introduced but only in moderate to low risk areas, certainly not in the areas of high risk. This regulation is necessary since the blasting in fragile terrain causes opening of cracks of the rocks and in some cases even increases the joint aperture (opening) and these openings serve as easy pathways for percolation of rainwater (into the rock mass) which in turn increases sliding force and decreases resisting force and finally triggers the failure. Conservation of natural drains On the pattern of forest conservation measures, there should be provisions for conservation of the existing courses of natural drains and new constructions should not be allowed within the active flood plains of perennial or seasonal steams and furthermore, the constructions that block the natural drainage courses should be removed. This can be done by time to time survey, identification and subsequent demolition of residential, commercial or residential cum commercial or any other construction that is blocking, narrowing or diverting the course of natural drains (nala/gadera in local parlance) or is otherwise causing choking of sewerage/drainage system of municipal body or local body or village.