LANDSLIDE HAZARD ZONATION MAPPING IN GOPESHWAR, PIPALKOTI AND NANDPRAYAG AREAS OF UTTARAKHAND

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1 IGC 2009, Guntur, INDIA LANDSLIDE HAZARD ZONATION MAPPING IN GOPESHWAR, PIPALKOTI AND NANDPRAYAG AREAS OF UTTARAKHAND P.K. Deshpande Department of Geology, Walchand College of Engineering, Sangli , (M.S.), India. J.R. Patil Professor of Civil Engineering & Vice Principal, D.Y. Patil College of Engg. Akurdi Pune , India. D.C. Nainwal Department of Geology, Government P.G. College, Gopeshwar, Dist. Chamoli , Uttarakhand, India. M.B. Kulkarni Tatyasaheb Kore Institute of Engg. & Technology, Warnanagar, Dist. Kolhapur , (M.S.), India. ABSTRACT: Garhwal Himalaya, the part of extra-peninsula that has been compressed 65% and resulted in the orogenesis to form very steep mountain range. The structural disturbances like folding, faulting and shearing are very common in this region. Slopes, deforestation, heavy precipitation and the road construction itself have found to be the main cause of slope instability. This area exhibits varieties of landslide movements. In the present work the attempt has been made to create the Landslide Hazard Zonation Map along with some predictive locations with the help of Remote Sensing data and the GIS layers mainly DEM, slope maps, and flow accumulation maps in small areas around Gopeshwar, Pipalkoti and Nandprayag in Uttarakhand state. The areas are structurally disturbed and lie in seismic zone IV and receive very high precipitation. Slope, lithology, water and road excavation are the main causes of landslide in this region. It has been confirmed after field visit that the slide prone sites mapped by flow accumulation, lithology and slope maps were really the landslide hazard zones with typical slope instability and many pre occurred slides have been observed during the groundtruthing field visit. 1. INTRODUCTION Gopeshwar, Nandprayag and Pipalkoti belong to Chamoli district of Uttarakhand state of India. Chamoli carved as a separate revenue district in 1960 out of the erstwhile Grahwal district, lies in the Central Himalya and constitutes a part of the celebrated Kedar Kshetra. The District Chamoli is surrounded by Uttarkashi in North-West, Pithoragarh in South-West, Almora in South East, Rudraprayag in South- West and Tehri Grahwal in West. The geographical area of the District is around 7520 sq.kms. The city of Gopeshwar is the district place of Chamoli district. It is situated on moderately sloping and southward descending spur. It is bounded by several landslide hazard zones in west, north and east side. There are some pre occurred slide events that had been triggered during Chamoli Earthquake. The rocks are mostly Limestones, structurally highly disturbed. Many prevention measures have been adopted in Gopeshwar city and along nearby roads. The area lies in seismic zone IV and receives heavy precipitations. Therefore, seismisity may be a triggering factor but slope, lithology and water are the main causes of landslides (Kolekar, 2007). In the present work the attempt has been made to create the landslide hazard zonation map along with some predictive locations with the help of Remote sensing data and the GIS layers mainly DEM, slope maps and flow accumulation maps. The similar type of criteria has also been applied for Pipalkoti and Nandprayag areas. Of these, Pipalkoti was found to be highly vulnerable site for slide hazard. 2. LOCATION AND SITE CONDITIONS 2.1 Location The study areas are lying between the latitudes "N to N and longitude E to E that includes Gopeshwar city of Chamoli district, the latitudes N to N and longitudes E to E, that includes the stretch of Chamoli-Joshimath 808

2 road near Pipalkoti and the latitudes N to N and longitudes E to E, that includes the area around the holy confluence of Alaknanda and Nandakini rivers. The area lies in the Survey of India toposheet No.53 N/7 covering the areas of sq.km, sq.km and sq.km respectively. The area is approachable through the road link and about 150 km far from Rishikesh on the way to Badrinath-Mana. 2.2 Geology The geology of the region shows Himalayan young mountain range. The section of the range in the district is deeply cut into by the headwaters of the Alaknanda River, this trunk stream seeming to have reached a latter stage of development than its tributaries. This much, however, is known that there has been intense metamorphosis and consists of rocks such as gneisses, limestone, phyllites, quartzite, sericite-biotite schist and slates. During the field work the team observed the formations of micaceous schist, gneisses, limestone, phyllites, quartzite and slates. All these rocks found to contain weak cohesion along the plains of schistosity. Splitting of the mass is very common along steep unstable slopes. The phenomenon is observed not only in the study area but also common along entire Rishikesh-Mana Highway. Physiographically the areas lie in a region of tectonic or folded and overthrust mountain chain with strata structurally marked by complex folds, reverse faults, overthrusts and nappes of great dimensions (Krishnan, 1982). All these, as well as frequent earthquake of varying intensity give the reason to believe that the region is still unstable. 2.3 Climate As the elevation of the district ranges from 800 m to 8000 m above sea level the climate of the district very largely depend on altitude. The winter season is from about mid November to March. As most of the region is situated on the southern slopes of the outer Himalayas, monsoon currents can enter through the valley, the rainfall being heaviest in the monsoon from June to September. 2.4 Rainfall Most of the rainfall occurs during the period June to September when 70 to 80 percent of the annual precipitation is accounted for in the southern half of the district and 55 to 65 percent in the northern half. The effectiveness of the rains is related to the vegetation cover that is poor or/and has steep slopes or the soils have been so denuded that their moisture absorption capacity has become marginal. Rain gauging stations put up at seven locations by Meteorological department of Govt. of India, represent the settled land mass of Chamoli district. 3. OBSERVATIONS AT SITES The following observations are noted at sites: The slope materials involved in the landslide are debris consisting of unsorted, angular weathered fragmental material with partially-cohesive lime rich soil matrix. The fracture zones, as above discussed, well split along road cut and slope and slightly deepened forming fracture controlled streams. The bedrock along the roads is fragmented into angular boulders. The blocks are dislodged from the slopes and toppled down and slided down along road causing the rock-fall and rockslide. Rock fall is associated with rapid down slope movement of angular fragmental colluvial material and upper soil layer causing the huge rock avalanching at several places. Debris flows are also common along the first or second ordered stream valleys. Some live debris flows have been observed during the fieldwork at Pipalkoti. 4. NOTE ON CAUSE OF SLOPE INSTABILITY The following factors together have caused the present landslides in all the three areas. 4.1 Slope, Water and Gravity Water is the most important factor. After percolation it reduces cohesion of the loose ground and makes it prone to slide has been observed here that the rain water, while percolating down, carries with it fine clay and silty material which may form a thin band at the interface of loose debris and underlying hard and structurally folded, faulted/sheared limestone. In the presence of water this clayey base, becomes very plastic and provides slippery base for a loose overburden to slip downwards. The presence of water also has increased the weight of the colluvium increasing the influence of gravity, and the slope is also above the angle of repose (more than 35 ). 4.2 Lithology The rocks are Limestones and Phyllites. Limestones have the organochemical origin and have the non plastic fine texture. Phyllites are the products of low grade dynamo thermal metamorphism of argillaceous sediments. Both these rocks are highly fractured (Krishnan, 1982). Since the Pipalkoti area lies at the intersection point of central boundary thrust and Srinagar thrust, the formation of steep slopes in loose pulverized mass is very common. The similar type of lithology but comparatively less slopes exist near Gopeshwar and Nandprayag. 4.3 Associated Structures The parallel fracture zones are found along the limbs of extensive folds along cutting across the road. In addition, 809

3 from the satellite data of (1.0 m resolution) the many features like light tone parabolic surface, have been identified in the area. They indicate the sights of pre occurred landslides. Some dislodged material on steep slopes alongside the Mana road is also observed and interpreted in hazard zone. 4.4 Deforestation Unfortunately, there is a very sever deforestation that is observed especially around Nandprayag and Chamoli, that have initiated considerable sliding movements. In future they may be converted into huge vulnerable zones and may interrupt the traffic rather transportation in the area. 4.5 Seismisity The area lies in seismic zone IV during all other favorable conditions to landslide. The minute, feeble to slight seismisity may have acted as a triggering factor. Seismically triggered landslides are observed along the road from Chamoli to Gopeshwar. 5. REMEDIAL MEASURES The failure of the slope is mainly dominated by the phenomenon of saturation of slope material due to intensive rainfall and permeability of soil. With the view of the above discussions following remedial measures are being suggested: a) Retaining wall may be constructed against the slope along the down slope roadside. b) A network of surface drains is to be provided in the uphill side of the road for efficient and quick drainage. The exact location and path may be derived from field geometry. The drains along fracture controlled streams may be sealed near road. A roadside deep trench drain with lining near the road is proposed in the uphill side. c) Unsorted, loose, colluvial debris or the glaciofluvial material resting along the angle of repose may be removed wherever possible. d) The affected cross drainage or culverts can be suggested to be in proper place so that water can pass through culvert and the water coming during rainfall may be discharged without percolation. Some large box culverts have already been constructed along the valley associated with sharp road turn. e) The part of fracture zones near the roadside and also at the foundation of retaining wall may be sealed by using proper grouting techniques. f) It is good that the sustainable measures are being taken to protect the plants in the uphill side of the road. The same may be continued to avoid the future deforestation. g) There is a need to develop a technique to construct a road without any excavation along the slide hazard zone, in some economic way. As the landslides in Gharwal regions are mostly initiated during the excavation of road and gradually turn in huge slope failure. Road and roadside village vulnerability is very common. Judicious excavations seems to be only way to avoid future failures. h) Considering the lithology, structural geology, physiographic and the seismisity in the area, it is suggested that even after applying the necessary landslide preventive measures, the constant monitoring and maintenance will be essential and may be provided. 6. METHODOLOGY FOR LANDSLIDE HAZARD ZONATION MAPPING The software ILWIS (Integrated Land and Water Information System) developed by ITC, Netherlands have been used, as it contains both the modules of GIS and image processing. It has found to be very fast, accurate, reliable tool to process, analyze, and present the spatial data and to use it in any effective decision making. Especially for the terrain investigation and planning ILWIS is really the wonderful tool to work at strategic level. a) Base maps were imported in ILWIS after converting them into ILWIS data format. b) Geo-coding and geo-referencing have been taken care by creating a geo-reference and assigning the latlon coordinate system to the generated raster. c) The segment maps were digitized in the respective domain for boundaries of areas, contours and drainage (Kumthekar & Deshpande, 2004). Some additional segment layers for roads have also been generated. d) After point digitization the village maps were generated. e) DEM was prepared after interpolating the contour segment data. f) DEM was analyzed by spatial filtering and the slope maps were derived. g) From DEM flow, direction maps and flow accumulation maps were prepared. h) The degree map was classified as per Youngs classification. i) The satellite image data was imported and properly georeferenced with respect to the base map. j) The data was interpreted by the image interpretation keys to locate pre-occurred landslides and slide hazard zones. k) The slope map layer, flow accumulation layer and the drainage order map were added on RS data. This layer combination was used to extract the landslide hazard zone and the predictive places of land slides. They were mapped by point and polygon on screen digitization. l) From DEM as DTM the steriopairs were prepared for various generated rasters like slope degree map, aspect map, satellite data (color composite) etc. m) The generated steriopairs were viewed as anaglyphs and the predictive sites and pre-occurred landslides were confirmed along with their vulnerability (Lillisand & Kiefer 2000). n) The layouts of various layer combinations were prepared, containing north arrow, scale, legend and map-title. 810

4 The layouts have been interpreted and presented in Figures 1 5 including GIS Layer, Classified Slope Map and Landslide Hazard Zonation Map for Pipalkoti site and Hazard Zonation Maps Gopeshwar and Nandprayag site. Fig. 3: Landslide Hazard Zonation Map Pipalkoti Site Fig. 1: GIS Layer Pipalkoti Site Fig. 4: Landslide Hazard Zonation Map Gopeshwar Site Fig. 2: Classified Slope Map Pipalkoti Site Fig. 5: Landslide Hazard Zonation Map Nandprayag Site 811

5 7. CONCLUSIONS Unstable slopes are really the challenges for practicing geotechnical and transportation engineers in the mountain terrains like areas of Chamoli district of Uttarakhand. Remote sensing data has been proved to be effective in generating fast, reliable and accurate information related to the slopes stability in inaccessible areas of Uttarakhand state. GIS software used, ILWIS, is really a wonderful tool in inputting, analyzing and presenting the huge geospatial data in the present work. The task of contour and drainage like segment digitization, creating the DEM, and analyzing it for the slopes, flow accumulation, etc., found to be very interesting. The ILWIS operations carried out for landslide hazard zonation mapping especially the comparative study of slope maps, flow direction and flow accumulation maps, high resolution RS data etc., have been found to be accurate after generating the predictive point layer in the three studied areas. The accuracy was well assessed during the groundtruthing field visit. The typical parabolic shapes with reflectance to visible band were interpreted to be the pre-occurred landslides. After geocoding and geo-referencing the RS data as per the base map, it has been observed that the landslides in slide zone are frequent along road side. It was concluded that the excavation for road itself is the main cause to initiate a landslide in soft, structurally disturbed and high relief areas of Uttarakhand. The same phenomenon was observed on all the roads in Gopeshwar, Pipalkoti and Nandprayag. There is a need of RS and GIS based landslide hazard zonation mapping as one of the major part of preliminary geological investigations before undertaking any road project in Uttarakhand. It gives the predictive idea about the landslide prevention measures like retaining wall, gabion structures, proper drains or box culverts etc. Above all there is a need to develop an economic technique of designing the stretch of road without any excavation in slide hazard zones, so as to prevent the road induced landslides. For this, it is concluded, that the high resolution data interpretation in GIS environment is the only economic solution before doing any field survey in precipitous terrains like Garhwal Himalayas. REFERENCES Kolekar S. (2007). Applications of Remote Sensing and GIS in Landslide Hazard Zonation Mapping in Part of Western Ghats, M.E. Dissertation, Shivaji University, Kolhapur, Maharashtra, India. Krishnan M.S. (1982). Geology of India and Burma, CBS Publishers, Delhi. Kumthekar M.B. and Deshpande P.K. (2004). Geomorphometric Analysis for Sustainable Water Resource Planning and Management Using Remote Sensing and GIS, Proceedings of Symposium on Prediction in Unjudged Basin for Sustainable Water Resource Planning and Management (PUBSWRPM), BITS, Pillani, Lillisand and Kiefer (2000). Remote Sensing and Image Interpretation, John Wiley and Sons Inc., New York. 812