Release of Landslide Hazard Zonation Atlas of India

New Delhi
January 30, 2004

Vast expanse of areas in the country, particularly, in the Himalayan and other hilly terrains, being highly fragile, are perennially under repeated threats of landslides and mass movements. Increase in population and rapid urbanisation have led to expansion of construction activities in hilly terrains and have catapulted frequency of landslides to dramatic proportions in recent decades. Most importantly, there has been paradigm shift in the policy of Government of India towards prevention and mitigation as against the traditional policy of response and relief in post-disaster situation.

Recognising the above, the Building Materials and Technology Promotion Council (BMTPC), Ministry of Urban Development & Poverty Alleviation, New Delhi and Centre for Disaster Mitigation & Management (CDMM), Anna University, Chennai have prepared the landslide Hazard Zonation Atlas of India, This Atlas is a natural extension of the Vulnerability Atlas of India with respect to earthquakes, cyclones and floods, published earlier by the BMTPC.

The Atlas presents the first ever Geographical Information System (GIS) based landslide inventory map and landslide hazard zonation maps of India at the scale of 1:6 million. A notable complimentary initiative in the Atlas is the inclusion of some of the worst landslides of India like Great Malpa Rock Avalanche of 1998, the Alaknanda Tragedy of 1970 and Amboori landslide of Kerala of 2001, which are still fresh in the minds of people as nightmares. These have resulted in creating wide public awareness on the subject, in the recent past, thereby justifying the need for this Atlas.

The Atlas will be useful in enhancing the preparedness to face the impact of future landslides and would pave way for effective decision making and planning micro level or large scale mapping for various development and regulatory activities in the mountaneous regions.

Summary

The First Landslide Hazard Map of India 

Landslide are among the major hydro-geological hazards that affect large parts of India, especially the Himalayas, the Northeastern hill ranges, the Western Ghats, the Nilgiris, the Eastern Ghats and the Vindhyas, in that order. In the Himalayas alone, one could find landslides of every fame, name and description – big and small, quick and creeping, ancient and new. Similarly most of the northeastern region is bristling with landslides of a bewildering variety. Then, there are landslides in the Western Ghats in the south, along the steep slopes overlooking the Konkan coast. Landslides are also very common in the Nilgiris, characterized by a lateratic cap, which is very sensitive to mass movement.

In our country, there have been numerous catastrophes due to landslides, unique and unparalleled. In the recent memory, the Darjeeling floods of 1968 destroyed vast areas of Sikkim and West Bengal by unleashing some 20,000 landslides, killing thousands of people. These landslides occurred over a three day period with precipitation ranging from 500 to 1000 mm in an event of a 100 year return period. The 60km mountain highway to Darjeeling got cut off at 92 places resulting into total disruption of the communication system. Yet another landslide tragedy of unprecedented dimension was the Alaknanda Tragedy of July 1970 that resulted from the massive floods in river Alaknanda, upon breach of a landslide dam at its confluence with river Patal Ganga. More recently, the Malpa rock avalanche tragedy, hit headlines as it instantly killed 220 people and wiped out the entire village of Malpa on the right bank of river Kali in the Kumaun Himalaya. Landslides in the southern India also revived public imagination when the recent Amboori landslide in the State of Kerala killed 23 people. In the avalanche value of the Nilgiris, majority of landslides do occur in a loose cover of debris consisting of boulders. The major landslides in the Nilgiri hills are the Runnymede landslide, the Glenmore slide, the Conoor slide and the Karadipallam slide. In the recent times, casualties and damage due to landslides have increased in the Nilgiri hills. During October-November 1978, 90 people died. The economic losses due to landslides are enormous, not to speak of strategic stakes.

In the above context, it was logical for the Building Materials and Technology Promotion Council, to extend the scope of the Vulnerability Atlas published by it in 1996 to include consideration of hazards due to landslides, alongside earthquakes, floods and cyclones. The first landslide hazard map of India now being published by BMTPC as a natural extension of the earlier Atlas is the result of this initiative. It was a joint effort by the Centre for Disaster Mitigation and Management, Anna University, Chennai and BMTPC, New Delhi.

The strategy and the approach to landslide hazard mapping were based on the current state-of-the-art, taking fullest advantage of the enormous amount of information and data on Indian landslides, mostly published and some unpublished. The thematic factor maps used in hazard mapping on a GIS platform are as listed in Table 1.

Table 1: List of published maps used for the preparation of Landslide Zonation Map of India

These maps were processed to achieve a common base on a GIS platform.

These maps were integrated on the GIS platform to produce the landslide hazard map by following the procedure outlined in Figure 1. In its simplest form, the four step procedure can be summarized as follows:

1. Production of Landslide Inventory Map of India making use of all the published information and data on landslides.

2. Integration of all the factors maps into an inferred landslide hazard map by using subjective weightings, relaying on the hazard history of the area in the backdrop of the Landslide Inventory Map.

3. Comparison of the inferred landslide hazard map with the landslide inventory map, and revaluation of the “weightings”.

4. Production of reversed landslide hazard map and its comparison of the landslide inventory map and iteration of the process until the best match is found between the observed hazard (inventory map) and the inferred hazard.

The landslide hazard map developed using the above procedure is presented in Figure 2. The importance of this map in the first quantitative overview of the distribution of landslide hazards at a scale of 1:6million. While it provides the direct bases for macro level planning, especially of landslide disaster mitigation initiatives, the state-of-the-art methodology so developed will find direct applicability in large scale landslide hazard mapping, flagged as a task of national importance.