LANDSLIDES IN INDIA

The Himalayas are prone to landslides, especially during the monsoon months, from June to October. The types of landslides include block slumping, debris fall, debris slide, rock fall, rotational slip and slumping.
The pressure of population and the economic exploi­tation of the mountain region have been major causes for landslides. Turning forest land into orchards (apple growing being a lucrative activity), the increased construction and road building activities, and grazing by cattle are some of the activities that have led to increased chances of land­slides. Factors such as deforestation by the timber industry and shifting agriculture have also contributed to the re­moval of valuable vegetation cover, leading to soil erosion and frequent landslides. Efforts are, however, being made to lessen the impact of landslides.

Of late, several thematic maps depicting geology, slope, drainage, land use, relief and landslide hazard comprising about 2,500 sq km of Alaknanda valley from Devaprayag to Nandaprayag have already been prepared. A criterion for zoning for landslide hazard has also been developed by the Central Building Research Institute (CBRI). These maps are useful because they enable the concerned authori­ties to take decisions on techno-economic feasibility of land use, geographical location of dams, construction of bridges and housing complexes, alignment of roads, and in under­taking suitable measures to combat hazards and preserve the ecology of the Himalayas. An innovative and cost­effective technology for designing and building rigid masonry retaining walls characterised by reinforced backfill has been developed. The new expertise has been success­fully tested by constructing a retaining wall, 11 metre high, located on the Hardwar-Badrinath road in collaboration with the Border Road Organisation. The CBRI has taken up a project related to the engineering behaviour of joints, discontinuities, slip surfaces and shear zones with specific emphasis on landslides and hazard assessment.

Engineering methods such as building underground wells or tunnels and surface channels by pumping out groundwater are useful in preventing landslides. Since the methods of checkinb landslides are prohibitively expensive, it seems to be more rational to concentrate on the preven­tion of the consequences of landslides. Prior knowledge of landslide may enable authorities to evacuate people before the loss of lives and property; but this requires vigilance, forecasting and constant monitoring.