Landslide Hazard in the Nainital township, Kumaun Himalaya, India: the case of September 2014 Balia Nala landslide

摘要

Nainital township located in the Kumaun Lesser Himalaya is known to be vulnerable to landslides since past, and it has been reported that half of the area of the township is covered with debris generated by landslide. A disastrous landslide in the Rais Hotel locality on the right side of the Balia Nala struck during September 2014 after the excessive rainfall. Geologically, the area dominantly comprises limestone with shale and slate which are highly crushed and weathered due to the presence of the Nainital Lake Fault that extends into Balia Nala as Balia Nala Fault. Ground-penetrating radar study depicts that these rocks are overlain by thin debris cover of the order of 5-10 m. The geotechnical studies confirm these rocks and the overlying soil as having very low strength. The landslide has triggered because of the excessive rainfall in the area. It has been observed that rainfall in the area has increased since 2010. An increase in more than 100 % intensity of rainfall during the monsoon from an average 33 mm per day (1995-2013) to 68 mm per day in 2014 is the main triggering factor for the initiation of landslide. The area has been continuously monitored for the last more than 3 years, as the distress in the area has been reported in the form of development of cracks. In order to prevent further sliding, immediate measures have to be taken to channelise water on both sides of the hill slopes so that the ingress of water into the slope is minimum.