Accelerated mass movement activities due to increased rainfall in the Nainital township, Kumaun Lesser Himalaya, India
Gupta, Vikram; Tandon, Ruchika S.; Venkateshwarlu, B.; Bhasin, Rajinder K.; Kaynia, Amir M.
published: Apr 1, 2017
published online: Mar 1, 2017
manuscript accepted: Feb 13, 2017
manuscript revision received: Feb 6, 2017
manuscript revision requested: Feb 3, 2017
manuscript received: Jan 3, 2017
ArtNo. ESP022006101003, Price: 29.00 €
Abstract Nainital township is known to be vulnerable to landslides and related mass movement activities since past and their record in the area dates back to as early as 1867. Previous studies estimate that about half the area of Nainital basin is covered with debris generated by landslides. GPR studies carried out in the area confirm that the thickness of the debris on the slope varies between 2 and 10 m. Geologically, the area constitute limestone, shale and slate belonging to Blaini, Krol and Tal formations of the Lesser Himalaya. These rocks are traversed by a major Nainital Lake Fault that runs all along the area in the NW-SE direction and the Hanumangarhi Fault that runs almost E-W. The off-shoots of these faults have also been many sections. The geotechnical properties of rocks and soils constituting the slope like poor rock mass conditions, negligible cohesion and moderate friction angle of the debris material also constitute a propensity towards its failure. It has further been observed that the area receive higher amount of rainfall particularly after 2009. There is an increase of about 73% annual precipitation as well as precipitation during monsoon season. This has caused the intensity of rainfall to have risen from 30 mm per day during 1995–2009 to 51 mm per day during 2010–2015. This increased rainfall intensity in the township has caused many slopes in the area to fail.