Prognosis and mitigation strategy for major landslide-prone areas Varunavat Parvat landslide in Uttarkashi

DPM
17,5
626
Plate 5.
Close view of Horticulture
Colony – Masjid Mohalla
slide
large slide zones in Bus stand, Masjid Mohalla and Horticulture colony areas. Present
study has revealed that during the series of cloud burst events of July/August, 2003 the
Ramlila Ground slide was triggered as a small slide zone of 40m length and 30m width
in the close vicinity of large active slide of Tambakhani on Varunavat Parvat. The
active slide zones of Ramlila Ground slide witnessed rapid headward shift during the
months of August and September, 2003 and completely merged with the active scarp of
large Tambakhani slide on 23 September, 2003, consequently, the slide debris and
rolling boulders started hitting multi-storied hotels in the Bus Stand area. It was with
in the short span of 24 hours that this slide zone transformed into a large complex slide
and multi-storied hotels, commercial and residential complexes at Bus Stand along
with 100 m stretch of National Highway were buried under the huge volume of slide
debris that gradually extended to Ramlila Ground. On 1 October 2003 the head-ward
shifting of another active slide scarp (developed in the upslope of Masjid Mohalla and
Horticulture Colony localities of Uttarkashi township) completely merged with the
active slide scarp of Ramlila Ground and Tambahkani slide (Plate 1), consequently, yet
another large slide zone emerged and slide debris and boulders damaged major part of
Masjid Mohalla and Horticulture colony.
Causative factors for these sliding events have been analyzed on the basis of
satellite image study and detailed field investigations. Interpretation of pre and post
disaster satellite images from Indian Remote Sensing Satellites (IRS 1D LISS-III False
Colour Composites of 13 April 2003 and IRS-P6 LISS-III False Colour Composites of 16
April 2004; 7 September 2004; 11 April 2005 and 9 August 2005) has been carried out to
precisely mark the extent of various landforms, extension of major discontinuities and
changes in the landscape after landslide activity of September/October, 2003. ARC GIS
9.0 software was used to create the morphotectonic map through integration of GIS
layers of geo-environmental parameters viz. geomorphology, structure and landslide in
order to assess the influence of tectonics on the landforms and landslide activity.
Response
Late in the evening on 23 September, 2003 some locals and officials of Irrigation
Department noticed major sliding activity in the form of large heap of debris material