Space Based Assessment and Review of Chamoli, Uttarakhand (North India)
Rockslide Event of February 07, 2021
Abstract
Today with the advancement in remote sensing technology, very high
resolution imaging together with the capability of stereo data
acquisition has greatly enhanced the disaster management of high
hazardous and inaccessible mountainous terrain. The Rishiganga valley in
the Chamoli district of Uttarakhand (North India) was impacted by sudden
flash floods triggered due to a massive rockslide, caused by wedge
failure on 7th February, 2021. This event caused loss
of more than 200 lives besides widespread damage to hydropower projects
downstream. Due to the high altitude of the terrain, huge flow of mud
and debris down the valley and disruption of road connectivity, made the
disaster site inaccessible through conventional means. Therefore most of
the preliminary and subsequent studies carried out to assess the impact
and the causes of the rockslide have heavily relied on the space based
observations. The Indian Space Agency (ISRO) activated (Call Id-803) the
International Charter “Space and Major Disasters” (ICSMD) to image the
area of the disaster in Uttarakhand. The ICSMD is a consortium of space
faring members having a constellation (61 as on date) of highly agile,
multi-sensor and multi-resolution of satellite resources, which can be
tasked based on type of disaster and requirement, very rapidly over the
disaster affected areas to collect information on being activated. These
satellite datasets are provided freely by the space agencies under ICSMD
platform to serve humanitarian response for the disaster affected sites,
keeping aside the commercial interests. The present study is carried out
with two objectives first highlighting the role of space data in quick
satellite based disaster response for this particular event which
assisted the Uttarakhand State Disaster Management Agency (USDMA), Govt.
of Uttarakhand to take immediate steps to mitigate the problem. The
second objective tries to do an assessment and review of major studies
published in peer reviewed journal between February and July, 2021 on
this disaster globally to have a synthesised understanding of the event.
The pre and post multi-temporal and multi-sensor and multi-resolution
satellite data from ICSMD over Rishiganga and Dhauliganga valleys
provided first-hand information on the chronology of the events, causes
and process mechanism of this unique event and identifying locations
impacted downstream. The high resolution images were useful in providing
in depth understanding of the damage to hydropower projects, changes in
the river geomorphology and the river impoundment due to the obstruction
in the flow of one of the tributaries of the Rishiganga joining from the
northeast. The satellite based inputs proved to be valuable source of
information during this event for the state machinery. From all the
analysis it has emerged that the satellite images have unequivocally
allowed researchers to determine and quantify various terrain parameters
(volume, ele