| Popis: |
A huge landslide blocked the flow of the Chenab River near Nalda village on the morning of 13th August 2021 in the Lahaul-Spiti district of Himachal Pradesh, which led to the flooding of several villages (Nalda, Jasrath, Tarang, etc.) in the Udaipur subdivision. The slope (∼200 m height, ∼220 m width, and approx. 30 m depth) on the left bank of the Chenab River failed, which brought colossal soil and debris. This resulted in the damming of the Chenab River near Leh Baring village, which lies upstream of Nalda Village Bridge and opposite to Junde village, creating a huge water reservoir that later started overflowing, posing a major threat to downstream villages. This caused damage to the houses located downstream, which were submerged, animals were also washed away, and a large part of agricultural land was also inundated. The event was observed and studied using satellite images of high-resolution obtained from Google Earth and Sentinel 2A. The Spatio-temporal satellite images were used to observe the scars developed in the region over the past few years along the river, which evidently show the early signatures of slope failure. To analyze the stability of the hill slope, the factor of safety of the hill was evaluated using SLOPE/W GeoStudio software. Slope map and drainage density map were also generated, showing the vulnerability of the hill slope. The debris flow runout simulation of the event was performed using the RAMMS debris flow model to calculate the volume of the landslide and the water reservoir formed due to damming of the Chenab River. The volume of the landslide (debris) due to slope failure was approx. 2.22 million m3 and the water reservoir volume was approximately 0.3 million m3. The significant factors accountable for the landslide i.e. the slope of the hill, geomorphology of the area, lithology (phyllites), presence of narrow and elongated valleys, the confluences of the river in the area, and continuous rainfall in the region during that period were evaluated. The paper also emphasizes monitoring of such vulnerable areas based on high-resolution time series satellite images, which are available on a regular basis to avoid the loss of human lives in the future. |
