Melamchi Flood- 15 June 2021

A flood in Melamchi Municipality of Sindhupalchowk district has caused a huge loss of life and property. The floods assumed to be caused by the huge landslides in the upstream region close to the glaciated region of the Melamchi watershed that blocked the Melamchi river. A huge landslide- blocked lake formed and breached on the Tuesday evening which caused extensive damage from Helambu, Melamchi Bazaar to the lower coastal area. More than 50 people are missing (https://myrepublica.nagariknetwork.com/news/more-than-50-people-missing-in-melamchi-flood/?categoryId=81) and 500 families are displaced (https://melamchimun.gov.np/en). This catastrophic flood is also assumed to be occurred due to the glacial lake outburst as news published in the Business Standard (https://www.business-standard.com/article/current-affairs/glacial-outburst-suspected-to-be-behind-flash-floods-in-central-nepal-121061700125_1.html).

Here, I tried to show some changes that occurred in the Melamchi watershed and its downstream region using optical and SAR images. I used Planet images of 21 June 2021, obtained from Milan Shrestha, Arizona State University, USA for the upstream region. The optical images are widely covered by the monsoon cloud in the region and difficult to get clear images to cover the area. Therefore, I checked Sentinel-1 Synthetic Aperture Radar (SAR) images of the European Space Agency using the Google Earth Engine platform. Here, I am showing images that show the changes in the Melamchi watershed using these images.

Figure 1: Pre and post-event Sentinel-1 SAR image from the Helambu Rural Municipality, where landslides assumed to be occurred. Some amplitude change (perhaps caused by the landslides) has been detected in the upper reach.
Figure 2: Planet image of 21 June 2021 from the upper reach of the Melamchi watershed. Huge deposition (red circle) has been observed
Figure 3: Planet image showing location of additional landslide in the Helambu Rural Municipality.
Figure 4: Extensive deposition and erosion has been observed in the Helambu Rural Municipality, upstream of the Melamchi bazaar.
Figure 5: Pre and post-event Sentinel-1 SAR image from the Melamchi Municipality, which is severely hit by the flood. Significant amplitude change has been detected in the Melamchi bazaar area and its downstream.
Figure 6: Pre and post-event Sentinel-1 SAR image from downstream of the Melamchi Municipality (i.e., Indrawati, Chautara).
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