Dharali Cloudburst: Did River Kheer Ganga Follow Its Old Route? ISRO Satellite Images Stir Debate

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The destruction in Uttarkashi's Dharali raised questions whether Kheer Ganga river, which caused the devastation, simply returned to an ancient path long buried under settlements
The destruction in Uttarkashi's Dharali town has raised troubling new questions, not just about what happened on August 5, but about whether the Kheer Ganga river, which caused the devastation, simply returned to an ancient path long buried under settlements. New satellite images released by the Indian Space Research Organisation (ISRO) and the National Remote Sensing Centre (NRSC) show that the river, instead of curving as it usually does before meeting the Bhagirathi, surged straight through buildings and roads, as if reclaiming an older route.
Captured by the Cartosat-2S satellite, the high-resolution images offer a before-and-after view of the disaster zone. The first image, from June 13, shows Dharali in a calm state. The second, taken on August 7, just two days after the flood, reveals an area covered in mud, debris, and rock over an estimated 20 hectares, right up to the banks of the Bhagirathi river.
At first, a cloudburst was suspected. But that theory was quickly ruled out. The Meteorological Centre confirmed that only 24 mm of rainfall was recorded across Uttarkashi district on August 5, far below the 100 mm-per-hour threshold needed to declare a cloudburst. In fact, Uttarkashi has seen among the lowest rainfall figures in the state this monsoon.
If not rain, then what?
One compelling theory comes from D D Chauhan, visiting professor at the Nityanand Research Institute, Doon University. He believes the river may have reverted to an older course under extraordinary pressure. 'The Kheer Ganga usually takes a bend before meeting the Bhagirathi," said Chauhan, adding, 'But on August 5, the river came down carrying heavy debris and boulders, and instead of turning, it moved straight, right through an area where homes, hotels, and lodges had been built."
Chauhan suggested that this abrupt shift may have been triggered by a glacial lake burst. Several small glacial lakes feed the Kheer Ganga at high altitudes. With continuous rains, even if not extreme, the water levels in one of these lakes may have breached a threshold, releasing a sudden and massive outflow. The lake water, mixed with glacial debris, would have surged into the river, amplifying the volume and destructive power of the Kheer Ganga without needing a cloudburst.
The satellite images appear to support this theory. They show how Dharasu, the larger region around Dharali, is surrounded on three sides by the Bhagirathi. The Kheer Ganga cuts through from the mountains and typically turns before merging with the Bhagirathi. On August 5, it didn't turn.
The river's straight run through residential and commercial areas, where it wasn't expected to flow, suggests either a diversion caused by forceful debris movement or a return to a previous natural path that had been altered or encroached upon over time.
ISRO has confirmed that the debris field covers 20 hectares and reaches the Bhagirathi's banks. Further scientific analysis is underway to establish whether a glacial lake outburst flood (GLOF) was the primary trigger, and whether future risks are likely in similar Himalayan towns built close to dynamic river systems.
The Dharali tragedy draws eerie parallels with past disasters in Uttarakhand. In February 2021, a glacier collapse in Chamoli led to a catastrophic flood in the Rishi Ganga and Dhauliganga rivers, killing more than 200 people. In 2013, the infamous Kedarnath calamity was also caused by the breaching of a glacial lake, leading to a death toll of nearly 5,000.
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