Alaknanda River Has Changed Colour After Uttarakhand Floods, Here's Why

The Alaknanda rises in the Satopanth glacier and is met at Vishnuprayag by the Dhauli Ganga, which carried deposits from the flash floods on February 7. The Alaknanda is then met by the Nandakini at Nandaprayag, Pindar at Karnaprayag, Mandakini at Rudraprayag, and Bhagirathi at Devprayag. Thereafter, it is known as Ganga, which flows to Rishikesh and Haridwar.

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The word 'prayag' means confluence, hence, the rivers join together to flow forward as the Ganga. But some of the pictures show the Alaknanda appear to be a different colour where it meets Bhagirathi at Devprayag during different seasons, and each time the region is hit by a calamity.

Is it just the change of seasons, or has the nature of the river changed over time? Are floods to be blamed for it? Let's find out.

Why the colour change

At Devprayag, the river was muddied by the landslide and flash flood in the Rishi Ganga and Dhauli Ganga on February 7. The muddiness, which persisted on Friday, is the result of suspended sand, clay, rocks, in the water making it look brown in colour, geologists and environment scientists in Uttarakhand said.

The river is usually clear in winter, Uttarakhand Pollution Control Board (UPCB) environment engineer Ankur Kansal said; it becomes muddy only in the monsoon. Kansal could not recall when the Alaknanda had been seen this muddy in winter.

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The flood weakened downstream of Tapovan, and the mud and debris reached Rishikesh on February 11, travelling 250 km in three days. UPCB data show the Ganga was clean at Rishikesh and Haridwar on February 6; it was classified as ¡°muddy¡± on February 11, and is currently ¡°turbid¡±.

What experts say

The volume of debris that fell into the Rishi Ganga and was carried downstream to the Alaknanda is difficult to estimate, Dr Kalachand Sain, Director, Wadia Institute of Himalayan Geology, said.

But it is estimated that a glacial rock mass of 0.2 to 0.4 million cubic metre volume fell from about 5,600 m to 3,600 m along a 40-degree incline, transforming into a muddy slurry as it picked up vegetation and loose rock along the way, Dr Sain said.

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Prof Y P Sundriyal of the Hemvati Nandan Bahuguna Garhwal University in Srinagar said no timeframe can be given for the water to flow clear again.

Other causes of change

Further, a search for images of Devaprayag yields a mix and it seems that the color of the waters in both Alaknanda and Bhagirathi rivers continuously swings back and forth with the change of seasons.

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Another reason for the change of colour can be -- Tihri dam. The dam is situated on Bhagirathi river, as a result silt gets settled in the dam and a much clear river emerges thereafter. Alaknanda covers much longer distance in greater Himalayan region as compared to Bhagirathi and that might be another cause as the river appear more blue green near the glacier but collects dust, sand as it goes further and covers a much longer distance.