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Himalayan Tsunami

Saturday, May 5th, 2012
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Dramatic rock formations below Annapurna 4 at the headwaters of the Seti River where geologists think an avalanche blocked the river 800 years ago. A similar avalanche on Saturday morning seems to have caused the flood on the Seti that led to loss of life and damage to infrastructure. PIC: GUDMUNDUR PALL OLAFSSON

What makes Nepal scenic is also what makes it so vulnerable to earthquakes, avalanches, landslides and floods. Pokhara’s scenery, in particular, is spectacular because the terrain is so vertical: the city lies only 900m above sea level and the mountains rise to above 8,000m to the north within a horizontal distance of only 35 km.

Amateur videos of Saturday morning’s flashflood roaring down the Seti River showed a wall of dirty brown water carrying floating debris that reminded us of pictures of the Japan tsunami. Shocking as these images were, they pale in comparison to what happened 800 years ago on this same river.

Pokhara is situated on the gigantic debris fan of a cataclysmic flashflood which geologists say was caused by the Seti bursting through a landslide or avalanche dam in its headwaters below Annapurna 4 about eight centuries ago. They have found a soft conglomerate layer on top of granite bedrock behind Machapuchre which they say is where the rockfall, probably caused by an earthquake, occurred in the 15th century.

Such river blockages are common across the Himalaya and occur at regular intervals. The Alakananda River in India was blocked by a landslide after an earthquake and unleashed a gigantic flood downstream in 1894. In Nepal, there is geological evidence of huge pre-historic floods on the Budi Gandaki, Kali Gandaki, Dudh Kosi, Arun, Tamur and most Himalayan rivers.

The Annapurna flood event 800 years ago was the most recent, and the terraced canyons around Pokhara bear witness to the violence of a flood that deposited boulders, sand and silt up to 100m thick in Pokhara Valley, blocking existing rivers and creating the Phewa, Begnas, Rupa and other lakes. One relic of this flood is the huge five-storey high Bhim Dhunga boulder that still rests in Pokhara Campus at the exact spot where it was deposited eight centuries ago. The video of Saturday’s flood shows the water tumbling across other boulders along the Seti banks, and roaring through canyons carved out by the river in the centuries after the flood.

The vertical terrain also gives Pokhara the highest rainfall in Nepal of more than 4,000mm per year in some places. The precipitation doesn’t just increase the flood danger, but also triggers massive landslides every monsoon in Kaski and surrounding districts.

DANGEROUSLY PRETTY: The raw beauty of Machapuchre from the headwaters of the Seti River is also what makes it so dangerous.The steep snowfields are prone to avalanches that can devastate settlements downstream. PIC : KUNDA DIXIT

Saturday’s flood wasn’t caused by a glacial lake outburst, nor can it be directly attributed to global warming. The dramatic terrain and high precipitation make Pokhara vulnerable to ice and water-induced disasters, however, climate change could exacerbate the problem making such floods bigger and more frequent. The relatively high casualty rate this time was probably due to settlements and sand mining activity along the river by people who don’t expect floods during the dry season.

Questions will immediately be raised about what we can do about it. Nothing can ever prepare us for cataclysmic floods like the one 800 years ago, but we can have a multi-disaster preparedness plan. Our ancestors were wise and located their permanent settlements high above the water, coming down to the river only to cross them or to visit the water mill to grind grain. Today, the there are large settlements along rivers, highways and hydro-electric projects lie directly on the path of future flashfloods.

The only way to deal with this is not to put all our big projects on one river basin, have an early warning system in place, monitor rivers regularly for blockages especially after earthquakes, and discourage large settlements directly beside rivers. We can also reduce flood damage by putting an immediate stop to rampant sand and gravel mining of river beds, which make floods much more devastating because of the higher velocity of water without the boulders to obstruct flow.

Sadly, in Nepal’s contemporary politics-heavy governance there just isn’t the culture of preparedness and prevention. The media is always there after an event, and doesn’t adequately serve to warn of future disasters. The state is distracted and woefully ill-equipped to deal with future flood events, so it will be up to local communities to make the best of it and to put their own plans in place.

Published in Republica 6 May 2012

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One Response to “Himalayan Tsunami”

  1. Avalanche-Triggered Flood Kills in Nepal | Lexlimbu on Says:

    [...] lost lives, the missing and the friends &families.PS. You might want to read this article from Nepali Times to understand more regarding why such a flood took place this morning. [...]


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