What makes Nepal scenic is also what makes it so vulnerable toÂ earthquakes, avalanches, landslides and floods. Pokharaâs scenery, inÂ particular, is spectacular because the terrain is so vertical: the cityÂ lies only 900m above sea level and the mountains rise to above 8,000m toÂ the north within a horizontal distance of only 35 km.
Amateur videos of Saturday morningâs flashflood roaring down the SetiÂ River showed a wall of dirty brown water carrying floating debris thatÂ reminded us of pictures of the Japan tsunami. Shocking as these imagesÂ were, they pale in comparison to what happened 800 years ago on this sameÂ river.
Pokhara is situated on the gigantic debris fan of a cataclysmic flashfloodÂ which geologists say was caused by the Seti bursting through a landslideÂ or avalanche dam in its headwaters below Annapurna 4 about eight centuriesÂ ago. They have found a soft conglomerate layer on top of granite bedrockÂ behind Machapuchre which they say is where the rockfall, probably causedÂ by an earthquake, occurred in the 15th century.
Such river blockages are common across the Himalaya and occur at regularÂ intervals. The Alakananda River in India was blocked by a landslide afterÂ an earthquake and unleashed a gigantic flood downstream in 1894. In Nepal,Â there is geological evidence of huge pre-historic floods on the BudiÂ Gandaki, Kali Gandaki, Dudh Kosi, Arun, Tamur and most Himalayan rivers.
The Annapurna flood event 800 years ago was the most recent, and theÂ terraced canyons around Pokhara bear witness to the violence of a floodÂ that deposited boulders, sand and silt up to 100m thick in Pokhara Valley,Â blocking existing rivers and creating the Phewa, Begnas, Rupa and otherÂ lakes. One relic of this flood is the huge five-storey high Bhim DhungaÂ boulder that still rests in Pokhara Campus at the exact spot where it wasÂ deposited eight centuries ago. The video of Saturdayâs flood shows theÂ water tumbling across other boulders along the Seti banks, and roaringÂ through canyons carved out by the river in the centuries after the flood.
The vertical terrain also gives Pokhara the highest rainfall in Nepal ofÂ more than 4,000mm per year in some places. The precipitation doesnât justÂ increase the flood danger, but also triggers massive landslides everyÂ monsoon in Kaski and surrounding districts.
Saturdayâs flood wasnât caused by a glacial lake outburst, nor can it beÂ directly attributed to global warming. The dramatic terrain and highÂ precipitation make Pokhara vulnerable to ice and water-induced disasters,Â however, climate change could exacerbate the problem making such floodsÂ bigger and more frequent. The relatively high casualty rate this time wasÂ probably due to settlements and sand mining activity along the river byÂ people who donât expect floods during the dry season.
Questions will immediately be raised about what we can do about it.Â Nothing can ever prepare us for cataclysmic floods like the one 800 yearsÂ ago, but we can have a multi-disaster preparedness plan. Our ancestorsÂ were wise and located their permanent settlements high above the water,Â coming down to the river only to cross them or to visit the water mill toÂ grind grain. Today, the there are large settlements along rivers, highwaysÂ 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 oneÂ river basin, have an early warning system in place, monitor riversÂ regularly for blockages especially after earthquakes, and discourage largeÂ settlements directly beside rivers. We can also reduce flood damage byÂ putting an immediate stop to rampant sand and gravel mining of river beds,Â which make floods much more devastating because of the higher velocity ofÂ water without the boulders to obstruct flow.
Sadly, in Nepalâs contemporary politics-heavy governance there just isnâtÂ the culture of preparedness and prevention. The media is always thereÂ after an event, and doesnât adequately serve to warn of future disasters.Â The state is distracted and woefully ill-equipped to deal with futureÂ flood events, so it will be up to local communities to make the best of itÂ and to put their own plans in place.
Published in Republica 6 May 2012
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