14 July 2016

Bhote Kosi, Nepal: serious damage after the failure of a landslide dam in Tibet

Posted by dr-dave

Bhote Kosi, Nepal

The Bhote Kosi valley, to the north of Kathmandu, was one of the areas most seriously affected by the 2015 earthquake in Nepal.  Much of the damage was caused by landslides, which occurred on many slopes.  Fortunately the comparatively benign 2015 monsoon season did not exacerbate the problems as much as had been feared, but the consequences of the next period of intense rainfall always looked grim. This is a section of the valley for example:

Bhote Kosi

Google Earth imagery of the Bhote Kosi valley, showing the multiple earthquake induced landslide

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Apart from the local population, this valley is important as it is the alignment of the Arniko Highway, which is one of only two links between Nepal and Tibet, and thus China.

The 2016 monsoon has arrived with a bang, bringing very heavy rainfall.  Last week a very large flood swept down the Bhote Kosi, with devastating effects.  This was almost certainly a landslide dam break flood from a blockage in the river in Tibet, and it must have been large.  However, as yet the location is unclear.  The Nepal media has various reports of the impact of the flood – the Himalayan Times for example reported that:

The deadly earthquake of last year had devastated Liping and Tatopani Bazaar of Sindhupalchowk. Before these places could recover, flood in the Bhote Koshi River has left these towns so battered that reconstruction seems impossible.  Of the 200 houses in Tatopani and Liping bazaars, the Bhote Koshi flood has washed away 67 houses till today noon, police said.

The best image of the aftermath of the flood is on the Himalayan Times website:

Bhote Kosi

Bhote Kosi flood: Himalayan Times image of damaged slopes and houses

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It is clear that much of the damage has been caused by erosion of the toe of slopes by the flood, and subsequent slope failures.  There is also a good gallery of images here.  But by far the best illustration of the damage is in this Youtube video, even though it is not in English.  The journalist has followed the line of the highway up to Kodari.  The damage to this very important road is startling:

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Sadly this may not be the end of the problems. Dinanath Bhandari of Practical Action tweeted this image of forecast 24 hour accumulated rainfall in Nepal:

Bhote Kosi

Bhote Kosi: forecast 24 hour rainfall for Nepal via RIMES

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This is the forecast for two days time.  Whilst the heaviest rain is forecast to fall in the south, large parts of Nepal may get heavy precipitation.