Saptakoshi River - Glaciers, Glacier Lakes and Outburst Floods

Glaciers, Glacier Lakes and Outburst Floods

In the Himalayas, glaciers are melting and retreating, which produces lakes insecurely dammed by ice or moraines. These dams are at risk of breaking, causing a Glacial Lake Outburst Flood (GLOF) with flows as great as 10,000 cubic metres a second.

In the past two decades GLOF has become a topic of intense discussion within the development community in Nepal. The Dig Tsho GLOF on 4 August 1985, completely destroyed the nearly completed Namche hydropower plant and all bridges, trails, cultivation fields, houses and livestock along its path to the confluence of the Dudh-Koshi and the Sun-Koshi rivers over 90 km (56 mi). The Dig Tsho glacier is on the terminus of the Langmoche Glacier. This event brought into focus the seriousness of such events and the studies to assess the glaciers, glacier lakes and GLOF followed.

Studies of the glaciers and glacier lakes were carried out in 1988 by a joint Sino-Nepalese team. The Arun-Koshi river basin hosts 737 glaciers and 229 glacier lakes, out of which 24 lakes are potentially dangerous. The Sun-Koshi basin is home to 45 glacier lakes, of which 10 are potentially dangerous. According to a Sino-Nepalese study, since the 1940s on at least 10 occasions, glacier lakes burst their dams. Among them were five bursts in three glacier lakes in the Arun River Basin and four in three glacier lakes of the Sun Koshi River Basin.

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