1.65 km2

1.65 km2

Figure 17.1. Tsho Rolpa Risk Reduction Project in Nepal as observed anticipatory adaptation.

The Tsho Rolpa is a glacial lake located at an altitude of about 4,580 m in Nepal. Glacier retreat and ice melt as a result of warmer temperature increased the size of the Tsho Rolpa from 0.23 km2 in 1957/58 to 1.65 km2 in 1997 (Figure 17.1). The 90100 million m3 of water, which the lake contained by this time, were only held by a moraine dam - a hazard that called for urgent action to reduce the risk of a catastrophic glacial lake outburst flood (GLOF).

If the dam were breached, one third or more of the water could flood downstream. Among other considerations, this posed a major risk to the Khimti hydropower plant, which was under construction downstream. These concerns spurred the Government of Nepal, with the support of international donors, to initiate a project in 1998 to lower the level of the lake through drainage. An expert group recommended that, to reduce the risk of a GLOF, the lake should be lowered three metres by cutting a channel in the moraine. A gate was constructed to allow for controlled release of water. Meanwhile, an early warning system was established in 19 villages downstream in case a Tsho Rolpa GLOF should occur despite these efforts. Local villagers were actively involved in the design of the system, and drills are carried out periodically. In 2002, the four-year construction project was completed at a cost of US$3.2 million. Clearly, reducing GLOF risks involves substantial costs and is time-consuming as complete prevention of a GLOF would require further drainage to lower the lake level.

Sources: Mool et al. (2001); OECD (2003b); Shrestha and Shrestha (2004).

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