Treading on Thin Ice

IMPACT OF GLOFs ON DOWN STREAM COMMUNITIES.

An increase in the frequency of GLOF events will have catastrophic social and economic impacts for the communities occupying the Himalayan valleys. In addition to the loss of hydropower stations such as the Dig Tsho GLOF event in 1985, outbursts can have substantial impacts on the agricultural economy that support most of the populations in these regions (Bajracharya et al., 2007). For example, a historic outburst event in the Nepal in ca. 1555 inundated 450km² of the Porkhara basin with up to 50-60m of debris completely covering the valley below (Richardson and Reynolds, 2000). A more recent outburst from the Langmonde Glacier in Khumbu, Nepal in 1985 deposited almost 900,000m³ of eroded moraine material over the first two kilometres below the lake (Kattleman, 2003). The removal of debris following an outburst is labour-intensive as access, particularly in the areas directly below the outburst prevents machinery being brought in the aid the operation. Alternative food sources may also be affected, such as fish populations which took approximately 10 years to recover following the Lugge Tsho outburst in the East Pho Chu Valley, China in 1994 (Watanbe and Rothacher, 1996). Therefore, ignoring the direct impacts on lives and property, the long-term impacts for communities can be highly significant and as more people and industries locate to these areas, the need for effective mitigation techniques is of growing relevance.

MITIGATION METHODS

Due to the isolation of many of these glacial lakes, attempts to mitigate against outbursts are highly problematic. With over 9,000 glacial lakes in the Himalayas and the limited resources available, inventories using remote sensing have been conducted to identify which lakes pose the most imminent threat to breach and mitigation has been focused on reducing the risk in these areas (Richardson and Reynolds, 2000). An inventory in Nepal classified four glacial lakes as ‘dangerous’ based on the lake size, estimated dam stability and the presence of communities downstream (Kattelmann, 2003). These included Tsho Rolpa, Imja, Thuglagi and Lower Banin and mitigation methods have been implemented in Tsho Rolpa to reduce risk of a future outburst. Adopting successful techniques used in the Peruvian Andes, a trial siphon (triple-inlet pipe) was installed in 1995, with the capacity of transporting 170 litres of water per second from the lake to an outlet below the moraine (Richardson and Reynolds, 2000). Although it was largely successful, snow loads in the winter caused the pipe to break up. Thus, in 2000 an artificial spillway, costing US$2.7 million, including US$1.1 million in transport costs, was installed lowering the lake level by three metres (Kattelmann, 2003). However, a recent report by UNESCO indicates that that the spillway has had no significant effect on reducing the risk of an outburst as increased snow melt have increased the discharge entering the dam (Figure 1) (Chalise et al., 2006). This suggests that further research needs to be undertaken to assess the success of these methods against changes in the dynamics of the lake itself as it is apparent that a practice that may be successful under current conditions may not be as effective under pressures of increased snow melt.

Figure 1: Discharge at Tsho Rolpa, Nepal following the installation of an artificial spillway in 2000 (Source: Chalise et al., 2007).

CONCLUSIONS
The impacts of GLOF on local communities in the Himalayan regions can be substantial, causing loss of property, agricultural land and energy sources. However, provided that glacial lakes are routinely monitored, and mitigation methods are put in place at hazardous lakes, Kattelman (2003) argues that it is technically feasible to reduce the possibility of outbursts in these regions. However, as glacial lakes continue to grow, attempting to identify and prioritise which lakes pose the most imminent threat will become increasingly difficult. This is encapsulated by the four hazardous lakes in Nepal, which have all formed within the last 30-45 years, and have grown by an average 33-71m yr^-1 (Richardson and Reynolds, 2000). Although the costs of these mitigation methods may be significant in the short-term balanced against the potential long-term impacts due to an outburst it is apparent that more investment needs to be spent protecting these remote communities from GLOFs. With rapid development occurring in these areas, the need to reduce the risk of outbursts in these areas is growing in importance, and will only increase as the number of hazards, whether moraine-dammed or ice-dammed, continues to increase with climate change. 

Reference:

Bajrachrarya, S. R., P. K. Mool and B.R. Shrestha (2007) ‘Impact of Climate Change on Himalayan Glaciers and Glacial Lakes: Case Studies of GLOF and Associated Hazards in Nepal and Bhutan, ICIMOD: Kathmandu.

Chalise, S.R., M. L. Shrestha, O. M. Bajrachrarya and B.R. Shrestha (2006) 'Climate Change Impacts on Glacial Lakes and Glacerised Basins in Nepal and Consequences for Water Resources, UNESCO: Nepal.

Hewitt, K. and J. Liu (2011) ‘Ice-dammed lakes and outburst floods, Karakoram Himalaya: historical perspectives on emerging threats’, Physical Geography, 31,6: 528-551.

Kattelmann, R. (2003) ‘Glacial lake outburst floods in the Nepal Himalaya: a manageable hazard?’, Natural Hazards, 28: 145-154.

Qingha, F. (1991) ‘Characteristic of glacial outburst flood in the Yarkant River, Karakoram Mountains’, GeoJournal, 25,2: 255-263.

Richardson, S.D. and J.M. Reynolds (2000) ‘An overview of glacial hazards in the Himalayas’, Quaternary International, 65: 31-47.

Shrestha, A. B. and R. Aryal (2011) ‘Climate change in Nepal and its impacts on Himalayan glaciers’, Regional Environmental Change: Natural and Social Aspects, 11, S1: 565-577.

Watanbe, T., and D. Rothacher (1996) ‘ The 1994 Lugge Tsho glacial lake outburst flood, Bhutan, Himalaya’, Mountain Research and Development, 16,1: 77-81.