Abstract
The frequency of glacier lake outbursts floods (GLOFs) is likely to increase with the ongoing glacier retreat, which produces new glacial lakes and enlarges existing ones. Here, we simulate the outburst of a potentially dangerous glacial lake in Bhutan by applying hydrodynamic modelling. Although the lake volume is known, several parameters connected to the dam breach and the routing of the flood are rough estimates or assumptions, which introduce uncertainties in the results. For this reason, we create an ensemble of nine outburst scenarios. The simulation of magnitude and timing of possible inundation depths is an important asset to prepare emergency action plans. For our case study in the Mo Chu River Basin, the results show that, even under the worst case scenario, little damage to residential buildings can be expected. However, such an outburst flood would probably destroy infrastructure and farmland and might even affect the operation of a hydroelectric powerplant more than 120 km downstream the lake. Our simulation efforts revealed that, by using a 30-m elevation model instead of a 5-m raster, flood magnitude and inundation areas are overestimated significantly, which highly suggests the use of high-resolution terrain data. These results may be a valuable input for risk mitigation efforts.
Highlights
The formation and extension of proglacial lakes as a consequence of the current glacier recession is a global phenomenon
For our case study in the Mo Chu River Basin, the results show that, even under the worst case scenario, little damage to residential buildings can be expected
Where glacier tongues retreat up-valley, they commonly expose depressions which are filled with melt water. These lakes are dammed by moraine walls from the little ice age or younger deposits, which bear the danger of failure, causing so-called glacier lake outburst floods (GLOFs) or ‘jökulhlaups’ [2]
Summary
The formation and extension of proglacial lakes as a consequence of the current glacier recession is a global phenomenon. Where glacier tongues retreat up-valley, they commonly expose depressions which are filled with melt water These lakes are dammed by moraine walls from the little ice age or younger deposits, which bear the danger of failure, causing so-called glacier lake outburst floods (GLOFs) or ‘jökulhlaups’ [2]. In the entire Hindu Kush Himalaya region, the number of glacial lakes, normalized by the total glacier area, is highest in Bhutan (1.8 × 10−2 ha/ha) [4]. This increase in the number and area certainly enhances both the possibility of GLOF occurrence and the risk potential. While the youngest incident happened in 2015 [6], the most devastating outburst took place in October 1994, when the collapse of the Lugge Tsho dam caused severe flooding in the Pho Chu Valley and a total of 21 fatalities [7]
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