In June 2013 the Himalayan pilgrimage city of Kedarnath in India was devastated by a colossal flood. Heavy monsoon rains had overloaded the moraine-dammed Chorabari Lake, causing the dam to breach and emptying the lake within the space of 10 minutes. Kedarnath, which lies 2km downstream of the lake, was inundated by 400,000 cubic metres of water that was released almost instantaneously into the already flooded Mandakini River. Further downstream, two hydroelectric power plants were severely damaged.
Throughout the 20th century dozens of these natural debris dams have failed catastrophically, with little warning. Regions at risk of outburst floods tended to have been sparsely populated, resulting in minimal loss of life and damage to infrastructure. But in recent years Asia’s soaring energy demands have meant that a growing number of hydroelectric power projects have sprung up along glacier-fed mountain rivers. At the same time there is concern that the impacts of climate change may make glacial lake outburst floods more likely. A new study shows that the exposure of Himalayan hydroelectric power plants to glacial outburst floods is indeed increasing.
Between 2000 and 2010 India’s energy consumption grew by 51%, while China’s energy consumption doubled. Assuming economic growth continues along a similar trajectory for these countries, energy consumption is likely to grow by another 75% by 2035. Hydroelectric power is seen as a good solution to satisfy this rapidly growing energy demand. To date, less than 20% of the 500GW hydropower potential of the Himalayas has been tapped, and for many the steep mountain valleys of this region seem like an ideal location for hydropower development. Yet such projects may be putting themselves at high risk of being swept away by a glacial outburst flood.
In order to assess this regional exposure, Wolfgang Schwanghart from the University of Potsdam, Germany, and his colleagues used a flood-wave propagation model to work out the risk of outburst flood at more than 2300 Himalayan lakes, and gauge the likely impact on the 257 hydroelectric power plants downstream.
The team found that two-thirds of the hydroelectric power stations surveyed were situated on potential glacial outburst flood tracks. And up to a third of these hydroelectric power plants could experience outburst floods greater than those they had been designed to withstand.
“More hydropower development means that more hydroelectric power plants are at risk from such short-lived lakes, even if they do not form and fail more frequently,” said Schwanghart. Add to this the likely increased risk of outburst floods due to climate change, and the increased hydropower development in this region looks like a recipe for disaster.
“Most Himalayan glaciers have been retreating during the past 50 years, and many have created depressions between the receding glacier tongues and the sediment that they piled up,” explained Schwanghart. “Melt water and runoff fill these hollows and form many new natural lakes.”
In the Himalayas the regions of most concern are those that have many lakes and many hydroelectric power plants. “India’s state of Sikkim is among those, and so are Bhutan and Nepal,” said Schwanghart. “These Himalayan regions also have the fastest dwindling glaciers.”
The scientists believe that monitoring these lakes, and setting up early warning systems, is essential if countries want to reduce their glacial outburst flood risk. Remote sensing is likely to be a useful tool to keep track of the tens to hundreds of lakes that can lie upstream of a hydroelectric power plant. Meanwhile, more accurate digital elevation models of individual lakes and their moraine dams could play an important role in estimating the probability of collapse, and the size of the resultant outburst.
Looking ahead, careful siting of hydroelectric power plants will play a key role in reducing risk. In particular, the trend to site hydroelectric power plants in higher locations, closer to glacial lakes, is of concern. Glacial outburst floods weaken as they travel downstream, but situating power plants so close to the source of the floods makes it much harder to calculate what the peak discharge will be.
“Moving hydroelectric power plants closer to headwaters requires careful evaluation of the glacier environment and surroundings,” said Christian Huggel from the University of Zurich, Switzerland. “In particular, future development with possibly additional new lakes also need to be considered.”
The team published their findings in Environmental Research Letters (ERL).
Source : Environmental Research Web
