Today's News for my Blog: Greenhouse gas emission

Stagnant water in hydroelectric dams is known to emit high levels of greenhouse gases (GHGs) such as carbon dioxide and methane from submerged rotting vegetation. “I recognise the fact that we have no other choices but to go ahead with the projects as planned. However, I hope that the government has looked into all aspects of the project in order to ensure that maximum benefit is derived from all the damages we are going to cause,” said a BO source. “There would be small climatic changes due to the dam,” said an advisor to the National Environment Commission, Dasho Paljor Jigme Dorji. “I hope the project is taken on an informed choice.” As a GHG, methane is known to be 20 times more potent than carbon dioxide. “The extent to which such an impact occurs will vary,” said the Executive Director of Royal Society for Protection of Nature, Lam Dorji. The height of the Punatsangchhu dam is 136 metres with a back flow of 10 km. According to Lam Dorji, in comparison with another project of this scale in lowlands, Punatsangchhu dam would emit lesser GHGs as the location of the project in the mountains allows efficient outflow of water and steep slopes on either side prevent large areas from being submerged. He said that, the issue of the dam’s GHG emission had not been raised for lack of factual data. “Gauging the GHG emission from the dams in Bhutan remains a plan for RSPN,” he said. The Joint Managing Director of Punatsangchhu phase I, Phuntsho Norbu, said care was always taken before the dam was filled with water. He added that, since the project is run-off the river scheme, there weren’t big chances of large deposits of submerged materials. Reservoir induced seismicity Another concern about the dams around the world is reservoir induced seismicity (RIS) or earthquakes caused by dams. The most widely accepted explanation of how dams cause earthquakes is related to the extra water pressure created in the small cracks and fissures in the ground under and near a reservoir. When the pressure of the water in the rocks increases, it acts to lubricate faults which are already under tectonic strain, but are prevented from slipping by the friction of the rock surfaces. Ambient stress field conditions, availability of fractures or faults, hydro-mechanical properties of underlying rocks, geology of the area, dimensions of the reservoir and nature of lake level fluctuation are some of the factors that affects RIS. “In general, it is extremely difficult to draw any quantitative analysis of probable dangers of reservoir induced seismicity based on the dam height and extent of reservoir,” said a Geophysicist of Geological Survey of Bhutan, Dowchu Dukpa. However, he said that, with availability of advanced technology, building a dam in earthquake prone regions like the Himalayas need not, in itself, be dangerous if all the aspects of seismic shaking are well understood and incorporated in the design. “It is rather impossible to predict accurately whether Punatsangchhu dam will cause earthquakes or how strong the tremors are likely to be,” he said. “A good understanding of the geo-tectonic setting of the dam and the vicinity area will help in assessing the nature of reservoir- induced seismicity from the dam.” Currently, Bhutan does not have a national earthquake station to monitor seismic activities and accurately delineate faults in the region prone to earthquakes. According to Dowchu Dukpa, the need for an earthquake station is critical for understanding the general seismo-tectonic characteristics of any region. He said availability of seismic data over a long time was of paramount importance to carry out any seismic hazard assessments. “Installation of local seismic monitoring equipment at the area of interest is the standard procedure to better understand the nature of reservoir induced seismicity at that particular site,” he said. By Kuenzang C Choden Retrieved from http://www.bhutanobserver.bt/2009/bhutan-news/08/punatsangchhu-dam-a-concern.html