Another scientist writes to govt, warns about climate change impact in Dibang Valley over hydro projects

Dibang Valley has close to 300 glaciers in an area of 200 sqkm and there are about 350 glacial lakes covering an area of 50 sqkm. Glacial lakes indicate these areas had much larger glaciers that have now completely melted due to warming, Sheth has said in his three-page letter.

Another scientist studying rivers in Arunachal Pradesh’s Dibang Valley has warned the government about climate change-induced natural hazards that hydropower dams may not be able to withstand.

The risk of hydropower projects upstream closer to glaciers and glacial lakes is extremely high due to the unpredictable nature of the volume and flow rate during glacial lake outburst floods.(Photo: Chintan Sheth/ HT)

Chintan Sheth’s letter to the Forest Advisory Committee (FAC) of the Union ministry of environment has come after several scientists issued a similar warning to the government over granting forest clearance for the 3,097 megawatt (MW) Etalin hydroelectric project in an area rich in subtropical evergreen and rain forests and rare flora and fauna.

Dibang Valley has close to 300 glaciers in an area of 200 sqkm and there are about 350 glacial lakes covering an area of 50 sqkm. Glacial lakes indicate these areas had much larger glaciers that have now completely melted due to warming, Sheth has said in his three-page letter.

Suggesting a cautious approach to siting hydropower projects in the region, the former research fellow with National Centre for Biological Sciences said Arunachal Pradesh has a vast elevation gradient and is drained by Tibetan rivers such as the Subansiri, Lohit and Siang.

It is well known that these rivers are primarily fed by melting glaciers, snow cover and monsoon rainfall so are the rivers in Dibang Valley, he said.

“I have currently mapped and detected rapid melting of glaciers since 2009 on the Mathũ (Mathun), Dri and Talõ (Tangon) rivers as well as recent emergence and expansion of glacial lakes,” he wrote.

“The Etalin hydroelectric power project proposes two dams on these rivers. The risk of such projects upstream closer to glaciers and glacial lakes is extremely high due to the unpredictable nature of the volume and flow rate during glacial lake outburst floods,” he said.

Though Sheth has flagged concerns for all projects in the region, FAC is currently considering granting forest clearance to the Etalin hydropower project.

The risk of hydropower projects upstream closer to glaciers and glacial lakes is extremely high due to the unpredictable nature of the volume and flow rate during glacial lake outburst floods.

Dam breach model studies for hydropower projects account for only extreme rainfall floods.

“Even if the dam structures do withstand a glacial lake outburst flood, the dam itself acts as a barrier effectively creating a lake that drains after overtopping. In effect, a dam creates a second lake that floods further downstream, after it over-topples, rapidly increasing the energy and flow rate of water,” Sheth said.

“In contrast the natural topography of a river allows the water to spread and dissipate energy across the length and width of the river channel decreasing the flow rates as the flood propagates downstream,” he added.

Anil Kulkarni, a glaciologist at Indian Institute of Science, said: “The glaciers there are relatively small and they have not been studied enough.”

“We have to understand that the climate is changing and will change significantly in the coming years. First, we need to understand how climate will change in the region and how the pattern of stream runoff will be influenced,” Kulkarni said over the phone from Bengaluru.

“Another study needed is will there be a change in the volume of water in future? Also in case of a run of the river projects, the distance between the dam and the outlet is usually dry which causes irreversible changes to aquatic life and water availability for local people. We need to critically study these impacts,” he said.

HT had reported on April 23 that a sub-committee of FAC, which visited the Etalin hydropower project site in February, has recommended in their report on April 21 that the project of 3097MW can be allowed with a condition that the developer deposit money for wildlife conservation in the area.

The project will involve diversion of 1150.08 ha of forest land and felling of 2.7 lakh trees in what is described as “subtropical evergreen broad-leaved forest and subtropical rain forests” in FAC’s documents.

“A decision on the Etalin Hydropower project will be announced when the minutes of the FAC meeting is released,” a committee member said.