GUWAHATI, June 7 - The authorities concerned should pay due attention to the fact that the Lower Subansiri Hydel Project needs to be modified in accordance with all the prevailing natural circumstances of its present location. Or else, the project has the potential to emerge as the cause of a major disaster, said Hemanta Borgohain, a former senior geologist of the State’s Directorate of Geology and Mining.
Subansiri hydel project’s dam is located within the 5 km diameter circle area of two major active faults and four small faults, which were identified long back by the State’s Geology and Mining Directorate. Earlier, the findings of the Geological Survey of India (GSI) stated that the Subansiri River itself is flowing through a major fault, running in a north-south direction from Tibet to the Brahmaputra Valley, in a zigzag manner.
According to Borgohain, the six faults that are surrounding the Subansiri hydel project dam include – the major faults of the Subansiri River and the Main Boundary Thrust and the small faults of the Dulung, Gerekuwa, Dirpai, Chauldhowa and the Pabho tributaries.
Among these faults, the Main Boundary Fault and the Subansiri River Fault are very deep-seated and active faults. The Main Boundary Fault is located in between the foothills of the Himalayas and the Brahmaputra Valley.
The above faults were identified by former Geology and Mining Director Dr BC Barooah and Borgohain in a two-year investigation between 1987-’89.
Now, location of the epicenters of the latest earthquakes measuring between 5 and 6 on the Richter Scale in the Arunachal and Tibetan Himalayas (upstream of the Siang River) and the Aalo district of Arunachal Pradesh, makes one wonder as to what major tectonic activities are in store in this region.
Moreover, due to deforestation in the Subansiri River catchment, the sediment load is increasing at a very fast pace on the Subansiri and this does not bode well for the health of this major river. It will also have adverse impacts on the Subansiri Hydel Project in the days to come.
Likewise, the typhoons lashing the Tibetan areas frequently also influence the Arunachal Himalaya. This is also an important area to be considered while building major hydel projects in Arunachal Pradesh.
The Lower Subansiri Hydel Project dam is located right on a base of highly dipping feeble sandstone. The foundation laid to support the dam is also not adequately strong to keep it in stable condition under the tremendous pressure of the water proposed to be stored in it.
The width of the Subansiri is between 230 metres and 300 metres in the hilly region and it traverses through a steep gorge of the height varying between 100 metres and 130 metres. The altitude of the area near the Subansiri dam is around 142 metres to 143 metres above mean sea level, whereas the altitude at Gerukamukh is around 104 metres above the mean sea level.
So, the slope gradient from the dam to Gerukamukh, within a distance of around 2.3 km, is around 38 metres or around 127 feet. Hence, the force of the water being released from the reservoir will be very high and this will be very risky for the downstream areas, including Majuli, the centre of the neo-Vaishnavite religion and culture of the State, in case a major earthquake hits the area.
Therefore, the extremely high hydel power potential of Arunachal Pradesh should be exploited by building small impulse/turbulent/spin hydel projects with the help of modern and highly modified turbines and using the pumped water storage technology. This will help in harnessing the Arunachal rivers, including the Subansiri’s hydel potential several times more than what has been proposed to be done with the Lower Subansiri Hydel Project now, said Borgohain.
He also pointed out to the fact that in Meghalaya’s Cherrapunjee and Mawsynram areas there is the scope for setting up innumerable turbulent hydel projects by exploiting the potential created by million cubic metres of rainwater in different gorge sections, without affecting the environment. Significantly, there will be no siltation problem in these areas because of the dependence on the rain water.
This will make Meghalaya not only power surplus but will also boost its economy in a significant manner, added Borgohain.