The Planning Commission has considered hydropower power as the best source of energy in its integrated energy policy report since it does not emit gas than the energy generated by coal.
But in the hydropower reservoirs the sediment is trapped, which gives rise to coastal erosion. Planning Commission has not kept this aspect in mind. This sediment prevents the erosion of the coasts.Hydroelectric reservoirs like Tehri trap these sediments. The Ganga carries less sediment to the coasts and the sea starts erosion of land. The large grounds of the Ganga and almost the entire land of Bangladesh are made by the soil lined by the Ganga, Meghna and Brahmaputra rivers. The world's largest and 20,000-year-old Sundarbans delta is also made from the sediment brought by the Ganga. The land of the Sundarbans Delta situated in Ganga Sagar is fast eroding.
Australian scientist Wasson has said in his report that 794 million tons of mud of Himalayas is provided by Ganga and 450 million tonnes of deposits are deposited in the lower delta such as the Sunderbans. The Wasson report is here.(mention at figure 1)
But the dams like Tehri have stopped this soil and have denied Sundarban from this soil.
In the Sundarbans, the Sundari tree (mangrove) trees are found in whose names the name of the delta is Sundarbans. These trees live in a mix of sweet and salt water. Due to being adjacent to the sea there is a mixing of sweet and salt water. But due to shortage of Ganga water for some years, the amount of salt water has increased here. Due to lack of sweet water there has been a decline in mangrove trees. Due to decrease in mangrove trees, erosion has started in the land and the land is getting eroded by the sea. In last 40 years, the area of 200 sq. km of Sundarban has been completed in the sea water.
We are giving a picture of the confluence of Bhagirathi, which is coming from Tehri, and the Alaknanda which is coming from Badrinath (before the construction of Srinagar dam) in which one can see Bhagirathi is of light color because in it the quantity of sediment is very low because that is trapped in Tehri.
Girish Gopinath of Marine Geology and Geophysical Department, Kochi University studied GangaSagar Island in West Bengal. He estimated that during the twenty years of 1976-96, GangaSagar reduced by 0.8 sq. Km per year. However, in the three years from 1976 to 1999 an increase of 5.5 kilometers per year has seen. The dams are responsible for this. You can see the full report here.(Page no.1, para 2).Photo of erosion at Sundarbans is given below.
Andhra University Visakhapatnam, Yamaguchi University, Japan; And Shimane University, Japan conducted a study of the Godavari Delta. They estimated that 1836 hectares of land has been lost in the last three decades. They attributed the reduction in the supply of sediments to be responsible for this erosion due to the construction of many dams.
We urge Shri Narendra Modi to order the Ministry of Power, Water Resources and Environment to assess the impact of all the coastal erosion impacts from Tehri Dam and stop the Pancheshwar and Renuka dam till the completion of this study.