Hyderabad: Live storage capacity in dams across the country and the states of Telangana and Andhra Pradesh has taken a major hit, according to the Centre's report on 'Sedimentation of Reservoirs in India 2020'.
The report says that the major reservoirs in these states were in the list of reservoirs that have lost more than 50 per cent of its gross water holding capacity, dead storage and live capacity.
The Nizamsagar Dam in Telangana reported a 60.47 percent loss in its gross capacity upto the last survey conducted in 1992. The Nagarjuna Sagar Dam that was last surveyed in the year 2009, had recorded a 40.73% loss of dead storage. Whereas, Andhra's Vamsadhara Dam has had a 60.43 percent loss of live storage capacity, upto 2004.
As a result, experts say that the storage in these reservoirs, among others, is receding at a far faster rate than anticipated, resulting in dire consequences in the future. Several reservoirs may already be choked, given the data from surveys conducted decades ago for most dams, the report warns.
The Union Ministry of Jal Shakti in its report from August 2020 had said that India can currently store 257 billion cubic metres (BCM) of surface water in its reservoirs, and that the quantity of water held in reservoirs or live storage could be extended to a maximum of 385 BCM in the near future.
The report also said that the Southern region, including Andhra Pradesh, Telangana, Karnataka, Kerala and Tamil Nadu, with 36 reservoirs that are monitored by the Central Water Commission have a total live storage capacity of 52.81 BCM. As per the Ministry's last 'Reservoir Storage Bulletin' dated 13.08.2020, the total live storage available in these reservoirs was 32.08 BCM, that represents only a 61% of thier total live storage capacity.
The average rate of siltation in these reservoirs, for instance at the Nagarjuna Sagar Dam and the reservoir it forms, has been observed to be more than what was designated as an acceptable rate of siltation. While the designed rate of silitation of thousand cubic metres per square km per year in Nagarjuna Sagar Reserovir was 0.22, the average observed rate of silitation came out to be 0.30.
Dead storage loss in Nagarjuna Sagar (40.73 %) is also a cause of concern. Dead storage is the total storage below the invert level of the lowest discharge outlet from the reservoir. It may be available to contain sedimentation, provided the sediment does not affect the lowest discharge.
Telangana is now planning to create vegetative cover along the catchment area, and also looking into the option of artificial reservoirs, construction of check dams on small streams to arrest sedimentation as much as possible, said Sridhar Rao Deshpande, OSD to Chief Minister K Chandrashekhar Rao. "It is a big task to desilt these huge reservoirs. This issue is not just limited to India, but is a problem world over. However, the southern states of India are much more affected than the north, due to the Himalayan rivers there", he said. The way ahead to prevent these reservoirs from dying is only to work towards preventing further damage through sedimentation, he said.