JOIN USState may build balancing reservoir downstream TB dam
The State government is mulling over the possibility of constructing ‘balancing reservoirs’ downstream of the Tungabhadra dam as one of the options to compensate for the loss of storage water due to the build-up of silt in the main dam over the last six decades.
The Tungabhadra dam constructed across Tungabhadra river near Hosapete town in Ballari district was designed for storing 133 tmc ft of water and was impounded for the first time in the year 1953. Over the years, the build-up of silt has gradually reduced the capacity of storage.
At present the storage capacity of the dam, which meets the drinking water and irrigation requirements of Ballari, Raichur and Koppal districts in Karnataka and three other districts in neighbouring Andhra Pradesh, is only 100 tmc ft. The build-up of silt has started to affect the irrigation utilisation from the dam by the two states. The build-up of silt continues with the dam losing 0.5 to 0.6 tmc ft of storage space every year.
The State government has now invited bids from global consultants to prepare Detailed Project Report (DPR) to restore Tungabhadra dam to its original capacity by studying various alternatives including construction of balancing reservoirs downstream the main dam. Karnataka Neeravari Nigam Limited (KNNL), the nodal agency for the project, has also suggested increasing the live storage of the existing dam by increasing its height.
Desilting the main dam by way of dredging would not be financially-viable.
“If all the silt in the dam is removed, it would require 50,000 acres of land for dumping even if it is piled up to a height of 15 feet. Besides, the cost factor will be very high. According to our estimate it would require Rs 10,000 crore for the desilting process by dredging and could take anywhere between two to five years”, says Aravind Galagali, director, technical sub-committee, Krishna Bhagya Jala Nigam Limited and resource person for the project.
Galagali said construction of new reservoir/s will require land acquisition and also there would be environmental and resettlement and rehabilitation issues to be addressed. “The short-listed consultant would have to study all aspects and prepare the DPR”, Galagali said. The cost of the project would be known only after the preparation of the DPR, he said.
Other aspects which will have to be studied by the consultant before preparing the DPR include capacity and sedimentation study of the Tungabhadra dam, examine various alternatives of restoring the design capacity of the dam and provide a cost benefit analysis among others. Once the DPR is ready, it would have to be sent to the Central Water Commission and the Tungabhadra Board for approval before executing the project.