The Bowatenna Reservoir, the main water source feeding the Kala Wewa basin, will be completely drained from August 24 for repair and maintenance work, authorities have announced.
Reservoir Engineer Buddhika Mahesh Nawaratne said the operation will be the first full-scale maintenance of the reservoir since it was built around 50 years ago.
Sediment has cut storage by more than half
The work has been prompted mainly by sediment build-up. Bowatenna was originally designed to hold about 56 million cubic metres of water, but a survey conducted in 2014 found capacity had fallen to roughly 23 million cubic metres.
Officials said sediment has also collected in the tunnel that supplies Kala Wewa and near the power generation facility, affecting the release of the 1,000 cubic feet per second required by the Kala Wewa basin.
The programme has been timed for the current dry spell, with the reservoir’s volume already down to about 11 million cubic metres. Water released ahead of the work has been stored in the Kandalama, Kala Wewa and Ibbankatuwa reservoirs.
Three weeks of work, refilling from September 14
The three-week programme will use machinery under the supervision of the Mahaweli Authority at an estimated cost of about Rs. 4 million. Refilling is scheduled to begin on September 14, with the water reserved at the Kotmale Reservoir.
During the maintenance period, a continuous flow of 1,000 cubic feet per second will be maintained through the Polgolla Dam, the Sudu Ganga and the Amban Ganga towards the Moragahakanda Reservoir. Authorities said the measure is intended to protect the aquatic ecosystem, including fish populations in the Amban Ganga.
The reservoir engineer urged the public not to enter the drained reservoir bed for fishing or sightseeing, warning that sediment accumulated over five decades could pose safety risks.
Once the work is complete, officials expect the reservoir to regain storage capacity and supply the Kala Wewa basin more efficiently.
