Work to completely empty the Bowathenna reservoir is due to begin on August 17, the engineer in charge of the reservoir, Buddhika Navaratne, has said.
The operation will serve as the pilot project for a national programme to remove accumulated silt from reservoirs across the island, according to Navaratne.
Bowathenna was built half a century ago with a recorded storage capacity of 56 million cubic metres. A survey carried out in 2014 found that capacity had fallen to 23 million cubic metres — a loss of close to 60 per cent of the reservoir’s design volume to sedimentation.
The immediate trigger for the drawdown is the tunnel that carries water from Bowathenna to the Kalawewa basin. The access canal feeding that tunnel is buried under roughly four metres of silt. With the reservoir emptied, crews plan to clear the canal along a 100-metre stretch, removing an estimated 10,000 cubic metres of silt.
The engineer said the shutdown will also be used for work that cannot be done with the reservoir in service. Surveyors will re-measure how much water Bowathenna can actually hold using newer technology, silt will be cleared from the hydropower generation route, and engineers will assess how much sand can be extracted from the reservoir bed.
Navaratne stressed that the operation will not interrupt water releases for farmland downstream.
Siltation has been a long-standing constraint on Sri Lanka’s older irrigation infrastructure, reducing both storage for cultivation and the head available for hydropower generation. If the Bowathenna exercise establishes a workable method, it is intended to be repeated at other reservoirs under the national programme.
