Draining of the Bowatenna Reservoir is to begin on Monday, the engineer in charge of the reservoir, Buddhika Navaratne, said — the first time the Matale district reservoir has been emptied to its bed in the 50 years since it was built.
The work will allow silt and sand accumulated over five decades to be surveyed and removed, and the reservoir cleaned. Silt is also to be cleared from the channel that carries water from the reservoir towards the Kala Wewa system.
Navaratne said the operation will not disrupt water supplies to downstream catchment areas.
A pilot for a national programme
The drainage is being carried out as a pilot project under a national programme to remove silt from reservoirs across the island, Hiru News reported earlier this month, quoting the same engineer.
The scale of the silting is substantial. Bowatenna’s capacity was recorded at 56 million cubic metres when it was commissioned, but a survey in 2014 found this had fallen to 23 million cubic metres — a loss of more than half its storage.
The immediate target is the access channel of the tunnel that supplies the Kala Wewa basin, which was found to be buried under about four metres of silt. Roughly 100 metres of that channel is to be cleaned, with some 10,000 cubic metres of silt earmarked for removal.
The operation is also intended to re-survey how much water the reservoir can still hold using newer technology, clear silt from the hydropower generation route, and establish how much sand can viably be extracted.
Timing
The August 2 report said the emptying was scheduled to begin on the 17th, indicating the start has slipped by about a week.
Hiru’s Sunday report carries an internal inconsistency on the date: its headline says the emptying has begun, while the engineer is quoted saying it “commences today (24)” — a Monday, though the report was filed on Sunday evening. At the time of writing no other verified Sri Lankan newsroom had published its own report of the operation.
