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Wet blanket plugs leak

The Samanalawewa reservoir in Sri Lanka saw the start of work recently to plug an ongoing leak in its dam. The project, reported to cost Rs2.6B, has been funded by Japan’s Overseas Economic Co-operation Fund and will be carried out by Kumagi Hazama Kajima, a Japanese company.

The project will see a ‘wet blanket’ of clay pebbles and sand dropped onto a 300m2 area which is suspected of leaking. The work will be completed in three phases, of which the first is expected to see 250,000m3 of the mixture put in place. The first and second stage will take around nine months. In the final stage some 500,000m3 will be placed over a period of 20 months.

The 100m-high dam is made of rockfill with a clay core and is built across the Walawe Ganga at its confluence with the Belihuloya. The dam was competed in 1992, as was the power plant it feeds, Kapugala. However, the dam was not filled completely to its design level of 460m until this year because since it was built it has leaked at a rate of 2m3/sec.

The ‘wet blanket’ technique is intended to reduce this

leakage and to lower the groundwater pressure in the right bank. This will allow the reservoir to be filled to capacity and allow the power station to operate to capacity — it is

currently estimated to waste some 15GWh of energy each year.