Samanalawewa leaks and CEB’s losses

The dam was originally located by the Department of Irrigation and never changed by any of the other studies carried out later. Late Consulting Engineer Carlo Fernando observed, “The consultants who were responsible for the final design in the construction stage knew very well about the weakness of the banks where it is now leaking. That is why they got grout holes drilled every three feet, each 300 feet deep and made intensive grouting.

However, it began to leak.”

BY G. A. D.Sirimal

Rtd. Asst. Secretary, SLASMinistry for Power and Energy

It has been reported that 78 million cubic metres of water leak from Samanalawewa hydro power reservoir, causing an annual loss of Rs.2.7 billion. As a result, the CEB has to increase electricity tariff to recover the loss or the government has to bear it and pass it on to the public by way of taxes.

Whatever that be, as one who handled this project from its inception, it is proposed to quote from my letters written in May 2005 and October, 2011 and also some extracts from a presentation at a seminar held by the Institute of Engineers and held at BMICH in January 1995. P. O. Squire of M/s Alexander Gibbs and Partners, S. Takashahi, of Nippon Koei. S. Parqasiriyan, Chief Chemist, Dr. A. N. S. Kulasinghe, Chairman CECB, S.H.C.de Silva Environmental Consultant T. Okada of Nippon Koei, Dr. S. M. Tariq, Chief Engineer, Tarbek Dam Project, Vernon Pereira, Engineering Geologist CECB, D. V. A. Senaratne, formerly of the Department of Irrigation and Consultant also submitted papers, which were discussed.

The project was studied way back in the 1960s by foreign engineering teams including Russian experts for a long period. The dam was originally located by the Department of Irrigation and never changed by any of the other studies carried out later. Late Consulting Engineer Carlo Fernando observed, “The consultants who were responsible for the final design in the construction stage knew very well about the weakness of the banks where it is now leaking. That is why they got grout holes drilled every three feet, each 300 feet deep and made intensive grouting. However, it began to leak.” He recommended the leak should be sealed with ‘CLAY BLANKET’ as the extensive grouting had failed. Fernando’s recommendation was based on his experience gained at the Tabella Dam project. About this suggestion Vernon F Pereira, Engineering Geologist addressing the seminar held on 13 January 1995 said ‘CLAY BLANKETING’ had been successful where the ingress point was known. There is no positive evidence of major ingress points at Samanalawewa. Water seems to be seeping into the aquifer over an extensive area via the river bed and its slopes. Clay Blanketing is therefore considered to be a hit-or-miss exercise.

S.H.C.de Silva, Consultant Large Dams Team Leader had made five proposals (a) Deep grout curtain (b) Drainage control pump (c) Conversion to run of the river (d)Dry blanketing (e) Wet Blanketing and in inconclusion said most suitable and practical approach to solve the current right bank leakage is Wet Blanketing.

On these recommendations and suggestions, Kulasinghe the then Chairman of CECB mentioned the Soza Commission report where Wet Blanket proposal had been rejected as a shot in the dark and the drainage proposal recommended for implantation.

Vernon F Pereira, Engineering Geologist says, “Highly reliable efficient drainage system is proposed in this area, accommodating a reasonable quantity of leakage and pumping it back to the reservoir” As far as I could remember, the design provides for pumping of water back to the reservoir but had been stalled   as it was considered not economical.

Another interesting finding was by S. P. Squire, Chartered Engineering Geologist of Sir Alexander Gibbs & Partners Ltd.: “The information now available clearly shows that control of the groundwater levels and leakage volumes by cut-off with its associated drainage through the right bank ridge in fractured rock will require the treatment of an enormous area, the base of which has yet to be identified. Plugging the leak on the downstream side of the Right Bank ridge as shown by the conditions recorded prior to and during the ’Water Burst’ are likely to lead to further instability.”

It should be mentioned that there was an allegation   by Dr. A. C. Visvalingam, who has experience in Isotope Technique and obtained his PhD on his findings was not consulted. I believe the CEB may have consulted him later.

It should be stated that CEB may have taken action on all or a few recommendations, but the problem still remains.

This submission is only to remind the authorities of the efforts taken to stop the Samanalawewa leak.

My fear is that if the leakage starts beneath the foundation of the dam, it may one day cause the collapse of the dam and the consequences I dread to imagine.