From PAUL BACK
I refer to the article in your 26 February issue by Fred Pearce entitled
‘Britain’s other dam scandal’.
I must ask for space to comment on just a few of the matters raised.
We are told in a bold crosshead that the Victoria Dam is leaking. In
the text which follows however, we understand that it may not be the Victoria
Dam but perhaps somewhere else in the catchment or perhaps again some other
dam. However, the clear intention is to suggest that there is a major problem
at the Victoria Dam – which is most certainly not true.
It is further mentioned that in 1983 the Victoria Dam site was grouted
extensively and a special drain and sump now cope with the problem as if
this was all done as a response to an unforseen problem. This again is
nonsense. The original tender drawings prepared in 1979 clearly show that
substantial grout curtain was always envisaged, as also was a drainage tunnel
and a sump to enable seepage under the dam (which any dam engineer knows
will occur) to be pumped out.
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In planning the dam, provision was made for pumps to handle automatically
the seepage into the drainage system below tailwater level (that is, where
simple gravity flow could not be used). At present one pump operates once
a day to empty the sump to deal with seepage flows of less than 5 litres
per minute. This is approximately 1/70th of what the system was designed
to handle. The total leakage past the dam (gravity + pumped) amounts to
42.5 litres per minute at full reservoir, which, for a dam 122 metres high
sealing a valley 500 metres wide, can only be described as insignificant
and surely not justifying the crosshead ‘Leaking Victoria’.
It is also implied that the switch of priority from irrigation to power
at Victoria was made against local advice and has damaged the interests
of the country. The rigorous economic evaluation which was carried out in
1978 demonstrated that the overwhelming benefit of the project was power
– with irrigation benefits contributing only 6 per cent to the total benefits
due to existing and shortly-to-be-constructed storage capacity of the system
downstream. Power shortage was a major problem at the time. It was common
to have six to eight hour-long power cuts every day. The Victoria project
added 40 per cent to Sri Lanka’s installed capacity and led to the virtual
disappearance of power cuts.
The article implies that the Samanalawewa dam has been an ‘enormous
blunder’ and will become an ‘archaeological site’ and a ‘write-off’. It
may be of interest to note that this ‘write-off’ has been steadily producing
energy to the grid for the last year, contributing 411.5 gigawatt hours
which is no less than 95 per cent of the originally planned firm output
to the system.
The leakage which developed through a hillside adjacent to the dam amounts
to around 2 to 2.5 cubic metres per second. This has to be compared with
the requirement to discharge 1.5 to 2 cubic metres per second through the
dam as compensation flow for riparian interests downstream. The actual water
loss for the purpose of power generation is at present therefore around
0.5 cubic metres per second or less than 3 per cent on an annual basis.
When the leak first developed there was a natural concern of the local
population as to the safety of the dam. An international panel of experts
was appointed by the government of Sri Lanka to inspect the site and advise
on remedial works. The unanimous opinion of the panel was that the dam was
completely safe and operating normally and they endorsed the proposal of
the engineers that the leakage could best be dealt with by ‘wet blanketing’
the short section of the river bed in the reservoir which had been identified
as the source of the leakage.
Other inaccuracies and distortions abound in the article. When a problem
of heavy leakage into the power tunnel occurred during construction, we
are told that the problem was only solved by ‘lining the tunnel with concrete
– an extremely expensive business’. The tender drawings always showed that
the tunnel would be lined with concrete throughout its length and that is
precisely what was done.
I am alleged to have said that the ‘supervising engineers failed to
make a detailed site investigation of the dam’s right abutment in 1986′.
I said no such thing. Indeed, a more detailed investigation of the dam’s
right abutment was made by the Japanese in 1986. What was not possible to
do with the budget available at that time (because no contracts had as yet
been entered into by the parties) was to extend the detailed investigation
further along the hillside. Since the Russian investigations had already
covered the area, it was agreed to rely on that information for the time
being, but to check it in detail when preparing the final cut-off design
during construction.
The comments regarding the decision to move the right abutment of the
dam are also incorrect. The small adjustment to the alignment was to exploit
a potential saving in costs which was indicated from the additional drilling.
The move was not – as stated in the article – ‘to get the shortest distance
between the two abutments’ – in fact it slightly increased the distance.
And why it can be said that the move was ‘an enormous blunder’ is incomprehensible.
It is beyond doubt, however, that the move made no difference whatever to
the leakage which occurs half a kilometre away downstream.
I could continue to describe the many other distortions in the article
– but from the few illustrations I have mentioned above I will leave it
to the readers to decide whether truth and integrity have been well served.
Both Victoria and Samanalawewa projects have been and will continue
to be great assets to Sri Lanka, providing power and water for irrigation
well into the next century and probably beyond. Between 1984 when the Victoria
project was first commissioned and February 1994, the Victoria and Samanalawewa
projects have contributed no less than 23 per cent of all the energy produced
in Sri Lanka over that time. For the first two months of 1994, the contribution
has been 34 per cent of the total system demand.
Paul Back Sir Alexander Gibb amd Partners Reading, Berkshire
