Retorts

Clyde Dam Concerns

Further to the review of our book, An Abuse of Power [Feb], the latest information to come from the construction engineers of the Clyde Dam states that reservoir filling should begin by mid 1992, and that repairs will cost less than (the $442 million?) estimated.

Notable was the admission that pumps in each tunnel would have to be kept going to clear water for the life of the project, perhaps 80 years. This would be based on the assumption, presumably, that the slides won't shift in that time and that the tunnels won't be wrecked or collapsed or rendered useless. With a water table presumably 100 metres above the lake level at the extreme tunnel lengths, re-drilling the tunnels wouldn't be possible even if the lake level were lowered, as water tables take some time to lower in response.

It is difficult to see these untried technical innovations being successful except in the very short term.

Then there is the question as to whether nature would be dutifully silent during the project's life. Late in January, chillingly close to us, was a rare combination of strength 6 earthquakes and associated swarms, and extreme rainstorms and flood conditions. This was on the West Coast from Westport to Inangahua.

Given the similarities Gerard Lensen found between the Cromwell Gorge geology and Inanguhua's, we wonder whether we can be safely assured that Electricorp's rickety arrangement of puny earthworks, grout curtains, blanket buttresses, tunnels and drill holes can really last 80 years.

We have seen nothing so far to suggest to us that we could sleep at nights were we to reside directly below the dam when it is filed. The element of risk would still be too high for us.

Trevor Reeves, Judith Wolfe, Dunedin