Re: renewable energy

[Leigh Palmer <palmer@SFU.CA>]

Chuck Britton reports:

> And the 'powers that be' are becoming more aware of the importance
> and possibility of limiting siltation by periodic release of silt
> laden water (water from the bottom of the lake rather than the 'top'
> water that normally flows through the penstocks.

Can that be done easily? Does one have to bore a tunnel in or near
the dam far below the lake level? Can this be done at, for example,
Hoover Dam?

It is my impression (gained from experience in British Columbia)
that dams are somewhat marginal - they are built just sufficiently
robustly that they work, and no stronger. As a result significant
leaks are not uncommon, not usually in the structure itself, but
rather in the soil and rock at the margins of the dam. Of course
making the dam twice as massive will always reduce the probability
of leaks, but large safety factors can be very expensive. I would
worry about retrofitting a marginal dam with a tunnel near its
base.