On the roof, a technician began installing a new ventilation system. Above him soared a
concave dam 80 stories high and more than half a mile wide at the crest. When operating
at full capacity, the plant's 10 interior penstocks funneled water from the reservoir behind
the concrete barrier to the hall below him, where it tore past the blades of 10 turbines,
spinning them with tremendous force before being flushed out of the hydro plant and
down the Yenisei River.