Water Resources: Hydraulics and Hydrology
that part gate operation was satisfactory with heads up to about 75 feet. These slide gates
were subject to heads up to 225 feet when the reservoir was full at Pine Flat. The
conclusion was that, with heads exceeding feet, the gates should not be operated part
open, they should be operated either closed or full open.
I think there are eight gated sluices at Pine Flat. All of them could be operated at once
part open with heads up to 75 feet. For higher heads, several gates could be operated full
open with all other gates closed to pass as much water as desired. Operation of the gates
wide open under high heads does not cause excessive vibration nor cavitation erosion
because the water coming through that gate section is five feet wide and eight feet high,
and that's the same cross-sectional dimension of the conduit all the way through the base
of the dam.
So there's no change at all?
A:
No change. But if we hadn't made these tests, the dam operator, for example, may have
operated a gate three feet open under 150 feet of head. The resulting severe vibration and
cavitation erosion may have damaged the gate so that it could not be closed. We
highlighted all that in an operating manual which was sent to the dam tender. He had to
follow it very strictly. He is required to strictly follow the outlined operation rules
outlined in the manual.
Do you remember any of the hydraulic design problems that you faced at Fort Randall?
A:
Yes. Fort Randall is an earth dam with a concrete spillway on the left abutment. I think
there were four concrete-lined diversion tunnels 30 or 36 feet in diameter. During
construction of the earth dam embankment, river flows were diverted through those
tunnels. When the embankment was completed, two of the tunnels were modified to
connect with hydroelectric power turbines located in a powerhouse. Flows through the
power turbines discharge into the power tailrace, which returns these flows to the river
downstream of the dam. The other two diversion tunnels were modified to serve as flood
control outlets. They have upstream gates for operation and a downstream stilling basin
because the downstream river bed and banks were quite erodible.
There was one problem in the stilling basin design that I had not encountered before. We
wanted to design the stilling basin so that it would operate satisfactorily with only one
tunnel flowing full under high head, and the other one closed. This could occur if the
gates for one tunnel could not be operated. We wanted to have a safety factor.
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