Water
Hydraulics and Hydrology
didn't, but we've learned a few things since then, and this is the way we think we ought
to do it."
It had to do with erosion of concrete due to high-velocity flow. He was good at figuring
out what kind of concrete was required for strong concrete beams, or mass concrete for
an ogee section, but he didn't know very much about concrete erosion by high-velocity
flow. He said, "Oh, this stuff is tough. It won't erode.
Not so?
A:
Well, it won't erode if you do the hydraulics and construction right, but too many times
the hydraulics isn't done right. Like the dam in Iran. They didn't construct it right. The
hydraulic design was right, but the construction wasn't right. At each joint, there were
small offsets that produced high negative pressures and cavitation erosion of the concrete
when high-velocity flows occurred.
Before cavitation erosion was experienced in full-scale structures, it was hard to convince
a concrete man, especially in the Corps of Engineers, that concrete would fail that way.
I learned [this], called their attention to it, [and] they learned it.
That's interesting, because an organization that has as much experience with construction
of large concrete structures, one would assume that they would have some sort of
information or track record on that kind of thing already?
A:
Well, they did have some. A good example is the Bureau of Reclamation's Hoover Dam.
There, the spillway is an overflow spillway, which discharges into a tunnel. The tunnel
has about a
vertical drop. At the bottom, there is a curve in the tunnel to turn
the water into a nearby horizontal diversion tunnel. The hydraulics design of the curve
was incorrect. The water didn't follow the curve, and you can get cavitation erosion of
the concrete. Downstream of that curve, the cavitation erosion scoured a large hole
through the tunnel lining into the rock. That happened in 1938.
A model of that tunnel was constructed at the Bureau lab in Denver, and I worked on that
model. There was previous experience with cavitation erosion, but not with free, open
flow over a spillway.
at the Corps' Pine Flat Dam, cavitation erosion occurred on a concrete splitter
block at the downstream end of an outlet conduit to spread the high-velocity flow over a
flip bucket. The water would hit the front part of the block, which was at 90 degrees with
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