Water Resources: Hydraulics and Hydrology
use model testing. That's a new technology. I suppose the next new technology is taking
model test results and using computers. From there on, I don't know of any further
advancement of technology.
Q ..
Well, how about some things in the construction side that would allow you in hydraulics
to make different kinds of designs, I mean a superior type of concrete or something like
that? Would that allow you to make a better design or a different type of design?
Yes, it would. There's been a lot of work in the last or so years to improve the
resistance of concrete to erosion. With ordinary concrete, if the physical shape of a
velocity spillway or outlet works is not designed correctly, cavitation erosion of the
concrete can occur quite readily. For example, cavitation erosion can occur on a concrete
spillway floor when the velocity exceeds feet a second and there is misalignment at a
floor joint.
If the upper edge of a downstream monolith is higher than the downstream edge of an
upstream monolith, then the high-velocity water striking the misalignment edge creates
negative pressures just downstream of the misalignment. The negative pressure area is
extended downstream a short distance by the high-velocity flow to positive pressures,
which cause the negative pressures to collapse very rapidly. The rapid collapse of
negative pressures produces high-tensile stresses. The high-tensile stresses are exerted on
the concrete floor a few inches from where the cavitation pressures are developed. The
concrete is porous enough so that the high-tensile pressures enter the concrete a short
distance, and progressively, erodes the concrete floor.
There has been considerable work on developing superior concrete to withstand cavitation
erosion. Epoxy solutions have been added to some concrete mixtures. It makes a stronger
concrete that withstands cavitation pressures much better.
I think that has been developed fairly well on a small scale, and it's used where cavitation
pressures are likely to occur. It seems to me there could be more effort made to make the
concrete stronger. I don't know how, but right now the concrete is not very strong
compared to steel.
So that's an area that requires additional research?
A:
I'm sure there's been considerable research done on it. It may well be that sufficient
research has been done to decide that the cost of making concrete approach the strength
of steel is beyond reason.
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