Water Resources: Hydraulics and Hydrology
consider in deciding whether an earth or concrete dam should be constructed.
Fort Peck Dam on the Missouri River is an earth dam constructed on a foundation with
very little rock. The dam is relatively low and the river is unusually wide. Construction
of a concrete dam was not even considered because the conditions strongly favored the
earth dam. The spillway and
diameter outlet tunnels were constructed of concrete
to carry the large, high-velocity flows. Concrete stilling basins were constructed at the
downstream ends of the spillway ad outlet tunnels to still the water flows before entering
the Missouri River's erodible channel.
even in those big earth dams, you still have a lot of concrete work that you have to put
in?
Oh, yes. There's a lot of concrete.
And that's where your skills come in?
That's right, the hydraulic engineer is involved with both concrete and earth dams because
in almost every case the spillway and outlet works need to be constructed of concrete.
Only for low dams and very good rock conditions, can the spillway be excavated in a dam
I may be jumping ahead here a little bit, but how much different is it in the hydraulics
when you have to do a multipurpose dam, when you're going beyond just flood control,
when you're starting to put in the penstocks and the hydro. Does that cause a lot more
difficulty in the design You have to look at a lot more things then, don't you?
In either case, there's no difference as far as the spillway is concerned. The difference is
in the outlet works. For a large dam, like all those on the Missouri that produce a lot of
power, one or more penstocks are needed. These are constructed of concrete underneath
the dam at its base to the power house and turbines that generate the power. In addition,
one or more conduits or tunnels are needed to serve as outlet works. During a large flood,
some water can be released through the power penstock, but not nearly as much as through
the same tunnel if it is not hooked up to a power turbine.
For example, Fort Peck Dam has, as I recall, about six big tunnels, of which four lead
into a stilling basin and are used as outlet works. Maybe it's the other way around--four
lead into the power houses, and two lead into a stilling basin. Normally, when water
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