Water Resources: Hydraulics and Hydrology
Horse Mesa Dam
I see you also worked for the Salt River Project.
Yes. I was a consultant on Horse Mesa Dam, which was constructed by the Bureau of
Reclamation. The Salt River Project Water Authority purchases its hydroelectric power
and is responsible for operation of the power plant, and some water releases for down
river use.
The dam is a concrete arch dam, about 200 feet high, with two spillways, one on each
abutment, and low ogee crests with no gates, but each one of them has three
gate
bays. Each spillway has a concrete-lined channel chute with a flip bucket above the
maximum water level downstream of the dam, which flips the water out into the
downstream river channel.
The two spillways were not designed to handle the maximum flood. A large
diameter concrete-lined diversion tunnel was constructed on the right abutment. Large
gates were constructed at the upstream end of the diversion tunnel, which, after the dam
construction was completed, remained closed to store water in the reservoir, except during
major floods when they were opened to assist the spillways in controlling the floods.
When a large flood occurred, the gates were opened fully, which caused the tunnel to flow
full. A flip bucket at the downstream end of the tunnel flipped the water into the river
several hundred feet downstream of the dam.
The tunnel was on the right side of the dam, and it was directed at about a 30 degree angle
to discharge in to the river. The river channel wasn't very wide, and both abutments were
quite steep. There was a road on the left river bank that was used for access to the
powerhouse. Large tunnel flows crossed the river and impacted on the left river bank,
washing out the powerhouse road. Each time the road was washed out, it would be
several weeks to three months before the road was repaired and the powerhouse was back
in service. This resulted in considerable loss of power revenue.
The Salt River Authority decided to study what could be done to prevent the road from
being washed out by every major flood. I was asked to serve as hydraulic consultant for
the study. They didn't have a board. I met with the authority's engineers, discussed some
preliminary plans that had been made and inspected the site. I suggested that a hydraulic
model be constructed to test several possible remedial plans. The authority agreed with
my suggestions.
The authority wanted to interview several laboratories and select the best qualified one to
make the model studies. I suggested they interview the Bureau of Reclamation laboratory
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