Originally published in the Seattle Post-Intelligencer, June 13, 1948
Army engineers finish valve system
By Fergus Hoffman
Like the glowering mouths of naval guns, the polished valves of Mud Mountain’s three 8-foot penstocks jut from beneath the control tower built into the solid rock of the outlet gorge. The penstocks, one on top and two below, are carried in, a 2,000-foot-long tunnel which is rammed straight through the solid mountain rock beside the dam. When this picture was made, only one of the three valves was open, jutting its terrific force against the canyon wall. (U. S. Army Corps of Engineers photo by R. A. Lee.)
MUD MOUNTAIN DAM, June 12.—Like a thousand crystal geysers rocketing into canyon sunlight from a 2,000-foot torpedo tube, the White River is earning its name today.
Thunderously white, spurting and spraying against the cliffs of a narrow gorge with-rock-polishing force, the White River has been tamed by Mud Mountain Dam, but the taming has dramatized the hitherto prosaic mountain stream which once posed an annual flood threat to the downstream valley.
Now, after 10 years of work and 12 million dollars in financing, the U.S. Army Corps of Engineers has control of the river, this last step due to completion this week of the valve system.
Only one valve, controlling one of the three eight-foot penstocks—or pipes, is open.
Dam built in box canyon
The dam is built in a narrow box canyon, opening through a rock cleft on the downstream end with vertical cliffs rising nearly 230 feet high on either side of the gorge. The dam site is 90 feet wide at the river bed and 150 feet wide at the top of the rock walls.
The dam is a giant rock fill, with a central watertight core covered with transition sections and supported by slopes of quarry rock and boulders.
Mud Mountain, the engineers stress, is a one-purpose dam. It wasn’t built to produce electricity. It wasn’t built to hold water for summer irrigation.
It is a flood control dam.
For this reason, the reservoir behind the dam normally is kept empty.
Crest of dam 425 feet high
It doesn’t look like much water for a dam to be holding back, but this reservoir behind Mud Mountain Dam is kept at low level whenever possible so there will be room for flood waters if storms or melting waters cause the White River to rise. View shows precipitous box canyon in which dam was built. Concrete spillway apron is visible between crest of dam and bank at right. Engineers are logging reservoir canyon to prevent erosion from landslides.
The crest of the dam is 425 feet above the lowest bedrock of the river. Not even this could withstand the terrific, immediate erosion if the water overflowed the crest.
So there is concrete-lined spillway, 315 feet wide at its crest, on the right bank.
The spillway discharge capacity is almost five times the greatest recorded flood on the White River. The engineers don’t expect such a great flood—but they believe in safety first.
There are two tunnels. The first is nine feet in diameter, designed to carry the unimpeded normal flow of the river.
The second tunnel is 24 feet in diameter. It has three penstocks—long steel pipes, each eight feet in diameter. Two lie side by side, the third resting on top of them.
Pipes controlled by 96-inch valve
This is the view of the thunderous outlet of Mud Mountain Dam as seen from the original bed of the White River where the stream cut its way through sheer rock walls. H.V. Tuttle, resident engineer in charge of operations, stands on concrete work which was built for migrating fish (now abandoned because the fish refused to cooperate and now are netted from the river and trucked to the waters above the dam). Normal flow of river is piped under the dam through small tunnel, just out of the picture at right, while controlled excess shoots 2,000 feet through a much larger tunnel, blasting forth in voluminous white spray. (Post-Intelligencer photos by Stuart Hertz.)
At the upstream face of the dam, there are intakes for the pipes. At the downstream ends of the pipe, each is controlled by a 96-inch valve. Each valve can be regulated to shut, open, or partly open positions.
A control house built in the solid rock just above the outlets is the “brain” of the dam. The engineer drives down a rough mountain road and across a high wooden trestle to the foot of the dam, then steps quickly from the canyon heat into the 55-degree coolness of an access tunnel running laterally onto the penstock tunnel.
Inside the air is raw with the smell of lately cured concrete. Steel doors sweat precipitation. There is silence, until the doors to the control room are opened and the engineer climbs a steel ladder to the balcony-like bridge.
Roar of water deafening
Then the roar of water smashing through the open valve is deafening. Outside, on the concrete wing of the control bridge, the sensation is the same as that on the flying bridge of a speeding navy cruiser far at sea.
The spray flies back into the faces of observers. Directly and far above, the wooden trestle is overhead. Dead ahead there is nothing but the white, foaming water of a river busy earning its name.
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