ContentsPutah and Cache: Monticello Dam

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"Glory Hole," from Narrow Way to Nearby

David Robertson

The Glory Hole, David RobertsonThe Glory Hole, Convolvulus concretis Ecotourist. Large concrete morning glory. Diameter of rim = 72 feet. Diameter of neck = 28 feet. Unique, but easily seen in its native habitat.

To worry about #1

Dam can't hold inflow

"48,000 CFS can go through the Glory Hole, max. The one remaining exit value (you remember the other value was taken by the hydroelectric plant) will let out 2,500 CFS. That's 50,500 CFS maximum outflow. In the early 80s, the maximum input ever recorded happened, 98,000 CFS." The lake rose 3 feet in a 4 hour period."

To worry about #2

Catastrophic dam failure with water at 456 feet

"Well, in the first place, the dam gains strength the higher the water level. The water pushes the dam in against the rock anchors. I mean, the dam is anchored into layers of the Great Valley Sequence that lean in a direction opposite to the dam's thrust. It is built to withstand a direct hit of a 5.0 earthquake."

To worry about #3

A direct hit by a 5.1 earthquake

To worry about #4

Cavitation of Glory Hole

"No evidence of cavitation has ever been detected. On the other hand, the water has only been 7 feet above the hole, and it can go to 16, since the Glory Hole is 440 feet above mean sea level, and the dam is 456. We have only computer modeling to tell us what would happen if water got that high. The computer says no cavitation."

To worry about #5

Concrete loses its integrity

"Concrete is porous. So the Bureau of Reclamation sends a drill down to take out thin cores at diverse places and tests them for give. It also tests for cracks that run laterally. One of these tests has just been conducted, but the results are not in."

To worry about #6

The whole dam moves downstream

To worry about #7

The two parts of the dam move out of sync

"The dam superstructure sways, .5 inches a year, back and forth. But, so far the base of the dam has not moved. The two parts, each 45 feet thick, move together, upstream-downstream, according to how much water is pushing it and what the temperature and humidity are. If they start moving in toward each other, you don't want to be in there. The B of Rec is so worried about his they have installed devices to monitor weak motion, and they do triangulation calculations from he nearby hills. They also put in a plumb line monitor on the inside, between the two sides of the dam. Information from all these instruments is fed into computers. I have a computer at home and at my office. A battery of phones here at the dam calls a series of numbers in sequence until someone answers. If someone answers and then doesn't show up, it is programmed to start through the list again."

To worry about #8

Sedimentation

"Not to worry about. It would take so many lifetimes. As long as it doesn't fill in 13 years and 7 months, when I retire, I'm happy."

But Ecotourist was still worried. After all, the dam is anchored to sedimentary rock that tectonics has turned almost straight up. So he got out the newly released "inundation map" and spread it across the floor of his computer room. The people at the Bureau of Rec. had always told him that the main thrust of water would not hit north Davis on the first flow through. It would go all the way to the Yolo Bypass levee and back up into his territory.

"Well," thought Ecotourist, "that would give me hours to do something, and the depth wouldn't be that great . . . probably. I could climb up on the furniture."

This is not what the map said. According to the "Monticello Dam Breach Simulation," the water would hit his Village Home in less than three hours on the first flow through. None of this going 15 miles past his house and coming back, lapping harmlessly at his back doorstep.

His subdivision was colored green. "This is surely a good sign," he said.

"Not so," said the legend, "green means a 4-5 meter depth of water."

"4-5 meters! That's higher than a basketball hoop."

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