The Whiskeytown Glory Hole
08/21/2015 08:38AM ● Published by Brandi Barnett
In All It's GlorySeptember 2015
By Laura Christman
Photos: Manda Reed
Whiskeytown Lake's glory hole spillway is a concrete curiosity. From the surface, it looks like a hole in the lake. If you could view it from below, you’d see an enormous funnel.
Much of the time it doesn’t do much. But when the lake is deluged with rain, the glory hole reveals its true purpose and power: It swallows water. Very quickly. Picture an Olympic size swimming pool gulped in about three seconds.
The glory hole, next to Clair A. Hill Whiskeytown Dam, is basically a big overflow drain. Its 24½-foot-diameter inlet narrows to a 21-foot-wide concrete-lined tunnel that drops water vertically more than 200 feet. Intake can be as fast as 28,650 cubic feet of water per second.
“It’s quite a sight to see when it goes,” says Jim Milestone, superintendent of Whiskeytown National Recreation Area. “You can feel the vibration.”
Water rushing through the glory hole goes to an outlet in the dam and is released into Clear Creek. “The water at the base of the dam shoots out like a jet for 100 feet. It’s amazing,” Milestone says.
That doesn’t happen often. Milestone has only witnessed the glory hole in flood-control mode three times during his 15 years at Whiskeytown.
The name comes from the morning glory flower, which has the same trumpet shape. The flood-control device also is called a bell-mouth spillway, drop inlet and shaft spillway. “It’s critical to the integrity of the dam,” Milestone says.
Regular, controlled releases from Whiskeytown Lake are through an outlet that sends water to Clear Creek, Clear Creek Community Service District or a small power plant at the base of the Whiskeytown Dam. Water also is discharged through Spring Creek Tunnel to Spring Creek Power Plant and Keswick Reservoir.
If a big storm pounds the Whiskeytown area, resulting in heavy runoff flowing into the lake, the glory hole provides backup. It slurps into action to prevent the lake from overfilling and slopping over the large earthen dam.
There’s no way to switch the glory-hole spillway on or off – or to regulate how much water goes in. The inlet draws water as soon as the lake rises above its circular opening.
“It’s an uncontrolled release when water is going over it,” Milestone says.
Spillway gates are a different flood-control method. Unlike the passive system of a glory-hole spillway, gates can be opened and shut to control how much water is released and when, but they require manpower.
John Ellingson, civil engineer with the U.S. Bureau of Reclamation in Denver, Colo., says glory-hole spillways are at 28 of the 475 dams the bureau maintains. They have been constructed throughout the bureau’s history and are found in lakes of various sizes with either concrete or earthen dams, he says.
Lake Berryessa in Napa County has one of the bureau’s larger gloryhole spillways, with a capacity of about 48,000 cubic feet per second. “I think it is a fairly unique structure,” says Peter Funkhouser, facility manager at the lake. Visitors often make a point to check it out, he says.
Milestone says Whiskeytown’s glory-hole spillway draws attention, too. There’s a sign explaining how it works near the John. F. Kennedy Memorial at the dam. The glory hole was part of the backdrop when Kennedy dedicated the dam in September 1963.
The area surrounding the glory hole is – no surprise – closed to boating and swimming.
“It’s a dangerous structure. We don’t want anyone near it,” Milestone says. “It’s a straight drop. It’s a huge hole.”
There haven’t been problems, he adds. The glory hole instills respect. There is a bit of an ominous vibe to the thing. Milestone says it reminds him of something from an old Prince Valiant comic strip – a deep, dark hole with a huge creature at the bottom.
“I imagine a giant squid arm coming out,” he says.