Caples Dam gates nearly done
By Michael Raffety
Friday, Jan. 17, Ballard Diving and Syblon Reid Construction had installed one of two new dam gates and were set to install the second by the end of that day.
The $329,000 construction project is on-schedule, according to El Dorado Irrigation District senior engineer Jake Eymann, with the sunny weather smoothing the way. Normally a cold wind blows at Caples Lake, Eymann said, but Friday was windless.
The deadline had been to complete the project before February to allow the gates to open for spring runoff, according to the Nov. 8, 2013, presentation Eymann made to the Board of Directors, which authorized the negotiated contract project. Syblon Reid had installed the gates five years before when the weather was snowier and colder at 7,900 feet elevation.
Eymann, whose primary engineering mission for EID is dam safety, had called for the gate replacement after the lower dam gate became stuck and was releasing 9 cubic feet per second from Caples Lake. Eymann called for replacing the upper gate as a precaution, since the actual gate was a small part of the project cost.
However, when the upper gate was pulled out it was found to have been damaged as well.
“It was a pretty disturbing finding,” Eymann said.
The gates had been installed in 2008 using a polyethylene/neoprene seal system. Looking at the removed gates, it was obvious the seals had failed, with pieces of the seals sticking out of the gates. The lower gate — 60 feet below the dam — had vibrated so much that the seal at the bottom of the gate was completely gone.
The second dam gate is 20 feet below the dam.
The two replacement gates were estimated to cost $11,000. This time the gates were constructed with 50 percent more steel and concrete encased by steel in the bottom of each gate. The steel-encased concrete at the bottom of the gate would create better fluid dynamics, Eymann said. The seals this time are made of UHM polyethylene. The new seal material will allow more leakage but is 50 percent larger than the old seals and will be sturdier and more resistant to vibration.
The gates were manufactured with the advice of Dr. B.T.A. Sagar, associated with GEI Consultants. That contract was $42,000. Dr. Sagar is chairman of the American Society of Civil Engineers’ Gates Committee and founding member of the U.S. Committee on Large Dams’ Subcommittee on Gates and Valves.
Eymann said Sagar’s conclusion that vibration was the cause of the lower gate’s failure was spot-on.
To allow the divers to work in the confined space and water that is 37-38 degrees Fahrenheit air is pumped down to the diver by hose instead of air tanks and heated water is pumped around their dive suits. To shut off the flow through the dam outlet a bulkhead is bolted onto the dry side of the outlet gates via an access shaft. After the bulkheads are attached the gates can be removed and replaced by the construction divers.
Divers spend 60-90 minutes in shifts, taking breaks to rise to 20 feet below the surface to avoid the bends. Fellow dive crew members monitor the diver on a video with audio link.
Fish flows into Caples Creek are maintained by a bypass that pumps 5.5 cubic feet per second (about 2,500 gallons per minute) out of Caples Lake. To float the 10-inch intakes for the pumps required Syblon Reid to cut the 3-4-inch-thick ice out with chain saws, Eymann said.
Despite the sunny weather the ice remained thick enough to support ice fishermen who walk out on the lake’s frozen surface.
Eymann said he would be back Monday to test the gates. The dam gates are raised manually via reduction gears. There is no power at the valve house, though PG&E is bringing power to the west end of Caples Lake, where Kirkwood Ski Resort has a water intake for its snow making equipment.
Syblon Reid will demobilize Friday, Jan. 24.
Eymann has worked for EID 14 years. He previously worked for the Division of Dams Safety, which overseas 1,400 dams in the state. EID has 10 dams, five of which are also overseen by the Federal Energy Regulatory Commission as well as DSOD. Eymann is EID’s chief engineer for dam safety, keeping track of hundreds of dam safety regulatory requirements, including FERC’s requirement that EID hire a dam safety consultant every five years, from whose report EID must create a plan within 60 days to implement the findings.
Caples Lake Dam was built in 1917 and completed in 1923.