Structures at dam get repair workLower water levels this spring are letting the Bureau of Reclamation do some catch-up work on repairs at the Jamestown Dam. Work started this week on two routine-maintenance projects on the dam’s outlet structure.
By: Keith Norman, The Jamestown Sun
Lower water levels this spring are letting the Bureau of Reclamation do some catch-up work on repairs at the Jamestown Dam. Work started this week on two routine-maintenance projects on the dam’s outlet structure.
Both projects require draining the stilling basin. This structure allows the water to slow after it flows from the outlet pipe.
“We’ve built a dike across the river and pumped out the stilling basin,” said Duane Krogstad, civil engineer with the U.S. Bureau of Reclamation. “Now we can work on and around the stilling basin structure.”
Krogstad said the hill to the east of the stilling pond contains a high amount of shale, which has ground water flowing through it. The drain tile system at the base of the east side of the stilling pond had become clogged and needed to be replaced. The new drainage system, when installed, will drain water away from the soil around the stilling pond and reduce pressure on the walls.
The second project will repair the stilling pond walls.
“The water table around the spillway has been so high we have water seeping into the concrete joints of the walls,” Krogstad said. “The freeze-thaw cycles have caused damage to the concrete.”
The plans call for chipping out any damaged concrete on the walls and replacing it.
Lake levels at the Jamestown Reservoir were drawn down to about seven inches below its normal summer level of 1,431 feet above mean sea level. This will allow for some additional inflows from upstream and any rain events during the repairs, according to Bob Martin, dam manager for the Pipestem and Jamestown dams.
“We will continue to have a flow of about 75 cubic feet per second from the Pipestem Dam until September,” he said. “That will be the only flow into the James River other than incidental seepage from ground water.”
Martin said the 75 cfs releases may seem small compared to recent high water years.
“But if you go back a few years to the dry years there were times there was no release of water from the dams,” he said.
The releases from Pipestem Dam will lower the lake’s level by about seven feet by the end of the summer. The lake will then be at 1,442 feet and at the planned level for the winter.
Releases from Jamestown Dam had been at 34 cfs before the start of repairs. Releases may not resume after the repairs depending on rainfall amounts.
Krogstad said the repairs to the stilling pond are routine and had been planned for 2011 but could not be accomplished because of high water.
Work is expected to be completed in two to three weeks depending on weather conditions. The project has an estimated cost of between $50,000 and $75,000. The project is being managed by the Bureau of Reclamation in conjunction with the Garrison Diversion Conservancy District.
Sun reporter Keith Norman can be reached at 701-952-8452 or by email at email@example.com