By Michael Raffety
Mountain Democrat, 11-23-12
One of the shorter flume sections is being rebuilt by the construction staff of the El Dorado Irrigation District.
Flume 3 is 109 feet long. It was relined by EID in 2000 and last rebuilt in 1946 by PG&E.
The flume is part of the 22-mile system of flumes, canals and tunnels that brings water collected from four alpine reservoirs and is eventually diverted from the American at Kyburz into this system that supplies one-third of EID’s water.
Because it is one of the shorter sections EID did not have to hire temporary workers to help construct it. Five EID employees work six days a week on the project. They began by tearing down the old wooden flume and building new footings that used 78 yards of concrete. The footings are 2 feet by 2 feet wide and the depths vary from 3 feet to 10 feet according to the terrain. That work took six weeks.
Each year the canal is dewatered in October and the powerhouse shut down while flume sections or canals are replaced and the banks above scraped and stabilized to prevent slides. The high priority sections were identified in a study and report by a private geotechnical firm. EID chooses the one most needed to be replaced each year.
Flume 3 is estimated to cost $450,000, according to EID engineer Cindy Megerdigian. That figure includes $200,000 worth of materials, $90,000 of helicopter work to remove the deconstructed material and deliver new wood and concrete. It also includes engineering design and capitalized labor and inspection on the project.
For the third year the flume support timbers are attached by bolted-on plates. This helps the flume better withstand earthquakes and makes it easier to deconstruct when it comes time to replace it. Megerdigian said the reconstruction will last 50 years and the lining will last 25 years.
Additionally the crew filled with rock from the hillside an area below the flume to create a bank that machinery can use to reach Flume 4 when it is rebuilt in three to five years. Its spillway was rebuilt with new foundations in 2009 when some of the timbers and the lining were replaced, according to Steve Lindstrom, hydro operations and maintenance supervisor. The section of Flume 4 west of the spillway was replaced after the 1992 Cleveland Fire.
Two other projects are under way at the same time. A $1.87 million bid was awarded to widen, remove rock outcropping, lay down geotechnical fabric and compacted aggregate base on a 6,230-foot-long road. This road and an all-weather equipment bridge across the canal will provide access to 1,050 feet of flume and will save $1.5 million in helicopter costs next year when 600-foot wooden Flume 41 is replaced with concrete flume sections next year. That is estimated to be a $5.3 million project.
The second project under way at a construction bid of $1.3 million extends the 14-mile Tunnel portal east to accommodate a larger trash rack and create space for a small loader to pick up trash from the rack. currently the trash is picked up by hand from above with a person held by a rope. Also part of this bid is upgrading Spillway 46, abandoning Spillway 47,repairing 200 feet of canal, removing large boulder that have fallen into the canal and stripping and stabilizing the slopes above.
This tunnel is the last one before a short section of canal empties into Forebay Reservoir in Pollock Pines.
All canal work must be completed by Dec. 7 when the canal is rewatered and the powerhouse starts up again.