By Michael Raffety
Mountain Democrat 10-28-11
Four regular construction crew members and four temp workers are busy hammering away at 336 feet of wooden flumes the El Dorado Irrigation District is rebuilding from the ground up. They began Oct. 3 and by Oct. 26 had all the framing in place.
The EID construction crew is rebuilding two flumes, identified as Flumes 39 and 40. The two flumes hook up on the east to a section that was rebuilt last year. Each flume section is separated by a short section that is a sharp turn and won’t be rebuilt until next year. That sharp bend is elevated and requires engineering and steel girders, according to Steve Lindstrom, hydro operations and maintenance supervisor.
Flumes 39 and 40 are remote enough that the demolished materials needed to be taken out by helicopter and the new, precut treated timbers and lumber needed to be helicoptered in.
A small portion of the flumes under construction are slightly elevated and required the crew to build concrete piers sunk 8 to 15 feet into the ground.
“Flume 39-40 is a 520-foot-long section with portions last rebuilt in 1951 and 1961,” wrote Cindy Megerdigian, EID water-hydro engineering manager.
“Replacement work has been occurring over a three-year period starting in 2010 with the last sections scheduled for replacement in 2012,” wrote Megerdigian. “District crews have been providing construction work with engineering and environmental (studies) provided by district staff and consultants. When full replacement is complete in 2012, the estimated cost for all labor, materials, design, and environmental is estimated to be just under $3 million.”
Wednesday several workers were using a palm power tool to attach metal strips securing the beam joints. Bigger metal strips were hand-hammered to the beams.
Meanwhile the top construction duo were hammering in the tongue-and-groove planking that covers the bottom of the flume. Each plank was tightened by using two 2x4s, with the outside 2×4 hammered down and the wooden wedges driven between the two 2x4s, which jammed the loose board against the plank.
Near Camp 5 four EID construction workers are rebuilding Spillway 42, with major concrete work and new timbers.
The spillway has two elements. One is three automated spillway gates that can be operated remotely by EID’s proprietary computer system. The spillway is opened in case of a blockage that causes the water in the flume to rise too high. This will prompt a canal worker to go out and inspect that section of the canal to see what is causing the high-water alarm to go off.
The second element of the spillway is a manually operated section in which flash boards are lifted one at a time. These flash boards are used to skim off ice in the winter and send it down the spillway.
Flume sections total 2.5 miles, tunnels total two miles, and the remainder of the upcountry water conveyance system is 17.5 miles of canal. It starts at a diversion dam near Kyburz. The low dam on the South Fork of the American River collects water sent down from four alpine reservoirs EID owns in three different counties – Echo Lake near Echo Summit, Lake Aloha in the Desolation Wilderness, Silver Lake in Amador County, Caples Lake in Alpine County.
About a mile or so west along a canal section east of Flumes 39 and 40 is Flume 41, which will be next year’s big flume replacement project. It will be put out to bid. This one won’t be rebuilt as wood, but will be concrete flume sections — 87 sections in all. Flume 41 is 1,200 feet long.
This section will require tree removal uphill and hand-scaling the dirt down to bedrock. There are also a number of granite outcroppings that are unstable and will need to be blasted down and broken up.
Before any work starts next year, the EID engineering department and environmental compliance officer will be commissioning bird surveys for spotted owls and goshawks. Then permits must be obtained from the Forest Service, the Federal Energy Regulatory Commission and the state Department of Fish and Game.
Flume 41 will be a more affordable project because it won’t require helicopter work at $200 a minute. It will be accessed via Rock Crusher Road and Oglesby Road, plus a bridge that EID will construct. That bridge will also provide access for future flume and canal work west of the bridge.
Daryl Noel, the EID engineer who oversees canal and flume design, is excited about Flume 41. It sits on a dry stack foundation that dates back to the flume’s original construction in 1875-76. Rather than replace it with caged crushed rock retaining walls and foundation, which was done on Flume 51 the year before last, he and Carlton Engineering have devised a more creative solution.
Carlton drilled core samples underneath Flume 41 from all the way to bedrock on the other side. What the engineers found was the dry stack foundation continues all the way under the flume with no fillers and doesn’t stop until it hits bedrock on the uphill side of the flume.
That means the engineers can keep the dry stack wall and fill its 30 percent void with shotcrete.
“From an engineering standpoint, it is cutting edge,” Noel said.
Besides that, it will save $700,000-$900,000 on this job and will mean it can be done within the October to mid-November six-week period in which the canal and powerhouse are shut down.
It’s solving engineering challenges like this and coming up with innovative solutions that cause Noel to say, “It’s pretty fun work.”