100-year lifetime: Flume 41 totally rebuilt

By Michael Raffety

Mountain Democrat

One of El Dorado Irrigation District’s biggest and most complicated flume projects is complete with the exception of some mechanical, electrical instrumentation and control work still under way, though the canal has been watered back up.

Project engineer Daryl Noel gave a report to the Board of Directors Jan. 27, including dramatic video footage of two contract workers, secured by safety lines, jack hammering a huge boulder on the hillside, which then rolled downhill and crashed into a section of wooden flume that was to be demolished anyway.

The wood from the flume timbers proved to be so rotten that it could not be recycled as originally planned.

Removing hazardous boulders and trees on the uphill side of the flume to protect the replacement flume against damage was one of the elements that added expense to the project.

The $5.8 million project replaced 700 feet of rickety wooden flume with cast concrete flume sections and relined 600 feet of canal. Also replaced with a concrete structure was Spillway 23. That spillway, part way into the 700-foot-long Flume 41, was a wooden structure whose supporting posts were resting on rocks placed on an unstable slope.

The flume had been relined by PG&E in 1948. Plywood had been added in 1978 to extend its life until a more permanent project could be implemented.

The concrete flume section will have a 100-year lifespan, according to Noel.

Flume replacements, whether concrete or wooden, are done in October when water to the El Dorado Canal is shut off until December.

Work on Flume 41 actually started in the summer, enabled by having previously spent $1.5 million to upgrade and extend Rock Crusher Road, which saved paying $13,000 an hour for helicopter service to bring in equipment and concrete flume sections. Total helicopter services for the construction project would have been $1.5  million-$2 million, according to Noel. Additionally, the new road provides access to other canal sections and saved having to pay a helicopter to remove empty propane tanks and replace them with full ones to run a generator that operates Spillway 23. Now the propane delivery truck can drive to the new generator shed’s propane tanks.

The work done by contractor ProVen during the summer was to stabilize 450 feet of stacked rock wall serving as a base for the flume since 1876. Two years prior Carlton Engineering had drilled into the stacked rock wall and found it to be stable with minimal voids — 30 percent. Carlton and EID engineering staff came up with an innovative design that saved $700,000-$900,000 by not having to replace the stacked rock foundation.

The work done in the summer was to cover the stacked rock wall with rebar and shotcrete. After the shotcrete set up, holes were drilled all the way through the stacked rock wall and into solid granite behind the rock wall. Anchor bolts were inserted and shocrete pumped into the tubes to bind the anchor bolts to wall and base rock.

After the wooden flume was demolished, holes were drilled from the top of the rock wall at 20-foot intervals and shotcrete was pumped in to fill the voids in the stacked rock wall. The rebar-and-shotcrete exterior wall kept the vertically injected shotcrete contained within the stacked rock.

Upstream of Spillway 23 the flume base for 250 feet was unstable. The contractor dug down to base rock and anchored a concrete retaining wall to the base rock and also to the new concrete base for Spillway 23.

On top of the concrete retaining wall another wall of MSE (Mechanically Stabilized Earth), held in by a stepped formation of wire cages, brought the level up to that needed for the concrete flume foundation.

The flume is part of the 22-mile-long El Dorado Canal, which brings water from four alpine reservoirs at 8,000 feet elevation. The water is captured by a diversion dam on the South Fork of the American River near Kyburz and sent into the canal. The whole system, called Project 184, provides one-third of the district’s water and serves customers all the way to El Dorado Hills in the winter when the pumps from Folsom Lake are normally shut down. It also runs a 21-megawatt powerhouse. Water rights associated with Project 184 date to 1856.

EID’s 2014-2018 Capital Improvement Plan lists two major flume projects — Flume 52A estimated at $1.7 million in 2017 and Flume 42-43 estimated at $3.2 million in 2018.

Replacing the El Dorado Conduit, a rusted pipeline clinging to the side of a granite wall and bringing water from Echo Lake to the South Fork of the American River, is estimated to cost $800,000, including engineering and materials.

Replacing the Camp 2 Bridge this year is estimated to be $1 million. In its current condition it cannot support heavy machinery, only pedestrians and a quad runner.

Five flume projects are under study — Flumes 45, 4, 44, 47 and 48.

“What we are doing at this time is reviewing the remaining flumes that are a high priority for replacement to determine the most feasible method for replacement.  That includes replacement with wood, concrete, or bypass with a tunnel. Who will perform the work will be determined later. The current CIP has each flume identified, but that is subject to change based on the upcoming feasibility report.  The board will receive an information item at the Feb. 24 meeting on the subject,” said Cindy Megerdigian, EID water and hydro engineering manager in an e-mail.

The list of tentatively scheduled meetings included on the Jan. 27 board agenda shows feasibility studies for Flumes 42-48 as an information item on the Feb. 24 agenda and again on the March 10 agenda.


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