Wednesday, April 23, 2014

Flume 41 being replaced

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CARPENTER FOREMAN Tom Dobbs taps a 2-by-4 into place to help brace the concrete form that will be part of the spillway for Flume 41. Democrat photo by Krysten Kellum

From page A1 | October 25, 2013 | Leave Comment

The construction crew for contractor ProVen was wrapping up the form for one side of the new spillway on Flume 41 and was expecting five truckloads of concrete about noon Wednesday.

The contractor has been working on the $4.1 million project since August when they added crisscrossed rebar to the sides of the stacked rock wall that dated back to 1876 and then sprayed shotcrete on the sides. The sides are also held together by anchor bolts driven through the stacked rock and 10 feet into solid granite on the interior side of the wall. Once the outer wall set up and cured grout was pumped into tubes set eight feet apart on the top of the stacked rock to fill up any voids between the rocks. The pumping was done at 10 psi, according to Dave Jermstad of Carlton Engineering. Along the outer perimeter of the top of the stacked rock were tubes set 20 feet apart that Carlton Engineering used to drill out cores and confirm that grout had spread throughout the rock wall.

The result of the two-part process was an historical rock flume bench essentially glued in place. El Dorado Irrigation District project engineer Daryl Noel said during a tour of Flume 41 two years ago that keeping the stacked rock and filling the 30 percent voids would save $700,000-$900,000.

Additionally the district saved $1.5 million-$2 million in helicopter expenses by spending $1.5 million to widen and improve Rock Crusher Road, add a wide and strong bridge over the canal and provide a marshalling site for equipment.

This road provides access to Flume 41 and other flume sections, allowing truck and equipment access.

By Wednesday’s visit the uphill side of the flume bench had been scaled of trees and of loose dirt. Loose boulders — about 150 years worth — had been rolled off the hillside and  busted up for use as retaining wall elsewhere to widen the pathway along the canal downstream of Flume 41. Some were described as the size of three cars.

The 697 feet of wooden flume had been removed and 603 feet of canal had been filled in to serve as a temporary road for equipment and concrete trucks to drive to the Flume 41 bench.

On the upstream side of the spillway forms was another section of Flume 41 where a tracked loader was removing loose boulders as a ProVen crew worked on a form for a concrete retaining wall. Eventually an MSE wall, which is Mechanically Stabilized Earthen wall, will be added above the concrete base. It is essentially crushed rock in metal cages, fabric and engineered packed earth. Each layer is built up, with each level moving inward like the sides of a stepped pyramid.

The 73 precast concrete flumes that will replace the 65-year-old wooden flumes are being made in Redding, according to Cindy Megerdigian, water and hydro engineering manager. EID shipped its forms up to Redding, where a subcontractor is actually pouring the forms and will deliver them for less than it would have cost EID to order concrete delivered all the way up to its form site above Pacific House. The concrete doesn’t become stale at the Redding site and it has an approved testing lab, which Carlton Engineering inspected.

After the concrete flumes are placed then the filled-in canal section will be regraded, install a subsurface drainage system, add reinforcing steel and a new concrete canal liner.

This is not the only work under way since the water to the canal system was shut off Sept. 29.

District crews added some bracing and a second plywood liner to 432 feet of Flume 42/43. District crews had lined this section in 2000 and added additional timbers and bracing then. The structure for this dates to 1948. On Flume 45 the district crew removed and rebuilt two sections about 20 feet long.

The final job district crews were wrapping up was removal of Spillway 47C near the 14-mile tunnel, whose entrance had been improved last year along with reconstruction of Spillway 46. Spillway 47C is now just a dirt swale protected by fiber coils. In its place is a new wooden flume section and substructure, plus a wider side path that will accommodate snow removal equipment.

All work on the flumes and canal, which are part of Project 184, get approved by the Federal Energy Regulatory Commission. The plans and a summary following construction are approved by one person in the San Francisco Office who is a geotechnical engineer. Environmental studies for Project 184 are forwarded from the San Francisco office to Washington, D.C., office for review and approval. Anything having to do with a dam requires double paperwork — to FERC and to the state Division Safety of Dams.

In September 2012 EID held a night workshop of its five-year Capital Improvement Plan, then pegged at $85 million, of which $40 million was in the hydroelectric category.

“Is here light at the end of the tunnel when this (flume) replacement and upgrading ends?’ asked Cameron Park resident Greg Prada then.

“We have four flume sections listed as high priority. It levels off after that,” EID General Manager Jim Abercrombie responded then.

The 22 miles of flumes, canals and tunnels bring water from four alpine reservoirs in three counties to Forebay Reservoir, which then provides one-third of the district’s water and runs a 21-megwatt powerhouse that brings in an average of $8 million of revenue annually.

Michael Raffety


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