Big Bertha challenges Flume 9 crew

By Michael Raffety

Mountain Democrat 11-5-10

As men in harnesses and ropes attached to tree stumps dig out dirt, rocks and small boulders on the hillside above Flume 9 “Big Bertha” towers over them. That’s the name the inspectors from the El Dorado Irrigation District have given to the granite outcropping the size of two office cubicles stacked on top of each other.

The question facing the contractor, Syblon Reid, EID engineer Cindy Megerdigian and the EID inspectors is how much to blast off into smaller pieces and what will remain stable and what can be anchored with bolts. The key will be the geotechnical report from Carlton Engineering’s Dave Jermstad.

Flume 9 is a 150-foot section of flume that is being replaced due to its deteriorated condition. The most important part of the $2 million project is the work the five-man crew of cliff dwellers is doing, taking the hillside down to solid, trustworthy rock. Because of the doubtfulness of the boulders above, the crew scraping off the hillside by hand ties their ropes to tree trunks and stumps, not rocks.

As was done last year on Flume 51, once the hillside is cleared and threatening boulders removed, it will be covered with geotextile fabric behind a shotcrete shell to promote drainage and minimize hydrostatic pressure. Additionally it will be anchored to the rocks. Megerdigian, manager of hydro and water engineering, indicated this hillside will include drainage pipes to syphon runoff.

Falling rocks and Big Bertha aren’t the only challenges on the site. It’s a two-mile walk into the Flume 9 site from the Alder Creek Syphon tender’s house. While walking to the site about 9:30 a.m. Oct. 7 an EID inspector saw a mountain lion come down the hill, jump the canal and walk toward him on the catwalk. The lion saw him and turned around and went down the hill. It was probably that chartreuse green vest with reflective white stripes that froze the lion and sent him over the deer fence in a different direction. That’s one heck of a notation for the inspector’s daybook.

Megerdigian held her hands apart to describe the size of the lion’s tracks, leaving a space that looked about 10-12 inches wide.

Besides mountain lions on the catwalks and bears, such as the one that pooped on the plastic covering protecting the new concrete on a canal section last year, the real enemy is rock. On the two-mile walk to Flume 9 there were rocks in the canal and some rocks large enough that you would have to be Arnold Schwarzenegger or Larry the Cable Guy to even think about lifting or moving them. As they made their way from somewhere farther up the hillside they left little dings in the sides of the new concrete flume sections that PG&E had put in between 1980 and 1983. The dings and chunks taken out also resulted in cracks along the base where the bottom of the concrete flume meets the sides.

When EID built the Mill Creek-to-Bull Creek Tunnel it took out some of the PG&E concrete flume sections to reuse elsewhere. It also gave the engineers an opportunity to study them and come up with a stronger design with more rebar, but still keep each section generally close in weight, since most often they are put in place by helicopter at $13,000 per hour.

When a wooden flume is replaced with a cast concrete one, the aim is to design and construct a replacement that will last 100 years, Megerdigian said. Flume 9, a wooden flume, was last replaced by PG&E 40 years ago. With slope stabilization and stronger cast concrete designs Flume 9 should meet that century standard.

Flume 9 will join 0.9 mile of concrete flume already in place. It will connect some concrete flume on one end and shotcrete lined canal on the other side. There are 15.7 miles of in-ground canal, 3.5 miles of tunnels in two different sections, 0.6 mile of pipes and 2.3 miles of wooden flume.

EID’s own construction crews are rebuilding three wooden flume sections at the same time Syblon Reid is rebuilding Flume 9. Rebuilding three wooden flumes in-house was estimated to cost $719,000. That may not be a final figure. The crews were replacing one box of a fourth section of another flume that had slumped below grade and found several other neighboring box sections rotted and in need of replacement, Megerdigian said.

The wood flume sections are joined by epoxy caulking that is suitable for drinking water and will hold up under freezing and thawing.

The $2 million figure for Flume 9 includes geotechnical engineering by Carlton Engineering and replacement of the fish screen on the Alder Creek diversion. Concrete for the new fish screen was brought in by helicopter and was being poured from 8:30 a.m. to about noon Oct. 13. It will take a few days for the concrete to set up, so EID was keeping its fingers crossed that the state Department of Fish & Game would allow a few days extension beyond the Oct. 15 deadline to complete the fish screen project.

The hillside at Flume 9 is supposed to be cleared by next week after the Mountain Democrat’s Oct. 13 visit to the site, Megerdigian said. The Syblon Reid cliff hangers are working seven days a week, 12-14 hours a day. Once the hillside is cleared the contractor will start digging down 7 feet below the existing flume grade and start building up an engineered base with the material collected on-site from the hillside. That base will be 95 percent compacted. It is tested every foot. Every 18 inches a geo-grid will be laid down.

This section is wide enough that a retaining wall won’t be needed. PG&E had buried timbers under the flume on this section to form a base. The contractor is digging those out and piling them up on the side. In place of those timbers there will be a concrete base on top of the compacted base.

The contractor accesses the site by an ATV with balloon tires so it can travel down the canal to the access road. Its tractor was helicoptered in.

The new flumes are due to be ready for water by Dec. 10 when the powerhouse will start up.

The 22.5-mile canal system was built by the El Dorado and Deep Gravel Mining Co. in 1876 at a cost of $650,000 to bring water to mining operations in and around Placerville. The canal is filled by a diversion dam on the South Fork of the American River near Kyburz. By the time the canal ends at Forebay Reservoir in Pollock Pines it is 1,600 feet above the river.

In 1907 it was sold to Sierra Water and Supply Co. for $40,000. That water company sold it to Western States Power Co. in 1916 for $215,000. In 1919 the state Railroad Commission gave the El Dorado Water Users Association 15,086 acre-feet of water from the project. Those water rights transferred to EID when it was formed and certified on Oct. 5, 1925.

Besides the canal and flumes, dams at Silver Lake and Caples Lake in Amador and Alpine counties, Echo Lake and Lake Aloha in El Dorado County store water for the project, designated as Project 184 by the Federal Energy Regulatory Commission, which licensed the hydro project in 1922. It was sold to PG&E in 1928.

In 1999 PG&E sold it to EID for $1 and gave the district $15 million to repair it after the 1997 flood ruined the generators and damaged sections of flume. EID now has a 50-year license to operate Project 184.

Project 184 supplies 30 percent of the district’s potable water. While the El Dorado Hills Water Treatment Plant was being rebuilt this winter it supplied all the water for El Dorado Hills via Water Treatment Plant No. 1 in Camino. It also can back up water supplies to Sly Park’s Jenkinson Lake via the Hazel Creek Tunnel.

In 2001 and 2007 Carlton Engineering studied the canals and flumes and made a priority list of flumes to replace. The five-year capital improvement plan lists nine sections varying in length from 40 feet to 400 feet, Megerdigian said. The flume replacement and improvement project will take about seven to eight years, she said, and then the district will start looking at the canal sections. Some sections will remain wood for practical and economy reasons.

Each October the hydro department dewaters the canal to do one 100-year flume replacement and a couple of wooden section rebuilds by the in-house construction and canal crews. Beating the weather is always a challenge. And, of course, every section has its Big Bertha, not to mention cougars.

E-mail Michael Raffety at mraffety@mtdemocrat.net or call 530-344-5067.

 

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