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Posted on June 6, 2017

Nevada County: Water Flows Again in South Yuba Canal Flume Following PG&E Repairs

By Mark Mesesan

Water is once again flowing through a reconstructed section of a PG&E flume on the South Yuba Canal — for the first time since February, when a storm-related landslide took out the flume.

This is not only good news for PG&E and the U.S. Forest Service, but also the Nevada Irrigation District, which uses water from the canal to service 13,000 customers in and around Grass Valley.

Water is once again flowing after recent repair work on a PG&E flume on the South Yuba Canal.

While PG&E crews still have several weeks of work left to complete the project, construction of the new timber box flume, with upstream and downstream reinforced concrete transition structures, has been safely completed.  Water started running in the canal at about 30 cubic feet-per-second, with expectations the flow rate will be ramped-up in the coming days.  Normal maximum flows at this time of year are at approximately 95 cubic feet-per-second.

PG&E’s Mike Jones, senior director of power generation project & asset management, acknowledged employees for their hard work.

“I want to recognize our employees who worked safely through adverse weather and other challenges, working long hours, including through the Memorial Day weekend to meet our deadline to return the flume to service,” he said.

The flume is located near the 8.5 mile marker of the canal, downstream from PG&E’s Spaulding 2 powerhouse.

Jack Ryan Naylor, PG&E project manager, said both the weather and terrain posed challenges on the repair project.  In addition to 16 inches of rainfall during April repair work had to be carried out on a steep hillside with limited access.

A downslope view of the recently-repaired flume on the South Yuba Canal.

“Getting equipment down the slope for excavation and getting material up the slope to off-haul were both very difficult and time-consuming activities,” Naylor said.  “Thousands of tons of rock was placed, graded and compacted to establish access and make the 3.5 mile road passable for dump trucks,” he added.  A helicopter also was routinely used to move material.

Nevada Irrigation District officials, who had been concerned about their water delivery capability to customers in Grass Valley and Nevada City due to the non-operational flume, asked for a 25 percent reduction in water usage for the last two weeks in May.  The conservation efforts, combined with available water storage and on-time delivery of the PG&E replacement project, prevented a more significant loss of service to the district’s customers.

Remaining PG&E work will include final grading of the slope and mid-slope drain; installing slope erosion protection; removing the last 12,000-to 15,000-cubic yards of material from the February landslide; and restoring ground in compliance with PG&E’s Stormwater Pollution Prevention Plan.

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