Historic flume up to speed | TheUnion.com

Historic flume up to speed

Construction crews from Pacific Gas & Electric Co. are rebuilding part of the South Yuba Canal, a historic flume that continues to supply fresh water to western Nevada County.

The work started about three weeks ago in the Bear Valley area. It will conclude Thursday in time for water to flow down the newly rebuilt section on Friday.

The flume was last rebuilt about 30 years ago, hydro-construction foreman Don Leal said.

The flume first was built in the early 1900s, running from the Spaulding No. 2 Powerhouse just below the dam at Lake Spaulding to the Deer Creek Powerhouse off Lowell Hill Road, 19 miles away.

It was built as part of the Drum-Spaulding Hydro System to deliver drinking and irrigation water to Nevada City and Grass Valley. The two powerhouses, along with Spaulding No. 1, generate electricity for customers in Northern California.

Five types of construction make up the canal. Workers are rebuilding a 759-foot section of box flume made of cedar.

The rot- and pest-resistant cedar comes from trees grown in Canada and Washington. The wood is specially milled in Washington into boards 2 inches by 12 inches by 16 feet long. The groove-and-spleen milling creates square grooves at each edge of every board; a square half-inch spleen fits in between. When the wood gets wet, it swells to form a leak-proof seal between each plank.

The milling is done the same way as when the box flume was first built around 100 years ago.

Workers nail the planks onto 4-by-4-inch trusses, which are milled from specially treated wood and also are being replaced in the reconstruction project. In some places, workers are building on the original crushed-rock base.

In the old days, mules would have packed in the materials.

But now, a helicopter is flying in the material and tools from a staging area in Bear Valley. The round trip takes about seven minutes. Service is provided by P.J. Helicopters of Red Bluff.

To get to their job site, the men walk on boards set atop the flume’s upper crosspieces, creating a wooden path about 18 inches wide. The trip is about three-quarters of a mile each way.

The rest of the canal consists of a steel-tube flume called the Lennon Flume, a couple of tunnels, cement canals and open ditches.

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