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Corps Scrambles to Dredge Napa River by Nov. 30 Deadline

Posted on November 22, 2016

By Howard Yune, Napa Valley Register

After a month-long detour and mechanical problems earlier this month, the dredging crew for a long-awaited project to excavate the Napa River now has less than two weeks to finish the job.

The U.S. Army Corps of Engineers is overseeing the first dredging project on the Napa River since 1998. Workers are facing a state-imposed Nov. 30 deadline to avoid disrupting fish migrations in the waterway.

Dredging in Napa began in late September but was soon halted as the Corps’ contractor, Ahtna Design-Build Inc. of Alaska, moved its equipment north to excavate the port of Fort Bragg ahead of the state’s Oct. 31 deadline there.

Upon returning to the Napa River this month, workers have had to cope with accumulated debris and silt from the past two decades. Workers began excavating near the Third Street bridge Tuesday but encountered mechanical problems that slowed progress into Thursday, according to city spokeswoman Jaina French.

“It’s construction and there’s a lot of moving parts,” said Pamela Patton, project manager in the Corps’ San Francisco district. “The cutter head on the dredger has sucked up tires and debris, and we’ve had to deal with getting it out of the head and disposing it. It’s because we haven’t dredged there for so long, there’s a buildup of miscellaneous debris that gets caught up in the machinery.”

The Corps is preparing, but has not yet locked in, arrangements for completing the work if parts of the river are not excavated by month’s end, she said.

Plans call for clearing 60,000 cubic yards of silt from various shallow spots on a 17-mile section of river, from the Third Street bridge down to Asylum Slough near Highway 37 in Vallejo. The project will ensure a minimum 9-foot depth on the river to downtown Napa, the limit of its navigable waterway.

The project will correct shoaling problems that have increased the hazards even for smaller vessels and caused the cancellation last December of the Napa Valley Yacht Club’s annual Lighted Boat Parade.

The work is being carried out with a barge-like vessel equipped with pumps, support poles to anchor the boat to the riverbed, and a cutter head attached to a pipeline, according to the Corps. After positioning the dredge over a shallow section of river, workers lower the cutter to the channel bottom, where the cutter head rotates and breaks up sediment.

A system of pipes and pumps conveys the sediment to one of two deposit sites, one near Imola Avenue and another near the future Napa Pipe development.

With the deadline fast approaching, the Corps has expanded its dredging schedule, which Patton said will run 24 hours a day for most of the river despite earlier plans to shut down work overnight within city limits. At the waterway’s northern tip in downtown, dredging will shut down between midnight and 6 a.m. to minimize the disturbance for guests at the Napa River Inn, she said.

The Corps has advised those living or working near a dredging zone to expect noise of about 90 decibels, with peaks of 100 dB, as crews shift from north to south down the river. A 90 dB sound level is equivalent to being 25 feet from a motorcycle, while 100 dB is about the noise level of lawn mower or garbage truck, according to Purdue University’s Department of Chemistry.

Such noise may affect guests at the Napa River Inn, where some guest rooms will be as close as 40 yards to the dredge, for about five days, according to the hotel’s manager Sara Brooks. But the impact, she added, will be less than it could be because the delays have pushed work into a quiet window between the Napa Valley Film Festival and Thanksgiving weekend.

“Because of the delay it actually benefited the hotel; occupancy (this week) just isn’t as high as it normally is,” she said Thursday.

Source: Napa Valley Register

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