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Posted 7/30/2012

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By Tyler M. Stalker

NAPA, Calif. – Downtown Napa has a long history of serious flood events, recording 15 significant flood events in the past 70 years, or about one flood every five years on average.

The U.S. Army Corps of Engineers Sacramento District would like to change that history, as it will wrap up construction Aug. 3 on a significant effort in downtown Napa to raise 3,300 feet of railroad tracks as much as six feet and construct two new bridges to help reduce the city’s flood risk. 

Nearly three years after an unexpected windfall brought up to $99 million to flood risk reduction projects in downtown Napa, the contract is the first of three significant components funded by the American Recovery and Reinvestment Act of 2009 to be completed.  

By awarding the $65 million sole source contract in 2008 to Suulutaaq, Inc., the Corps was able to expedite flood risk reduction efforts at a reasonable cost.

While sole-source contracts are not put out for competitive bid, they are still awarded in accordance with federal regulations, and compared and negotiated against a detailed government estimate to ensure fair and reasonable pricing for all project costs.

“Anytime you work in an urban area, particularly one with historical structures, you’re going to find things you didn’t expect and those can drive up the costs,” Corps project manager Dave Cook said.

Costs for this phase will rise to nearly $79 million, but downtown Napa’s flood risk could not be reduced without completing this work first.

“This is not the end for us,” Cook said. “We’ve still got to focus on completing ongoing construction on Napa Creek and beginning construction on the oxbow bypass channel.”

Construction of the new dry bypass channel is key.

According to Cook, raising and relocating critical infrastructure—as well as removing a bridge that historically caught debris preventing water from passing—provides some benefits, the real flood risk reduction benefits come from creating an easier path for potential flood water to get down the Napa River. 

The Napa River has an oxbow, a large U-shaped bend in the river, near downtown Napa. When water reaches the bend, the water slows down, often overtopping the levees during large storm events and bringing increased flooding into the downtown area. 

To address the flooding the Corps plans to construct a dry bypass that creates a straight path across the oxbow, allowing water to get downstream easier and more quickly, but only after completing the current phase.

In order to be able to construct the channel, crews first had to raise the railroad tracks onto an elevated bridge, so the new bypass could be constructed beneath it.

It’s the combination of these three components that will hopefully help the region avoid a repeat of the record flooding encountered in 1986 and 2005. 

The 1986 flood was estimated to be a 35-year event, meaning it was a storm that has a three percent chance of occurring in any given year. The flood resulted in three deaths, 27 injuries, thousands of evacuations, hundreds of homes destroyed and a bill surpassing $100 million in damages.   

The most recent flood event in the region occurred in 2005, but didn’t have the same impact as the 1986 event thanks to ongoing work in Napa.

The Corps has been working with the city of Napa and the Napa County Flood Control and Water Conservation District to reduce the city’s flood risk since 2000 when the first construction contract for the Napa River Flood Control Project was awarded.  

“This project continues to take a total team effort,” Cook said. “But with each completed phase, we can slowly alter the city’s long history of flooding and reduce the flood risk for the residents and businesses of downtown Napa.”

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