[Water_news] 1. DWR'S CALIFORNIA WATER NEWS - Top Item for 12/26/07

Department of Water Resources

California Water News

A daily compilation for DWR personnel of significant news articles and comment

 

December 26, 2007

 

1.  Top Item

 

Flood control project starts; A new spillway at Folsom Dam will boost the facility's ability to move American River water

Sacramento Bee - 12/25/07

By Matt Weiser, staff writer

 

More than 20 years have passed since it became clear that the American River needs better flood control. Now the solution to that problem is finally under construction.

 

Workers began construction on a new spillway at Folsom Dam on Dec. 13. The 1,700-foot-long concrete spillway, adjacent to the existing main dam, will boost its ability to prevent dangerous floods, effectively doubling protection for about a half-million people living downstream.

 

The spillway will achieve 1-in-200-year protection, or the ability to survive a flood with a half-percent chance of striking in any given year.

 

Construction is a huge milestone for the project, which has seen as many twists and turns as the American River itself.

 

"It's actually almost miraculous that things have come together the way they have," said Sacramento Mayor Heather Fargo, also chairwoman of the Sacramento Area Flood Control Agency, a local sponsor of the project. "What it means to the community at risk from the American River is a huge increase in flood protection."

 

Built in 1955, the dam at Folsom contains eight small river outlets below the water line and eight larger spillway gates on top.

 

The river outlets can release water at 35,000 cubic feet per second. Maximum releases of 165,000 cfs – the design capacity of downstream levees – can be achieved only once the reservoir rises to reach the larger spillway gates.

 

By this time, the reservoir would lose much of its flood-storage capacity. This design seemed fine when the dam was built.

 

But bigger storms to come – in 1986 and 1997 – proved that the dam had to perform better.

 

Those near- disaster years showed that longer, wetter storms could theoretically force dam operators to let more water out of the spillway gates than levees can hold. Deadly flooding in Sacramento might be a result.

 

A solution took decades, partly due to politics and penny-pinching. It didn't help that the project is the region's biggest engineering challenge in a generation.

 

Sacramento leaders first suggested a smaller Auburn dam as a solution. But conflict over environmental and earthquake concerns killed that concept, just as it did when the original Auburn Dam died in 1979.

 

This led Sacramento leaders to take a fresh look at Folsom Dam. They found that improving the dam's outlets and raising the dam slightly could make huge flood-control improvements possible.

 

The initial design involved enlarging the eight existing river outlet gates in the main dam and adding two more.

 

But in spring 2005, construction bids came in three times more expensive than expected, and Sacramento's most important flood-control project again ground to a halt.

 

Contractors, it turned out, saw too much risk in the project because it involved working underwater to enlarge the outlet gates on a dam that was still protecting a metropolis. One mistake could mean disaster, and that threat drove up the bids.

 

This led officials back to the drawing boards for a rare collaboration between the U.S. Army Corps of Engineers, which governs flood control, and the Bureau of Reclamation, which owns the dam.

 

In just two years, they won approval for the new auxiliary spillway now under construction.

 

It will contain six new outlet gates, each larger than the combined eight existing river outlets in the main dam. These new gates also will be deeper.

 

The result: The new spillway will be able to move a full 165,000 cfs out of the reservoir, and do it sooner in a storm. Dam operators will be able to create more storage in the reservoir ahead of a storm and keep more of it available during a flood, boosting safety for everyone downstream.

 

The spillway also will serve as a relief valve in case of an overtopping threat to the dam, a key function required by bureau.

 

The design means no working underwater, and no one chiseling away at the existing dam.

 

"The bottom line is, everything's on schedule," said Mike Finnegan, area manager for the bureau. "The story here, in my view, is the partnership. I can't say enough about the technical people and their creativity and talent in bringing this off."

 

The first construction phase involves simply clearing a path for the new spillway on the hill beside the dam. Next week the contractor, Kiewit Pacific Co. of Concord, is expected to start excavation, a long process that involves moving 3.5 million cubic yards of dirt and rock.

 

Future stages include raising earthen dikes around the reservoir 3 1/2 feet to add flood storage.

 

The $1.5 billion project is expected to be finished in 2015. Sacramento residents are paying 10 percent of the cost via property taxes. A groundbreaking event is planned for Jan. 11. #

http://www.sacbee.com/101/story/591496.html

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