New Phase begins on Folsom Dam Facelift (Sacramento Bee)

The Sacramento region's biggest flood control project enters an important phase this week as construction begins on giant gates that will allow Folsom Dam to handle bigger storms.

The project is an enormous new spillway being built next to the existing dam. It will allow water to be released more quickly from Folsom Reservoir into the American River before the lake reaches its brim.

Last week, Martin Brothers Construction of Sacramento completed a $63 million project to excavate the spillway channel in the hillside adjacent to Folsom Dam. As long as eight football fields, it took 18 months to complete.

That project was overseen by the U.S. Bureau of Reclamation, which owns and operates the dam.

Now the U.S. Army Corps of Engineers takes the lead on the project. It is charged with finishing the spillway and building flood-control gates that will release water into it.

The Corps awarded a $126 million contract for that job to Granite Construction of Watsonville, which took over the site Thursday and is expected to start work this week.

"It's a great milestone, but it's no time to rest," said Mike Finnegan, Bureau of Reclamation area manager. "We've got to get it done."

Both agencies view the modification of Folsom Dam as one of the nation's top flood-control priorities because of the potential risk to 1 million people downstream in the greater Sacramento area.

The project addresses a major weakness in Folsom Dam's original design: The eight small outlet gates in the face of the dam can't empty the reservoir fast enough when a major storm strikes. The larger gates at the top of the dam can move a lot more water, but by then the reservoir is already dangerously full.

In contrast, the new "auxiliary spillway" includes six steel gates about as large as those atop the dam itself, but 49 feet lower in the water.

This means the reservoir can be emptied more rapidly when big runoff from the upstream watershed is expected.

Construction of the gates is expected to take nearly four years.

"It is definitely the most complex portion of the design," said Jason Magness, Corps of Engineers senior project manager. "You can think of it as a secondary dam with the six new gates."

The project has benefitted from a slow construction climate. The spillway excavation cost $70 million less than the original estimate. The winning bid to build the spillway gates came in $100 million less than the estimate.

When completed, at a total cost of about $1.5 billion, the dam is expected to handle at least a 200-year storm, or double its current rating.

The local funding share comes from state water bonds and a property assessment collected by the Sacramento Area Flood Control Agency.

"This is one of the most effective and ambitious flood protection projects in the Sacramento region … and when completed will significantly improve the region's flood protection," said Rep. Doris Matsui, D-Sacramento, who has pressed to keep the project a priority for federal funding.

The original plan for the project was to enlarge the eight existing outlet gates in the face of the dam.

But about five years ago, the technical challenges of that design nearly killed the project.

Reclamation, the Corps, and SAFCA then collaborated on the current auxiliary spillway design.

http://www.sacbee.com/2011/01/25/3348867/new-phase-begins-on-folsom-dam.html

By Matt Weiser
mweiser@sacbee.com
Published: Tuesday, Jan. 25, 2011 - 12:00 am | Page 1B