A significant milestone toward completion of the $900 million, years-long undertaking to improve flood control and the safety of Folsom Dam was reached Tuesday.
The process to place water against an auxiliary spillway control structure began in earnest Tuesday morning. The process, called impoundment, will continue until water reaches the same elevation on the spillway side and the other side of a temporary earthen dam that has kept the construction area dry.
The filling is expected to take about 24 hours, said Katie Charan, project manager with the U.S. Army Corps of Engineers. Eight powerful pumps were sending water through two 24-inch pipes from the lake into an approach channel and against the spillway control structure.
Placing water against the new spillway structure means that the spillway is much closer to being ready to use. Charan said it is expected to be operational by the end of the year, about five months ahead of schedule.
“(Tuesday’s) announcement is a significant milestone for the Folsom Dam auxiliary project, and for ongoing efforts to ensure that Sacramento has the flood protection it needs and deserves,” Rep. Doris Matsui, D-Sacramento, said in a written statement. “The impoundment process indicates that we are one step closer to the completion of the spillway, which will more than double Sacramento’s current level of flood protection.”
The project includes a channel that will funnel the water from the lake into the spillway and six submerged gates that will be controlled in coordination with the gates on the main dam.
The auxiliary spillway adds to the functions of the main Folsom Dam. The spillway gates are 50 feet lower than the main dam’s gates, allowing earlier and safer water releases from Folsom Lake during periods of high water.
Brandon Muncy, deputy director of the project, a joint undertaking of the Army Corps of Engineers and the federal Bureau of Reclamation, said the auxiliary spillway also will allow greater flexibility in operating the dam for functions other than flood control, such as water supply, recreation and environmental protection.
Luis Paiz, project manager for contractor Kiewit Pacific, said the spillway project has benefited from the drought. Low lake levels allowed work that otherwise would have been done from barges to be done in dry conditions, making it easier to ensure the quality of the work, he said.
Last week, the spillway was in the news when a leak was discovered in a cofferdam. The earthen cofferdam, built on the lake side of the dam, is a temporary structure to allow construction for the spillway.
A leak the size of a stream partially filled the approach channel construction area. Crews abandoned the area and left behind some equipment until the leak could be patched. Once the leak was fixed, construction machinery and materials were removed.
Although the spillway is expected to be operational by the end of this year, the entire project, including environmental restoration work around the construction site, is scheduled to be completed in October 2017.
Muncy said the Bureau of Reclamation began excavation for the spillway in 2008 and the Corps of Engineers took over the construction phase in 2010. He said 65 percent of the funding for the project is provided by the federal government, and the other 35 percent by the state of California and the Sacramento Area Flood Control Agency.