Army Corps Schedules CA Dam Spillway Repairs


According to reports, a design flaw in the Folsom Dam spillway in California has left the structure at risk for corrosion due to cracks in the coating, leading to a $16 million repair project.

The spillway was reportedly used for the first time last month, following a series of strong winter storms in the state that allowed more water to be released from Folsom Lake.

What Happened

In 2017, work was completed on the cooperative effort between the U.S. Army Corps of Engineers and the U.S. Department of the Interior, Bureau of Reclamation, on the Folsom Dam Auxiliary Spillway project. The almost $1 million spillway included:

  • A 1,100-foot-long approach channel to funnel the water from the lake into the spillway;
  • A control structure with six submerged gates controlled in coordination with the gates on the main dam to control water releases;
  • A 3,027-foot-long spillway chute that transports the water from the control structure to the American River below; and
  • A stilling basin that slows the racing water back to normal flow levels that the river channel will be able to withstand.

However, CBS News recently reported that parts of the spillway are broken, due to a design flaw resulting in damage to the system. According to reports, the metal rods that open and close the steel gates have cracks in the coating that allows water to seep through, causing corrosion that could eventually prevent the system from operating. 

Now, the Army Corps plans to conduct a $16 million repair project to replace the 12 defective rods, starting in 2025.

“This is a case where, with all the best intent, we applied a particular technology that wasn't optimum,” said Bradley Call from the Army Corps.

The impact on flood control along the river is not anticipated to be significant, as only one gate at a time will be repaired. Additionally, lake levels will not need to be lowered during the work, according to the Army Corps.

“Our goal is to keep the auxiliary spillway in service as much as possible because it could be needed on short notice,” said Call. He also acknowledges that the original construction phase was not done correctly, but assures that repairs will “make it right.”

Work is expected to occur in the summer and fall, when the spillway is not typically in use.

Other CA Spillway Repair

Last year, in July, the California Department of Water Resources announced that work on a multi-year project to perform maintenance repairs on the eight radial gate hoist assemblies at the Oroville Dam Spillway would begin soon.

The repairs come more than five years after the Oroville Dam crisis, which involved a $1.1 billion emergency spillway reconstruction project to allow the spillway to handle extreme flooding. The gates were not damaged in the event, but are almost 50 years old, thus requiring renovation from wear and tear over the years.

The eight radial gate hoist assemblies operate on the Oroville Dam’s Flood Control Outlet, or main spillway. The repairs are being completed for the Oroville Radial Gates Maintenance Repair Project, which was established after the 2017 emergency to maintain the safe and reliable operation of the FCO, Thermalito Diversion Dam and Thermalito Power Canal radial gates.

According to the DWR's update, contractor Unico will perform an as-found site inspection of radial gate hoist assembly #8 to obtain dimensional and operational data that will be used to finalize the maintenance repair plan and to reverse-engineer the hoist assembly design for the fabrication of a replica hoist assembly. 

Then, the spare radial gate hoist assembly, which includes gear motor, wire ropes, gears and pinons, will be installed while an existing hoist is removed for inspection and maintenance to address any deficiencies due to wear, age and serviceability of the equipment.

Beginning in 2023, maintenance repairs will be performed on one gate hoist assembly per year during the dry season, which runs from May 1 to Oct. 31. This will ensure that all eight existing radial gate hoist assemblies are available and fully operational throughout flood season.

An engineer working on the project said that there is going to be a replica of each gate, and will likely be painted the same, so Oroville residents might not even know that it’s new.

The nine-year plan is expected to be completed in 2031, with a projected cost of $5 million. Construction will reportedly involve concrete grading, as well as mechanical work on the hoists above the spillway as the project moves forward.


Tagged categories: Coating Materials; Coatings; Corrosion; Corrosion protection; Flood Barrier; Locks and dams; NA; North America; Program/Project Management; Quality Control; Rehabilitation/Repair; Steel; U.S. Army Corps of Engineers; Upcoming projects

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