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Oroville Spillway Update: Main Spillway Construction, Emergency Spillway Construction and Forensics Investigation

Continued Construction on the Main Spillway

Construction efforts at the Lake Oroville spillways remain focused on repairing and reconstructing the gated flood control spillway, also known as the main spillway, by November 1.
There are 56 days left on the construction timeline to reconstruct the 2,270 feet of main spillway that will be completed this year: Placement of reinforced, structural concrete is 20 percent complete. By November 1 there will be 1,220 feet of spillway chute with structural concrete – 870 feet on the upper chute of the spillway and 350 on the lower chute of the spillway.

The 1,050-foot middle section of the spillway chute, including filling in the two scour holes, is now 33 percent complete, with approximately 100,000 cubic yards of roller compacted concrete placed. This middle section will be completed to final design with structural concrete in 2018.

Crews have installed more than 5,000 feet of underdrains in the structural concrete sections.

The 730 feet of main spillway leading to the radial gates will be patched, reinforced and left in place this year. It will be removed and reconstructed with structural concrete in 2018.

Construction at the Emergency Spillway

DWR continues to make progress at the emergency spillway, and is still on schedule to complete construction of the secant pile wall, or cut-off wall, in late December 2017 or early January 2018.
Crews have completed 15 percent of the secant pile wall.

Forensic Investigation

Tuesday, the Independent Forensics Team released an interim memo summarizing its current findings on the physical factors that caused the Lake Oroville spillway failure. A full report that will include human factors is expected later this fall. After reviewing the memo, DWR released a statement reiterating that protecting public safety is the state’s top priority and expressing its commitment to apply lessons learned from the Lake Oroville spillways incident. DWR agrees with the Forensic Team’s conclusions that dam owners need to reassess current procedures as visual inspections would not have caught what happened in February.

Last week, DWR released the Assessment of the Vegetation Area on the Face of Oroville Dam, which explains the cause of vegetation that occasionally grows on the face of the dam. Based on five decades of data and observation, the Department has concluded the vegetation area does not pose a threat to the integrity of the dam.

The independent Board of Consultants met for the eleventh time with DWR on August 24 and 25. DWR presented the findings and conclusions of the Assessment of the Vegetation Area on the Face of Oroville Dam to the BOC members, who agreed the cause of the vegetation area does not pose a threat to the integrity of the Oroville Dam. The BOC’s eleventh memo, which will contain this conclusion, will be posted soon after it is transmitted to DWR.

One Response to Oroville Spillway Update: Main Spillway Construction, Emergency Spillway Construction and Forensics Investigation

  1. Don Colson Reply

    September 10, 2017 at 10:56 am

    If this is a Forensic Investigation, why hasn’t anyone commented on the fact that the Main Spillway Chute was not built as intended by the original Designers.

    During construction a change was made that doomed this spillway. Yes, there are several design flaws, but this was not the root cause for the slab that finally failed. I am surprise the slab lasted 49 years since construction was complete in 1968.

    If this truly is a forensic investigation, then they should be able to say who and why this chute slab was not built, as the one remaining design drawing that is available to the public and found in Bulletin 200 shows, which was the intent of the original designers. It is a drawing that has been overlooked. Some DWR manager in the chain-of-command authorized the change that lead to this failure. Please, do the job of a Forensic Team.

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