The California Department of Water Resources reports that on its Nov. 1 deadline, the agency “met our objective to repair and reconstruct the main Lake Oroville spillway to handle flows of up to 100,000 cubic feet per second.”
The primary objective of the Lake Oroville Spillways Emergency Recovery Project was to prepare the main spillway for the rainy season.
“Today is a truly significant day for DWR, our state, federal and local agency partners, and the contractors who have worked together so well to meet this critical milestone,” said California DWR Director Grant Davis. “However, today is only a milestone and we have much more work to do before the project is complete.”
According to contractor Kiewit Infrastructure West Co., more than 600 Kiewit workers put in more than 720,000 hours since May on the project to reconstruct both the main and emergency spillways.
According to DWR’s website, work after this deliverable date “will focus on sealing drains, concrete seams, and drain pipes, as well as site clean up.”
Regarding the emergency spillway, which also suffered significant damage during the high flow events in February 2017, DWR says work to complete construction of the underground secant pile wall intended to prevent uphill erosion if the emergency spillway is ever used again will continue until January 2018.
California DWR says: “During the second phase of construction in 2018, we will place additional structural concrete on the main spillway and complete the emergency spillway buttress and splashpad.”
DWR released an operations plan for the 2017-2018 flood season earlier this month, which calls for DWR to maintain lower than average lake levels during the winter months “to provide space for inflows and manage releases from the substantially reconstructed main spillway,” according to a press release.
Background on Oroville
As Hydro Review magazine reported in September, spillway erosion occurred at Oroville Dam in February 2017. A complete timeline of events is available in that article. A contract for the repair work, valued at $275 million, was awarded in April 2017. News agencies are reporting that the actual total cost of the work was closer to $500 million.
An independent forensic team is investigating the incident and released its interim findings in September, indicating physical inspections alone are not adequate to identify risks and manage safety. The report identifies four physical factors likely involved in the observed damage at the emergency spillway and provides three lessons learned. The team’s final report is to be issued before the end of 2017.