Sacramento – The Board of Consultants determined the forensic teams’ list of potential Oroville Dam spillway failures are being addressed in the new design, according to a new memorandum published Last week.

The board’s report said the spillway design is ready for final review, with major redesigns including heightening walls beside of the main spillway.

Also, a wall dug into the ground that would block erosion up the emergency spillway weir has been moved 350 feet downhill, and is now 600 feet below the spillway weir. That is because there is better quality rock closer to the surface in the new location, according to the report.

“The root cause of the initiation of the destructive damage has not been specifically identified at this time, but most certainly lies with one or more of these factors in combination,” the memo reads. “(The redesign meets) current standards of practice and provides a conservative solution to address all original design deficiencies.”

The board did not note any major discrepancies in its findings compared to those of the Department of Water Resources and its contractors, though it does ask for more information on several issues and recommended again an open ditch draining system beside the spillway, addressed in memo form previously. The group requested geographical exploration data in real time, geological information about the cutoff wall, water pressure recordings by piezometers under the upper chute of the spillway prior to May and an assessment of groundwater hydrological conditions that may affect piezometer readings outside the spillway chute.

The group also asked for the following: a bid schedule, summary of work, memorandum directives and change orders, claims or disputes, serial and contractor letters and a submittal register, or list of job materials.

This memo is the first including new members Paul Schweige and John Egbert, both professional engineers, who joined the team in May after two original members resigned.

NEW FAILURES ‘VERY UNLIKELY’

The memo discusses a briefing on a workshop titled “Potential Failure Modes Analysis,” which is required by the Federal Energy Regulatory Commission, or FERC, any time a structure fails or undergoes remedial work or major modification. Participants of the workshop included representatives from FERC, the Division of Safety of Dams, DWR and Kiewit, the contractor doing reconstruction.

They worked to identify potential causes for water to be released from the reservoir uncontrolled, coming up with 22. About one-third of the next page is blacked out because it contains Critical Energy Infrastructure Information, DWR representatives have said previously.

The board was also recently briefed on a U.S. Army Corps of Engineers semi-quantitative risk assessment, looking into possible impacts of closing the flood control outlet before June 1, including the likely reservoir levels in doing so and also the risks of operating the main and emergency spillways in their current condition.

Through the study, it was determined that closing the flood control outlet in May presented low risk and the failure of the emergency or main spillway was “very unlikely.” The board of consultants found the study to be comprehensive, according to the memo.

WHAT’S HAPPENING

Meanwhile on the main spillway, Kiewit has removed what was left of the lower 2,000 feet of the chute, except for the huge baffles at the bottom, using excavators and controlled blasting.

The contractor is also removing the bottom 600 feet of the upper chute, leaving the 1,000 feet immediately below the floodgates in place. That part of the upper chute has been deemed structurally sound and will not be replaced this year, but just patched and anchored. Next year it will be removed and replaced.

Preliminary foundation preparation work has begun on the lower chute, including pumping concrete into smaller gaps in the rock. Two large gaps will be filled with roller compacted concrete, and then a final layer of construction grade concrete will be poured for the floor, and walls will be added.

Reach reporter Risa Johnson at 896-7763.