Massive effort in motion to repair Oroville Dam Spillway (VIDEO)
OROVILLE SPILLWAY INCIDENT
Feb. 7 — In anticipation of higher rainfall, water releases from the flood control spillway are increased. DWR employees notice an unusual flow pattern. Spillway flows are stopped to investigate. Engineers find a large area of concrete erosion.
Feb. 8 — DWR begins ongoing consultation with other dam safety agencies. DWR runs flows down the damaged spillway and monitors for further erosion, while preparing for possible use of emergency spillway. 24/7 emergency operations activate to implement response to flood control spillway and related structures, with careful study of weather forecasts.
Feb. 11 — Inflow to Lake Oroville brings lake level above 901 feet. This engages the emergency spillway for the first time in the history of the facility.
Feb. 12 — Anticipated erosion begins to progress faster than expected at the base of the emergency spillway. The Butte County Sheriff’s Office issues mandatory evacuation orders for the Oroville area. To ease pressure on the emergency spillway, the flood control spillway outflow is increased to 100,000 cubic feet per second (cfs). After several hours, water flowing over the emergency spillway stops. Erosion to the emergency spillway hillside assessed.
Feb. 14 — As Lake Oroville levels continue to decline, the mandatory evacuation order is modified to an evacuation warning. Crews continue working around the clock to repair the emergency spillway. An elevation of 850 feet is targeted for lake levels.
Feb. 16 — Flood control spillway flows are reduced below 100,000 cfs to facilitate the clearing of debris from below the spillway. Lake levels continue to decline. Crews continue to armor the emergency spillway.
Feb. 20 — Lake Oroville reaches 848.95 feet at 11 a.m. Repairs continue around the clock.
Feb. 27 — Flood control spillway flow reduced to 0 cfs to clear out debris in the diversion pool channel.
March 3 — Flood control spillway gates remain closed to dredge material from the diversion pool. With 168,000 cubic yards of material removed, the Hyatt Powerplant resumes operations at 7 a.m. producing 2,650 cfs of outflow.
March 10 – Flood control spillway flows remain at 0 cfs and the lake level is 860 feet. All five operational units at the Hyatt Powerplant are running, allowing for a total outflow of 12,900 cfs.
March 17 — Flood control spillway gates reopened to release 40,000 cfs, 1.25 million cubic yards of debris excavated from diversion pool channel.
March 23 — Butte County Sheriff Kory L. Honea lifts all evacuation warnings and advisories for Butte County residents affected by the Feb. 12 emergency evacuations.
March 23 — Lake Oroville levels decline to 837 feet and flood control spillway flow reduced to 0 cfs.
Source: Department of Water Resources
It’s been six months since a failure of the Oroville Dam Spillway led to the evacuation nearly 200,000 people, including hundreds who took refuge at an evacuation center at the Nevada County Fairgrounds as well as hotels in the Grass Valley and Nevada City area.
The evacuation order came five days after a worker checking the dam’s alert siren system took a look down the spillway and saw trouble.
“He could see that the water was having an irregular flow and he could see some splashing, that wasn’t over the wall, but he could see it in the chute making a mess,” said Matt Murray, a Department of Water Resources engineer. “By the time we got the water shut down, we had already seen that huge hole that’s been so famously pictured.”
That hole was just the beginning.
As water continued to fill Lake Oroville from Northern California’s wettest winter on record, and water was released down the damaged spillway, the dam’s emergency spillway was used for the first time in the facility’s nearly 50-year history.
Erosion arose faster than expected at the base of the emergency spillway, leading the Butte County Sheriff to issue mandatory evacuations for the Oroville area. Flows were increased to 100,000 cubic feet per second down the main spillway to alleviate pressure on the emergency spillway, which just hours later was no longer overflowing, but damage was done — and continuing to be done down the area of the main spillway in the days that followed.
Repairs on that damage have continued ever since, with more than 600 people from the Department of Water Resources and Kiewit Infrastructure working in shifts around the clock, seven days a week.
A recent tour of the site showed both the progress and work still to be done with the restoration project, which the Department of Water Resources estimates will cost $500 million, including a $275 million construction contract with Kiewit.
As of July, $22.8 million in FEMA funding had been received, including about $8.6 million to reinforce the emergency spillway and $14.2 million in federal funds for the clearing of 2.2 million cubic yards of debris and the removal of debris and sediment from the Feather River.
Following cleanup work that included removing nearly 1.5 million cubic yards of debris at the base of the main spillway, reconstruction is ongoing while workers also build an underground secant pile wall downhill from the emergency spillway to avoid further erosion.
The main spillway remains segmented, as crews work from both the top and bottom toward restoration. But between the upper and lower sections of the spillway were two massive holes — one at 100 feet and another more than 50 feet deep — that must be filled with concrete while workers continue to climb the hillside restoring the slope of the spillway. According to officials, work progresses up the spillway on average of 5 feet each day. That work also entails bulldozers building temporary access roads for equipment, essentially climbing the hillside ahead of the crews repairing the spillway in order to bring material — such as concrete developed at an on-site facility — to workers.
The current work, according to the Department of Water Resources, is geared to ensure by Nov. 1 that the system “can safely accommodate potentially heavy inflows from the Feather River watershed to Lake Oroville and subsequent releases from the lake. Construction on the main and emergency spillways will continue into 2018.”
Some of the work underway will actually be removed and reconstructed for final updates during the 2018 construction season.
“The plans for upgrading the flood control spillway and the emergency spillway will use modern design and construction standards,” the Department of Water Resources website states, “while providing increased capacity to manage flows starting this winter.”
Contact Editor Brian Hamilton at firstname.lastname@example.org or 530-477-4249.
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