Over 50 California Department of Fish and Wildlife staff conducted a successful relocation over the past two days of 6.5 million young Chinook salmon imperiled by raging, muddy flows of 65,000 cfs below Oroville Dam as a giant hole caused by erosion continues to expand.
The California Department of Water Resources (DWR) this afternoon boosted the water release from 40,000 cubic feet per second (cfs) to 65,000 cfs with hopes that they could avoid the use of the emergency spillway at the Lake Oroville and Oroville Dam site in Butte County, according to DWR.
However, the agency just issued an update saying they plan to reduce the releases to 55,000 cfs to prevent erosion along the north side of the spillway from compromising nearby power line towers.
“Whether the emergency spillway is used or not, Oroville Dam itself is sound and there is no imminent threat to the public,” emphasized DWR Acting Director William Croyle. “We’re ready to use the emergency spillway if needed. But we’re trying to avoid it because there will be sediment and debris impacts downstream.”
Staff have relocated the 6.5 million fall-run and spring run Chinooks from the Feather River Hatchery in Oroville to the hatchery annex near the Thermalito Afterbay, according to Andrew Hughan, CDFW spokesman. These fish, approximately 1 inch long each, would die from suffocation in the turbid, sediment-laden water if left in the raceways of the hatchery.
Approximately 1.5 million juvenile salmon will remain in the hatchery where they will be benefit from sediment ponds set up to cleanse the water. Engineering staff have also set up a charcoal filtration system utilizing a fire hydrant pump for the 1 million eyed steelhead eggs remaining in the hatchery.
“Right now we consider our rescue operation to be a good success,” said Hughan. “We brought in staff from hatcheries all over the state to help in this emergency effort.”
“We used 8 trucks to move the fish and have done everything as fast as we can,” Hughan noted.
In March 2016, CDFW staff estimated that Feather River salmon accounted for 63 percent of the California recreational ocean harvest and 76 percent of the commercial ocean harvest.
Once the young salmon reach 2 to 4 inches in length, 100 percent of the spring-run stock and 25 percent of the fall-run stock will be adipose fin clipped and implanted with coded wire tags prior to release, according to the CDFW. Biologists use the information from these tags to chart the survival, catch and return rates of the fish.
This has been a relatively good year for steelhead. The hatchery has trapped over 1,130 steelhead to date this year, compared to just 125 steelhead last season. according to Anna Kastener, hatchery manager. The steelhead are normally released in the winter as yearlings.
In an update Friday evening, DWR announced that they will slow the releases down the gated spillway from 65,000 cubic feet per second (cfs) to 55,000 cfs. in order to prevent erosion along the north side of the spillway from compromising nearby power line towers:
“The slight shift in operations is intended to balance risks caused by erosion in the dam’s main spillway, but the dam itself is sound and there is no imminent threat to the public or the dam.
Based on analysis of the waning inflows to the lake, weather forecasts, and other factors, DWR officials say that a sustained discharge of 55,000 cfs may keep the lake level below 901 feet elevation, the point at which water flows over the emergency spillway’s concrete weir, down an unpaved hillside, and into the Feather River. There are many variables involved, and the public should not be surprised if some water flows into the emergency spillway. Such a spill would be the first in the dam’s 48-year history, but it would be within DWR’s contingency plans and pose no flood threat downstream.
Regardless of whether water flows from the reservoir through the gated spillway, Hyatt Power Plant outlets, or the emergency spillway, DWR does not expect releases to the Feather River to exceed the carrying capacity of any channels downstream. The releases would be on the order of half the downstream flood system capacity and consistent with flood releases made this time of year in wet years such as this.
Typical winter operations at Oroville were complicated Tuesday when the lower portion of the reservoir’s gated spillway began to erode. To manage the lake level, DWR continues to use the damaged spillway while closely monitoring the spillway erosion. Two side-by-side towers carrying power lines to Hyatt Power Plant may be at risk if the erosion spreads. Without power lines to carry electricity into or away from the power plant and its outlets, the plant outlets would be unable to discharge at a capacity of 14,000 cfs.
Flows out of the power plant were halted Thursday evening because debris downstream of the damaged spillway had caused water to back up in the Diversion Pool portion of the Feather River immediately downstream of Oroville Dam, and the elevated levels affect the ability of DWR to operate the power plant.
DWR and federal, state, local, and utility partners are working on various contingency plans to both restore operation of the power plant and to protect the electrical lines to the plant. DWR also is clearing debris and making reinforcements to minimize erosion in the hillside corridor where water would flow should the emergency spillway be used.
DWR is coordinating closely with state and federal wildlife and dam safety officials at Oroville Dam. Those involved in contingency planning and response include the Federal Energy Regulatory Commission, the U.S. Army Corps of Engineers, Butte County Sheriff’s Office, Pacific Gas and Electric Company, the Governor’s Office of Emergency Services, the state’s Division of Safety of Dams, CAL FIRE and state and federal wildlife agencies.”
Lake conditions, including lake levels, inflows, and outflows can be obtained via a recorded message at 530-534-2307. More information is available on the California Data Exchange Center .
Photo by Brian Baer, California Department of Water Resources.