With back-to-back storms slated to hit California in the coming days, state officials are scrambling to make strategic releases of some key reservoirs in hopes of preventing a repeat of the deadly flooding that claimed nearly two dozen lives in January.
At least 10 rivers are forecast to overflow their banks due to the incoming storm “Pineapple Express,” which is expected to drop warm, heavy rain and melting snow as it moves from the Central Coast into the Southern Sierras beginning Thursday at night until Saturday.
Among them are rivers that flooded earlier in the year, when nine atmospheric river storms hit the state. The waterways include the Cosumnes River near Sacramento, where more than a dozen levee breaches sent flooding to highways and low-lying areas, trapping drivers and contributing to at least three deaths along Highway 99.
“This is a very dynamic system,” said the director of the Department of Water Resources, Karla Nemeth, during a briefing on Thursday. “Rivers and streams can rise very quickly, so it has the potential to be a dangerous situation, particularly in areas that have experienced flooding before.”
Officials activated the State-Federal Flood Operations Center Thursday morning, Nemeth said, indicating a heightened level of coordination and monitoring ahead of the approaching storm.
Another atmospheric river is expected to follow early next week, and there is a chance a third will follow around March 19, according to state climatologist Mike Anderson.
By early January, “we were well on our way to a fourth year of drought,” Anderson said. “We are in a very different condition now.”
In fact, the upcoming storm will bring down sodden ground and some of the deepest snowpack on record for California, both of which can exacerbate the potential for runoff and erosion.
Conditions are in some ways similar to those that led to the near-catastrophic failure of the Oroville dam in 2017, when heavy rains damaged an emergency spillway and threatened to send floodwaters into communities below. below.
Officials said Thursday there is no danger of a similar event now that the spillway has been reconstructed with several feet of thick concrete. However, California’s second-largest reservoir is about 60 feet below its maximum elevation, said Ted Craddock, deputy director of the DWR’s State Water Project, and operators have begun releasing water to ensure space for incoming flows. .
Discharges from Oroville’s Hyatt power plant began Wednesday, Craddock said, with additional discharges scheduled to begin Friday from its closed landfill at a combined rate of 15,000 cubic feet per second from both facilities.
“This is a relatively small release from the spillway and as we further look at the forecast, with the possibility of additional storms, we will adjust the releases from the lake,” Craddock said.
Officials with the DWR, the US Office of Recovery and the US Army Corps of Engineers are also increasing releases at other locations ahead of the storm, including Lake Shasta and Lake Millerton, Levi said. Johnson, deputy manager of operations for the Central Valley Project with USBR.
Folsom Lake, which primarily acts as a flood control system for the Sacramento area, still has “plenty of storage space,” Johnson said, but officials anticipate flows there will increase with current storms. Emissions will climb to about 15,000 cubic feet per second on Thursday and then increase to 30,000 on Friday.
Despite the assurances, some people in the Central Valley said they are concerned about the risks of devastating flooding in the coming days.
“I fear levee failure and flooded houses,” said John Ennis, a civil engineer who owns a consulting firm in Fresno.
Ennis said he’s concerned that “there’s going to be too much water on top of the snowpack and it’s going to dissolve all at once,” a scenario that could lead to flooding from the Sierra Nevada to the Central Valley.
In high-elevation areas, the biggest threat from the storm will likely be structural damage, as rain makes snowpack even heavier, UCLA climate scientist Daniel Swain said during a briefing. The state has already seen a series of roof collapses due to heavy snowfall, including a grocery store providing critical supplies in Crestline.
“The biggest concern with flooding is actually at low to mid elevations,” Swain said. That includes areas at about 5,000 feet or below in central California and the Southern Sierra.
“There really is going to be significant melting of snowpack, which is substantial at those elevations, as heavy rains fall,” he said. “But really, the main flood threat comes from the fact that the storm will bring a significant amount of rain in its own right.”
According to the National Weather Service, some of the highest flood risks will be in the coastal areas from Salinas to San Luis Obispo, and throughout the Central Valley.
officials in ash tree, Wood, Modest and Santa Cruz Counties have already issued evacuation warnings for some of their communities due to potential flooding. San Luis Obispo County, which experienced significant flooding during January storms, has the “potential for similar impactsfrom the incoming system, the weather service said.
Swain said some impacts from the storm may not be felt immediately, but the state’s heavy snowpack “will have to come down eventually.”
“Although the flood peaks don’t look extremely high in any individual river system with this event, what is going to start to happen is that we are going to see high flows in many major rivers for a very long period of time. – So not just for hours or even days, but quite possibly more like days, weeks or more, ”he said.
Ennis, a Fresno resident who works with developers and farmers, said he is concerned about potentially dangerous circumstances, including sudden levee breaches that could put people at risk.
“There is only one thing that keeps me up at night as a civil engineer, and that is water. It’s this kind of situation,” he said. “You are potentially talking about insane volumes of water.”
