California water officials are frantically releasing water today from the Oroville Dam, located about 75 miles north of Sacramento, as concerns remain about erosion of the nation’s tallest dam.
The Sacramento Bee reported this morning that Blackhawk helicopters have been called in to drop huge bags of rock to shore up the emergency spillway at the state’s second largest reservoir.
Meanwhile, nearly 200,000 people, who were evacuated Sunday, await word on when they can return home. Complicating matters, yet another storm in this extraordinarily wet winter is expected to arrive Wednesday night.
(Editor’s Note: The evacuation order was lifted shortly after 2 p.m. PST Tuesday. Meteorologists are now saying this week’s storms won’t pack as much precipitation as recent storms, and they are supposed to be colder, meaning more snow and less rain to immediately flow into the reservoir. Currently, water is being released at the rate of 100,000 cubic feet per second, while the inflow is about 20,000.)
Rivers and reservoirs are swollen throughout California. Large amounts of water have pooled in the Yolo Bypass, a water storage area designed to minimize flooding in Sacramento. Sediment stirred up during the flooding has turned waterways throughout northern California a dark shade of brown.
With weather stations in the northern Sierra Nevada recording remarkably high levels of precipitation for the 2016-17 water year, reservoir levels are well above the historical average in the Sacramento Valley and elsewhere in California.
Following the most recent storms, Lake Oroville stood at 151% of the historical average. Folsom Lake was at 144%, Lake Shasta — the state’s largest reservoir — was at 138%, Don Pedro Reservoir was at 141%, and Lake McClure was at 182%.
At the Oroville Dam, the situation became dire on Feb. 7, when a large hole appeared in the main concrete spillway, a part of the dam managers use to release excess water in a controlled fashion. The hole limited how much water authorities could safely release through the spillway, so water levels in the reservoir continued to rise.
A few days later, water began flowing over an emergency spillway that has never before been used. When that spillway began showing disturbing signs of erosion on Sunday, authorities ordered the evacuation of 188,000 people living downstream.
Lake Oroville’s levels have declined since the evacuation order and the risk of a catastrophic failure has lessened. But reservoir managers remain concerned that rain showers forecast for this week could elevate reservoir water levels and stress the spillways again.
As for growers, even they have had enough for now. In fact, almond growers in Northern California have not been able to get sprayers into their orchards to apply much-needed fungicides.