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.
Fortunately, the state Department of Pesticide Regulation (DPR) granted an emergency exemption to orchards with standing water.
According to a blog post by Dani Lightle, Orchard Systems Advisor, University of California Cooperative Extension in Glenn County, California DPR has granted an emergency exemption for fungicide applications to orchards that have standing water until June 1. This applies only to the following counties: Butte, Colusa, Glenn, Sutter, Tehama, and Yuba
DPR is granting the exemption because the rain has made ground orchard access difficult to impossible for many growers, says Lightle. The exemption allows for aerial application of certain fungicides to orchards with standing water. The key issue to be aware of when considering these applications is that any of the standing water cannot be pumped offsite, or flow offsite due to run-off.
The conditions for application are:
1) Water must be standing and will not flow into state waterways where fish and wildlife are likely to be affected. Applications are not allowed if water is flowing off the intended application site.
2) Standing water will not be pumped from the orchard after the fungicide application.
3) Applications are made in accordance with all other label directions.
Additionally, you cannot do an application if:
1) Soil moisture is at field capacity and a storm event is to occur within 48 hours following the application, or
2) A storm event that is likely to produce runoff is forecasted to occur within 48 hours following the application.
If you have standing water and want more information, be sure to read the full order and ask your county agricultural commissioner if you have any questions.