Less than halfway through the month, recent rainstorms have already propelled precipitation numbers well past last year’s February total, and there’s more on the way.
Storms fueled by a plume of moisture stretching over the Pacific Ocean almost to Hawaii dumped rain on the state this week. The phenomenon, known as an atmospheric river, hit Northern California hard this week, with Turlock Irrigation District Utility Analyst Olivia Cramer estimating during Tuesday’s Board of Director’s meeting an excess of 10 inches of precipitation falling in the foothills.
The Tuolumne River Watershed accumulated 6.81 inches of precipitation through Feb. 10 — almost an inch more than last year’s total for the entire month, which was 6.1. Through Saturday, the National Weather Service predicted an additional total of 3.18 inches of rainfall at Don Pedro and 1.08 inches of rainfall in Modesto.
An atmospheric river can be 250 to 370 miles wide, and, on average, around 30 to 50 percent of water stored in the state’s snowpack comes from just a few yearly atmospheric river events. According to Cramer, the atmospheric river passing through this week was classified as “moderate to strong.”
Prior to the influx of heavy rain, the Don Pedro Water Bank sat just below the maximum allowed level at 570,000 acre feet. Total storage for the reservoir was 1,566,653-acre feet as of Feb. 10 — just under the flood control level of 1,690,000-acre feet. During the week prior, Don Pedro’s storage was about 42,000-acre feet less. The reservoir’s elevation was also about 11 feet away from the flooding level as of Sunday.
Cramer said that TID does not plan to increase releases at Don Pedro as talk of the atmospheric river brought back memories of flooding in 2017. Then, storms wrecked the spillway at Oroville Dam in Butte County and saw one of three controlled spillway gates at Don Pedro opened for the first time in 20 years.
Following this week’s storms, Cramer estimated Don Pedro’s elevation to reach about 802 feet. The level is a 10th of a foot over the reservoir’s flood control level.
“We’ve informed the Army Corps of Engineers that we will be encroaching slightly, and they’re going to allow it due to the fact that it’s going to become dry after this week’s storm,” Cramer said.
With little rain in the upcoming forecast, Cramer added that levels in the reservoir will be able to be drawn down without increasing flows from Don Pedro, avoiding any flooding.