A huge storm system doused Sonoma in much-needed rain this weekend, with officials reporting upward of 10 inches of rainfall in the Valley.
Rain started with a smaller storm on Wednesday and Thursday, followed by a pounding “Pineapple Express” that arrived on Friday morning. An atmospheric river settled over Sonoma and parts of Petaluma and Napa, said Sonoma Ecology Center director Richard Dale. The Ecology Center monitored the rainfall and collected data during the storm.
According to Bill Randall, at General Vallejo’s home in Sonoma, where daily rainfall data is collected, Sonoma received nearly an inch of rain Thursday, a half-inch Friday, over six inches on Saturday and nearly four more inches on Sunday. Steve Anderson, at the National Weather Services Bay Area headquarters, said many areas throughout Sonoma County received more than 5.5 inches of rain over the weekend.
More rain fell during this storm than during the epic flood in 2006, Dale said, adding this is the largest storm in the area on record and that Sonoma sat squarely in “the bullseye” of the weather system.
“Had it not been for the record drought going into the storm, we’d have seen record-breaking flooding,” Dale said, noting creeks started to rise on Saturday morning after nearly 4 inches of rain, with Sonoma Creek topping out at 3,700 cubic feet per second. Nearly 2 billion gallons of water, or 6,000 acre-feet, surged past the United States Geological Services automated gauge at Agua Caliente Road during the storm, according to Dale, with about 25 billion gallons falling in the Sonoma Creek watershed.
The national weather service issued flash flood warnings throughout the weekend, prompting the closure of several county roads, including Green Valley Road between Ross and Thomas roads, Rohnert Park Expressway and Valley Ford Road at Highway 1. The Highway 116 and Highway 121 intersection in Schellville was also closed, as usual, due to flooding.
The Russian River, which had been reduced to a trickle by the dwindling pool in Lake Mendocino, was swollen to nearly 20,000 cubic feet per second in Guerneville, but stayed well below flood stage.
The campground at Sugarloaf Ridge State Park was closed as Sonoma Creek flooded over the culvert at the entrance of the campsites.
The Sonoma region, Dale said, has now received 12.5 inches of rain, adding “we may sneak out of a drought year yet with a few more decent — not crazy big like this one — storms over the next three months.”
Ecology center staff and volunteers took advantage of the wet weather to monitor sediment moving through Sonoma Creek during the storm. Groups of four people worked in shifts, 24 hours a day, to collect data from Friday to Sunday evening.
The project is part of the center’s Sonoma Creek watershed monitoring program that looks at sediment in streams to better understand how to reduce it in order to improve the area for fish like steelhead and Chinook, and to recharge the dwindling groundwater supply, Ecology Center biologist Caitlin Cornwall said.