How January rains helped SLO County’s lakes
Growing up in Sonoma County in Northern California, I vividly recall looking out the windows of Mark West Elementary School at the endless days of rain.
Nearby, Mark West Creek flowed like a raging waterway into the Russian River that would eventually always flood Guerneville and the surrounding areas. That’s the way I recalled the winters where I grew up.
This winter along the Central Coast brings back a lot of those memories, with numerous days of rain but with a twist, we haven’t had any “gully washers” this season.
So far, the highest 24-hour rainfall total at Diablo Canyon was 1.5 inches recorded on Nov. 29, 2018. However, we have seen 54 days of measurable rainfall at the power plant. Last year, there were only 37 days of measurable rain for the entire rain season (July 1, 2017, through June 30, 2018) with over 4 inches of rain recorded on one day, March 22, 2018.
Even during the terrible dry years of 2013, ‘14 and ‘15 where seasonal rainfall totals didn’t even reach 10 inches, we had occurrences of 24-rainfall totals reaching over 1 inch; nearly 2 inches was recorded on Dec. 12, 2014 when that rain season only saw a total of 7.5 inches at the power plant.
So far, most Central Coast weather stations are already over their annual rainfall season averages.
Rocky Butte typically receives 40 inches, but as of Saturday has recorded nearly 46 inches. Cal Poly (home of climatology for San Luis Obispo) is over 23 inches; the annual average for that station is 22 inches. The Paso Robles Airport is now over 13 inches but usually gets 12.5 inches. Much like the Paso Robles Airport, the Santa Maria Airport receives about 13 inches each rain season but so far has seen nearly 14 inches of rain.
All these days of steady, but lighter, rain have dramatically risen lake and reservoir totals throughout the Central Coast.
Lake Nacimiento went from 17 percent of capacity as of January to 79 percent of capacity as of Friday. Lake San Antonio is at 36 percent. According to data from SLOCountyWater.org, here are the other San Luis Obispo County lake and reservoir percent of capacity figures: Lopez Lake is at 55 percent, Salinas Reservoir near Santa Margarita is at 104 percent with water flowing over its spillway into the Salinas River, and Whale Rock Reservoir near Cayucos is 84 percent.
In Santa Barbara County, Gibraltar Reservoir is releasing water into the Santa Ynez River, which flows into Lake Cachuma. In January, Lake Cachuma was at 31 percent of capacity but had risen to 71 percent as of Saturday. Even Twitchell Reservoir, which was mostly dry at the beginning of February, is now reporting 20 percent of capacity. Nearby, the Santa Maria River is flowing to the ocean.
Not only are the lakes and reservoirs rising, but also the groundwater tables.
“Since the rains started in earnest back in November, levels in seven hard rock water wells near Prefumo Canyon, which I monitor, have risen from 6 to 24 feet, or an average of over 14 feet,” said Chris Arndt at SLOWeather.com in western San Luis Obispo.
To estimate the time lag as the water percolated from the surface to the water table, he graphed the accumulated rain and the water level in one representative well for the last four months.
“The water level tracks the rainfall remarkably well, with what appears to be a one- to two-week lag. This well’s static water level when drilled was 140 feet deep. So, the percolation time would seem to be about 13 feet per day or 21 inches per hour. Historically, the levels in these wells top out in April or May and then start their decline as water is pumped out.”
By the way, SLOWeather.com is reporting 140 percent of average rainfall as of Saturday.
Looking up to the mountains, the above average precipitation in the months of November, January and February have produced a 160-plus percent of average snowpack in the Sierra Nevada. That snowpack in the Sierra acts as a storage reservoir for water. As the reservoir melts in spring and summer, it slowly releases water for the needs of forests and agriculture, households, industry, domestic animals and endangered species. It also provides energy for hydroelectric power.
Overall, if you asked ranchers and farmers, water and emergency managers, Caltrans, PG&E crews and other first responders, you could not ask for a better rain season scenario. Despite the above average rainfall amounts throughout the Central Coast, there hasn’t been much flooding to report or severe soil erosion, but plenty of the wet stuff to turn our hills to emerald green and the promise of a spectacular wildflower bloom later this month into April.
Please remember, even though the United States Drought Monitor has removed the drought “Intensity and Impact” level indicators from nearly all of California, including the Central Cost, water is a precious resource and needs to be conserved.