January storm boosted SLO County lake levels. Here’s how much
A recent winter storm that hit the Central Coast brought lots of flooding, fallen trees, sinkholes and downed power lines. But how did the storm, which dropped as much as 17 inches of rain in some spots, impact San Luis Obispo County lakes and reservoirs?
The answer? It varies, and dramatically so.
One lake nearly doubled its capacity, for example, while others grew by much more modest amounts.
The “dragon” of Lake Nacimiento, located in the very northern part of the county adjacent to the higher elevations where rain fell the hardest, saw the largest jump in water levels: from about 725 feet to 751 feet.
Its capacity rose from 21% to 41% after the storm, a current total of about 50.5 billion gallons of water, according to Layla Decker, the general manager of Lake Nacimiento Resort.
“That big of a jump from just one storm — that’s excellent,” Decker said. “We’re sitting pretty for the summer.”
Decker said the new rainfall, and runoff that continues to steadily flow into the lake from its massive watershed even a week after the storm, will help the lake maintain a healthy water level for recreation both on and off the water for the summer months.
“Going into the summer, you technically want to be about 30, 31%. You never want it too high, just because you lose all of that day-use area,” she said. “So in some sense, you know, you love the rain and you want it. But too much of it also can affect our business because we lose all that extra space.”
Before the summer season starts, Decker said there will be several releases from the reservoir — which typically cause a 2% to 3% decrease in capacity every month. So, the 41% capacity the lake is sitting at now is “just great,” she said.
“It’s going to be a great summer,” Decker said.
Nacimiento, however, is the exception rather than the norm. Other reservoirs in San Luis Obispo County did not see such drastic changes in elevation levels and capacity.
Santa Margarita Lake — also known as the Salinas Reservoir — went from an elevation of about 1,289 feet to 1,291 feet after the storm. That translates into a 4% capacity increase to the 73.3% the lake is at now, or 5.7 billion gallons.
On Friday morning, the county confirmed a “live stream” in the Salinas River, meaning managers will stop releases at Santa Margarita Lake and begin storing water.
Lopez Lake northeast of Arroyo Grande increased from 479 feet to 480 feet of elevation since the rainstorm. It’s now at 40.4% of capacity. Unlike the Nacimiento area, the South County topped out at about 6 inches of rain, which explains the smaller gains at Lopez.
Ken Klis, a parks superintendent at San Luis Obispo County Parks, said that the recent rainfall wasn’t really enough to drastically affect the lake levels.
“You need several storms to get the creeks going and saturate the soils,” he said. “And the recent storm just didn’t cut it.”
Klis said that most of the creeks around Lopez Lake are still dry.
And Whale Rock Reservoir near Cayucos saw about one foot in elevation gain, which reservoir supervisor Noah Evans said is unusual for the lake since the winter storm only brought about 5.8 inches of rainfall to the area.
“It typically takes about 10 inches of rain for us to start seeing any elevation gain,” he said. “But this rain storm was particularly flashy — lots of rain in a little amount of time — so we saw a lot of runoff.”
San Luis Obispo County will need more rain, however, to bring those reservoir levels up even more.
How lake levels compare to this time last year
Across the county, reservoir levels are below what they were this time last year.
Lopez Lake was at 51.6% capacity this time last year, so it’s about 11 points down today, according to the San Luis Obispo County Public Works Department. And Santa Margarita Lake is about 10% below its capacity level this time last year.
“It’s been a dry year, I am worried about that,” Klis said. “We need some more rains, that’s for sure.”
There currently is no rain forecast in the near future for the Central Coast, according to the National Weather Service.
Whale Rock Reservoir had an elevation of about 205 feet in January of 2020 — it sits at about 201 feet currently, according to Evans.
But the lower elevations aren’t necessarily a cause for concern, Evans added.
There’s enough water to go around, and the county is only one month into its typically three-month rainy season, so there may be more rain to come.
“The way it’s looking now, the current forecast looks like a little dry spell, so we’re just gonna have to kind of ride it out and hope that the season provides us with some more precipitation,” Evans said.
One other positive note: The recent rainstorm brought the county out of the moderate drought conditions and into “abnormally dry” status, according to the U.S. Drought Monitor.
This story was originally published February 5, 2021 at 5:00 AM.
