SLO County reservoirs swell after rain storms. How much did water levels rise?

Recent storms have caused water levels at local reservoirs to swell dramatically after years of drought shriveled the important resources.

One San Luis Obispo County lake was overflowing as of Wednesday, while another nearly doubled in capacity.

“This is fantastic news,” said Shane Taylor, Arroyo Grande’s utilities manager. “This is just what we needed.”

An incredible amount of rain has fallen over San Luis Obispo County in December and January — which are typically some of the rainiest months of the year.

In Atascadero, nearly 16 inches of rain has fallen since the beginning of December. That’s 87% of the area’s typically annual rainfall recorded in just over a month, according to the San Luis Obispo County Public Works Department.

At Camp San Luis Obispo, 21 inches have fallen since Dec. 1 — 105% of that area’s annual normal amount, the Public Works data show.

And at Rocky Butte near San Simeon, more than 45 inches of rain has fallen since Dec. 1. That’s about 114% of the mountainous region’s typical rainfall accumulation.

The recent inundation of rain across the county stands in start contrast to the previous rain year, when skies cleared after a stormy December and hardly any precipitation fell after the first day of 2022.

Reservoir levels skyrocket from recent rainfall

Reservoirs in San Luis Obispo County have seen levels go from the lowest seen in years to bursting at the seams.

The Salinas Dam at Santa Margarita Lake was overflowing Wednesday with the reservoir at about 109% of its capacity, according to the county public works department.

The lake has spilled pretty much as much water as it holds over the past few days, according to David Spiegel, a supervising engineer at the Public Works Department.

As of Wednesday afternoon, the lake was holding about 26,060 acre-feet of water — its capacity is 23,843 acre-feet.

For context, one acre-foot of water is about 325,851 gallons. That means Santa Margarita Lake has about 722.4 million too many gallons within its banks that are overflowing into the Salinas River.

Lopez Lake east of Arroyo Grande also saw huge gains from the recent storms.

Since Dec. 1, the reservoir has nearly doubled in storage. It went from about 10,837 acre-feet to holding 21,594 acre-feet on Wednesday afternoon.

That represents a capacity gain from 21.9% to 43.7%, according to Public Works.

Whale Rock Reservoir near Cayucos went from 28,100 acre-feet on the first day of 2023 to holding 32,292 acre-feet on Wednesday, according to Noah Evans, the reservoir’s manager with the city of San Luis Obispo.

The lake is now at 82.9% capacity, up from 72.1% at the beginning of the month, according to Evans.

Lake Nacimiento also saw massive gains from the recent storms.

The huge reservoir in northern San Luis Obispo County went from 27% capacity holding 103,630 acre-feet of water at the end of December to 73% capacity holding 275,060 acre-feet of water on Wednesday, according to the Monterey County Water Resources Agency.

That’s a gain of 55.9 billion gallons of water.

Drought-related water restrictions remain

Reservoirs in San Luis Obispo County are important drinking and irrigation water sources for those living in the region.

Lopez Lake provides water to South County cities such as Arroyo Grande, Grover Beach and Pismo Beach.

Lake Nacimiento sends water to Atascadero, Paso Robles and San Luis Obispo.

The city of San Luis Obispo also gets water from Santa Margarita Lake and Whale Rock Reservoir.

Even though the reservoirs have seen huge increases in water levels due to recent storms, all cities in the county must keep water restrictions in place.

In March 2022, Gov. Gavin Newsom issued an executive order requesting municipalities enact their water shortage contingency plans to cut consumption by 10 to 20%.

The governor’s order still stands as of Wednesday — so those water restrictions must remain.

Local purveyors say the water conservation measures have worked and therefore saved water from being sucked from the reservoirs or groundwater sources.

“Huge shoutout to our customers — they’ve done really well,” Taylor said of Arroyo Grande water users.

The purveyors also noted that they expect per-capita water use to decline as the rainfall eases drought conditions in the region.

“With all the rain, it’s not like anyone is going to be irrigating outside,” said Mychal Boerman, San Luis Obispo’s utilities deputy director.

Mackenzie Shuman

The Tribune

805-781-7844

Mackenzie Shuman primarily writes about SLO County education and the environment for The Tribune. She’s originally from Monument, Colorado, and graduated from Arizona State University’s Walter Cronkite School of Journalism and Mass Communication in May 2020. When not writing, Mackenzie spends time outside hiking and rock climbing.