Another California reservoir is about to leak – for the first time in 24 years

Heavy rains from a series of atmospheric river storms have filled another lake in San Luis Obispo County to the brink of overflowing for the first time in more than two decades.

Lopez Lake near Arroyo Grande was at 92.6% occupancy as of Friday afternoon, a massive gain from where it was three months ago, according to data from SLO County Public Works.

As of December 10, Lopez was only 22% utilized. On January 1st it was 24%.

However, less than a week ago the reservoir was 66% full.

The combination of multiple atmospheric fluxes in January and March has now pushed it to almost full capacity.

“It’s definitely going to be phased out,” Paula McCambridge, spokeswoman for the San Luis Obispo County Department of Public Works, told The Tribune. “It’s the last of the reservoirs (run by the county) to reach 100% capacity.”

McCambridge said because the reservoir continues to fill up with runoff from the recent storm, the lake level is rising every day. If the region stopped raining, she said Public Works estimates Lake Lopez would overflow in about eight days.

“Tuesday’s storm could be enough to topple it,” she said.

McCambridge said the last time the reservoir spilled was in 1999. In the more than five decades the lake has been in operation, it has spilled a total of 18 times, she added.

The water level at Lopez Lake was 518 feet as of Friday afternoon, while the spillway level is 522 feet, according to Public Works.

The reservoir, which was formed in 1968, has a maximum capacity of 49,388 acre-feet of water, according to the data, and contained 45,751 acre-feet of water as of Friday. It is also used for recreational activities such as boating, camping, fishing, and mountain biking, and provides water to residents of SLO County’s Five Cities area.

The view of Lopez Lake from Hi Mountain Condor Lookout on August 4, 2010.

The view of Lopez Lake from Hi Mountain Condor Lookout on August 4, 2010.

Public works to monitor the impact of flooding from lake spills

Although the lake has not spilled in 24 years, McCambridge has said Public Works has ensured the condition of the spillway itself – which will channel the overflowing water into Arroyo Grande Creek – has been maintained through regular maintenance and inspections during that time.

“We want the public to know that we don’t just take notice of the reservoirs when it rains heavily,” she said. “It is our top priority, public safety. So we don’t wait to react to situations.”

According to McCambridge, when the reservoir is drained, the public works department will keep a close eye on gauging gauges and conduct on-site monitoring for possible flooding along the creek area.

“It’s possible that there will be flooding,” she said. “If we have a strong storm, we expect a lot of water.”

Oceano, in particular, was already at risk of flooding during this winter’s extreme storms, thanks to its location near the Arroyo Grande Creek levee. During recent storms, officials issued evacuation warnings and, in some cases, orders as water levels rose in the area.

McCambridge said if an evacuation was required due to extreme water inflow into the creek during the next storm, the county was ready to issue orders immediately.

“We have boots on the ground and people on their computers and so at the earliest sign of information that the public needs to have, the public will have them,” she said.

Two other reservoirs in SLO County are already leaking

Lopez Lake would be the third local reservoir to reach capacity this winter.

Earlier this week, Whale Rock Reservoir near Cayucos spilled for the first time in 18 years.

The last time Whale Rock was near capacity was in May 2019 when it hit 90%.

On the afternoon of March 11, the reservoir reached 111% capacity.

And Santa Margarita Lake has been overflowing into the Salinas River since January 9th.

On Friday it was 105% busy.


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