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

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

Lake Lopez near Arroyo Grande was at 92.6% capacity Friday afternoon, according to SLO County Public Works data, a massive gain from just three months ago.

As recently as December 10, Lopez was only at 22% capacity. On January 1, it was 24%.

Less than a week ago, however, the reservoir had improved to 66% full.

The combination of several atmospheric rivers in January and March now has it almost at capacity.

“It’s definitely going to roll over,” San Luis Obispo County Department of Public Works spokeswoman Paula McCambridge told The Tribune. “This is the last of the reservoirs (maintained by the county) to reach 100% capacity.”

McCambridge said that because the reservoir continues to fill with runoff from the recent storm, the lake level is rising daily. If the area doesn’t get any more rain, she said Public Works estimates Lake Lopez will drain in about eight days.

“Tuesday’s storm might be enough to put it over the top,” she said.

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

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

The reservoir, which was created in 1968, can store a maximum of 49,388 acre-feet of water and held 45,751 acre-feet of water as of Friday, the data showed. It is also used for recreational activities such as boating, camping, fishing, and mountain biking and also provides water to residents of the Five Towns area of ​​SLO County.

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

Public works to monitor the impacts of flooding from the lake outflow

Although the lake has not spilled for 24 years, McCambridge said Public Works has ensured the condition of the spillway itself – which will direct water discharged into Arroyo Grande Creek – is maintained during this time. through regular maintenance and inspections.

“We want the public to know that the reservoirs are not something that only catches our attention during heavy rains,” she said. “It is our top priority, public safety. We therefore do not wait to react to situations.

According to McCambridge, when the reservoir overflows, the public works department will closely monitor stream gauges and conduct on-site monitoring to watch for potential flooding along the creek area.

“It is possible that there will be flooding,” she said. “If we have a high impact storm, we expect a lot of water.”

Oceano in particular has already been threatened with flooding during this winter’s extreme storms thanks to its location near the Arroyo Grande Creek levee. During recent storms, authorities issued evacuation warnings and, in some cases, orders, as water levels rose in the area.

McCambridge said if it is necessary to evacuate due to an extreme influx of water into the creek during the next storm, the county is ready to issue orders immediately.

“We have boots on the pitch and people in front of their computers, and so at the first sign of information the public needs, the public will have it,” she said.

Two other SLO County reservoirs are already spilling

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 Lake Santa Margarita has overflowed into the Salinas River since January 9.

It was at 105% capacity on Friday.


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