The rain is continuing to fall and the intensity increasing in what could be a second wet year across the Central Coast.
On January 9, 2023, the Arroyo Grande Creek Levee breached and flooded nearby homes and farmland in Oceano. This winter's rain could bring an even bigger problem. To help explain why, you have to head north to Lopez Lake.
Usually, the lake helps to hold back some of the water that would flow down the creek. In a typical year, it has plenty of space, but last March, it filled up and spilled over for the first time in 25 years.
Right now, the lake is still about 95% of capacity, so for the first time in a quarter of a century, it could start spilling at the beginning of the rainy season. That possibility is causing some concern for officials.
"Yes, it's a little more concerning. We definitely looked at what would have happened in the January storms if Lopez had been spilling and have estimated we'd have about 20 to 40 percent higher peak flows. And the other thing to keep in mind is that it would be spilling and so those high flows would be happening longer, so we may have longer-term evacuation orders," said Courtney Howard, San Luis Obispo County Public Works Water Division Manager.
To prevent more flooding this year, the county launched a project to remove excess sediment from Arroyo Grande Creek, restore its flow capacity, and repair the levee to match the condition it was in back in 2020.
"We were able to install and repair some turf reinforcement mat for when it does overtop. It kind of protects the soil there so it doesn't erode further," Howard said.
There are still some additional mitigation measures planned, but the county is waiting on a contractor.
"It's a hydraulic barrier that will go down the center of the levee on the north side and the south side in the spots where we saw holes forming. Basically, that made the levee more vulnerable," Howard said.
She adds that the levee can only withstand so much water. It's designed for what's called a 10-year storm.
In any given year, there's about a 10 percent chance of a big enough storm to overwhelm the system. If and when Lopez Lake starts spilling, more water flowing down the creek will make the potential for flooding even greater.
Howard says the reinforcements put into place should prevent the levee from breaching again, but it could still overflow. If the water does top the levee, it's designed to head south away from homes in the area.
