After years of talk, SLO is dredging Laguna Lake for the first time ever. Here’s why
After decades of discussion and planning, San Luis Obispo’s Laguna Lake will be dredged using hydraulic equipment for the first time.
The work, which will take place this summer and cost an estimated $500,000, will focus on removing about 2,000 cubic yards of accumulated sediment at the mouth of Prefumo Creek.
The creek flows into the lake, snaking into the city from the Irish Hills.
The idea of dredging Laguna Lake has been a talking point in San Luis Obispo for several years, without fruition, but removing large amounts of sediment across the natural lake would cost millions of dollars.
Over the years, the city has removed sediment from Prefumo Creek and the manmade Prefumo Arm, and altered the boundaries of the lake in the 1960s to make way for new development around Oceanaire Drive.
But hydraulic dredging hasn’t take place in the larger, core portion of the lake, which is the plan for this project, said Richard Burde, a city engineer.
The city has an initial five-year plan for its initial removals of sediment, and city officials forecast spending a total of about $1.65 million.
According to a 2016 city report, removing the sediment would deepen the lake and create community benefits that include enhancing wildlife habitat, critical for threatened steelhead trout and local and migratory birds, as well as recreational opportunities such as kayaking, canoeing, stand-up paddle boarding and fishing.
Another benefit would be stormwater management and flood control, including better preventing storm drain backups, the report said.
Laguna Lake dredging will be years-long process
In addition to dredging, the Laguna Lake pilot program includes stabilizing about 90 linear feet of the lake’s bank near the main parking lot to prevent further deterioration there and to stop asphalt from eroding into the lake.
The staff expects to learn from this project and “leverage this knowledge for future phases of dredging,” Burde said in a staff report on the project.
The city received permits from the U.S. Army Corps of Engineers, California Department of Fish and Wildlife, and the California State Water Resources Control Board. The city has an option for a one-time extension on permitting for an additional five years.
The city is allowed to dredge up to 4,000 cubic yards of sediment, but is focusing on a smaller amount in the first year to gauge effectiveness of methods.
“We’ll learn a lot this summer and we’ll drill in on the project a little better at that point for future spending,” Burde told The Tribune.
SLO forecasts annual city spending on project
Budgets haven’t been set, but the city is forecasting the project will cost $350,000 in 2021, $400,000 in 2022 and an additional $400,000 in 2023, Burde said.
The city’s allocation of $500,000 combines a budget allocation of $150,000 in 2019, which rolled over to 2020, and $350,000 in 2020, which kicks in starting July 1 with start of the fiscal year. The work is projected to start in August.
City officials, who will put the project out for contractor bidding, estimate the project work will cost $380,000. Additional costs for contingencies, environmental monitoring and water quality sampling bring the total amount to $496,500, according to the city.
In 2016, the city discussed spending between $5 million to $20 million on Laguna Lake dredging, with the more expensive options spanning larger swaths of the lake.
Sandbar is blocking flow at Prefumo Creek mouth
Without any dredging, levels of silt have worsened since Prefumo Creek was rerouted into the lake through the Laguna Lake Golf Course in the 1960s. Creekside banks have eroded, contributing to the problem, according to city officials.
“We’re trying to address issue at Prefumo Creek now to help keep the problem from getting worse,” Burde said. “A sandbar is accumulating. We’re trying to punch a hole so there’s unobstructed flow. The water currently hits a sandbar and makes a 90-degree turn and slows down the water, and that allows for more sedimentation.”
Costs are partly dependent on hauling materials, Burde said.
“It will be interesting to see what kind of bids we get,” he said.
The city removed about 1,300 cubic yards of sediment already in 2018 from Prefumo Creek a quarter-mile from the lake, where the creek flattens out and the water slows down, Burde said.
And the city had conducted other sediment removals in past years of that Prefumo Arm, a waterway established in the 1960s, along with other area alterations, such as the re-route of Prefumo Creek and the Southeast Arm as the Oceanaire neighborhood was established, according to a 2014 city report.
This story was originally published January 16, 2020 at 5:10 AM.
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