San Diego Union-Tribune (Sunday)
LAGOON PREP A STUDY IN SILT
Crew determining depth, makeup of Buena Vista Lagoon ahead of work to restore tidal flows, health of habitat
The sounds of drilling echoed across the Buena Vista Lagoon from a small barge anchored in the weir basin Wednesday morning.
On the barge, a geotechnical crew was wrapping up a monthlong study of the sediments, depth and topography of San Diego County’s only freshwater lagoon, part of the preparations for its long-planned restoration.
Located at the Oceanside-carlsbad border, the coastal lagoon is the only one in the county not open to the Pacific Ocean. That is the result of a weir or low dam installed in the 1940s and replaced multiple times to prevent the lagoon’s surface from rising and falling with the tides.
That will change with the removal of the weir under a plan approved in 2020 by the San Diego Association of Governments. Along with removing the weir, the plan includes restoring part of the creek channel and excavating years of accumulated sediment, some of which could be used to replenish the sand on nearby beaches.
The geotechnical investigation began Jan. 9 and was scheduled to end Saturday. Work is prohibited after Feb. 15, which is the beginning of the Ridgway’s rail nesting season. Environmental constraints are a big part of the project.
The progress is exciting for groups like the Buena Vista Audubon Society, which has a nature center at the edge of the lagoon along South Coast Highway in Oceanside.
“As a key stakeholder in this project and a strong advocate for opening up the lagoon to the ocean, the Buena Vista Audubon Society is thrilled to see the sampling and topography analysis occurring now,” said the group’s executive director, Natalie Shapiro, in an email Thursday.
“While it is a first step in the restoration process, it has been years in the making and the community, local cities, and SANDAG have worked hard to bring this project to fruition,” Shapiro said. “We look forward to the day when we see a healthy, functional lagoon, open to tidal flows.
“With climate change a daily reality, it is even more urgent that we restore our coastal estuaries to help our communities be resilient to sealevel rise,” she said. “Lagoons and associated wetlands not only provide critical habitat for birds and other wildlife; they store carbon, which is one of the best ways to reduce greenhouse gas emissions. They also buffer communities from flooding and impacts of king tides.”
Oceanside and Carlsbad also are partners in the project. Each city contributed $100,000 toward the completion of the required environmental documents.
“It’s a beautiful project,” Oceanside Mayor Esther Sanchez said Thursday. “It would do a lot for Oceanside. We’re all excited about it.”
In January and early February the geotechnical crew drilled as deep as 100 feet in spots within the “weir basin,” which is the area between the weir and the railroad bridge. Elsewhere in the lagoon and along its edges the crew drilled to 10 feet, including the “rail basin” between the railroad bridge and South Coast Highway.
“They want to see what’s down below,” said Kim Smith, a senior regional planner at SANDAG.
Information from the core samples taken will help determine how much of the dredged material is clean enough to place on the beach, Smith said.
Sediment samples collected at selected intervals will be tested for things such as grain size, density and shear strength. The material also will be analyzed for any metals and other constituents, and to determine what types of plants could grow in it.
The deepest testing took place in an area within the weir basin that could be used as a pit to temporarily store sand during the excavations, as was done during the recent restoration of the San Elijo Lagoon at the border of Encinitas and Solana Beach. At the end of the dredging, sediment that’s not placed on the beach could be left in the pit and covered with a layer of clean sand.
An aerial survey, boundary surveys and base mapping were done to create a topographical map of the Buena Vista project site, SANDAG officials said. The topo map will show the contour elevations of land above sea level.
A bathymetric survey also was performed to map the underwater area, utilizing a single-beam digital acoustic echo sounder operated from a shallow-draft boat within the lagoon. A satellite system was used to determine the precise locations and elevation of the sounder during the survey.
Silt has been accumulating in the 220-acre lagoon since the weir was built and contributes to its degradation. Always shallow, the lagoon has been growing more shallow and its surface area has been shrinking as cattails and reeds slowly increase along the banks. Also, for much of the year the water is stagnant, which kills fish and harbors mosquitoes.
“Nobody wants to see it become a meadow,” Sanchez said. “It has the potential for teeming with wildlife and just being a beautiful place for visitors and residents alike.”
Restoration will improve the water quality, increase biodiversity, reduce the wildfire risk and alleviate concerns about mosquitoes and other disease carriers, Smith said. The project has been discussed for decades.
Disagreements about the best way to do the restoration stalled the project for years.
Property owners around the weir wanted to keep the weir because of the wide expanse of open water it creates. Environmentalists and government agencies wanted to remove the barrier to create a more natural saltwater marsh and provide homes for marine life and native plants.
In the end, the compromise approved in 2020 should do both. It removes the weir but includes an area of deeper, open water to be created near the homes at the western end of the lagoon.
“That is the challenge,” Smith said. “Everybody wants a project, and if we can’t all agree on something, there’s no project.”
Completion of the geotechnical investigation will help take SANDAG to the 65 percent complete stage of the engineering and design work needed to make the restoration project “shovel-ready.” The term shovel-ready means the project is ready to apply for the grant money needed to begin construction.
SANDAG expects to reach the shovel-ready stage by the end of 2025 or early 2026, Smith said. Construction is expected to take about two years and cost at least $80 million, as estimated in 2019 dollars.
Just getting to the 65 percent stage has cost the agency $4 million, Smith said. The money included a $3 million grant from the state Wildlife Conservation Board in 2019, and $1 million awarded in June 2022 by the state Department of Fish and Wildlife. An additional $5.9 million is needed to finish the preliminary work, and SANDAG has applied for grants to cover those costs.
“Our limiting factor has always been identifying funding,” she said.
Funding for the 141-acre San Elijo Lagoon restoration, which cost a total of $87 million, was obtained when the project qualified as mitigation for the Caltrans North Coast Corridor project, which included widening Interstate 5 and the I-5 bridge across the lagoon.
The Buena Vista Lagoon restoration also was proposed as mitigation for the North Coast Corridor project, however, that opportunity has passed. Now SANDAG is looking for other funding sources.
philip.diehl@sduniontribune.com