Sand replenishment begins at Cardiff State Beach


Sand replenishment began last week at Cardiff State Beach, one of the first milestones in a $120 million, four-year effort to restore the San Elijo Lagoon.

Improved water quality, greater wildlife diversity, more public recreational trails and a greater resilience to environmental change are among the long-term goals of the restoration, which has been planned for decades.

“There have been a lot of sleepless nights leading up to this,” lagoon conservancy president and chief scientist Doug Gibson said during a recent visit to the work site. Despite his nervous nights, the restoration began in December and is off to a good start.

The project is expected to produce nearly 600,000 cubic yards of sand, which is being pumped onto nearby beaches through an 18-inch diameter, high-density polyethylene pipe in a slurry of 20 percent sand and 80 percent water.

About half of the sand will be deposited along the shore at Cardiff, just outside the lagoon, over the next six weeks. After that, the rest of the sand will be piped south as far as Fletcher Cove in Solana Beach, and some could be deposited offshore in the ocean and stored there for future replenishment projects.

Details such as the amount of sand and the dimensions of the project have been worked out in detail, but the numbers could change as the plan goes from paper to reality, Gibson said.

“We did all the science,” he said. “Now it’s all construction.”

The beach-quality sand is coming from an “overdredge pit” being created in the lagoon along the eastern side of the railroad tracks.

When finished, probably in mid-July, the pit will be about 30 feet deep and will cover 12 to 13 acres, Gibson said. Then, as the project proceeds, the pit slowly will be filled back up with nutrient-rich sediment dredged from the lagoon channels, mud flats and marshes.

Sediment dredged from many parts of the lagoon can’t be placed on the beach, in part because it’s contaminated with organic nutrients left years ago when untreated and lightly treated sewage flowed into the waterway. When the restoration is finished, the sediment-filled pit will be capped with a four-foot-thick layer of beach quality sand.

Without the restoration, the lagoon would continue to slowly fill with sediment, probably eventually becoming a meadow.

Money to pay for the restoration comes from the half-cent sales tax known as TransNet approved by San Diego County voters.

The environmental project qualifies for the funding as part of the North Coast Corridor Program, which includes the widening now underway of the Interstate 5 and coastal railroad bridges across the lagoon. Altogether, the many transportation, environmental and coastal access projects in the corridor program are expected to cost a total of about $6 billion over the next 30 years.

Also underway at the San Elijo Lagoon is a separate $9.5 million construction project to replace the 52-year-old onshore outfall pipe that extends from the nearby San Elijo Joint Powers Authority wastewater treatment plant.

“We wanted to replace this before the pipeline had a break or a major failure, especially with this major lagoon restoration underway,” said Michael Thornton, general manager of the JPA.

The new 2,600-foot-long, 30-inch diameter pipe extends from the treatment plant on the northeast side of the lagoon, near the conservancy’s visitors center, under the lagoon at a depth up to 65 feet, to the beach just south of “restaurant row” at Cardiff.

The new pipe was installed using “trenchless technology” to minimize the environmental effects of construction. Workers drilled horizontally, beginning at a staging area at the beach, to reach the treatment plant, and then pulled the new high density polyethylene pipe through the hole from the plant to the beach.

At the beach, the pipe connects to the existing ocean outfall, where it discharges treated wastewater into the Pacific Ocean about 1.5 miles from shore at an average depth of 100 feet.

The pipeline carries an average 10 million gallons a day of treated wastewater from Encinitas, Solana Beach and Escondido.

“A lot of thought and work went into (planning) this,” Thornton said. Projects like the outfall replacement and the lagoon enhancement require the coordinated efforts of many people at multiple local, state and federal agencies.

Two Cardiff residents walking past the work site Feb. 27 said they were pleased to see sand replenishment begin.

“We walk here every day, and it’s been interesting to watch,” said Robin McLynn, with her husband, John. They’ve lived nearby for 30 years.

Every sand replenishment project helps the beach, she said. Without them, at high tide there would be nothing but rocks to walk on.

“Most of the beach we have here today is from the last (replenishment project),” her husband said. “It really helps out.”

Sites such as the lagoon restoration’s dredge pit produce some of the region’s best sand, a clean, fine-grained quality similar to that which occurs naturally on the beach, said Gibson, the conservancy’s chief scientist.

Beach restoration projects sometimes use sand from construction projects or dredged from nearby offshore deposits. Along San Diego County’s coast, that has produced a more coarse sand that some people consider of lesser quality.

-- Phil Diehl is a reporter for The San Diego Union-Tribune.