Posted on October 9, 2024
Agua Hedionda Lagoon dredging this winter could provide up to 400,000 cubic yards for southern shores
Carlsbad beaches should get their next replenishment this winter with the dredging of Agua Hedionda Lagoon, which is expected produce as much as 400,000 cubic yards of sand.
Workers could begin setting up equipment in the lagoon as soon as Jan. 1, said Dominic Massaro, a senior engineer working on the project.
Originally expected to begin this fall, the start was delayed by difficulties getting permits from all the federal, state and local agencies involved. However, the deadline for completion remains April 15, 2025.
All the permits should be obtained by the end of this year, Massaro said in a presentation Tuesday to Carlsbad’s Beach Preservation Commission.
Agua Hedionda, Spanish for “stinking water,” has been dredged every few years since the 1950s, most recently in 2021. Most of the sand goes onto the beach near the end of Tamarack Avenue.
Initially, the dredging was required to keep the lagoon open as a source of cooling water for the Encina power plant run by the San Diego Gas & Electric Co. Today, the water supplies the Claude “Bud” Lewis Carlsbad Desalination Plant, and the desal plant’s owner, Channelside Water Resources, shoulders the responsibility for lagoon maintenance.
The 400,000 cubic yards is more sand than is produced by most other replenishment projects in the region.
If placed on top of a high school football field, 400,000 cubic yards would be 62.5 feet deep.
Oceanside’s annual harbor dredging, for example, produced 266,000 cubic yards in May that went onto beaches near the city’s municipal pier. The U.S. Army Corps of Engineers oversees that project to remove sediment from the harbor entrance and keep the channel open for navigation.
Sand removed from Agua Hedionda will come from a shoal that accumulates as the result of tidal flows in the lagoon’s outer basin between Carlsbad Boulevard, also known as Highway 101, and the North County Transit District’s railroad bridge.
The project is one of several Carlsbad is monitoring that could bolster eroding beaches in the next few years, said Nick Stupin, a city parks planning manager. Coastal cities throughout Southern California are looking for sources of fresh sand for the eroding shoreline.
Another upcoming Carlsbad replenishment is expected from maintenance dredging planned for Batiquitos Lagoon, which is south of Agua Hedionda near the city’s border with Encinitas.
The Batiquitos dredging was delayed a year because of the upcoming replacement of NCTD’s old wooden railroad trestle across the lagoon, Stupin said. Now the maintenance is expected to go from late 2025 through the spring of 2026, producing about 118,000 cubic yards of sand for southern Carlsbad.
Batiquitos was first dredged in a three-year restoration project completed in 1997 as environmental mitigation for an expansion for the San Pedro Harbor by the Port of Los Angeles. The Los Angeles port district paid for the restoration and set up a trust account to cover the costs of periodic maintenance.
In addition to the maintenance project, which is overseen by the state Department of Fish and Wildlife, the lagoon’s bridge replacement also is expected to produce beach sand.
The bridge project, led by the San Diego Association of Governments, will continue until 2028. During that time it is expected to produce about 60,000 cubic yards of material that will be distributed on the southern beaches of Carlsbad’s nearly 7 miles of shoreline, Stupin said.
Further out, the planned restoration of the Buena Vista Lagoon on the Carlsbad-Oceanside border could generate large quantities of sand to be shared by the two cities.
“It’s about a million cubic yards of sediment that will be produced from this project,” Stupin said.
Some of the material to be excavated during the restoration could be contaminated by the sediment from years of storm drain runoff. The Buena Vista is the county’s only lagoon that is blocked by a dam-like weir at the beach, so it only flows to the ocean when there’s significant rainfall.
Much of the year the lagoon lies stagnant. The weir, which has been in place since the 1940s, will be removed as part of the restoration to restore tidal flows and improve water quality.
“At this time it is unknown how much of that will be beach-viable sand,” Stupin said. “We do believe there will be a substantial amount.”
Clean sand from the lagoon will be placed on southern Oceanside and northern Carlsbad beaches. Both those areas are much eroded and rarely get material from replenishment projects.
SANDAG approved environmental documents for the Buena Vista restoration in 2020 after more than two decades of on and off work on the plan. The project is now in the design and engineering stage, but it still needs money for construction, Stupin said.
Also a few years away is a possible third regional sand project, a collaboration of five to seven coastal San Diego County cities led by SANDAG that would take sand from ocean deposits outside the surf zone. The previous regional project was completed in 2012 and provided 1.5 million cubic yards of clean sand.
“We would expect to see about 350,000 cubic yards of sand dispersed throughout the beaches of Carlsbad” from the SANDAG project beginning as early as 2028, Stupin said.
Construction and monitoring of the replenishment have been estimated at $37 million. Most of those costs should be covered by state and federal grants, with a small part to be shared by the cities involved in the project.
Beach commission acting Chair Lisa Stark asked if city staff could assemble a spread sheet showing all the Carlsbad projects and details such as dates, costs, amounts of sand, funding sources and agencies involved.
Parks and Recreation Director Kyle Lancaster said that will be done, and the updated information will be presented to the commission.
