TIDAL CIRCULATION

Each spring, residents and visitors of Cardiff-by-the-Sea may notice the appearance of construction equipment and dredging activities at the inlet of San Elijo Lagoon. 

The small opening, just south of San Elijo State Beach Campground, is the lagoon's only access to the Pacific Ocean. Keeping the inlet open to the ocean is critical to maintaining the health of San Elijo Lagoon. Left unattended, it would remain closed much of the year from buildup of sand transported by high incoming tides, surf, and storm surges.  

The Conservancy’s efforts to keep the inlet open to tidal flushing have substantially improved habitat quality relative to the stagnant conditions that previously developed when the inlet was closed for prolonged periods.

San Elijo Lagoon Conservancy experimented with different types of inlet openings between 1994 and 1999. These experimental openings yielded a method that kept the inlet open to the ocean for an average of 79% of the year.

WHY WE DREDGE
In 2001, a long-term financial endowment was established to actively fund maintenance of tidal flushing. Efforts to keep the lagoon open to tidal circulation have shown that significant ecological benefits result from increased tidal flushing, as evidenced by:

• increased diversity and abundance of fishes
• improved water quality
• reduced production of mosquitos and midges
• expanded nesting areas for California Least Terns, Belding's Savannah Sparrows, and Western Snowy Plovers
• increased foraging by birds.

  Dredging of the inlet (Photos on this page: SELC Archives) 

These ecological improvements have also fostered significant public enjoyment of the lagoon and beaches. Keeping the inlet open improves trail access to all regions of the reserve.

However, much more work is needed to sustain productivity and enhance habitat values of the lagoon. The inlet becomes intermittently blocked by an accumulation of sand in the tidal channel during the winter storm cycles. The cool weather helps keep oxygen levels in the lagoon in the safe zone. As temperatures rise in the spring and the demand for oxygen increases, an inlet operation is conducted before problems arise.

SPRINGTIME DREDGING
Typically, the sand berm that forms west of Pacific Coast Highway 101 is breached by excavation equipment. Larger dredging operations remove sand accumulations east of Highway 101 and under the bridge. Clean sand removed from the tidal channel is deposited south onto Cardiff State Beach. Conservancy staff manage these operations.

A major dredging operation to remove accumulated sand and cobbles can cost nearly $100,000. Timing this procedure in the spring after the winter storm cycle greatly increases the chances of continued inlet circulation throughout the warmer summer months. Previous experimental openings showed that a dredging operation in the winter has little chance of keeping the inlet open during the winter storm season.

A MODIFIED LAGOON
It has been decades since San Elijo Lagoon was naturally connected to the Pacific Ocean. Human modifications to hydrology occurred at a rapid pace after the 1880s. The first bridge and berm crossing the lagoon was constructed in 1887 for Santa Fe Railroad, followed by Pacific Coast Highway 101 (1891) and the completion of Interstate 5, which divided the wetland in half, in 1965. This "partitioning" of the lagoon created altered flows for both fresh and saltwater, leading to accelerated sediment deposition, dramatically-reduced water quality, and a reduction in native estuarine habitats due to increased runoff from development upstream.

Thanks to funding from California State Coastal Conservancy and CalTrans, our efforts in the last decade have improved tidal circulation with significant ecological and recreational benefits.