CARLSBAD, Calif. – An emergency authorization issued by the Los Angeles District’s Carlsbad Regulatory Office allowed the City of Carlsbad to place about 1,200 tons of stone and other material along a 270-foot segment of shoreline along the Pacific Coast Highway, stabilizing the shoreline and protecting a vital roadway along Southern California’s coast.
Just south of Palomar Airport Road along southbound Carlsbad Boulevard, which is part of the Pacific Coast Highway, sits a low-point along the coast, about 10 feet above sea level. “King Tides” occurred during the week of December 16, bringing higher than normal tides to the coasts, rapidly eroding the shoreline bluffs and compromising the highway. The City of Carlsbad requested the Corps assess the situation and process an emergency permit under Regional General Permit 63.
The Army Corps met with City staff and advised the city of the information the Corps needed in order to coordinate with other agencies and proceed with a permit. Given the emergency situation and persistence of King Tides throughout that week, the Corps allowed the city to proceed with stabilizing the banks on the beach along the road to protect the roadway, while continuing to work on an after-the-fact permit.
The repairs are designed to mitigate the emergency situation, although in the upcoming weeks and months the shoreline will be subject to the same significant oceanographic conditions that caused the damage. It is also likely that the emergency repair will take a year or more for the regular coastal development permit to be issued.
The proposed emergency repairs needed be robust enough to withstand the anticipated wave action and the time required to design and permit permanent repairs. Designers did not use softer shore protection solutions such and sand bags and geotextile tubes because they are not designed for repeated wave driven cobble attack.
Rip rap or quarry stone revetment is more often used as an emergency protection system due to the durability of the material, the simplicity of construction in a very dynamic environment, and the proven performance. Nearly every section of the Pacific Coast Highway located on the ocean in lower lying areas in San Diego County is protected by a quarry stone revetment.
The construction consisted of placing ¼- to ½-ton rip rap along the bluff, about 2 feet thick, and approximately of x cubic yards of two- to four-ton rip rap rock from a mine in Chula Vista, providing an additional six feet of protection. Fabric placed behind the rip rap will retain the fine particles, preventing further erosion along the banks.
Work began on December 23 and was completed around December 31.