The reef balls are designed to attract native oysters that would form a living barrier instead of concrete walls and shoreline riprap used in the past to protect the coast from wave erosion.
Environmentally Friendly Habitat
The idea is to use nature to protect the shoreline with the side benefit of providing “environmentally friendly habitat structures,” Maher said.
The reef balls, made of concrete mixed with local sand and oyster shell aggregate, are arranged in a series of six arrays. Each array has 15 groups of four reef balls and is about 88 feet long by 45 feet wide.
A reef ball, which is perforated, is about three feet in diameter, about three feet tall, and is mounted on a base that’s about four feet in diameter.
A secondary goal of the project is to build up the mud flats around the reef ball structure, Barrett said. Oysters also filter the water.
Nature Based Solution
Developed by the Port of San Diego in partnership with the California Coastal Conservancy and the U.S. Fish & Wildlife Service, the Chula Vista project is modeled after a similar one in San Francisco Bay.
Larison Contracting Corp., based in Long Beach, finished the reef ball installation in late December. Environment Science Associates, based in downtown San Diego, worked on the design of the project.
“This project demonstrates the potential of nature-based solutions to help one of California’s most iconic and vibrant waterfronts to keep pace with rising seas,” said Amy Hutzel, executive officer of the Coastal Conservancy.
If it works, similar reef ball reefs could be installed elsewhere along the San Diego County coastline.
“The city of San Diego and a number of other cities with shorelines are looking at the idea of natural shorelines as well,” Barrett said.
About 75% of the coastline is lined with seawalls, concrete barriers and riprap – piles of rock and other materials, what scientists like Barrett refer to as armoring.
“The hardened, armored shoreline is no longer a viable solution for us,” Barrett said. “We’re looking to add resilience to San Diego Bay.”
A total of 360 reef balls were installed in Chula Vista, covering 5,760 square feet of shoreline. Besides protecting the coast from rising sea water, the project is designed to create a reef habitat for fish, birds, invertebrate sea creatures and aquatic plants.
The reef ball barrier is among several initiatives that the Port of San Diego is taking to deal with rising sea levels. Others include an artificial reef installed on Harbor Island in early 2021 to replace a riprap barrier of boulders and a dune restoration project in Cardiff. Both are showing promising results, according to scientists.
The Chula Vista reef ball installation will be studied for five years to see how well it works and how it might be applied elsewhere.
“This has a lot of eyes on it,” Barrett said. “This is the first of its kind on San Diego Bay. There’s a lot of people tracking it.”