COASTLINE OPTIONS
STORM surges and large waves cause property damage
and beach erosion on a nearly annual basis. A study
published by the National Oceanic and Atmospheric
Administration predicts a substantial increase in storm
damage in the future. “The large increases in tropical Atlantic Sea
surface temperatures projected for the late 21st century would
imply very substantial increases in hurricane destructive potential
— roughly a 300 percent increase by 2100.”
In places including Hawaii and Southern California, a network
of outer reefs acts as a safety net, dissipating wave energy, which
protects the shoreline. Most of the time, those reefs are invisible to
the naked eye, until a major swell event hits the coast. Then waves
can be seen breaking a long way out in places where the water is
typically calm.
“After watching powerful waves chew away at the sandy coastlines
along the East Coast, one might wonder how tropical islands manage
relentless swells without severe erosion,” says Dan Ginolfi, director of
coastal resilience for Coastal Strategies, a consulting firm for beach
nourishment and dredging projects, aquatic ecosystem restoration,
the Corps of Engineers, the Federal Emergency Management
Agency, and many others.
“The reason these islands are still here today is they all have one
thing in common — offshore reefs to dissipate wave energy.”
This is a strong contrast to a major swell event on the East Coast,
where large waves resulting from long-period swells usually break all
at once near the coastline. Surfers call this phenomenon a “close-out.”
Since it is practically impossible to ride in any direction other than
straight, the surfer is effectively closed-out from making the wave.
Large waves marching forward unimpeded and breaking near the
beach pose a danger for swimmers and boaters. Smaller is preferable
from a safety standpoint.
“There are reef breaks worldwide where 20-plus-foot surf is
occurring a quarter-mile offshore, but the waves reaching the
beach are small and playful,” Ginolfi says.
A network of outer reefs can protect the inner reefs as well as
the waters inside lagoons. There are those within the coastal
community advocating artificial reefs as a key component of a
coastal protection strategy.
Above: In Palm Beach, Australia, a completely submerged artificial reef protects the coastline and produces a wave that runs for around 65 yards,
attracting local surfers and visitors who want to avoid the frustration of dealing with “close-outs.” Opposite, top and middle rows: A network
of artificial reef ball units was used in hopes of replenishing sand lost from coastal storm surges at the Marriott Beach Resort in the Cayman
Islands. After three months, the artificial reef produced a shoreline accretion of nearly 60 feet. Opposite, bottom row: A barge lowers artificial
reef structures in place for the South Walton County, Florida, Artificial Reef Association (SWARA). Since 2015, SWARA has deployed around
700 artificial reefs at 16 different sites, using a combination of steel, concrete and Florida limestone.
CITY OF GOLD COAST
Artificial reefs can be a key part of a system of innovative solutions
BY FRITTS CAUSBY
22 november 2021
WBM