City installs ‘sand mattress’ to combat erosion at Kuhio Beach

The city unveiled an emergency erosion control measure Sunday at Kuhio Beach Park which officials hope will thwart erosion in the middle of the state’s tourism epicenter.

The project, called a “sand mattress,” was laid down last week using hand tools. It is the first of its kind to be installed in the state and is considered a lightweight erosion control measure.

Joshua Stanbro, executive director of the city’s Office of Climate Change, Sustainability and Resiliency, said erosion had exposed the concrete foundation of a demolished structure known as the Waikiki Tavern in the 1940s and was tearing away at the clay embankment beneath the sand. He pointed to climate change as one of the causes.

“This is the new normal,” he said. “We’re going to be facing these kinds of issues over and over again.”

Mayor Kirk Caldwell said the roughly 85-foot-long mattress covers dangerous objects exposed in the sand and keeps the clay from washing into and polluting the water.

Also Sunday, in another case of erosion on Oahu, the city’s Ocean Safety and Lifeguard Services Division warned the public to stay away from Sunset Beach on the North Shore because a storage building was teetering on the edge of a 20-foot drop.

Shayne Enright, Ocean Safety spokeswoman, said erosion had cut away the ground near the structure, and the city will decide today what to do next.

Back in Waikiki, Dolan Eversole, a coastal geologist with the University of Hawaii, said the Waikiki Tavern, once separated from the ocean by about 20 feet of sand, was largely forgotten until erosion exposed its concrete foundation about four years ago.

The exposed area, near the Kuhio Beach hula mound, is subject to seasonal erosion with water levels 6 to 10 inches higher than normal in the summer due to the stacking effect from high surf, tides and other ocean phenomena.

Eversole said the sand mattress was installed with a $3,000 donation from the Waikiki Beach Special Improvement District Association, a group working for the health of Waikiki Beach.

The mattress resembles a pool float with tubes about a foot wide and a half-foot deep, filled with sand. The tubes are about 12 feet long, running from shore to land. The mattress, covered by a layer of sand, is about 85 feet wide and holds down the clay beneath it when waves wash over.

Eversole said the mattress is a temporary measure, but it could last for 10 to 20 years. A long-term solution for erosion control in the area would probably be a sandbag groin starting on the beach and extending about 40 feet into the ocean. The groin would sit in the footprint of a previously removed groin and create a “sandbox” to keep sand on the beach.

He said the improvement association formed a community advisory committee to help select the final design, which must be approved by federal, state and county agencies.

Rick Egged, president of the special improvement association, said the group hopes the sandbag groin is finished by 2018. He said another groin in Waikiki near the Royal Hawaiian hotel could fail at any time and that the association is working with the state to replace it at a cost of about $1.5 million.