A $3,000 ‘sand mattress’ is actually helping save a portion of Waikiki Beach

Sand mattress experiment successfully combats beach erosion in Waikiki, experts say

WAIKIKI (HawaiiNewsNow) - With beach erosion a growing problem, experts have been closely watching a Waikiki Beach mediation project — and so far the results are positive.

A year ago, crews installed a 100-by-12 foot sand-filled mattress as an emergency measure to stabilize the shoreline.

It’s no silver bullet. But ...

“It has been a big success. This erosion mattress has done exactly what was intended," said Dolan Eversole, the Waikiki Beach management coordinator for the University of Hawaii’s Sea Grant College Program.

“It doesn’t magically solve the erosion, but it simply keeps the dirt fill in place.”

City officials said there was a minor problem in August caused by a south swell that coincided with the king tides.

“Waves overtopped the entirety of that area of Waikiki Beach by the hula mound, and there was some slumping as water went behind the mattress and sucked out some of the sand,” said Matthew Gonser, the coastal and water program manager for the city’s Office of Climate Change, Sustainability and Resiliency.

As a temporary fix, crews added sandbags, which are now almost completely buried with the shift in seasons.

“There’s a lot of seasonal variability. That’s why it’s important to do the monitoring and maintenance now, in the quieter, calmer period so that we can get prepared for another investigation, as the south shore swells come back into the summer,” Gonser said.

Experts said without the mattress, the area would look a lot different.

“Almost certainly, the shoreline would have moved landward. How far landward, it’s hard to say, but I would estimate between 10 and 20 feet more landward,” said Eversole.

The Waikiki Beach Special Improvement District Association donated $3,000 to the city for the cost of the mattress.

According to the city, the product vendors worked on the job pro bono for two to three days, while the rest of the labor was done by city staff.

Longer-term plans include a new sandbag groin at Kuhio Beach to replace the deteriorated groins that the state removed in 2012. Officials hope construction for a separate groin replacement project near the Royal Hawaiian will also start next winter.

“We know how much that area means to folks locally and the recreational resource for visitors,” Gonser said.

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