Recent coastal erosion near Rocky Point on Oahu's North Shore is the worst in decades, University of Hawaii coastal geologist Charles "Chip" Fletcher said Monday.
Affected homeowners don't have many options to save their houses, he said.
"The only thing that can be done at this point for those homes are to take emergency measures to attempt to minimize further erosion," said Fletcher.
Another option would be to build a seawall. But often times, it causes the beach in front of it to disappear and Fletcher said surrounding properties experience accelerated erosion.
"As they would then build a seawall, you get this sort of unzippering effect down the length of a beach, where one seawall after another means that eventually the entire beach, or a majority of the beach gets seawalled off and a majority of that beach disappears," he said.
This is the reason why there are government regulations against seawalls.
Fletcher said the best thing homeowners can do is hope the sand comes back on its own.
"It's very rare that you would get the same amount of sand returning to the shoreline once it's been eroded away," he said. "At the end of this winter season, we may see a fair amount of sand come back. Whether it's going to completely replenish the land that's been lost, it's impossible to know at this point."
Fletcher said the city should reexamine how close Oahu homeowners can build to the shoreline.
The city's building setback law is 40 feet for existing structures and 60 for new ones. He said the law should be more like Kauai's, which is the strictest in the state.
It takes the rate of annual erosion, multiplied by 70 years, which is the expected life of a wood-frame home.
"Plus they added a buffer of 40 feet to that to account for storm damage and an estimate of sea-level rise," Fletcher said.
He said another long-term solution is to pay property owners to not develop the land.
"And then erosion would simply release the sand that is under that land," said Fletcher. "That sand would then fuel the beach and you would not experience beach loss."
Buying coastal land comes at a hefty price though.
But Fletcher said, "We have the legacy lands commission at the state and we have similar commissions within each county that acquire millions of dollars each year in order to buy land to prevent it from being developed."
Something Fletcher said is the only thing we can do to prevent more destructive coastal erosion.
"We've over a century of long-term sea-level rise in Hawaii. Because of climate change, we know that sea-level rise is going to continue and it's going to accelerate," he said.
"We need to put ourselves on a more proactive footing, rather than a reactive basis such as we are right now."
Maui County has a setback law like Kauai, but not quite as strict. Still, Fletcher said it protects homes much better than Oahu's law.