NORTH SHORE (KHNL) - About a quarter of Oahu's beaches have been lost over the last century.
Healthy beaches have lots of sand.
But when landowners permanently armor the shoreline with seawalls, the supply of sand is restricted and beaches erode.
"On one side coastal erosion can be bad because it threatens property and structures that may be in the are but it's also good in that it feeds the beach a new supply of sand when it's most needed," said coastal geologist Dolan Eversole.
Eversole says the solutions to coastal erosion are temporary at best.
This wall failed at Haleiwa beach park on Oahu's North Shore, and the ocean is taking back it's beach.
"Most of the environment in Hawaii has a big coastal dune and the erosion of that dune is what feeds the beach it's source of sand," said Eversole.
At popular surf spot Pipeline, foot traffic is taking it's toll exposing vegetation.
Homeowners build walls to protect the land, resulting in beach loss.
Eversole says this hardening of the shoreline is a short term solution to a long term problem.
"What we need to be looking at is more long term solutions and that usually involves not locating developments so close to the shoreline allowing the shoreline to migrate naturally."
He says you can save the land or the beach, but not both.