Thanks to the Hawaii Legislature and Gov. David Ige for the passage of Act 16 this summer, amending the State Coastal Zone Management Act, which improved Hawaii’s readiness for climate change, particularly with respect to the protection of our world-famous beaches.
Act 16 is an important step forward because we’ve reached a tipping point in Hawaii in which the loss of our beaches is a realistic future. The root of the issue stems from the fact that many beachfront residences and public infrastructure were built over coastal sand deposits (sand dunes). These dunes were formed in centuries or millennia past when waves from storms stockpiled sand just inland of the shoreline where ordinary waves could not reach.
Now that sea level has risen to the point that waves can seasonally reach these stockpiles, the sand dunes are becoming increasingly transient, exposing the structures on top of them to extreme coastal hazards like erosion. The typical reaction to combat shoreline erosion is to armor the shoreline with seawalls, rubble mound revetments, sandbags and so on.
While shoreline armoring can, albeit temporarily, stop erosion and protect whatever lies behind it, the act is profoundly destructive to the beach because it cuts off the beach’s supply of inland sand, which the beach needs to remain healthy during periods of higher sea level. Seawalls essentially starve beaches of sand.
The other major impact armored structures have on beaches is that they do not allow wave energy to naturally dissipate. When a wave crashes against a hardened feature, whether it’s a seawall or natural geologic feature, the force of that impact causes water to speed up such that sand is picked up and carried away. But when a wave washes up and slowly back down a sloping sand beach, water moves slowly enough that sand can fall out of suspension and be deposited which assists with beach formation.
I do not wish to vilify shoreline armoring or argue against its use under the right circumstances. Exactly where shoreline armoring is appropriate depends on the nature of the thing being protected and the underlying geology of the site — e.g., clay bank vs. sandy substate (beach sand).
But if we want to have beaches where the underlying geology is sand, we need to step aside and allow erosion to happen so our precious beaches can remain wide and healthy for all to enjoy.
Sam Lemmo is administrator of the Office of Conservation and Coastal Lands, state Department of Land and Natural Resources.
