If you see a foot-high cliff in the sand, that’s a sign of heavy erosion.
Geospatial analyst Anna Mikkelsen has beenstudying Waikīkī’s shoreline since 2018 to see if there are any patterns to the erosion.
She says that large south swells push sand onto the beach in Waikīkī, but high trade winds from the east and higher sea levels result in a faster loss of sand.
Waikīkī's longshore transport — sand moving from one end to the other — stands out from standard beach models where sand is moved from nearshore to offshore.
Mikkelsen says building too close to the shoreline makes erosion move faster. The buildings block access to backshore dunes where beaches can collect more sediment when sea level rises or as large waves come in.
"By building roads and houses on those, the beaches no longer have access to essentially their own resources and we therefore see erosion taking place much faster. Same goes with building sea walls," Mikkelsen explained.
When Mikkelsen surveyed Waikīkī from 2018 to 2020, she could not find any seasonal differences in erosion pace.
“Instead of seeing high volumes of sand in summer, and low volumes in winter, we saw consistently increasing beach volume the first 12 months of the study and then erosion of the beach the following 10 months,” said Mikkelsen.
Mikkelsen predicts Waikīkī will have to add sand more frequently as the sea level rises.
