Sea Level Rise Driving Shoreline Changes in Hawaii

Sea level rise (SLR) is a primary factor driving historical shoreline changes in Hawaii, according to a new study.

The global annual SLR average over the last century was roughly 2 millimeters, with previous studies indicating that this rate is now approaching 3 millimeters and may accelerate in coming decades, according to the researchers.

These changes, according to the new report, are playing a significant factor in historical shoreline change in Hawaii and will likely only become increasingly more influential with time, confirming that future SLR ought to be a major concern for decision-makers overseeing beach management.

On Maui, for example, 78 percent of beaches eroded over the past century with an island-wide average shoreline change rate of 13 centimeters per year. On Oahu, meanwhile, 52 percent of beaches eroded with an overall average shoreline change rate of 3 centimeters of erosion per year.

"The research being conducted by SOEST provides us with an opportunity to anticipate SLR effects on coastal areas, including Hawaii's world famous beaches, coastal communities, and infrastructure. We hope this information will inform long range planning decisions and allow for the development of SLR adaptation plans," said Sam Lemmo, an administrator at Department of Land and Natural Resources in the Office of Conservation and Coastal Lands, in a press release.

In coming to these figures, the researchers used shoreline positions taken from aerial photographs and survey charts. Shoreline positions, meanwhile, were manually digitized using photogrammetric and geographic system software (GIS) from aerial photo mosaics and topographic and hydrographic survey charts provided by the National Ocean Service (NOS). Finally, shoreline movement over time was determined using GIS software.

All along, the researchers controlled for non-SLR influences, including sand mining and the construction of seawalls.

"It is common knowledge among coastal scientists that sea level rise leads to shoreline recession," Dr. Brad Romine, coastal geologist with the University of Hawaii Sea Grant College Program, said. "Shorelines find an equilibrium position that is a balance between sediment availability and rising ocean levels. On an individual beach with adequate sediment availability, beach processes may not reflect the impact of SLR. With this research we confirm the importance of SLR as a primary driver of shoreline change on a regional to island-wide basis."