Sea level rise driving Hawaii coastal erosion

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The Hawaiian Islands, courtesy NASA Earth Observatory.

New data to help long-term coastal planning

By Summit Voice

FRISCO — A team of scientists have taken a close look at coastal erosion trends in Hawaii and determined that sea-level rise is the main driver, outweighing other factors like waves, sediment supply and coastal development.

The researchers from the University of Hawaii – Manoa, School of Ocean and Earth Science and Technology and the State of Hawaii, Department of Land and Natural Resources said that knowing that sea-level rise is a primary cause of shoreline will help resource managers and planners going forward.

“It is common knowledge among coastal scientists that sea level rise leads to shoreline recession,” said Dr. Brad Romine, coastal geologist with the University of Hawaii Sea Grant College Program. “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.”

Globally-averaged sea-level rose at about 2 mm per year over the past century. Previous studies indicate that the rate of rise is now approximately 3 mm per year and may accelerate over coming decades.

“Improved understanding of the influence of SLR on historical shoreline trends will aid in forecasting beach changes with increasing SLR,” said Dr. Charles Fletcher, Associate Dean and Professor of Geology and Geophysics at the UHM SOEST.

“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, Administrator, Department of Land and natural Resources, Office of Conservation and Coastal Lands.

Results of island-wide historical trends indicate that Maui beaches are significantly more erosional than beaches on Oahu. On Maui, 78 percent of beaches eroded over the past century with an overall (island-wide) average shoreline change rate of 13 cm of erosion per year, while 52 percent of Oahu beaches eroded with an overall average shoreline change rate of 3 cm of erosion per year.

The variation in long-term relative SLR rates along the Hawaii archipelago is due, in large part, to variations in island subsidence with distance from actively growing Hawaii Island and/or variations in upper ocean water masses.

 

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