Sea Level Rise Impacts Hawaii: Historical Shoreline Retreat

First Posted: Sep 02, 2013 08:08 AM EDT
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Sea level rise is becoming a huge issue for island nations as water levels continue to encroach on beaches. Now, Hawaii is feeling its effects. It turns out that sea level rise is a major cause for coastal erosion, yet there are differing rates of relative sea level rise on the islands of Oahu and Maui. Now, researchers have revealed that these rising waters are the primary factor driving historical shoreline changes in Hawaii and that historical rates of shoreline change are actually two orders of magnitude greater than sea level rise.

"It is common knowledge among coastal scientists that sea level rise leads to shoreline recession," said Brad Romine, one of the researchers, in a news release. "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."

In order to find out how sea level rise has impacted Hawaii, the researchers examined island-wide historical trends. It turned out that Maui beaches are significantly more erosional than beaches on Oahi. In fact, 78 percent of beaches over the past century in Maui with an overall average shoreline change rate of 13 cm of erosion per year. That's a stark contrast to Oahu, which had beaches that had an overall average shoreline change rate of a mere 3 cm per year.

What does this mean? The variation in long-term relative sea level rise rates along Hawaii is due partly to variations in island subsidence. The distance for this is due to the fact that Hawaii is actively growing. In addition, there may be variations in upper ocean water masses.

 "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," said Sam Lemo, Administer of the Department of Land and Natural Resources, in a news release. "We hope this information will inform long range planning decisions and allow for the development of SLR adaptation plans."

The findings are important for better understanding the impact of sea level rise. In addition, they show that not all areas are affected equally by these rising waters. This could have major impacts on how exactly researchers defend the coast against the encroaching ocean.

The findings are published in the journal Global and Planetary Change.

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