HONOLULU - Eighty-five percent of sandy beachfront has eroded and 4.2 miles has been lost on Maui in the past century, according to a U.S. Geological Survey and University of Hawaii report released this week.
Those percentages were the highest in the report covering 150 miles of sandy shoreline or "essentially every beach" on Maui, Oahu and Kauai.
"The entire Kihei coast is eroding, except for a handful of places where sand is being trapped by walls," said Charles Fletcher, associate dean of the University of Hawaii School of Ocean and Earth Science and Technology and lead author of the report "National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands."
Kaanapali Beach has shown an annual erosion rate of 3.2 inches over the last century, according to a U.S. Geological Survey and University of Hawaii report. Maui has lost 4.2 miles of sandy beach in the last century, according to the report, which is titled “National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands.”
University of Sydney / ANDREW D. SHORT photo
The "spires of the French Frigate Shoals" will be the inevitable fate of the Hawaiian Islands in millions of years and sea level rise is a natural factor in erosion, the report said. But the erosion is not all natural, and seawalls are among the leading man-made culprits.
In Kihei, which the report said lost 1.2 miles of beaches from 1900 to 2007, Fletcher noted how seawalls sprung up one after another along the Halama Street area near Kalama Park as residents attempted to protect their shorefronts. Erosion rolled north and beaches were lost.
"If you have a beefy seawall, it will protect the land for a few decades," said Fletcher in a phone interview Monday. "It will destroy the beach and the beaches adjacent to it."
The information presented in the report can help communities make decisions, he said.
"Where do you want beaches in the future and where do you want to protect the land?" asked Fletcher. "There is no magic wand."
In a news release about the report, Fletcher noted that a century of building has gone on along the shorelines of Hawaii without "this sort of detailed knowledge about shoreline change."
"This has led to development that is located too close to the ocean," he said. "A better understanding of historical shoreline change and human responses to erosion may improve our ability to avoid hazards in the future."
For the report, researchers used historical data sources, such as maps and aerial photographs, and Geographic Information System software to measure shoreline changes at more than 12,000 locations.
On Maui, using data from 1899 to 2007, the average rate of beach loss during that period was put at 6.7 inches annually, the highest rate of the three islands. The average beach loss for Maui, Oahu and Kauai was 4.3 inches annually.
The nearly 56 miles of sandy beaches on Maui were broken up into three parts in the report: North Maui from Waihee to Paia; Kihei from Maalaea to Makena; and West Maui from Lahaina to Kapalua.
North Maui beaches, with an annual erosion rate of 10.2 inches, had the highest regional rate among the three islands and showed an "overall trend of chronic erosion," the report said.
Leading the way was Baldwin Beach Park with an erosion rate of nearly 5 feet annually. The report blamed the erosion in part on a sand-mining operation for a defunct lime kiln that wiped out a tombolo linking the beach to a bench of beach rock.
Other beaches noted with severe erosion in North Maui were Kanaha Beach Park with beach loss as much as 5 feet annually and Waiehu Beach Park with as much as 1.6 feet lost annually.
During the study period of 1912 to 1997, West Maui lost about 2.5 miles of beaches or 14 percent. That was the highest percentage among the regions in the state in the report. During the reporting period, West Maui beaches lost 5.9 inches annually.
"The results of this research provide critical coastal change information that can be used to inform a wide variety of coastal management decisions," said Rob Thieler, sponsor of the study with USGS.
* Lee Imada can be reached at firstname.lastname@example.org.