PHOTO COURTESY OF COASTAL GEOLOGY GROUP UH research found that the average beach width in the Halama Street-Kalama Park area in South Maui has decreased 57 percent, to 28 feet in 1997 from 65 feet in 1949.

Weather, seawalls
cited in Maui
beach erosion

A UH study finds a 29 percent
loss over 50 years in South
and West Maui shorelines

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By Gary T. Kubota
gkubota@starbulletin.com

LAHAINA >> Beaches in South and West Maui have decreased in size by an average of 29 percent in the last 50 years, according to a University of Hawaii researcher.

John Rooney, a researcher with the university's Coastal Geology Group, said the study was done through an examination of aerial photographs of the shoreline.

"My guess is it will continue, but that's it -- it is an educated guess," Rooney said.

"We can't predict the weather more than five days, and ... it is dependent on the weather."

Rooney cited weather patterns, storms and the construction of seawalls as contributing factors to beach erosion.

Rooney, who recently completed his doctoral studies about Maui beaches, will present his findings and possible solutions as the guest speaker at the Kihei office of the Hawaiian Islands Humpback Whale National Marine Sanctuary at 7 p.m. tomorrow.

There are significant variations in the rates of erosion at West and South Maui beaches, according to Rooney and other researchers in the group.

One of the fastest rates of erosion is in West Maui near the mouth of Mahinahina Stream, about 3 feet a year, while nearby Honokowai has an erosion rate of .07 feet a year, according to the group.

At the 1.5-mile Kaanapali beach where there are multimillion-dollar hotels, the most recent trend indicates erosion is occurring at an average rate of nearly 1 foot a year, according to the group.

At Hanakao'o Beach Park to the south of Kaanapali, the erosion rate is 2.61 feet a year, while there has been a 6 percent increase in sand at the Westin Maui Resort farther north.

In the Halama Street-Kalama Park area in South Maui, the average beach width has decreased 57 percent to 28 feet from 65 feet between 1949 and 1997, according to the group.

The beach width in that area decreased by 24 feet between 1975 and 1987, following the construction of seawalls.

Rooney said in South Maui the sand sometimes has drifted away from some properties and accumulated in specific locations elsewhere, such as the Veterans of Foreign Wars beachfront in Kihei.

He said in other instances, seawalls have been built to protect the loss of beachfront property, as in Kalama Park in Kihei, preventing the normal migration of sand in seasonal currents.

"You'll protect the coastal land, but you'll lose the beach in front of it," he said.

Rooney said the beach movement has been caused by an interaction of waves and currents. He said an additional factor influencing the erosion has been a rise in the sea level around Maui, about an inch a decade.

Rooney cited a phenomenon known as the Pacific Decadal Oscillation that has affected weather patterns in Hawaii.

He said sand has been moving southward because of a positive phase of the Pacific Decadal Oscillation that has persisted for 20 to 30 years. That positive phase has meant fewer Kona storms, less rain on the leeward side of the island and less wave energy from the southwest, he said.

Rooney said some researchers speculate that the weather patterns have shifted to a negative phase in the Pacific Decadal Oscillation, where there will be a greater likelihood of Kona storms with accompanying wave energy. That, he said, could shift the sand northward, but researchers are still debating whether there has been a shift in phases.

"It's too early to tell," he said.

Rooney said three methods of protecting the coastline include the development of seawalls, the installation of concrete groins as was done at Kuhio Beach in Waikiki, and replenishing the beaches with sand.

He said one of the favorite methods used to maintain a beach is to install a structure in the water and backfill it with sand. He said the U.S. Army Corps of Engineers has been looking at the feasibility of helping Hawaii in recreational beach restoration projects.

A change in the corps' definition of recreational resources in its cost benefit analysis could allow it to help battle beach erosion in places like Waikiki and South Maui, Rooney said.

For more information, log on to www.soest.hawaii.edu/coasts/presentations/kiheishorech.html