A new study that quantifies how quickly Hawaii’s beaches are being lost to erosion is arming researchers with information they hope will be used to protect the state’s shorelines.
Some 70 percent of the beaches on Oahu, Kauai and Maui are experiencing long-term erosion, according to a federal study.
Kualoa Point beach on Oahu’s Windward shore is disappearing most rapidly in a comparison of long- and short-term erosion rates among coastal areas on the three islands, the study said.
Kualoa shrank by nearly 6 feet annually.
The U.S. Geological Survey study found 85 percent of beaches are eroding on Maui, 71 percent are eroding on Kauai and 60 percent of Oahu’s beaches are eroding.
Hawaii’s beaches draw millions of visitors annually, driving the state’s No. 1 economic engine.
The study, "National Assessment of Shoreline Change: Historical Shoreline Change in the Hawaiian Islands," used mainly aerial photographs to measure the ebb and flow of shoreline from early 1910 to 2007.
Lead researcher Chip Fletcher said the study, funded by a number of government agencies and foundations, took about 10 years and was designed to help manage the development of coastal areas.
State Land Board Chairman William Aila Jr. said he sees the new information as helpful for establishing policies to protect beaches.
"This will vastly improve upon public safety and will ensure that Hawaii’s beautiful beaches will be protected from inappropriate shoreline development," Aila said.
Fletcher, a University of Hawaii professor, said cities have been built too close to coastlines, damaging the environment and leaving areas vulnerable to hurricanes, storms and rising sea levels.
The study brings home a sobering reality that islanders will have to face, along with choosing whether to save the buildings by constructing sea walls.
Fletcher said people have preferred to build the sea walls, often resulting in the loss of beaches.
Of the 9 percent of beaches lost on Oahu, Maui and Kauai totaling 13.3 miles in the past century, nearly all of them have been lost due to the building of sea walls, he said.
"We need to be careful where we put sea walls because they can kill beaches," he said.
Based on global projections, the sea is expected to rise on average by 1 foot by about 2050 and 3 feet by the end of 2100. The study shows in the past century sea level rise was 6 inches on Oahu and Kauai and 10 inches on Maui.
Fletcher said the sea level rise is expected to accelerate on the islands, and he expects it will be close to 3 feet by the end of 2100.
"The truth is our future is going to be dominated by sea level rise," he said.
"How are we going to implement that future for ourselves? Our grandkids deserve beaches, too. How are we going to make sure we’re going to have them?"
Fletcher said in some instances, such as in resort areas like Waikiki and Kaanapali, spending millions of dollars to replenish a beach may be economically feasible, but the options aren’t the same for many residential areas along the coastline.
He said with the new information about coastal erosion, government agencies have the ability to develop new policies to establish building "setbacks" based on erosion rates of a specific property.
For instance, on Maui the county requires a new building to be set back 50 times the annual rate of coastal erosion for the property, plus 20 feet, he said.
The setback is greater on Kauai, where it’s 75 times the annual rate of erosion, plus 40 feet.
On Oahu it’s now 60 feet for new lots and 40 feet for existing lots, he said.
The study showed Waikiki Beach near a long line of hotels has remained relatively stable over the past century, especially with sand replenishment programs, but in recent decades erosion has dominated along much of the Waikiki shoreline.
For instance, there has been beach loss west of the Waikiki Natatorium.
"That’s just a place where they built too close to the ocean," Fletcher said.
On Maui about 87 percent of the north shore beaches have been eroding, with the most at Baldwin Park where there was sand mining in the past for a now-defunct lime kiln.
Fletcher said the sea level rise is expected to be higher on Maui, partially because it’s a relatively new island and the ground is subsiding.
