Sea-level rise is a significant factor in the major shoreline change underway in Hawaii, where 52 to 72 percent of beaches on the chain of islands have eroded over the past century, a recent study has found.
The more than 7 million tourists who flock to Hawaii's beaches each year are part of an array of contributors to erosion. In addition to the influx of visitors, developments along the coasts continue to provoke shoreline changes.
To capture the breadth of erosion's causes and to propose solutions, scientists have isolated differing rates of sea-level rise as the prime contributor to coastal erosion in the islands of Maui and Oahu.
In partnership with the state's Department of Land and Natural Resources, researchers at the School of Ocean and Earth Science and Technology (SOEST) at the University of Hawaii published a report in the journal Global and Planetary Change urging residents and officials in coastal zones to target sea-level rise impacts in their programs and long-term planning.
The rate of coastal erosion was 78 percent in Maui, while some sections were closer to 90 percent.
"We looked at every beach on both islands and eliminated factors, such as waves, storms, past practices and sand mining, to measure how much sea-level rise was a key contributor to erosion," said Chip Fletcher, a lead author of the study and a professor at the University of Hawaii SOEST.
Photo by: Flickr user benswing
Reluctance to move away
Globally, sea levels rose by an average of about 2 millimeters per year over the past century. The rate of rise may accelerate in the coming decades, with studies estimating a rate of rise at 3 millimeters every year.
The study calculated islandwide and regional historical shoreline trends for the islands using aerial photographs, survey charts and shoreline positions.
Over the past century, Maui experienced the most significant loss of beach during the time span, with 78 percent of beaches eroding, compared with 52 percent on Oahu.
Increasing development along the coast is exacerbating the issue, said Bradley Romine, a lead author of the study and a coastal geologist at the University of Hawaii.
Although new construction projects follow a mandate that requires building away from erosion-prone zones, the rule is not enforceable for existing structures. "Coastal erosion management plans prescribe methods for beach nourishment as an alternative," Romine said.
The state has proposed buyouts for homeowners facing the risks of sea-level rise inundating their property. Yet, like residents offered property buyouts along the East Coast, only a few residents have opted for the incentive.
The cost of short-term fixes
Although legal challenges will persist, "the best solution is to move back away from the shoreline," Romine said.
In some cases, solutions come down to an economic question, Fletcher said. Tourists spent $12.6 billion in the state last year.
In Waikiki Beach, on the south shore of Oahu, 24,000 cubic yards of sand was pumped from an offshore site to replenish and widen the beach by 37 feet. The project two years ago cost $2.5 million, which is far below revenue from tourism and local businesses.
Inexpensive solutions fall in the category of maintenance. "When you put a coat of paint in your house and you need to do it again and again, that is the same as sand nourishment," Fletcher said. "It doesn't last forever, and it's extremely expensive."
Waikiki Beach is a rare example where tourism revenue exceeds the costs of maintenance.
"Purchasing private property and removing all development in that land is the only way that we'll have beaches in Hawaii towards the second half of the century," Fletcher said.
Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500.
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