WAILUA — Shoreline erosion is slowly claiming the parking area located at the foot of the Bryan J. Baptiste Bridge along Kuhio Highway at the mouth of the Wailua River.
Higher-than-normal tides caused by the new moon Monday tumbled more rocks from the parking area into Wailua Bay, eating away at the parking area to the extent of exposing more of the erosion-prevention screening material. This was further added to by the tsunami advisory issued by the Pacific Tsunami Center following a magnitude 7.5 earthquake off Alaska.
No tsunami was generated.
Earlier in the month, Tropical Storm Marie, formerly a Category 4 hurricane, generated an east swell that started the erosive action, exposing some of the installed erosion-control hardware and adding to the erosive action that include the felling of mature ironwood trees and the undermining of portions of Ke Ala Hele Makala‘e along Kuhio Highway fronting the former Coco Palms Resort.
Ruby Pap, a coastal land-use extension agent with the University of Hawai‘i Sea Grant College Program and the county’s Planning Department, responded to some of the concerns.
“According to my records, this erosion event started around November 2019 on the north end of the beach,” Pap said in an email last week. “I have photographic records of the worsening erosion since then, (erosion that) claimed the beach, dune, vegetation, trees, boulders and the shower (tree located at the Horner’s end of the beach).”
Pap said higher-than-normal tides combined with persistent trade wind swells and storms to cause major erosion issues all along the Wailua-Kapa‘a corridor during the 2019 winter.
“It appeared the south end of Wailua Beach near the bridge and parking lot would be spared, but that started eroding significantly this past summer,” Pap said.
“There is often a large sandbar at the river mouth. We had large rainstorms around Christmas and March where the sandbar was breached. There was also bridge damage from the flooding and debris that came down the river.”
The state Department of Transportation moved sand around during the initial repairs to the bridge that took place in April and May. They also received permission to push sand on the north end of the beach to mitigate the parts of the multi-use path that were undermined by erosion. The DOT is installing, or has recently installed, a revetment or apron around one of the undermined bridge abutments to protect against scour.
“Then, we had our summer King Tides,” Pap said. “The south end of the beach eroded. This was the most erosion I had ever seen on that end after moving here in 2012, and there was practically no swell, just higher-than-normal tides.
“This really demonstrates to me the power just six inches to a foot of sea-level-rise can do. I do note the last time I was out there a few weeks ago, the sandbar was recovering, but there is a significant amount of sand mauka of the bridge.”
She said sea-level-rise resulting from climate change is and will continue to exacerbate erosion trends across the Hawaiian Islands. There are studies indicating that erosion rates could double by the year 2050.
“For Wailua Beach, according to the Hawai‘i Sea Level Rise Viewer (hawaiisealevelriseviewer.org), just one foot of sea-level rise will undermine the highway with erosion,” Pap said. “Future predictions for sea-level rise are at least 3.2 feet by mid- to late-century, and six to eight feet is physically plausible.”
Sea levels are rising at increasing rates due to global warming of the atmosphere and oceans and melting of the glaciers and ice sheets, states the Hawai‘i Sea Level Rise Vulnerability and Adaptation Report produced by the state Department of Land and Natural Resources in 2017.
Rising sea levels and projections of stronger and more-frequent El Nino events and tropical cyclones in waters surrounding Hawai‘i all indicate a growing vulnerability to coastal flooding and erosion.
Chronic flooding with 3.2 feet of sea-level rise would render more than 25,800 acres of land in the state unusable, the report states. Statewide, about 34% of that potentially lost land is designated for urban use, 25% is designated for agricultural use, and 40% designated for conservation.
Across the state, more than 6,500 structures located near the shoreline would be compromised or lost with just 3.2 feet of sea-level rise. Some of these vulnerable structures include hotels, shopping malls and small businesses, resulting in the interruption, relocation or even closures of the impacted businesses.
Other types of structures that may be impacted include churches, schools and community centers. Houses and apartment buildings are vulnerable, with the loss of these structures resulting in more than 20,000 displaced residents in need of new homes.
The value of the land projected to be flooded is more than $19 billion across the state.
Pap said the University of Hawai‘i Sea Level Center monitors and predicts water levels across the Pacific using satellite altimetry and modeling technology (uhslc.soest.hawaii.edu/sea-level-forecasts/).
“I believe we’re starting to see the effects of sea-level rise,” Pap said.
“To be specific with this recent erosion event in Wailua, starting in November, we had higher-than-normal water levels, high winds and persistent trade-wind swell. We had some big rain storms around the holidays and March, which blew out the sandbar and the sand went offshore on the south end of Wailua Beach. Then, this summer, we had our King Tides in July and August that eroded the south end.”