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Online tool predicts rising sea levels

Forecast makes predictions for 12 West Maui shoreline regions

Waves splash onto an Olowalu stretch of Honoapiilani Highway in October. An online forecasting tool can now predict rising sea levels in different areas of West Maui. The Maui News / MATTHEW THAYER photo

A new online tool is being used to help predict rising sea levels in West Maui, which in recent years is “one of the hardest hit areas on Maui” in terms of coastal erosion, property damage and sediment pollution.

Called the PacIOOS Wave Run-Up Forecast, for the Pacific Islands Ocean Observing System, the tool can anticipate potential high sea levels and site-specific wave impacts on 12 shoreline regions in West Maui up to six days in advance.

The model that generates the forecast takes in multiple factors into account and uses data submitted by the community. The forecast is on the PacIOOS website.

“West Maui is one of the hardest hit areas on Maui with respect to waves and erosion impacts that are expanding and worsening in the face of sea level rise,” said co-investigator Tara Owens of the University of Hawaii Sea Grant College Program. “We do have a lot of good information about past trends and now future projections of these types of impacts, but West Maui is where we knew we needed more tailored information, site-specific information, to help with preparedness and planning.”

Owens, who is serving as the point of contact between the Pacific Islands Ocean Observing System team and local partners, stakeholders, and community members, said this tool was created as a source of information for the public to take appropriate actions and implement safety measures when either traveling, planning or building near the coastline. Owens and other researchers introduced the tool in an online presentation Tuesday night.

“Maybe you would avoid traveling on Honoapiilani Highway during a high wave event or maybe you would avoid going to certain beaches with your family,” she said. “Or if you manage a resort property, you can post warning signs for your guests who would not have otherwise known what the conditions might be, or a land owner might want to relocate chairs or umbrellas away from shorelines or move boats or kayaks.”

The PacIOOS Wave Run-Up Forecast was developed by a team of researchers and led by co-investigator Douglas Luther, a professor in the Department of Oceanography at UH’s School of Ocean and Earth Science and Technology (SOEST).

Wave run-up is defined as the vertical reach (how high or low) of seawater onto the land at any given time. When run-up levels are high, the risk for flooding and inundation increases.

Luther said that there are 12 West Maui regions, from Papalaua Wayside Park in the south to Lipoa Point in the north, that reflect very complex shorelines with different wave impacts based on multiple factors including wave dynamics, offshore reef systems, beach features and infrastructure.

In addition to the forecasted sea level and wave run-up heights, which is updated hourly, the online tool includes the current sea level, tide cycle, large wind systems and other features.

The public can also view thresholds of the 12 regions in West Maui up to six days in advance to see whether the forecasted conditions are going to cause light impacts, hazardous impacts or critical impacts.

Fiona Langenberger, communications and program coordinator for PacIOOS, said the tool is more accurate when viewing the model closer to the day of interest.

The forecast is not accurate when a tsunami, tropical storm or cyclone warnings are in effect, she added.

Owens said that the seasonal waves and king tide events, like the ones that are known to flood Honoapiilani Highway in Olowalu or that wash over the Kaanapali Beach public walkway or erode Napili Bay, are what the team tries to model and predict.

Those waves have been chipping away at land-based sediments, which can affect water quality, she said.

“The water level of the ocean is changing constantly, you all know that. Sea level rise itself occurs over a period of years and leads to germanely elevated water levels,” she said.

“On top of that, there are water level anomalies that can lead to higher than normal water levels, sometimes temporarily. These anomalies can sometimes be caused by ocean-wide conditions related to El Nino periods or these rotating bodies of water that are warm and they cause sea level to rise temporarily.”

There is also day-to-day water variability that changes due to the water cycle. In addition to those, there are many wave-driven components that influence the total wave run-up, such as regular seasonal waves, infragravity waves (really long, gradual waves that are hard to spot), high winds and a high swell.

Martin Guiles, a post doctoral researcher with SOEST, said West Maui is more so at risk than other areas on the island because of a fringing reef system that allows for more short-period waves entering the shoreline.

“Regardless of how big of a swell we really get, if we add sea level to a fringing reef system, we allow more energy to reach our coast,” Guiles said.

Combined with longterm rising sea levels over the past couple decades, he added that this creates more opportunities for wave events to “eat away at our shorelines.”

Owens said that the characteristics of the seafloor also play an important role in the “magnitude of the wave run-up.”

“West Maui is majorly affected by the refraction of wave energy, or the bending and focusing of the wave energy into the shoreline area,” she said. “The impacts are not going to be the same everywhere throughout West Maui at any given time and that’s important, and that’s one of the reasons why we’re tailoring this information in West Maui.”

Now that the forecast is up and running, Owens said the team wants to continue to collect information on how waves affect specific places in West Maui in order to increase community resilience as well as develop long-term planning and preparedness for any stakeholders, agency representatives and property owners.

The PacIOOS team encourages the public to submit photos around peak tides or swells or anytime waves overtop beach features because the data helps to calibrate the model. The public is also asked to include comments with the photos if they recognize any damage or impacts.

For more information or to view the forecast model to anticipate wave impacts, visit www.pacioos.hawaii.edu/shoreline-category/runup-westmaui/.

The development of the West Maui Wave Run-Up Forecast was made possible through funding by NOAA’s Regional Coastal Resilience Grants Program. Additional funding was provided by the Joint Institute for Marine and Atmospheric Research, UH Sea Grant, and PacIOOS.

* Dakota Grossman can be reached at dgrossman@mauinews.com.

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