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West Side beaches and properties face erosion from large surf

By Staff | Feb 25, 2016

Waves smash into a seawall near Kahana Sunset.

KAHANA – On deadline, it’s early Monday morning (Feb. 22), a full moon is setting and another high surf warning has been issued by the National Weather Service for the north shore of Maui and north and west shores of Molokai until Tuesday at 6 a.m.

“A combination of strong northwest winds associated with a fast moving cold front and a very large wintertime northwest swell will generate life-threatening surf along most north and west facing shores through early Tuesday morning. Ocean water may periodically surge and sweep over beaches and coastal roadways, especially from midnight tonight through daybreak Monday morning around the time of high tide.” It’s been an all-to-familiar Civil Defense message posted this winter by the County of Maui.

Surf along the north-facing shores of Maui and Molokai is projected to reach 45 to 55 feet.

The West Side, however, only sees a fraction of that, reaching about ten to 15 feet along the northwest coastline.

Napili resident Tamara Paltin is in the water daily.

“Generally speaking, West Maui is very lucky to have Molokai to the west of us deflecting the full force of the wave energy,” she said.

The impact, however, can be equally devastating to life and property.

The Civil Defense Emergency Alert is a strong warning: “Expect ocean water surging and sweeping across beaches, coastal benches and lava flows, creating the potential for impacts to coastal properties and infrastructure, including roadways; powerful long shore and rip currents will be present at most beaches.”

“I believe they are calling this an El Nio year, and there have been more consistent large swells,” Paltin added, “and when it is big enough, we do see the effects of a west swell even at D.T. (D.T. Fleming Beach Park).”

On Facebook, Tara Owens, a coastal processes and hazard specialist with the University of Hawaii Sea Grant College, serving as a liaison to the County of Maui Planning Department, posted on Feb. 21, “Another big swell is coming with extremely high wave run-ups forecasted. Worried. Some of our beaches and shoreline areas can’t take much more this season.”

Owens has been in this role for the past six years and has plenty of experience.

“Back-to-back large swells this year are related to strong El Nio conditions causing increased storminess in the Pacific Ocean, which contributes to our active swell season. This affects our entire island, and particularly the north shore and West Maui due to their exposure to NW swells, and all of Hawaii,” she said.

In an interview last week with Lahaina News, the specialist identified West Side hot spots.

“Several sites in West Maui have been impacted over the last few years by chronic erosion. A few notable sites include: chronic erosion at Kahana Bay that is threatening condominiums; the Hyatt Regency Maui has been experiencing rapid shoreline erosion along the Kaanapali Beachwalk in front of the Grotto; several sites along Honoapiilani Highway are vulnerable to erosion and waves; chronic and seasonal erosion at Maui Kai condos in North Kaanapali is leading to flanking of the existing revetment; chronic erosion in the Honokowai region has resulted in seawall failure at several properties.”

Owens was detailed in her explanation about the reasons why these sites are considered hot spots.

“Generally speaking, West Maui shorelines are sand-starved, and there is not a rich source of sand in the coastal plain to feed the beaches. As sea level rises and forces shoreline retreat, the lack of sand contributes to a condition of chronic erosion and narrowing beaches.

“Other local conditions that contribute to erosion are somewhat site-specific,” Owens continued. “West Maui is subject to the larger northwest swells during winter season, so there is always some degree of seasonal erosion at sites where sand is transported down-coast or offshore in association with seasonal waves and currents. This year in particular, the strong El Nio conditions have contributed to back-to-back high wave events with high wave run-up causing inundation and increasing wave energy and pressures on the immediate shoreline areas.”

Owens was recently asked to inspect conditions at Keoni Nui Bay, when a suspicious plume of red-dirt water was photographed polluting the nearshore waters on Feb. 10.

“What a difference a day or two makes. The good news is that water quality in the bay on Friday was very good, and there was no evidence of active land-based sediment pollution,” she observed.

“In this case,” Owens noted, “it’s likely that the degraded water quality observed on Wednesday was caused by natural erosion of the beach, followed by exposure and erosion of the underlying land-based sediment layers (clay). This was verified to me on Friday (Feb. 12) by one of the onsite groundskeepers. I have observed some exposure of this clay during past visits in association with high seasonal erosion, though I’ve never seen it exposed to the degree it must have been on Wednesday.”

“Speaking generally,” she advised, “these types of conditions will likely become more frequent with continuing beach erosion forced by sea level rise and episodic events. This will be particularly true for West Maui and parts of the north shore, where the geology of the backshore is predominantly land-based sediment (i.e. not sand rich).”

Owens is responsive and vigilant.

“I’m glad that the community is attentive to these events, so we can at least monitor the sediment sources. I’ll try to include this site (Kahana Sunset) on my regular rounds in West Maui since I’m there pretty often these days for various beach issues,” she said.