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UH Study: Honolulu, Waikīkī Vulnerable to Affects of Rising Sea Level

Posted March 28, 2017, 09:38 AM HST Updated March 31, 2017, 12:42 PM HST
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Sea level rise lifts freshwater, causing groundwater inundation in low-lying areas. Credit: UHM Coastal Geology Group.

New research from the University of Hawai‘i at Mānoa reveals a large part of the the heavily urbanized area of Honolulu and Waikīkī, Hawai‘i is at risk of groundwater inundation—flooding that occurs as groundwater is lifted above the ground surface due to sea level rise.

“Ultimately, what will happen is when the water table breaks out on the ground’s surface, you create, what we all know, is a wetland,” said Chip Fletcher, associate dean at UH Mānoa School of Ocean and Earth Science and Technology. “And a wetland in an urban, vital corridor is not a good thing.”

Simulations of groundwater inundation (blue) and narrow unsaturated space (yellow) today and considering sea level rise of approximately 1, 2 and 3 ft during an average spring (monthly maximum) tide stage. Credit: UHM Coastal Geology Group.

Shellie Habel, lead author of the study and doctoral student in the UH Mānoa Department of Geology and Geophysics, School of Ocean and Earth Science and Technology (SOEST), and colleagues developed a computer model that combines ground elevation, groundwater location, monitoring data, estimates of tidal influence and numerical groundwater-flow modeling to simulate future flood scenarios in the urban core as sea level rises three feet, as is projected for this century under certain climate change scenarios.

“With about three feet of rise, about a quarter of the study area will be flooded, so that study area includes Waikiki, Kaka‘ako and Mo‘ili‘ili,” said Habel.

“This flooding will threaten $5 billion of taxable real estate; flood nearly 30 miles of roadway; and impact pedestrians, commercial and recreation activities, tourism, transportation and infrastructure,” said Habel. “The flooding will occur regardless of seawall construction, and thus will require innovative planning and intensive engineering efforts to accommodate standing water in the streets.”

This construction trench in Waikiki shows that the water table is nearly at the ground surface at high tide. Credit: UHM Coastal Geology Group

Surprisingly, the team of researchers also discovered 86% of active cesspools in the study area are likely currently inundated by groundwater. This suggests that cesspool effluent is now entering coastal groundwater and coastal environments in the study area. Sea level rise of approximately three feet would fully inundate 39 cesspools, introducing effluent at the ground surface where people work and live. This presents a serious health concern that will become progressively more serious as contaminated waters begin breaching the ground surface.

They also found that the water table is close to the ground surface—within two feet at high tide—in many places. This narrow unsaturated space means that groundwater inundation will become a serious concern well before the end of the century. When it rains and infiltration fills this space, it is a problem already.

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“Waikīkī,, the gateway of the state’s tourism industry, currently has such narrow unsaturated space that many construction projects working below the ground surface have to dewater the excavation before construction can begin,” said Habel.

“Our findings suggest that coastal communities in Hawai‘i and globally are exposed to complex groundwater flooding hazards associated with sea level rise in addition to the typical concerns of coastal erosion and wave overtopping,” said Chip Fletcher, professor of Geology and Geophysics and associate dean in SOEST and principal investigator on the study. “Groundwater inundation will require entirely unique adaptation methods if we are to continue to live in and develop the coastal zone. Coastal planners and community stakeholders will need to work with architects, engineers, geologists, ecologists, economists, hydrologists, and other innovative thinkers in order to manage these problems.”

“The results are going straight to our city and state agencies and they are working with them in terms of making sure that there is no interruption to commercial activity or tourism activity,” said Fletcher.

This study identified particular locations and infrastructure that will be vulnerable to future flooding and is a crucial first step towards addressing future challenges. The team of researchers hope to use this methodology to identify future flooding and at risk infrastructure in other locations, as well as assist in developing adaptation efforts among vulnerable coastal communities.

This work was funded by Hawai‘i Department of Land and Natural Resources, the Honolulu Board of Water Supply, University of Hawai‘i Sea Grant and HKL Castle Foundation.

The paper may be accessed here.

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COMMENTS

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Byron Matthews Good thing the sea levels arent risingMarch 28, 2017 09:45am
Stew B Doo So would you build a wall to keep the undocumented water out ?March 28, 2017 09:54am
Glenn Brown But they are.March 28, 2017 09:58am
Christopher A White Carry the unwanted water out on the light rail train.March 28, 2017 10:02am
Susanne Holland Yeah, but will it threaten Trump Tower? Apparently that's the only measure that matters at this juncture.March 28, 2017 10:08am
Jeff Walsma Well who's fault is it that u built everything right on the water and in a low lying area.March 28, 2017 10:15am
Quinn Masson Not to worry the sun burns out in 6 billion years but if your Bible Thrump er it will never happenMarch 28, 2017 10:19am
Donald Klees And of course almost all of the important infrastructure such as airports, oil storage, and electrical power plants are all within a few feet of the current sea levels. What geniuses came up with those ideas? And there there are key words in the article such as "estimates" and "some climate change scenarios" that are very easy to overlook or for many people, to embrace those words as facts. Building close to the water is no different in Hawaii as it is all over the world but especially on the mainland where those locations are so coveted. Big storms hit and people continue to get money to rebuilt their destroyed homes or businesses in the exact same places. Reality check time in my opinion.March 28, 2017 10:23am
James Kong When the millionaires, billionaires, and corporations start selling their properties, then you should start to worry about it.March 28, 2017 12:59pm
Daryl Bickell But they aren't.March 28, 2017 03:05pm
Les Miller The Russians are causing the sea to rise 😂😂😂March 28, 2017 06:36pm
Glenn Brown Nearly all studies to date published in the peer-reviewed literature agree that global sea level has risen during the past century, and that it will continue to rise over the next century. Tide gauges throughout the world have documented rising sea levels during the last 130 years. This rise has been further confirmed over the past 20 years by satellite observations, which are highly accurate and have nearly global coverage. Recent studies have shown current sea level rise rates are increasing, and project that future sea level rise over the rest of this century will be faster than that of the last 100 yearsMarch 28, 2017 06:37pm
Ed Moran We'll make Antarctica pay for it.March 28, 2017 08:37pm
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