As the sea level continues to rise, low-lying parts of
Hawai`i will face attack on two fronts.
We can plan for driving through vast pools of brackish water
throughout much of low-lying Honolulu, including much of Waikīkī.
(Image: Flooding in Māpunapuna. Credit: University of
Hawaii.)
The rising seas will push shoreward, but at the same time,
groundwater will back up and further raise the water level, says a new study: “Assessment
of groundwater inundation as a consequence of sea-level rise.”
The report, published in the journal Nature Climate Change, was
written by Kolja Rotzoll of the Water Resources Research Center at University
of Hawaii, and by Charles “Chip” Fletcher, of the University of Hawai`i School
of Ocean and Earth Science and Technology.
“Besides marine inundation, it is largely unrecognized that
low-lying coastal areas may also be vulnerable to groundwater inundation, which
is localized coastal-plain flooding due to a rise of the groundwater table with
sea level,” they write.
Their work suggests that sea level rise alone can’t be
isolated as the source of flooding.
“The flooded area including groundwater inundation is more
than twice the area of marine inundation alone,” they write.
Looking just at Honolulu, their work concludes that,
particularly at high tide, there will be massive regions of flooding—ponds and
lakes of standing brackish water that could represent 10 percent of all the
low-lying land within a kilometer of the coast as sea level rise reaches one
meter.
In many parts of the Islands, groundwater is already very
near the surface in the lowest lying areas like Waikīkī and other parts of Honolulu.
In some areas, including parts of Māpunapuna, the streets already flood
during the highest tides.
“With groundwater tables near the ground surface, excluding
groundwater inundation may underestimate the true threat to coastal
communities,” said Rotzoll.
“Finding that the
inundated areas double when including groundwater inundation in coastal
flooding scenarios will certainly be a surprise for everyone assessing the
effects of (sea level rise) without considering the local groundwater table,”
Rotzoll said.
The authors recommend continuous groundwater level
monitoring in the coastal zone, along with “rigorous planning” for the impacts
of brackish water inundation. And they
recommend residents of coastal communities everywhere study their own potential
situations.
“We hope other coastal communities use our research as the
basis for conducting their own localized analysis,” Rotzoll said.
Fletcher, an associate dean at the University of Hawai`i and
a coastal geologist who has been studying sea level rise and erosion issues
statewide, said the planning won’t be easy.
“This research has implications for communities that are
assessing options for adapting to (sea level rise). Adapting to marine
inundation may require a very different set of options and alternatives than
adapting to groundwater inundation,” Fletcher said.
The paper: Rotzoll, K. and Fletcher, C.H. Assessment of
groundwater inundation as a consequence of sea-level rise. Nature Climate
Change, DOI: 10.1038/NCLIMATE1725
The abstract can be viewed here.
Fletcher’s website on Hawaiian sea level rise impacts
includes a virtual fly-through of those impacts.
© Jan TenBruggencate 2012
No comments:
Post a Comment