Tsunami Threat to Hawaii and West Coast Underestimated Models Do Not
Account for Multiple, Bigger Waves Inundating Populated Areas
By: Public Employees
for Environmental Responsibility Published: Jul 12, 2006 at 08:06
New evidence
from the 2004 Indian Ocean tsunami is causing civil defense modelers to reassess recommended
evacuation zones and the hazards of multiple waves, according to scientific presentations to be given today at a planning
conference and released by Public Employees for Environmental Responsibility (PEER). These new analyses suggest that the tsunami
threat to Hawaii, particularly the south shore of
Oahu, and California
may be much greater than previously calculated.
One ominous aspect of the new studies is the increased vulnerability
of populated coastal areas. Man-made developments along the shore slow the retreat of the flood caused by the first tsunami
wave. Later waves then ride over the already-flooded area higher and faster. U.S. Geological Survey scientists have also warned
NOAA of the multiple wave pile-up effect, caused by slow drainage of the tsunami because the seaward component of gravity
is small in flat areas. The next tsunami wave arrives before the water from the previous waves returns to the ocean.
As
a result, recommended evacuation zones, particularly in areas with harbors and channels or rivers, would have to be expanded
to account for larger waves coming in a series of increasing heights. In the December 2004 tsunami, one observer described
effects occurring on Sri Lanka a full
kilometer from shore:
"It wasn't one wave; it came in great surges, each one deeper than the last. Subsequent waves
ride over a region already flooded resulting in higher and faster waves. The first wave knocked them off their feet, the second
picked them up and carried them, often up to 50 km/hr, and the third bore them up to 15 meters high or sucked them under."
Ironically,
the National Oceanic and Atmospheric Administration (NOAA) is relocating its Pacific
Tsunami Warning Center
to an island in the middle of Pearl Harbor on the south coast of Oahu, a location with a
high tsunami danger. NOAA staff scientists are concerned that the tsunami warning center could not function in this new location,
called Ford Island,
after the first tsunami wave hits. NOAA is vetoing plans to co-locate the tsunami warning center with Hawaiian state and local
civil defense offices 300 feet above sea level on the high slopes of Diamond Head Crater.
"Like the plumber with leaky
pipes in his own house, NOAA has yet to integrate new risk assessment data into its own tsunami planning," stated PEER executive
Jeff Ruch, pointing to a recent Government Accountability Office report which reached the same conclusion. "If NOAA cannot
protect its own assets, how can it play a useful civil defense role in the event of a tsunami?"
Ford Island, where
NOAA is planning to build a quarter-billion dollar complex housing all its Hawaii-based staff and assets, is flat, so the
drainage will be slow and additive effects of waves are more likely. In addition, the Admiral
Clarey Bridge, which provides the only egress
to Ford Island,
is in danger of being damaged or destroyed. According to one of the State of Hawaii's Civil
Defense advisors:
"Since the natural period of Pearl Harbor is longer than any tsunami
that is likely to hit it, the harbor will not be able to drain entirely between waves. The water level might therefore inch
up with each wave, and could conceivably do so for hours. If the water level rose high enough, the bridge might bind in whatever
position it was left in: open or closed. Knowing of that possibility, the guardians of the bridge would probably want the
thing kept open, which would make access impossible."
The papers are being presented by Hawaii State Civil Defense
Modelers at the Tsunami Technical Review Committee (TTRC) Meeting today in Honolulu,
Hawaii.
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