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."