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Transcript for Hurricane Force - A Coastal Perspective, segment 09 of 12
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Hurricane Iniki's landfall on the Hawaiian island of Kauai in nineteen ninety-two illustrates how geology can control storm impacts. Iniki's winds approached one hundred fifty miles per hour, taking an islandwide toll on structures, agriculture, and Kauai's lush natural vegetation. The Waimea River, which drains the world's wettest spot, swelled up into a raging, muddy torrent. Iniki's eye wall and destructive right half crossed Kauai's south coast near Poipu Beach where storm surge inundated the area. Submarine channels and adjacent headlands focused Iniki's waves and storm surge onto Poipu Beach, in many cases leaving only foundations of once-costly beachfront homes. Some had been rebuilt only ten years earlier following Hurricane Iwa which passed further to the west. Within days of Iniki's departure, scientists from the U. S. G. S. and the University of Hawaii surveyed the coastal zone.
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What we wanted to look at was to document from the air the damage on the coast, videotape that so we'd have a permanent record of the damage, and then go in afterwards, a short time afterwards, and, and go along the coast, measure overwash, which is the, the water excursion inland, around the island and try and relate that to processes during the storm. We found, you know, quite significant overwash up to nine meters above normal water levels, and as you can expect, a lot of damage to coastal structures in certain parts of the island. What we're looking for - any debris that we could associate with, with running water, and that included pieces of housing, often roads, whole sections of asphalt were lifted up and moved, pieces of seawall, boulders, and then sediment from offshore, anything that looked like it had been in the marine environment.
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The scientists found that the inland excursion of water is in part controlled by the depth of the offshore. Wide shallow areas such as reefs tended to absorb wave energy, reducing overwash and protecting the coast, while areas that dropped more quickly into deep water were generally hit with the full force of Iniki's waves, maximizing their impact on the coast.