Saturday, March 19, 2011

Tides and Coastal Barriers

Japanese see in the moon a rabbit pounding rice cake. With a full moon this week, the rabbit will be more visible than usual and she brings with her higher than normal tides. The water will rise from the sea onto the beaches an extra foot or two. This tide may bring up even more corpses. Bodies have been washing up since Monday and coroners have been overwhelmed. NHK shows families seeking out wooden coffins of their loved ones, draped with white chrysanthemums and a plastic bag holding the shoes the victim was wearing at the time of his or her death.

The Sendai airport is a mere 6 to 7 feet above sea level. People in the airport at the time of the tsunami ran to the roof and the control tower. 1400 were saved. Those at lower levels weren’t so lucky. A heart-wrenching youtube video shows a dog racing madly to avoid being sucked into the tidal vortex of the receding wave and failing.

This week’s tides will be flooding at 1.46 meters on average. At Shiogama near Sendai, for example, the highest tides will occur between March 19th and 24th, with highs at 1.44 meters and above. Tides will flood above 1.44 meters or 4.7 feet twelve times. The average flooding is 1.1 meters or 3.6 feet, so for that week the coast will experience flooding that is about a foot above normal. This may not sound like much, but when your international airport is six feet above sea level you need every foot you can get.

How is it that Japanese people living in the alluvial areas can protect themselves from this? Most major metropolitan areas in Japan are on alluvial plains. 73% of Japan is mountainous and living there is difficult. 14-16% of land is arable and much of this arable land is covered in concrete and prone to flooding.

New Orleans was in an even worse situation lying 6.5 feet below to 20 above sea level. Katrina hit New Orleans hard because its protective wetlands had been eroded by development. The draining of the wetlands for construction of roads, condos, and marinas has shrunk the coastline. Louisiana loses 25 miles of coastline every year to construction (Independent, September 2005). Levees and dams have been built to protect the city from hurricanes and floods but they’ve had the kind of side effect we see in Japan. The coastlines cannot build up natural barriers. Japan’s coastline is highly engineered with man-made barriers to stop tides and tetrapods to presumably stop erosion. The engineered coastline and waterways cased in concrete essentially funneled water into towns and cities. The saltwater islands and coastal marshes that used to buffer the coast from weather events now no longer do.

We’re all in this together.