Monday, December 04, 2006

Turning Japanese

Japan apparently has a simple yet novel way of protecting their cities from potential flooding.

The Arakawa spillway and other engineering improvements -- chiefly, a more modern system of levees and locks that manage water flowing from the Arakawa -- have drastically reduced river flooding in Tokyo. As in New Orleans, the levee system means the city depends on pumps to keep low areas from flooding after heavy rains, a battle the pumps don't always win. (The Tokyo government is upgrading its pumps to handle 2 inches of rain in an hour, roughly the amount for which New Orleans pumps are designed.)

nd as in New Orleans, other forms of flooding are possible: a typhoon that brings heavy rain, for instance, or a storm surge that tops levees and causes them to fail. Or, worse, an earthquake that ruptures levees and sends a tsunami through the breach. (The levee system in Tokyo includes roughly 60 miles of oceanfront breakwaters.)

To minimize those possibilities, the Japanese have been replacing the traditional levees along the Arakawa with what they refer to as "superlevees."

There's nothing gee-whiz about these ramparts, no high-tech gimmickry comparable to the computer-controlled storm gates and permeable levees deployed by the Dutch in their eternal struggle with the North Sea. Superlevees are actually no higher than the levees they replace; their effectiveness lies in their extraordinary width.

Rather than dropping back to grade level at the same steep pitch on both sides, a superlevee is severely asymmetrical, sloping down gradually on its backside for a distance of perhaps several blocks. The goal, one the Japanese believe they have achieved, is a breach-proof levee.

Imagine a Mississippi River levee that doesn't stop shy of the river road but continues all the way across Tchoupitoulas Street to Annunciation, and you get a sense of how seriously the Japanese have taken the responsibility to mitigate flooding.

Unfortunately Japanese doesn't translate well into Creole. While these "superlevees" may be practical in more recently developed or undeveloped areas of a city, how do proponents of "superlevees" in New Orleans propose that we build such a levee without destroying the MOST historic parts of the city. This most surely a case if cutting off one's nose despite its face.

However, the "superlevee" idea is not totally without merit in southeast Louisiana. There are many miles of levees that exist in undeveloped areas. The problem is that it is not that important to protect marshland from storm surge. One advantage to the "superlevee" is that it creates land that is high and dry and is ripe for development.

The problem with this scenario is the the Corps of Engineers is not too keen on people building anything in their levees. Besides, most earthen levees held up well during the onslaught that was Hurricane Katrina. It was the smaller, I-wall levees that failed during the storm. The Japanese don't seem to have an answer to that problem.

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