© Bill Lemmond (Actually, you're welcome to download and share these web-resolution images, and you probably won't be happy with printing them.)

Pizza from Scratch presents Purple Prose, 44

11 September, 2006

Buildings that float on soft soil, above flood waters

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As part of its coverage of Hurricane Katrina, its aftermath, and the Louisiana levee system, National Public Radio interviewed a soils scientist. He said most of the Mississippi basin (and certainly New Orleans) is on about a thousand feet of silt, deposited by the river. The silt is always settling, but when the river floods, it deposits more silt, keeping the land beside it from sinking.

He said that New Orleans has been sinking, ever since the levees went up. Various parts of New Orleans have been sinking at a rate of 1 to 5 feet, every hundred years. New Orleans has been sinking for about 200 years. There are places where people can look UP and see ships passing.

So what could have been done? Back in the teens of the 20th century, architect Frank Lloyd Wright and his engineers figured out how to float the Imperial Hotel on swampy land no one else had ever wanted, in the middle of Tokyo. It simply used the same volume displacement lift that allows steel ships, weighing thousands of tons, to float in water. The Imperial Hotel was built with huge concrete footing pads that pushed down into the soil, and the weight of surrounding loose soil pushed back.

And it was one of few buildings that survived a 1920s earthquake. The soft soil acted as a buffer, and maybe a few plates were broken.

This displacement principle wasn't new, even then. but at least almost 100 years ago, people could have rebuilt New Orleans on elevating reinforced concrete support structures, to lift New Orleans above the highest flood of the Mississippi or the Gulf of Mexico.

As an added benefit, the silt deposited on farmland beside the river would bring with it a rich supply of nutrients for crops. Before the Aswan High Dam was built in Egypt, annual flooding by the Nile continued the soil ammendment that for thousands of years enabled Egyptian civilization to flourish.