Civil Engineering: A Very Short Introduction (Very Short Introductions) by Wood David Muir

Author:Wood, David Muir [Wood, David Muir]
Language: eng
Format: epub
Publisher: Oxford University Press
Published: 2012-09-26T16:00:00+00:00

New Orleans 2005

It wasn’t the miles of buildings stripped of their shingles and their windows caved in or the streets awash with floating trash or the live oaks that had been punched through people’s roofs. It was the literal powerlessness of the city that was overwhelming. The electric grid had been destroyed and the water pressure had died in every faucet in St Bernard and Orleans parishes. The pumps that should have forced water out of the storm sewers were flooded themselves and totally useless. Gas mains burned under water or sometimes burst flaming from the earth, filling the sky in seconds with hundreds of leaves singed off an ancient tree. The entire city, within one night, had been reduced to the technological level of the Middle Ages.

The disaster that struck New Orleans in 2005 provided the factual background for a gritty novel by James Lee Burke more extraordinary than any fictitious description.

New Orleans is located in the Mississippi River Delta on the banks of the Mississippi River and south of Lake Pontchartrain, 170 km upriver from the Gulf of Mexico. Originally located on the natural levees and high ground along the Mississippi, the city was given permission early in the 20th century to put into effect a drainage plan for the swamp surrounding the city in order to permit expansion and, it was hoped, economic growth. Pumping for drainage increases the stresses in the soil, leading to subsidence of the drained ground, as in Venice. Some parts of the city are as high as 6 m above sea level but the average elevation is about 0.5 m below sea level: some locations are as low as −3 m. Climate change produces a small annual rise in sea level, and there is continuing lowering of the level of the delta sediments as a result of both continued pumping and also the loss of organic surface materials through oxidation by exposure to the air. Ironically, before many of the protective flood control structures were constructed the Mississippi would have kept the delta topped up with new sediments to counter some of the subsidence. Such are the unintended consequences of human intervention.

New Orleans has always been vulnerable to flooding. Flooding caused by Hurricane Betsy in 1965 killed 76 people. The subsequent Flood Control Act of 1965 required the US Army Corps of Engineers to design and construct flood protection in the New Orleans metropolitan area, but in 2005 completion was forecast for 2015. Heavy rain in May 1995 revealed the inadequacy of the pumping system. Both of the elements – protection and pumping – which might have reduced the extent of flooding were in an uncertain state when Hurricane Katrina arrived on 29 August 2005, producing intense winds and a tidal surge.

The failure of most of the protective levees throughout the metropolitan area left 80 per cent of the city underwater – in places to a depth of 4.5 m. Some failed because the embedment of the walls was insufficient to withstand

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