Immediately after Hurricane Katrina pummeled New Orleans last August, President George W. Bush and the U.S. Department of Homeland Security declared that no one could have predicted such devastation. Yet scientists, engineers and Louisiana state politicians had warned for years that a Category 4 or 5 storm crossing the Gulf of Mexico from a certain direction would drown the region. In 1998 computer models at Louisiana State University simulated such a terrible inundation. That same year the state proposed a $14-billion plan to restore the delta's natural wetlands--which, by absorbing water, can help protect inland areas from sea surges. But Congress turned it down.
What is more, engineering firms, as well as the U.S. Army Corps of Engineers, which is largely responsible for flood protection, had proposed constructing higher earthen levees as well as huge gates that could have prevented storm surges from pouring into inner-city canals and bursting their concrete flood walls. Indeed, documents show that various gates had been recommended as far back as 1968 and in each decade since.
None of these designs has ever been funded. The reason, for the most part, is turf battles among the Corps, local and state politicians, and Congress. In the meantime, countries such as the Netherlands and the U.K. have erected effective surge barriers that the U.S. has ignored. In Katrina's wake, the blueprints for all these structures are rapidly being dusted off, augmented and integrated into several grand plans by L.S.U., big engineering companies, and the Corps that could safeguard New Orleans and southeastern Louisiana. Similar measures could save populated coastal communities around the Gulf, the U.S. and the globe.
The Mississippi River Delta is not alone in being endangered. Deltas worldwide are in trouble because human development is causing the land to sink. The soft delta earth compacts naturally, but annual river floods top-coat the slumping ground with new sediment. Yet man-made levees built to prevent floods in many of these regions also cut off the sediment supply. At the same time, underground extraction of oil, natural gas and freshwater deflates the land's support structure. As the surface subsides, saltwater from the ocean streams in, poisoning the usually thick expanses of wetland mangroves, trees and grasses. Without these lush buffers, even moderate storms can push sea surges far inland.
The earth's oceans are also rising, compounding the problem. At current rates, sea level will be one to three feet higher in 100 years. Low-lying cities from New York to Shanghai may have to armor themselves with walls and pumps and add revetments (waterproof masonry) to the bottom few feet of every building in town, measures already under way in Venice.
One third of the world's people live in coastal zones, particularly the deltas. Rich in farmland, seafood and underground resources, these areas are also key exit and entry points for armadas of ships carrying piles of goods. Cairo, at the tip of the Nile River, is home to 16 million people. The Red River and Mekong deltas in Vietnam each support 15 million inhabitants, yet both are eroding. Shanghai has 13.5 million, the Ganges in Bangladesh, 10 million. Other threatened deltas include the Orinoco in Venezuela and the Rhine, Rh¿ne and Po in Europe.
The Mississippi Delta, home to 2.2 million, represents the worst-case scenario. It is sinking and losing wetlands faster than almost any place on earth and faces the most hurricanes annually. The record sea surge that prompted the Netherlands and Britain to erect barriers was 15 feet; Katrina's peaked at 28 feet.
Fundamental to the trouble is that for the past century the Corps, with the blessing of Congress, leveed the Mississippi River to prevent its annual floods so that farms and industries could expand along its banks. Yet the levees have starved the region of enormous quantities of sediment, nutrients and freshwater. Natural flooding at the river's mouth had also sent volumes of sediment west and east to a string of barrier islands that cut down surges and waves, rebuilding each year what regular ocean erosion had stolen. But because the mouth is now dredged for shipping lanes, the sediment simply streams out into the deep ocean, leaving the delta--and New Orleans within it--naked against the sea.�