Word: silt
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...protect the city from water surges have had a perverse effect: they have actually made it more vulnerable to flooding. That's because New Orleans has been kept in place by the precarious balance of two opposing forces. Because the city is constructed on 100 feet of soft silt, sand and clay, it naturally "subsides," or sinks, several feet a century. Historically, that subsidence has been counteracted by sedimentation: new silt, sand and clay that are deposited when the river floods. But since the levees went up--mostly after the great flood of 1927--the river has not been flooding...
Then, in the late 1920s, after a flood that spread the river 40 miles from its banks, the U.S. Congress made levee construction Washington's responsibility. Billions of tax dollars from elsewhere--probably tens of billions, in modern money--were spent constricting the Mississippi's channel, so its silt began washing straight out to sea and off the continental shelf. By the 1970s, more than half the historic sediment load was coming to a dead stop behind dozens of upriver dams--especially seven monstrous structures erected on the Missouri...
...saltwater invasion has cost the Cajun economy, rooted in fishing and trapping and hunting, dearly. But payment will soon be demanded farther north. Hydrologists are now proposing formerly unthinkable ideas--such as breaching the levees from New Orleans to the river's mouth--if only to spread enough silt to slow the Gulf's encroachment on the city. Even if that's done (it would probably cost New Orleans its port), it's hard to believe the Missouri dams will be removed, so the land loss will go on. Pieces of Plaquemines Parish might remain above water a few decades...
...Most ocean pollution doesn't come from ships. It comes from land. Gravity is the sea's enemy. Silt running off dirt roads and clear-cut forest land ruins coral reefs and U.S. salmon rivers. Pesticides and other toxics sprayed into the air and washed into rivers find the ocean. (Midway's albatrosses have in their tissues as much of the industrial chemicals called PCBs as do Great Lakes bald eagles.) The biggest sources of coastal pollution are waste from farm animals, fertilizers and human sewage. They can spawn red tides and other harmful algal blooms that rob oxygen from...
...roads that crisscross the national forests. "They are the heart of a lot of controversy," says Marty Hayden, director of policy for the Earthjustice Legal Defense Fund. Environmentalists complain that the roads, cut for the timber companies and maintained by the Forest Service, are degrading watersheds, filling streams with silt and subdividing wildlife habitats. "It is simply time to stop logging our national forests," says Sierra Club executive director Carl Pope...