Let nature help

THE CATASTROPHE THAT DEVASTATED New Orleans has been centuries in the making. Since its founding in 1718, the city has lain uneasily between two watery and potentially lethal boundaries: Lake Pontchartrain to the north and the Mississippi River to the south.

Engineers have protected the city over the years by fortifying the earthen barriers between high water and low land. New Orleans’ efforts to keep dry also sank it lower -- a process called subsidence, caused when groundwater is pumped regularly out of silty soil. At the same time, the levees and canals around New Orleans diverted the flow of river sediment, dumping it in the Gulf of Mexico instead of allowing it to spread to the protective marshes and islands at the river’s mouth.

In 1965, Hurricane Betsy brought a heavy hint of the dangers when a surge of storm water caused Lake Pontchartrain to overflow the levees, flooding large parts of the city. But that flood pales in comparison to the devastation of Hurricane Katrina’s water surge, which caused a series of levee breaks that allowed the lake water to fill the bowl that is greater New Orleans.

For the next several weeks, and possibly months, the Army Corps of Engineers will pump the water out. Meanwhile the Corps, Congress and the Bush administration need to figure out how to avoid a repeat of last week’s disaster. Clearly, if they plant the 1.3 million residents back in the bowl, after billions of dollars spent on cleanup and rebuilding, they’ll need to devise better protection.

After Hurricane Betsy, Congress authorized a $732-million effort to raise the levees around the city to 16 feet. After a flood in 1995 claimed six lives, lawmakers authorized an equally ambitious venture to refortify the city’s slowly sinking defenses. Finishing these projects took a back seat during the last few years to war and homeland security. Even if they are now fast-tracked to completion, they aren’t enough to guarantee New Orleans protection against another Katrina-strength storm. Other nations -- most notably the Netherlands -- have engineered stronger, smarter levees and other coastal defenses, such as floodgates and raised shelters.

Devastating hurricanes are more likely in coming years. Warmer ocean surface temperatures, no matter what their cause, fuel more violent hurricanes, which derive their power from the water’s heat.

One of the most effective shore defenses has been not only ignored but undermined. Barrier islands and the marshes of the Mississippi River Delta used to present hurricanes with a formidable land barrier to cross before reaching New Orleans. But the very levees and canals that protect New Orleans and provide navigation divert replenishing sediment. Louisiana loses about 24 square miles of this land barrier each year.

A plan backed by environmentalists, industry and the Corps of Engineers would spend $2 billion to dredge sediment from the Gulf to be used in rebuilding the land, and divert some river sediment toward the marshland. Congress should not only approve that project but should start giving serious consideration to the rest of a $14-billion coastal restoration project supported by 11 state and federal agencies.

Funding environmental projects isn’t just a luxury that makes tree-huggers happy. It’s a natural way to protect people and a bargain compared with the economic and human toll exacted by Katrina.