Melting glaciers and rising waters are two of the major concerns of global warming, and their impacts are particularly unnerving for low-lying, coastal cities around the world.

As this ScienCentral News video reports, cities like New Orleans are in a battle with nature that threatens to wash them away.

Rolling on the River

Italy’s historic Venice is under siege by the surging Adriatic Sea much of the year, and they’re not alone. Here in the United States, many cities will be facing the same fate. In fact, the Federal Emergency Management Agency issued a report estimating that a quarter of homes within 500 feet of the coastlines and along the Great Lakes will fall victim to erosion by 2060.

FEMA’s predictions are already starting to come true in many areas, including Smith Island in Maryland’s Chesapeake Bay and in states along the Gulf Coast.

Louisiana is losing as much as 35 square miles of land a year, much of it in the swamplands along the coast. These swamps serve as the only barrier from hurricanes that roll-in from the Gulf. This is especially dangerous because of the risk of evacuation routes being flooded when a storm hits.

“What you saw with Tropical Storm Isidore and with Hurricane Lili is that many evacuation routes flooded more quickly than in previous years. And that made it very hard for coastal residents to get out of harm's way,” says Roy Dokka, director of the Louisiana Spatial Reference Center (LSRC) at LSU, who has been measuring subsidence levels around the state as part of a joint effort with the National Oceanic and Atmospheric Administration National Geodetic Survey. He adds, “Lives are at stake, and that big storm might be right around the corner.”

In New Orleans, with its proximity to the Mississippi River, the problem is more pronounced. The “Big Easy” sits on the soft silt of the Mississippi and is literally sinking under its own weight. According to Dokka, much of the city is already below sea level and it’s still sinking. “In areas adjacent to New Orleans, we see rates as much as an inch a year,” he says.

Making matters worse for New Orleans, the man-made levees that hold back the waters of the Mississippi and Lake Pontchartrain also keep out the natural sediments—mud that once naturally restored the delta to higher levels.
With every inch that New Orleans sinks below sea level comes a greater risk of flooding.

The current flood protection levees are designed to withstand a Category 3 storm, says Joseph Suhayda, a civil engineer and former director of the Louisiana Water Resources Research Institute.

Suhayda believes that the city would be flooded by a Category 4 or 5 storm. He’s proposed a plan called the “Community Haven” to guard residents from flooding waters in the event of a major storm. In his proposal, Suhayda would take advantage of existing hurricane barriers and build an extension—a wall that would run in the middle of the city and create an area that would be protected from a strong storm.

There may be some relief on the way. A multi-agency task force is considering a fifty-year, $14-billion project to restore the Gulf coastline from Mississippi to Texas that would slow both an incoming storm and erosion on the mainland.

But Suhayda, who’s been involved in the Gulf Restoration project for the last fifteen years, believes even such an ambitious offensive won’t end the battle to keep New Orleans from rolling on the river. “What we’re faced with is a long commitment," he says, "knowing that it’s probably going to be an unending fight.”