Geography
New Orleans is located at 29°57′53″N 90°4′14″W / 29.96472°N 90.07056°W / 29.96472; -90.07056 (29.964722, −90.070556) on the banks of the Mississippi River, approximately 105 miles (169 km) upriver from the Gulf of Mexico. According to the United States Census Bureau, the city has a total area of 350.2 square miles (907 km2), of which 180.56 square miles (467.6 km2), or 51.55%, is land.
The city is located in the Mississippi River Delta on the east and west banks of the Mississippi River and south of Lake Pontchartrain. The area along the river is characterized by ridges and hollows.
New Orleans was originally settled on the natural levees or high ground, along the Mississippi River. After the Flood Control Act of 1965, the United States Army Corps of Engineers built floodwalls and man-made levees around a much larger geographic footprint that included previous marshland and swamp. Whether or not this human interference has caused subsidence is a topic of debate. A study by an associate professor at Tulane University claims:
| “ | While erosion and wetland loss are huge problems along Louisiana's coast, the basement 30 to 50 feet (15 m) beneath much of the Mississippi Delta has been highly stable for the past 8,000 years with negligible subsidence rates. | ” |
On the other hand, a report by the American Society of Civil Engineers claims that "New Orleans is subsiding (sinking)":
| “ | Large portions of Orleans, St. Bernard, and Jefferson parishes are currently below sea level—and continue to sink. New Orleans is built on thousands of feet of soft sand, silt, and clay. Subsidence, or settling of the ground surface, occurs naturally due to the consolidation and oxidation of organic soils (called "marsh" in New Orleans) and local groundwater pumping. In the past, flooding and deposition of sediments from the Mississippi River counterbalanced the natural subsidence, leaving southeast Louisiana at or above sea level. However, due to major flood control structures being built upstream on the Mississippi River and levees being built around New Orleans, fresh layers of sediment are not replenishing the ground lost by subsidence. | ” |
A recent study by Tulane and Xavier University notes that 51% of New Orleans is at or above sea level, with the more densely populated areas generally on higher ground. The average elevation of the city is currently between one and two feet (0.5 m) below sea level, with some portions of the city as high as 20 feet (6 m) at the base of the river levee in Uptown and others as low as 7 feet (2 m) below sea level in the farthest reaches of Eastern New Orleans.
In 2005, storm surge from Hurricane Katrina caused catastrophic failure of the federally designed and built levees, flooding 80% of the city. A report by the American Society of Civil Engineers says that "had the levees and floodwalls not failed and had the pump stations operated, nearly two-thirds of the deaths would not have occurred".
New Orleans has always had to consider the risk of hurricanes, but the risks are dramatically greater today due to coastal erosion from human interference. Since the beginning of the 20th century, it has been estimated that Louisiana has lost 2,000 square miles (5,000 km2) of coast (including many of its barrier islands), which once protected New Orleans against storm surge. Following Hurricane Katrina, the United States Army Corps of Engineers has instituted massive levee repair and hurricane protection measures to protect the city.
In 2006, Louisiana voters overwhelmingly adopted an amendment to the state's constitution to dedicate all revenues from off-shore drilling to restore Louisiana's eroding coast line. Congress has allocated $7 billion to bolster New Orleans' flood protection.
According to a study by the National Academy of Engineering and the National Research Council, Levees and floodwalls surrounding New Orleans—no matter how large or sturdy—cannot provide absolute protection against overtopping or failure in extreme events. Levees and floodwalls should be viewed as a way to reduce risks from hurricanes and storm surges, not as measures that completely eliminate risk. For structures in hazardous areas and residents who do not relocate, the committee recommended major floodproofing measures—such as elevating the first floor of buildings to at least the 100-year flood level.
Read more about this topic: New Orleans
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