Why Is New Orleans So Vulnerable?

Scott Jennings Violent Weather 70867-FA-15 Why is New Orleans so Vulnerable? Early morning of August 29, 2005, Hurricane Katrina struck the Gulf Coast of the United States. When the storm reached land, it had a Category 3 rating on the Saffir-Simpson Hurricane Scale bringing winds of 100–140 miles per hour. The Hurricane ran some 400 miles across. Hundreds of thousands of families in Louisiana, Mississippi and Alabama lost their homes, and experts estimate that Katrina caused more than $100 billion in damage. By the time Hurricane Katrina struck New Orleans, it had already been pouring
rain for hours. With a storm surging more than 9 meters high, Katrina overwhelmed and depleted many of the city’s unstable levees and drainage canals. Water made its way through the soil underneath some levees and swept others away altogether. By early morning, low-level places in the city were under so much water that people had to scramble to attics and rooftops for safety. Eventually, nearly 80 percent of the city was under some quantity of water. Clearly, New Orleans is a city more vulnerable than most cities when it comes to hurricanes or storms. There are two main explanations for this. The first being New Orleans’ low elevation in relation to the sea level. The second is the lack of wetlands and barrier islands, these being Mother Nature’s best defense system. The level of New Orleans was originally very low in relation to sea level, but human interference has caused the city to sink even lower below.
When New Orleans was being constructed they ran out of good land. Engineers drained swamplands to make more room around the area so they could continue expansion. The drainage of the swamplands resulted in Subsidence which is sinking or settling to a lower level. In New Orleans case, it was the earth’s surface sinking below sea level. Because of this, present day New Orleans is on average, six feet below sea level. Following this problem is the construction and placement of levees. New Orleans sits between the levees along the Mississippi River, and those around Lake Pontchartrain. This predicament leaves New Orleans in a “bowl” effect. Due to this unfortunate effect, once water floods into the city, it is extremely difficult to get it
out. The second major factor in New Orleans’ susceptibility to storm surges is their lack of nature’s best natural defenses against them; wetlands and barrier islands. For every mile of continuous wetlands a storm surge can be reduced by three to eight inches. Although it doesn’t seem like much, those valuable inches can be the difference between a city under water and a city completely dry. In an undisturbed area wetlands are naturally replenished every year by sediment from a flooding river, in this case the Mississippi. However, human interference has caused the wetlands and barrier islands off the coast of New Orleans to disappear at an incredible rate. Dams upriver from the city have caused the amount of sediment in the river to be reduced by up to 67%! Along with that, the levees built around New Orleans to protect it now divert the river’s flow much further out into the Gulf of Mexico, meaning that much of the remaining sediment is washed out to sea, and not deposited in either the wetlands or the barrier islands. These factors are denying nature’s best defenses their replenishment, and causing them to disappear. Over the past 50 years the wetlands have been disappearing at a rate of about 60 square kilometers per year. Between the low elevation and lack of natural defenses, New Orleans has proven to be a combination that leads to extreme vulnerability when faced with a large storm surge.
Metro New Orleans approaches the busiest period of the hurricane season with the best flood control system of any coastal community in the United States: A billion network of levees, floodwalls and pumps that could eliminate flooding for a possible 100-years and exponentially reduce flooding from much larger hurricanes. But that system has limits, experts say. The city's natural defenses, barrier islands and wetlands that once gave it many surge-absorbing marshes, have never been as decimated. That's why experts are requesting civilians and families to respect the remaining storm risk as the area enters the six-week window, peaking Sept. 10. The massive system includes near-complete protection from flooding from so-called "100-year storm surge event", one with a 1 percent chance of occurring in any given year. The new and improved levees also provide a significant reduction in flooding from the much more damaging 500-year surge event, larger than Hurricane Katrina, according to advanced computer engineering by the U.S. Army Corps of
Engineers.