Hurricane Katrina was a natural disaster of epic proportions in the United States. New Orleans communities were destroyed and lives uprooted as water came cascading onto the Bayou. Did the damage have to be so devastating? Some say that the extent of the damage could have been lessened if New Orleans' natural barriers were not compromised. New Orleans has the cards stacked against it when it comes to natural disaster defense. For sure, the number one reason is its peculiar natural geography. However, some say that oil exploration in the Gulf of Mexico played an important role in leaving the city unprotected. The correct answer may be that it was some combination of factors that made the devastation of Hurricane Katrina so intense.
Natural landscaping can be considered a city's Achilles' heel when it is faced with an oncoming hurricane. New Orleans, being below sea level, is a prime example of that. The city lies at the bottom of a "soup bowl" with the Mississippi River running right through it. As the river reaches the Gulf of Mexico, it slows down and creates a fan of sediment or what is commonly known as a delta. This sediment could have traveled thousands of miles through 40 of the 48 contiguous states before it eventually dumps into the Gulf. It is such a huge amount of sediment being transported that the Earth's crust literally sags underneath it. Every time a sag forms, new sediment fills the gap. Through millions of years, the Mississippi has changed course east and west creating six delta lobes, which has formed the entire coastline of southern Louisiana. Lake Pontchartrain, twice the size of New Orleans, lies on the lip of the bowl to the north and coastal wetlands lie to the east, west, and south of the city. Flood control engineering was designed to hold back spring floods and make New Orleans an important port city for oil exploration and transportation. This man-made flood control concept contributed to the disappearance of coastal wetlands. Since silt and nutrients, the bread and butter for marshland growth, were unable to be replenished, the existing land sunk and the wetlands turned to open water. A natural sponge for soaking up the floodwaters and protecting New Orleans against hurricanes had disappeared.
Louisiana is the hardest working wetlands in America. It produces or transports more than a third of the nation's oil and a quarter of its natural gas. It is also an important commercial fishing area falling only behind Alaska. 1.1 billion kg of fish and shellfish (around 40% of the United States supply) comes from the Gulf.
The French founded New Orleans in the early 1700s. As the population grew in New Orleans, the swamps and marshlands were drained and turned into habitable land. Seeing no inherent value in the swampy areas, other than the harvesting of the bald cypress forests, early settlers drained the marshlands to control mosquito-borne diseases. In the 1930s, after a flood protection barrier was in place, the city could now extend its streets to the shores of Lake Pontchartrain. The once soggy floodplains could now be inhabited and turned into farms to meet the needs of an expanding urban population. As the wetlands were drained, however, the moisture rich peat soils began to dry out and sink, eventually bringing New Orleans below sea level. It also brought the city below the level of Lake Pontchartrain resulting in catastrophe when Katrina's rains hit and the lake spilled over.
Oil production in Louisiana began in 1902 and peaked at 1970. This industry has had profound impacts on the essential plants of the Mississippi delta. For vegetation to have high productivity, it needs natural and regular flow of sediment. Levees and canals have diverted this flow. As a result, a phenomenon known as depressurization has lead to subsidence, a fancy word for sinking. In other words, the delta is analogous to a glass with soda pop in it and a drinking straw is similar to an oil-drilling pipe. Suck on the straw and your soda pop or your oil comes to the surface. However, when that happens, the level of the liquid drops as the pressure underneath is lessened. As oil is pumped from the ground, New Orleans is sinking. Subsidence in the Mississippi Delta is thought to be around 10mm per year. Depressurization can go hand in hand with sediment build up. The levees have stunted sediment build up, which could offset depressurization.
The inner wetland areas lie at a lower elevation than the coastal areas and are essentially starved of nutrients and then inundated by tides. Constantly submerged, coastal wetlands, freshwater swamps, and bald cypress forests start to die off. The pattern starts from the center and continues moving outwards to the gulf. Some geologists believe that if the trend continues, New Orleans would be exposed to worse damage from hurricanes as more of the city is exposed to open water making a virtual hurricane highway. Oil and gas facilities and a valuable fishing industry, which contain nurseries for shrimp, blue crab, oysters, and redfish, would all be at serious risk if that were to happen.
In the 20th century, 4000 square kilometers of wetlands have been lost due to the construction of flood control levees.
Legal action has been taken against a number of oil companies for damage to wetlands. They claim that had the wetlands not been compromised, the impact of Hurricane Katrina would not have been so severe. Oil and gas canals have long been blamed for allowing salt water into the marshlands and eroding the land. Oil companies argue that a hurricane the size of Katrina would have done just as much damage even if the wetlands were healthy. In November of 2005, the National Academies released a report, Drawing Louisiana's New Map: Addressing Land Loss in Coastal Louisiana. In it, the report states that two factors were involved in the flooding of New Orleans, one being the man-made levees and another being a non-native invasive species called Nutria, which grazed on marshland vegetation. The report also states that the 10 canals currently in Louisiana have drowned wetlands and allowed saltwater intrusions into freshwater ecosystems. An older shipping canal was thought to have served as a funnel for Katrina's rage. Researchers are suggesting a rejuvenation of the wetlands and barrier islands to protect against the next hurricane.
Oil is important to the New Orleans economy and so are the wetlands. What are the options to serve both? The first order of business seems to be to fix the levies. Without the levees, right now, New Orleans would be inhabitable. However, as we have seen, just fixing the levees clearly is not the answer. Researchers are talking about replacing the silt to the wetlands in a controlled manner eliminating the need to flood the whole area. Periodic flooding through a control such as a dam could help bring back the wetlands. The new sediments dumped by this method should offset the sinking of New Orleans. If this is done, or at least started, maybe the next hurricane would hiccup on one of the barrier islands and wetlands instead of unleashing its fury on the residents of New Orleans again.
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Tim Fitzpatrick. New Orleans, Hurricane Katrina, and the Oil Industry. EnvironmentalChemistry.com. June 30, 2006. Accessed on-line: 12/12/2013