The Mississippi River has recently been in the spotlight because of Katrina, but it has always held a great importance in our country.  At 3,705 kilometers from its source to where it empties into the Gulf of Mexico, The Mississippi River is the third longest river in the world, draining about 40% of the United States.  As a result, it has been incredibly useful over history for the trade purposes of bringing goods upstream.  However, the trade advantages of the river have also caused it to be a popular site for settlement, and trade vessels prefer a more navigable river.  Humans have been building structures to control and restrict the river for many years, in the process creating a Mississippi River that is easier to navigate and areas along it that are relatively protected from floods by levees.  The Lower Mississippi today (south of Cairo, Illinois) has been greatly changed by human interaction.  This regulation has been primarily an attempt to control flooding, which has occurred many times since 1844, its greatest flood on record.  The Lower Mississippi has not been dammed, but extensive levee systems have existed since the river’s first levees were built in 1727.  Today the levees total at around 2700 km in length, along both sides of the river.  As a result, the floodplain area has been restricted by about 90% (Mississippi).

Currently, the Mississippi presents some threats to New Orleans and its surroundings, in part as a result of past attempts to control it.  Levees have prevented the river from its natural changing of course, and the result is that its lobe in the delta has extended so far that the river’s sediment is dumped over the edge of the continental shelf.  If the river could change its course, it would deposit sediment in the wetlands that surround the coast around New Orleans.  Many studies agree that the loss of this natural deposition is the cause of the huge decline in the wetlands that we see today.  Indeed, the wetlands around Mississippi are losing 24 square miles of wetlands each year (Neary, 2006).  This loss deprives New Orleans of an important buffer against hurricane damage and storm surge.

Another pressing issue with the Mississippi is the height of its bed.  Already the river is maintained at a much higher altitude than the city of New Orleans, thanks to the levees that restrict its course.  Medium and coarse sand is entering the river much faster than it is naturally being removed, also a result of the levees—the floodplain is restricted such that much sediment that would be dispersed there cannot be.  If current rates of net influx of sediment continue, the river bed will rise 16 feet in the next 100 years (Julien, 2002). Additionally, the rest of the New Orleans area is subsiding, due to the motion of a fault line.

Army Corps of Engineers structures, especially levees and spillways including the Bonnet Carre spillway (about 30 miles north of New Orleans, this flows, when open, into Lake Pontchartrain), have significantly reduced flooding in New Orleans since the construction of the Bonnet Carre spillway following the flood of 1927.  The Bonnet Carre spillway is opened when the flow in New Orleans approaches 1.25 million cubic feet per second; it has been opened seven times between the flood of 1937 and, most recently, 1997 (Bonnet Carre Spillway). During that time, flood crests may be compared in sites upriver of the (S Bonnet Carre spillway (such as Reserve and Donaldsonville) to those downstream in New Orleans; New Orleans has experienced a significant drop in peak flood stages since pre-1927 days, while Reserve and Donaldsonville (further-reaching historical data is available for Donaldsonville) have remained much more consistent.  This data indicates that Army Corps structures have been effective in protecting the city from Mississippi River based floods; since peak hurricane and peak flow seasons do not coincide, the chances of having a storm surge through Lake Pontchartrain as well as the spillway open at the same time are almost negligible.  In the short term, the chances of a major Mississippi River flood are extremely small; however, we still must admit the risk of an extremely large flood that can overwhelm both the spillway and the levees (Advanced Hydrologic Prediction Service).