As bays are slowly opened at the head of the Morganza Floodway to manage Mississippi River flows, Louisiana residents in the Floodway are retreating from the rising floodwaters, like those in the Birds Point Floodway evacuated prior to the controlled demolition of levees in Southeast Missouri. This raises the question: Why are we causing flooding as a response to flooding? As so many questions do regarding the Mississippi River, we have to go back to decisions made after the 1927 Mississippi flood.After the ’27 flood, the Mississippi River and Tributaries (MR&T) project was developed by the Corps’ Mississippi River Commission. In essence the MR&T was designed to manage a “project flood,” which is a combination of storms from 1937, 1938, and 1950. The project flood is about 25% greater than the 1927 flood.Obviously the project flood is a lot of water, and so the MR&T project sought to control and manage this water. This was accomplished through mainly three methods: levees, river channelization, and floodways.LeveesThe core of the MR&T is obviously levees: there are 3,787 miles of levees and floodwalls in the system, the majority of which are along the mainstem of the Mississippi River, while the rest are along other parts of systems, such as the guide levees for the floodways. When the levees reach flood stage, we must rely on the floodways. But before that, we will briefly look at the second method.River ChannelizationBetween 1932 and 1942, a decision was made to dredge and channelize the Mississippi River between Cairo, IL and the Old River Control Structure in Louisiana. The idea behind this seemed to be two-fold. One was based on 19th century thinking in that the main goal was to move water as fast possible by dredging the River and taking out several bends in the river allowed the water to move faster. The second was a result of the faster moving water it carved out a deeper and wider channel that could accommodate a higher volume of water.FloodwaysWhen levees reach their maximum capacity, the third component of the MR&T comes into use: the floodways. There was quite a bit of politics and several lawsuits that went in to designating the floodways, but in the end the MR&T contains four. From north to south they are:1. The Birds Point-New Madrid Floodway (utilized this year, as well as in 1937)2. The Morganza Floodway (just opened on as well as 1973)3. The West Atchafalaya Floodway (never utilized)4. The Bonnet Carré Floodway (utilized this year, as well as 1937, 1945, 1950, 1973, 1975, 1979, 1983, 1997, and 2008)The idea of these floodways was to store and divert Mississippi flood water into farm land and open water. Because these areas were designated as official floodways and part of the MR&T, the federal government had to secure proper flowage rights and easements.Because of the legacy of the 1927 floods, and the walling-off of the Mississippi River, we end up in the position of flooding areas to prevent flooding. This is not a situation anybody wants to be in, especially folks that are in the direct path of the Morganza Flooday. For the short term, we need to make sure that everyone gets out of harm’s way. Once the floods recede, it’s time that we re-think about how we “manage” the river. For more information, check out these four information papers released by the Corps. They are a bit biased towards the Corps’ view of their engineering prowess, but definitely worth a read if you are interested in the MR&T.The Mississippi River & Tributaries Project: Controlling the Project Flood The Mississippi River & Tributaries Project: Floodways The Mississippi River & Tributaries Project: Designing the Project Flood The Mississippi River & Tributaries Project: Birds Point-New Madrid Floodway Matt is GRN’s Science and Water Policy Director.
