In this blog post, I wanted to express some thoughts on the flood that is presently moving south along the Mississippi River. I grew up in Vicksburg, Mississippi, where some of the worst flooding has been observed, and my father was a civil engineer for the U.S. Army Corps of Engineers (USACE) Vicksburg District. I retired from the USACE Research Center in Vicksburg.
One thing that is very obvious when looking at the current situation is that the flood control system that was designed and built following the Great Flood of 1927 is working as intended. In addition to the levees that the USACE built, floodways and spillways were also constructed and have been integral to the successful operation of the flood control system.
The levees have been built along the Mississippi to protect as much rural area and as many cities as possible. The levees are not small structures. In some places, they measure 120 feet across at the base and 30 to 40 feet high. Once the USACE builds the levees, the maintenance of the levees is turned over to local levee boards. Most of these levee boards take this responsibility seriously and are very active in maintenance programs. However, when a flood occurs, there might be problem areas along the levee system. After each flood, problem areas are identified, and the USACE comes in to correct them. For example, the height of the levee may be raised following a flood. I know this occurred in several places after the 1973 flood. There will be remedial actions following this flood as well.
The spillways, such as the Bonnet Carre, were designed to relieve the pressure of floods on downstream levees. The Bonnet Carre was developed to relieve the flood pressure on the levees south of it (mainly the levees around the New Orleans area).
Floodways are large areas that have been designated to be flooded when required. Two of the major floodways in the flood control system have been activated during this flood. One is the New Madrid Floodway and the other is the Morganza Floodway. These floodways were developed to offer protection to urban areas in the area – New Madrid to protect the city of Cairo, Illinois, and Morganza to protect the lower Mississippi, including the major cities of Baton Rouge and New Orleans, Louisiana. These floodways have been designated for a long time, and supporting infrastructure has been developed. These floodways have levees along the side of the floodway to limit the flood water to the floodway. People living within a floodway must realize that, at some point, they will be flooded. As a result, they usually cannot get flood insurance; this should be a warning sign that building a house or installing a trailer is not a good idea.
The majority of the flooding in the Vicksburg area is happening in areas that are between the levees and the river, and backwater flooding is taking place in the delta.
Backwater flooding occurs when the rivers and streams within an area can no longer drain because of the height of the water in the Mississippi. As a result, the water begins to spread out in the countryside.
All in all, I believe the flood control system is working and the amount of flooding has been greatly reduced as a result of this system.
Author: Phillip Doiron, Homeland Security Specialist