Sunday, January 2, 2011
Levees and Agriculture
I grew up under the "protection" of a levee system in Monroe County, IL. My family has lived on the same farm for over 150 years, so you can imagine how much our lives and livelihoods depend on levees. Levees to relieve agricultural flooding date back to before the Civil War. Grant took Vicksburg by marching around the city on the levees on the Arkansas side of t he river. In those days farmers built levees that protected the low lying areas by connecting ridges, so protection was minimal. Groups of farmers formed levee districts and worked on building levees with shovels and tumble scrapers pulled by mules or horses. Everyone was given a number of hours of labor to provide based on their acreage that was protected. The highest river stage in St. Louis in the 19th century was in 1844. In 1927 there was a huge flood on them Mississippi River that changed the course of flood protection and the history f our country. The flood was so devastating in the south that Congress determined that Federal involvement was warranted.
Levees in my home area were federalized in the late 1940's and 1950's as a result of flooding in the 40's. The levee below was built around 1960. During the flood of 1993 this was one of the levees that held. The thing is that just because the levee does not beach, there can still be internal flooding.
During periods of normal river levels, internal water is moved thru the levee in large gated culverts. During "high" water, internal water must be pumped into the river using high capacity pumps such as those located in this pump house. The pumps usually barely keep up with the accumulating water and are very expensive to run.
Seepage is always a problem during floods. It is OK as long as soil ins not carried along with the water. Soil movement can undermine the levee and cause it to fail. Below is a relief well that operates as and artesian well during flooding. It is supposed to reduce the risk of seepage by giving the water a controlled path to follow. Seepage and flowing relief wells at to the internal water that needs to be pumped out. Floods during the growing season almost always lead to some loss of crops even if the levees hold. Prior to 1003, the last time that the levee broke in my home area was 1903. On the one hand, we felt pretty secure behind the big federal levees. On the other hand we always realized the need to maintain them. Most routine maintenance is done by the local levee districts.
Levees help us to maintain our livelihood in the river valleys just as irrigation projects help farmers in the west. The acreage of cropland protected by levees increases as you move south. South of the confluence of the Ohio River, there is an elaborate system of floodways and flood gates that can be used to relieve downstream areas. New Madrid Floodway is a big one. Morganza Spillway and the Bonnet Carré Spillway . While the cost of all this is high, The value of the protection is much higher. Flood protection is not a sure thing. It is just a tool we use to minimize impacts. On the Mississippi, the level of protection is high, so when there is a failure the failure is big. Farmers cannot live without flood protection