In early June, 2008 the United States Midwest was hit by a steady string of rainstorms. The precipitation completely saturated the ground and produced record flooding in many parts of Iowa, Illinois, Missouri and other Midwestern states. Flooding was severe enough to exceed 500-year levels in several areas.
The damage caused by the flooding was very high. At least 24 people were killed and nearly 200 injured. Billions of dollars worth of homes and businesses were destroyed. Flooding of spring crops caused billions of lost dollars for Midwest farmers.
Along these flooding rivers many levees were breached and many were overtopped. Although the flooding result is the same in both of these situations they are different types of problems. In the case of a breach an engineered structure failed but in the case of an overtopping the structure was successful but the flood waters exceeded its design height. In both cases people who had homes, farms and businesses behind the levee thought that they were protected but suddenly they were not.
The graph at right is a stage hydrograph from a United States Geological Survey gaging station on the Mississippi River near Hannibal, Missouri. It shows the height of the Mississippi River in feet on the vertical axis and the date on the horizontal axis. Flood level is marked on the hydrograph as a red horizontal line at a gage height of about sixteen feet.
This hydrograph clearly shows the severity and duration of flooding in the Hannibal area. It shows that the Mississippi River reached flood level on the morning of June 4. The river then kept rising for over two full weeks. During that time it reached a gage height of almost thirty feet - a height of nearly fourteen feet above flood stage.
Although the cause of the flooding is different, this type of inundation is just as damaging as what was experienced by New Orleans as a result of Hurricane Katrina.
(www.geology.com)
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