What are levees?
Rivers naturally prone to peak flood flows during spring runoff develop natural overflow levees, deposited when the low flow channel overtops its channel (see Figure 1). Natural flow levees are typically comprised of more coarse grained sediment, like sand, while the flood plain (Figure 2) is usually covered in extremely fine silt. 75% of all the sediment deposited upon the continent is overbank silt, deposited upon well-defined flood plains. Unfortunately, we have concentrated much of our societal infrastructure upon these flood plains, and have thereby placed such property in peril anytime the rivers begin to reach flood stage. In their natural state rivers tend to flow onto their respective flood plains during peak runoff periods, generally during the late spring months in North America. However, sustained precipitation can cause flooding throughout the summer, depending on antecedent soil moisture levels. During the Lower Missouri River Flood of 1993 the river remained at flood sta
