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6.3A Page 21 Some earthen materials tend to become saturated with water very easily. When this happens, they loose stability and can't support their own weight. If a stream or river embankment is composed of these materials, the embankment will slump off and move down the slope into the river, causing a bulge at the base of the slope. When river banks break down like this as in Figure 3, they are said to have slope stability problems and need to be repaired. Slope failures can lead to serious problems, especially if the failure occurs near a levee or floodwall. Levees, like riverbanks, are subject to the same soil saturation effects during a flood or period of heavy rainfall. Levees are generally less susceptible to slope stability problems because of the materials they are made of and because of their shallow slopes. However, slope failures have occurred during prolonged periods of high water or heavy rainfall. Figure 4 shows an earthen embankment that failed as floodwaters receded. While slope failures will generally occur on the riverward slope of a levee, be aware that slope failures on landward slopes are also possible. A levee should be carefully inspected for slope stability problems after these events. A related slope failure/ stability problem involves trees growing on or near the levee slopes. It's very important to prevent tree growth near levee embankments, because when the roots of these trees decay they leave voids in the soil, which allow water to quickly saturate the slope and cause a slope failure. Trees can also be uprooted and deflect flood flows into the embankment, accelerating the erosion of the bank. The classic signs of slope stability problems are listed below, and you should watch for these signs during routine inspections. a. Wide deep cracks that parallel the levee crest. These cracks may also extend down the slope of the levee. b. Vertical movement of the material along the crack. Remember that this movement may be very obvious or very subtle if the stability problem is just starting to develop. c. If the slope has slumped or is starting to slump, examine the area along the toe of the embankment. In many cases there will be a noticeable bulge in the slope. Deep seated sliding often requires the removal and replacement of that section of the levee, and the stabilization of the area with a soil or rock berm. If you identify signs of a developing slope stability problem, it is very important that you contact your local US Corps of Engineers (Corps) district office for an investigation and to get technical assistance as to the best way to repair the problem. 14 April 2008