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6.3A Page 23 generally most effective immediately after the levee has been mowed. Animal burrows that are identified should be thoroughly excavated and inspected, backfilled with compacted soil that is similar to material of the levee, and reseeded. This will avoid the possibility of water piping through unfilled portions of the burrows during a flood. D. Cracking It's important to closely monitor and evaluate all visible areas of cracking on a levee, to ensure they don't develop slope stability problems. Cracks in a levee develop when the levee material is saturated with water and when it is overly dry. Clay, like most impervious materials. will shrink as it dries and re-expand when wet. Clay levee surfaces tend to shrink and expand slightly, and some cracks in the surface of the levee are to be expected. Shrinkage cracks are generally narrow and shallow, not extending more than more then a few inches into the levee, but during long periods of drought they may extend as much as two feet into the levee. These cracks can run longitudinally or transverse to the levee or may appear as blocks. If the cracking becomes excessive, it needs to be corrected even if the levee appears to be stable. It's important that you contact the local Corps district office for guidance on how to repair cracks observed in your levee. E. Ruts and Depressions Ruts and other depressions often develop along levees or patrol roads as a result of pedestrian or vehicular traffic, settlement, or because of an inadequate crown slope. Ruts and depressions are a problem because they allow water to pond on the levee crest or access road. If left uncorrected, the ponded water will seep into the levee's interior or into roadway embankment, saturating the foundation material, and making the levee more susceptible to failure during a flood. The levee or access road should be inspected for ruts, pot holes, and areas of standing water after it rains. To correct these problems, the topsoil and sod should be removed and the existing levee surface should be roughened. This is ideally done when the ground is not frozen; if there are ice crystals in the ground then the entire frozen layer should be removed. Loose fill material should be added evenly, in approximately 6 inch layers. Add water or dry the backfill materials as necessary to attain optimal moisture content during compaction. Compact in place by hand or mechanical methods in order to bring the levee back to its original shape. The topsoil should be replaced and the area should be reseeded and mulched for erosion control. F. Seepagel Sand Boils Sand boils and seepage problems are not generally identified during routine inspections because these problems typically only appear under 16 April 2008