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and levees may require local, state and/or Federal permits. These permits are generally needed to protect other properties from any adverse impacts, to avoid filling in wetlands, and to maintain regulatory floodways. Therefore, the need for such permits should be investigated early in the planning process to avoid last minute delays, redesign of the protection, or changing to an alternate flood proofmg measure. While it is possible to design floodwalls and levees for large flood forces associated with major flood protection projects, flood proofing measures are generally restricted to a height of six feet or less. This restriction is usually necessary because of limited space, cost, visual concerns, and less complex design analysis. The most important consideration of all is that the property owners who have constructed a flood wall or levee should not have a false sense of security about their property protection. Every flood is different, and the one that exceeds the design height and overtops the floodwall or levee can happen at anytime. For this reason, the protected area should always be evacuated prior to flooding. If a floodwall or levee fails due to overtopping, damage to the protected structure will be as great or greater than if no protection was provided. Additional damage could result because it takes longer to remove the flood water from the inside of the flood wall or levee once flood levels subside. Levees Typically, levees are constructed of compacted fill taken from locally available impervious soils. Depending upon the availability of suitable local soil, levees may be one of the least expensive of all flood proofing measures. Levees are usually built parallel to the river and extend to high ground when it is available. Levees have the advantage of being compatible with the landscape since they are easy to shape. The property owner can plant grass and other forms of light vegetation on an earthen levee to help prevent erosion and provide aesthetic enhancement. Impervious earth can also be constructed against a building in lieu of a free standing levee and pleasingly landscaped. This could be considered a dry flood proofing technique. Although levees may be attractive in terms of economics and appearance, they have a number of distinct drawbacks that may make them impractical for many property owners. One potential problem is that levees can impede the natural flow of water in a flood plain, possibly resulting in increased flooding of adjacent property. Similarly, they can also block the natural drainage from surrounding property. Another major drawback is that levees take up a great deal of property space. To minimize erosion and to provide adequate stability, their embankment slopes must be fairly gentle, usually a ratio of one vertical to two or three horizontal. Because of this. a levee's width will be several times its height. An important factor in determining the feasibility of a levee involves the availability of suitable fill material for the levee, as well as the adequacy of the underlying soil that must support the levee. Most types of soils are suitable for constructing levees. The exceptions are very wet, fine grained, or highly organic soils. The best soils are those which have a high clay content, and are therefore highly impervi- ous. Impervious soils minimize seepage problems either through or under the levee system. In those cases where suitable fill material is not locally available, the expense of transporting proper material to the site can be significant. This additional cost could be a major factor in determining the feasibility of this option. While all levee slopes should have vegetation, one way to further protect a levee from erosion is to armor the vulnerable areas with resistant material such as stone riprap. 10 8