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<br />4. A levee to be built with relatively permeable soil can be improved <br />by building an impermeable core. The core could be compacted im- <br />pervious soil, a sheet pile wall, or a concrete wall (see illustra- <br />tion). Such cores could be tied to an impervious layer to prevent <br />seepage through the underlying soil. <br /> <br /> <br /> <br />t!.!.....~1 <br /> <br />~Ri .. <br /> <br />Levee with impervious core. <br /> <br />Shallow levee built up to flower <br />boxes in front of house provides <br />a more pleasing appearance. <br /> <br />5. The sod and topsoil should be removed and saved for covering the <br />final surfaces. Special measures should be taken if a levee is <br />tied in to a floodproof wall to ensure that there will be no seepage <br />at the joint. <br /> <br />6. A levee is built up in layers. Each layer is no more than 9 inches <br />thick before compaction (less if you are compacting by hand). If <br />you will be using both pervious and impervious soils, put the im- <br />pervious soils on the flood side. <br /> <br />Floodwalls: A floodwall has two advantages over a levee: it takes less <br />space and it is impermeable. It also has two disadvantages: it is <br />typically more expensive and it is harder to blend in with the natural <br />landscape. A floodwall can be "camouflaged" with a brick face,for <br />example, and give the homeowner a privacy fence (don't use a facing <br />that would be damaged by floodwater). <br /> <br />The lateral pressure of standing water increases greatly for every foot <br />of depth. A watertight brick or block wall may not withstand this <br />pressure at a depth of over two feet. There are two ways to build a <br />floodwall strong enough to withstand the pressures of deeper (higher) <br />flood waters: <br /> <br />4 <br />