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" Swollen by melting snowpack and heavy spring rains, the Mississippi River has overflowed its banks in several states, causing widespread flooding and forcing the evacuation of thousands of residences. Ahead of the deluge, some intrepid homeowners tried to save their houses by building makeshift earthen levees. In a number of fortunate cases, these mounds apparently worked. Jaw-dropping photos have emerged of pockets of dry land ringed by floodwaters, where homemade levees created islands with houses smack in the middle.  Regardless of your home-preservation instincts and DIY spirit, don&amp;#039;t ignore evacuation orders to battle rising floodwaters. But if you know the wall of water is coming and you have materials and a little bit of time, it is possible to erect a resilient earthwork. For a guide to building your own levee, look no further than America&amp;#039;s professional levee builders: the U.S. Army Corps of Engineers (USACE). Many of the best practices that the Corps and other organizations have developed for enormous levees can apply to homeowners looking to protect their personal property. Here&amp;#039;s a step-by-step guide to building an earthen levee that stands a decent chance of holding its own against the force of nature.  1. Gather Your Materials First, the tools: You&amp;#039;ll need gloves, shovels, sand bags, sheets of polyethylene plastic and a wheelbarrow.  In an emergency, you&amp;#039;ll have to build a levee with the dirt beneath your feet. But, Colorado State University engineering professor Neil Grigg says, for the task of floodproofing, not all soil is created equal. If there&amp;#039;s time to be choosy, opt for the finer-grain stuff. Gaps between particles of coarser material, such as gravel, can allow for &amp;quot;piping&amp;quot;\u2014that&amp;#039;s what happens when water seeps through a dam, often to ruinous effect. To avoid this, go with sand or, better yet, clay. &amp;quot;Once clay is compacted tightly, like the kind you would use to fire a fine piece of china... it&amp;#039;s practically impervious,&amp;quot; Grigg says.  2. Site Selection and Prep The levee&amp;#039;s route depends on property lines, topography and terrain. However you lay out your earthen barrier, leave ample space between your home and the levee. That gives you the chance to build it higher and wider if you need to, according to the USACE levee-building guide.  Mark Koenig, emergency manager for the St. Paul District of the USACE, says it&amp;#039;s important to clear the area of topsoil and, if time permits, shrubs and other material. &amp;quot;Strip the ground first so there&amp;#039;s no vegetation where you might create a seepage plain between the ground and the levee you&amp;#039;re building,&amp;quot; he says. Also remove organic debris from the soil you will use for the levee. &amp;quot;You want the soil to be homogenous,&amp;quot; Grigg says. 3. Dig a Trench Don&amp;#039;t just pile up earth on the bare land. First, dig a 1- or 2-foot trench where the levee will go. Fill this trench with your most impervious material, such as clay, to make a small foundation. Griggs says this core will help cut down on underseepage, the flow of water under an earthen levee that can lead to its collapse.  Another good tip to limit groundwater intrusion is to sink a &amp;quot;cutoff wall&amp;quot; several feet into the ground. In commercial construction, concrete walls usually do the trick, but in a hurry you probably don&amp;#039;t have the time or materials for that. Instead, try sinking particle board into the ground as a cutoff wall, and piling up and compacting earth around it. Wood will degrade in the long term, but in the short term it should provide a protective boost to a temporary barrier.  4. Build the Mound Now begin to heap clay, sand, soil or whatever you&amp;#039;ve got onto the line or ring where your levee will stand. Compaction is critical. In a rush, use your feet or hands in lieu of heavy-duty equipment such as a sheepsfoot road roller or a bulldozer (even some back-of-the-shovel thwacks are better than nothing). Compact the levee in layers, not chunks; press down on 6 inches&amp;#039; worth of piled-up earth rather than stomping on a mound several feet high, Grigg says.  Make your levee relatively flat. Steep slopes offer a skinnier buffer for water to penetrate; plus, a sharp angle to your earthworks will lend the flowing waters more of a destructive, erosive assist from gravity. The Corps of Engineers recommends that you lay out the levee about three times as wide as it is high. The top of the levee should be at least several feet wide (if you have room).  Try to build the top of the levee at least a couple of feet higher than floodwater crest estimates so water doesn&amp;#039;t surmount your barrier. That said, be reasonable. If floodwaters are supposed to rise a few feet, you might be able to build a levee that&amp;#039;s a few feet higher than that. But if experts expect an inundation of 20 feet, head for the hills. (Before you go, though, check out PM&amp;#039;s flood evacuation advice.)  5. Cover the Levee If you can, cover the water-facing side of the levee with plastic tarps. When anchored, this layer will provide a key layer of water impermeability, slowing erosion and increasing the levee&amp;#039;s lifetime. For best results, anchor the tarps in front of the levee with sandbags, then roll the sheets up to the levee&amp;#039;s top and secure them there with additional sandbags. If sandbags are at a premium, run rope between sets of two of them on either side of the levee to lash down the plastic. &amp;quot;Make sure there&amp;#039;s counterweighting so the wind doesn&amp;#039;t pick [the poly] up like a big sail,&amp;quot; Koenig says. You can also bury the poly&amp;#039;s edges in front of and on top of the levee, or use rocks as weights.  Overlap successive rolls of plastic by 3 feet or so, laying them from downstream to upstream. That way, the force of moving water won&amp;#039;t catch the tarps&amp;#039; edges, lift up on them and wrench them away. Finally, if you&amp;#039;ve got sandbags left over, stack them on the levee walls to delay the intrusion of insistent waters. 6. Contain Sand Boils If you&amp;#039;re still on-site when the floods come, some maintenance can keep the levee strong. A chief concern: sand boils, which look like bubbling springs on the landward side of your homemade barrier. High floodwaters put pressure on groundwater and can force it under the levee, and this underseepage can attack and weaken the levee&amp;#039;s foundations. If the water flowing out of the ground is clear, that usually means the levee itself is not disintegrating, Grigg says. But should the sand boil be, well, sandy, that means water is carrying away the material. &amp;quot;It&amp;#039;s a danger signal,&amp;quot; Grigg says.  When a sand boil erupts, the best bet is to surround it with sandbags or to build up a mini ring levee around it. That little levee will create a pool, and once it fills up, the weight of the water in the pool will help staunch the flow of the sand boil. &amp;quot;You want to do anything to allow the water to pond up over the boil,&amp;quot; Koenig says. &amp;quot;You&amp;#039;re trying to equalize pressure on the boil inside [the levee] with the water pressure from the other side.&amp;quot; What you don&amp;#039;t want to do is just dump material over the boil itself to try to plug the leak. Water is too crafty for that; it will seek the path of least resistance and start a boil elsewhere that could undermine the levee. George Riedel, deputy executive director of the Association of State Floodplain Managers, says that even the best-built levee may not hold up to the emergency at hand, and there will always be a bigger flood. &amp;quot;Levees are one tool in the toolbox for fighting floods,&amp;quot; he says. &amp;quot;But to my mind they come in two varieties: ones that have failed or been breached, and ones that will fail or be breached.&amp;quot; And as Led Zeppelin famously said, &amp;quot;When the levee breaks, mama, you got to move.&amp;quot; "^^<http://www.w3.org/2001/XMLSchema#string>
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