How to build a homemade levee (© Scott Olson/Getty Images)

A levee protects a home surrounded by floodwaters near Vicksburg, Miss., in May. // © Scott Olson/Getty Images

Swollen by melting snowpack and heavy spring rains, the Mississippi River overflowed its banks in several states in May, causing widespread flooding and forcing the evacuation of thousands of residences. In June, floods in Minot, N.D., also hit thousands of homes.

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. (Bing Cube: View more photos of homemade levees)

Regardless of your home-preservation instincts and DIY spirit, don'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's professional levee builders: the U.S. Army Corps of Engineers. Many of the best practices that the USACE and other organizations have developed for enormous levees can apply to homeowners looking to protect their personal property. Here'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.

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1. Gather your materials
First, the tools: You'll need gloves, shovels, sand bags, sheets of polyethylene plastic and a wheelbarrow.

In an emergency, you'll have to build a levee with the dirt beneath your feet. But, Colorado State University engineering professor Neil Grigg says, not all soil is created equal for the task of floodproofing. If there's time to be choosy, opt for the finer-grain stuff. Gaps between particles of coarser material, such as gravel, can allow for "piping" — that's what happens when water seeps through a dam, often to ruinous effect. To avoid this, go with sand or, better yet, clay.

"Once clay is compacted tightly, like the kind you would use to fire a fine piece of china ... it's practically impervious," Grigg says.

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2. Site selection and prep
The levee'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 needed, according to the USACE levee-building guide.

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Mark Koenig, emergency manager for the St. Paul (Minn.) District of the USACE, says it's important to clear the area of topsoil and, if time permits, shrubs and other material.

"Strip the ground first so there's no vegetation where you might create a seepage plain between the ground and the levee you're building," he says.

Also remove organic debris from the soil you will use for the levee. "You want the soil to be homogenous," Grigg says.

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3. Dig a trench
Don'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 "cutoff wall" several feet into the ground. In commercial construction, concrete walls usually do the trick, but in a hurry you probably don'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.

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4. Build the mound
Now begin to heap clay, sand, soil or whatever you'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 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' 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 USACE 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't surmount your barrier. That said, be reasonable. If floodwaters are supposed to rise a few feet, you could build a levee that's a few feet higher than that. But if experts expect an inundation of 20 feet, head for the hills.

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