A properly built levee takes a lot of space. Its sheer mass keeps it from moving. Long, gentle side slopes increase stability and provide for easier maintenance. A typical levee 3 feet high should be 21 feet wide. If the inner edge is 4 feet from the building, its outer edge will be 25 feet from the building.
Where the property line is too close to allow an adequate levee, a floodwall or other floodproofing technique can be used in combination with a partial levee to provide a complete barrier system.
For a given height of flood protection, a permanent earthen levee is about half the cost of a floodwall and slightly more than a commercial water-inflatable dam.
It is easier to increase your flood protection level with a levee than with other permanent systems. When built with a broad, well-compacted base, levees can be topped with sandbags or water-inflated dams.
To keep the permanent levee at a low or variable height, you may choose to build the system to protect against frequent, low-level floods, but design the base so the levee safely can be topped with temporary barriers for the less frequent, higher floods.
If the depth of flood risk increases in the future, a well-founded levee can be topped with a permanent floodwall or additional earthen material.
Neighbors often view levees as aggravating their own flood situations. Protecting the area right around a building may be less objectionable than excluding water from your entire lot.
Things to Remember
- Levees must be built to withstand the forces of standing water and flowing water. The potential effects of water currents should be analyzed by an engineer.
- Levees may require underground extensions to prevent seepage through the soil, depending on soil type, water depth and flood duration.
- You must provide drainage for rain that falls inside the levee system when it's NOT flooding and when it IS flooding.
- It's very hard to add drains once the levee is built, so make sure the number, size and locations are right before you pile on the dirt.
- A pump is needed inside the protected area. Water can seep under or through the levee, and rain will fall on the inside. You have to pump it out during a flood. Placing the levee closer to the building may reduce your dependence on pumps.
- Levees have natural enemies: burrowing creatures and tree roots. Check your levee each year for signs of tunneling.
- Check with the local building or permit office to see if a permit is required. Some communities review plans to be sure the levee will not interfere with drainage and will not diminish flood storage capacity in violation of local law.
- Avoid damaging underground gas, water and electrical lines or your sewer line during construction. In Louisiana, call 811 (LA One Call) to get help with locating these lines.
- When water goes over the top or breaks a levee, the protected area may fill with water rapidly. Rushing water and debris may come crashing into the building.
- Plan for your safety. Decide in advance when you will abandon a flood fight and save your life.