Floodwalls

Patricia Skinner, Baker, Eugene  |  3/16/2005 12:33:31 AM

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A floodwall is a self-supporting barrier to floodwater. It may look like a garden wall or privacy fence, but it has more internal reinforcing and a more substantial foundation. This heavier construction keeps the wall from tipping or sliding. The foundation also blocks seepage of water under the wall.

A floodwall does more than keep the building dry. It protects the building from unequal pressure on its walls and erosion (or scour) at its foundation. It also protects the building from damage from floating debris.

Wood, cement blocks, bricks or poured concrete can be used. Use structural and waterproofing materials that will not be damaged by termites, wildlife or pets.

Considerations

The typical floodwall 4-foot high will cost about twice as much as a permanent levee of the same height.The floodwall, however, will take less ground surface area while requiring more, deeper excavation.

It is difficult to justify a private floodwall taller than 4 feet. For many homes, it is less expensive to raise the building 5 feet than to construct a reliable floodwall that tall.

Neighbors often view floodwalls and 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. Placing the wall close to the building also will reduce construction costs and your dependence on pumps.

Fail Safe Design

Your floodwall should be designed to allow water to come over the top before the wall is broken by the unbalanced pressure created by standing water. If a floodwall fails suddenly, the water and parts of the wall may come crashing into your building.

Never add to the height of a floodwall without making sure the foundation can handle the extra load.

A system with well-maintained automatic closures and pumps will provide protection when no one is home.

Openings in a floodwall need closures that are as strong as the wall, watertight and easy to install quickly in a flood threat.

Tips

  • Floodwalls must be built strong enough, above and below ground, to withstand the force of standing water. Have an engineer analyze the design to make sure it can handle the stress of potential water current.
  • Before you dig, find out where water, gas, electrical and phone lines are. Ask your utility providers to mark these lines for you. Also locate and avoid cutting your sewer line.
  • Rain that falls inside the wall needs a way to get out when it's NOT flooding (through drains) and when it IS flooding and the drains are plugged (using pumps).
  • Test the closure and pump systems annually.
  • Floodwalls have natural enemies: burrowing creatures and tree roots. Check your floodwall each year for cracks and signs of tunneling.
  • A floodwall may require a building permit and may fall under height and set-back limitations of a fence ordinance. Check with the local building or permit office.
  • Some communities review plans to be sure the floodwall will not interfere with drainage and will not diminish flood storage capacity in violation of local law.
  • Plan for your safety in a flood. Decide ahead of time when you'll abandon a flood fight and save your life.
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