Preventing Flood Damage
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Stop Sewer Back-Up

In most areas of Louisiana, the sewer system and rain drainage system are separate. It is not unusual, however, for floodwater to infiltrate the sewer system, causing it to back up into homes. These back-ups can occur both inside and outside the identified flood hazard areas and can be caused by things other than floodwater entering the system.

When there is more water outside than inside a building, a floodwall or a levee, water continually tries to get inside. Obvious paths of intrusion are sewer drains for the bathtub and toilet and drainage tubes in floodwalls and levees. Floor drains in some areas of buildings also could provide such a path. Any drain that has its opening (inside the home) below flood level must be blocked. The drains may not be obvious – such as air-conditioning condensate drains – so look carefully.

Using Valves, Plugs, Caps and Seepage Barriers in Flood Protection

The typical home has interior plumbing drains that converge under ground near the house into a single 4-inch sewer line. The simplest, least-expensive way to prevent backflow is with a flap valve installed on the single sewer line; it allows water from the home to flow to the sewer system but closes when water flows backward toward the house. You must provide a means of accessing the valve so it can be cleaned at least semi-annually and if something obstructs the flap.

To provide the best possible protection from a flooded sewer system, the valve should have a good seal and operate automatically. Several valve types are described below. In an emergency, if you have no valve or if the valve fails, try the bag-o-rags technique.

A ball or gate valve that is closed by hand is less likely to fail because debris is preventing its closing, but it won’t stop a backflow unless someone is home to close it. Automated or hydraulically operated backflow valves are considerably more expensive but provide reliable protection at all times. It may be beneficial to combine a flap valve (for automatic closure) with a ball or gate valve that requires manual closure but provides a more-positive seal.

Installing any of these valves in an existing sewer line is equally difficult, since it requires digging up the sewer line. The benefits far outweigh the trouble and cost of preventing unhealthy sewage backflow, however, even if you don’t keep surface floodwater out of the building.

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LSU AgCenter Publication - PDF

Last Updated: 4/27/2014 10:21:00 AM
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