In some flood prone areas, flooding can cause sewage from sanitary sewer lines to back up through drain pipes. These backups not only cause damage that is difficult to repair but also create health hazards.
A good way to protect your property from sewage backups is to install backflow valves which are designed to block drain pipes temporarily and prevent return flow. Backflow valves are available in a variety of designs that range from the simple to the complex. The figure shows a gate valve, one of the more complex designs. It provides a strong seal, but must be operated by hand. The effectiveness of a gate valve will depend on how much warning you have of impending flooding.
Among the simpler valves are flap or check valves which open to allow flow out of the structure but close when the flow reverses. These check valves operate automatically but do not provide as strong a seal as a gate valve.
Benefits of Using This Mitigation Strategy
Keep these points in mind if you have backflow valves installed:
Having a plumber or contractor install one backflow valve will cost approximately $1,400 for a combined gate/flap valve or about $600 for a flap valve. These figures include the cost of excavation and backfilling.
Technical Information Provided by FEMA