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May 2008: Flood Mitigation

We occasionally see on TV news where buildings are inundated or submerged in flood water after heavy rain, typhoons or hurricanes. Many people believe it never happens to their own buildings. But is that really true? If you have any doubts, you should check to see if your site has been subject to such events in the past, or if it is potentially exposed.

In the U.S., you can obtain this information through Flood Insurance Rate Maps on the FEMA website ( In the other countries, similar flood maps may be available prepared by local authorities. Unfortunately, however, such information is not generally available in many developing countries, where it is most needed.

You may not be able to trust old flood maps, especially where the areas have been developed drastically since the effective date. The ability to absorb water may have been reduced significantly where the soil has been paved.

If maps are not readily available, you should try to find the following information which is typically used in the insurance industry to determine the severity of flood exposure.

For construction projects, such information is gathered in advance for the purpose of evaluating a site.

If flooding is possible for your site, you should find out what the finished floor elevations are for important buildings or structures. You can then determine to what elevations the floodwaters are expected. Based on the potential damage to the buildings that you identify, you should consider, but not be limited to, the following permanent physical flood protection measures.

While a "flood" is usually defined as a large volume of water such as a rain-swollen river or lake overflowing, heavy rain events alone can cause similar damage in well developed downtown areas where no river or lake exists. Due to poor, old or inadequately designed public sewer systems, rainwater can enter basements and ground floors where important utility equipment is located. Transformers, switchgears, power control rooms, boilers or fire pumps are often seen in basement floors where real estate and occupancies are expensive. The same considerations as stated above should be given in such cases.

Risk Logic can help in determining the potential flood hazard that may exist to a building and its operations.

"Fixing levees isn't easy or cheap," USA Today - Friday, February 2, 2007