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IT RAINED FORTY DAYS AND FORTY NIGHTS

You answer the phone and you listen to a hysterical voice on the other end describe how the water was pouring in from everywhere and swirling all around their basement. If you didn't know better you would think that the voice was describing the vents leading up to the launching of Noah's ark. Whether it's a rare or common occurrence, basement flooding is a distress not only to the homeowner but the insurance adjuster as well. To help shed some encouraging light on the matter, here are some of the common sources of basement flooding:

A high water table or a home erected near the bottom of a valley is the most common source of frequent flooding problems. Whether it is the run-off from a storm or the spring waters from melting snow, these two sources are assured to produce recurring nightmares. Common sense dictates that a house built on high ground has less of a chance of receiving flood waters than one built on low ground.

In adequate run-off design refers to both overland water run-off and sewer run-off. In areas with a low building or road density, a large majority of the rainfall enters the soil while the remainder flows over the surface into streams, rivers, and reservoirs. However, in built up areas, the water which would have normally entered the soil must make its way into a storm sewer system through a network of catch basins, gates, pipes, and holding reservoirs. The amount of water run-off in some developed areas may be as much as ten-fold, compared to the area's undeveloped state. Sewer systems are generally designed to handle a certain duration storm that has a chance of occurring once every 25 or 30 years arrives, and seems to return with greater frequency. This then becomes an issue for both liability and risk analysis.

Poor landscaping and settlement problems in the vacinity of a house may allow water to accumulate in areas adjacent to a building. This water can penetrate into a basement or crawl space if it is not diverted away from the building. However, for water to enter the basement, poor construction or design may also be a contributing factor.

Directing rain run-off to city sewers through the basement drain system, as found in some older homes, can back up during heavy rainfalls. A network of pipes carrying run-off from the downspouts and converging at the basement is now considered an unacceptable practice.

The absence of a back-flow value in the pipe leading from the basement to the city sewer permits water (and other debris) to enter the basement in the event of a sewer backup. A back-flow valve will allow water to flow from the basement to the sewer but shuts off when back pressure develops in the sewer system.

A rather simple and systematic approach can be developed to determine the source of any basement flood. This knowledge will provide relief when others are in search of building plans for an ark.

 
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Walters Forensic Engineering | 277 Wellington Street West, Suite 800 | Toronto, ON M5V 3H2
Information contact: engineering@waltersforensic.com