Flood walls are architectural structure designed to contain water from lakes, rivers or other waterways in the event that they rise to abnormal levels. Flood walls differ from drainage canals primarily because of how they're used. Flood walls are more common in areas where space is limited or where larger designs may interfere with existing buildings, businesses or other structures. Though very useful, flood walls have limitations and disadvantages.
Flood walls are the preferred choice for narrow areas. Though they may be built to any height, due to cost, aesthetics and several other factors, the height is generally limited to approximately 1.2 m (4 feet). This height may not be sufficient if water levels rise higher that what is expected. After three or four days, water will begin to seep through the structure, meaning a flood wall is not enough for extended periods of flooding. If failure does occur, the resulting damage is the same as if there is no protection.
The design and application of a flood wall must be executed very carefully, as a structure that is poorly or incorrectly designed could have disastrous consequences. Among the most serious consequences is damage to local drainage, which may lead to flooding of other towns or cities. A single flood wall should be used as part of a well-designed flood plan, part of which will include a way to redirect water without causing other problems.
Most modern flood walls are traditionally built using concrete that may or may not also include masonry work. This material is substantial enough to stay strong against heavy water pressure without breaking or being upended. The cost of concrete, particularly in such large amounts, may cause serious strain on a budget. According to Louisiana State University, the cost of building a 1.2 m (4 foot) flood wall as of 1998 was approximately £78 per linear foot. This figure doesn't include the annual cost of maintenance and repairs if necessary.
Evacuation and insurance
In areas where flooding is a fairly regular occurrence, flood walls will not be enough to prevent evacuation. Flood walls are also ineffective at reducing the cost of flood insurance for homeowners in areas prone to flooding. Though helpful, these structures don't always cure flooding problems. One example of this is the flood wall and levee failures of New Orleans, Louisiana, during Hurricane Katrina. This event showed that no matter how prepared, flood walls may not be enough to prevent serious damage, and that regular maintenance and care is an essential part of keeping flood walls operational.