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1: \ f t , ~'i ~-. Floodwalls of reinforced concrete take little space and are often suitable for use in heavily developed areas. However, they are costly and often block views. This wall prevented flooding in Sunbury, Pennsylvania, when Tropical Storm Agnes struck in 1972. lying areas behind the protective walls by blocked drainage usually requires equipping the structures with a pumping . system or other provisions for getting rid of unwanted water. Areas behind a wall or levee may need to be set aside for storing drainage until it can be pumped or discharged through or over the wall. Levees and walls can't be used in as many ways as reservoirs. However, they can sometimes be used as roads or paths for access to riverfront or beach areas, fishing sites, and boat launching lanes. They may also be used as trails and even road. rights-of -way for recreational purposes. A different type of wall, called a "jetty" or "groin" is sometimes used in coastal areas. Their purpose is usually to break the force of waves or control erosion. However, they disrupt natural processes and sometimes have unanticipated adverse effects. . Levee, f1oodwall, landfill or other constriction --l--~==~T==::~"''''' ~ "t---~-----T------- Flood ... I'" Bou~dary FI?od Boundary, _ Stream Channel _ Downstream With Without Constriction Flood Boundary Constriction 1 pIP'" .. ...."""'........""'''"'~..._- 1 1 ------ --------~ ------ ------- // -- -- ------- r. " A bottleneck in a stream which causes or aggravates upstream flooding may be created by a narrow bridge opening, levees or flood walls too close to the channel, or by other constrictions. 33 ~;