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Slide AS. Flood warning siren This person's first task is to warn people who may be in danger. There are many ways to do this. A siren, as shown here, is often used. A siren is effective if people know what it means and what to do when they hear it. Some communities rely on getting the message out by radio, or they send policemen with bullhorns to vulnerable neighborhoods. Sometimes, emergency responders go door-to-door warning people. Regardless of how the initial warning is delivered, it must be accompanied by information telling people what to expect, when, and what 'actions they need to take. Slide A6. Cross section of floodplain Warnings are not useful unless you have identified the areas subject to flooding- usually low-lying areas adjacent to rivers and streams or other drainage channels. These areas are called floodplains. As shown on this cross section, a floodplain is composed of a channel defined by the banks of a stream; a flood way which carries the bulk of floodwaters, particularly the high velocity floodwaters; and a flood fringe which carries low velocity floodwaters that are not as deep as in the flood way. Slide A7. Terms for flood frequency The 100-year floodplain is the area that would be flooded by the 100-year flood. The 100-year floodplain is a conventional measure of flood vulnerability and is used by FEMA as the basis for requirements in the National Flood Insurance Program. The slide defines a 100-year flood and a 1 % flood. The terms are two ways of saying exactly the same thing. The lOO-year flood is a statistical approximation saying that over many, many centuries such a flood will occur on the average of once every 100 years. It has a 1 % chance of being equaled or exceeded in anyone year. Two points are important: 1) Floods much larger than the l00-year flood can and do occur, and 2) It is possible for a 100-year flood to occur two or three years in a row. It has the same probability of occurring each year. Slide AS. Flood insurance map showing A, B, and C zones FEMA provides flood-prone communities with maps showing the 100-year floodplain. The most commonly used maps are called Flood Insurance Rate Maps or FIRM's. This slide shows a FIRM. Zone A on the map is the 100-year floodplain. The numbers shown in Zone A are elevations above sea level. Zone B is the 500-year floodplain and Zone C is outside the 500-year floodplain. Interestingly, more than 30% of the flood insurance claims have been for damage to properties outside Zone A. Vulnerability to floods does not stop at the 100-year flood line or even the 500-year flood line. The map shows gradations in risk from flooding. Local officials must evaluate the information they receive about the severity of the approaching flood and decide what areas to evacuate. Script-Task A, page 2