APPENDIX C: MITIGATION ALTERNATIVES
Threat Recognition The first step in responding to a flood is to know when weather conditions are such that an event could occur. With a proper and timely threat recognition system, adequate warnings can be disseminated. The National Weather Service (NWS) is the prime agency for detecting meteorological threats. Severe weather warnings are transmitted through NOAA's Weather Radio System. Local emergency managers can then provide more site-specific and timely recognition after the Weather Service issues a watch or a warning. A flood threat recognition system predicts the time and height of a flood crest. This can be done by measuring rainfall, soil moisture, and stream flows upstream of the community and calculating the subsequent flood levels. On smaller rivers and streams, locally established rainfall and river gauges are needed to establish a flood threat recognition system. The NWS may issue a "flash flood watch." This is issued to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area, but the occurrence is neither certain nor imminent. These events are so localized and so rapid that a "flash flood warning" may not be issued, especially if no remote threat recognition equipment is available. In the absence of a gauging system on small streams, the best threat recognition system is to have local personnel monitor rainfall and stream conditions. While specific flood crests and times will not be predicted, this approach will provide advance notice of potential local or flash flooding. Warning The next step in emergency response following threat recognition is to notify the public and staff of other agencies and critical facilities. More people can implement protection measures if warnings are early and include specific detail. The NWS issues notices to the public using two levels of notification: • Watch: conditions are right for flooding, thunderstorms, tornadoes or winter storms. • Warning: a flood, tornado, etc., has started or been observed. A more specific warning may be disseminated by the community in a variety of ways. The following are the more common methods: • CodeRED countywide mass telephone emergency communication system • Commercial or public radio or TV stations • The Weather Channel • Cable TV emergency news inserts • Telephone trees/mass telephone notification • NOAA Weather Radio • Tone activated receivers in key facilities • Outdoor warning sirens • Sirens on public safety vehicles • Door-to-door contact • Mobile public address systems • Email notifications Just as important as issuing a warning is telling people what to do in case of an emergency. A warning program should include a public information component.
Wake County Multi-Jurisdictional Hazard Mitigation Plan 2019
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