"Both the National Weather Service (NWS) and the emergency management community recognize the importance of flood warning systems (FWS) for protecting lives and livelihoods. Communities across the country have created FWS to warn areas of flood danger, and to provide NWS with critical rainfall, stream level, and other hydrometeorological data. [...] FWS, however, require a high level of ongoing commitment and support beyond one-time installation costs. Those with the most success have proactive, energetic staff members; strong long term operational funding; and a good rapport with the local NWS forecast office. This manual provides guidance for working with local communities who want to develop, implement, and operate FWS. [...] The basic benefit of a local flood warning program is an increased lead time for watches and warnings at locations subject to flood risk. The information can be used to predict whether a flood is about to occur, when it will arrive, and how severe it will be. Organizations and individuals are given notice by the system so they can protect themselves and their property."
National Weather Service, National Oceanic and Atmospheric Administration: http://www.nws.noaa.gov/