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4, Inform Local Officials Each step is critical in the process of recognizing that a flood threat exists and in determining the magnitude of flooding. This chapter discusses these steps in relation to the basic types of local flood warning systems now in use, Tvpes of Local Flood Warning Svstems There are two basic classifications of local flood warning systems available for community use: manual systems, which are relatively simple and inexpensive, and automated systems, which use state-of-art automated data collection, warning transmission systems, and computers to provide flood forecasts, There are many variations within these two basic types, The basic concept of a local flood warning system is simple. River and rainfall data are collected upstream from a community, Data are then transmitted to a central collection point. This information is used to predict the magnitude of expected flooding, where flooding will occur, and when flooding will begin. Manual local flood forecast systems consist of: (I) a data collection system; (2) a community flash flood coordinator; (3) a simple-to-use flood forecast procedure; and (4) a communication network to distribute warnings to appropriate emergency response officials, including the mass media and the National Weather Service (NWS), The forecast system should be linked to a community response system, Automated local flood warning systems consist of the following components: (I) automated precipitation and river gages; (2) a communication system; (3) automated data collection and processing equipment;(4) data collection and system forecasting software; and (5) a warning distribution system, Automated stream forecasting has developed in the past decade as a result of rapid growth in the application of hydrologic models to computer technology, coupled with decreases in the cost of computers, The evolutionary development of automated systems continues to improve the accuracy, timeliness, and reliability of flood warning capability, Automated flood warning systems are gaining in popularity around the nation, Automated system operation may vary from a simple flash flood alarm that audibly announces imminent flooding, to the continuous computerized analysis of precipitation and streamflow and a hydrologic model to forecast flood levels, Manual Svstems The most common flood warning systems are manual or self-help systems that typically use volunteer observers and inexpensive equipment to collect data. Data transmission is normally by phone, The following table lists the advantages and disadvantages of a manual system, 10