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<br />c. Selection of a Local Flood Warnin~ System (LFWS) <br /> <br />Selection of the type of local flood warning system most appropriate for a <br /> <br />particular community should be based on an evaluation of the hydrologic <br /> <br />characteristics of the watershed, the frequency of damaging floods, the <br /> <br />warning time vs. benefits, the need for other hydrologic capabilities, and the <br /> <br />cost of the system. Automated flood warning systems cost more but can provide <br /> <br />greater benefits, including the ability to meet other hydrologic forecast <br />needs. Manual systems are inexpensive but limited in their capabilities. <br /> <br />. <br /> <br />In the selection process, the accuracy, warning lead time, and reliability <br /> <br />requirements should be determined. Accuracy and reliability affect the <br />credibility of warnings and the extent of actions that can be taken in <br /> <br />response to them. The costs of flood response actions must be balanced <br /> <br />against the accuracy of the warnings and confidence in the local flood warning <br /> <br />performance. <br /> <br />Accuracy varies according to the type of warning system selected, the quantity <br /> <br /> <br />and quality of the data input to the warning system, the hydrologic procedure <br /> <br /> <br />or hydrologic model used and the hydrologic characteristics of the watershed. <br /> <br />. <br /> <br />The reliability of the local flood warning system is another important <br />factor. Electrical and telephone service is disrupted during moderate or <br /> <br />severe floods. Power disruption or the failure of gages or other elements may <br /> <br />limit the usefulness of a system, So care must be exercised in selecting the <br /> <br />components. The planning must also include consideration of a backup <br /> <br />operation. <br /> <br />20 <br />