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<br />tie in closely ~ith the local flood response plan. <br /> <br />The potential ~arning time -- the time bet~een the first measurement of <br /> <br />rainfall and the first occurrence of flooding -- may vary from minutes to <br /> <br />~eeks, depending on the ~atershed. The actual ~arning time is less than the <br /> <br />potential ~arning time because of the time required to recognize that a flood <br /> <br />threat exists and to issue a ~arning. The potential ~arning time (TWp) is <br /> <br />equal to the sum of the time required for rainfall to accumulate in rain gages <br /> <br />before the system ~i11 recognize that a flood ~i11 occur (Tr) and the actual <br /> <br />~arning time (TW). The primary objective of a local flood ~arning system is <br />to increase the actual ~arning time until it is as close as possible to the <br /> <br />potential ~arning time. <br /> <br />Other hydrologic characteristics that help define the nature of the flood <br /> <br />threat are the rate-of-rise and the length of time the flood waters remain <br /> <br />above flood stage (Ts). <br /> <br />. <br /> <br />B.Z. Frequency of Flooding <br /> <br />, <br /> <br />An important factor in evaluating the potential benefits of a local ~arning <br /> <br />system is the likelihood or frequency of a damaging flood. The key questions <br />are: What are the potential damages, including loss of life, at various flood <br /> <br /> <br />levels? What is the likelihood that such a flood ~i11 occur? The benefits of <br /> <br /> <br />a flood ~arning system increase as the likelihood of damaging floods <br /> <br /> <br />increases. Also, the likelihood that a system's effectiveness will be <br /> <br />maintained increases with the frequency of its use. The rarer a flood event <br /> <br />~ith damaging potential, the more difficult it is to maintain community <br /> <br />13 <br />