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<br />5. OPERATION OF THE FLOOD WARNI:NG SYSTEM USING AUTOMATED <br />FLOOD DETECTION DEVICES <br /> <br />5.1 General Flood Operation <br />5.1.1 Alarm Operation <br />Flood warning would be provided 'to the City of Wiggins when <br />the water reaches the flood alarm, gage floats, causing them <br />to tip and activate the tape dialer locatE~d in the instrument <br />shelter. The tape dials the phone numbers programmed on it <br />and plays a warning message 1:0 each alarm receiver. The oc- <br />currence of an alarm, as well as th.~ time between the lower <br />and upper float alarms, is importan'l: in estimating how severe <br />the flood will be. <br />All phone numbers are diale,d and messages played, regard- <br />less of whether individual phones ar.~ answered. The tape di- <br />aler will reset after all of the messages have been played. <br />As long as the water level in the s1:illinq well remains above <br />the float, it will not react:ivate. 'rhe alarm will reactivate <br />if the stream stage falls below 'th.~ float level and rises <br />again. <br />5.1.2 Alarm Sequences <br />Due to the design of the Acle,mco 61:2 alarm dialer, 'che lower <br />alarm circuit must be broken in order to enable the upper <br />alarm to activate during a flood. 'rhe middle float switch, <br />which is normally closed when at: rest, breaks the lower cir- <br />cuit as it tips. While the wat,er is above the middle float, <br />only the upper alarm circuit can close. After the 'f/ater re- <br />cedes below the middle float" following the flood crest, the <br />lower alarm circuit will again be cleJsed. This will result <br />in a second low stage alarm after a :Elood crest has passed. <br />5.1.3 Use of a Second Low Stagre Alarm <br />5.1.3.1 When two low stage alarms are received without a <br />high stage alarm, there are 2 possibilitiE~s. One possibility <br />is that the water rose above t:he, middle float, but not up to <br />the high stage alarm and thEm fell belOlf the middle float <br />again. This would result in 2 closures of the lower alarm <br />circuit. <br />The second possibility is 1:hat: the stream level rose above <br />the lower float, fE!ll back below the lower float and then <br />rose again. Only a visual reading of the staff gage would <br />allow the flood coordinator 1:0 determine which condi,tion gen- <br />erated the two successive Imler alarms. <br />5.1.3.2 When a low stage alarm is follOlfed by a high stage <br />alarm and then a second low e:tage alarm, it means that the <br />flood crest has passed the flood alarm gage. In 'that se- <br />quence, the second low stage alarm 'f/ill occur when the flood <br />water falls below the middle float as flooding recedes. <br />Note that the stream could rise again, rapidly, in response <br />to more rain, or flooding from upstr'2am rc~gions, and another <br />high stage alarm may occur. This is the situation that was <br />modeled for the downstream <,age as a result of a basin-wide <br />500-year flood. If another high stac;e alarm occurs after the <br />sequence described above, 1:he st:ream must be watched very <br />closely. The already swollE~n st:ream could rise quickly above <br /> <br />J.8 <br />