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<br />flood stage at a much faster rat:e than indicated by 'l'able 3. <br /> <br />5.2 Flood warning Procedure <br />5.2.1 Discussion of the use of' flood warning times <br />5.2.1.1 Use of Alarms - Tables 3, 5 and 6 are provided to <br />give the flood coordinator a qeneral idea of the flood warn- <br />ing time available fell' floods of differen1: sizes. '1'he times <br />given in the tables are estimates. '1'hey l~ere developed using <br />a hydrologic model of the bas-in and' rain storms developed <br />from National Weather Service rainfall probability charts. <br />Heavy rain over the entirE~ .ratershed was assumed in their <br />derivation. <br />During a basin-wide storm, serious flooding at Wiggins <br />could be expected any time "the lower and upper alarms occur <br />within 20 minutes of each other ai: the HicJhway 52 (upstream) <br />alarm gage and within 6 hours of each other at the County <br />road gage (do1.mstream). Once both floa'!: alarms; have been <br />tripped within that time guid"E~l:Lne, water may reach the town <br />within 6 to 8 hours of the upper float alarm from the up- <br />stream gage and from 1 to 3 helurs from the receipt of the up- <br />per float alarm from the dow:nstream gage. Less warning time <br />may be available if the str-eam was already swollen before <br />more rain set Ciff the upper float alarm. <br />5.2.1.2 Use of' Volunteer Observers - Additional lead time <br />can be obtained by having local volunteers read the staff <br />gage and report the rate of rise following the lower stage <br />alarm, or by calling people living upstream to gE~t reports on <br />rainfall and st:ream rise. '1'he volunteer observers that have <br />been helping Wiggins detect floods in upstream portions of <br />the basin Sh01;lld be encoura'Jed to continue their important <br />work. <br />The model used t:o derive 'the flood warning times assumed a <br />heavy rainstorm centered over and covering the entire basin. <br />Sharp rises and flood alarms could result from an extremely <br />heavy rainfall over a smaller porti.on of the basin. Although <br />the rise time in one pal:t of the basin may match that of a <br />lOa-year flood, t:he runoff volume may be small enough that a <br />damaging flood would not actually occur at Wiggins. <br />By encouraging the existing network of volunteer observers, <br />the city flood coordinator would be, able to distinguish be- <br />tween isolated intense storms and widespread flooding, as <br />well as gain additional warning t.ime during an actual flood <br />emergency. Also, valuable information can be obtained by <br />contacting the National Weather Service and obtaining <br />radar-based rainfall forecasts, once the lower float alarm <br />has sounded. <br />5.2.2 Cooperation with the National Weather Se:rvic:e The <br />National Weather Service has agreed to provide current <br />radar-based rainfall forecasts in exchange for a report of <br />flooding at thE~ systems that are already operational. It is <br />likely that a similar arrangement can be made wi'!:h the Limon, <br />Colorado office of the National Weat:her Service. <br />5.2.3 Response to flood warning .- Along with other informa- <br />tion obtained by volunteers, the flood warning gages can be <br /> <br />19 <br />