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<br />the upstream l:lood warning gi~ge sit.e at Highway 52 is shown <br />in Figure 2 and the rating curve for the downstrE~am gage site <br />at the County Road crossing is shown in Figure 3. <br /> <br />2.2 Travel TiDles <br />Travel times felr the reach from Highway 52 downstream to the <br />Burlington Northern Railroad (BNRR) Bridge at Wiggins were <br />prepared usin9 the HEC-2 mod,al and cross section data taken <br />from USGS 7 1/2 minute Quadrangle maps. These 1:ravel times <br />were computed for a constan"t discharge and can not be di- <br />rectly transla1:ed to flood warning t.imes. Flood warning time <br />includes flood hydrograph b,ahavior at both of the warning <br />gages and at the town, as well as travel time. Travel times <br />for constant discharges of 2,000 cfs and the 10,50,100 and <br />500-year magni1:ude are presen-ted in Table 1. <br /> <br />TABLE 1. <br />TRAVE]~ TIME FOR SELECTED DISCHARGES IN HOURS <br />(Constant Equilibrium Flow) <br /> <br />2,000* <br /> <br /> REACH <br />Hwy 52 to Co. Road Hwy 52 to <br />Co. Road t:o BNRR to BNRR <br /> 3.8 1.4 5.2 <br /> 4.5 2.0 6.5 <br /> 3.6 1.7 5.3 <br /> 3.3 1.6 4.9 <br /> 2.7 1.3 4.0 <br /> <br />DISCHARGE <br />(cfs) <br /> <br />14,200 <br />(10-yr) <br /> <br />36,000 <br />(50-yr) <br /> <br />49,000 <br />(100-yr) <br /> <br />96,000 <br />(500-yr) <br /> <br />*Note that ':he travel time for a flash flood discharge of <br />2,000 cfs, be1:ween Highway 52 and wiggins would be consid- <br />erably longer than 5.2 hours. ~~hat duration represents <br />travel time under equilibrium condit:ions, such as an extended <br />snow melt runoff. <br /> <br />2.3 Stage and Discharge Relationships <br />A firm rela":.ionship betwe,en stage at t:he warning gage and <br />stage at Wigqins cannot be established. Flood hydrograph <br />volume, as well as peak discharge, enters into any stage re- <br />lationship be-tween separat:e locat:ions em a stream. Flood <br />hydrograph characteristics are a function of rainfall pat- <br />terns as well as basin and channel features. stage relation- <br />ships are also subject to shifting and seasonal backwater <br />variations, which further complicat:es development of a single <br />relationship blatween observed stage at an upstream gage and a <br /> <br />4 <br />