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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Subbasin <br />Unnamed (l2A) <br />Unnamed (l2B) <br />Split Creek (lA) <br />Split Creek (1 B) <br /> <br />Table 5. Tributary Basin Characteristics <br />Drainage Curve <br />Area Number <br />0.372 64 <br />0.133 78 <br />0.500 64 <br />0.480 78 <br /> <br />Travel Time, hour <br />Overland Shallow Channel <br />0.30 0.51 0.08 <br />0.08 0.18 <br />0.30 0.63 0.08 <br />0.30 0.63 0.16 <br /> <br />Lag <br />Time <br />0.53 <br />0.16 <br />0.61 <br />0.66 <br /> <br />The computer program was used to compute tributary hydrographs and peak flow. <br />Table 6 compares the results of the rainfall runoff to regional regression estimates of <br />snowmelt runoff for both tributaries. <br /> <br />Table 6. Tributary Peak Flow <br />Tributary <br /> <br />Split Creek <br /> <br />10-year <br />50-year <br />100-year <br />10-year <br />50-year <br />100-year <br /> <br />Rainfall <br />Peak <br />21 <br />54 <br />68 <br />32 <br />95 <br />122 <br /> <br />Snowmelt <br />Peak <br />32 <br />38 <br />41 <br />54 <br />67 <br />72 <br /> <br />Unnamed <br /> <br />This analysis shows that peak flow on these small tributaries varies between <br />snowmelt and rainfall. Snowmelt appears to be the dominant cause of flooding for more <br />frequent runoff while rainfall causes larger floods for the 50- and 1 OO-year flood events. <br /> <br />Floods on both the Unnamed and Split tributaries are relatively small. Overflow from <br />the 100-year flood would easily be carried in the section of a local street and therefore <br />would not result in any significant flooding of adjacent property. It is recommended that <br />these tributaries be dropped from inclusion in the FIS update. <br />