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. ",." . 3) Synthetic Unit Hydrograph: This nll'thod is described in "Hydrology for Engineers" by Linsley, Kohler and Paulhus, NcGraw-lIill Co., 1958. The following information was used in the computations. = 48.6 ft/mile measured from tapa sheets " " " " " " " " Computed (From CSU data) Computed L = 36.6 miles L = 23.7 miles ca . Sst Lag = 4.5 hours Cp = 0.60 . tp = 4 hours Unit graph peak - 12,600 cfs laO-year, I-hour rainfall = 2.2 inches USWIl Tech. P"per 40 . Basin Rainfall = 2.2(0.7)=1.54 in. Area reduction, US).))) TP40, Fig. 15 ,. Using an average infiltration rate of l.O-inch per hour and a rair,fa'Ll distr.ibution as suggested by Eagleson, "Dynamic Hydrology," McGraw- Hill, 1970, a rainfall excess of 0.70 inches was computed. Based on the above computations, the 100-year peak discharge was computed to be B,700 cfs. . One other comment that may be beneficial in the final decision was offered by Clifford Jenkins of this office. Cliff made a field inspection of Wellington following the 1961 flood. He stated that lloxeldEr Creek was flowing about one-half full or about 7 feet deep. . Coal Creek: I:uring the field inspection Ted Hurr and I >Talked the channel of Coal Creek in the vicinity of North Pouch:e Ditch about 3 miles north of \Vellington (drainaGe area equals 70.2 sq. mi.). Upstream from the Ditch, the channel is poorly defined but i,1cntifiable, A berm along the south side of the Ditch averages 4 feet in h',ight and would intercept almost all flood flow except for a small amount that might flow through an opening just east of the railr"nd. South lOf this berm the channel can be identified for about 1,000 feet until it reaches the north-south road in section 15. From this point south no evidence of the channel could be located. The land lws been leveled for irrigated farming and several small field dit~hes cross the "rea. . I . 2 .