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<br />10-year = 1.330 cfs <br />50-year = 2.040 cfs <br />100-year = 2.720 cfs <br />500-year = 4,000 cfs <br /> <br />These values were plotted on leg-probability paper toO detell11ine peak discharges for additional return <br /> <br />periods of interest: <br /> <br />1.25-year <br />1.5-year <br />2-year <br />5-year <br />25-year <br />200-year <br /> <br />= <br /> <br />570 cfs <br />660 cfs <br />780 cfs <br />1,080 cfs <br />1,800 cfs <br />3.300 cfs <br /> <br />= <br /> <br />= <br /> <br />3.1.2 Tributaries <br /> <br />Peak fiows from tributaries we-E. developed from published estimates of peak fiows for Cascade and <br /> <br />Portland Creeks (Simons. Li & Associates. Inc., 1982). The fiows for Skyrocket and Bridalveii Creeks were <br /> <br />determined by ratioing drainage areas. Published peak discharges were only available for the 10-. 50- and <br /> <br />1 OO-year events. These discharges were developed utilizing rainfall/runoff modeling. Peaks on the smaller <br /> <br />tributaries are a result of intense. short duration thunderstorms. Table 3.1 a lists the various peak discharges <br /> <br />and runoff volumes associated with the four tributaries. The effect .of mud and debris fiows can be accounted <br /> <br />for by bulking the water discharges. SaEed on Simons. Li I~ Associates. Inc. (1ge2). a bulking factor of 1.87 <br /> <br />was applied to the peak water discharge to develop combined water and debris peaks. To determine the total <br /> <br />volume of water and sediment during the. runoff events. a factor of 1.37 was applied (SLA, 1982). rable 3.1 b <br /> <br />lists the bulked event volumes. <br /> <br />The hydrGlogy for the tributaries is very approximate. If mitigation measures or flooding i:npacts along <br /> <br />the individual tributaries are analyzed for future projects, site specific studies of each tributary should be <br /> <br />performed which consider individual untested characteristics such as topography, geology and soils. The <br /> <br />values in Tables 3.1 a and 3.1 b provide a satisfactory basis for the qualitative discussion of tributary impacts <br /> <br />on the Uncompahgre River presented in this report. <br /> <br />3.2 <br />