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<br />~` from the previous study and are locations where both water quality and discharge <br />were measured. Stations C2 and C6 are on Trout Creek and C3 is located on the <br /> spill point from an abandoned box cut near the foot of West Ridge in the Edna Mine. <br /> Annual runoff from the Trout Creek and Oak Creek watersheds is dominated <br /> by sno wmelt. Hydrographs depicting the seasonal runoff characteristics as measured <br /> at TR-a, TR-b and C6 are shown in Exhibits 2.5-3 and 2.5-4. Daily discharges <br /> (averaged over each week) were used to construct these exhibits. The C6 gaging <br /> station data are for 1975. The 1975 peak daily discharge at C6 occurred on June <br /> IS and was estimated to be 445 cfs. Discharges of similar magnitude were measured <br /> this spring (1980). <br /> Exhibit 2.5-5 shows the seasonal hydrograph measured as part of this study at <br /> station OK-a on Oak Creek near the office and loading facilities. The peak daily <br /> discharge measured at OK-a was 113 cfs and occurred on both May 7 and May 8, <br /> 1980. Comparison of the hydrographs for Trout and Oak Creek shows that spring <br /> runoff on Trout Creek is somewhat delayed relative to that on Oak Creek,reflecting <br /> the higher elevation of the headwaters on Trout Creek. <br /> Rainfall-runoff hydrographs are not available for any of the stations at the <br /> time of this writing. In~Fieu of measured rainfall-runoff hydrographs, unit <br />~ <br />~` hydrographs (Exhibits 2.5-6 and 2.5-7) were synthesized using the hydrologic units <br /> described in Tables 2.5-I and 2.5-2. The method used to generate the unit <br /> hydrograph was the Soil Conservation Service method. The volume of runoff <br /> represented by these curves is one inch over the entire watershed. Twenty-four hour <br /> storms with a recurrence interval greater than 100 years are required to produce the <br /> runoff shown by these unit hydrographs. Peak discharge for the 100 year <br /> precipitation event was calculated using the Colorado Regionalization Method and <br /> compared to that obtained using the unit hydrograph for Trout Creek shown in <br /> Exhibit 2.5-6. The peak discharge for the 100 year event estimated by the Colorado <br /> Regionalization is 835 cfs, while That derived from the unit hydrograph is 875 cfs. <br /> This provides an independent check on the reasonableness of the curve number used <br /> to generate the unit hydrograph. It should be noted that the peak discharge <br /> presented in Exhibit 2.5-6 requires a 24 hour storm of approximately 3.5 inches, well <br /> above the 100 year precipitation event. <br /> No long-term discharge records are available on Trout Creek and, therefore, <br /> a reliable mean annual discharge cannot be obtained. In 1975, The annual discharge <br />- at Station C6 was estimated to be 34,900 acre-feet from a watershed area of 49.5 <br /> square mile. This represents an average volume of runoff per unit area of I.I feet. <br />Revised 7-81 2.5-8 <br />