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(52) <br /> <br /> <br />2.04.7(2) Surface Water Information <br />According to data collected at station 600 (Table H,7), the highest monthly mean <br />' discharge for Fourmile Creek, a perennial stream, occurs in May. The lowest monthly <br />mean discharge occurs in September. <br />~, For purposes of comparison, the 10-year peak flow event was estimated using three <br />methods, a regression analysis, the soil conservation service (SCS) Peak flow method, <br />' and frequency analysis using the recorded data from Fourmile Creek. <br />i <br />i <br />Method 1 Regression analysis using Technical Manual 1 by the Colorado Water <br />I <br />~.' Conservation Board and the USGS. <br />r The following regression was developed for the Mountain Region of Colorado: <br />' Q10 - 0.12 A0,815P1,592 <br />where Q is discharge (cfs), A is drainage area (square miles), and P is normal annual <br />' 1 precipitation (inches), 1931-1960. <br />~ , a. In the Fourmile Creek basin, A is 38.3 sq. mi. and P is 30 in. Therefore: <br />Q10 = 0.12 (38.3)0'815(30)1.592 <br />' Q10 = 526 cfs for Fourmile Creek at confluence with Roaring Fork <br />b. In the permit area for Sunlite Mine, there are two subbasins that will be <br />t evaluated separately, Drainage Area 1 (105 acres) and Drainage Area 2 (75 acres) as <br />shown in Figure H.4. Drainage Area 2 flows into Fourmile Creek near the mine site. <br />L' Drainage Area 1 flows into an unnamed tributary that enters Fourmile Creek several <br />miles downstream of the mine site. <br />L <br />t Drainage Area 1 <br />105. 0.815 1.592 <br />410 = 0. 12(~b40) (30) <br />i 410 = 6.2 cfs <br />~1 <br />1 <br />`i 3 2 <br />