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- J7 - <br />~ ' Drainage Area 2 <br />410 = 0.12( 75)0.815(30}.592 <br />~' 'b'~U <br />410 = 4.7 cfs <br />1, <br />~' (It should be noted that the smallest basin in the data base used to develop this <br />regression is 7.1 sq. mi.) <br />~' c. The 10-year peak flow at the Gaging station location near the mine site <br />(drainage area 16.7 sq. mi.) is: <br />~' 0 815 1.592 <br />Q10 - 0.12 (16.7) ' (30) <br />I' Q10 ° 267 cfs <br />I ' <br />Alethod 2 5C5 Peak Flow Method <br />' ' In the permit area for Sunlite Mine, there are two subbasins that will be evaluated <br />I' separately, Drainage Area 1 (105 acres) and Drainage Area 2 (75 acres) as shown in <br />Figure H.4. The !0-year peak flow will be calculated for premising and postmining <br />' watershed conditions. <br />~ Drainage Drainage <br />-' 1, na+a S~ m aty Area 1 Area Z <br />I Curve Number (Premining)(1) 75 75 <br />L ' Curve Number (Postmining)(1) 75 76 <br /> <br />L 10-yr., 24 hr precipitation (in. <br />Length of longest watercourse, L )(2) 2.0 <br />2500 2.0 <br />1200 <br />, Elevation difference in basin, H (f t) 670 760 <br /> Drainage area, A (sq. mi.) 105 1 6 75 = .12 <br />' <br />l 640 640 <br />~ (1) Soil Conservation Service, National Engineering Handbook No. 4 Hydrology. <br />I <br />(2) <br />National LJeatlier Service, Atlas No. <br />2, Precipitation-Frequency Atlas of <br /> the k'es[ern United States. <br />_' <br />~a <br />y <br />35 <br /> <br /> <br />