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JD -7 Mine - Drainage Design Plan 11 <br />Table 4. Regression Equations for Southwestern Colorado <br />(from Kircher, et al., USGS, 1984) <br />Discharge <br />Regression <br />Regression coefficient <br />Number <br />Mean standard <br />Characteristic <br />constant <br />of basin characteristics <br />of <br />error ( %) <br />Stations <br />Q <br />a <br />b1 <br />bZ b3 <br />b4 <br />Annual mean <br />0.097 <br />0.888 <br />1.74 <br />54 <br />55 <br />October mean <br />2.84 <br />0.806 <br />1.11 <br />54 <br />100 <br />November mean <br />1.83 <br />0.815 <br />1.13 <br />54 <br />87 <br />December mean <br />1.22 <br />0.872 <br />1.26 <br />54 <br />77 <br />January mean <br />0.933 <br />0.916 <br />1.34 <br />54 <br />77 <br />February mean <br />0.647 <br />0.913 <br />0.96 <br />54 <br />77 <br />March mean <br />0.124 <br />0.861 <br />0.502 <br />54 <br />53 <br />April mean <br />0.0422 <br />0.961 <br />1.13 <br />54 <br />62 <br />May mean <br />0.1 <br />0.948 <br />2.24 <br />54 <br />55 <br />June mean <br />0.0317 <br />1.01 <br />2.76 <br />54 <br />98 <br />July mean <br />11.2 <br />0.85 <br />1.68 <br />54 <br />123 <br />August mean <br />5.13 <br />0.79 <br />1.32 <br />54 <br />135 <br />September mean <br />3.65 <br />0.811 <br />1.3 <br />54 <br />142 <br />90 percent duration <br />1.35 <br />0.902 <br />2.08 <br />54 <br />179 <br />70 percent duration <br />1.61 <br />0.863 <br />1.56 <br />54 <br />108 <br />50 percent duration <br />2.1 <br />0.855 <br />1.3 <br />54 <br />106 <br />25 percent duration <br />6.51 <br />0.862 <br />1.34 <br />54 <br />88 <br />10 percent duration <br />20.1 <br />0.857 <br />1.34 <br />54 <br />65 <br />2- year -7 -day low <br />1.87 <br />0.83 <br />2.22 <br />54 <br />177 <br />2- year -7 -day high <br />0.501 <br />0.847 <br />1.89 <br />54 <br />51 <br />10- year -7 -day high <br />1.54 <br />0.845 <br />1.58 <br />54 <br />41 <br />50- year -7 -day high <br />3.24 <br />0.834 <br />1.36 <br />54 <br />37 <br />100- year -7 -day high <br />4.27 <br />0.829 <br />1.28 <br />54 <br />38 <br />2 -year peak <br />7.87 <br />0.732 <br />0.847 <br />51 <br />38 <br />5 -year peak <br />53.9 <br />0.686 <br />51 <br />42 <br />10 -year peak <br />69.4 <br />0.685 <br />51 <br />41 <br />25 -year peak <br />91.1 <br />0.683 <br />51 <br />41 <br />50 -year peak <br />109 <br />0.682 <br />51 <br />43 <br />100 -year peak <br />128 <br />0.68 <br />51 <br />45 <br />200 -year peak <br />149 <br />0.679 <br />51 <br />47 <br />500 -year peak <br />179 <br />0.677 <br />51 <br />52 <br />The USGS improved on the understanding of the flood characteristics of streams in and lands by using a <br />regional perspective and a large database of streamflow- gaging- station records for the southwestern United <br />States, including "Region 9" for southwestern Colorado (Thomas, et al., 1997). Methods were developed <br />for estimating magnitude and frequency of floods of streams in basins of less than about 200 mil in the and <br />southwestern United States. The authors pointed out that reliable estimation of flood frequency relations for <br />both gaged and ungaged streams that drain these and basins is complex because rainfall is variable in time <br />and space and the physiography of the drainage basins is extremely variable. The development of accurate <br />flood - frequency relations at gaged sites was difficult in some areas because of the variability of annual <br />peak discharges and short records and because, at some sites, most years have no flow. At other sites, <br />commonly used probability distributions do not appear to fit the plot of annual peak discharges. The <br />volume of runoff generated by the 2 -yr, 5 -yr, 10 -yr, 25 -yr, 50 -yr, and 100 -yr recurrence interval storms for <br />a given basin area and mean elevation can be calculated using the equations provided in Table 5. <br />4149A.140207 Whetstone Associates <br />