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r <br />i 11 <br />~ R~ <br />Rainfall Factor (Rl <br />Data for calculating R values were obtained fry a r..;*~ae in Northgate, <br />Colorado, the closest reooniing rairxrgaage to the mine site. A Fisher-Fbrter <br />' ,-a; n~ma~e has been reoordiSY3 individual storm events at Northgate since 1979. <br />Data are oonipiled by the National Oceanic and Atmospheric Adm;*+;~*ation (NOAA) <br />in monthly Hourly Precipitation Reports. A relationship between precipitation <br />depth and duration and single storm R values fos type II storms in the U.S. has <br />been developed (Iiot~, 1973). The relationship is expre_sSed as: <br />Type II Storm FYosion Index = 19.25 p2.2 <br />* ~,;, H0.4672 <br />s~ <br />F,~ <br />~':~' Pis rainfall in inches <br />~~'~" a rte. His rainfall duration in hours <br />c <br />r ~~~ <br />Due to Pv*a+~~ periods of missi.nq data fr[~ the Northgate gage, only 3 years of <br />consecutive data were used (1981,82,83). A total of 323 i.rrlividual storm events <br />were reoorrled during these years. Using the above equation, single storm R <br />values were calculated and sun®ed for each year, then averaged to obtain an <br />average annual R of 40.7 (Table 1). The isoerodent map for the ppntino.,ral U.S. <br />app*r+Y~+~tes R for the study site as 30 (W~~~+~++p~er aryl Smith, 1978). The site <br />specific data were used in this calculation. Average ~a~+nai R values were also <br />calculated (Table 1). The highest amount of rainfall erosivity occurred durirrq <br />the summer ~mnths, when precipitation is dominated by tluurlesstorm activity. The <br />lowest amount of rainfall erosivity ooarrred during the winter months. <br />Since alternate s~-?;+~*+* control strategies and ,~+~a~,*+~ need to be <br />effective year rani, the average annual R value was used. ~11C 1S a <br />