Laserfiche WebLink
2.1.1 RAINFALL FACTOR (R) <br />The rainfall factor addresses the interrelationship of the erosive forces of falling <br />raindrops and runoff to predict both rill and inter -rill erosion. In this demonstration, <br />an average annual value of R was computed based on a Type II storm event <br />(Barfield, Warner, and Haan, 1983). The equation used to compute the R factor is <br />as follows: <br />Average Annual R = 27*(P2 6)2.2 <br />where P2,6 is the 2 -year, 6 hour precipitation in inches from published rainfall data <br />(e.g., Miller, et al, 1973). <br />The 2 -year, 6 -hour Type II storm event for the Somerset, Colorado area was <br />conservatively identified as 1.1 inches of rainfall (U.S. Dept. of Commerce, 1961). <br />The annual average R factor was computed to be 33.30 for both the reclaimed and <br />adjacent undisturbed areas. <br />2.1.2 SOIL ERODIBILITY FACTOR (K) <br />The soil erodibility factor K is a measure of a soil's susceptibility to erosion and <br />was determined from several published sources (USDA, 1981, 2020, EPA, 1977). <br />Six soil map units were determined to be present within the reclaimed areas and <br />extended reference undisturbed areas (USDA NRCS, 2020). These are identified <br />below, with their associated K factor value. Where K factors varied by soil horizon <br />in the literature, the K factor value for the surface soil horizon was used for the <br />native undisturbed areas, and an average of the K factor value for the upper and <br />underlying soil horizon for reclaimed areas (as activity at the reclaimed areas was <br />assumed to affect the soils to a depth of 12-20 inches). <br />............................................................................. <br />............................................................................. <br />Oxbow Mining, LLC Elk Creek Mine Page 3 <br />Phase 11 Bond Release Sedimentology Evaluation 2020 <br />