2010-12-27_REVISION - C1981019 - Laserfiche WebLink

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Phase II RUSLE Soil Loss Data 5. Based on the information in the discussion above, please revise the vegetative cover factor, the "C" factor, in Table 4 for both the premining and post- mining conditions. Please use site - specific data from the 2006 -2009 vegetation sample years to justify the "C" factors. Please recalculate the average annual soil loss in RUSLE using the new "C" factors. Please provide the Division with the revised pages in Section 4 of SL -04 justifying the "C" factors and please provide and updated Table 4 with the new "C" factors and revised soil loss calculations. Colowyo Response: Colowyo acknowledges that the selection of an appropriate "C" factor for the pre- mining and the reclaimed conditions is subject to considerable judgment and interpretation. We are certainly open to using the values suggested by CDRMS that are based mainly on cover density, and note that when combined with the other factors in the sediment yield calculation, including modifications to the "P" factor discussed below in response to Comment No. 6, the reclaimed condition still produces somewhat less sediment than the pre- mining condition. Colowyo selected the "C" factor for the pre- mining condition based on Table 5.A.3 of "Applied Hydrology and Sedimentology for Disturbed Areas ", ©1981 , by Professors B.J. Barfield, R.C. Warner and C.T. Haan. This text is an update of an earlier text "Hydrology and Sedimentology of Surface Mined Lands" by Professors Haan and Barfield. Both texts are focused on hydrologic and sediment imacts of surface mined lands pursuant to the adoption of the SMCRA. The methods in the text are also the basis of the computer program SEDCAD, and the default values for the "C" factors in that program essentially track with those provided in the table referenced here. For the pre- mining condition, Colowyo assumed the rangeland consisted of 25% canopy, with cover mainly herbaceous plants (Type "W" in that table). Colowyo assumed cover canopy was only about 25 %, and that ground cover was on the order of 70 %, with "tall weeds or short brush" representing the sagebrush lands and "appreciable brush or brushes" representing the mountain oak lands. This resulted in interpolated values for "C" of about 0.07 for sagebrush areas, 0.08 for mountain shrub areas, and 0.013 for grass areas (essentially 0% canopy). When area weighted to the various vegetative covers in the 28 identified reclaimed sub - areas, the average "C" factor was 0.072 (not area weighted). This is considerably higher than CDRMS' suggested values of 0.005 to 0.011 for mountain shrub and sagebrush areas respectively, and would therefore be expected to produce larger sediment yields, all other factors remaining unchanged. However, as noted above, the resulting estimated yield does not change the conclusion that the reclaimed lands do not produce more sediment than the pre- mining condition. Colowyo therefore have incorporated CDRMS suggested values into the revised Table 4.