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Rob Zuber December 31, 2015 Page 3 The following is an excerpt from Barfield, B.J., Warner, R.C., Hayes, J.C., 1994, Design HydroloQy and Sedimentology for Small Catchments: "Several cautions about the use of RUSLE should be considered. Predictions from RUSLE represent soil loss averaged over many storms and years. It also represents averages over a total field or disturbed area. At points on a slope or field, the soil loss will almost always be less than or greater than the average values. For example, on long slopes, the upper part of the slope will have lower erosion rates that the lower part of the slope, but the average over the entire slope over a long period of time should be approximated by the RUSLE predictions. " The important point of the above excerpt not only applies to the slope component of RUSLE but to all the factors. Each factor, rainfall excluded, is an estimate based on the best available information. By far, the most accurate of any of the factors is cover, since it is based on actual scientific sampling (veg sampling) of the reclaimed area and the reference area (adjacent, non -mined area). Not only is RSULE a sediment model that requires the selection of various factors, but it also requires an understanding of the underlying assumptions of the model itself. In this case, we are comparing the results of a sediment model estimating annual sediment yield from the reclaimed area to a similar area of adjacent, non - mined land. A simple way to think of it is super -imposing the vegetation and soil characteristics of the non -mined area on the topography of the reclaimed area. Remember, the reclaimed area is required to meet the Coal Rule requirements for approximate original contour. SL -02 clearly states on page 32, "EM has successfully ... graded all disturbed area to the approximate original contour... " The rationale for the selection of each factor was clearly discussed in the sediment demonstrations that were submitted in SL -03. Specific to the LS factor, it is not appropriate to use different slope values for the non -mined area as compared to the reclaimed area. For example, using very steep slopes from a well -vegetated, non -mined area, would produce higher sediment yield that a nearly flat, similarly vegetated reclaimed area, all other factors being equal. This comparison would not be appropriate, since the variation in slopes incorrectly led to the conclusion that the reclaimed area consisted of a vegetative cover necessary to control excessive erosion. What is appropriate is to use average values for slopes (LS) that are representative of both the non -mined area and the reclaimed area. Technical literature and actual practice support this fact. Vegetation and litter values (C factor) were taken from the reference area for the non -mined model and from the reclaimed area for the reclaimed model. Why not use the slopes from the reference area one may ask? The first and most important reason is for the reasons described above. However, another basic reason is that reference areas are not chosen for the slope characteristics and how well they will be suited for sediment modeling purposes at bond release. For the sediment modeling demonstration to be valid, the comparison must estimate factors based on the best information available and include basic assumptions that validate the comparison of two land areas. In this case, the main concern is whether the established, native vegetation and hydrologic conditions present on the reclaimed area is similar to or better than an adjacent, non -mined area, specific to the production and transport of sediment. This fact is clear when one compares the two RULSE calculations in the RESULTS section of each sediment demonstration. In our case, and for reasons justified in the sediment demonstration text, the only factor that varies is the C factor, which is based on ALL of the vegetation sampling results from 2013 and 2014. These values are also averaged.