Laserfiche WebLink
• USING THE UNIVERSAL SOIL LOSS EQUATION <br />R (rainfall) factors are assigned by geographical regions based on weather data <br />furnished by the U.S. Weather Service. R values are based on rainfall amount, time, <br />and intensity. In the mountains, R values were computed primarily for valley areas and <br />have been increased to account for run-off from snow melt. The R factor used for this <br />calculation is derived from an iso-erodent map, Figure 2, and is the same for both the <br />reclaimed slope and the adjacent natural slope. <br />K (soil erodibility) factors are assigned to each soil series and they are used to predict <br />the erodibility of a soil and its tolerance to erosion in relation to specific kinds of land <br />use and treatment. Soils having the highest K value are the most erodible. The K <br />value used for this calculation is picked from the U.S. Department of Agriculture Soil <br />Survey, Rifle Area, and is based on the soils classification; Nihill. The K factor of 0.24 <br />is the same for both the reclaimed slope and the adjacent natural slope. <br />LS (length and percent slope) factors account for the length and percent slope. These <br />factors are taken from Table 1. Length of slope begins at the top of the micro <br />watershed. This is usually at the top of a hill, ridge, terrace or diversion. The length of <br />slope is considered to end for a given field at one of the following places: (1) the point <br />where the slope decreases to the extent that deposition occurs, (2) the point where <br />runoff enters a well-defined channel, gully, terrace or diversion , or (3) where water <br />leaves the field. The LS for the reclaimed slope was measured at the portal areas <br />where the disturbed area length is about 300 -feet and the slope is about 29%. The LS <br />factor for the reference area is considered to be equal to the LS factor for the reclaimed <br />portal areas above the upper access road and reclaimed areas west of the access <br />and haul roads, the "Portal Area". <br />The LS factor for the benches below the portal areas and above the irrigated haylands <br />• is determined by an average length of 340 feet and a slope of about 14%, the "Benches". <br />C (cropping - management) factors are the ratios of soil losses from lands cropped <br />under specified conditions to the corresponding losses from tilled, continuos fallow. C <br />factors for land uses other than cropland are included on Figures 7,8, and 9. The <br />percent ground cover is the primary item to consider because a slight change in the <br />percent ground cover will result in a significant change in the erosion prediction. <br />Figure 7 - "C' Factors for Permanent Pasture and Rangeland <br />BASELINE - ADJACENT AREA - "C" FACTOR <br />Reference Area <br />Appreciable canopy. Canopy is assumed to be the combined cover contributed by trees and shrubs. <br />Based on the 2000 vegetation study the combined tree and shrub cover totals 26.5%. The percent <br />ground cover for the reclaimed area shown on the preceding page is 83.1 %. Use figure 7 identified <br />above and interpolate to determine the C factor for 83.1% cover and 26.5% canopy. <br />CANOPY APPRECIABLE BRUSH <br />PERCENT GROUND COVER <br />80.0 83.1 100.0 <br />25% G 0.012 0.011 0.003 <br />26.5% Baseline Factor <br />50% 0.003 <br />4-58iii <br />06/01 <br />