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The rainfall information has been plotted on curves for various <br />locations. This information can be used to predict erosion for periods <br />less than 12 months. See Figure 10. <br />K (soil erodtbility) factors are assigned each soil series. Soil <br />scientists have developed a listing of "K" factors for all soil series being <br />mapped in Colorado. The "K" factor will change for a given soil series <br />as different horizons are exposed by a land disturbing activity. Therefore <br />it was necessary to assign "K" factors for the various soil horizons <br />occurring in a soil series. See Tables 1-5. <br />LS (length and percent slope) factors account for the length and per- <br />cent slope. These factors will be taken from Table 14. <br />Length of slope begins at the top of the micro-watershed. This is <br />usually 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: <br />(1) the point where1he slope decreases to the extent that deposition <br />occurs, (2) the point where runoff enters a well-defined channel, gully, <br />terrace, or diversion, or (3) where water leaves the field. <br />If terraces or diversions are used to achieve the proper LS factor for <br />s the given situation, they must be constructed in accordance with appro- <br />priate engineering Standard and Specifications. <br />Uniform slopes are ideal for use in the USLE, but are uncommon. <br />Slopes are usually convex (steepening substantially toward the lower end) <br />or concave (flattening toward the lower end). <br />When the- lower end- of the slope is steeper than the upper end (con- <br />vex-slope), the gradient of the steeper segment should be used with the <br />overall slope length to enter the LS chart. <br />on a concave slope, deposition may occur at the lower end of the <br />slope. In such cases, the appropriate length and gradient are those of <br />that segment of the slope that is above the point where it flattens enough <br />for deposition to occur. <br />If the field is divided into segments according to degrees of erosion, <br />each segment must be treated separately as needed. If the field remains <br />as one segment, it must be treated to control the most severely eroding <br />areas. <br />C (cropping management) factors are the ratios of soil losses from <br />• lands cropped under specified conditions to the corresponding losses from <br />tilled, continuous fallow. <br />-64-