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<br />" <br /> <br />N <br />cae <br />I>> <br />.."'" <br /> <br />Use of the Rating Chart of Factors Affecting <br />Sediment Yield in the Pacific Southwest <br /> <br />The following is the sediment yield classification originally presented <br />on page 2. <br /> <br /> Sediment Yield <br />Classification Rating AE/sQ.mi. <br />1 ?' 100 3.0 <br />2 75 - 100 1.0 - 3.0 <br />3 50 - 75 0.5 - 1.0 <br />4 25 - 50 0.2 - 0.5 <br />5 0 - 25 <0.2 <br /> <br />In most instances high values for the A through G factors should corre- <br />spond to high values for the H and/or I factors. <br /> <br />" <br /> <br />An example of the use of the rating chart is as follows: <br /> <br />A watershed of 15 square miles in western Colorado has the' following char- <br />acteristics and sediment yield levels: <br /> <br /> Factors Sediment Yield Level Rating <br />A Surface geology Marine shales 10 <br />B Soils Easily dispersed, high <br /> shrink-swell character- <br /> istics 10 <br />C Climate Infrequent convective <br /> storms, freeze-thaw <br /> occurrence 7 <br />D 'lunoff High peak flows; low volumes 5 <br />E Topography Moderate slopes 10 <br />F Ground cover Sparse, little or no litter 10 <br />G Land use Intensively grazed 10 <br />H Upland erosion More than 50% rill and <br /> gully erosion 25 <br />I Channel erosion Occasionally eroding banks <br /> and bed but short flow <br /> duration -1 <br /> Total 92 <br /> <br />This total rating of 92 would indicate that the sediment yield is in <br />Classification 2. This compares with a sediment yield of 1.96 acre-feet <br />per square mile as the average of a number of measurements in this area. <br />