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<br /> <br />Use of the Rating Chart of Factors Affecting <br />Sediment Yield in the Pacific Southwest <br /> <br />Rating <br /> <br /> <br />The following is the sediment yield classification originally presented <br />on page 2. <br /> <br /> Sediment Yield <br />Classification Rating AF/sq.nd. <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 />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 <br /> <br />A <br />B. <br /> <br />Surface geology <br />Soils <br /> <br />C <br /> <br />Climate <br /> <br />D <br />E <br />F <br />G <br />H <br /> <br />Runoff <br />Topography <br />Ground cover <br />Land use <br />Upland erosion <br /> <br />I <br /> <br />Channel erosion <br /> <br />Sediment Yield Level <br /> <br />Marine shales <br />Easily dispersed, high <br />shrink-swell character- <br />istics <br />Infrequent convective <br />storms, freeze-thaw <br />occurrence <br />High peak flows; low volumes <br />Moderate slopes <br />Sparse, little or no litter <br />Intensively grazed <br />More than 50% rill and <br />gully erosion <br />Occasionally eroding banks <br />and bed but short flow <br />duration <br /> <br />10 <br /> <br />10 <br /> <br />7 <br />5 <br />10 <br />10 <br />10 <br /> <br />25 <br /> <br />Total 92 <br /> <br />.--2 <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 />