Laserfiche WebLink
<br /> <br />- 2 - <br /> <br /> <br />Characteristics of each of the nine factors which give that factor high, <br />moderate, or low sediment yield level are shown on the attached table. <br />The sediment yield characteristic of each factor is assigned a numerical <br />value representing its relative significance in the yield rating. The <br />yield rating is the sum of values for the appropriate characteristics for <br />each of the nine factors. Conversion to yield classes should be as follows: <br /> <br />Rating Class <br />~100 1 <br />75 - 100 2 <br />50 - 75 3 <br />25 - 50 4 <br />o - 25 5 <br /> <br />Guidelines which accompany the table are an integral part of the procedure. <br />They describe the characteristics of factors which influence sediment yield <br />and these are summarized in the space provided on the table. <br /> <br />The factors are generally described, for purposes of avoiding complexity, <br />as independently influencing the amount of sediment yield. The variable <br />impact of anyone factor is the result of influence by the others. To <br />account for this variable influence in anyone area would require much more <br />intensive investigational procedures than are available for broad planning <br />purposes. <br /> <br />To briefly indicate the interdependence of the factors discussed separately, <br />ground cover is used as an example. If there is no vegetation, litter or <br />rock fragments protecting the surface, the rock, soil, and topography express <br />their uniqueness on erosion and sediment yield. If the surface is very well <br />protected by cover, the characteristics of the other factors are obscured by <br />this circumstance. In similar vein, an arid region has a high potential for <br />erosion and sediment yield because of little or no ground cover, sensitive <br />soils and rugged topography. Given very low intensity rainfall and rare <br />intervals of runoff, the sediment yield could be quite low. <br /> <br />Each of the 9 factors shown on the table are paired influences with the excep- <br />tion of topography. That is, geology and soils are directly related as are <br />climate and runoff, ground cover and land use, and upland and channel erosion. <br />Ground cover and land use have a negative influence under average or better <br />conditions. Their impact on sediment yield is therefore indicated as a neg- <br />ative influence when affording better protection than this average. <br /> <br />It is recommended that the observer follow a feedback process whereby he checks <br />the sum of the values on the table A through G with the sum of H and I. In <br />most instances high values in the former should correspond to high values in <br />the latter. If they do not, either special erosion conditions exist or the <br />A-G factors should be re-evaluated. <br />