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3 ~ fragments. Some judgment must be exercised in establishing the ~ salt content of a soil that is actively becoming sediment because ~~ large limestone or lime rich sedimentary rock fragments may not completely break down in transport to yield the full percentage of salt content. The salt content of a soil can be obtained by direct sampling and chemical analysis ina laboratory or by estimating the salt content from previous published analyses of comparable soils. .,It should be noted that SCS soil survey reports contain some s.oil salt data. This data often refers only to the solution prone soil salt content and does not take into account the salt content of rock fragments that can be yielded by a combination of mechanical and chemical .weathering processes that occur in the stream transport of sediment. The salt delivery percentage is not always a direct relationship with the sediment delivery percentage. In the Colorado Plateau, as well as in the intermountain basin region, streams will trap sediment in channel bar and bank deposits. In some very active streams with dominant mechanical weathering characteristics the salt content of stream sediments is yielded long before the sediment is transported out of the watershed and may even be yielded before the sediment is trapped in deposition within the watershed. The decision of what percentage of salt is contained. in a sediment yield load and how much of that percentage is. yielded is a matter of a combination of empirical analyses and judgement based on experience and observed .stream transport characteristics. Modification 6: It is proposed that the numerical sediment yield classification system be reversed to reflect that the highest sediment yield be given the highest category rating. The present rating of low numerical rating for high sediment yield class has. led to considerable confusion. It is also proposed that the five categories of sediment yield be given written characterizations that will allow for consistent written accounts of the severity. . of sediment yield categories. The proposed written classifications are as follows: Old Class New Class Range (ac-ft/sq mi) Description 1 5 > 3.0 very High 2 4 1. 0-3.0 High 3 3 0.5-1.0 Moderately High 4 2 0.2-0.5 Moderate 5 1 < 0.2 Low It is recommended that the point rating be eliminated from the above classification scheme because in the original PSIAC there is a discrepancy between the 75 point class limit and the assigned sediment yield value of 1.0 acre-feet/square mile (75 points is equal to 1.225 acre-feet/square mile). The use of acre-feet for the development of classification is adequate for rating purposes.