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<br />., <br /> <br />7 <br /> <br />~ applicability. The concept~of gross soil erosion (USLE) and net <br />00 sediment yield are separate processes and should not be equated. <br />~ Also, the concept of ground cover canopy (USLE) andqround cover in <br />~ a concentrated overland flow sense (PSIAC) should not be equated. <br /> <br />In terms of litter, it should be noted that not all litter is' <br />effective in controlling erosion or overland flow. An area with <br />15% litter on the surface may have most of the litter oriented, <br />parallel to flow paths. Also, sticks may have only the ends in <br />contact with the ground~ thereby forming an arc with flow possible <br />under the J\\iddle of the stick. This ,is ineffective litter. t.itter <br />,should be considered in an "effective" sense. Litteroriented <br />perpendicular to flow paths and in contact with the ground is <br />effective litter. Abundant small pieces of litter may actually be <br />floated by overland flows and not act as a sediment yield control <br />agent. Tbe rating of litter should be carefully considered in <br />terms of effectiveness. <br /> <br />The ground cover rating section on field sheets Should include the <br />items VEGETATION, LITTER and ROCK with some space behind each word <br />for the percentage rating of each item. This allows the rater to <br />document and consider the relative value of each item in terms of <br />sediment yield. These items could be important in determining FWOP <br />conditions and, FWP proposed land treatment, measures. :,The <br />vegetation,litter and rock ratings should be made in the field by <br />direct observation a.nd paced transect. Each item should be rated <br />to the nearest five percentage point value. This eliminates <br />developingarquable digit ratings and relates to the sensitivity <br />level of the -10 to +10 rating system (see below). <br /> <br />The percentage rating of effective ground cover is made by totaling <br />the' percentages of' vegetatio;m, litter and rock. An Effective <br />Ground Cover rating chart is included in the Revised PSIAC Rating <br />Sheet. <br /> <br />In developing the FWP and FWOP conditions, the modelling of the <br />Ground Cover (f) factor is critical. The increase of litter and <br />vegetation should be estimated from experience in previous type of <br />trea.tments or rated by example in the field if a previously treated <br />area is available. <br /> <br />MOdification 12: It is proposed that the Land Use (g) rating <br />factor be re-evaluated. The cultivated land factor should be <br />removed froJ\\ rating consideration. If cropland is present within <br />a geomorphic unit; for instance, it cannot, be assumed that because <br />50% of the area is cultivated that a necessarily high sediment <br />yield ratinq is deserved. The sediment yield rating of cultivated <br />cropland should be characterized by the USLE procedure (or other <br />appropriate model) and a sediment delivery ratio should be applied <br />for complete characterization. <br /> <br />The term "intensively grazed" should be removed as a rating <br />