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<br />4 <br /> <br />1',) <br /><0 <br />CD <br />C.YI <br /> <br />Modification 7: It is recommended that the section of the PSIAC, <br />1968 report referred to on the title page as "Selection and <br />Evaluation of Measures for Reduction of Erosion and Sediment <br />Yield in the Pacific Southwest" be eliminated. The elimination <br />of this major section of the report is necessary because the <br />rapidity with which the field of conservation land treatment is <br />changing. The 1968 section is out of date and if a new section <br />were proposed, it too would become out of date in a very short <br />time. <br /> <br />It is recommended that a conservation land treatment reference <br />section be added to the report at the end of the sediment yield <br />procedure section. This new section would refer the user to the <br />annually updated planning manuals and technical guides of the <br />following agencies: (1) US Department of Agriculture, Soil <br />conservation service, various conservation planning handbooks and <br />manuals; (2) US Department of Agriculture, Forest Service, <br />various conservation planning procedures and documents; (3) US <br />Department of Interior, Bureau of Land Management, various <br />conservation planning handbooks and manuals; (4) Cooperative <br />Extension service, an organization in every state funded by state <br />and federal money; various conservation planning handbooks and <br />manuals. The BLUE PAGES in telephone directories will have <br />addresses and telephone numbers of state and field offices of the <br />above mentioned agencies. The handbooks, manuals and other <br />references or guides can be obtained through the Freedom of <br />Information Act for a reproduction fee (or free for a small <br />number of pages) by contacting state or national offices of the <br />above agencies. . <br /> <br />Modification 8: It is proposed that the PSIAC rating factor <br />Geology (a) is given too much weight in the rating system (ten <br />points) and that this rating factor be given 'a rating maximum of <br />five points. This modification proposal is based on research <br />that has occurred since 1968. Hereford (1976) documents the <br />sediment yield from the shale and sandstone units in the Chinle <br />Formation as having a 1.8 year recurrence interval. This is an <br />almost two year time gap between sediment yield within drainages <br />of the Colorado Plateau that have deeply weathered sandstone and <br />shale bedrock on the surface. These badlands areas are subject <br />to intense and infrequent thunderstorm events. After a major <br />sediment yielding storm event, the next storms would result in <br />minimal to no sediment yield due to the upland having been <br />stripped of weathered soil and sediment. It would take an <br />average of almost two years for the bedrock to weather by freeze <br />and thaw, temperature differentials and chemical weathering <br />before the area would yield sediment again. <br /> <br />The PSIAC sediment yield procedure results in an annual figure of <br />sediment yield from an area. In light of the above work by <br />Hereford (1976) it is proposed that the Geology (a) rating factor <br />should not be given equal weight as the Soil (b) rating factor. <br />