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<br /> <br />001390 <br /> <br />FACTORS AFFECTING SEDIMENT YIELD IN THE PACIFIC SOUTHWEST AREA <br /> <br />Recommendations of the Water Management Subcommittee <br />Sedimentation Task Force, PSIAC <br />October 1968 <br /> <br />Introduction <br /> <br />The material that follows is suggested for use in the 'evaluation of sediment <br />yield in the Pacific Southwest. It is intended as an aid to the estimation <br />of sediment yield for the variety of conditions encountered in this area. <br /> <br />The classifications and companion guide material are intended for broad plan- <br />ning purposes only, rather than for specific projects where more intensive <br />investigations of sediment yield would be required. For these purposes it <br />is recommended that map delineations be for areas no smaller than 10 square <br />miles. <br /> <br />It is suggested that actual measurements of sediment yield be used to the <br />fullest extent possible. This descriptive material and the related numerical <br />evaluation system would best serve its purpose as a means of delineating <br />boundaries between sediment yield areas and in extrapolation of existing data <br />to areas where none is available. <br /> <br />This may involve a plotting of known sediment yield data on work maps. Pre- <br />pared materials such as geologic and soil maps, topographic, climatic, vege- <br />tative type and other references would be used as aids in delineation of <br />boundaries separating yield classifications. A study of the general relation- <br />ships between known sediment yield rates and the watershed conditions that <br />produce them would be of substantial benefit in projecting data to areas with- <br />out information. <br /> <br />Sediment Yield Classification <br /> <br />It is recommended that sediment yields in the Pacific Southweat area be <br />divided into five classes of average annual yield in acre-feet per square <br />mile. These are as follows: <br /> <br />Classification 1 ::> 3.0 acre-feet/square mile <br /> 2 1.0 - 3.0 " " <br /> 3 0.5 - 1.0 " " <br /> 4 0.2 - 0.5 " " <br /> 5 <:: 0.2 " " <br /> <br />Nine factors are recommended for consideration in determining the sediment <br />yield classification. These are geology, soils, climate, runoff, topography, <br />ground cover, land use, upland erosion, and channel erosion and sediment trans- <br />port. <br /> <br />