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• The soil, however, has a significant fraction of material up to cobble in size. A "type" particle <br />distribution of the "erodible" fraction (that fraction considered as erodible in SEDCAD+ <br />analyses), is presented in the following table. <br />Table 2.2-1 Erodible Fraction Sieve Analysis (Type) <br />• <br />• <br />Screen Sizes in nun Percent of Eroded Particle Size Fraction <br />Passing <br />4.00 100 <br />2.00 99 <br />1.00 90 <br />0.500 88 <br />0.250 85 <br />0,125 82 <br />0.063 74 <br />0.016 56 <br />0.003 38 <br />0.0001 0 <br />The large quantity of cobble-sized materials in the erodible matrix are expected to quickly armor <br />a ditch lining. Therefore, a velocity of 5.50 feet-per-second (fps) is allowed for ditches <br />(erodible channels) in the material (Graded Silts -Cobbles Colloidal). <br />2.3 Vegetation <br />The natural vegetation of the sites is primarily oak brush with chokecherry and serviceberry <br />mixed in. There is a good layer (minimum of 2 inches) of brush litter on the ground. <br />3. SEDCAD+ INPUT PARAMETERS COMMON TO ONE <br />OR MORE AREAS <br />3.1 Rainfall Depth <br />The rainfall depth fora 10-year, 24-hour and a 100-year, 24-hour storm event in the vicinity of <br />the proposed work was determined to be 1.90 inches and 2.8 inches respectively [National <br />Oceanic and Atmospheric Administration (NOAA) Atlas 2, Precipitation -Frequency Atlas of <br />the Western United States, Volume III -Colorado, & Previous Reports]. <br />(Lone Pine Gulch SAES Demonsvation, 12 October 95, Page 5 of 13) <br />