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the curves, published by the MRCS in the Farm Irrigation Rating Index (FIRI) - A <br />method for planning, evaluating, and improving irrigation management, June 1991. <br />Figure 9 <br />Conveyance Efficiency Factor <br />1.00 <br />0.90 <br />a <br />v <br />~ 0.80 <br />.v <br />W <br />v 0.70 <br />c <br />R <br />a <br />N <br />0 0.60 <br />U <br />0.50 <br />0.40 <br />Ditch Length -Feet <br />Ding <br />ig <br />/Silt <br />i <br />~y loam <br />id <br />~Ily <br />The MRCS STATSGO soil mapping was reviewed to determine the relationship between <br />permeability in the lower soil layer and soil description so the curves shown in Figure 9 <br />could be used. Table 3 shows the general relationship for the Rio Grande between soil <br />description and permeability. Other soil types are not present in the irrigated portion of <br />the basin. <br />Table 3 <br />Relationship between Soil Classification and Permeability <br />Soil Descri tion Permeabilit inches/hour <br />Clay/Silt Loam 0.2 - 1.0 <br />Sandy Loam 1.0 - 7.0 <br />Sand 7.0 - 15.0 <br />Gravelly-Sand 15.0 - 20.0 <br />Figure 10 shows the soil permeability and soil descriptions in the Rio Grande basin and <br />the location of the large ditches. As shown, most of the San Luis Valley ditches flow <br />through soil described as sand. <br />appendB_cropcu_6-2004.doc B-12 of B-19 12/13/00 <br />0 1000 2000 3000 4000 5000 <br />