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• July 1993 -19- 923-2515 <br />5.1.5 Potential Flood Irri ag tion <br />Soils: The major areas of alluvium, undifferentiated valley fill and related deposits along Grassy <br />Creek are characterized by the Silas loam, Silas Variant loam, Coutis fine sandy loam, and the <br />Dunckley-Skyway complex (Figures 1 and 3). <br />The Silas loam is a deep well-drained soil in narrow valleys formed in alluvium. This mapping <br />unit has small areas of the poorly drained Aquolls soils. The permeability of the Silas soil is <br />moderate, available water capacity moderate, and the runoff slow. The effective rooting depth <br />of plants is 60 inches or more. This soil is potentially flood irrigable provided the slopes are <br />3% or less (Moore 1993). <br />The Silas Variant loam is a deep, somewhat poorly drained soil on stream terraces and <br />. floodplains formed in mixed alluvium. Permeability of this soil is moderate, available water <br />capacity high, and runoff slow. The seasonal high water table is at a depth of 20-30 inches in <br />May and June and is at a depth of 30-50 inches the remainder of the year. This soil is <br />commonly irrigated in Routt County to grow hay and pasture grasses. <br />The Coutis fine sandy loam is a deep somewhat excessively drained soil formed in alluvium and <br />residuum. Permeability and available water capacity is moderate and runoff is slow. The <br />effective rooting depth is 60 inches or more. This soil is not irrigable because it generally <br />occurs on steep slopes (3-2540. <br />The Dunckley-Skyway complex soil occurs on mountain slopes. The Dunckley soil is deep, well <br />drained soil formed in colluvium derived primarily from sandstone. This soil has a moderate <br />permeability, a moderate available water capacity and a medium runoff. The effective rooting <br />depth is 60 inches or more. This soil is not irrigable due to the steep slopes (25-65%) on which <br />_._ • <br />it occurs. <br />Golder Associates <br />