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<br />July 1993 -21- 923-2515 <br />If the water was not ponded, but diverted from the stream when needed in June, July, and <br />August less acreage could be irrigated since about 78% of the water would have flowed <br />downstream without being diverted. The mean flow of Grassy Creek at station YSGFS in June, <br />July and the first six days in August, 1992 is 0.236, 0.135, and 0.109 cfs, respectively (Table <br />5.1). According to the SCS (Fulton 1992) a stream flow of 1 cfs is required to flood irrigate <br />40 acres. Thus, in June, 9.44 acres could be irrigated. Likewise, 5.4 acres could be irrigated <br />in July and only 4.36 acres in August. Because of the decrease in stream flow from June to <br />August, the maximum azea which could be continuously irrigated is 4.36 acres. However, it <br />is unlikely that a stream flow of such a low volume could be successfully used for flood <br />irrigation since the alluvial materials have moderately high permeability rates. <br />All water quality parameters which include the sodium adsorption ratio (SAR), chloride, boron, <br />• etc. aze within acceptable limits for crop irrigation. The salinity levels for the three sites, <br />measured as electrical conductivity, are 1.095, 1.116, and 2.458 mmhos/cm, respectively. <br />These salinity levels exceed the suspect level for threshold crop damage which occurs at 1.0 <br />mmhos/cm for the Yampa basin (CMLRD 1988). The threshold salinity values of irrigation <br />water for hay crop species in the region aze: alfalfa, 1.3 mmhos/cm; smooth brome, 1.5 <br />mmhos/cm; and orchard grass, 1.0 mmhos/cm (CMLRD 1988; Peabody Coal 1992b). There <br />are no values for the moderately tolerant timothy (Phleum praterue), or for Garrison foxtail <br />barley (Alopecurus arundinaceus). Thus, the quality of the surface water is poor to unacceptable <br />for growing hay grasses and alfalfa. All other water quality pazameters, which include the <br />sodium adsorption ratio (SAR), chloride, boron, etc. are within acceptable limits for crop <br />irrigation. <br />Summary: There is a 25-30 acre site of productive irrigable soils near the junction of Grassy <br />and Little Grassy Creeks which meet the size criteria for irrigation. However, there is only <br />sufficient stream flow during the growing season to irrigate about 4.36 acres assuming the very <br />• low stream flow could be directed across the moderately high permeable soils. If a dam were <br />constructed it would be potentially possible to irrigate 22 to 25 acres. However, the mazginal <br />Golder Associates <br />