2008-07-25_GENERAL DOCUMENTS - C1981010 (2)

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The four gulches (No Name, Johnson, Pyeatt, and Flume) lack sufficient water availability for flood irrigation. According to the Soil Conservation Service, local irrigation requires approximately 5 acre-feet of water per acre, after allowing for evaporation losses (letter from Hill, 1980 referenced on page 2-539 of permit application). Summertime evaporation in Moffat County exceeds precipitation by approximately 30 inches (Evaporation from Lakes and Reservoirs by A.F. Meyer, 1942, Minnesota Resources Commission, page 58). The largest annual water yield for any of the four gulches is calculated to be the 225 acre-feet yield from Flume Gulch (page 2-412 of permit). This amount of water would irrigate only 45 acres based on the 5 acre-feet of water per acre requirement, rendering flood irrigation an uneconomic business venture. Flood irrigation is generally the only type of irrigation practiced in small stream valleys in northwestern Colorado where wheat, alfalfa, and hay are grown; the 77-day growing season limits farming in Moffat County to these or similar crops. Sub-irri ation Agricultural Potential OSM's Alluvial Valley Floor Identification and Study Guidelines (page C-10) explains that in terms of alluvial valley floors, sub-irrigation occurs if enough water is available for a sufficient time to have a recognizable effect on the species type and the productivity of a plant community. Agricultural crops or rangeland must receive enough sub-irrigation that the community is notably more productive or more agriculturally useful when compared to dry land areas. Sub-irrigation of agricultural plants can be expected to occur in the wide, flat valley bottoms of the Yampa River and Williams Fork River. The four gulches (NO Name, Johnson, Pyeatt and Flume), though, lack sufficient water availability for sub-irrigation agricultural activities based on examination of those valleys in connection with renewal application RN-04/PR-05. Two Division representatives and two representatives of the applicant jointly examined Flume Gulch in order to verify the presence of AVF features. No evidence was found for the increased agricultural plant productivity that would be expected in the bottom of the drainage if a significant amount of sub-irrigation was occurring. Agricultural species types and productivity appeared uniform across the drainage. Wetlands plants (cattails) are growing in the lower end of Flume Gulch within the channel area, but the wetlands preclude the potential for sub-irrigation agricultural activities. A Division representative also inspected parts of Pyeatt, Johnson, and No Name drainages. Agricultural species types and productivity appeared uniform across those drainages. Alluvial Valley Floor Determination Based on the presence of unconsolidated stream-laid holding streams and the presence of water availability sufficient for flood irrigation agricultural activities, the following two alluvial valleys have been determined to be alluvial valley floors: the Yampa River in the Big Bottom area and the Williams Fork River near its confluence with the Yampa River. The four gulches (No Name, Johnson, Pyeatt, and Flume) are determined to not be alluvial valley floors based on their absence of water availability sufficient for irrigation or sub- Trapper Mine 30 July 25, 2008