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requirement, rendering flood irrigation an uneconomic business venture. Flood irrigation <br />is generally the only type of irrigation practiced in small stream valleys in northwestern <br />Colorado where wheat, alfalfa, and hay are grown; the 77-day growing season limits <br />farming in Moffat County to these or similar crops. <br />Sub-irrigation Agricultural Potential <br />OSM's Alluvial Valley Floor Identification and Study Guidelines (page C-10) explains <br />that in terms of alluvial valley floors, sub-irrigation occurs if enough water is available <br />for a sufficient time to have a recognizable effect on the species type and the productivity <br />of a plant community. Agricultural crops or rangeland must receive enough sub- <br />irrigation that the community is notably more productive or more agriculturally useful <br />when compared to dry land areas. <br />Sub-irrigation of agricultural plants can be expected to occur in the wide, flat valley <br />bottoms of the Yampa River and Williams Fork River. The four gulches (No Name, <br />Johnson, Pyeatt and Flume), though, lack sufficient water availability for sub-irrigation <br />agricultural activities, based on examination of those valleys in connection with renewal <br />application RN-04/PR-05. Two Division representatives and two representatives of the <br />applicant jointly examined Flume Gulch in order to verify the presence of AVF features. <br />No evidence was found for the increased agricultural plant productivity that would be <br />expected in the bottom of the drainage if a significant amount of sub-irrigation was <br />occurring. Agricultural species types and productivity appeared uniform across the <br />drainage. Wetlands plants (cattails) are growing in the lower end of Flume Gulch within <br />the channel area, but the wetlands preclude the potential for sub-irrigation agricultural <br />activities. A Division representative also inspected parts of Pyeatt, Johnson, and No <br />Name drainages. Agricultural species types and productivity appeared uniform across <br />those drainages. <br />Alluvial Valley Floor Determination <br />Based on the presence of unconsolidated stream-laid holding streams and the presence of <br />water availability sufficient for flood irrigation agricultural activities, the following two <br />alluvial valleys have been determined to be alluvial valley floors: the Yampa River in the <br />Big Bottom area and the Williams Fork River near its confluence with the Yampa River. <br />The four gulches (No Name, Johnson, Pyeatt, and Flume) are determined to not be <br />alluvial valley floors based on their absence of water availability sufficient for irrigation <br />or sub-irrigation agricultural activities. (This determination applies, as well, to the <br />approximate 20-acre area in the upper part of Flume Gulch previously determined to be <br />an AVE In addition, that area lacks a stream channel meeting the minimum size criteria <br />of greater than 3 feet in bank full width and greater than 0.5 feet in bank full depth <br />[Section 1.04(142)]; and therefore, that area does not contain an unconsolidated stream- <br />laid holding stream.) (2.06.8(3)(c)) <br />Trapper Mine 36 September 21, 2009