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<br />Map M35A in the permit application package shows that the following six drainages are <br />the only drainages in the vicinity of the Trapper Mine which contain unconsolidated <br />stream-laid deposits holding streams: Yampa River, Williams Fork River, No Name <br />Gulch, Johnson Gulch, Pyeatt Gulch, and Flume Gulch. <br /> <br />Any of those alluvial valleys would meet the regulatory definition of an alluvial valley <br />floor if the valley has water availability sufficient for flood irrigation agricultural <br />activities \[Section 1.04(10)\] or has water availability sufficient for sub-irrigation <br />agricultural activities \[Section 1.04(10)\]. <br /> <br /> Irrigation Agricultural Potential <br /> <br />Flood irrigation is practiced on the valley floors of the Yampa River in the Big Bottom <br />area and the Williams Fork River near its confluence with the Yampa. The four gulches <br />(No Name, Johnson, Pyeatt, and Flume) lack sufficient water availability for flood <br />irrigation. According to the Natural Resources Conservation Service, local irrigation <br />requires approximately 5 acre-feet of water per acre, after allowing for evaporation losses <br />(letter from Hill, 1980 referenced on page 2-539 of permit application). Summertime <br />evaporation in Moffat County exceeds precipitation by approximately 30 inches <br />(Evaporation from Lakes and Reservoirs by A.F. Meyer, 1942, Minnesota Resources <br />Commission, page 58). The largest annual water yield for any of the four gulches is <br />calculated to be the 225 acre-feet yield from Flume Gulch (page 2-412 of permit). This <br />amount of water would irrigate only 45 acres based on the 5 acre-feet of water per acre <br />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 /> <br /> Sub-irrigation Agricultural Potential <br /> <br /> 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 /> <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 RN04/PR05. Two Division representatives and two Trapper representatives <br />jointly examined Flume Gulch in order to verify the presence of AVF features. No <br />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 /> <br /> <br />40 <br /> <br />Trapper MineJuly 9, 2013 <br /> <br />