GENERAL38637 - Laserfiche WebLink

Home Browse Search

a (2) The alluvial valley has water availability sufficient for flood irrigation agricultural activities [Section 1.04(10)]. (3) The alluvial valley has water availability sufficient for subinigation agric~.:ltural activities [Section ].04(10)]. Map M35A in the permit application shows that the following six drainages are the only drainages in the vicinity of the Trapper Mine which contain unconsolidated stream-laid holding streams: Yampa River, Williams Fork River, No Name Gulch, Johnson Gulch, Pyeatt Gulch, and Flume Gulch Imeation Atricultural Potential Flood irrigation is practiced on the valley floors of the Yampa River in the Big Bottom area and the Williams Fork River neaz its confluence with the Yampa. 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). Stunmertirne evaporation in Moffat County exceeds precipitation by approximately 30 inches (Evaporation from Lakes and Reservoirs by A.F. Meyer, 1942, Minnesota Resotuces Commission, page 58). The lazgest 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 imgation practiced in small stream valleys in northwestern Colorado where wheat, alfalfa, and hay aze grown; the 80-day growing season limits farming in Moffat County to these or similaz crops. Subirrigation Agricultural Potential OSM's "Alluvial Valley Floor Identification and Study Guidelines" (page C-]0) explains that "In terms of the alluvial valley floor regulatory program, subirrigation occurs if enough water is available for a long enough time to have a recognizable effect .in the species type and the productivity of a plant community. Agricultural crops or rangeland must receive enough subirrigation that the community is notably more productive or more agriculturally useful when compared to dryland azeas." Subirrigation of agricultural plants can be expected to occur in the wick:, flat valley bottoms of the Yampa River and Williams Fork River. The four gulches, though, lack sufficient water availability for subirrigation agricultural activities based on examination of those valleys in connection with renewal application RN-03/PR-04. Two Di~iision representatives and two representatives of the applicant jointly examined Flume Gulch in order to verity 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 Trapper Mine 30 ~ May 13, ].998