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<br />"'r""3~8 <br />u ~t (~ ~ <br /> <br />. <br /> <br />Diversions on Ute Mountain Ute Reservation <br /> <br /> <br />hrigation diversions from the Mancos River for irrigation on the Ute <br /> <br /> <br />Mountain Reservation have historically been made at a location 1.6 miles up- <br /> <br /> <br />stream of the USGS gage near the Highway 666 bridge. There is no measuring <br /> <br /> <br />device in the ditch, and the Water Commissioner has not maintained records <br /> <br /> <br />of diversions. The ditch is approximately three miles in length and is used to <br /> <br /> <br />provide an inigation supply for a 134 acre area located on the west side of <br /> <br /> <br />Highway 666. hrigation return flows enter the Mancos River downstream of <br /> <br /> <br />the gage. <br /> <br />. <br /> <br />Notations in the annual USGS gaging station records indicate that the <br />irrigation diversion facility was in existence in 1951 and has continued to the <br />present. The 1951 notation states that the irrigated area was about 50 acres, <br />but 100 acres was listed in all subsequent notations. Examination of the 1973 <br />aerial photograph indicates that about 134 acres were irrigated at that time, <br />and a 1985 field inspection verified that the same general area irrigated in <br />1973 is presently served by the ditch. <br /> <br />Ditch diversions cross under Highway 666 in a 29-inch by 58-inch corru- <br /> <br /> <br />gated pipe arch. On August 19, 1985, the ditch was diverting all of the flow <br /> <br /> <br />of the Mancos River, estimated to be about five cfs. On September 26, 1985, <br /> <br /> <br />the ditch was diverting about two cfs, although the flow of the Mancos River <br /> <br /> <br />at that time was considerably greater than 10 cfs. Based on high water marks <br /> <br /> <br />at the culvert and flow velocity measurements, it is estimated that the maximum <br /> <br /> <br />diversion through the ditch has been in the range of seven to nine cfs. <br /> <br />In order to determine the historic flow of the Mancos River at the diversion <br /> <br /> <br />point upstream of the USGS gage near Highway 666, it was necessary to estimate <br /> <br /> <br />the typical diversions through the inigation ditch. The following monthly average <br /> <br />diversions were estimated: <br /> MAY JUN JUL AUG SEP TOTAL <br />Average cfs 4.0 5.0 5.0 5.0 4.0 <br />Acre-Feet 250 300 310 310 240 1,410 <br /> <br />. <br /> <br />-12- <br /> <br />ii_ , <br />