Laserfiche WebLink
<br />Qf1[l3'!'J <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />PART X. VIRGIN STREAMFLOW CALCULATIONS FOR MANCOS RIVER <br />ON UTE MOUNTAIN UTE RESERVATION <br /> <br />The virgin flow of the Mancos River on the Ute Mountain Ute Indian Resel'- <br /> <br /> <br />vation is equal to the virgin flow at the confluence of the West, Middle, and <br /> <br /> <br />East Mancos rivers, as described in Part IX above, plus inflows to the river <br /> <br /> <br />downstream of the confluence, less river losses. Inflows consist of two compo- <br /> <br /> <br />nents: (1) short-term runoff events that occur as a result of thunderstorm <br /> <br /> <br />activity in the basin during summer months and (2) general precipitation through- <br /> <br /> <br />out the year. The following subsections describe the methodology used in the <br /> <br /> <br />calculation of river losses, short-term runoff, and river gains. <br /> <br />River Losses <br /> <br /> <br />Water use by riparian vegetation along the Mancos River results in a signifi- <br /> <br /> <br />cant stream loss during the growing season. Evaporation from the water surface <br /> <br /> <br />in the river also contributes to the stream loss. During much of the growing <br /> <br /> <br />season, stream losses exceed inflow from side tributaries downstream of Mancos, <br /> <br /> <br />resulting in a "losing stream." During critical dry periods, losses are estimated <br /> <br /> <br />to be sufficient in magnitude to almost result in a dry stream at the Colorado- <br /> <br /> <br />New Mexico state line under virgin flow conditions. Stream losses were analyzed <br /> <br /> <br />by two methods as described in Subsections A and B below. Based on the results <br /> <br /> <br />of these analyses, stream losses were estimated for each reach of the Mancos <br /> <br /> <br />River on a monthly basis, as described in Subsection C below. <br /> <br />A. Comparison of stream flows at the Johnson Canyon Gage and Highway <br />666 Gage. <br /> <br />Daily gage records are available for the flows of the Mancos River near <br /> <br /> <br />Cortez, located 0.8 mile upstream from the confluence of Johnson Canyon, <br /> <br /> <br />for the period of July 1976 through June 1979. The gage was relocated <br /> <br /> <br />to a site O.l mile downstream of Johnson Canyon in July 1979. Since <br /> <br /> <br />there is no appreciable flow in Johnson Canyon during most of the year, <br /> <br /> <br />relocation of the gage has little hydrological significance. Daily records <br /> <br />-29- <br /> <br />.t1 <br />