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<br />ilu[JM'7 <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />PART J. SUMMARY <br /> <br />The Mancos River drains 790 square miles in the southwestern corner <br /> <br /> <br />of Colorado and discharges into the San Juan River at a point about one mile <br /> <br /> <br />south of the Colorado-New Mexico state line. Except for approximately 50 <br /> <br /> <br />square miles of desert lands in New Mexico, all of the drainage basin for the <br /> <br /> <br />Mancos River is located within Colorado. The Mancos River flows from east <br /> <br /> <br />to west across the Ute Mountain Ute Indian Reservation and most of the reserva- <br /> <br /> <br />tion is located within the Mancos drainage basin. Most of Mesa Verde National <br /> <br /> <br />Park is also included within the drainage basin. Elevations vary from 4,800 <br /> <br /> <br />feet at the Colorado-New Mexico state line to over 13,000 feet in the La Plata <br /> <br /> <br />Mountain Range. Annual precipitation varies from less than eight inches to <br /> <br /> <br />over 40 inches per year. The general location of the Mancos River basin is <br /> <br /> <br />shown on Figure 1. <br /> <br />The headwater tributaries of the Mancos River are in the La Plata <br /> <br /> <br />Mountains, and runoff from this area provides a water supply for irrigation <br /> <br /> <br />of up to 11,500 acres in the vicinity of the town of Mancos. Generally, May <br /> <br /> <br />and June are months of maximum flow, resulting from snowmelt runoff high <br /> <br /> <br />in the mountains. During the remainder of the year, the river has a much lower <br /> <br /> <br />flow with minimums occurring from September through January. Flow in other <br /> <br /> <br />tributaries of the Mancos River is typically short-term response to snowmelt <br /> <br /> <br />and infrequent rainstorm runoff. Since flows in Navajo Wash, a tributary of <br /> <br /> <br />the Mancos River, are the result of diversions from the Dolores River for irriga- <br /> <br /> <br />tion near the town of Towaoc, such flows have not been considered as a part <br /> <br /> <br />of this analysis. <br /> <br />Gaging station records are available for several locations along the Mancos <br /> <br /> <br />River, but a long-term period of record has been developed at only one site, <br /> <br /> <br />located in the lower reach of the river near the Colorado-New Mexico state <br /> <br /> <br />line. Gages near the headwaters were established in 1937 and 1938 near the <br /> <br /> <br />confluence of the West Mancos, Middle Mancos, and East Mancos rivers to provide <br /> <br /> <br />basic streamflow data for the planning and design of the Jackson Gulch Reservoir <br /> <br />-l- <br />