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<br />,.... <br />CJl <br />a <br />OJ <br /> <br />supply project on the lower Virgin River in Nevada. The study found the proposal was not cost <br />effective. <br /> <br />Mancos Valley <br /> <br />The Mancos Valley Unit is a 9,2oo-acre irrigated area along the Mancos River, a tributary to the San <br />Juan River. The report, Irrigation Improvements for Mancos Valley, was completed liy USDA in <br />1985. The recommended plan includes 3,200 acres of sprinkler systems and other water <br />management/salinity control treatment on about 5,500 total acres. About 17 miles of canal and lateral <br />lining would combine many old earthen laterals. Total salt-load reductions are estimated to be 8,800 <br />tons per year with about 7,700 tons resulting from lateral improvements. About 57 landowners and <br />15 lateral companies or groups of landowners would be involved. This unit has not yet been included <br />in the Colorado River Salinity Control Implementation Plan, and no implementation actions have been <br />taken. <br /> <br />McElmo Creek <br /> <br />The McElmo Creek Basin is located in southwestern Colorado and covers approximately 720 square <br />miles. About 150 square miles of the basin, mostly in the east, are agricultural land. Early studies <br />show that salt loading results from both irrigation and diffuse sources, with irrigation being the main <br />contributor. <br /> <br />The total irrigation diversion into the area averages 105,200 acre-feet per year. The average salt load <br />contributed by the McElmo Creek Basin was estimated at 119,000 tons per year. The Montezuma <br />Valley Irrigation Company diverts water from the Dolores River to serve irrigation in the McElmo <br />Creek Basin. The salinity of the diversion averages 130 mg/L. Return flows from agriculture <br />increase the salinity in McElmo Creek to about 2,600 mg/L at the Colorado-Utah State line. <br /> <br />Studies included testing canal seepage, developing a hydrosalinity budget, and evaluating salinity <br />control alternatives. The study tested canal seepage at 15 sites along 115 miles of canals. <br />Ground-water monitoring included 125 wells for water table elevation, salinity, and hydraulic <br />conductivity. Irrigation research was done on seven test farms representing various soil types"farm <br />sizes, irrigation methods, and farm management. <br /> <br />Results indicate seepage rates for most of the Montezuma V alley Irrigation Company distribution <br />system are low to moderate except for locations where canal sections have been cut through shale. <br />The plan is to improve three sections of Montezuma Valley Irrigation Company canals, two on the <br />Lone Pine lateral and one on the Upper Hermana lateral, and to install laterals from the <br />Towaoc-Highline Canal to serve the Rocky Ford Ditch service area. The Rocky Ford Ditch would <br />then be abandoned as part of the plan, and its flows would be combined into the Towaoc-Highline <br />Canal. The plan will reduce ground-water seepage from canals by 4,060 acre-feet a year and reduce <br />the amount of salt returned to McElmo Creek. <br /> <br />The McElmo Creek Unit was authorized for construction by Public Law 98-596 in October 1984 as <br />part of the Dolores Project, a participating project of the Colorado River Storage Project which is <br /> <br />32 <br /> <br />I <br />,. <br />, <br />