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The McElmo Creek Basin is located in southwestern Colorado and covers approximately 720 square miles. About 150 square miles of the basin, mostly in the east, are agricultural land. Early studies show that salt-loading results from both irrigation and diffuse sources. Irrigation is the main contributor. The total irrigation diversion into the area averages 105,200 acre feet per year. The average salt load contributed by the McElmo Creek Basin was estimated at 119,000 tons per year. The Montezuma Valley Irrigation Company diverts water from the Dolores River to serve irrigation in the McElmo Creek Basin. The salinity of the diversion averages 130 mg/L. Return flows from agriculture increase the salinity in McElmo Creek to about 2,600 mg/L at the ColoradoUtah State line. Plan Reclamation.-- Reclamation lined laterals and constructed the Towaoc Canal to control seepage.Buried pipe laterals have been brought down from the Towaoc Canal to serve areas once served by the now abandoned Rocky Ford Ditch. These actions reduce groundwater seepage from canals by 4,060 acre feet a year and reduce the amount of salt returned to McElmo Creek.
USDA-The McElmo Creek USDA salinity control report was published in 1983, with the final environmental impact statement released in 1989. The recommended plan calls for treatment of about 21,550 acres with sprinkler irrigation systems and about 270 miles of onfarm ditch and lateral lining. Implementation of the USDA program has been underway in this area since 1990. The major salinity reduction practices being installed are side-roll sprinkler systems, underground pipelines, and gated pipe. A fully coordinated implementation effort is underway, so design and installation of the laterals by Reclamation complement the onfarm irrigation systems. Joint planning actions with Reclamation have made it possible to install gravity pressure sprinkler systems on an additional 9,000 acres. Development Investigations Reclamation´s initial study from 1977 to 1984 included testing canal seepage, developing a hydrosalinity budget, and evaluating salinity control alternatives. The study tested canal seepage at 15 sites along 115 miles of canals. Groundwater monitoring included 125 wells for water table elevation, salinity, and hydraulic conductivity. Irrigation research was done on seven test farms representing various soil types, farm sizes, irrigation methods, and farm management.Results indicate seepage rates for most of the Montezuma Valley Irrigation Company distribution system are low to moderate except for locations where canal sections have been cut through shale. Reclamation did associated investigations on the Dolores Project, including a 1977 Final Environmental Statement. Reclamation´s December 1988 Definite Plan Report and a 1989 Final Supplement to the Definite Plan Report defined how the salinity features would be incorporated into the Dolores Project.. Verification Studies-Reclamation is maintaining a gauge in McElmo Creek to monitor the outflow from the unit area, but because of the unit's relatively small size and the concurrent construction of the Dolores Project (irrigation), the effects of canal and lateral lining will probably be masked. Irrigation efficiency improvements in other project areas have been shown to be effective. Without seepage, there can be no salt pickup from canals and laterals. Authorization Public Law 93-320 originally authorized this study as part of the Salinity Control Act as part of the Salinity control investigations in the Dolores Project area were conducted under the McElmo Creek Unit of the Colorado River Quality Improvement Program. The Colorado River Basin Salinity Control Act of June 24, 1974 (Public Law 93-320) originally authorized the unit as part of a basin wide program of works to enhance and protect Colorado River water quality.Public Law 98-560 of October 30, 1984, authorized construction of the McElmo Creek Unit salinity control features as part of the Dolores Project. Irrigation Improvements Through these actions, Reclamation and the U.S. Department of Agriculture have improved the irrigated areas so that they produce more crops and use less water. Salinity Control The 1999 Progress Report estimates that the McElmo Creek Unit in the Dolores project removes 23,000 tons of salt per year, for a total capital cost of $44,700,000 and an annual O&M cost of $33,000--for a cost of $160 per ton. |
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