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The Lower Gunnison Basin Unit is located in west-central Colorado in Delta and Montrose Counties. For Reclamation study purposes, the Unit was broken into two study areas, the Uncompahgre Project area and the North Fork area. The Uncompahgre Project is a federal development constructed in the early 1900's to irrigate approximately 86,000 acres adjacent to the cities of Montrose and Delta. Approximately 34 percent of the irrigated lands are on Mancos Shale derived soils lying east of the Uncompahgre River. These soils are naturally high in both salt and selenium. An estimated 360,000 tons of salt is added to the Colorado River from the Uncompahgre Project annually. This area has also been estimated to be the source of about 60% of the selenium load to the upper Colorado River. The North Fork study area, is located in Delta County. It includes irrigated areas on the North Fork of the Gunnison River and areas north and east of the city of Delta along the Gunnison River. Areas north of Delta and southeast of Hotchkiss contribute large amounts of salt. The total off-farm salt contribution from the North Fork area was estimated to be approximately 148,000 tons per year. Studies of these areas indicate that salt loading occurs when irrigation conveyance system seepage and irrigation return flows pass through highly saline soils and the underlying Mancos Shale Formation. By reducing the amount of groundwater percolating through these saline soils, salt loading to the Colorado River is being reduced. Reclamation and the Natural Resources Conservation Service (NRCS, formerly the Soil Conservation Service) of the USDA have implemented various salinity control measures in the area. Reclamation was given primary responsibility for reducing salinity loading resulting from the "off-farm" irrigation water delivery facilities, i.e. the canals and laterals. Reclamation works primarily with the irrigation districts or companies. The NRCS is primarily responsible for addressing the "on-farm" sources of salt loading and primarily works with individual farmers to implement control measures. Salinity Control Plan Reclamation´s --- A Feasibility Report/Final Environmental Statement was completed by Reclamation in 1984 for the Uncompahgre Project Area. The report recommended the construction of irrigation delivery system improvements on the more saline, east side of the Uncompahgre Project area and winter water replacement facilities throughout the project service area. The Salinity Control Act authorized the construction of these facilities. The recommended delivery system improvements involved lining off-farm irrigation canals and laterals. Although authorized for construction, canal lining is not currently competitive with other, lower cost alternatives within the Salinity Control Program. However, a recent re-analysis of the plan found that piping of the irrigation laterals may be competitive. The winter water replacement program was designed to eliminate the need for watering livestock from the unlined canals and laterals during the winter. Water is made available for livestock through an expansion of the existing domestic water system which is used to fill stock water tanks. These improvements allow for the elimination of water from the canal system throughout the winter months and thus reduces seepage during the non-irrigation season. This reduces salinity loading from the canal system by about 30 percent. In the North Fork area, Reclamation studied off-farm salinity contributions from saline springs and seepage from unlined canals and laterals. Emphasis was placed on identifying and quantifying off-farm sources of salinity and formulating alternative solutions to diminish the salt loading to the river system. However, a detailed study showed the cost of the selective lining of canals and laterals and winter water replacement to be prohibitive. Additionally, at that time, there was little interest from local irrigators in participating in the Salinity Control Program. NRCS- The NRCS salinity control plan for the Lower Gunnison Basin was prepared in 1981, and an environmental impact statement was published in 1982. The NRCS plan calls for treatment of approximately 135,000 acres of irrigated land and some improvement of off-farm laterals. Authorization The unit was authorized for investigation by the Salinity Control Act (Public Law 93-320) of 1974. Portions of the unit were later authorized for construction in 1984 by an amendment to the act, Public Law 98-569. Construction Winter Water Program: With Reclamation funding, local water districts completed the construction of winter water facilities in the Uncompahgre Project area in 1995 and subsequently, water is no longer carried in the Project's canals and laterals in the wintertime. The total capital cost was approximately $24 million and annual operation and maintenance costs are about $444,000. Off-farm Delivery System Improvements: The East Side Laterals proposal to pipe off-farm laterals on the east side of the Uncompahgre Project area is currently competing for funding in Reclamation's Basinwide Salinity Control Program under the authorities of Public Law 104-20. In FY98, Reclamation solicited proposals for salinity control efforts under this program. The Uncompahgre Valley Water Users Association (UVWUA) submitted a proposal for a demonstration project to be cost shared with the Department of the Interior's National Irrigation Water Quality Program (NIWQP). The NIWQP is interested in reducing selenium loading from the area and their cost share enabled the proposal to be competitive with other salinity control projects. The project was selected for implementation and construction is scheduled to be completed in FY2000. The UVWUA is replacing approximately 7.5 miles of existing unlined earthen irrigation laterals with buried pipe in the Uncompahgre Project's South Canal system. The project has an estimated cost of $1.6 million will reduce salinity in the Colorado River by about 2,300 tons of salt per year. Extensive monitoring of return flows is underway to document the project´s selenium and salinity reduction effects. If this salinity control measure can be shown to effectively control selenium, more joint projects may be pursued between the two programs. On-Farm Improvements: On-farm improvements being implemented by the NRCS include upgrading irrigation systems and improving irrigation management. Implementation was initiated in 1988 by targeting funds into the Tongue Creek sub-area in Delta County. Since that time, funding has been allocated to the other subareas, and implementation is now underway in all of the Lower Gunnison Basin Unit. The major practices being installed are underground pipelines, ditch lining, land leveling, irrigation water control structures, sprinkler systems, gated pipe, and surge irrigation systems. Currently, proposals for on-farm improvements from individual farmers are competing for funding under NRCS´s Environmental Quality Incentives Program and under supplemental funding from the Basin States Cost Sharing Program. Salinity Control Winter Water Program: This portion of the project, which has been completed, is estimated to prevent about 41,000 tons of salt from entering the Colorado River system each year at a cost of $57 per ton. Off-Farm Improvements: The East Side Lateral proposal, if implemented in its entirety, would prevent approximately 64,000 tons of salt from entering the Colorado River System each year at a cost of approximately $70 per ton (1994 prices). On-Farm Improvements: Through FY-1996, the NRCS program estimates it has reduced salinity loading to the Colorado River system by approximately 34,000 tons per year at a cost of $54 per ton. Ultimately, there is potential to reduce loading by an additional 132,000 tons per year if all the planned improvements are implemented. |
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