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The Grand Valley Unit is located in west-central Colorado along the Colorado River near Grand Junction. The unit was authorized for construction by the Salinity Control Act (Public Law 93-320) of 1974. Public Law 98-569, enacted in 1984, amended Title II provisions of that act and authorized the Colorado River Salinity Control Program.
The purpose of the Grand Valley Unit is to reduce the estimated 580,000 tons per year of salt added to the Colorado River as a result of irrigation system seepage and agricultural practices in the valley.
Studies indicate that salt loading to the Colorado River (Figure 1) occurs when seepage from irrigation water conveyance systems, such as canals and laterals, irrigated fields, and irrigation return flows pass through highly saline soils and the underlying Mancos Shale Formation in the Grand Valley. By reducing the amount of groundwater percolating through these saline soils, salt loading to the Colorado River is decreased.
Reclamation conducted conveyance systems improvements as a cost-effective method of reducing off-farm seepage and salt loading. On-farm improvements, including upgrading irrigation systems through cost assistance and improving irrigation management to reduce deep percolation from farm operations, are being implemented by the U.S. Department of Agriculture. The improvements include installing underground pipelines, gated pipe, concrete-lined ditches, land leveling, drip irrigation systems, and a variety of other practices.
Reclamation`s program in the Grand Valley primarily focuses on off-farm irrigation system improvements. Off-farm systems include the main supply canals and the ditches or laterals that deliver water from the main canals to individual properties. In the Grand Valley, there are 6 different entities responsible for irrigation water delivery. The Federally-owned Grand Valley Project is operated by the Grand Valley Water User`s Association on the north side of the Colorado River and by the Orchard Mesa Irrigation District on the south side of the Colorado River and east of the Gunnison River. Irrigation water is delivered to the Palisade and Mesa County Irrigation Districts through the Grand Valley Project`s main canal, the Government Highline Canal. The Grand Valley Irrigation District owns and operates the largest private system in the valley. The privately-owned Redlands Water and Power Company delivers water to land to the south of the Colorado River and west of the Gunnison River. Collectively, these irrigation systems have about 200 miles of main canals and 500 miles of laterals delivering water to approximately 70,000 acres of land.
The Grand Valley Unit was completed in two stages. Stage One (approximately 10 percent of the valley) was used as a test area to refine analysis and construction techniques used on the balance of the project (Stage Two). After completing environmental studies in 1978, Stage One construction began in October 1980. As part of the development, 6.8 miles of the Government Highline Canal were concrete lined, and 34 miles of unlined laterals were consolidated into 30 miles of piped laterals. Construction of Stage One was essentially completed in April 1983.
Monitoring of the Stage One area began in 1976 and continued through 1984. Under the monitoring program, flow and salinity measurements were taken in the Reed Wash study area, a hydrologically isolated basin within the Stage One area. The data were used to evaluate the effects of the Stage One improvements on groundwater, surface flows, and water quality. Analysis of the monitoring data indicated that canal and lateral seepage was decreased by approximately 5,700 acre-feet and salt loading to the Colorado River decreased by approximately 21,900 tons, supporting recommendations for initiating construction of Stage Two.
Beginning in November 1981, Stage Two investigations included re-evaluating various alternatives and analyzing salinity control measures other than concrete lining of the canals and laterals. The Grand Valley Project, Final Environmental Impact Statement describes alternatives for the construction and operation of the Grand Valley Unit. The report was filed with the Environmental Protection Agency on May 23, 1986.
Stage Two of the Grand Valley Unit originally planned to cover most of the remaining canal and lateral systems in the valley. The recommended plan included piping and lining only selected portions of the private and Federal irrigation systems to reduce seepage into the groundwater system. Construction started in 1986 and was essentially completed in 1998.
Verification Studies-In 1994, the U.S. Geological Survey (USGS) and Reclamation executed a cooperative agreement to monitor the main river system and evaluate the effectiveness of the salinity control improvements in the Grand Valley Unit. The first review of the project`s effectiveness was published in 1995 by USGS as a Water Resources Investigation Report (No. 95-4274). The analysis shows downward trends in salinity, suggesting that the salinity control program is decreasing salinity. However, the study was limited by the availability of post-project data. Reclamation and USGS plan to continue to monitor the system and update the analysis about every 5 years. USGS has conducted studies within the washes draining the area. Results from this analysis indicate significant downward trends in salinity in the washes.
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Analysis and development of Stage Two was divided into 16 sections of canal and lateral systems. Since of the planned improvements were for private irrigation systems, it was necessary to obtain permission and support from those entities. Due to concern over Federal involvement in the operation of their private canal system, the Grand Valley Irrigation Company voted not to participate in the salinity program improvements. Soil types in the Redlands and on the Orchard Mesa are not nearly as saline as those found north of the Colorado River, so those areas were not improved. As a result, only 8 of the 16 sections were improved. A summary of the resulting improvements is shown in Figure 2.
Figure 2 - Summary of Grand Valley Unit Salinity Control Improvements
To reduce costs, the Stage Two improvements to the Federal canal used a plastic membrane lining instead of concrete. It was more cost effective to place the smaller privately-owned canals in underground pipes. Laterals for both the Federal and private irrigation systems were converted from open earth ditches to buried pipelines.
Improving the Federally-owned canals involved shaping the canal bottom and banks. Since this work was being done in an existing canal after the irrigation season, site conditions were difficult at times. Most of the time this work proceeded without incident, but other times things did not go so well. After the canal was shaped, the plastic membrane lining was pulled across the canal. The plastic lining is strong, but needs protection from exposure to the sun and operation and maintenance activities. Consequently, a 15-inch-thick layer of gravel was placed over the membrane lining. The completed canal looks (redo this link w new picture) much like the original canal, but includes the membrane lining to prevent future seepage.
Replacement of the open earth ditches with buried pipelines also required several steps. After digging the trench, the pipe was placed in the trench. Sometimes a Henry Pipelayer was used for placing the pipe. Using this piece of equipment, a crew was able to lay up to 800 feet of pipe in a day. After the pipe was placed in the trench, backfill was placed around the pipe and the trench was filled in. Pipe sizes varied from 4 to 48 inches in diameter. Nearly all pipe larger than 24 inches was reinforced concrete pipe and the smaller sizes were plastic pipe.
As canals and laterals were improved in the Grand Valley, scattered wetlands and other wildlife habitats were dried up and lost. To compensate for this loss, Reclamation worked with the U.S. Fish and Wildlife Service and Colorado Division of Wildlife to acquire, develop and preserve permanent wildlife habitats along the Colorado River. The program has received broad support from local governments and the public.
A total of 5 wildlife areas have been developed under the program: Horsethief Canyon State Wildlife Area, Grand Junction Wildlife Area, Colorado River Wildlife Area, Orchard Mesa Wildlife Area, and DeBeque Wildlife Area. These areas encompass about 2,300 acres of prime wildlife habitat along the Colorado River. Developments on the properties have stressed restoration of native cottonwood riparian forests, creations of wetlands, and plantings of permanent grassland and shrub habitat. Refugia ponds on two of the properties are used for endangered Colorado River fish. The areas are managed by the Colorado Division of Wildlife and the Mesa County Land Conservancy.
These areas will continue to be managed for the primary purpose of replacing wildlife habitat. In the long term they will be key factors in preserving the rapidly disappearing Colorado River riparian habitat as growth and development continues to expand in western Colorado.
The Grand Valley Unit removes 115,700 tons of salt per year, for a total capital cost of $168,700,000 and an annual operation and maintenance (O&M) cost of $635,000. The annual cost per ton for salt removed is figured as follows. Compute an annualized cost for the capital costs at 5-5/8 percent interest over a 50-year period, or $10,147,000. Add the annual O&M cost to the annualized capital costs ($10,147,000 + $635,000 = $10,782,000). Divide that sum by the tons of salt removed per year ($10,782,000 / 115,700 = $93). The resulting cost for the Grand Valley Unit is $93 per ton of salt removed.