|
General Description
The Uinta Basin Unit is located in northeastern Utah. The area includes portions of Duchesne and Uinta Counties and is situated between the Uinta Mountains on the north and the Tavaputs Plateau on the south. The principal communities within the area are Duchesne, Roosevelt, and Vernal.
Reclamation has conducted extensive studies in the area. Most of the salt pickup from the unit area is from the dissolution of salts from the soil and subsurface materials, principally from soils of marine origin which underlie most of the Uinta Basin. Seepage from conveyance systems and deep percolation resulting from irrigation are the primary processes which dissolve salts from the soils and shales and convey the salts through the groundwater system to natural drainages and ultimately to the Colorado River. The Uinta Basin contributes an estimated 450,000 tons of salt per year to the Colorado River.
Reclamation-Several proposals have been received under Reclamation's Basinwide Salinity Control Program, Request for Proposals, and have been accepted. Environmental compliance on these plans will need to be completed before they may be implemented, but several show promise.
USDA-The USDA Uinta Basin Salinity Control Plan was prepared in 1979 and amended in 1987 to include off-farm lateral improvements. In 1992, the plan was expanded to bring in 20,000 acres of adjoining irrigated lands which were not included in the original plan. The total salt-load reduction goal for this area is 106,800 tons per year.
Since 1987, implementation has been accomplished under the authorities of the USDA Colorado River Salinity Control Program. The application of salinity reduction practices continues at an increasing rate. The major practices installed are wheel-line sprinkler systems, improved surface systems, underground pipelines and gated pipe. In this area, many groups of farmers are replacing leaking earthen laterals with pipelines which provide gravity pressure for onfarm sprinkler systems.
Verification Studies-USGS reported in their National Water Summary 1990-91, Water Supply Paper 2400, a downward trend in dissolved solids concentration (salinity) in the Duchesne River, immediately downstream of the project area. They pointed out that much of the base flow of the river was from irrigation return flows. From table 4a in the appendix of this report, salinity discharge has dropped from 206,000 tons in 1981 when USDA first started irrigation improvements to 169,000 tons in 1993-a 37,000-ton reduction. Based on the amount of irrigation improvements installed, USDA estimates that irrigation improvements through 1992 have reduced the salinity discharge by about 55,500 tons per year (1993 Joint Evaluation Report). Recent studies have also shown a downward shift in the salt/flow relationship (for a given flow, salinity is lower). This data supports the theory that onfarm irrigation practices can be effective at reducing salt loading. Monitoring and analysis will continue. |
