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.' - - "001327 "_,"-1-... dams along the Uncompahgre River. In 1901, the State of Colorado began building the 5.8-mi-long Gunnison Tunnel from the Gunnison River to supply more water to the Uncompahgre Valley. Because of insufficient funding, the State could not complete the tunnel, and the BOR completed construction of the Gunnison Tunnel in 1909 (fig. I) and a diversion dam on the Gunnison River in 1912. The Uncompahgre Project, as it was called, included ,existing and new canals and laterals. Taylor Park Reservoir (fig. I) was built in 1937 to supply the project with a dependable water supply. Operation and maintenance of the Uncompahgre Project was transferred to the Uncompahgre Valley Water Users Association in 1932. The Uncompahgre Project supplies water for irrigation of about 86,000 acres in the lower Gunnison River Basin (figs. I and 2). About two-thirds of the irrigated land is west of the Uncompahgre River, where soils are more conducive to agriculture. Histor- ically, diversion of water from the Gunnison River accounted for about two. thirds of the irrigation water for the project, and water from the Uncompahgre River accounted for the remainder of the irrigation water. The Gunnison Tunnel discharges into the SOUlh Canal near Highway 50 east of Montrose (fig. I). Some water from the South Canal is used to irrigate land southeast of Montrose, but most of the water discharges into the Uncompahgre River to augment flows for downstream canal diversions. The irrigation season normally is from early April through October. Historically, water was di verted from the Uncompahgre River into canals during winter (hereinafter referred to as winter water) to provide water for livestock. A part of the subsurface-irrigation drainage and surface-return flow discharges into the Uncompahgre River upstream from Delta. Much of the water di verted by canals downstream from Montrose consists of return flows (subsurface and surface) from upstream irrigated areas. Between Peach Valley Arroyo and Roubideau Creek (fig. 2), irrigation drainage and return flows from Uncompahgre Project land discharge into the Gunnison River through natural drainage pathways or manmade ditches. There is considerable irrigated land in the lower Gunnison Ri ver Basin upstream from Delta, such as in the Smith Fork, North Fork, and Tongue Creek Basins (fig. I). Grand Valley Settlement began in the Grand Valley in 1881, and the private Grand Valley Canal (fig. 3) was completed prior to 1910. The Grand Valley Canal irrigates approximately the southern one-half of the Grand Valley that is north of the Colorado River between Palisade and Lorna (fig. 3). The Government Highline Canal (the Grand Valley Project) was completed in 1917. The Federal system provides water to areas between the Government Highline Canal and the Grand Valley Canal, to Orchard Mesa, and to some areas between Clifton and Palisade. The Grand Valley Water Users Association operates and maintains the Federal system north of the Colorado River, which serves about 30,000 acres. The remainder of the valley north of the Colorado River is served by the private Grand,Valley Irrigation Company. Orchard Mesa is served by the Orchard Mesa Irrigation District, and the Redlands area (fig. 3) is served by the private Redlands Water and Power Company. The Colorado River is the source of all irriga- tion water for the Grand Valley, except for the Redlands area, which uses water from the Gunnison River that is diverted about 2 mi upstream from the mouth of the Gunnison River. The Government Highline Canal diverts water from the Colorado River immediately upstream from the confluence with Plateau Creek (fig. 3), and the Grand Valley Canal diverts water near Palisade. Much of the subsurface- irrigation drainage and surface-return flow discharges into natural streams and washes that dissect the Grand Valley (fig. 3) and discharge into the Colorado River. In addition to natural drains, there is about 600 mi of man-made surface drains, many of which are in the private irrigation system. Salinity-Control Projects In 1974, the Colorado River Basin Salinity Control Act (Public Law 93-320) was passed by the U.S. Congress. That law authorized various investiga- tions and construction of projects with the objective of decreasing the salt (dissolved-solids) loading to the Colorado River. The Uncompahgre Project and the Grand Valley have been included in the salinity- control program. The Lower Gunnison Basin Unit of BOR's Colorado River Water Quality Improvement Program includes the Uncompahgre Project and INTRODUCTION 13