Gunnison River Basin
The Gunnison River begins high in the mountains of central Colorado and flows west, stretching across more than 8,000 square miles of western Colorado, from the Continental Divide to its confluence with the Colorado River near Grand Junction. After this confluence, the volume of the Colorado River is almost doubled by the Gunnison River.
According to the Colorado Water Plan, forest area covers more than 50% of the basin, and about 5.5% of the land in the basin is planted, supporting a vibrant mix of farms, vineyards, orchards and ranches.
Acre-feet of water storage capacity in Colorado’s largest reservoir, Blue Mesa
The Gunnison River Basin contains the largest reservoir in the state, Blue Mesa Reservoir, completed in 1965 with a 940,800 acre-foot water storage capacity, according to the Colorado Division of Water Resources. Other major reservoirs in the basin include Morrow Point Reservoir, Taylor Park Reservoir and Ridgway Reservoir.
Only small quantities of water are imported into the basin, but a number of transbasin diversions move water out of the basin. Through the Redlands Canal or Redlands Diversion Dam each year about 500,000 acre-feet of water is diverted from the Gunnison River close to its confluence with the Colorado River near Grand Junction. The water is used for power generation and for irrigation in the Grand Valley.
Water users in the basin convene for water planning purposes and to share information through the Gunnison River Basin Roundtable.
The Gunnison River Basin is governed by the following compacts:
Upper Colorado River Compact (1948): Apportions a percentage of available river water to each Upper Basin state as follows: Arizona, 50,000 acre-feet each year; Colorado, 51.75%; Utah, 23%; Wyoming, 14%; and New Mexico, 11.25%. The Upper Colorado River Commission, with representation from Colorado, Wyoming, New Mexico, Utah and the federal government, oversees compliance.
Colorado River Compact (1922): Apportions 7.5 million acre-feet of consumptive use per year to the upper basin and the same amount to the lower basin. The upper states may not cause the flow of the Colorado River at Lee Ferry, Arizona, to be depleted below an aggregate of 75 million acre-feet for any period of 10 consecutive years.
Mexican Treaty on the Rio Grande, Tijuana and Colorado Rivers (1944): Guarantees delivery of 1.5 million acre-feet of Colorado River water per year to Mexico except in times of extraordinary drought when the United States can reduce deliveries in the same proportion as it cuts its own consumptive use. If the river does not have adequate water to meet the obligations under the treaty, the Upper Colorado River Basin and Lower Colorado River Basin must share the obligation of reducing use to make up deficiencies.