Colorado River Basin

It’s not a stretch to call the Colorado River the lifeblood of the American Southwest. Flowing from the Continental Divide to the Sea of Cortez in Mexico, the Colorado provides water to more than 40 million people in seven U.S. states and Mexico. Less than 20 percent of the entire Colorado River Basin lies inside Colorado, but about 75 percent of the water that feeds the river originates here, according to the 2015 Colorado Water Plan.

Within the state, the Colorado River Basin encompasses about 9,830 square miles. Rangeland and forests are predominant landscapes, comprising about 85 percent of the area. Elevations in the basin range from more than 14,000 feet near the headwaters to about 4,300 feet at the Colorado-Utah state line.

The bottom and top elevations in the Colorado River Basin

In Western Slope headwaters communities, the Colorado River supports fishing, rafting, ski area snowmaking, and wildlife habitat. As it flows west, it supports livestock grazing; timber harvesting; oil and gas drilling; the orchards and vineyards of Palisade; the wheat and alfalfa fields of the Grand Valley; the communities of Grand Junction and other towns; and fish and wildlife populations. Water users and managers working to solve water-related issues and meet the needs of the many water users in the basin convene through the Colorado Basin Roundtable.

Transbasin diversions reroute a significant amount of water from near the Colorado River headwaters, between 450,000 and 600,000 acre-feet annually, Much of that water goes to Colorado’s Eastern Slope, where it makes up roughly half of Denver’s water supply and serves many other cities and farms on the Front Range and Eastern Plains.

The largest transbasin diversions include the Adams Tunnel, which is a principal component of the Colorado-Big Thompson Project and carries an average of 216,570 acre-feet annually from the Colorado to the South Platte Basin; as well as the Roberts Tunnel, Moffat Tunnel and Boustead Tunnel, which are each responsible for 50,000-60,000 acre-feet of water diverted out of the Colorado Basin each year. The largest storage project in the basin is Granby Reservoir, which is part of the Colorado-Big Thompson Project and is the second largest reservoir in the state.

The Colorado River Basin is governed by the following compacts and treaties:

The Colorado River Compact of 1922 divides the waters of the Colorado among the basin states for the people who rely on its waters.

The Mexican Treaty on the Rio Grande, Tijuana and Colorado Rivers (1944) also 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 the United States cuts its 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.

Signed in 1948, the Upper Colorado River Compact 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.