How Western Slope water sustains the Front Range |

How Western Slope water sustains the Front Range

Colorado River Water Conservation District/guest commentary

EDITOR’S NOTE: This is part four in a series of columns that talks about the complexity of water in the West. The columns are produced by the Colorado River Water Conservation District, of which Summit County is a member.

Taxpayers support the River District with a small mill levy to help defend Western Slope water interest.

Transmountain diversions may single-handedly be the most controversial and divisive water issue in Colorado.

A transmountain diversion (TMD) removes water from one river basin in the state and transports it across a mountain barrier into another river basin.

Locally, the water in Dillon Reservoir is the beginning of a transmountain diversion.

The Roberts Tunnel syphons it over the Continental Divide where it pours into the North Fork of the South Platte River for the benefit of Denver Water customers.

In Grand County, the Northern Colorado Water Conservancy District takes water through the Adams Tunnel to the Big Thompson where it is diverted up and down the Front Range and into the South Platte.

This removal of water is not only legal, but the entitlement to do so is written into the state’s constitution.

Why is this done? Colorado can be divided into two distinct halves by the Continental Divide.

The Divide spans the length of Colorado, from its northern border with Wyoming south to New Mexico.

Rain and snow that falls on the west side of this dividing line will run to the Pacific Ocean, and precipitation that falls on the east side of the Divide heads in the direction of the Atlantic Ocean.

The Western Slope, the lands west of the Continental Divide, receive the vast majority of Colorado’s moisture, about 80 percent, while the Eastern Slope on the other side receives only 20 percent.

The problem is more than four out of every five Coloradans live on the much drier, eastern side of the Divide.

To sustain these large and growing populations in major Eastern Slope cities such as Denver, Boulder, Colorado Springs, Pueblo and Aurora, these municipalities have come to rely on diverting water from the wetter Western Slope to the eastern half of the state through transmountain diversions projects.

One of the first transmountain diversions occurred around 1900 when enterprising and scrappy farmers from northeastern Colorado dug the Grand River Ditch to siphon off water from the Colorado River’s headwaters in what is now Rocky Mountain National Park by “just going over there and taking it.”

Today, 12 major transmountain water diversions are removing water from the Colorado River Basin.

These 12 diversions combine to remove between 450,000 and 600,000 acre-feet of water from the Colorado River basin per year, which is enough water to cover the entire Denver metro area from five feet to more than six feet deep in water.

The loss of water out of Western Slope counties affected by transmountain diversions can be as high as 65 percent of the streamflow being diverted away to the other side of the Divide.

Since water is used multiple times as it flows downstream, removing water from a basin through transmountain diversions means the loss of water can be felt in multiple ways.

When water is diverted out of a basin, the ability to use and reuse that water is lost completely to the basin of origin.

Transmountain diversions can lead to a loss of economic, recreational and aesthetic benefits and have negative impacts to water quality and animal habitat.

A number of Western Slope agencies keep a vigilant eye on existing and proposed future transmountain water diversions.

Among them are the Colorado River Water Conservation District, Northwest Colorado Council of Governments, the Middle Park Water Conservancy District as well as county governments and local Western Slope water conservancy districts and agencies.

The Colorado River Water Conservation District was chartered by the Colorado General Assembly in 1937 for the conservation, use, protection and development of the water resources of the Colorado River Basin. The district includes Routt, Moffat, Grand, Eagle, Summit, Pitkin, Garfield, Rio Blanco, Mesa, Gunnison, Ouray, Delta and portions of Montrose, Saguache and Hinsdale counties. Saturday’s column will look at basin of origin issues. To read other parts of the series, log on to

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