Beneath the glacier-carved peaks and valleys of Rocky Mountain National Park, below the alpine lakes and rushing streams, a concrete-lined tunnel belies the illusion of a pristine wilderness. In 1944, the two ends of the Alva B. Adams Tunnel were connected with a blast of dynamite, creating the largest water diversion project in the state of Colorado. This monumental engineering feat re-directed the Colorado River and several other rivers and streams and reshaped the state’s political landscape. From statewide debates that preceded its construction to current disagreements over how much of the Colorado River headwaters should be sent from the Western Slope to the Front Range, the Adams Tunnel has served as a conduit for not only water but also controversy and collaboration.

Colorado–Big Thompson Project

The Adams Tunnel is the linchpin of the Colorado–Big Thompson Project (C-BT), which spans 250 miles from water collection on the Western Slope of the Continental Divide to water delivery on the Eastern Slope. Runoff from the Rocky Mountains at the headwaters of the Colorado River is captured in Grand Lake, a natural body of water, and in three reservoirs – Shadow Mountain Reservoir, Lake Granby, and Willow Creek Reservoir. The diverted water flows by gravity through the Adams Tunnel beneath Rocky Mountain National Park for 13.1 miles, the length of a half marathon.

After exiting the tunnel’s East Portal, the water merges with the Big Thompson River and cascades nearly 2,900 vertical feet down the slopes of the Front Range, passing through a series of six power plants to generate hydroelectricity. On the plains below, the water is stored in three Eastern Slope reservoirs in the South Platte River basin – Horsetooth Reservoir, Carter Lake, and Boulder Reservoir. Canals and pipelines distribute water from these reservoirs to more than 640,000 acres of farmland and ranchland, to industries, and to approximately 860,000 people in portions of eight counties (Boulder, Broomfield, Larimer, Logan, Morgan, Sedgwick, Washington, and Weld) and cities such as Fort Collins, Boulder, Longmont, and Greeley. Each year on average the Colorado–Big Thompson Project delivers more than 200,000 acre-feet of water (1 acre-foot of water is considered enough to meet the needs of two families for one year).

During the late nineteenth century, as agriculture expanded in Colorado, the northeastern plains provided farmers with fertile soil and abundant sunshine. But in drought-stricken summers their irrigation ditches ran dry. For relief they looked to the Western Slope, where approximately 70 percent of the state’s water flows. In the 1890s, construction began on Grand Ditch. Carved with hand tools into rugged mountainsides of the Never Summer Range on the Western Slope, Grand Ditch allowed Colorado River water to cross the Continental Divide by way of La Poudre Pass into the Cache la Poudre River. The ditch was expanded several times until 1936. During the Dust Bowl and the Great Depression of the 1930s, local leaders in northeastern Colorado conceived of a trans-mountain diversion much more massive than Grand Ditch that would send liquid relief to their parched fields. Unable to fund the mega-project themselves, they turned to the federal government.

The US Bureau of Reclamation, guided by President Franklin D. Roosevelt’s New Deal policies to develop public works projects, was eager to build water infrastructure in the West. But before the bureau could showcase its engineering prowess by building this project and the fields of northeastern Colorado could receive a steady flow of irrigation water through the Adams Tunnel, water wrangling between political factions on opposite sides of the Continental Divide had to be settled. Congress was reluctant to authorize the project if Colorado’s leaders were not unified in wanting it built. But tension between residents on the Eastern Slope, who demanded more water, and those on the Western Slope, who wanted to keep their water resources local, is a theme that runs throughout Colorado’s history.

Politicians on both sides of the Continental Divide agreed that water from the Colorado River should be put to use in the state of Colorado instead of escaping downstream to be used by California and Arizona, both of which were growing rapidly. Unified by the threat of losing water to downstream states and by a shared interest in securing federal water development funds for Colorado, representatives from the Western Slope and the Eastern Slope managed to bridge the divide. They agreed that the Western Slope would get a water storage project of its own – Green Mountain Reservoir on the Blue River near its confluence with the Colorado River – to help compensate for water transferred to the Eastern Slope. This agreement, along with other provisions to protect the Western Slope’s water rights and future water needs, was formalized in a federal document approved by Congress in 1937, and it cleared the way for the C-BT project to proceed. Also in 1937, the Northern Colorado Water Conservancy District was established as a public agency in the state of Colorado to contract with the federal government to build the C-BT and distribute water from the project to counties on the Eastern Slope. Construction began in 1938.

Progress slowed during World War II, and inflation and design changes sent the final cost of the project spiraling to almost four times the original estimate. Nonetheless, when the C-BT was finally completed in 1957, water diverted through the Adams Tunnel increased agricultural productivity in northeastern Colorado. But as population swelled on the northern Front Range, sugar beets were supplanted by suburban housing, and potato fields gave way to office parks. Much of the water to support this urban development was converted from agricultural water delivered by the C-BT. Congress had authorized the project primarily for the purpose of providing supplemental irrigation water, but in response to population growth, water originally intended for farms made its way to subdivisions.

Windy Gap Project

In 1967, cities of the northern Front Range, concerned about running short of water, started pursuing another project on the Western Slope to increase the amount of Colorado River water delivered through the Adams Tunnel. The Western Slope opposed the project, as expected, and there was also staunch resistance from the environmental movement, which was gaining momentum across the nation. Opponents of the proposed Windy Gap Project used federal environmental laws passed in the late 1960s and early 1970s, such as the National Environmental Policy Act and the Endangered Species Act, to slow the proposed project to a crawl. Proponents of Windy Gap finally managed to navigate the legal labyrinth and secure the necessary permits. The project was completed in 1985, but because of a lack of storage capacity and a lack of water in dry years, the Windy Gap Project could not send a reliable supply of water to the Eastern Slope.

Windy Gap Firming Project

In December 2014 the Bureau of Reclamation approved the Windy Gap Firming Project, which will create a new reservoir on the Eastern Slope to "firm up" - make more reliable - the supply of water diverted from Windy Gap through the Adams Tunnel. Opponents of the project cite studies by state biologists that have identified extensive damage to the upper Colorado River caused by the Windy Gap Reservoir and by water being diverted out of the river basin. They argue that protecting the health of the state’s namesake river, which serves as the lifeblood of the Western Slope’s economy, is paramount.

Proponents of the project point out that a gap between water supply and water demand is widening as the population of Colorado’s Front Range continues to grow. They insist that to fill this gap, more water must be diverted from the Colorado River to the Eastern Slope. All parties involved agree that the state’s economy and environment will be significantly impacted in coming years by the management of water diversions sent through the Adams Tunnel. They are working toward a collaborative agreement to increase the amount of water diverted while also protecting the river's health.