For over six million years, the Colorado River flowed from the Never Summer mountains in what is now Rocky Mountain National Park, to the sea of Cortez- cutting through over a vertical mile of a vast landscape while carving majestic canyons along the way. When the Ute and Arapaho tribes came to the Grand Lake area, near the headwaters of the Colorado River, they saw what was once a raging river. But through transmountain diversions, like Colorado- Big Thompson, the river seen by early inhabitants is not the same river it is today.
At the turn of the Century, when spring snow melt occurred, the waters of the Colorado would fill the banks and flood mountain valleys. While on the other side of the Continental Divide, farmers and ranchers along the plains were starving for water. In 1933, the Greeley Chamber of Commerce formed a committee to survey a transmountain diversion that would tap into the Colorado River headwaters near Grand Lake.
The groups lobbying for the diversion- named Colorado- Big Thompson (C-BT)- got their way in 1938 when Congress approved the project. And 19 years later in 1957, the project was completed. The C-BT was the biggest transmountain water diversion the state of Colorado has ever seen.
The water from the Upper Colorado flows from Lake Granby (which acts as the storage facility), then it is is pumped into Shadow Mountain Reservoir where it then flows down into Grand Lake. From Grand Lake, the water then is pumped through the 13.1 mile long Alva B. Adams Tunnel under the Continental Divide and flows into the Big Thompson River. From there, the water drops into power plants that supply the pumps on the western slope.
In it's first year, 230,000 acre feet were transferred across the divide annually. Since then, the number of acre feet taken from the Upper Colorado is around 213,000 according to Northern Water. The tunnel can also contain flows of 550 cubic feet per second.
While the project is able to keep the eastern slope alive during drought years and helps support Colorado's agriculture economy, the Colorado River itself is harmed. In order to build the C-BT, Green Mountain reservoir needed to be constructed along the Blue River. This was built in order to store water that the C-BT took out of the Colorado.
However, there are about 34 miles of river between Lake Granby- where water is taken- and the Blue River confluence- where the water is returned. This leaves a "hole" in the river. Along this stretch, the river and it's fishery is slowing fading away.
As the flows of the Upper Colorado are depleted by the diversion projects, the natural cleansing of the river fails to occur. Each spring, rivers experience flushing flows- an increase in water flow that breaks up sediment buildup along the stream bed. When the river isn't able to clean itself from sediment buildup between cobblestone, it doesn't allow for insects to hatch or fish to spawn.
Insects in the river hatch from the bottom of the cobblestone, but when the sediment concretes between the rocks, they aren't able to access the underside of the rock and hatch- leaving limited food sources for the trout in the water. The trout also needs the rocks to spawn as they turn rocks over to create their redds, which can't be done when sediment cements the rocks in place.
Under Senate Document 80- the document approving the C-BT and requiring the construction of Green Mountain reservoir- the document also states that the project needs, "to preserve the fishing and recreational facilities and the scenic attractions of Grand Lake, the Colorado River, and the Rocky Mountain National Park."
The West needed water to expand. Currently, 80 percent of Colorado's population is on the east of the Divide while 80 percent of the water is on the west side. This means that in order to thrive, water needed to be diverted. The C-BT opened the door to other transmountain diversions- including the Moffat Tunnel from the Fraser River, another tributary of the Upper Colorado headwaters.
While these diversions help the east slope, they are hurting the river. Through collaboration work among TU and water suppliers with hemp from very passionate individuals, we are working together to bring the river back to health.
The river will never be what is once was when the Ute and Arapaho tribes hunted and fished along its shores, but the river can return to a health that is good for people, insects and trout alike.