In the mid-1960s, a partnership between the cities of Colorado Springs and Aurora installed a diversion dam in the Arkansas south of Granite near Clear Creek Reservoir as part of a pipeline to bring water from the western slope of the Continental Divide to the Front Range.
That diversion lead that portion of the river to be non-navigable without portaging one’s raft or kayak.
By the end of this year, Colorado Springs Utilities is on schedule to complete a 3-year project to build new river diversion that will allow boaters to float right through, meaning that the 2020 rafting season will be the first in over 50 years in which the entirety of the Arkansas can be travelled without portage.
“We’ll see how the snow treats us over the next couple weeks, but we’re really down to some final boulder work in the river and general site cleanup at this point,” said CSU project manager Brian McCormick.
The intake that pumped water out of the Arkansas (which, legally speaking, comes from the Eagle River Basin as part of the Homestake Project) destined for Aurora and the Springs, “as with anything in the river for 50-plus years, it look some wear and tear,” McCormick said. “By about the mid-2000s, the cities recognized we needed to rehabilitate this structure to keep it as a reliable facility and ensure safety of the river users.”
After years of budgeting the $9.1 million project, which includes $1.2 million in grant funding from the Arkansas Headwaters Recreation Area, Colorado Parks and Wildlife and the Colorado Water Conservation Board, followed by years of engineering the project, construction on the new diversion began in 2016.
“You look back at the mid-‘60s things like fish passage and whitewater recreation were not very high on anyone’s minds,” McCormick said. “So this project has not only been a chance to upgrade and modernize the structure, but also to make sure it provides for all the multiple demands we place on our rivers.”
Significant to water consumers in Colorado Springs and Aurora, the project built a new intake and piping structure that sends water to the Otero pump station, he said.
Significant to boaters is a chute constructed of boulders and mortar with six two-foot drops that will allow them to pass the intake facility without exiting the river. McCormick said that CSU put the call out to members of Colorado’s river recreation community to take the chute for a spin in November, testing the Arkansas’s newest whitewater feature.
“For someone launching at Granite, historically they’d get two miles downstream to this structure and they’d need to portage. Basically they’d need to pull their boats out and walk them around, because the rock-fill diversion dam was not considered a navigable piece of the river,” McCormick said. “Next whitewater season, in 2020, they’ll be able to launch at Granite, avoid that mandatory portage and just run through Granite Gorge, through this project and on down through Pine Creek and the Numbers.”
For the performance tests on the chute, “We’ll be working with the Bureau of Reclamation to release some extra water from Twin Lakes to get this into a good testing flow range, then we’ll do the things that whitewater users generally do whenever they encounter a new rapid: we’ll stand there and look at it for a while, visually evaluate the hydraulics, where things are going, we’ll see what the wave shapes look like, how it looks like it wants to run.”
Then they’ll verify those observations by watching the movement of neutrally buoyant tracers (sticks and logs) through the feature.
“Then we’ll progress by sending users down: Kayaks, rafts, swimmers, et cetera,” he said.
Significant to the scaled, Omega-3 rich denizens of the Arkansas who swim upstream to spawn every year, the new diversion also features a structure called a fish ladder: a sequence of weirs and pools that give Brown and Rainbow trout a route to move up the river to their spawning grounds.
“It’s a series of engineered troughs with pools in between that allow fish to make their way upstream, rest in a pool, do what’s called a burst (The equivalent of a sprint on land) … so they’ll jump over the weir into the next pool, rest and recover, then jump over the weir into the next pool,” McCormick said.