Scientists are taking a close look at the streambed of Eleven Mile Canyon after the removal of an abandoned concrete dam to understand how the ecosystem will repair and reshape itself.

Crews removed the former Colorado Springs Utilities diversion dam last year as part of a $4.8 million project to unite 45 miles of river, prevent the dam from potentially failing in the future and allow rainbow and brown trout to migrate more easily. The dam previously split two popular fishing areas.

On a sunny April day, researchers armed with rods used to take GPS measurements slowly mapped the bottom of the river bed in granular detail, taking a measurement every 20 centimeters along a suspended tape measure as the water of the South Platte River rushed past their feet.

They plan to return after water is released from Eleven Mile Dam, which remains in place, to see how the bottom of the streambed has been reshaped.

They also sampled the rocks in the streambed to better understand the habitat where bugs at the base of the food chain, such as immature mayflies, typically live, explained Charlie Shobe, a research geomorphologist with the Forest Service’s Rocky Mountain Research Station.

While old dams are coming down across the U.S., it’s unusual to have one come down in a steep mountain canyon, he said.

“The idea is that we can take what we gained from this study, to make it easier to predict how other places will respond if we remove dams like this in the future,” he said.

American Rivers, a nonprofit, reports 80 dams came down across the nation last year, with two in Colorado, counting the one in Eleven Mile Canyon. Along the Arkansas River near the river trail in Pueblo, crews are expected to take down a concrete dam and replace it with a different diversion structure, providing a passage for boaters and fish, according to Pueblo Water.

Large dams along the South Platte, at Eleven Mile and Cheesman reservoirs have to remain in place to meet Front Range municipal water needs and that dynamic is interesting to researchers as well.

“It’s kind of a case study in how we can improve habitat over large reaches of a river and improve the functioning of the river channel while still meeting user water needs,” Shobe said.

He also expects the canyon will be somewhat insulated from the effects of climate change because it is down stream from Eleven Mile Canyon dam, which dictates how much water is released.

The measurements the researchers took in April will be mapped against measurements taken after a big spring water release, to see how the stream bed changes.

Shobe expects some change, but not deep channelization because of the bedrock and boulders.

The team will also collect bug larvae later in the spring to understand how the base of the food chain is recovering, he said.

High resolution imagery down to the centimeter of the canyon collected with a drone will also inform the research expected to continue through at least next year.

The stream got a head start toward health when crews took out 17,000 cubic yards of sediment that built up behind the removed dam over about 70 years and a mammoth pile of cattails. The cattails were still awaiting burial near a planned parking lot in April, reminders along with a bathtub ring on rocks of a slower, wider river.

In place of the cattails, crews were planting willows and grasses along the river banks. A new trail and parking lot is also going in ahead of the popular area reopening to the public in 2025.

While most construction is expected to finish in May, a year will give the area time to revegetate, said Josh Voorhis, district ranger for the Pike and San Isabel National Forest. Crews also need to return in the fall to finish replanting.

For the fish, who tried constantly to leap the dam, sliding off each time, the improvement was immediate.

“The fish were swimming right through so they can get to and from their spawning grounds,” he said.

Visitors also seem largely pleased.

“Probably 95% of the comments have been excited to see the dam removed,” Voorhis said.