When the culvert was built in the ‘70s, planners knew it would be a problem for fish. The box culvert is two channels, each 10 feet wide and 300 feet long. It runs beneath Interstate 70 west of Glenwood Springs, connecting the cascading Canyon Creek with its final yards before it joins the Colorado River.
Canyon Creek is similar in size to Grizzly Creek. The natural stream is moderately steep and features big boulders and lots of cobble areas — good habitat for trout. But, for about 50 years, the culvert has impeded, though not entirely excluded, spawning trout.
Built to carry 100-year floods, the concrete rectangular tube flows with huge velocity during spring runoff, but is barely inches deep with water in fall. This creates problems for brown trout during low flow, as they struggle to swim the culvert. Rainbow trout spawn in the spring and are also affected, with flow velocities preventing some from getting through. During spawning, hundreds of trout stack up in the pool below the culvert. The mouth of the creek has fishing closures in spring and fall to protect these reproducing fish.
To fix the problem, the project’s engineer modeled different features for the floor of the culvert to determine how to simultaneously slow flows and make them deeper. The best model called for a combination of hemispheres and baffles that create a less direct flow of water and help water pool. Baffles resemble the tire stops common in parking lots. In this case, the contractor cast more than 300 hemispheres and more than 20 baffles. Both shapes were cast in concrete off site, and then later glued and grouted into the floor of the culvert.
Concrete hemispheres and baffles are being installed on the floor of the culvert. In modeling, the features have been shown to slow the flow of water and increase depths, which should aid spawning trout in both spring and fall. Photo by Olivia Emmer
The engineer on the project, Scott Schreiber, of Wright Water Engineers, says the modeling used for this project is cutting-edge technology in the fish passage world. According to presentation documents, the new features should reduce maximum velocities by more than half and increase minimum depth from just a few inches to about one foot.
If trout can’t access a tributary to spawn in, they’ll spawn near its confluence or in the Colorado River. But, as Kendall Bakich, an aquatic biologist for Colorado Parks and Wildlife (CPW) explains, trout do best with large, clean gravel to spawn in. Much of the Colorado River has fine sediment in it, exacerbated locally by debris flows from the Grizzly Creek Fire. Also, steeper and more turbulent streams are better at aerating the eggs.
Bakich speculates about the size of the population that will be aided by the project, “I’ve never censused that pool [below the culvert] during a spawning run, but one day I was there — there had to be at least three to 500 fish in there… You could say 1,000 fish and that might even still be an underestimate.” Once this culvert is improved, fish will have easier access to over a mile of habitat, before encountering another barrier upstream, an irrigation diversion.
Says Richard Van Gytenbeek of Trout Unlimited, “What we’re doing is we’re starting out at the bottom of these streams and moving up through them. Each time we do, we open more and more spawning and juvenile-rearing habitat.” In this case, the impediment was a highway culvert, but Van Gytenbeek says irrigation structures are a more common barrier. As he explains it, the many creeks which come off of the Flat Tops and drain into the Colorado River have a lot of underutilized capacity as spawning and nursery habitat for fish. If passage can be improved on some of these streams, he sees it as a win-win for the environment and recreation. “It’s really great to be able to have that kind of natural reproduction capacity supplying a mainstem river which has so much public access.”
The culvert retrofit is the result of three years of planning by partners: Trout Unlimited, Wright Water Engineers, CPW and the Colorado Department of Transportation (CDOT). Since the culvert is highway infrastructure, CDOT’s support and permission was critical. It’s a $250,000 investment that was funded by the Colorado Water Conservation Board, the Fish and Wildlife Service, the Colorado River District, Trout Unlimited donors, the Trout and Salmon Foundation and in-kind contributions. The project is on track to wrap up on Dec. 12.
A raft floats below the Canyon Creek confluence with the Colorado River. Trout Unlimited’s Richard Van Gytenbeek is enthusiastic about improving fish access to the creeks that come off the Flat Tops, citing their capacity as fish nurseries and the resulting benefits to recreation. Photo by Olivia Emmer