Trout Unlimited and The Nature Conservancy are working to improve fish habitat and riparian health on the upper and lower Dolores River.
Matt Clark, director for the Dolores River Chapter of Trout Unlimited, is organizing a project to install a fish passage and improved diversion dam at the Redburn Ranch north of Dolores.
Currently, landowners have to build a cobble push-up dam across a wide section of river every year to get enough draw into a nearby diversion that irrigates the pastures.
The make-shift dam blocks fish from moving up and down the river and washes out every year at high flows.
“During the nine months out of the year it is up, there is no water flowing over it, preventing fish passage,” said Clark. “Plus it is a pain for the landowner to maintain.”
The solution is to build three, large-rock dams 200 feet apart that step down.
“Each one drops down the river a foot and has a pour-over,” Clark explained. “A side benefit is that it forms pools and ripple-habitat structure in between.”
In addition a new head-gate will be installed for the irrigation diversion.
Clark said there is anecdotal evidence that juvenile fish are getting trapped in that area of the river.
“A health trout fishery requires a connected river system,” he said. “When fish spawn higher up in the system, their larvae drift down and need to spread out without obstructions.”
The project is expected to be installed next fall, with cost estimates between $200,000 and $300,000. The Redburn Ranch fish passage project has been awarded a $50,000 grant from the Southwest Basin Roundtable, and $98,000 from the Colorado Water Conservation board. Trout Unlimited contributed $20,000, and the landowner contributed money as well, Clark said.
“We’re piecing it together,” Clark said. “It is a win-win for ranch management and fish habitat. Plus the pour-overs allow for easier passage for recreational boat passage.”
Meanwhile on the Lower Dolores River below McPhee dam, The Nature Conservancy is committed to improving riparian habitat by eradicating invasive tamarisk and planting native species.
TNC, along with the Southwest Conservation Corp, and the BLM formed the Dolores River Restoration Partnership. So far the effort has created 175 jobs and restored 821 acres.
“The impact of tamarisk is huge — they rob waterways of their health and make recreational access cumbersome,” says Peter Mueller, director of the Conservancy’s North San Juan Mountain Program in Colorado.
But, he adds, “When you get rid of this wicked tree, all of a sudden you can see the light, and you can see the river again.”
Aiding the effort is the spread of the tamarisk beetle, introduced into the West in the 1990s as a biological control agent. The U.S. Department of Agriculture imported tamarisk beetles from Eurasia, where they keep tamarisk in check, and after years of quarantine and testing, released them in Utah, Wyoming and Colorado.
“These beetles are one of the most tested biological agents we have and there’s little risk of them harming other plants,” says Mueller.
Over the last three years, the beetles have defoliated a majority of the tamarisk on a 60-mile reach of the Colorado River. From the release site in Utah, the insects have now moved into Colorado and the Dolores River watershed.
The lower Dolores is a more difficult river to tame because damming has altered its flow and flood timing, a condition that favors tamarisk and other exotic species.
“Restoring the health of the Dolores will require not only tamarisk removal, but improved water management and planting of native species,” Mueller said.
Native willow, sumac, and cottonwoods are planted, and native grass seeds are spread around where tamarisk once dominated.
jmimiaga@cortezjournal.com