We are loving the good news from Delta, Colorado!! Cary Denison of Trout Unlimited has been busy at the Hartland project post-construction as a ‘go to’ guy, encouraging the oh-so important tasks of 1) monitoring the site to see how project objectives have been met and 2) checking in to identify need for on-going maintenance. Looking back at the past three years, he has only good things to say about the project, and believes upcoming monitoring will further verify the renovated dam’s design performance.
Metric #1: Verifying low velocities for lousy swimmers
Redesigning a river to encourage fish passage is all about creating velocities that the species of interest likes for swimming. Specifically, we need to create velocities that they can handle. At the Hartland Dam, the challenge was to keep the velocities pretty low for somewhat non-athletic natives: Roundtail Chub, Flannelmouth Sucker and Bluehead Sucker.
“We did not have reliable pre-dam data to know what the fish would like,” notes Cary, “but we did conduct an extensive literature search on swimming capabilities of similar species and interviews with fisheries biologist to determine favorable passage conditions. Detailed multi-dimensional hydraulic modeling was then performed to know what the resulting velocities would be once the restoration was constructed.”
“It worked,” he continues. “We measured velocities at seventy-two (72) locations in the project reach and the velocities are just like we thought (and calculated) they’d be!! This sounds easy, but has not often been achieved measurably.”
Metric #2: Confirming that the dam doesn’t mind high water
During the spring of 2014, flow as the dam peaked at 11,500 cubic feet per second (cfs). The structure handled this flow just fine, confirming its structural integrity and allaying any concerns for needed maintenance a common problem at many river structures in Western Colorado.
Metric #3: Worrisome Debris: not in our channel
Cary continues. “There was another success, too. We were curious to see how much debris would be collected by the chevron-shaped obstacles in the fishway channels, particularly after the high flows. To everyone’s pleasure, there was nothing that required maintenance or created a safety hazard.” By contrast, a similar chevron style fishway nearby on the Colorado River requires regular maintenance including debris removal to remain effective.
NEXT: Warm up the fish counters!
Although there have been many reports of catching the native fish above the Hartland dam post construction, anecdotes are not “scientifically” reliable. To remedy the situation Cary and others are going to put some real numbers to the fish passage story. During the latter part of September, 2014 Cary will join fisheries biologists from Colorado Department of Natural Resources and Colorado Parks and Wildlife as they tag and count fish below and above the dam to establish a baseline for the whereabouts of natives. Next year, they plan to repeat the exercise to learn the level of movement or shift in the populations of these three species.
