The Bureau of Reclamation (BOR), tasked with the management of river operations that feed into Lake Powell and Lake Mead, has recently initiated a public commentary period on the Draft Supplemental Environmental Impact Statement for the Glen Canyon Dam Long-Term Experimental and Management Plan. This initiative stems from concerns over the rising temperatures of the Colorado River below Glen Canyon Dam, attributed to the declining water levels of Lake Powell. The increased water temperatures are believed to facilitate the spawning and proliferation of smallmouth bass, a species that poses a significant threat to the native and endangered humpback chub.
The BOR’s apprehension is not unfounded. Smallmouth bass, a nonnative predator, thrive in water temperatures of 60 degrees Fahrenheit and above, conditions that are becoming increasingly common due to the dam’s lowered water outputs. The spawning of smallmouth bass in these warmer waters could lead to a significant disruption in the ecosystem, primarily affecting the humpback chub populations that the BOR aims to protect. In response, the BOR has proposed six alternative action plans to address this burgeoning issue, inviting public feedback to refine and implement the most effective strategy.
Among the alternatives, the first, dubbed the “No Action” alternative, would maintain the current management strategy, which includes the possibility of Experimental High Flows (HFE) based on projected water levels. However, given the past occurrences of smallmouth bass found beyond the dam, the efficacy of HFE releases in curbing the bass population is questionable.
The second alternative proposes a “Cool Mix” strategy, adjusting water releases on a monthly basis through both penstocks and the river outlet to maintain temperatures below the critical 60 degrees Fahrenheit mark. The specifics of whether temperature monitoring would occur at river mile 15 or mile 61 remain unclear.
The third option suggests implementing up to three 8-hour “flow spikes” when water availability permits, in an effort to disrupt the spawning conditions for smallmouth bass by rapidly increasing water flows.
The fourth strategy, “Cold Shocks,” aims to release water at 55 degrees Fahrenheit, a temperature lower than the spawning threshold for smallmouth bass, on a weekly basis to prevent the fish from spawning.
The fifth alternative, a combination of “Cold Shock with Flow Spike,” would initiate a minimum of 48-hour cold shock releases, supplemented by up to three 8-hour flow spikes, to induce colder water temperatures downstream.
Lastly, the “Non-Bypass” alternative, which has garnered support from the BlueRibbon Coalition for addressing both ecological concerns and recreational interests on Lake Powell, proposes substantial river stage changes. This strategy involves weekly cycles of low-flow releases to dewater potential nesting areas, followed by high-flow releases to increase water velocities and disrupt smallmouth bass nests and spawning activities.
The BOR’s comprehensive approach to managing the ecological balance below Glen Canyon Dam underscores the complexity of river management and the critical need for public engagement in safeguarding endangered species. As the public commentary period progresses, the collective input will be crucial in shaping the future management strategies that will protect the Glen Canyon Reach and its native inhabitants from invasive species while balancing recreational and environmental interests.
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