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| Navajo Dam in the United States |
A team from University of Washington then is investigating an emerging solution to help in maintaining freshwater conservation goals by re-envisioning the ways in which water is released by dams. The hope is that 'designer flows' downstream from dams can be tailored to endure the water needs of humans while altogether promoting the success of native fishes over undesirable invasive fish species. The investigation is described in a paper in Nature Communications.
"Rapidly changing water availability demands new dam management strategies to supply water downstream that balances societies and ecosystems needs." said Julian Olden, which is the senior author and also professor of aquatic and fishery sciences at University of Washington. "So, the question is whether designer flows can be engineered to meet human water consumption demands, and take benefit of mismatches between native and non-native species' responses to flow to provide the greatest conservation benefit."
The researchers investigated the designer flow concept-model in the San Juan River, a major tributary to the Colorado River that flows through parts of Utah, Colorado, Arizona, and New Mexico. Every cubic of water that flows are substantial in this arid landscape, and along the river's roughly 380-mile length, the mighty 402-foot Navajo dam is difficult to ignore. The river is home to at least eight native fish species, but over the years a number of invasive fish species have also taken up residence, including predatory channel catfish, red shiner and common carp.
By integrating multiple decades' worth of data about dam operations, river hydrology and fish species abundance into a multi-objective model, the researchers were able to identify specific water-release schedules that benefitted native fish over the invasive fish -- while still ensuring that all of the domestic and agriculture needs that relay on the San Juan River's water are met.
"We were also pleased to discover that our model predicts that the ecological benefits of designer flow releases do not evaporate during times of drought," Olden said.
This method can lead water management in any river with enormous dams, Olden said. It's particularly relevant in more arid regions of the American Southwest where water is at a premium, but major rivers like the Columbia or Mississippi, which are similarly peppered with dams, also could have their dams programmed to release water in ways that aim to benefit both humans and freshwater ecosystems.
These tailored water releases are not trying to mimic the natural flow of a river before it was dammed, but rather emphasize the most important flow events for native fish in an altered river system, the researchers explained. According to their model, water releases in the San Juan River should occur in late winter, late summer, and mid-autumn to get the best outcomes for native fishes over invasive ones.
While both designer and natural flows were predicted to be beneficial for native fishes, they found that designer flows could lead to double the loss dammed rivers will flush a deluge of water downstream, attempting to mimic natural river flows -- but with mixed success for fish. This study suggests that such efforts could be better optimized.
This work is still in the modelling phase, and the researchers want to look next at how these water-release practices could potentially benefit other aspects of dammed river systems, such as restoring shoreline vegetation, benefiting aquatic insects and even bolstering river recreation by manipulating the water releases to encourage formation of large sandbars. Ultimately, the researchers hope to test their designer flows in a real river system, in cooperation with dam operators, engineers and water users.