Multiple benefits are derived from the thousands of dams built along U.S. rivers and streams — electricity for homes, water storage for agriculture and recreational opportunities. However, fish derive no benefits due to significant downstream impacts, evident as reduced and altered water flows that fish rely on for spawning, feeding and migration.

University of Washington researchers are investigating an emerging solution to help achieve freshwater conservation goals by revamping how water is released by dams. Designer flows engineered downstream from dams might be tailored to meet the water needs of humans while promoting the success of native fishes over undesirable invasive fish species.

The designer flow concept was studied in the San Juan River, a major tributary to the Colorado River that The San Juan River’s Navajo Dam and reservoir above. Source: U.S. Bureau of Reclamationflows through parts of Utah, Colorado, Arizona and New Mexico. 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.

Data about dam operations, river hydrology and fish species abundance for the 1985-2014 period were integrated into a multi-objective model. The analysis helped to define specific water-release schedules that benefited native over invasive fish while still ensuring that all domestic and agriculture needs are met.

The approach can guide water management in any river with large dams, and it’s particularly relevant in more arid regions of the American Southwest where water is at a premium. Major rivers like the Columbia or the Mississippi, which have numerous dams, also could have these structures programmed to release water in ways that benefit both humans and freshwater ecosystems.

The researchers explain that 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 model suggests 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.

Both designer and natural flows were predicted to be beneficial for native fishes, but designer flows were shown to double the loss of invasive fishes in the river, compared with a dam-release scenario that mimicked natural flows prior to dam construction.

The research is published in the journal Nature Communications.