Fall Creek Reservoir, Oregon, after the annual autumn short-term drainage in 2016. Photo courtesy of Steve Hamilton, Michigan State University.
Water levels in many reservoirs of the Pacific Northwest are lowered in the fall and winter. However, since 2011, the Falls Creek Reservoir, Oregon, has been annually drained to the streambed to help juvenile salmon migrate out to sea. Sherri Johnson, research ecologist with the station, and her colleagues investigated the ramifications of this novel management strategy on both salmon and the broader aquatic food webs within reservoirs.
Johnson and her colleagues pointed out that some questions remain about the broader impacts of reservoir drainage for fisheries management, including the impact of exporting large pulses of sediment, the role of invasive fishes on downstream aquatic communities, and the effect of the annual drainage on salmon life histories. Short-term draining of a reservoir, however, offers a novel management approach that benefits juvenile salmon and may increase salmon survival over time.
The repeated draining may serve as a method to reduce invasive fish species in reservoirs. This type of research and monitoring before and after major changes in management of a reservoir is crucial for improving the ability to balance water availability, while maintaining native species. Based on these findings, the U.S. Army Corps of Engineers plans to adjust its management of reservoirs, and the timing and magnitude of drawdown for multiple reservoirs.