UW Aquatic & Fishery Sciences Quantitative Seminar

Will Chen

Quantitative Ecology and Resource Management, University of Washington

Optimizing river flows for simultaneously meeting human water demand and managing riverine fish assemblages in a drier future

Abstract

Dams have proven critical to human societies by providing a reliable supply of water, mitigating damaging floods, and supporting energy via hydropower. At the same time, dams alter rivers’ natural flow regimes to the detriment of native fishes and benefit of non-native populations below dams. As mountain snow packs and spring runoff water decrease in response to climate change, the conflict between meeting human water needs and conserving freshwater ecosystems is likely to grow, particularly in more arid regions such as southwestern United States. We need novel quantitative tools to support the management of both native and non-native species. Here, we present an optimization scheme that incorporates human water demands and the flow responses of native and non-native fishes to prescribe dam releases and water diversions that minimize the tradeoffs among supplying water for human use, supporting native fishes, and disadvantaging non-native fishes. Using the Navajo Dam in the San Juan River as a case study, we show that even for large dams, there is a wide scope for simultaneously meeting human water demands and promoting a desirable downstream fish assemblage, even in scenarios of low water availability. In addition, we illustrate the benefits of managing flows in periods of drought to promoting desirable fish communities, which has historically been downplayed due to the perceived futility of regulating flows when there is less water to manage. Finally, we present the individual fish responses to our flow regime prescriptions to show the effectiveness of our approach for managing at the species level.