Juggling Water: Optimizing Dam Releases to Balance the Water Needs of Humans and Native Fishes

Dams provide water security, flood protection, and hydropower to human societies. However, dams also alter rivers’ natural flow regimes to the detriment of native fishes and their associated ecosystem functions and services. To mitigate the negative impacts of dams, managers have typically emulated pre-dam flow regimes or targeted specific species of concern. However, dam construction has favored the establishment of non-native populations below dams. To meet the challenges of ecologically-sustainable water management, novel quantitative tools are needed to guide dam operations to support native and suppress non-native species while continuing to meet human water demands. Here, we develop an optimization scheme that incorporates human water demands and the flow requirements of native and non-native fishes to minimize the tradeoffs in allocating limited water to supply water for human use, support native fishes, and disadvantage non-native fishes. Using the Navajo Dam on the San Juan River (New Mexico) as a case study for large dams, we show that prescribing dam releases to mimic pre-dam flow regimes is suboptimal due to indirect tradeoffs between benefiting native versus disadvantaging non-native fishes. Our results highlight the importance of seeking new opportunities to dynamically manage dam operations to better balance human and ecosystem water needs.