Developing environmental flows and metrics to quantify river ecosystem needs for regional water planning in Georgia, USA

Effective water management requires the capacity to make trade-offs among diverse uses of water such as municipal water supply, irrigation, and ecological outcomes. Environmental flow management seeks to understand the relationships between river flows and ecosystem processes to evaluate the relative change in ecological outcomes associated with different strategies for river management. However, operationalizing ecological flow thresholds remains technically and administratively challenging, particularly at large scales. Here, we present a case study identifying environmental flow targets using the functional flows framework in the Oconee River Basin, Georgia, USA. Quantitative discharge thresholds are developed for five ecologically relevant flows addressing channel maintenance, floodplain connectivity, springtime pulses, reproductive season baseflows, and dry season baseflows. We demonstrate how these targets integrate ecosystem water needs into a broader state-level water planning process. Four themes emerge from this case study that are applicable in other geographies and contexts. First, environmental flow targets cannot be abstracted from their physical, ecological, and political geography, and context-specificity is critical to developing management-relevant flow targets. Second, quantitative environmental flow thresholds help establish ecological outcomes on equal footing with socio-economic uses of water in planning processes. Third, environmental flow frameworks should align with the management scope so that metrics also align with established evaluation criteria. Finally, decision makers should be provided with information to evaluate and interpret different outcomes for environmental flow targets alongside other water management targets. Despite these complexities, environmental flow analyses remain an essential tool to address the threats to freshwater ecosystems and biodiversity driven by human alteration, water use, and global change.