A framework for ecological flow allocation in multiple reservoir operation

Abstract:

Water allocation trade-offs between human and ecosystem needs pose a challenge to water resources management—particularly if both hydroclimate and water demands are non-stationary. Existing frameworks to deliver environmental flows via reservoir releases traditionally consider historical (pre-dam) flow conditions. However, evaluating reservoir operations based on historical conditions may not accurately capture best management options under current or future climates; further, restoring ‘natural’ flow conditions is rarely feasible. Here we propose a multi-reservoir framework that explicitly considers both human water demands and ecological flow requirements, in order to maximize outcomes with independence of historical climate baselines. This framework was implemented and tested in the Apalachicola-Chattahoochee-Flint (ACF) River Basin, Southeastern U.S., a basin that supports high levels of imperiled native biodiversity (including endemic mussels and fish) as well as a productive estuarine ecosystem. We studied four major multiple-purpose reservoirs that alter flows in the basin, leveraging reservoir operation data (storage, inflows, outflows, water supply, and hydropower generation) from the U.S. Army Corps of Engineers. We used a newly-developed multi-reservoir simulation program, Generalized Reservoir Analyses using Probabilistic Streamflow (GRAPS), to analyze the system. Feasible sequential quadratic programming (FSQP) and iterative linear programming (ILP) were then used to solve the multi-objective problem. Tradeoffs based on the changing climate identify opportunities to enhance ecosystem health while supporting human needs. This framework could advance sustainable water management in other river basins, as optimal water allocation strategies that recognize flow for humans and nature will become increasingly important under more variable climates.