Optimizing environmental flows between dams

The protection of riverine ecosystems downstream from dams requires reservoir operations to satisfy environmental flow (e-flow) requirements. In practice, this often involves re-regulation of downstream river flows within the constraints of water resource demands for human supplies and irrigation. In this paper, we develop a method to assess how reservoir storage may be used more effectively to meet both water supply and downstream ecosystem needs. The latter are met by providing seasonally variable baseflows, including dry season flow recession at natural rates, and high-flow pulses and bankfull flows synchronized with natural events. A series of reservoir operating rules are derived based on both reservoir storage and reservoir inflows to trigger reservoir releases. For a given water supply reliability, the method seeks to minimize the degree of hydrological alteration below a dam. We present a case study of the Tanghe Reservoir in China's Tang river basin to show that the proposed method could help reservoir managers and planners evaluate e-flow scenarios to reduce the negative impacts of dams and reservoirs on riverine ecosystems