Cost Distribution of Environmental Flow Demands in a Large Scale Multi-Reservoir System

Abstract:

This paper investigates the recovery of a prescribed flow regime through reservoir system reoperation, focusing on the associated costs and losses imposed on different power plants depending on flows, power plant and reservoir characteristics and systems topology. In large-scale reservoir systems such cost distribution is not trivial, and it should be properly evaluated to identify coordinated operating solutions that avoid penalizing a single reservoir. The methods combine an efficient stochastic dual dynamic programming algorithm for reservoir optimization subject to environmental flow targets with specific magnitude, duration and return period, which effects on fish recruitment are already known. Results indicate that the distribution of the effect of meeting the environmental flow demands throughout the reservoir cascade differs largely, and in some reservoirs power production and revenue are increased, while in others it is reduced. Most importantly, for the example system modeled here (10 reservoirs in the Parana River basin, Brazil) meeting the target environmental flows was possible without reducing the total energy produced in the year, at a cost of $25 Million/year in foregone hydropower revenues (3% reduction). Finally, the results and methods are useful in (a) quantifying the foregone hydropower and revenues resulting from meeting a specific environmental flow demand, (b) identifying the distribution and reallocation of the foregone hydropower and revenue across a large scale system, and (c) identifying optimal reservoir operating strategies to meet environmental flow demands in a large scale multi-reservoir system.