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Hydropower provides a source of reliable and inexpensive energy, producing approximately 20% of the global energy supply, though it comes at a cost to riverine ecosystems. To maximize revenues, major hydropower facilities store and release water with respect to short-term changes in energy price, causing significant sub-daily flow regime alterations that impact downstream ecological communities. In the United States, the Federal Energy Regulatory Commission (FERC) is responsible for hydropower regulation and this is administered, in part, during periodic relicensing of existing facilities. The process of relicensing provides the opportunity to evaluate the goals and concerns of interested parties and evaluate potential operational changes in licensure which may support these goals, often including constraints aimed at supporting ecological improvements.

This paper explores potential changes in reservoir operating rules for a series of five peaking hydropower facilities on the Connecticut River undergoing FERC relicensing that should complete in 2019. This paper evaluates the trade-offs between two primary goals: maximizing revenues from hydroelectric power generation and returning the river to a more natural flow regime. These trade-offs are assessed using the Connecticut River Hydropower Operations Program (CHOP), a linear programming (LP) optimization model applied at an hourly time-step to capture the sub-daily effects to the flow regime. The model objective function is formulated to maximize hydropower revenues with respect to historical regional energy price data and is demonstrated to accurately mimic hydropeaking operating conditions and match historical power generating rates.

A case study compares modeled hydropower operating conditions between current hydropeaking operations and a strict run-of-river condition, where dam inflows must be directly released as outflows at all times. Analysis suggests that the run-of-river condition would result in a total economic loss of 7-9% of average annual revenues at the four mainstem facilities and as much as 17% at the larger, pumped-storage facility. However, an exploration of operating revenue losses at the pumped-storage facility suggests that there is potential for reoperations within the run-of-river operating condition to substantially reduce these losses. The run-of-river operation is demonstrated to improve the Connecticut River’s flow regime on the sub-daily time scale, with significant reductions in rates of change in flows to levels that approach those observed at a nearby unaltered location. The modeled improvements to the flow regime demonstrate the merit of this run-of-river condition as a potential reoperation for the hydropower system.