Characterizing Ice Cover Formation during Freeze-Up on the Regulated Upper Nelson River, Manitoba

Flow control programs on regulated rivers can improve winter flow conveyance for hydropower operations. On the Upper Nelson River, station flows at Jenpeg Generating Station are reduced during freeze-up to promote formation of a smooth ice cover in often turbulent upstream areas. This ice cover reduces the risk of frazil generation, which could otherwise result in blockages and subsequent energy losses. In this study, a characterization of freeze-up conditions for the Upper Nelson River is presented through 15 years of historical observations, supplemented by a short-term detailed monitoring program (2015-2018). Observations of rapid leading edge celerity are associated with increased ice production under dampened hydraulic conditions. Analysis of ice cores and drone footage highlights the role of skim ice runs in early cover formation, while predictions of skim ice formation show agreement with ice floe taxonomy from the literature. Establishing a baseline of freeze-up conditions for the region will assist in the development of predictive tools, such as numerical models, to optimize flow control decisions for this significant hydropower system.