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Abstract

For mine sites in cold climates, characterized by long winters and large snowpacks, the large water volume at freshet is often the most significant challenge operators face regarding water quantity management. Additionally, for remote and inactive mine sites with dams holding these freshet flows, elevated water levels can threaten dam safety and affect downstream environments and communities. Therefore, accurate information about freshet water volume is crucial for making risk-informed decisions. Since 2018, we have been working at a site located north of 60 degrees latitude that possesses these characteristics and needs. The initial assumption at the start of the work was that 100% of the freshet volume from the contributing watershed would convert to runoff due to the frozen ground beneath the snowpack. This is a simplification and a conservative assumption with regard to anticipation of large freshet volumes. This approach worked well most years; however, two recent freshet seasons contradicted this assumption. A review of the site conditions suggests a strong correlation between the freshet season melt rate (using the simple temperature-index method) and the remaining snowpack as snow water equivalent, which defines the point in time at which the ground may be considered unfrozen and has the potential to infiltrate meltwater. While frozen ground and melt dynamics are quite complicated, we propose a relatively simple method to improve freshet forecasting at the mesoscale that may be incorporated into hydrologic models. The challenge with this approach is that both the melt rate during freshet and the snowpack quantity are dynamic. Triggering the switch from frozen ground to thawed ground needs to be automated, dynamic, and conditional on these variables.