Flow alteration impacts on Hudson Bay river discharge.

This study explores flow regulation controls on daily river discharge variations and trends into Hudson Bay from four highly regulated and 17 moderately regulated/unregulated systems over 1960–2016. These 21 rivers contribute ~70% of the total annual riverine freshwater export to Hudson Bay, with highly regulated and moderately regulated/unregulated rivers accounting for 47% and 53% of the discharge, respectively. Daily observed streamflow data from the Water Survey of Canada, Manitoba Hydro, Ontario Power Generation, and Hydro‐Québec are used. Decadal hydrographs of the mean and coefficient of variation of daily river discharge are developed to assess the changing hydrological regimes in both systems. Decadal spectral analyses reveal the dominant controls on daily river discharge input to Hudson Bay from the regulated and unregulated systems. Apart from expected peaks in spectral power on annual timescales arising from the nival regimes in both systems, a strong secondary peak emerges at weekly timescales from flow regulation due to hydropower production. Hydrographs that consider the day of the week reveal distinct weekly cycles in regulated rivers with ~10% declines in daily river discharge during weekends and statutory holidays relative to weekday averages, demonstrating the importance of regulation on the timing of freshwater into Hudson Bay. [ABSTRACT FROM AUTHOR]