Abstract
Abstract In hydropower (HP) reservoirs, the large and rapid variations in water level can destabilize the ice cover, posing hazards to people and wildlife crossing the surface. Monitoring ice conditions to control safety in such systems is often challenging, and the role of water level regulation strategies on ice stability is not yet fully understood, especially in reservoirs with complex bathymetry. In this study, we inspected the state of the ice cover of two Norwegian HP reservoirs with complex bathymetry over nine winters (2014–2023) using multi‐sensor remote sensing data (Synthetic Aperture Radar and optical). Water level and meteorological data were analyzed to identify the primary driver and mechanism of cracking. Simple mechanical and thermal expansion models were used to interpret the results of data analysis and to isolate the effects of changes in water level from those of temperature fluctuations. Large cracks in the ice cover were consistently detected during early winter, propagating from sharp bathymetric features, and were still observable at the end of the ice season. Our results suggest that the primary cause of cracking in our study sites is the stress concentration over bathymetric obstacles during water level descent. This work highlights the importance of investigating the role of focused modulation of the HP operations to ensure ice cover integrity during the critical period for crack formation. Future studies should extend these findings to other systems with complex bathymetry to provide a solid background for informed management of HP reservoirs.