Assessing the Impact of Subsurface Ice Roughness on Hydrodynamics in Ice-Covered Rivers

In the current climate, approximately 60% of rivers in the Northern Hemisphere freeze during winter, draining over a third of the planet's land area and forming a crucial part of the cryosphere. Climate change shortens these ice-cover durations, which significantly affects river hydrodynamics, water levels and flow velocities. However, understanding these dynamics is difficult due to the challenges in obtaining detailed field data about ice roughness, flow characteristics, and pressure conditions, resulting in limited knowledge across diverse ice-covered flow scenarios. Flume experiments have proven valuable in studying ice-covered flows, but they often utilize smooth or floating materials that fail to accurately represent the stable subsurface ice roughness observed during mid-winter in (sub)arctic rivers. This research investigates how subsurface ice roughness affects hydrodynamics in ice-covered rivers through flume experiments, using field observations from the subarctic Pulmankijoki River in northern Finland to inform the setup and experimental conditions. Conducted in a 16 m long, 0.6 m wide, and 0.8 m deep flume, the study employs a stable proxy ice material with subsurface ice roughness and bedforms derived from mid-winter measurements at Pulmankijoki. By systematically varying the combinations of smooth bed and bedforms, along with smooth ice and subsurface ice roughness, the experiments aim to evaluate the impact of subsurface roughness on river hydrodynamics. Flow velocity and pressure measurements are used to enhance our understanding of ice-covered river dynamics and their response to climate change.