Hydrodynamics of Ice-Covered Rivers: Insights from Flume Experiments

In the present climate, nearly 60% of rivers in the Northern Hemisphere freeze during winter, draining more than a third of the planet's land area and forming a crucial part of the cryosphere. Climate change is altering the river ice regimes, leading to shorter ice-cover durations. These ice covers significantly influence river hydrodynamics, affecting water levels and flow velocities compared to open-channel conditions. A stable ice cover effectively doubles the wetted perimeter, increasing flow resistance. Despite the importance of understanding these dynamics, due to the challenges in acquiring detailed field data, such as ice roughness, flow characteristics, and pressure conditions, the knowledge remains limited from different ice-covered flow situations. Therefore, most laboratory flume experiments rely on smooth ice covers or artificially roughened surfaces, characterized using Manning’s roughness coefficient based on measured flow conditions instead of direct roughness measurements. Recent advancements in acquiring roughness details of subsurface ice provide a more accurate approach to understanding these dynamics between river ice cover and hydraulics. Additionally, previous flume experiments use flexible ice covers, which behave differently from stable ice covers in terms of hydrodynamic impact. As a result, the hydrodynamics beneath stable ice covers, especially under pressurised and non-pressurised flow conditions, remain poorly understood.

This study proposes new flume experiments using a proxy ice material in a 16 m long, 0.6 m wide, 0.6 m deep flume. This setup will allow a more comprehensive exploration of ice cover effects across a range of conditions, informed by field measurements, to enhance our understanding of ice-covered river dynamics. The roughness characteristics of both the subsurface of the ice cover and the flume bed will be derived from mid-winter field measurements collected in the subarctic Pulmanki River in northern Finland. Discharge rates will be systematically varied to replicate conditions observed in the Pulmanki River. Flow velocity and pressure measurements will be collected to assess the dynamics under both pressurised and non-pressurised flow conditions. This approach aims to advance our understanding of the hydrodynamics of ice-covered rivers and their response to a changing climate.