Progress in the study and management of river ice jams

River ice jams can cause extreme flood events with major consequences to infrastructure, riverside communities, and aquatic life. Yet, it is only in the last few decades that concerted efforts have been made to understand and predict ice-jam occurrence and severity. Building on a 1990s state of the art review, new physical knowledge, prediction capabilities, and management methods are discussed herein. The thickness and hydraulic roughness of ice jams have been elucidated, and flow through ice-jam voids quantified. Under-ice transport of frazil ice, which can lead to enormous freezeup accumulations, has been placed on a more rigorous footing, while heat exchange with the water flowing under a jam can be predicted with some confidence. Systematic field measurements have produced new understanding of the waves that are generated by ice-jam releases. Increased understanding of the physical processes has enhanced confidence in older numerical models and motivated development of more sophisticated ones, leading to two-dimensional dynamic algorithms based on continuum as well as discrete element approaches. Ice-jam management and control continue to be difficult tasks, but new structural and non-structural techniques offer promising avenues, at least in the case of relatively small rivers. The emerging issue of climate change and the growing appreciation of related ecological linkages have led to important, but still few, insights on how ice jamming regimes can be modified by altered climatic conditions and what the repercussions might be on river ecology. Despite the progress, there are still major unknowns, particularly related to the conditions of formation and release of ice jams.