INFORMATION NEEDS WHEN ESTIMATING ICE JAM FLOODS AND ICE RUNS

摘要

Ice jams are a major cause of floods in mid- to high-latitude regions. This paper discusses the information needs in estimating ice jam floods and for forecasting major ice runs (sometimes called ice gorges) that may precede ice cover formation and jamming, or be consequent to the sudden collapse of a jam. It outlines how ice-jam floods are influenced not only by most of the same group of factors usually associated with river floods durng ice-free conditions (flow discharge, channel capacity), but also by three broad additional sets of factors. One group pertains to thermal conditions, notably those governing ice formation and ice deterioration, snowmelt, and runoff. The second set pertains to hydrologic factors affecting flow magnitude and distribution. And the third group concerns the ways whereby flow conditions influence ice formation, ice breakup, and ice conveyance along a river; included here are the influences of water discharge, natural channel morphology (e.g., bends and confluences), engineered changes in channel morphology (e.g. channel narrowing), river use for water-resource purposes (e.g., diversions), and the presence of certain hydraulic structures (e.g., bridges) along a river reach. Each of these additional sets of factors entails substantial information needs, and thereby greatly compounds the overall difficulty of forecasting water levels associated with ice jam floods and the damage done by ice runs.