Author(s): Benoit Turcotte; Brian Morse
Keywords: No Keywords
Abstract: Every winter, the ice produced along many fast flowing cold region river reaches accumulates at specific locations. The amount produced depends on the rate of heat exchange and on the cumulative open water surface area. Where ice accumulates, it forms a hanging dam that can significantly increase water levels and can cause flooding even when the discharge remains very low. The amount of ice that accumulates at specific locations does not only depend on meteorological conditions, but also specifically on runoff events. For example, a mid-winter rain-on-snow event can trigger a partial breakup that yields a substantial additional amount of ice to the accumulation zone while leaving the channel exposed to cold air for further frazil to be produced. This paper presents a frazil accumulation model that accounts for these processes. The model simulates ice production along a 25 km-long gravel bed river segment of the Ste. Anne River, QC, Canada, ice coverage along reaches of distinct geomorphology, as well as the formation of a hanging dam in the downstream reach (where the Town of Saint-Raymond is located). The model was used to simulate the ice accumulation response to past hydrometeorological scenarios. The model was also used to evaluate the efficiency of mitigation measures and to predict the Town’s residual vulnerability. Finally, the model has also been adapted to be used in conjunction with an early flood warning system. This research emphasizes the importance of field investigation to quantify winter processes including frazil ice production over time and the ice-clearing discharge along reaches of different morphologies. It also demonstrates how this new type of model can be used to understand historical events, predict floods and evaluate the potential impact of climate change.