Abstract
Abstract. Floods resulting from river ice jams pose a great risk to many riverside municipalities in Canada. The location of an ice jam is mainly influenced by channel morphology. The goal of this work was therefore to develop a simplified geospatial model to estimate the predisposition of a river channel to ice jams. Rather than predicting the timing of river ice breakup, the main question here was to predict where the broken ice is susceptible to jam based on the river's geomorphological characteristics. Thus, six parameters referred to potential causes for ice jams in the literature were initially selected: presence of an island, narrowing of the channel, high sinuosity, presence of a bridge, confluence of rivers, and slope break. A GIS-based tool was used to generate the aforementioned factors over regular-spaced segments along the entire channel using available geospatial data. An ice jam predisposition index (IJPI) was calculated by combining the weighted optimal factors. Three Canadian rivers (province of Québec) were chosen as test sites. The resulting maps were assessed from historical observations and local knowledge. Results show that 77 % of the observed ice jam sites on record occurred in river sections that the model considered as having high or medium predisposition. This leaves 23 % of false negative errors (missed occurrence). Between 7 and 11 % of the highly predisposed river sections did not have an ice jam on record (false-positive cases). Results, limitations, and potential improvements are discussed.
Highlights
Ice jams result from the accumulation of fragmented ice on a section of a river, obstructing the channel and restricting the flow
When breakup occurs and ice starts to move downstream, another key question is, where would the released ice be susceptible to jamming? The goal of this study is to provide some answers to the aforementioned question by developing a simplified geospatial model that would estimate the predisposition of a river channel to ice jams
We focused on 118 historical observations: 61 ice jam reports for the Chaudière River, 33 for the SaintFrançois River, and 24 for L’Assomption River
Summary
Ice jams result from the accumulation of fragmented ice on a section of a river, obstructing the channel and restricting the flow. The goal of this study is to provide some answers to the aforementioned question by developing a simplified geospatial model that would estimate the predisposition of a river channel to ice jams. Being developed for an eventual application over large areas and multiple rivers, the geospatial model uses simplifications and provide a “first level” assessment of the predisposition to ice jam along the river channel. It has been developed on three Canadian rivers in the province of Québec: the Chaudière River, the Saint-François River, and L’Assomption River (Fig. 1), which are all tributaries of the Saint Lawrence River. A reduction in channel top width, the existence of meander-
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