| Résumé | In countries where rivers freeze in the winter, severe flooding events along river shorelines can be caused by ice. This happens because the presence of that ice slows down river flow, which then causes the water levels to rise. The rougher the ice’s undersurface, the higher the rise in water levels upstream of it. Ice jams have the highest flooding potential because they can form thick rubble piles that constrict the flow. The release of an ice jam can also induce floods downstream of where it formed.
One common risk reduction component is an ice control structure (ICS). These are either removable, such as booms, weirs and nets; they can also be fixed, such as permanent weirs, piers and floodwalls. Earthworks are a third, more involved option – they include channel modifications, artificial islands, groins and levees. Means to reduce flood risks can also be of a non-structural nature. This is done by favoring the formation of an ice cover with a smooth undersurface or promoting ice cover breakup (with ice breaking, cutting or melting techniques, surface treatment, or warm affluents). The removal of ice jams is yet another way to minimize flood risks.
The resilience of a site against ice-induced floods can be assessed. It begins with an overall understanding of the river at that site and its ability to withstand rises in water levels. What is currently in place or can be readily implemented to anticipate floods? This assessment can be done for the short term (days to weeks), and long-term, i.e., to assess the impact of climate change over future decades. |
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