Ice Jam Formation and Release Dynamics - Hay River, NWT

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Each year during the spring, river breakup brings the threat of ice jam floods to many of the communities across Canada that are situated around rivers. Breakup ice jams occur when snowmelt swells the stream, and lifts and breaks the ice cover suddenly. The ice pieces may initially be carried along with the snowmelt flow, but often become congested - perhaps at a bridge, at a tight bend in the river, or in amongst islands - and when this happens an ice jam is formed. The streamflow is blocked by this dam of ice, and water levels can rise at rates approaching 60 to 90 centimeters (2 to 3 feet) per minute, with virtually no advance warning. The Town of Hay River, situated on the south shore of Great Slave Lake in the Northwest Territories is one such community; ice jams form there every spring. The most extreme flood in recent decades occurred in 1963. Local resident Roy Fabian (former Chief of the Kátl`odeeche First Nation) was a boy at the time of the flood and recounted for us a terrifying story of being rescued by boat, from the second story window of his house. They paddled furiously towards the bush, and as he looked back, he saw a wall of water surging from the channel. He said he could not see 30 foot high trees on the opposite river bank the ice had piled so high once the jam formed. More recently, severe flooding occurred in 2003 and 2008, and minor flooding in 2005, 2007 and 2009. To ensure the safety and security of people and property in the many communities across Canada that are threatened by ice jams each spring, practical and reliable river ice jam flood forecasting tools are needed. To develop such models we need to study ice jam behaviour, both to understand its complexities, and to have the needed data to test our models. With its propensity for ice jam occurrence, and its need for flood warning systems, Hay River represents an ideal location for such scientific studies. Research at this site also affords us the opportunity to directly help the community in their flood forecasting efforts each spring.