Frequency and Severity of Past Ice Jams on the Grass River

Breakup ice jams can significantly impact the operation of water resources projects, river ecology, residential property and the infrastructure of local communities. The complex mechanisms involved and the usual lack of observed data make it difficult to determine the timing and severity of past ice jams. In this paper, frequency and severity of past ice jams on the lower Grasse River were estimated from historical and anecdotal evidence, the results of an extensive survey of tree scars along the banks, and a hindcasting analysis based on water discharge and estimated ice thickness at the time of breakup. From analysis of the historical data, site specific criteria were derived for mechanical breakup and jamming potential based on ice thickness and stage increase during the breakup period