Applicability of Criterion for Onset of River Ice Breakup

The breakup of an ice cover may lead to ice jamming. However, tested methods for predicting the ice cover breakup are lacking. One method uses hinge resistance at riverbanks as a tentative criterion for ice cover breakup in relatively straight rivers. In the present study, data from 6 years of observations of the Mississippi River at Anoka, Minn. are used to evaluate the applicability of that criterion. The observations include the date, the flow, and the thickness of the ice cover at the onset of cover breakup. An effort is made to estimate the shear stress on the ice cover with reasonable accuracy; and this shear stress is used to determine the counteracting hinge resistance at the onset of cover breakup. The calculated value of hinge resistance does not vary much from year to year, and thus the proposed criterion appears to be applicable for the study site.