Field investigation of frazil jam evolution: A case study

Using field measurements of frazil jams from 1982 to 1989 in the Hequ Reach of the Yellow River, this paper discusses both the mechanism of evolution of a frazil jam, and the associated variation in water level. The variation in water level depends not only on the thickness of the frazil jam but also on the ice discharge. An empirical power-law relationship between the dimensionless ice thickness and Froude number is established. It has been found that the critical Froude number (under an ice cover condition) describing the transition from an ice jam to a hanging dam (overloaded ice jam) is about 0.075, with a dimensionless ice thickness of about 0.4. Interestingly, the results from the St. Lawrence River show a similar tendency with similar limits.