Analysis Of Ice Blocks Movement And Study On Flow Rate During River Ice Thawing-breakup Period

In winter,ice cover is a natural phenomenon prevalent in cold regions rivers.With a sustained drop of air temperature,the ice floes and large ice blocks are transported along with the water flow and drifts downstream.Bridging or “arching” of ice block at constriction and submergence of ice blocks in front of ice cover are prone to occur.As the upstream floating ice is continuously transported to the downstream,it further develops into ice jams.This resulted in high water levels and increased channel storage during icecovered period.As consequence,ice-induced flooding may occur and hydraulic structures may be damaged or destroyed.Bridging or “arching” of ice block is the precondition for submergence of ice blocks,Submergence of floating ice blocks in front of ice cover is critical for the development of an ice jam,and the collapse of ice jam is the cause of flooding during river ice thawingbreakup period.In this study,the effect of the rotation angle of ice blocks on the submergence of ice block was assessed.Considering both the maximum moment for anti-overturn of an ice block,and the associated rotation angle,equations for describing the criteria for ice block entrainment in front of ice cover have been derived.On the basis of the theorem for moment equilibrium,relating the moment acting on a horizontal ice block with the maximum anti-overturn moment of an ice block,the criteria for assessing the overturnand-submergence of an ice block have been proposed.Using proposed method calculated critical flow velocities agree well with those of experiments.Base on three-dimensional two-phase flow numerical model of CFD-DEM coupling,river ice blocking phenomenon was simulated and critical floating ice area concentration was obtained by changing the ice block size and number of it produced per minute.Compared with the measured data,the results show that critical floating ice area concentration is consistent with the experimental results.During the period of river ice thawing and breakup process(termed as “ice cover thawing-breakup”),vast amount of water stored in ice-covered river reach will be released comparing to that under open flow condition.In present study,water released from ice cover thawing process is considered as the lateral inflow to the channel flow during propagation process of flood wave from upstream to downstream.A model for the flood routing process during river ice thawing-breakup period has been developed.Results showed that the simulated hydrographs using developed model agree well with those of field measurements.