The impact of ice conditions on local scour around bridge piers

Ice cover imposes an additional boundary layer on a river channel and can influence sediment transport around bridge structures. The main objective of this study was to gain a better understanding of how ice cover is related to local scour around bridge piers. A set of flume experiments were completed investigating local scour around bridge piers under open channel, smooth ice and rough ice cover conditions. Three different non-uniform sediments were used with D50's of 0.47, 0.50 and 0.58 mm. The location of the average maximum velocity under rough ice cover ranged from 0.36-0.43H and for smooth cover was 0.41H, with depth (H) measured from the channel bed to water surface. Turbulent intensity was greater under ice cover than open channel conditions. Local pier scour under rough and smooth ice cover was on average 37 and 20 percent greater than open channel scour depth respectively. The maximum scour depth always occurred at the pier face. Greater pier scour under ice cover is related to larger streamwise and downward flow velocities at the pier face under rough ice cover. The scour hole velocity for rough and smooth ice cover was 33 and 15 percent greater than open channel scour hole velocity respectively. Under all channel covers an armour layer formed in the scour hole. For all experiments, as the armour layer size increased, the maximum local scour depth decreased. A critical assessment of current bridge research and construction was also conducted in order to address how this study contributes to modem day bridge design. It was found that this study addresses current knowledge gaps in bridge manual used in North America. Specifically, study results concerning scour hole depth under ice cover and scour hole flow fields under ice cover are important contributions to the field of bridge hydraulics