Impacts Of Bridge Piers On Ice Accumulation And Variations In Water Level Caused By Ice Jam In Bend Channel–an Experimental Study

River ice jam is one of the most important hydrologic phenomenon in cold regions.Ice jam can result in significant increase in water level and thus ice flooding,and damage of hydraulic structures.An ice cover alters the hydraulics of an open channel by imposing an extra boundary to the flow,altering the water level and flow velocity,and decreasing the ice transportation compared to the ice free case.The setup of the piers alter the boundary conditions of the flow,thus raise the possibility of ice jam formation in the river.In addition,the formation of ice jam also pose a threat to the bridge infrastructure.Natural river courses are not always formed in an ideal straight line but in wind,the laws of the evolution of ice jam may be complicated.As a result,to analyze and research the ice accumulation and the variation in water level has an important significance for mitigating ice jam flooding in northern regions.Experiments have been carried out in an “S-shaped” flume in laboratory under both open flow and ice-jammed conditions to study the impacts of bridge piers in bend channel on ice accumulation and the variation in water level.The equation describing the increment in water level during equilibrium ice jammed period with appearance of bridge piers is derived.Results suggest that the increment in water level along the concave bank is more than that of along the convex bank.It is revealed that bridge piers in the S-shaped channel have obvious impacts on ice accumulation and water level.The increment in water level with appearance of bridge piers is less than that of without bridge piers in the channel.Different setup of bridge piers results in different time for ice jam to achieve an equilibrium condition and different increment in water level.When one bridge pier is installed in the straight section of channel(between 2 bends)and another one at the bend apex,the time for ice jam to achieve an equilibrium condition is between the time with a single bridge pier located in the straight section of bend channel and the time with a single bridge pier located at the bend apex,and it is the same rule with the increment in water level during equilibrium ice jammed period.Results also show that the increment in water level during equilibrium ice jammed period increases with the average thickness of ice jam and ice jam volume.