The presence of bridge piers in natural rivers significantly changes the flow and boundary conditions.As a consequence,ice jams can often be initiated in front of bridge piers.With the changes in flow conditions,two types of ice jam formation may appear:surface accumulation of ice blocks (surface ice blockage) and thickened accumulation of ice blocks (vertical ice blockage).In the present study,the initiation process of ice jam was studied based on experiments.It is found that the critical ice concentration for ice jam blockage depends on the ice block dimension,channel opening and flow conditions.Under surface blockage conditions,a larger ratio of ice cube dimension to channel opening (between piers) can result in a smaller critical ice concentration for ice jam blockage,which has no obvious relation with flow conditions.Under vertical blockage conditions,the critical ice concentration for ice jam blockage increases with flow Froude number and decreases with the ratio of ice dimension to channel opening (between piers).Based on experiments conducted in laboratory,equations for determining critical ice concentration for these two types of ice jam blockage have been developed.
展开▼
机译：Effects of Cotrimoxazole Prophylaxis Initiation and Discontinuation on Mortality and Attrition Rates among HIV Patients Who Initiate ART in Southwest China: An Observational Cohort Study
