Local scour around spur dikes under ice-jammed flow conditions

The occurrence of ice jams in rivers in cold regions during winter complicates the local scour process around spur dikes. In this study, laboratory experiments were conducted to investigate the effects of flow Froude number, ice-water flow ratio, the ratio of spur dike length to flume width, sediment median particle size, and other factors on the maximum scour depth around spur dikes, as well as the thickness distribution of ice jams around different spur dike configurations. The maximum scour depth around spur dikes under open flow and sheet-ice cover conditions was compared. The experimental results indicate that, compared with open flow conditions, the maximum scour depth around spur dikes under sheet-ice cover increases by 10-30%, while under ice jam conditions, it increases significantly by 150-200%. Under ice jam conditions, the maximum scour depth around spur dikes is positively correlated with the ice-water flow ratio and flow velocity, and negatively correlated with the median sediment particle size. Under open flow conditions, the maximum scour depth around spur dikes increases with an increasing ratio of spur dike length to flume width. In contrast, under ice jam conditions, the maximum scour depth initially decreases and then increases as the ratio of spur dike length to flume width increases. During the upstream progression of an ice jam, a critical flow Froude number exists at the (cross-section) CS where the spur dike is located, which is primarily influenced by the ratio of spur dike length to flume width, the ice-water flow ratio, flow velocity, and water depth.