The complex flow structure in sharp bends may cause a series of water and sediment problems which are of great risk to flooding control and engineering safety. For this reason, there is of great significance to study the characteristics of secondary flow in sharp bends. In this article, the characteristics of vorticity and longitudinal velocity in sharp bends are studied by laboratory experiments and theoretical analysis. The results showed that there are two opposite circular currents on every cross-section in the bend. The two circular currents show a trend of increasing and decreasing streamwise. Vorticity is used to indicate the secondary flow intensity and is used to adjust the formula of longitudinal average velocity. The new formula fit the experiment data well and can describe the phenomenon of the maximum longitudinal average velocity appearing near the bed surface.

Ice problem widely exists in the north rivers, especially the ice disaster of the water elevation rise triggered by local ice jam in melting period caused by flowing ice. Therefore, it is of great significance to study the formation and influence of ice jam during the melting period. In this paper, the characteristics of ice flow in Yumenkou reach of the Middle Yellow River during the melting period is studied by laboratory physical model tests using paraffin as model ice. The results showed that: The formation of ice jam is controlled by flow rate and ice density during the melting period. When the flow rate is small and the density of flowing ice is high, there are enough ice cubes in a certain space who have enough time to combine with each other to form an ice jam. An ice jam is made up of at least two ice cubes stacked on top of each other vertically whose backwater influence is at least greater than the maximum height of one ice cube. An ice jam is more likely to form in the wider reaches of the river. The reason for that is, when the flow ice density reaches a certain level, the flow velocity is reduced more due to the wider river width, and the ice cubes are more likely to collide, squeeze and combine with each other, which are not easily transported by water with low flow intensity.