Erosion characteristics of outburst floods on channel beds under the conditions of different natural dam downstream slope angles

Abstract

To explore the influence of natural dam downstream slope angles on the erosion characteristics of outburst floods on channel beds, five natural dam failure tests with different dam downstream slopes were conducted. The results show that the increase in the dam downstream slope angle enlarges the breaching discharge and shortens the duration. The farther away from the dam, the weaker the erosion intensity is on the channel bed. The absolute value of the erosion rate at each section is smaller in the late stage of the failure process, and the erosion intensity gradually decreases. For the channel bed near the dam, the erosion rate is larger, and the erosion ability is stronger than those for the channel bed farther from the dam. With the increase in the dam downstream slope angle, the erosion rate increases in the early stage, which changes little in the late stage. The sediment concentration first increases and then decreases, and with an increase in the dam downstream slope angle, the peak sediment concentration first decreases and then increases. For natural dams with gentle dam downstream slopes, the peak sediment concentration is primarily affected by the dam volume; when the dam downstream slope gets steep, the breaching discharge is the dominant factor affecting the sediment concentration. The final topography of the channel bed after dam failure under different dam downstream slope angles is basically the same. When the failure process comes to an end, sandbars are formed on the channel bed, which are distributed on both sides of the channel, forming a braided river downstream. The channel bed surface represents an obvious “S” shape.