Flume model test on the behavior of debris flows into the reservoir and the impact pressure acting on the dam embankment

Abstract The number of cases of damage to reservoirs due to debris flows has increased. In this study, granular material was released down the slope in a flume model to observe the debris flow morphology in a reservoir and to examine the impact pressure on a model dam embankment. The model flume had a slope angle of 30°, slope section width of 300 mm, and reservoir section width of 800 mm, and a model embankment with pressure and water pressure gauges was installed. Several experiments were conducted by varying the grain size of the granular materials to 3, 6 mm, mixed, and initial water storage levels. Observations from a high-speed camera indicate that when the debris flow enters the reservoir, the momentum rapidly decreases immediately after inflow. However, a solitary wave was generated, with heights reaching up to 2.5 times the initial water level. Additionally, during the impact of the debris flow on the model embankment, a large impact pressure was instantaneously generated. The magnitude and frequency of the occurrence tended to be more pronounced when the grain size was large. Additionally, the instantaneous impact pressure reached approximately twice the average impact pressure. However, with the exception of instantaneous large impact pressures, the existing equations used in the design of Sabo dams and coefficients with a specific range proposed in previous studies can be used to successfully calculate the impact pressure acting on the embankment in relation to the velocity.