Study on the ultimate depth of scour pit downstream of debris flow sabo dam based on the energy method

• Scouring law downstream of debris flow sabo dam was analyzed by energy method.
• The relationship between and energy difference changes of profile was established.
• Presuming the scour pit as a whole and generalizing the profile as triangle
• Theoretical formula for the ultimate depth of scour pit was established.
• Serial flume experiments were developed to verify the formula.

The ultimate depth of a scour pit downstream of a debris flow sabo dam is an important design parameter in determining the foundation bearing depth of a debris flow for Sabo dam. This paper considers the scour pit system as a black box, neglecting the energy consumed by inter-particle collision of debris flow and the collision between debris flow and the valley bed. A formula was developed for the ultimate depth of a scour pit using the energy method to establish debris flow energy changes in and out of scour pit, combined with the energy needed by sediment incipient. When the results of the formula are compared with a series of indoor flume experiments, the error ranged from 3.1% to 17.6%. The calculated and experimental values agreed well, indicating that the method based on the energy method is reasonable and feasible.