Experimental study on the critical condition of river blockage by a viscous debris flow

A debris flow flowing into a river may cause river blockage and form a dam. When the dam breaks, large floods can occur in the areas downstream, which can lead to fatalities and property damage. In this study, the parameters of river blockage were classified as three types of factors: morphological factors, dynamic factors, and characteristics factors of debris flows. The confluent angle, the dimensionless volume, the unit discharge ratio, and the dimensionless yield stress are important parameters for river blockage. They are all independent and dimensionless parameters. The degree of river blockage was divided into 4 stages: minor blockage, partial blockage, major blockage, and complete blockage. A classification based on the blockage coefficient is proposed to assess the degree of blockage. An experimental study was conducted with a total of 61 experimental runs. Based on the blockage coefficient of each run of the tests, the relationships between the degree of blockage and the key parameters (i.e., the confluent angle, the dimensionless volume, the unit discharge ratio, and the dimensionless yield stress) were obtained. A prediction model of the degree of river blockage is proposed based on these relationships. The area total of 21 debris flow tributaries and their corresponding rivers in China were selected to validate the prediction model. In these 21 tributaries, 24 events involving a debris flow flowing into a river resulted in partial blockage, major blockage, and completely blockage of the rivers. The prediction model was successful validated using the 22 events in China involving partial blockage, major blockage, and complete blockage.