A Study on the Features and Criteria of Debris Flow Partially Blocking Big River (PAP014337)
LUI Cuirong, DU Cui
Land use and Floods, landslides and erosion
The practices of the post-earthquake flood season indicate that debris flow is the most active disaster type, and debris flow blocking river has become a frequent disaster event, thus there is no time to delay the study on the laws of debris flow blocking big river. Aimed at the phenomenon that in the Minjiang River Valley most debris flows partially block the main river in the form of barrier dam, the author conducts the large-scale indoor flume experiment to reproduce the course that the high-density debris flows run into main river when the intersection angle is 90 degrees. The experimental results show that the thrust force of the follow-up debris flow is the major dynamic force driving the debris flow into the main river; The total volume of debris flows has important effects on river blocking, the more total volume, the more serious blocking. In the process of debris flow blocking river, when damming coefficient 'R' increases, velocity of main river firstly increases and then decreases: when R is less than 0.8, very little material of debris flow is lost (washed away), and head-water level increases linearly; When R is more than or equal to 0.8, the serious amount of material of debris flow is lost (washed away), and head-water level increases exponentially. Based on water and sediment dynamic process, as well as the dynamic equation of debris flow at different slopes, the author considers the interaction between barrier dam and the flow of main river, and establishes the formula to calculate the run-out distance of debris flow in main river. In view of the phenomenon that the material erosion is very serious when debris flow blocking big river, the erosion coefficient is obtained according to the test data of flume experiment. On the basis of the formula to work out the total amount of debris flow blocking main river, proposed by ZHOU Bi-fan, the author presents the relevant conditions amended in the light of the erosion coefficient. Eventually, the criteria of debris flow partially blocking big river is set up in terms of the formula of dynamic process and total amount of material.