Study On Characteristics Of Flow And Sediment When Debris Flow Confluence With The Main River

Debris flow is one of the most common geological disasters in mountainous areas. When debris flows that carried a lot of sandstone and boulder converge into river, varying degrees of disaster will be caused. River silted, forming rapids or shoals, influencing the navigation; or blocking off the river, forming a submerged and flood disaster, endangering people’s lives and property, if the disaster is more serious. For the purpose of study the movement characteristics of flow and Sediment in confluence area. Firstly, through data collection and field survey, we analyzed the characteristics, patterns, results and determinants of debris flow confluence with river; Then, the model tests of debris flow confluence with the main river are carried out, we gained the influence of various parameters on the shape parameters of the accumulation body in the confluence area, analyzed the model and mechanism of debris flow blocking river; Finally, based on the momentum conservation theory, the degree of blocking river caused by debris flow is calculated in theory.Moxi River debris flow blocked Dadu River physical model test showed that:Debris flow density has a great influence on the shape parameters of accumulation body, there are stable accumulation body formed in confluence area when debris flow density is more than 1.7g/cm3. With the increase of density, the range of accumulation body increased linearly; With the same conditions, the greater the total amount of debris flow, the river blocked more seriously. According to similar conditions, when the total amount of debris flow reached 47.5 ×104 cubic meter, the Dadu River will be completely blocked partly, or if the total amount of debris flow reached 85.5×104 cubic meter, the Dadu River will be completely blocked. Moxi river debris flow have the ability to blocking the Dadu River again.Intersection angle is widely believed to be an important parameter influencing the result of debris flow and the main river. In order to study the influence of the conjunction angle(α), to further exploring the general law of debris flow confluence with main river, a flume experiment of debris flow into the main river was carried out. The tests indicate that: Right angle is the most beneficial to debris flow blocking the main river; When the degree of blockage coefficient is greater than 0.4, the upstream water level uplift phenomenon appeared, the value of water level uplift depends on degree of blockage and blocking mode. The experiment also got four different types of blocking river: completely blocked; Partly blocked from one shore; Partly blocked from both shore; Submerged dam blocking. The probability and time length of each type are consistent with the natural conditions.The debris flowed into the relatively flat riverbed from steep tributary, based on Takahashi’s equation of motion of the debris flow in the variable slope channel, riverbed resistance and water flow resistance are considered and the calculation formula of the movement distance of debris flow on river bed is derived. It is used to calculate the accumulation body shape parameters and the degree of blockage. Theoretical analysis results agree well with the experimental results. The experimental results and theoretical analysis can provide meaningful reference to identify whether the debris flow can block the river.