The Discrimination Model Based On The Formation Process Of Overtopping Outburst Debris Flow

With the global warming and frequently occurred extreme weather and climate events,coupled with seismic effects,the number of outburst debris flow triggered by overtopped natural dam failure has risen.The outburst debris flow which triggered by the unsteady flow erosion is different from every other type of debris flow.The prediction of this type of debris flow is not feasible because the formation mechanism of outburst debris flow is still unrevealed.This paper carries out a lot of flume experiments to analyze the formation process of the overtopped outburst debris flow,thereby establishing the discrimination model of the overtopped outburst debris flow,and intends to identify the formation position and time of debris flow.The main conclusions are as follows:(1)By analyzing the results of the flume experiments,and discussing the influence that experimental materials,the upstream inflow,and the dam height on the evolution of sediment elevation of the riverbed surface.It is found that the sediment elevation of the riverbed has exhibited a stronger instability under different conditions of sediment materials,the upstream inflow and the height of the dam.And,the variation range of sediment elevation on riverbed near the dam with the dam failure is larger than that on riverbed section far from the dam.As the medium diameter of the material is increased,the range of change in the river bed will increase,and the peak elevation of the river bed is reduced.In addition,during the dam failure,when the medium diameter of the sediment particles is large,the river bed elevation is decreasing downstream along the riverbed direction,while the medium diameter of the sediment particles is small,mid-river bed elevation is the largest.As the reduction of inflow discharge and the reduction of the dam height,the range of changes in the river bed elevation is shown in a reduced trend.(2)Under different experimental conditions,the sediment erosion rates at the positions of riverbed section I,II and III show a stronger instability with the dam failure.When the median diameter of the sediment particles decreases,the variation range of the erosion rate on the riverbed will decrease,which means that when the dam that composed of lager median diameter of the sediment particles is failed,the impact on the downstream river bed will be larger.When the inflow discharge is increased,the variation range of sediment erosion rate on the river bed will increase.With the dam height increased,the peak discharge of the outburst flow will increase,which can affect the flushing and siltation of the sediment of the riverbed.(3)The influence of the experimental materials,the upstream inflow and the dam heigh on the sediment volume concentration at the end of the flume is more obvious.The specific performance is the increase in median diameter of the sediment particles causes the reduction of maximum volume concentration,and the increase of minimum value of volume concentration.The maximum value,minimum value and mean value of sediment volume concentration increase with the increase of inflow discharge.When the dam height is reduced,the maximum value of the sediment volume concentration will decrease,and the peak of the sediment volume concentration appears early.(4)Considering the movement process of sediment-laden flow with dam failure,a new discrimination model of overtopping debris flow is established by using the hydrodynamic equation and the erosion equation.This discrimination model can calculate the key parameters such as the debris flow formation time,formation position,velocity and discharge of debris flow in the whole process of dam failure.The accuracy of the discrimination model is verified by comparing the numerical simulation results with the experimental results.The research results in this paper help to clarify the formation process of overtopping debris flow,provide reference for the identification of overtopping debris flow disasters,and have important guiding significance for debris flow risk assessment.