Partitioning Prediction Study Of Landslide-tsunamis In The Wu Gorge Of The Three Gorges Reservoir Area

The Wu Gorge in the Three Gorges reservoir area is characterized by steep terrain,intricate structure,abundant karst features,and fragmented rock formations,which contribute to frequent landslide disasters.The water transportation in the Wu Gorge is frequent.Once a landslide slides into the river,it can trigger landslide-tsunamis disasters that spread upstream and downstream for several kilometers or even tens of kilometers,posing a huge threat to the waterways,passing ships,coastal docks,and local residents.However,at present,the mechanism and propagation law of landslide-tsunamis inside the Wu Gorge cannot be fully understood,and the existing methods for predicting landslide-tsunamis wave properties are difficult to quickly and accurately control the risk of landslide-tsunamis in this area.Therefore,conducting a detailed study on the landslide-tsunamis in the high and steep bank of the Wu Gorge is of practical significance for disaster prevention and risk control of landslide-tsunamis disasters,and for the management of the landslide disaster chain.The present study takes the landslide-tsunamis caused by landslides on the high and steep reservoir bank in the Wu Gorge as the research objects.It summarizes the geological model of the landslide-tsunamis in the research area.Base on the numerical simulations and 81 physical model experiments,it investigates the generation reason and dynamic attenuation rules of the propagation of landslide-tsunamis in the Wu Gorge.The characteristics of the landslide-tsunamis wave in the river channel are found have regional characteristics,and the crietira for dividing the"ring-parallel"propagation zone of landslide-tsunamis are proposed for the refined analysis of the propagation area.At the same time,a detailed simulation study was carried out using multidimensional methods such as simulation,experimentation,and field investigation,focusing on the examples of the Gongjiafang landslide-tsunamis.The applicability and scientific validity of the predictive model presented in this paper were comprehensively verified.The specific research results and conclusions are as follows:(1)The river channel and landslide characteristics of the steep and high Wu Gorge of the Three Gorges Reservoir area were summerised.By collecting and analyzing geological background information,landslide development characteristics,and river channel topography of the study area,the following conclusions were drawn:(1)The river channel with steep and high banks is deep and narrow;(2)There are mainly medium to large submerged landslides.It may cause sliding and destructive movement in periodic operation in the reservoir.(2)The generation mechanisms of landslide-tsunami waves in the river channel with high and steep banks in the Wu Gorge area are revealed.Based on a summary of the river channel and landslide features in the study area,physical experiments and numerical simulations were conducted to explore the generation mechanism of landslide-tsunami waves under the conditions of high and steep bank slopes,including the degree of water body occupation by the landslide,the law of energy conversion of the landslide,and the type of the first wave generated.The results show that:(1)The first wave of landslide-tsunami waves is directly formed by the landslide impacting the water body,the second wave is caused by turbulence generated by the collapse of the air cavity of the landslide,and the subsequent wave trains are caused by water surface oscillations formed by the wave run up and run down along the slope;(2)The main types of the leading wave are Stokes-like waves and Cnoidal-like waves;(3)Under different bank slope angles,the thicker the tongue of water formed,and the smaller the volume of water displaced by the landslide,the larger the bank slope angle.(4)Under the condition of high and steep bank slopes,the energy attenuation velocity of the landslide after entering the water is faster.However,under the same water depth condition,the influence of the bank slope angle on the energy conversion rate between the landslide and the water body is small.The minimum energy conversion rate for producing the leading wave is 0.4%,and the maximum is 8.2%.(3)The characteristics of the propagation and run-up of landslide-tsunamis in the river channel with high and steep banks are clearly defined.Through analysis of physical model experiments and numerical simulation results,it was found that the attenuation of propagated waves has specific regional characteristics in space,which are manifested as follows:(1)the flow field in the near-field area of the landslide surging waves is complex,while it becomes relatively simple in the far-field area of the river channel;(2)the propagated waves in the river channel are of medium-water wave,and the degree of nonlinearity decreases as the distance from the landslide increases;(3)The frequency dispersion of the propagating wave in the near-field zone is strong,and it decreases as the propagation distance and angle increase;(4)the propagated waves in the near-field area of the landslide mainly propagate radially in a circular pattern,with a rapid decay rate of wave amplitude.While the propagated waves in the far-field area propagate parallel to the riverbank,with a slower decay rate of wave amplitude.After analyzing the spatial differences in wave attenuation in the river channel,the channel is divided into"ring"and"parallel"propagation zones based on the ratio of the propagation distance to the river width.In the"ring"propagation zone,it was found that when the propagation angleγ≤45°,the influence of reflected waves is small;whenγ>45°,the degree of influence of reflected waves increases.For the entire"parallel"propagation zone,the influence of reflected waves is strong.(4)A decoupled prediction model for landslide-tsunamis in the Wu Gorge of the Three Gorges reservoir area has been constructed.By introducing decoupling concepts into the landslide-tsunamis prediction,a complete process prediction model for generation,propagation and run-up of landslide-tsunamis has been proposed.The model can predict the characteristics of the leading wave,propagation wave,and run-up very well.The prediction values have a good fit with experimental results,with the coefficient of determination R~2of the leading wave crest amplitude and wave height being 0.82 and 0.90 respectively,R~2of the maximum propagation wave attenuation in the propagation zone exceeding 0.80,R~2of the prediction model for the maximum propagation wave arrival time exceeding 0.80,and R~2of the prediction models for the maximum run-up of edge wave height and the opposite wave being 0.80 and 0.85respectively.(5)Fine-grained calculations were conducted on the Gongjiafang landslide-tsunamis,and the applicability of a decoupled prediction model for the landslides-tsunamis in the Wu Gorges with high and steep reservoir bank of the Three Gorges Reservoir area has been verified.Through comprehensive comparisons of field investigation data of landslide-tsunami with numerical simulation results,calculated values of exist empirical formulas and the predicted values of this study,it indicates that the model of this study has a small prediction deviation for the leading wave characteristics in the generation area and the wave characteristics in the"ring-parallel"propagation zone in the river channel.Although the wave height of some propagation waves in the"parallel"propagation zone and the run-up of the opposite wave may be overestimated,compared with exist empirical formulas,this model has higher prediction accuracy and good applicability.