Study On The Wave Field Characteristics Of Impulse Waves Generated By Three-dimensional Landslides In Curved Gorge-type Reservoirs

For alpine reservoirs impulse waves are particularly significant,due to steep shores,narrow reservoir geometries,possible large slide masses and high impact velocities.The resulting impulse wave is strongly nonlinear due to severe disturbance of water by the rock and soil mass.If the landslide is not completely submerged in the watercourse after deposition,it can be defined as a landslide into shallow water.The reason why landslide into shallow water can cause near-field topographic changes is that large rock masses remains on the water after deposition.The momentum rate from a landslide at impact in a water body,from the perspective of momentum balance,is the driving force behind the generation of impulse waves.Analysis of this problem is presented and used to derive theoretical relationships for the maximum near-field wave amplitude generated by three-dimensional deformable landslides.Taking field data of parameters and fracture developments of typical rockslides in Three Gorges Reservoir and on the basis of following similarity criterion,the physical modelling of impulse waves generated by three-dimensional cataclastic rockslides in shallow water area.On this basis,this paper focuses on the near field characteristics of impulse waves in shallow water.In addition,movement characteristics on the water of rockslides with different shapes and volumes,breaking indexes and wave run-up along coast are analyzed.The main conclusions are as follows:?1?The momentum rate from a landslide at impact in a water body,from the perspective of momentum balance,is the driving force behind the generation of impulse waves.Analysis of this problem is presented and used to derive theoretical relationships for the maximum near-field wave amplitude generated by three-dimensional deformable landslides.This is accomplished for momentum transfer using both hydrostatic and hydrodynamic assumptions.The comparisons between the measured values and the predicted wave amplitudes using novel momentum-based equations indicate that the maximum near-field amplitude generated by three-dimensional landslides is far less than the solitary wave breaking limit,and thus the wave will not break in the near-field.The results of the theoretical equations are in agreement with laboratory data if the landslide is completely submerged after deposition.However,for landslides into shallow water it should be noted that if the water depth is below the critical depth the measured near-field amplitudes will decrease sharply with decreasing water depth,which is opposite to the theoretical relationships.?2?The fractured rock mass produces a velocity gradient along the thickness direction during sliding,resulting in slide mass stratified into water.The maximum landslide thickness decreases exponentially with the increasing sliding distance.For wide and thick rock mass,special"butterfly-wing"movement feature will appear during sliding.?3?Landslides into shallow water will form large-scale splash zone above the slide impact zone.The water body in the splash zone does not contribute to wave generation as a dissipative term,resulting in a low conversion rate.Between 1 and 18%of the kinematic slide impact energy propagated outward in the impulse wave train.Between 1and 7%of the wave train energy was located in the leading wave crest.The observed impulse waves were classified based on the slide Froude number F and the dimensionless slide thickness S into three different wave types:non-linear oscillatory wave,non-linear transition wave,and bore.?4?Wave amplitude attenuation:As for being in the propagation direction?from-75°to 75°,the radial attenuation of leading wave amplitude satisfies?cos??ⁿ,and the leading wave trough decays faster than wave crest;the attenuation of leading wave along relative propagation distance satisfies power function.The attenuation coefficient is constant in the straight channel,while varies with?in the curved channel.?5?The first crest wave celerity is very similar to solitary wave celerity except that a large amplitude oscillation occurs in linear dimensionless phase wave velocity under extreme deep water conditions?a/h<0.05?.The celerity of the leading wave trough is less than solitary wave celerity and linear shallow water celerity,the average dimensionless phase velocity should be taken for calculation.?6?Two breaker zones are found in the offshore water:One is located near the axis of the landslide which is approximately equal to slide width,called positive breaker zone;The other is located in the concave bank within?=15°²5°,called bevel breaker zone.The breaker index of oblique wave is greater than the forward wave,and the increase in wave height caused by shoaling is more obvious.According to the experimental results,the formula for calculating the breaker index is established.?7?The measured breaking heighta_c1-b is used to modify Synolakis's runup law.Validation with modified equation of runup law and experimental results indicate that the model presented here can predict opposing hill slope maximum runup.The results show that the predicted values are in good agreement with the modified formula except for a few cases in which the near-shore waves are unbroken.The runup attenuation is established used dimensional experimental data from the coastal measuring points.Finally,the results are analyzed with the Hongyanzi landslide case.