Experimental Study Of Surge Waves By Ice Avalanche And Its Impact On Failure Of Moraine Dam

Moraine dams,impounding glacial lakes,are among the weak natural dams because of their slope,freeboard and composition.Glacial lake outburst floods occurring due to the failure of moraine dams are significant hazards for the valley downstream the failure,as they possess a huge amount of hydraulic energy that can kill thousands and destroy infrastructures and riverine landscape.Also,the entrainment of debris to the flow from the breaching process and downstream channel may develop the flow into a much bigger disaster or even a series of hazard chain.Ice and rock avalanche or landslide,glacier calving,degradation of ice cores,earthquake and atmospheric events trigger the breaching phenomenon which generates a series of waves overtopping the dam or seepage causing the failure of the dam.Various approaches have been discussed to produce an understanding of the failure mechanism of moraine dams: experimental works,empirical relationships,analytical solutions,and numerical modelling.No concrete experimental investigations and parametric solutions pertained to the failure mechanism of moraine dam are found in the literature review,but various empirical relationships are discussed,and suitable approaches for numerical modelling are suggested as per the requirement of the task.Ice avalanche is one of the major triggering factors for the failure of the moraine dam across the globe.To produce a better understanding of the impact of ice avalanche on the failure of the moraine dam,we conducted a series of experiments in an experiment flume.This flume contained a reservoir simulating glacial lake in which a block having the same density as that of ice was slid to imitate as an ice avalanche which triggered the failure of the dam that resulted in the flood along a long channel.Surge waves having maximum vertical displacement of 5 cm were generated by the impact of the blocks on the reservoir.The influence of the size of an avalanche,sliding angle and sliding length on the strength of surge waves generated are investigated.The strength of the surge wave was found to be increasing with the increase in the size of the block.The strength of surge waves increased with a steeper slope for sliding in the case of a normal block whereas,for a broken block,a clear relationship was missing between the strength of surge waves and angle of inclination of the slider.Furthermore,the sliding length was determined to be directly proportional to the strength of surge waves.Two different modes of failure of the moraine dam: wave overtopping and piping have been illustrated along with the displacement waves,and seiche waves originated by the impact of an ice avalanche.Hydrograph generated by different dam materials,the crest of the dam,the height of the dam and dam angle are compared.A machine learning model has been developed to predict the peak discharge based on the experiment results.The model suggested that the peak discharge value of our experiment can be predicted optimally by knowing the type of block,dam material and the height of the dam.The normal R2 value and the adjusted R2 value of the model was 0.967 and 0.944 respectively,signifying a strong prediction capability of the model.The particle size distribution of the channel after the failure of the moraine dam is analyzed to correlate with the riverine morphology.The particles of size categorized as very fine were found to be in an abundant amount at the collection tank.Therefore,small-sized particles travel to a very long distance compared to other size particles along with the water flow during the flood.