Numerical investigation of hydro-morphodynamic characteristics of a cascading failure of landslide dams

A cascading failure of landslide dams caused by strong earthquakes or torrential rains in mountainous river valleys can pose great threats to people’s lives,properties,and infrastructures.In this study,based on the three-dimensional Reynoldsaveraged Navier-Stokes equations(RANS),the renormalization group(RNG)k-εturbulence model,suspended and bed load transport equations,and the instability discriminant formula of dam breach side slope,and the explicit finite volume method(FVM),a detailed numerical simulation model for calculating the hydro-morphodynamic characteristics of cascading dam breach process has been developed.The developed numerical model can simulate the breach hydrograph and the dam breach morphology evolution during the cascading failure process of landslide dams.A model test of the breaches of two cascading landslide dams has been used as the validation case.The comparison of the calculated and measured results indicates that the breach hydrograph and the breach morphology evolution process of the upstream and downstream dams are generally consistent with each other,and the relative errors of the key breaching parameters,i.e.,the peak breach flow and the time to peak of each dam,are less than±5%.Further,the comparison of the breach hydrographs of the upstream and downstream dams shows that there is an amplification effect of the breach flood on the cascading landslide dam failures.Three key parameters,i.e.,the distance between the upstream and the downstream dams,the river channel slope,and the downstream dam height,have been used to study the flood amplification effect.The parameter sensitivity analyses show that the peak breach flow at the downstream dam decreases with increasing distance between the upstream and the downstream dams,and the downstream dam height.Further,the peak breach flow at the downstream dam first increases and then decreases with steepening of the river channel slope.When the flood caused by the upstream dam failure flows to the downstream dam,it can produce a surge wave that overtops and erodes the dam crest,resulting in a lowering of the dam crest elevation.This has an impact on the failure occurrence time and the peak breach flow of the downstream dam.The influence of the surge wave on the downstream dam failure process is related to the volume of water that overtops the dam crest and the erosion characteristics of dam material.Moreover,the cascading failure case of the Xiaogangjian and Lower Xiaogangjian landslide dams has also been used as the representative case for validating the model.In comparisons of the calculated and measured breach hydrographs and final breach morphologies,the relative errors of the key dam breaching parameters are all within±10%,which verify the rationality of the model is applicable to real-world cases.Overall,the numerical model developed in this study can provide important technical support for the risk assessment and emergency treatment of failures of cascading landslide dams.

Flood cascading on critical infrastructure with climate change:A spatial analysis of the extreme weather event in Xinxiang,China

Floods caused by extreme weather events and climate change have increased in occurrence and severity all over the world,resulting in devastation and disruption of activities.Researchers and policy practitioners have increasingly paid attention to the role of critical infrastructure(CI)in disaster risk reduction,flood resilience and climate change adaptation in terms of its backbone functions in maintaining societal services in hazard attacks.The analysed city in this study,Xinxiang(Henan province,China),was affected by an extreme flood event that occurred on 17–23 July 2021,which caused great socio-economic losses.However,few studies have focused on medium-sized cities and the flood cascading effects on CI during this event.Therefore,this study explores the damages caused by this flooding event with links to CI,such as health services,energy supply stations,shelters and transport facilities(HEST infrastructure).To achieve this,the study first combines RGB(red,green blue)composition and supervised classification for flood detection to monitor and map flood inundation areas.Second,it manages a multiscenario simulation and evaluates the cascading effects on HEST infrastructure.Diverse open-source data are employed,including Sentinel-1 synthetic aperture radar(SAR)data and Landsat-8 OIL data,point-of-interest(POI)and OpenStreetMap(OSM)data.The study reveals that this extreme flood event has profoundly affected croplands and villagers.Due to the revisiting period of Sentinel-1 SAR data,four scenarios are simulated to portray the retreated but‘omitted’floodwater:Scenario 0 is the flood inundation area on 27 July,and Scenarios 1,2 and 3 are built based on this information with a buffer of 50,100 and 150 m outwards,respectively.In the four scenarios,as the inundation areas expand,the affected HEST infrastructure becomes more clustered at the centre of the core study area,indicating that those located in the urban centre are more susceptible to flooding.Furthermore,the affected transport facilities assemble in the north and east of the core study area,implying that transport facilities located in the north and east of the core study area are more susceptible to flooding.The verification of the flood inundation maps and affected HEST infrastructure in the scenario simulation support the series method adopted in this study.The findings of this study can be used by flood managers,urban planners and other decision makers to better understand extreme historic weather events in China,improve flood resilience and decrease the negative impacts of such events on HEST infrastructure.