Landslide-generated Waves Research Articles

Deformation and stability analyses of a near-dam rocky slope and its potential landslide-generated wave threats

Occurrence of a reservoir landslide and its potential secondary hazards near a dam can result in significant losses and casualties, such as those that resulted from the Vajont landslide. In this study, a cataclinal rock slope in the Maoergai reservoir was taken as a case to study the characteristics of the gravitational deformation process and to analyse the potential threat. The stability of the rock slope was analysed using the limit equilibrium method, and the potential landslide movement and subsequent waves were simulated. Results indicated that lithology, geological structure, reservoir water-level changes and artificial activities all play an important role in large deformations of rock slopes that are characterized by a combination of bending–toppling and, principally, shear slip. Pre-calculations of potential threats indicated that the impact of a landslide wave would be greater at dead water levels than at the normal water level and could result in the blockage of the inlet to the water-diversion structure on the opposite right bank. These findings provide implications for the control of reservoir rock slopes: (i) serious attention should be paid to the influence of water on rock strength in the early investigation of geological disasters; and (ii) infiltration must be prevented during water-level rise.Thematic collection:This article is part of the Role of water in destabilizing slopes collection available at:https://www.lyellcollection.org/cc/Role-of-water-in-destabilizing-slopes

Numerical estimation of landslide-generated waves at Kaiding Slopes, Houziyan Reservoir, China, using a coupled DEM-SPH method

Numerical estimation of landslide-generated waves at Kaiding Slopes, Houziyan Reservoir, China, using a coupled DEM-SPH method

Runup of landslide-generated waves breaking on steep slopes captured using digital imagery and hydrochromic paint

Runup of landslide-generated waves is an important natural hazard in coastal regions, and can result in major damage to the natural and built environment. Past work has investigated the runup of non-breaking waves, whereas, in contrast, little data is available on the runup of waves at the point of breaking prior to interaction with the opposing shore. In the present study, impulse waves were generated in a series of laboratory flume experiments by releasing a range of different slide source volumes of highly mobile slide material (water) into different reservoir depths, to observe the runup of breaking and non-breaking waves at the point of arrival at steep slopes ranging from 25° to 45°. Water surface characteristics including the maximum wave amplitude were measured using wave probes and digital imagery was obtained using high-speed cameras. The maximum runup, and the cross-slope variability in runup, of each wave was captured using hydrochromic paint, which changes colour on contact with water. The experimental results indicate that in the near-field the runup of breaking waves is dependent on the wave amplitude relative to the water depth, and is nearly independent of the slope angle. Statistical analysis of the runup observations for breaking and non-breaking waves indicate that the variability of runup across the width of the slope increases with increasing incident relative wave amplitude. These observations, combined with runup data from previous studies, are used to develop a new semi-empirical equation for the maximum runup of breaking and non-breaking waves. The formulation is valid over an extended range of relative wave amplitudes, relevant for near-field runup that has been documented in major field cases. The experimental observations in the present study provide, for the first time, a comprehensive dataset of runup for impulse waves involving breaking and no breaking on arrival at a slope.

Hydro-sediment-morphodynamic processes of the baige landslide-induced barrier Lake, Jinsha River, China

A large landslide impacting a river may cause a multi-phase chain of hazards, comprising landslide-generated waves, inundation as a barrier lake develops upstream of a landslide dam arising from rapid sediment deposition, and downstream flooding due to barrier lake outburst. Two major landslides (each of volume ~ 107 m3) occurred successively on 10th October and 3rd November 2018 at Baige village, Tibet, China. Both landslides led to a natural dam that completely blocked the Jinsha River, along with a barrier lake filled with upstream river inflow. Although the first barrier lake breached naturally, a significant quantity of residual material from the first landslide dam was left behind without being eroded. After the second landslide occurred, a flood channel was urgently constructed to facilitate an artificial breach of the barrier lake as it formed. The Baige landslide-induced barrier lake is unique having triggered by two successive landslides and outbursts a mere five weeks apart. Here a computational investigation is presented of the hydro-sediment-morphodynamic processes of the Baige barrier lake, using a recent 2D double layer-averaged two-phase flow model. This is the first modelling study of the whole field and whole processes for the formation and outburst of a landslide-induced barrier lake as well as the resultant floods, without evoking presumptions on dam breach (which have prevailed for decades and bear much uncertainty). The computed results agree well with field observations in terms of landslide-generated waves, landslide dam morphology, stage and discharge hydrographs at the dam site and downstream flood hydrographs. The artificial flood channel is shown to be effective for alleviating downstream inundation. Water and grain velocities are demonstrated to be distinct, characterizing the primary role of grains in landslide dam and barrier lake formation and the dominant role of water in barrier lake outburst and the resultant flood. Relatively low inflow discharge and large initial landslide volume favour landslide dam and barrier lake formation, but delay the outburst and downstream flood. The present 2D double layer-averaged two-phase model holds great promise for assessing future landslide-induced multi-hazard chains in rivers, and informing mitigation and adaptation strategies.

Application of a Hybrid SPH - Boussinesq model to predict the lifecycle of landslide-generated waves

Landslide-generated wave (LGW) events are particularly dangerous as they are associated with a high risk of loss of life and severe economic damage. The lifecycle of a LGW can be decomposed into various distinct stages, such as generation and propagation. The modeling of the entire LGW lifecycle through the use of a single model is difficult as the hazard characteristics of LGWs differ widely across spatial and temporal scales. Therefore, this study proposed a Hybrid Smoothed Particle Hydrodynamics (SPH) - Boussinesq model to overcome the limitations of individual models and to acquire a more reliable method of analyzing LGWs. An SPH two-layer depth-integrated model was combined with a Boussinesq model (FUNWAVE) through the implementation of a transformation zone. The proposed hybrid model was then applied within the evaluation of the potential risk for the generation of LGWs by impulsive waves generated by the Halaowo Landslide in Jinsha River, China. This study provides a discussion of the process for predicting waves and generated a risk map according to the reference emergency response plan.

Experimental study on the pressure of impulse waves generated by landslides on a bank slope

Impulse waves generated by landslides lead to serious secondary disasters. To investigate the effects of impulse waves on a bank slope, a three-dimensional physical model test was conducted considering multiple factors, such as the width, thickness, and volume of the landslide body, inclination angle of the landslide, and bank slope angle. The results show that the wave did not break upon the first crest. And the waves break and swirl locally when fallback water flowed into the trough. The pressure acting upon the bank slope included pulsating pressure and impact pressure, of which the latter was largely affected by repeated tests, measuring frequencies, and measurement point densities. The existing empirical formulas cannot accurately reflect the wave pressure on the bank slope under the action of landslide-generated impulse waves. The maximum pulsating pressure increased proportionally with width, thickness, volume and inclination angle of the landslide body. This study better restores the interaction process between landslide, impulse waves and bank slope in actual river channels, and provides relevant support for the formulation of water pressure prediction formulas.

Physical Modelling of Roll and Pitch Motions of Travelling or Stationary Ship in Large-Scale Landslide-Generated Waves

Large-scale landslides often occur in river-type reservoirs, and landslide-generated waves affect navigation channels and the navigation of ships. Thus, such waves cause widespread regional disasters. This study establishes a mechanical model of landslide-generated waves via field investigations and data collection, reveals the mechanism and process of landslide-generated waves, and investigates the propagation characteristics of landslide-generated waves along a sloping wave. The feasibility of the model is verified via (i) regularity analysis, (ii) comparative analysis of the effect of landslide-generated waves of mountain river channel reservoirs on the movement characteristics of navigation vessels and stationary vessels, (iii) deviation from the equilibrium position, and (iv) an in-depth study of the influence of large-scale landslide-generated waves on ships in different navigation positions in a river channel. Countermeasures are proposed for a sailing ship to tackle a sudden landslide-generated wave; these measures can provide a theoretical basis for ships to sail safely through large-scale landslide-generated waves.

Coastal landslides in Palu Bay during 2018 Sulawesi earthquake and tsunami

In this paper, we investigate the sources for Palu Bay tsunamis, which occurred in September 2018 after a Mw 7.5 earthquake struck on a strike-slip fault. Previous land-based field studies have identified numerous coastal landslides as possible sources for tsunami generation. Here, we present new post-earthquake bathymetry survey data in the bay. We compare the new very detailed nearshore bathymetry with the pre-earthquake data so as to quantify the magnitudes and configurations of coastal landslides and the characteristics of landslide-generated waves. We perform numerical simulations of tsunami propagation, isolating the coastal landslides as the only sources. The results show that, although the landslide-generated waves characteristically have shorter periods than the observed tsunami waves, the combination of the waves is able to produce long waves comparable with those observed, due to the ringing effects of the trapped waves inside the bay. Therefore, we conclude that landslide-generated waves played a significant role in the tsunamis in Palu Bay. Nevertheless, it is likely that the tsunamis were caused by a combination of tectonic and landslide sources.

Semi-empirical predictive equations for the initial amplitude of submarine landslide-generated waves: applications to 1994 Skagway and 1998 Papua New Guinea tsunamis

Accurate predictions of maximum initial wave amplitude are essential for coastal impact assessment of tsunami waves generated by submarine landslides. Here, we analyse the existing predictive equations for the maximum initial amplitude ( eta_{text{max} } ) of submarine landslide-generated waves and study their performance in reproducing real-world landslide incidents. Existing equations include various landslide parameters such as specific gravity (γs), initial submergence (d), slide length (B), width (w), thickness (T) and slope angle (θ). To determine how landslide parameters affect wave amplitude, we conduct a systematic sensitivity analysis. Results indicate that the slide volume (V = B × w × T) and d are among the most sensitive parameters. The data from the 1994 Skagway (observed eta_{text{max} } : 1.0–2.0 m) and 1998 Papua New Guinea (PNG) (observed eta_{text{max} } : 10–16 m) incidents provided valuable benchmarks for evaluating the performance of the existing equations. The predicted maximum initial amplitudes of 0.03–686.5 m and 3.7–6746.0 m were obtained for the 1994 and 1998 events, respectively, indicating a wide range for wave amplitudes. The predicted estimates for the smaller-sized event, i.e. the 1994 Skagway, appear to be more accurate than those made for the larger event, i.e. the 1998 PNG case. We develop a new predictive equation by fitting an equation to actual submarine landslide tsunamis: eta_{ text{max} } = 50.67 left( {frac{V}{d}} right)^{0.34} , where V is the slide volume (km3), d is initial submergence depth (m), and eta_{text{max} } is in metres. Our new equation gives wave amplitudes of 1.6 m and 7.8 m for the 1994 and 1998 landslide tsunamis, respectively, which are fairly consistent with real observations.

Turbulence models evaluation in MPS Lagrangian simulation of marine waters

ABSTRACT An advanced and well-equipped Moving Particle Semi-implicit which is a Lagrangian method is employed to simulate hydrodynamic behaviour of water wave evolution. Unlike most recently developed MPS models that consider inviscid or laminar flow, the present developed model is based on the turbulent nature of the fluid flow. In order to consider the turbulence stresses, three turbulence closures are included in the model, which are constant eddy viscosity, mixing length and k-ε model. The developed model was applied to different case studies including wave run-up on an inclined wall, wave train induced by wavemaker and landslide-generated wave. The model results were compared with analytical, empirical and experimental data cited in the literature and a good agreement was found. The results also showed that deploying a turbulence model could improve the stability of the MPS model. Results obtained through this research reveal that the application of k-ε model in combination with MPS method produces accurate and reliable results in addition to a stable solution for free surface prediction in wave mechanics.

Far-Field Characteristics of Linear Water Waves Generated by a Submerged Landslide over a Flat Seabed

Understanding the propagation of landslide-generated water waves is of great help against tsunami hazards. In order to investigate the effects of landslide shapes on the far-field leading wave generated by a submerged landslide at a constant depth, three linear wave models with different degrees of dispersive properties are employed in this study. The linear fully dispersive model is then validated by comparing the results against the experimental data available for landslides with a low Froude number. Three simplified shapes of landslides with the same volume, which are unnatural for a body of incoherent material, are used to investigate the effects of landslide shapes on the far-field properties of the generated leading wave over a flat seabed. The results show that the far-field leading crest over a constant depth is independent of the exact landslide shape and is invalid at a shallow water depth. Therefore, the most popular non-dispersive model (also called the shallow water wave model) cannot be used to reproduce the phenomenon. The weakly dispersive wave model can predict this phenomenon well. If only the leading wave is considered, this model is accurate up to at least μ = h0/Lc = 0.6, where h0 is the water depth and Lc denotes the characteristic length of the landslide.

Numerical simulation of landslide-generated waves during the 11 October 2018 Baige landslide at the Jinsha River

Landslides at river embankments can block watercourses, imperiling the safety of vessels and downstream hydropower stations. The Baige landslide, which occurred on 11th October 2018, is taken as an example to study the landslide motion and landslide-generated wave evolutions. The elasto-viscoplastic and renormalization group (RNG) turbulence models are employed in the FLOW3D software, treating the motion of the Baige landslide as a viscous flow. Numerical results show that the maximum velocity of the slide was approximately 75 m/s when entering the Jinsha River. Further, the waves triggered by massive debris avalanches at three different locations are investigated. The maximum velocity of the landslide-generated wave and the maximum run-up in the Jinsha River reached 45 m/s and 53.9 m, respectively, on the slide axis. The maximum run-up terrain elevation of the wave was 3039.7 m. The simulation results are basically consistent with the actual field observations and fit well with high-speed flow-like landslides. In this case, the displaced water was dominant due to the significant volume of the failure mass and the shallow watercourse of the Jinsha River. The run-down waves located on the source region axis contribute to the rise of water level downstream and upstream. The results from this case study serve as a practical inspiration for research on disaster processes.

Uncertainty Quantification of Landslide Generated Waves Using Gaussian Process Emulation and Variance-Based Sensitivity Analysis

Simulations of landslide generated waves (LGWs) are prone to high levels of uncertainty. Here we present a probabilistic sensitivity analysis of an LGW model. The LGW model was realised through a smooth particle hydrodynamics (SPH) simulator, which is capable of modelling fluids with complex rheologies and includes flexible boundary conditions. This LGW model has parameters defining the landslide, including its rheology, that contribute to uncertainty in the simulated wave characteristics. Given the computational expense of this simulator, we made use of the extensive uncertainty quantification functionality of the Dakota toolkit to train a Gaussian process emulator (GPE) using a dataset derived from SPH simulations. Using the emulator we conducted a variance-based decomposition to quantify how much each input parameter to the SPH simulation contributed to the uncertainty in the simulated wave characteristics. Our results indicate that the landslide’s volume and initial submergence depth contribute the most to uncertainty in the wave characteristics, while the landslide rheological parameters have a much smaller influence. When estimated run-up is used as the indicator for LGW hazard, the slope angle of the shore being inundated is shown to be an additional influential parameter. This study facilitates probabilistic hazard analysis of LGWs, because it reveals which source characteristics contribute most to uncertainty in terms of how hazardous a wave will be, thereby allowing computational resources to be focused on better understanding that uncertainty.

Physical Model Study on Discharge over a Dam Due to Landslide Generated Waves

Impulse waves generated by landslides falling into reservoirs may lead to overtopping of a dam and, in turn, to flooding of the downstream area. In the case of an embankment dam, the overtopping may lead to erosion of the downstream slope, ultimately resulting in breaching and complete failure with consequent further hazardous release of water to the downstream area. This research deals with the overtopping process of a dam due to landslide generated waves in a three-dimensional (3D) physical scale model setup. Experiments have been conducted with varying the slide, reservoir, and dam parameters. The primary focus is on investigating the feasibility of employing the steady state weir equation in order to predict the overtopping discharge over a dam crest due to landslide generated waves. Calibration and validation of the coefficient of discharge values for the different dam section are conducted for the specified model setup. Accordingly, a two-step calculation procedure is presented for predicting the overtopping discharge based on the maximum overtopping depth values. Hence, for the fixed setup, which includes a constant slope angle of the landslide surface, a predictive equation for maximum overtopping depth is proposed, based on slide volume, slide release height, still water depth, upstream dam slope angle, and dam height. The relative slide volume and relative still water depth both seem to have a significant effect on the relative overtopping depth.

Numerical analysis of landslide-generated impulse waves affected by the reservoir geometry

Impulse waves generated by landslides are a potential major hazard for the operation of hydropower reservoirs, as they pose a serious threat to the dam, to residents and to properties along the shoreline. A number of experimental studies have been conducted based on generalized models to predict the wave characteristics, but using the results from these models to predict landslide-generated impulse waves may result in significant errors due to wave reflection caused by changes in the reservoir width. To investigate the effects of reservoir geometry on the characteristics of landslide-generated waves during propagation, 14 numerical experiments were performed using Tsunami Squares. The real-sized numerical models were based on statistical data from the Yangtze River and a generalized cross section of the Gongjiafang landslide located in the Three Gorges Reservoir, China. Two types of generalized reservoir geometries were investigated – namely with converging and diverging reservoir widths. It is shown that the wave amplitudes decrease with increasing reservoir width, while wave heights and troughs have a complicated dependence on changes in reservoir width. Compared to the amplitudes of the leading waves, the wavelengths and start-up time of wave amplitudes were more affected in the converging reservoir models by variations in the reservoir width.

Case Study of Dam Overtopping from Waves Generated by Landslides Impinging Perpendicular to a Reservoir’s Longitudinal Axis

Landslide-generated impulse waves in dammed reservoirs run up the reservoir banks as well as the upstream dam slope. If large enough, the waves may overtop and even breach the dam and cause flooding of the downstream area with hazardous consequences. Hence, for reservoirs in landslide-prone areas, it is important to provide a means to estimate the potential size of an event triggered by landslides along the reservoir banks. This research deals with landslide-generated waves and the overtopping process over the dam crest in a three-dimensional (3D) physical model test, presenting a case study. The model set-up describes the landslide impacting the reservoir in a perpendicular manner, which is often the case in natural settings. Based on the experimental results, dimensionless empirical relations are derived between the overtopping volume and the governing parameters, namely the slide volume, slide release height, slide impact velocity, still-water depth, and upstream dam face slope. Predictive relations for the overtopping volume are presented as applicable for cases relating to the specific model set-up. Measured overtopping volumes are further compared to a two-dimensional (2D) case reported in the literature. An important feature regarding the overtopping process for the 3D case is the variation in time and space, resulting in an uneven distribution of the volume of water overtopping the dam crest. This observation is made possible by the 3D model set-up, and is of value for dam safety considerations as well as for foundation-related issues, including erosion and scouring.

A SPH two-layer depth-integrated model for landslide-generated waves in reservoirs: application to Halaowo in Jinsha River (China)

In this work, a two-layer depth-integrated smoothed particle hydrodynamics (SPH) model is applied to investigate the effects of landslide propagation on the impulsive waves generated when entering a water body. In order to deal with the open boundary in practical engineering problems, an absorbing boundary method, based on Riemann invariants which can be applied to arbitrary geometries, is implemented. In order to examine the accuracy of the proposed formulation, the model is tested against both available laboratory tests and numerical examples from the literature. Then, it is adopted to model the characteristics of the impulse waves generated by the Halaowo landslide in the Jinsha River, China. The results provide a technical basis for the emergency plan to the Halaowo landslide and benefit the disaster prevention policy, which helps mitigating future hazards in similar reservoir areas.

EMPIRICAL AND NUMERICAL MODAL ANALYSIS OF COASTAL AREAS PRONE TO TSUNAMI RISK

In this paper the Empirical Orthogonal Function (EOF) method and the k-f spectral technique are applied to extract from experimental data related to landslide-tsunamis propagating around the coast of a conical island, the wave modes that contribute to the wave field. The relevant modes are then compared with those obtained through numerical eigenanalysis of the long wave equation around the considered island. It is shown that it is possible to associate each EOF mode with some eigenvectors and the corresponding eigenfrequencies, both on the basis of the spatial shape, the wavenumber calculated along the coast and the frequency. Results confirm that landslide-generated waves propagate along the coast as trapped edge waves and the zero-th order mode is the most important.

Insights on the Source of the 28 September 2018 Sulawesi Tsunami, Indonesia Based on Spectral Analyses and Numerical Simulations

The 28 September 2018 Sulawesi tsunami has been a puzzle because extreme deadly tsunami waves were generated following an Mw 7.5 strike-slip earthquake, while such earthquakes are not usually considered to produce large tsunamis. Here, we obtained, processed and analyzed two sea level records of the tsunami in the near-field (Pantoloan located inside the Palu Bay) and far-field (Mamuju located outside the Palu Bay) and conducted numerical simulations to shed light on the tsunami source. The two tide gauges recorded maximum tsunami trough-to-crest heights of 380 and 24 cm, respectively, with respective dominating wave periods of 3.6−4.4 and 10 min, and respective high-energy wave duration of 5.5 and >14 h. The two observed waveforms were significantly different with wave amplitude and period ratios of ~16 and ~3, respectively. We infer tsunamigenic source dimensions of 3.4–4.1 km and 32.5 km, for inside and outside of the Palu Bay, respectively. Our numerical simulations fairly well reproduced both tsunami observations in Pantoloan and Mamuju; except for the arrival time in Mamuju. However, it was incapable of reproducing the maximum reported coastal amplitudes of 6–11 m. It is possible that these two sources are different parts of the same tectonic source. A bay oscillation mode of ~85 min was revealed for the Palu Bay through numerical modeling. Actual sea surface disturbances and landslide-generated waves were captured by two video recordings from inside the Palu Bay shortly after the earthquake. It is possible that a large submarine landslide contributed to and intensified the Sulawesi tsunami. We identify the southern part of the Palu Bay, around the latitude of -0.82oS, as the most likely location of a potential landslide based on our backward tsunami ray tracing analysis. However, marine geological data from the Palu Bay are required to confirm such hypothesis.

Comparison between the first and second wave crest amplitude generated by landslides

The landslide-generated wave which is largest is of particular interest due to hazard prevention. Among all wave trains, the first or second wave crest has the maximum amplitude. Whether the first wave crest amplitude is larger or not is undoubtedly affected by the landslide dimension and impact velocity. This paper presents a criterion for comparison between the first and second wave crest amplitude. 49 test runs are carried out based on an orthogonal design array, and in 39 runs wave crest amplitudes of the second waves are larger than those of the first waves. This study systematically investigates the effects of dimensionless front area, dimensionless top area, dimensionless two-dimensional volume and dimensionless three-dimensional volume on wave crest amplitude and wave amplitude ratio. An optimal criterion, including slide Froude number and dimensionless two-dimensional volume of slide, is proposed to determine which wave crest has the larger amplitude. The criterion is well verified by 157 test runs of two previous experiments.