Structural, geotechnical, and hydrogeological investigation of the Lake Cuejdel Landslide Dam, Eastern Carpathians: a facies-based characterization of internal dam properties

Landslide dams have been recognised as significant components of multi-hazard cascading systems, linking slopes and rivers. Despite the potential for catastrophic consequences, landslide dam breaching and evolution remain under-researched and poorly understood, often due to the remoteness of large volume, valley-blocking landslides and the general lack of high resolution pre- and post-failure survey data. The Hapuku Rock Avalanche presents a unique opportunity to study landslide dam evolution and breaching timelines due to the accessibility of the site and the availability and resolution of pre- and post-failure remote sensing data. Field observations and mapping, sampling, geophysical surveying, and 27 remote sensing surveys from 2016 to 2022 have provided detailed data on the dam. The Hapuku landslide was the largest rock avalanche triggered by the 2016 Mw 7.8 Kaikōura earthquake sequence, occurring ∼9 km upstream of the main highway and rail corridor on the South Island of New Zealand. It dammed the Hapuku River, which rapidly formed a lake behind the 80 m-high deposit. Four major erosion events and three significant partial breach events, identified through observations and remote sensing data differencing, resulted in water outflow from the lake, significant erosion of the dam and deposition of sediment into the river. The partial breaches correspond with less than 1 in 10-year rainfall events in 2017 and 2018, and the first occurred 141 days after dam formation. Seepage and internal erosion of the dam were observed to be progressing upstream before the partial breaches, in which water overtopped the dam. The third partial breach event, 2 years after dam formation, was the most significant erosional event in the last 6 years. The dam has eroded episodically and more locally since 2018, and the degree of erosion appears to be decreasing with time, despite more intense storms. A small lake remains. The evolution of the Hapuku Rock Avalanche dam emphasises the complexity of dam and breaching evolution, which are often oversimplified.

River blocking caused by landslide dams is a common geological disaster in mountainous regions worldwide, threatening the safety of human lives and infrastructure. However, studies on the formation process of landslide dams and the criteria of river blockage are still at an early stage. This paper built a laboratory-scale experimental apparatus for simulating the formation and evolution process of landslide dams, and then carried out a total of 29 experiments. It analyzed the common evolution stages of river blocking, including landslides, dam formation, and dam breaching in detail. Then, we investigated the influences of the landslide volume, the landslide discharge, and the water flow rate on a criterion and the time length of river blockage. The experimental results suggest that the formation condition of a landslide dam is related to the ratio of the landslide discharge to the water flow rate. Based on this understanding, we proposed a dimensionless River Blockage Criterion (RBC) to judge the formation of landslide dams. The criterion indicates that when RBC > 1.5, a landslide dam may form; otherwise, a landslide dam may not form. Additionally, the time length of river blockage was found to be related to the landslide volume and the water flow rate. Subsequently, we proposed a model for predicting the time length of river blockage and verified it by the 29 experimental results. The Baige River-blocking event, which occurred on the Jinsha River, China, in 2018, was used as a case study to further verify the RBC and the proposed model. The results show that the proposed RBC agreed well with reality, and the percentage difference between the calculated and the actual time length of river blockage was 11%. The findings of this study could contribute to the early warning and emergency response of river-blocking disasters.

Geohazards chain in watershed contains a landslide, which contributes to the propagation on the slope, intruding into river channels forming a landslide dam, a subsequent dam breach, and outburst flooding. Since the sub-process belonging to one chain are all coupled, one or several sub-processes can be the triggering factors of the subsequent one. They can generally own a larger space and time scale than that of a single disaster resulting in greater destructive power and amount of impact area. In this study, the most recent geohazard chain event that happened in the 2018-Baige landslide in Sichuan province, China is adopted for a numerical case study. This event can be divided into several sub-processes according to the coupling order within the chain process. The first landslide generates a landslide dam followed by another landslide and landslide dam sharing the same location. The second landslide overlapped with the first one forming a higher landslide dam. A larger-scale dam breach and resulting outflow occurred eventually. For solving this, a series of validated depth-averaged containing models for geohazards chain is adopted to simulate the whole coupling sub-processes, as well as, the standard LxF central differencing scheme is adopted for retaining high resolution and avoiding Riemann characteristic decomposition. The numerical study simulates the landslide propagation process using a viscos-inertial friction law. The numerical prediction is verified by values from field measurement in the literatures, indicating the feasibility of the (K) viscos-inertial rheology in simulating the large-scale landslide and the landslide dam formation. The overtopping failure process of the two overlapping landslide dams and the outburst flooding is numerically modeled by the proposed model. The results of maximum discharge illustrate the proposed model for landslide dam failure can simulate the interaction process of dam breach and outburst flood. The numerical results, validated by the literature provide reliable assessment and emergency relief support of the actual event. This proposed modeling framework is expected to improve mitigation strategies for geo-hazard chain hazards.

Landslide dams formed by successive rock slides in the same location may cause severe and long-term destruction to affected areas. However, studies on the formation of landslide dams that result from successive rock slides are still at early stages. In this paper, a flume test that could model rock fragmentation and the flow of fragmentary material is used to study the formation of landslide dams triggered by successive long-runout rock slides. The tests assess the effects of number of blocks, the number of times the blocks are released, and the initial arrangement of blocks before release on the dam geometry. The maximum and minimum landslide dam heights rise with the increasing number of blocks in each series of tests, while there is minimal or even no growth in the dam length for some series. Additionally, more block releases produce larger minimum dam height but smaller maximum dam height. Together, these results indicate that more releases are prone to fully block the flow channel by forming a steep dam. Furthermore, the initial block arrangement is also found to influence the landslide dam formation. In this study, landslide dams caused by successive rock slides are divided into two types: the stable type, namely, the landslide dam(s) already formed by the previous slide event(s) maintains general stability before the next slide lands on the dam surface; the unstable type, namely, the landslide dam(s) by the previous slide episode(s) has failed before the next damming slide occurs. Field investigations showed that slide episodes in both types of successive landslide dams are influential for the dam formation and river morphology.

Quantitative risk assessment of two successive landslide dams in 2018 in the Jinsha River, China

The formation and impact of landslide dams – State of the art

The Attabad landslide dam caused significant property losses and many human casualties in Pakistan, and also greatly affected the operation of the China-Pakistan Karakoram Highway (KKH). This paper discusses the risk of dam breach and hazards to the KKH project construction site following a dam breach. The paper examines the following three topics. (1) The geomorphologic dimensionless blockage index (DBI) and the analogy method were used to analyze the stability of the Attabad landslide dam. The long-term behaviors of landslide dams downstream of the Attabad landslide dam indicate that the risk of a dam breach exists, but the probability of a total dam failure is low. (2) The peak discharge of a potential breach of the Attabad landslide dam was calculated for scenarios in which 1/4, 1/3, 1/2, and total failure of the dam was breached. The potential breach discharge decreases with the downstream distance. (3) The potential impacts of the landslide dam breach on the KKH project construction site were analyzed. Based on the composition of the landslide dam, the probability of a 1/3 dam breach is high. To ensure the safety of downstream areas, disaster preparedness plans that correspond to the 1/2 dam breach scenario should be developed. Based on experience in addressing the landslide dam that was caused by the Wenchuan Earthquake, artificial controlled drainage measures are suggested and provide a technical reference for addressing the Attabad landslide dam and achieving recovery and normal operation of KKH.

1. The formation and behaviour of natural and artificial rockslide dams implications for engineering performance and hazard management S.G. Evans, R.L. Hermanns, A.L. Strom, G. Scarascia-Mugnozza, and K.B. Delaney 2. Risk-reduction measures for landslide dams R.L. Schuster 3. Technical and human aspects of historic rockslide dammed lakes and landslide dam breaches C. Bonnard 4. Rockslide and rock avalanche dams in the Southern Alps, New Zealand O. Korup 5. Landslide dams in the Central Andes of Argentina (Northern Patagonia and the Argentine northwest) R.L. Hermanns, A. Folguera, I. Penna, L. Fauque, and S. Niedermann. 6. Rock avalanche dams on the Trans-Himalayan Upper Indus streams: a survey of late Quaternary events and hazard-related characteristics K. Hewitt 7. Landslide dams in the high mountains of India, Nepal and China - stability and life span of their dammed lakes J.T. Weidinger 8. Volcanic natural dams associated with sector collapses: textural and sedimentological constraints on their stability L. Capra 9. Formation and behaviour of landslide dams and associated Quake Lakes emplaced during the 2008 Wenchuan Earthquake, Sichuan, China P. Cui et al. 10. The importance of geological models in understanding and predicting the life span of rockslide dams: the case of Scanno Lake, central Italy G. Bianchi-Fasani, C. Esposito, M. Petitta, G. Scarascia-Mugnozza, M. Barbieri, E. Cardarelli, M. Cercato, and G. Di Filippo 11. Formation, characterization, and modeling of the Val Pola rock-avalanche dam (Italy) G.B. Crosta, P. Frattini, N. Fusi, and R. Sosio 12. The 1786 Dadu River landslide dam, Sichuan, Chin C.F. Lee and F.C. Dai 13. La Josefina landslide dam and its catastrophic breaching in the Andean region of Ecuador G. Plaza, O. Zevallos, and E. Cadier 14. The Flims rockslide dam A. von Poschinger 15. Usoi natural dam, Lake Sarez, Pamir Mountains, Tajikistan: considerations of security and stability A. Ischuk 16. Rock-avalanche size and runout - implications for landslide dams T.R. Davies and M.J. McSaveney 17. Prospects for prediction of landslide dam geometry using empirical and dynamic models O. Hungr 18. The grain-size distribution of rock-avalanche deposits: implications for natural dam stability S.A. Dunning and P.J. Armitage 19. Incorporating the effects of groundwater and coupled hydro-mechanical processes in slope stability analysisE. Eberhardt and D. Stead 20. Paleohydrology of break-out floods from volcanogenic lakes in the Taupo volcanic zone, New Zealand V. Manville and K.A. Hodgson 21. The characterization of the 2000 Yigong River (Tibet) landslide dam and associated impoundment by remote sensing S.G. Evans and K.B. Delaney 22. The classification of rockslide dams R.L.Hermanns, K. Hewitt, A.L. Strom, S.G. Evans, S.A. Dunning, and G. Scarascia-Mugnozza 23. Russian experience with blast-fill dam construction V.V. Adushkin 24. Utilisation of data derived from large-scale experiments and study of natural blockages for blast fill dam design V.F. Korchevskiy, A.V. Kolichko, A.L. Strom, L.M. Pernik, and K. Abdrakhmatov

The Yangtze River is one of the most important rivers in China due to its large basin size, the large population along the river, and the numerous large dams and reservoirs on the river. The Jinsha River, the upper reach of the Yangtze River, was dammed twice recently at Baige, Tibet, one on 10 October 2018 and the other on 3 November 2018 (UTC + 8). Accordingly, two large landslide dams, 61 m and 96 m in height to the lowest dam crest, were formed in a 3-week interval. Due to the large inflow rates at the time of damming, the barrier lake level rose rapidly, posing huge risks to the downstream residents and properties. In managing the landslide dam risk, one of the important tasks is to predict the dam breaching flood beforehand. This paper focuses on rapid prediction of the dam breaching hydrograph and breach geometric parameters of the two landslide dams. The predictions were made timely before the breaching of the two landslide dams using both erosion-based empirical equations and numerical simulation and were refined based on detailed field investigation at the site after breaching. Comprehensive field investigations were conducted to determine the geological structures of the landslide dams, characterize the erodibility of dam materials, and measure the final beach dimensions. The simulated dam breaching processes, outflow hydrographs, lake water level changes, and final breach dimensions were validated by field observations. Compared with the hypothetical scenario without a diversion channel on the second landslide dam, a diversion channel 15 m in depth successfully lowered the peak flood discharge by about one third and helped to mitigate the flood risk significantly. The analysis outcome serves as basis for warning and evacuation of the downstream residents and making appropriate engineering risk mitigation plans.

An Ms 6.5 earthquake shocked the Ludian County, Yunnan Province, China, on 3 August 2014 and triggered the Hongshiyan landslide dam. The dam, with a height of 83 m and a lake capacity of 260 × 106 m3, threatened more than 10,000 people. A unique feature of this landslide dam was that it formed between a man-made dam and a hydropower plant. An existing drainage tunnel connecting the lake and the hydropower plant became a natural drainage conduit for the landslide dam, which played an important role in the mitigation of the landslide dam risks. This paper reports a quantitative risk assessment for the Hongshiyan landslide dam considering both engineering and non-engineering risk mitigation measures. The risk assessment is divided into three stages according to the implementation of two engineering measures: construction of a diversion channel and excavation of a branch drainage tunnel. The dam breaching hydrographs, flood zones, population at risk, and likely fatalities in each of the three stages are analysed. The optimum evacuation strategy in each stage is also studied based on the principle of minimum total consequence. It is found that the diversion channel decreases the dam breaching peak discharge and the associated risks significantly. The branch drainage tunnel prevent the landslide dam from overtopping failure in non-flooded period; however, the landslide dam may fail by overtopping in a future flood if the inflow rate is larger than the outflow rate through the drainage tunnels, resulting in serious losses of lives and properties. The dam breaching risks in all the three stages could be largely reduced by the optimal evacuation decision, which shows that timely evacuation is vital to save life and properties. The study provides a scientific basis for decision making in landslide dam risk management.

Cascading breaching of the Tangjiashan landslide dam and two smaller downstream landslide dams

Landslide dams are common geological features in mountainous areas, which may have serious consequences due to sudden breaching of the dam. An effective emergency response requires rapid and accurate forecasts regarding the landslide dam breach process. However, most existing models use physical, mechanical, and erosion properties of the mean or characteristic grain sizes to represent the landslide deposits. The grain size distribution and variations in soil erodibility with the depth in the landslide dam are not considered, resulting in an incorrect estimation of the breach flow hydrograph. In this paper, a simplified landslide dam classification is presented based on the formation mechanism and grain size distribution of landslide dams. Additionally, the influences of grain size distribution on the residual dam height and breach process of landslide dams are analyzed. This paper proposes a numerical method to rapidly obtain the breach hydrographs and breach morphology evolution of landslide dams. The new method can quickly classify landslide dams according to geological survey data and predict the landslide dam breach process. Three types of representative landslide dams in China are simulated to validate the proposed method. The breach flow discharge is significantly affected by spillway excavation. This contribution can provide rapid prediction of the landslide dam breach process and can be used for the emergency response planning before dam breaching.

Analysis of landslide dams induced by the 2008 Wenchuan earthquake

Geomorphometric characteristics of New Zealand landslide dams

A landslide dam is a natural hazard that results from a landslide of any type whose runout and interaction with local topography and relief deposits it to form a barrier or dam that can hold back river water in the upstream region. The water held behind the dam forms a lake upstream and risks breaching at any moment due to the unconsolidated landslide material. When this dammed lake is breached, it increases the risk of flash floods called Landslide Lake Outburst Floods (LLOF) in the downstream region, posing significant risks to infrastructure and livelihood. LLOFs are prevalent hazards in mountainous regions globally, including the seismically active Himalayas. The northwestern Indian Himalayas (Jammu & Kashmir, Ladakh, Himachal Pradesh, and Uttarakhand) are particularly susceptible to landslides and landslide dams due to weak, sheared bedrock and confined river valleys. This review critically evaluates the current knowledge on landslide dams in Uttarakhand, India. While paleo landslide dam and LLOF assessments are common, proactive monitoring and hazard mitigation strategies remain limited. Here, we comprehensively review historical and contemporary landslide dams in Uttarakhand, categorising existing research methodologies into past, present, and future studies. Past studies primarily focus on paleolakes formed after the Last Glacial Maximum (LGM) and employ various dating techniques for reconstruction. The present studies discuss the landslide dams from 1857 to the present and analyse the most affected catchments, districts, months of occurrence, and the dominant landslide types. Future studies review the utilisation of geospatial technology, numerical modelling, and machine learning algorithms to determine the formation and stability of landslide dams. This comprehensive review of historical, ongoing, and future research on landslide dams in Uttarakhand sheds light on these dynamic natural threats. By deepening our understanding, we aim to empower the development of robust mitigation strategies, ultimately contributing to the enhanced disaster preparedness, risk reduction, and effective mitigation measures in the region.