Search

The safety of tailings impoundments has long been a concern of academic researchers globally. The tailings dam breaks are extremely likely to induce secondary disasters such as mudflows, landslides and water and soil pollution, thus further aggravating the risk of accidents. On the basis of practical engineering, this study performed a dam-break physical model experiment and theoretical analysis to examine tailings dam overtopping and dam body collapse processes. It also discussed the leaked tailings flow evolution characteristics after dam failure, based on important parameters such as the dam-breach variation rules after dam break, flow velocity of the leaked tailings flow, particle deposition characteristics and submerged depth. Our research discovered that dam-breach development was mainly constituted by water current erosion-induced longitudinal downcutting and dam-breach slope instability-caused horizontal expansion. A large sand inrush amount resulted in a high downstream flow rate and large sediment depth after dam failure. In addition, when the sampling site was > 100 cm (model scale) away from the dam site, the discharged tailings flow size grading phenomenon was obvious during dam breach, and the particle size gradually decreased with increasing distance between the sampling characteristic sites and dam site.

This paper aims to systematically study kinematic characteristics of Wenjiagou rock avalanche triggered by the M8.0 2008 Wenchuan earthquake and one of subsequent debris flows that occurred on August 13, 2010 (8.13 debris flow), using a numerical approach. The kinematic characteristics of the rock avalanche are back-calculated using an energy-based runout model. The erosion process of the subsequent rainfall-induced debris flow is analyzed using a progressive scouring entrainment model incorporated in the energy-based runout model. The results indicate that Wenjiagou rock avalanche traveled farther than most other rock avalanches with a maximum velocity of approximately 73 m/s detected at about 1700 m away from the source zone. The erosion of the 8.13 debris flow mainly occurred right after the dam failure which contributes to more than 97% of the total eroded volume. Besides, four different scenarios, including no blockage of the runoff (scenario I), no dam failure (scenario II), dam failure at the end of precipitation (scenario III), and no erodible material (scenario IV), are supposed to study the effect of the failure of a check dam on the erosion characteristics of the debris flow. The results reveal that the blockage of the channel without failure could reduce 86% of the total volume and the failure of check dams is the main reason for the destructive consequence of the 8.13 debris flow. This paper proposes an approach to explore kinematic characteristics of a rock avalanche and erosion process of the subsequent rainfall-induced debris flows and also innovatively provides a method to indirectly assess mitigation strategies that can be used for the design of mitigation projects.

It has been found that the less care is shown while constructing the water retention structures as compared to the amount of care shown in designing for it. This is more often in earthen embankments, where soil properties need to be controlled within the designed limits. The life and stability of embankments are entirely based on the extent to which the design assumptions are achieved in the field. History shows many failures were due to the lack of quality control during construction. In India every year many water storage structures fail, but very few were reported. Till date, only 37 dam failures in India are reported but not appropriately analyzed. This paper is focused on compiling the Indian dam failure list with relevant data which can be used for developing breach parameters equation. The data are collected from Government reports, articles news reports and magazines. This paper is also focused on developing new empirical equations for breach parameters and peak outflow from the dam failure which suits Indian condition. In developing the regression equation for breach depth, average breach width, peak discharge and failure time, different combinations of control variables is highlighted such as the dam height, reservoir capacity, average dam width, dam type, failure mode and dam erodibility. In this study, we incorporate the dam average thickness as another control variable for finding out the breach parameters and found suitable for breach depth calculation. New equations are proposed to compute the peak outflow rate. Further, these equations are compared with other developed regression equations for breach parameters and peak outflows.

The study of dam-break analysis is considered important to predict the peak discharge during dam failure. This is essential to assess economic, social and environmental impacts downstream and to prepare the emergency response plan. Dam breach parameters such as breach width, breach height and breach formation time are the key variables to estimate the peak discharge during dam break. This study presents the evaluation of existing methods for estimation of dam breach parameters. Since all of these methods adopt regression analysis, uncertainty analysis of these methods becomes necessary to assess their performance. Uncertainty was performed using the data of more than 140 case studies of past recorded failures of dams, collected from different sources in the literature. The accuracy of the existing methods was tested, and the values of mean absolute relative error were found to be ranging from 0.39 to 1.05 for dam breach width estimation and from 0.6 to 0.8 for dam failure time estimation. In this study, artificial neural network (ANN) was recommended as an alternate method for estimation of dam breach parameters. The ANN method is proposed due to its accurate prediction when it was applied to similar other cases in water resources.

Failure modes for earth dams are extensively reviewed and analysed using a three-pronged approach including a literature review, physical observations of a representative earth dam site and finite element structural analysis of the dam wall. Several failure scenarios are used for predicting consequences in terms of downstream inundation and damage. The fluid flow component is performed using the mesh-free smoothed particle hydrodynamics method. For a representative earthen dam, piping and landslip are identified as key failure modes based on a combination of finite element analysis, theory and physical observations. Inundation behaviour is very different for the two failure modes. The landslip failure is the most critical one for the dam studied with flood water breaking the river bank and affecting surrounding property and farmland. For the piping failures, water flow from the initial pipes formed for significant periods before they collapse, but the flow rates are small compared with that of the much larger landslip mode. After failure, fragments of the collapsing wall block the breach and can considerably restrict the flood discharge. In some cases, the water pressure is able to push the obstructing material downstream and some minor flooding occurs, but in others cases the breach can remain blocked with little flooding occurring. A prototype risk framework is developed using the small database of the pre-computed flooding scenarios and key variables that affect inundation such as water level in the reservoir. This can be used to estimate inundation maps for as yet non-computed scenarios through interpolation and superposition techniques. The implementation of the risk framework is demonstrated by the estimation of inundation maps for two in-between non-computed reservoir levels. Inundation due to multiple breaches is also estimated by superposition of three single-breach scenarios. Results are compared against the simulated multiple breach. A preliminary implementation of this risk framework into a geographic information system is also described.

The problem of dam safety is one of the most important research topics of water conservancy projects, and many researchers pay much attention to study the risk of earth dam overtopping. This paper synthesizes in the definition of risk the probabilities of dam failure and the corresponding losses, including the probability estimation, losses evaluation and criteria exploring risk approaches. Then, a comprehensive risk assessment system of dam flood overtopping is established, which is widely applicable. Gate failure, randomness of flood, initial water level and time-varying effects are incorporated in the failure probability model. Many complex factors are simplified in losses estimation. In addition, thresholds of various types of losses are proposed and are adapted to the national conditions. The methodology is applied to the Lianghekou hydropower station in China to illustrate the assessment process of flood overtopping risk and to evaluate its safe loophole with a view to the failure of spillway gates. Monte Carlo simulation and JC method programs are adopted to solve the model based on MATLAB tools and DELPHI. The results show that the losses pose significant impact on the risk assessment and should be considered in the assessment of risk. Probability calculation and loss estimation could be well combined with standards, providing a basis for risk management and decision-making.

Rockfill is the most abundant building material. It is often used for water retention under different contexts, such as dams, embankments or drainage systems. Climate change may cause water levels to rise in reservoirs. As rockfill structures are not able to resist strong overtopping flow, rising water levels will constitute a danger for rockfill dam stability as well as for people living nearby. This work is aimed at the development of an empirical formula that enables calculation of the critical water level of overflow at the crest from the geometrical and physical parameters of a dam. To achieve these objectives, several experimental tests on a rockfill dam model with two different impervious cores, moraine with a sand filter and an empty wooden formwork, were conducted in a hydraulic channel at the hydro-environmental laboratory at Ecole Polytechnique de Montreal. The purpose of these tests was to study the initiation of a riprap failure under the influence of different variables, such as rock size, riprap bank, downstream side slope and bed slope. Results showed linear trends between the critical water level and both the downstream side slope and bed slope. Also, a power trend was observed between the critical level and riprap grain size. A formula that gives the critical overtopping water level was developed from these results.

The present model and methodology described in Part I of this work are applied to perform a comprehensive risk analysis of the dam-break flood of five reservoirs in the Haihe River Basin, China. The results indicate that the three-dimensional numerical simulation considering complex terrain can reflect the characteristics of flood routing and the three-dimensional phenomena. Based on the simulation results, it can be concluded that the risk grades of the consequences induced by a gradual or instantaneous dam break of the Dongwushi reservoir are extremely serious, as determined through the attribute synthetic approach. The results obtained from ranking the risk by the technique for order performance by similarity to ideal solution method are that the Dongwushi reservoir has the most serious consequences when the dam breaks followed by the Lincheng reservoir, the Miaogong reservoir and the Yunzhou reservoir, and the Youyi reservoir has the least severe consequences. Though the ranking of the relatively comprehensive risk coincides with that of the consequences, the dam safety measured by the dam failure probability plays an important role in ranking the risk. A sensitivity analysis is performed by individually increasing the weight of each criterion by 20 %, and the ranking order is not changed, suggesting that the evaluation model is reasonable, stable and reliable.

Flood and sediment disasters caused by glacial lake outbursts have occurred frequently in recent years in the Himalayas of Nepal. Glacial lake outburst floods (GLOFs) can cause catastrophic flooding in downstream areas with serious damage to lives and property. It is thus important to investigate outburst floods from potentially dangerous glacial lakes. In this study, the characteristics of potential outburst floods from the Tsho Rolpa glacial lake due to two types of moraine dam failure caused by seepage flow or water overtopping were analyzed with various scenarios by using integrated modeling system of three numerical models: (1) the flow and bed-surface erosion model, (2) the seepage model and (3) the slope stability model. Flood inundation areas were also identified by using the numerical model of the flow and moraine dam failure and geographical information system tools. Possible threats and damages due to the potential GLOF events from the lake were also analyzed based on numerical results, flood inundation maps and field investigations.

The standard procedure in Quebec, Canada, for evaluating the failure of an embankment dam, per the Loi sur la securite des barrages, specifies a 30-min-long failure scenario with a breach width equal to four times the maximal height of the dam. We demonstrate a new method for evaluating the flood overtopping failure scenario for embankment dams with concrete upstream slope protection, using Toulnustouc dam for example computations. Our new methodology computes safety factors for a range of potential failure mechanisms taking into account geotechnical, hydraulic, and structural factors. We compile the results of our investigations of the various dam failure mechanisms and compare the corresponding dam failure hydrographs to the current hydrograph specified in the standard analysis procedures. Our investigations tend to invalidate the current standard procedures for evaluating the failure of rock-fill dams with concrete upstream faces, by indicating that the current standard procedures underestimate the peak failure discharge and overestimate the time to the peak discharge.

After the catastrophic failure of a red mud reservoir in Hungary, we performed a persistent scatterer radar interferometry (PSI) deformation analysis to investigate the stability and motion history of the entire area focusing on the dam walls of the collapsed structure. Our aim was to contribute to the better understanding of the disaster and, more importantly, to see whether it was possible to prognosticate and consequently prevent the failure of the reservoir and to help avoiding such occurrences worldwide. Our earlier data revealed that the surroundings were generally very stable over the investigated 8 years time interval, whereas significant continuous motions were detected on the embankments. After these first results, we continued our PSI deformation study with the processing and evaluation of the complete ascending pass ENVISAT dataset and later with the combination of the results of the two different observation geometries. From our descending and ascending data, it was possible to combine motions determined in line-of-sight directions and to investigate horizontal and vertical components allowing the estimation of ‘total’ velocity vectors, magnitude and directions, at those locations of the reservoir and on the entire study area where reflections from both projections were available. It was also possible to get information from several other segments of the embankments of the failed reservoir where the descending geometry was unfavorable. With the combination, the complete ENVISAT PSI analysis using both ascending and descending orbit data enabled us to constrain the role of the soil structure and to look at the differential uplift or subsidence due to swelling soil effect. It also enabled us to constrain the role of the deposited mud, slurry, and accumulated water, and the strength and design of the structure in the failure of the red mud reservoir. Models were also constructed to visualize the observed motions of the reservoir embankments and to highlight the location of strain and stress accumulation providing significant constraints on the natural and anthropogenic origin of the disaster.

On October 4, 2010, the embankment of No. 10 red mud—waste product during bauxite refining—reservoir of MAL Co. Ltd. alumina plant collapsed. Around 700 000 cubic meter of alkaline slurry with 11–13 pH value flooded three nearby settlements. Ten people were killed, 123 wounded, and about 350 houses were damaged or became uninhabitable in one of the biggest industrial and ecological catastrophe in modern history of Hungary. Synthetic aperture radar interferometry (InSAR) is the only geodetic technique that can reveal the past stability and motion history of the broken reservoir. We performed a persistent scatterer InSAR (PSI) analysis to contribute to the better understanding of the disaster. The key question we address in this study is whether there were signs prior to October 4th event which may have prognosticated the disaster. The PSI results could reveal if the dam was stable in the past without prior signs of the failure or there were definite indications of deformation before the collapse and proper monitoring of motions could have highlighted the risk and the disaster may have been prevented. This is a rare event and its PSI study is unique and may be critical in understanding it and helping to prevent other similar occurrences.

Landslide dam failure can trigger catastrophic flooding in the downstream. However, field observation of such flooding is rarely available, while laboratory experimental studies are sparse. The mechanism of landslide dam failure and the flood has so far remained insufficiently understood. Here, we present an experimental investigation of landslide dam failure and the flood. A total of 28 runs of experiments are carried out in a flume of 80 m × 1.2 m × 0.8 m, with differing inflow discharge, dam composition, dam geometry, and initial breach dimension. An array of twelve automatic water-level probes is deployed to measure the stage hydrographs along the flume, and the video recording of the dam failure processes facilitates an estimation of the widening of initial breach. Under the present experimental conditions with dams composed of homogeneous materials, landslide dam failure is primarily caused by erosion of overtopping flow, and lateral mass collapse is also considerable during the cause of breach widening. Cohesive clay may act to mitigate the seepage through the dam and thus its subsidence and appreciably modulate the dam failure process and the flood. However, the impacts of clay may be readily overwhelmed by a large inflow discharge and initial breach. Gravels in the dam may appreciably depress the rate of the dam failure process and thus modify the flood. The present work provides new experimental data set for testing mathematical models of the flood flow due to landslide dam failure.

A coupled 2D mathematical modelling study of landslide dam failure and flood is presented, complementing our experimental investigation presented in the companion paper. The model is built upon the shallow water hydrodynamic equations. The governing equations are numerically solved using the total-variation-diminishing version of the second-order weighted-average-flux method along with the HLLC (Harten, Lax and van Leer with Contact wave restored) approximate Riemann solver. Two parameters related to bed-load sediment transport and critical slope stability are calibrated using the measured stage hydrographs from two runs of the flume experiments. The calibrated model is then applied to other independent runs of the experiments featuring different inflow discharges, dam geometry, dam composition and initial breach dimensions. It is found to be able to satisfactorily reproduce the measured stage hydrographs and the widening of initial breach. The experimental observation of the prime role of the inflow discharge and initial breach in dictating the dam failure process and flood is unequivocally resolved, along with the impacts of dam geometry as well the content of cohesive clay and gravel in the dam. Interestingly, the downstream peak discharge and stage of the flood are substantially reduced by initial breach, which clearly exemplifies its role in modulating the flooding.

It is necessary for China to establish a feasible method to verify whether an emergency evacuation plan (EEP) provides timely evacuation under the threat of flooding as a result of dam failure. Based on simulating the inundation area resulting from failure of the Huaxi Dam, this paper puts forward a quantitative approach to assess the effectiveness of an EEP by estimating the evacuation clearance times. Differences between urban and rural areas are considered, and two transportation modes are selected. Total evacuation clearance times in rural and urban areas are 135 and 80 min, respectively. Results show that total evacuation clearance times are longer than the time it takes for the flood wave to reach some communities in the area. The paper also makes some suggestions on how to decrease the total clearance time and thus enhance the effectiveness of the EEP for the Huaxi Dam.

Without any omen, massive landslides induced by the Chi-Chi earthquake blocked up gorges of Ching-Shui creek, and produced a new landslide lake. Although emergency spillways have been constructed to prevent dam failures, overtopping and possible breaching may still occur due to excessive inflows in raining seasons. As a result, the downstream valleys will have serious inundation and the safety of people and properties will be in immediate danger. The purpose of this work is to simulate and to analyze the inundation potentials downstream of Tsao-Ling landslide lake using a hydrologic/hydraulic approach and GIS (Geographic Information System) technology. Hydrologic analysis is employed to describe regional rainfall-runoff characteristics and to design rainfall/runoff scenarios. One-dimensional dam break flood routings are performed with different return periods of rainfall events and dam failure durations for downstream creeks. The depletion hydrographs of dam break routings are applied into two-dimensional overland flow simulations for downstream lowlands. The results of hydraulic computations are evaluated with GIS maps for inundation potentials analysis, which can be used to assist the planning of emergency response measures.

The waters of Lake Nyos are impounded by a fragile natural dam composed of pyroclastic rocks ejected during the formation of the lake crater (maar). Lateral erosion of this dam has reduced its width from over 500 m to only 45 m. Published whole-rock K-Ar ages of about 100 ka on juvenile basalt from the dam suggests that erosion has been slow and that the dam poses no imminent threat. New apparent 40Ar/39Ar ages of 1.4 to 232 Ma on xenocrystic K-feldspar contained in the basalt show that the xenocrysts, whose source is the 528-Ma crystalline basement, are carriers of inherited radiogenic 40Ar and would cause the whole-rock K-Ar ages to be too old. The best estimate for the age of the maar is provided by a 14C age of 400 ± 100 yr BP on charcoal from the base of the dam. This young age indicates that the dam is eroding at a relatively rapid rate; its failure, perhaps within a few decades, would result in a major flood and imperil thousands of people living downstream in Cameroon and eastern Nigeria.