Dam Overtopping Research Articles

Study on numerical simulation method of overtopping dam break of concrete faced sand-gravel dam

Based on the field investigation of dam break cases, a numerical simulation method of concrete faced sand-gravel dam overtopping break is proposed. The method is mainly composed of three parts: (1) Aiming at the erosion and scour of vortex flow on dam body, appropriate model is used to simulate the flow movement; (2) The interaction between water flow and sand particles in dam break process is accurately simulated; (3) Based on moment balance method, the failure process of concrete face slab under dead weight and water load is determined. The results show that the proposed mathematical simulation method can accurately simulate the reverse erosion of the dam and the detailed evolution of the face slab break during the dam break process. The relative error between the measured data and the calculated peak breach flow, the development of the breach of the rockfill body, the duration of the dam break and the length of the face slabs are all less than 15%, which verifies the rationality of the numerical model.

The 2020 glacial lake outburst flood process chain at Lake Salkantaycocha (Cordillera Vilcabamba, Peru)

Glacial lakes represent a threat for the populations of the Andes and numerous disastrous glacial lake outburst floods (GLOFs) occurred as a result of sudden dam failures or dam overtoppings triggered by landslides such as rock/ice avalanches into the lake. This paper investigates a landslide-triggered GLOF process chain that occurred on February 23, 2020, in the Cordillera Vilcabamba in the Peruvian Andes. An initial slide at the SW slope of Nevado Salkantay evolved into a rock/ice avalanche. The frontal part of this avalanche impacted the moraine-dammed Lake Salkantaycocha, triggering a displacement wave which overtopped and surficially eroded the dam. Dam overtopping resulted in a far-reaching GLOF causing fatalities and people missing in the valley downstream. We analyze the situations before and after the event as well as the dynamics of the upper portion of the GLOF process chain, based on field investigations, remotely sensed data, meteorological data and a computer simulation with a two-phase flow model. Comparison of pre- and post-event field photographs helped us to estimate the initial landslide volume of 1–2 million m3. Meteorological data suggest rainfall and/or melting/thawing processes as possible causes of the landslide. The simulation reveals that the landslide into the lake created a displacement wave of 27 m height. The GLOF peak discharge at the dam reached almost 10,000 m3/s. However, due to the high freeboard, less than 10% of the lake volume drained, and the lake level increased by 10–15 m, since the volume of landslide material deposited in the lake (roughly 1.3 million m3) was much larger than the volume of released water (57,000 m3, according to the simulation). The model results show a good fit with the observations, including the travel time to the uppermost village. The findings of this study serve as a contribution to the understanding of landslide-triggered GLOFs in changing high-mountain regions.

Experimental study on the longitudinal evolution of the overtopping breaching of noncohesive landslide dams

The failure of landslide dams is a sudden geological disaster, and thus their formation and failure greatly threaten the security of people's lives and property. In this research, the influences of different flume gradients, dam heights, and downstream slope angles relative to the flume bed on the overtopping breaching process of noncohesive landslide dams are explored through 12 sets of model experiments. Based on these experimental results, the dam overtopping breaching can be divided into four stages: initiation, head cutting, acceleration, and riverbed rebalancing. The variation in the erosion rate ( E AX and E BX ) and the downstream slope angle relative to the horizontal line ( Φ ) exhibit clear differences in the different stages. The influences of the flume gradient, dam height, and downstream slope angle on the breaching process of landslide dams are different. In our experiments, accumulation bodies could only form in the middle and lower parts of the downstream dam face when the total height from the spillway to the flume bed was greater than 15 cm. In addition, the downstream slope angle relative to the horizontal line determined the breaching process and stage of the dam overtopping breaching. Since the dam breach evolution mode and dam overtopping breaching process were mainly affected by the dam height and downstream slope angle relative to the horizontal line, the evolution of the longitudinal section in the process of dam body failure can be divided into four modes based on our experimental results. The applicability of the widely used empirical equations for the erosion rate was assessed using the experimental data, which revealed obvious differences between the measured and calculated erosion rates. However, the erosion rate and the shear stress at the soil/water interface exhibited a good correlation in every test. Therefore, these widely used empirical equations need to be improved in future research. This preliminary research provides a basis for subsequent studies of dam breaching using models and a scientific reference for the prevention and mitigation of landslide dams. • Twelve experimental tests were designed to reproduce the breaching process of landslide dams. • The influences of the flume gradient, dam height, and downstream slope angle on the dam breaching process are different. • The breaching process of landslide dams can be divided into four stages. • The longitudinal evolution of dam breaching was classified into four modes according to three critical values.

A study of the overtopping breach of a sand-gravel embankment dam using experimental models

Sand-gravel embankment dams are increasingly being built using sand and gravel as these materials provide advantageous characteristics of a large compressive modulus and small porosity. Floods, landslides, and seismic surge waves can result in dam overtopping, which may further result in a breach of a sand-gravel embankment dam. Many factors affect the breaching process of a sand-gravel embankment dam, including the failure of the anti-seepage face slab and the initial seepage field. This study conducted overtopping breach experiments of a sand-gravel embankment dam without an upstream face slab to study the breaching process and identify the influence of the initial seepage field and drainage zone. Experimental models of sand-gravel embankment dams with three different initial seepage fields were established. The breach flow, breach expansion processes, and pore water pressure during the breaching process were observed. The results showed that the breaching process can be roughly divided into four stages: (1) downstream dam slope erosion; (2) gully expansion; (3) breach expansion and; (4) breach stabilization. The high phreatic line and large saturation zone intensified the dam breaching process, which aggravated breach expansion, increased the peak flow, and shortened the breach duration. The drainage zone in a sand-gravel embankment dam effectively restrained the dam breach process.

Formation and evolution characteristics of dam breach and tailings flow from dam failure: an experimental study

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.

Effects of toe configuration on throughflow properties of rockfill dams

Rockfill dams must be equipped with defence mechanisms to counteract the destabilizing effects of throughflow forces under accidental leakage scenarios. A key component of the rockfill dam overtopping system is the rockfill dam toe, constructed in tandem with the downstream rockfill shoulder. Quantitative descriptions of effects of different toe configurations on throughflow hydraulic properties of rockfill dams are currently unavailable in international literature. To address this, experimental investigations were conducted on 1 m high model rockfill dams with disparate toe configurations. Investigation outcomes describe the effects of internal, external and combined toe configurations on pore-pressure distributions within rockfill dam models subjected to throughflow conditions. Research outcomes provide vital information which can facilitate effective decision-making with regards to rockfill dam design. The accumulated data sets could also enable development, calibration and validation of numerical design tools and dam breach models.

Analysis of Mukakuning and Duriangkang Reservoir’s Capacity to Fulfill The Raw Water Demand of Batam City

Batam City is the economic center of Riau Province with a predicted population of 1.8 million people in 2025. To support economic development, Batam City needs a reliable supply of raw water. Mukakuning and Duriangkang reservoirs, which are cascade reservoirs, are the largest contributors to raw water supply in Batam City. This study aims to determine the maximum capacity of the two reservoirs to meet current and future raw water demand. Discharge in the watershed is calculated using daily HEC-HMS model calibrated using Duriangkang Reservoir water level data. The storage of Mukakuning and Duriangkang Reservoir are 6.3 and 106.1 million m3 respectively, equivalent to 39% and 77% of the runoff volume of each watershed, classifying the two reservoirs in the multi-year category. Using current operation, the two reservoirs can supply up to 3.24 m3/s at 100% reliability, compared to existing capacity of 3.1 m3/s. The water loss is dominated by evaporation which reaches 32.6 million m3/year while spilled water is only 8.3 million m3/year. At 95% reliability, the reservoirs are almost at maximum capacity and able to supply 4.03 m3/s of raw water with the spilled water is only 0.4 million m3/year. Efforts to increase capacity by increasing normal water levels are not effective and lead to dam overtopping in PMF condition. More effective way to increase water supply can be obtained by changing operating patterns. If the reservoir is in dry condition, determined by predicted SPI, the water supply is limited so that the discharge can be utilized for a longer period.

A novel simulation–optimization strategy for stochastic‐based designing of flood control dam: A case study of Jamishan dam

AbstractThis study presents a novel stochastic simulation–optimization approach for optimum designing of flood control dam through incorporation of various sources of uncertainties. The optimization problem is formulated based on two objective functions, namely, annual cost of dam implementation and dam overtopping probability, as those are the two major concerns in designing flood control dams. The nondominated solutions are obtained through a multi‐objective particle swarm optimization (MOPSO) approach. Results indicate that stochastic sources have a significant impact on Pareto front solutions. The distance index (DI) reveals the rainfall depth (DI = 0.41) as the most significant factor affecting the Pareto front and the hydraulic parameters (DI = 0.02) as the least. The dam overtopping probability is found to have a higher sensitivity to the variability of stochastic sources compared to annual cost of dam implementation. The values of interquartile range (IQR) indicate that the dam overtopping probability is least uncertain when all stochastic sources are considered (IQR = 0.25%). The minimum annual cost of dam implementation (2.79 M$) is also achieved when all stochastic sources are considered in optimization process. The results indicate the potential of the proposed method to be used for better designing of flood control dam through incorporation of all sources of uncertainty.

3D simulation of Vajont disaster. Part 1: Numerical formulation and validation

This work presents a numerical method for the simulation of landslides generated impulse waves and its application to the historical Vajont case study. The computational tool is based on the Particle Finite Element Method (PFEM), a Lagrangian strategy that combines the finite element solution of the governing equations with an efficient remeshing strategy to deal with large deformation problems. After presenting the numerical formulation, different landslide impulse wave problems with Froude number ranging from 0.5 to 2.8, are analyzed to validate the proposed methodology. The computational method is shown to be able to reproduce accurately the landslide runout, the momentum transfer between the sliding material and the impounded water, and the consequent wave propagation observed in experimental physical models. Then, the PFEM model is applied to the numerical simulation of the Vajont disaster, which is analyzed with a fully-resolved three-dimensional model. The numerical results are discussed and compared to the post-event observations and the numerical results of other computational methods. The results in terms of landslide velocity and runout, geometry of the deposit, maximum water runup, dam overtopping wave, and water discharge in the downstream valley are in good agreement with observations and reconstructions. The calibration and validation performed for this study form the basis for the PFEM analyses presented in a companion paper finalized to simulate different scenarios of the Vajont rockslide considered in the experimental tests done a year before the disaster.

Glacial Lake Outburst Floods (GLOFs) in the Cordillera Huayhuash, Peru: Historic Events and Current Susceptibility

The aim of this paper is to create a glacial lake inventory for the Cordillera Huayhuash in Peru and to evaluate the susceptibility of lakes to the generation of glacial lake outburst floods (GLOFs). Using high-resolution satellite images, we undertook qualitative and quantitative analysis of lake type, characteristics and distribution, and placed our findings within the context of existing Peru-wide lake inventories. We also mapped and analyzed past GLOFs, revealing a total of 10 GLOFs and 4 ambiguous events, most of which have not been reported before. We found that past GLOFs usually occurred as a result of moraine dam breach during the proglacial stage of lake evolution. Further, we used our lake inventory to evaluate GLOF susceptibility of all lakes larger than 20,000 m2. Of 46 evaluated lakes, only two lakes (Lake Tsacra and Lake W014) are currently susceptible to generating a GLOF, which would most likely be through dam overtopping resulting from a flood originating in smaller lakes located upstream. The future perspectives of lake evolution and implications for GLOF hazard management are discussed in light of the post-Little Ice Age glacier ice loss as well as in the context of extensive related research undertaken in the nearby Cordillera Blanca.

A quantitative risk analysis model for cascade reservoirs overtopping: principle and application

Quantitative and effective flood control operation of cascade reservoirs under emergency conditions can guarantee the safety of dams, reduce the social loss caused by flood disaster. A quantitative and practical risk analysis model of cascade dams overtopping breach (DAMSBREACH) has been developed based on the improvements to the analytical method of single dam breach. A single dam breach module, a flood routing module, a cascade dam overtopping and warning module have been assembled in the DAMSBREACH for predicting cascade dams overtopping flood and risk warning. The main improvements include a hyperbolic soil erosion model, the circular slip surface used in lateral enlargement modeling, and a numerical algorithm that uses velocity increment and allows straight forward calculation for the breach flood hydrograph. The DAMSBREACH is applied to Xiaerxia–Dawei–Shuangjiangkou of three cascade dams, which located in the upper reaches of Dadu river in southwest of China. The results show that only under the condition to open all release structures of Shuangjiangkou reservoir while Dawei dam starts to break, Shuangjiangkou reservoir will not be overtopped and the highest water level reaches 2507.56 m that is lower than the elevation of dam crest 2510.00 m. The integrated risk of cascade reservoirs has a direct relationship with the initial water level, uncertainty flood from the upstream, the discharge capacity and warning time of the reservoir. The risk analysis model of cascade dams overtopping break can help the decision-makers choose the best operation mode according to the characteristic of the reservoir under different emergency operating conditions.

Risk analysis for clustered check dams due to heavy rainfall

Check dams are commonly constructed around the world for alleviating soil erosion and preventing sedimentation of downstream rivers and reservoirs. Check dams are more vulnerable to failure due to their less stringent flood control standards compared to other dams. Determining the critical precipitation that will result in overtopping of a dam is a useful approach to assessing the risk of failure on a probabilistic basis and for providing early warning in case of an emergency. However, many check dams are built in groups, spreading in several tributaries in cascade forms, comprising a complex network. Determining the critical precipitation for dam overtopping requires a knowledge of its upstream dams on whether they survived or were overtopped during the same storm, while these upstream dams in turn need the information for their upstream dams. The current paper presents an approach of decomposing the dam cluster into (1) the heading dam, (2) border dams, and (3) intermediate dams. The algorithm begins with the border dams that have no upstream dams and proceeds with upgraded maps without the previous border dams until all the dams have been checked. It is believed that this approach is applicable for small-scale check dam systems where the time lag of flood routing can be neglected. As a pilot study, the current paper presents the analytical results for the Wangmaogou Check Dam System that has 22 dams connected in series and parallel. The algorithm clearly identified 7 surviving dams, with the remaining ones being overtopped for a storm of 179.6 mm in 12 h, which is associated with a return period of one in 200 years.

Strategic Assessment of Dam Overtopping Reliability Using a Stochastic Process Approach

AbstractEarth-fill dam overtopping could pose significant threats to public safety if the necessary reliability assessments are not taken into consideration in the design process. Dam overtopping i...

Analysis of the characteristics of seismic and acoustic signals produced by a dam failure and slope erosion test

Landslides and floods occur with a significant generation of energy release producing seismic and acoustic signals. The analysis of these signals aims to identify vital and specific characteristics of landslide and flood events, such as frequency content, spectral magnitude, energy variation, and timing of the events. This study examined the seismic and acoustic signals recorded during a large-scale physical dam model failure test. The tests were conducted on the streambed under the No. 2 Bridge in Huisun Forest Experimental Station in Nantou, Taiwan. A dam and a slope model were constructed, and dam failure and slope erosion tests were induced by releasing water to slowly accumulate at the upstream side of the dam and letting water overtop the dam, causing a breach. After dam overtopping, the lowering of the dam crest led to dam failure, causing a large volume of floodwater, resulting in erosion of the toe of the slope model, triggering landslides. Accelerometers and microphones were installed to collect the acoustic and seismic signals produced by the water flow and landslides generated. Unmanned aerial vehicles were used to continuously capture the topography of the slope to produce elevation models to calculate the volumes of the six landslides. Hilbert–Huang transform (HHT) was performed to evaluate the time–frequency spectra for the seismic and acoustic signals, and their spectral magnitudes were discussed. The results showed that the acoustic signals depicted and reacted to the failure event earlier than seismic signals; however, both types of signals were in agreement. The velocity of the flood energy was estimated to be 5.71 and 5.06 m/s by monitoring the seismic signals at different locations of the riverbank and through the analysis of spectral magnitude, respectively. Furthermore, the Arias intensity and the landslide volumes were found to be correlated through a quadratic relationship.

A Deterministic Monte Carlo Simulation Framework for Dam Safety Flow Control Assessment

Simulation has become more widely applied for analysis of dam safety flow control in recent years. Stochastic simulation has proven to be a useful tool that allows for easy estimation of the overall probability of dam overtopping failure. However, it is difficult to analyze “uncommon combinations of events” with a stochastic approach given current computing abilities, because (a) the likelihood of these combinations of events is small, and (b) there may not be enough simulated instances of these rare scenarios to determine their criticality. In this research, a Deterministic Monte Carlo approach is presented, which uses an exhaustive list of possible combinations of events (scenarios) as a deterministic input. System dynamics simulation is used to model the dam system interactions so that low-level events within the system can be propagated through the model to determine high-level system outcomes. Monte Carlo iterations are performed for each input scenario. A case study is presented with results from a single example scenario to demonstrate how the simulation framework can be used to estimate the criticality parameters for each combination of events simulated. The approach can analyze these rare events in a thorough and systematic way, providing a better coverage of the possibility space as well as valuable insights into system vulnerabilities.

Risk Assessment of Dam Overtopping Based on The Extended Three-parameter Distribution and Stochastic Differential Equation

For earth and rockfill dam, overtopping is intolerable especially for those dams where cascade hydropower stations exist in the river basin. The flood safety of control reservoir directly relates to the safety of the dam. It is necessary to carry out an accurate analysis for flood risk. Based on the extended three-parameter Burr XII distribution of the maximum reservoir inflow design flood computation, the results are larger than the design standard using analysis method which is also based on Person O distribution. The flood risk analysis of uncertainty factors is considered based on the stochastic differential equation. Combination of these two methods, dam overtopping risk is calculated, greater risk is obtained than the traditional JC method, and the conclusion is much more rational. When determining the crest elevation in water conservancy engineering, the design of dam safety evaluation and risk analysis should be considered using more uncertain factors involved, and the new method is more feasible and reasonable than traditional methods.

Quantitative Vulnerability Model of Earth Dam Overtopping and its Application

Dam failure constituted a considerable threat to human life and created corresponding losses. Hence, this paper proposed a quantitative vulnerability evaluation model to estimate the consequences of dam overtopping, including loss assessment and vulnerability degree calculations. A composite normalized function was applied to convert dam overtopping loss to a vulnerability degree ranging from 0 to 1. In addition, many complex factors were simplified in the loss estimation, and the thresholds of various types of losses were proposed and adapted to the national and regional conditions. Then, loss of life, economic loss, social loss and environmental loss were incorporated into the vulnerability degree model based on a comprehensive evaluation method and were further assigned weights. Finally, vulnerability degree grading criteria was divided based on three significant cut-off values, and the corresponding guidelines for vulnerability evaluation were explained in detail. The methodology was applied to Chengbihe Reservoir in China to illustrate the assessment process of flood overtopping loss and to evaluate the vulnerability degree of the area. The results indicated that (1) dam overtopping vulnerability degree of the Chengbihe Reservoir was 0.89, which was within the range of “extremely high vulnerability” and (2) countermeasures were necessary; for example, early flood warning and forecast systems must be developed for the reservoir so that people and property in flooded areas can be safely evacuated during the process of emergencies.

Centrifugal Model Test on the Failure Mechanism of Barrier Dam Overtopping

In order to study the failure mechanism of barrier dam overtopping, centrifugal model tests of dam failure were conducted in this research. A calculation method of rectangular weir flow in the centrifugal field was derived. The process and mechanism of barrier dam overtopping were intensively analyzed. They were further verified by the breach flow curve and the development curve of the breach top width acquired from model tests. Results showed that the barrier dam breach developed during the entire process of overtopping in the width direction. The development of the barrier dam breach in the depth direction, however, ceased at an earlier time on account of the large particles accumulated in the downstream slope. Moreover, coarsening in the downstream slope could be clearly observed in the last stage of overtopping. Thus, it was concluded that the bottom part of the barrier dam could survive after dam breaching and that a full dam failure is relatively rare for a barrier dam. Furthermore, the size of the remaining breach would be less than that of a homogeneous earth dam under the same conditions.

Hydrological Risk Assessment of Gibe III Dam by Using L-Moment

A hydrological analysis for assessing the risk of dam overtopping is required for both dam designing and dam safety checking. There is enormous amount of water to be stored in the reservoir to provide valuable service such as hydroelectric power generation and flood control. However dams can cause catastrophic damage to both life and property if they experience performance failures due to overtopping and inadequate spillway design. The hydrological risk was computed from historical peak flow data of Gilgel Gibe near Abelti, Gojeb near Shebe and Wabi near Wolkite, of major rivers flowing towards Gibe III Dam, respectively. From the flood statistics of rivers, the general extreme value (GEV) distribution was fitted to peak flow using L-moment. In this research made an attempt, the extreme event or probability of maximum discharge occurrence at dam site analyzed by associating peak occurrence with the service life of Dam and estimated the hydrological risk at Gibe III Dam. It finds PWM method is very suitable for three river flow condition flowing toward Gibe III Dam. The hydrological risk at Gibe III predicted for 50, 100 and 150 years with respect of Discharge range of 2730m3/s to 3180m3/s was observed there is a risk decreases as return period increases.

Probable Maximum Precipitation Comparison using Hershfield’s Statistical Method and Hydro-Meteorological Method for Sungai Perak Hydroelectric Scheme

One of the potential risks attributed to the occurrence of dam overtopping and dam wall failure due to the inadequacy of the spillway capacities is the loss of life and property damages in the downstream area. The current practices in most countries in minimizing these risks are by analyzing the extreme precipitation that leads to extreme flood. Extreme precipitation is best known as Probable Maximum Precipitation (PMP) and this estimation is useful in determining Probable Maximum Flood (PMF) in reviewing the spillway adequacy of dam structures. This paper presented PMP estimations using two approaches; physical method (Hydro-meteorological Method) and statistical approach (Hershfield’s Method) at the Sungai Perak Hydroelectric Scheme that consists of four cascading dams namely Temengor dam, Bersia dam, Kenering dam and Chenderoh dam. The highest PMP estimates from these two methods will be chosen as the rainfall input to establish PMF hydrographs. Estimations using Hydro-meteorological generalized map produces 40-50% higher estimates compared to Hersfield’s method with the PMP values of 550mm (1hours), 600mm (3hours), 800mm (6hours), 820mm (12hours), 1300mm (24hour) and 1600mm (72 hours). Accepting the Hydro-meteorological Method to determine PMF values for this hydroelectric scheme may be the best course since the estimations of the extreme precipitations using this method are the highest.