Reservoir Water Fluctuation Research Articles

Physical Model Test of Deformation Self-Adaptive Mechanism of Landslide Mass

Reservoir impoundment induces a large amount of cumulative deformation of landslide body, leading to damage to the geological environment. Due to many yearly cycles of reservoir water fluctuation, the cumulative deformation of landslides tends to be stable, showing a self-adaptive deformation phenomenon. The study of the self-adaptive deformation mechanism is very important for evaluating landslide stability and achieving the safe operation of hydropower stations. To study the mechanism of self-adaptive deformation, two sets of physical models were used to monitor the groundwater, earth pressure, and cumulative deformation of landslide under periodic fluctuations of the reservoir water level. The results showed that the soil consolidation compaction, release of sliding stress, and increase in permeability are the three main factors of the self-adaptive deformation of landslide accumulation. The overall permeability decreased first and then increased, the front permeability increased greatly, and the middle and rear permeability decreased. The main factors that affected the permeability change were deformation and seepage force.

Response of denitrification microbiome to the nitrogen flux in three Gorges reservoir (TGR) sediments during two seasonal water fluctuation events

Three Gorges Reservoir (TGR) water fluctuation creates high water level (HWL) and low water level (LWL) condition in TGR aquatic ecosystem. HWL fluies significant nutrients, mainly introducing carbon and nitrogen into the ecosystem. The nitrogen input is a concern for water quality management of TGR since the possible eutrophication caused by nitrogen spike. Sediment denitrification is widely recognized as the dominant nitrogen removal process in freshwater ecosystem. Therefore, the response of TGR sediments microbiome to the input nitrogen flucatution is crucial for both nitrogen balance and the eutrophication status of the ecosystem. Using high throughout sequencing of 16S rRNA gene and the predicted denitrification enzyme, and qualitative PCR of denitrification functional genes, we investigated how TGR sediments denitrification microbiome respond to the input nitrogen flux during two seasonal water fluctuation events. Concomitant to expected input carbon and nitrogen, we observed distinct microbial community structure and denitrification microbiota in HWL and LWL, and also in seasonal sampling events. Sediments pH, total nitrogen and nitrate were the significant impact factors in shaping the microbial community structure. Important denitrification microbiota (e.g., Saprospiraceae, Gemmatimonadaceae, Pseudomonas) are the main taxa of the microbial community and also showed water level and seasonal variation. The relative abundance of denitrification enzyme (nar, nir, nor, nos) and function genes (nirS, nirK, nosZ) were higher in LWL than HWL. Denitrification enzyme were significantly (p < 0.05) correlated with the nitrate concentration. In addition, the relative abundance of denitrification enzyme and function genes increased during the transition from 2014 HWL to 2015 LWL. Results suggested that TGR sediments denitrification is nitrate concentration dependent. The denitrification microbiome is initially inhibited due to high nitrate input, then they developed denitrification ability in response to high nitrate concentration.

Working performance and mechanism of a novel upper-hollow drainage anti-slide pile under the effect of reservoir water fluctuation and precipitation

Working performance and mechanism of a novel upper-hollow drainage anti-slide pile under the effect of reservoir water fluctuation and precipitation

Revealing the time lag between slope stability and reservoir water fluctuation from InSAR observations and wavelet tools— a case study in Maoergai Reservoir (China)

ABSTRACT Reservoir water fluctuation in supply and storage cycle have strong triggering effects on landslides on both sides of reservoir banks. Early identification of reservoir landslides and revealing the relationship between slope stability and the triggering factors including reservoir level and rainfall, are of great significance in further protecting nearby residents’ lives and properties. In this paper, based on the small baseline subset time series method (SBAS-InSAR), the potential landslides with active displacements in the river bank of Maoergai hydropower station in Heishui County from 2018 to 2020 were monitored with Sentinel-1 data. As a result, a total of 20 unstable slopes were detected. Subsequently, it was found through a gray correlation analysis that the fluctuation of the reservoir water level is the main triggering factor for the displacement on unstable slopes. This paper applied wavelet tools to quantify the time lag between slope stability and reservoir water fluctuation, revealing that the displacement exhibits a seasonal trend, whose high-frequency signal displacement has an interannual period (1 year). Based on the Cross Wavelet Transform (XWT) analysis, under the interannual scale of one year, the reservoir water fluctuation and nonlinear displacement show a clear common power in wavelet. Additionally, a time lag of 65–120 days between slope stability and reservoir water fluctuations has been found, indicating that the non-linear displacements were behind the water level changes. Among the factors affecting the time lag, the elevation of the points and their distance to the bank shore show Pearson’s correlation coefficients of 0.69 and 0.70, respectively. The observed time lag and correlations could be related to the gradual saturation/drainage processes of the slope and the drainage path. This paper demonstrates the technical support to quantitatively reveal the time lag between slope stability and reservoir water fluctuation by InSAR and wavelet tools, providing strong support for the analysis of the mechanisms of landslides in Maoergai reservoir area.

Evolution trend of the Huangyanwo rock mass under the action of reservoir water fluctuation

Evolution trend of the Huangyanwo rock mass under the action of reservoir water fluctuation

Physical Modeling for Large-Scale Landslide with Chair-Shaped Bedrock Surfaces under Precipitation and Reservoir Water Fluctuation Conditions

The deformation and failure mechanisms of historical landslides, characterized with different types of bedrock surface shapes which are known to have been induced by rainfall and reservoir water fluctuations, is an important issue currently being addressed by many researchers. The Zhaoshuling Landslide of the Three Gorges Reservoir Region, which was characterized with a chair-shaped bedrock surface under rainfall and reservoir water fluctuation conditions, was selected as an example in this study’s physical modeling process. The results of different parameters, including the displacements, pore water pressure, and total soil pressure during the landslide event, revealed that the Zhaoshuling Landslide with a chair-shaped bedrock surface had been extremely sensitive to heavy rainfall coupled with the rapid lowering of the water levels. Then, based on the data analysis results of the monitoring of the rainfall and groundwater levels, as well as the reservoir water levels, a conceptual model was put forward to explain the failure mechanisms. It was believed that the chair-shaped bedrock at the toe of the slope had been subjected to a localized zone of high transient pore water pressure, which had significantly adverse effects on the mechanisms of the slope stability.

Centrifugal model test on a riverine landslide in the Three Gorges Reservoir induced by rainfall and water level fluctuation

Frequent soil landslide events are recorded in the Three Gorges Reservoir area, China, making it necessary to investigate the failure mode of such riverside landslides. Geotechnical centrifugal test is considered to be the most realistic laboratory model, which can reconstruct the required geo-stress. In this study, the Liangshuijing landslide in the Three Gorgers Reservoir area is selected for a scaled centrifugal model experiment, and a water pump system is employed to retain the rainfall condition. Using the techniques of digital photography and pore water pressure transducers, water level fluctuation is controlled, and multi-physical data are thus obtained, including the pore water pressure, earth pressure, surface displacement and deep displacement. The analysis results indicate that: Three stages were set in the test (waterflooding stage, rainfall stage and drainage stage). Seven transverse cracks with wide of 1–5 mm appeared during the model test, of which 3 cracks at the toe landslide were caused by reservoir water fluctuation, and the cracks at the middle and rear part were caused by rainfall. During rainfall process, the maximum displacement of landslide model reaches 3 cm. And the maximum deformation of the model exceeds 12 cm at the drainage stage. The failure process of the slope model can be divided into four stages: microcracks appearance and propagation stage, thrust-type failure stage, retrogressive failure stage, and holistic failure stage. When the thrust-type zone caused by rainfall was connected or even overlapped with the retrogressive failure zone caused by the drainage, the landslide would start, which displayed a typical composite failure pattern. The failure mode and deformation mechanism under the coupling actions of water level fluctuation and rainfall are revealed in the model test, which could appropriately guide for the analysis and evaluation of riverside landslides.

Interaction Mechanism between Formation Process of Bank Collapse Disaster Chain and Territorial Space Utilization of Large Reservoirs

Number of reservoirs in China ranks the first in the world. Due to the complex geology, and superimposing rainfall and reservoir water fluctuation, the bank collapse chain is prone to disasters. The Yangtze River Reservoir is key geological disaster prevention area. Studying the process of reservoir disaster is significant because of the limited territorial space utilization. Scientific and technological issues, i.e., the mechanism of bank collapse disaster chain of large reservoirs, the interaction mechanism of bank collapse disaster chain and territorial space utilization, the early identification, monitoring technology and ecological prevention and control technology system of disaster chain, and the territorial space geological safety and control technology system are focused. We consider the material transformation, energy transfer and information transmission in disaster chain; adopt the survey, Space-Air-Ground integrated monitoring, theoretical analysis, numerical simulation and the multidisciplinary research methods; reveal the chain source development, evolution process of secondary and derivative disasters; explore the interaction mechanism of disaster chain and territorial space utilization; construct the system of early identification, monitoring, early warning, control and ecological preven-tion to achieve Emission Peak and Carbon Neutrality; provide theoretical and technical support for the territorial space geological safety, regulation and utilization of large reservoirs.

A numerical investigation of slope stability influenced by the combined effects of reservoir water level fluctuations and precipitation: A case study of the Bianjiazhai landslide in China

Slope failure near a reservoir area is mainly influenced by rainfall and reservoir water fluctuation. This study provides insights into the deformation and failure process of the Bianjiazhai landslide near the Suofengying reservoir located at the Wu River in Guizhou province, China. Firstly, stability analyses were carried out to assess the overall strength of the slope and identify the most vulnerable section of the site. Secondly, transient hydromechanical analyses were performed to analyze the effects of rainfall and the reservoir water level fluctuations on the selected slope. The hydromechanical analysis is divided into three different scenarios to study combined as well as the individual effects of rainfall and reservoir water level fluctuation on slide formation. The results indicate that the sudden reservoir water level fluctuations are critical for the stability of the slope. Strength reduction analyses confirm that the deformation behavior of the slope is dominated by shear slip phenomena and identify relevant shear zones. The numerical results from both hydromechanical and stability analysis indicate that the stability of the slope is greatly reduced during large and sudden drawdown. The results from this study will be useful for preventing landslide disasters and for guiding reservoir operation in a similar context.

The triggering threshold estimation of Majiagou landslide based on data mining

The deformation of the reservoir landslide is mainly governed by the combined action of rainfall and the fluctuation of the reservoir water level. The determination of the threshold of triggering factors is of great significant in the stability analysis and evaluation of the potential landslide. Existing empirical threshold model is mainly based on statistical analysis to fit the explicit function between triggering factors and displacement, which is widely used in rainfall-triggered landslides. However, for reservoir landslides, the relationship among rainfall intensity, reservoir water level, fluctuation rate and landslide displacement is highly nonlinear, which hindered the application of existing empirical threshold model. To tackle the scientific challenge, a novel data mining-based threshold estimation method is proposed in this study. The Majiagou landslide, located in the Three Gorges Reservoir (TGR) region, is selected as the study stie. Firstly, the Distributed Fiber Optical Sensing (DFOS) technology has been adopted to record the rainfall, reservoir water level fluctuations, and deformation information for two years in real time; Then, the evolution pattern of Majiagou landslide was analyzed in depth; Finally, the cluster analysis and decision tree algorithm are used to determine the threshold value of the rainfall and the fluctuation of the reservoir water level. Among which, 80% of the data set is used for training model, and the remaining 20% is used for validation. The study here provides a new and effective method to estimate the triggering threshold and contribute to the prediction and early warning of reservoir landslides.

Centrifugal model test of deformation law under different reservoir water fluctuation rates: Muyubao landslide case study

Many ancient landslides have become active due to the impoundment of the Three Gorges Reservoir. Considering the Muyubao landslide in the Three Gorges Reservoir area as the research object, we analyzed the long-term deformation law since the impoundment of the reservoir and conducted centrifugal model tests of the landslide deformation process under different reservoir water fluctuation rates. The monitoring data analysis reveals that the deformation of the Muyubao landslide is mainly affected by the elevation of the reservoir water level and its rising and falling rate. A deformation greater than 30 mm mainly occurs at the water level of 165–175 m. A higher reservoir water rising rate promotes landslide deformation, with a monthly cumulative displacement of above 30 mm in the reservoir water rising stage. Further, a lower reservoir water decline rate can promote several landslide deformation events with monthly cumulative displacement greater than 30 mm. A Centrifugal model test demonstrates the Muyubao landslide deformation to the hydrodynamic buoyancy pressure of reservoir water. The head difference inside and outside the slope is minimal when the reservoir water rising and the falling rate is small, and the reservoir water buoyancy controls the deformation of landslides. However, the head difference inside and outside the slope increases with the reservoir water rise and fall rate, leading to increased hydrodynamic pressure, which weakens the landslide deformation in the reservoir water rising stage, and strengthens the deformation in the reservoir water-falling stage. The results provide a significant reference for landslide control and reservoir operation optimization in the Three Gorges Reservoir area.

Characterizing the Development Pattern of a Colluvial Landslide Based on Long-Term Monitoring in the Three Gorges Reservoir

Since the impoundment of the Three Gorges Reservoir (TGR) in June 2003, the fluctuation of the reservoir water level coupled with rainfall has resulted in more than 2500 landslides in this region. Among these instability problems, most colluvial landslides exhibit slow-moving patterns and pose a significant threat to local people and channel navigation. Advanced monitoring techniques are therefore implemented to investigate landslide deformation and provide insights for the subsequent countermeasures. In this study, the development pattern of a large colluvial landslide, locally named the Ganjingzi landslide, is analyzed on the basis of long-term monitoring. To understand the kinematic characteristics of the landslide, an integrated analysis based on real-time and multi-source monitoring, including the global navigation satellite system (GNSS), crackmeters, inclinometers, and piezometers, was conducted. The results indicate that the Ganjingzi landslide exhibits a time-variable response to the reservoir water fluctuation and rainfall. According to the supplement of community-based monitoring, the evolution of the landslide consists of three stages, namely the stable stage before reservoir impoundment, the initial movement stage of retrogressive failure, and the shallow movement stage with stepwise acceleration. The latter two stages are sensitive to the drawdown of reservoir water level and rainfall infiltration, respectively. All of the monitoring approaches used in this study are significant for understanding the time-variable pattern of colluvial landslides and are essential for landslide mechanism analysis and early warning for risk mitigation.

Permeability of the reservoir water fluctuation zone of landslide bodies in the Three Gorges Reservoir Area, China

The fluctuation of water level in the Three Gorges Reservoir is up to 30 m, and the reservoir water fluctuation zone is the important channel of reservoir water flowing in and out of a landslide. The permeability characteristics and parameters of the reservoir water fluctuation zone of landslide bodies are of great significance for calculating the seepage of the reservoir landslide and evaluating the stability of the landslide. In this paper, 396 landslides in the Three Gorges Reservoir Area were studied, and 1188 test pits were sampled. In an analysis based on test data, the classification indicators of landslides can be divided into two types: provenance lithology and compositional structure. According to provenance lithology, the landslides can be divided into dolomite and limestone, marl, sandstone and mudstone inlaid rocks, siltstone, and argillaceous limestone. In addition, according to the compositional structure, landslide bodies can be divided into fine-grained soil, soil containing gravel stone, soil clip gravel stone, crushed rock soil, and fractured rock mass, where there are three types and five sub-categories. Based on this study, we found that the permeability of the landslide bodies has regional distribution characteristics, which is positively correlated with gravel content and provenance lithology strength and is mainly medium and better.

Impact on buildings while the parameters of geotechnical materials change

The cyclic rise and fall of the water level in a reservoir will destroy the rock and soil mass of the slope, cause deterioration of its material parameters, cause the uneven settlement of the building foundation and then cause structural damage of the upper building. In order to explore the rule and mechanism of structural failure of bank-slope buildings under the action of water-level cyclic fluctuation. On the basis of obtaining the parameters of the soil material after saturated water loss test and based on the finite-element interaction analysis method, the slope–building model is established by using the Ansys software program. The results indicate that with the ascending of the number of reservoir water lifting and lowering cycles, the differential settlement of the bank-slope foundation begins to aggravate. Although the growth rate slows down after five cycles, it does not stop. This shows that the mechanical damage caused by reservoir water fluctuation to the soil materials of the slope is a cumulative process and continues to increase the uneven settlement of the superstructures. The maximum horizontal displacement of prefabricated buildings increases by 2.3 times under the action of reservoir water lifting.

Dynamic development of landslide susceptibility based on slope unit and deep neural networks

The Three Gorges Reservoir is one of the areas with the most serious landslide hazards in China. Landslide susceptibility indicates where landslides are prone to occur in the future under the influences of certain geoenvironmental and triggering conditions and is an important way for landslide prevention. This work employs multi-source and three-temporal landslide monitoring data (geology, terrain, hydrology, and remote sensing data) to reveal the dynamic change of landslide susceptibility with time in the Badong-Zigui section in the Three Gorges area. Nine influence factors for landslides (land use, aspect, engineering rock group (ERG), slope, distance to river (DTR), relative relief, normalized difference water index (NDWI), normalized difference vegetation index (NDVI) and annual cumulative rainfall (ACR)) are generated from the monitoring data. The algorithms of slope unit segmentation and deep neural networks are adopted to conduct landslide susceptibility evaluations in the 3 years of 2002, 2007, and 2017 and to investigate the dynamic change of landslide susceptibility. Moreover, this work also reveals the dynamic response of landslide susceptibility to the changing factors of rainfall, reservoir water fluctuation, soil moisture, and land use. Some new viewpoints are suggested as follows. (1) The main factors affecting landslide occurrence are DTR, NDWI, relative relief, and ERG. Among them, DTR contributes most in all the 3 years; thus, reservoir water fluctuation has the most important impact on landslide occurrence in the study area. (2) From 2002 to 2007, the new high-susceptibility areas mainly appeared along the Yangtze River and also distributed around the roads. From 2007 to 2017, more than half of the new high-susceptibility areas were distributed around the roads, and susceptibility increases also occurred in the mountainous areas far from the Yangtze River. (3) The development of landslide susceptibility from 2002 to 2007 was mainly caused by the rising of reservoir water level as well as road construction. The change of landslide susceptibility from 2007 to 2017 was mainly caused by rainfall and road construction. This work may provide some clues on landslide prevention and control according to the dynamic development of landslide susceptibility and the causes of the susceptibility changes.

Effect of spatially variable saturated hydraulic conductivity with non-stationary characteristics on the stability of reservoir landslides

Conventional landslide analyses, based on deterministic methods or simple random variable methods, cannot consider the spatial variability and the depth-dependent nature of saturated hydraulic conductivity (Ks) in accumulative landslides. However, studies show that these conditions exist objectively and have a large impact on the seepage and deformation of landslides. Thus, the non-stationary characteristics of Ks need to be properly accounted for. In this paper, the Baishuihe landslide is taken as a case study. First, based on surface nuclear magnetic resonance (surface-NMR) technology, spatial variability and the depth-dependent nature of the Ks are obtained. Then, a non-stationary random field model is established to model the trend and fluctuating components of the Ks individually, and a deterministic model is established to model the trend of the Ks with depth. Finally, numerical simulations of the stochastic model and deterministic model under reservoir water fluctuation conditions are carried out by the non-intrusive stochastic finite element method, and the seepage-deformation and stability characteristics of the landslide are analyzed. The results show that compared with that in the deterministic model, the change in pore pressure in the stochastic model obviously lags, during reservoir water drawdown, the displacement of the trailing edge in the stochastic model is larger than that in the deterministic model, with increasing reservoir water deceleration, the hysteresis of the pore pressure in the stochastic model is more notable, and the deformation is larger and the stability is worse in the stochastic model. It is demonstrated that ignoring the spatial variability of the Ks will overestimate the stability of the landslide.

Study on the Spatially Variable Saturated Hydraulic Conductivity and Deformation Behavior of Accumulation Reservoir Landslide Based on Surface Nuclear Magnetic Resonance Survey

Saturated hydraulic conductivity (Ks) is spatially variable in accumulation landslide sites that exert significant effort onto landslide seepage and deformation behavior. To better understand spatial variability and the effect of Ks on the slide mass of an accumulation landslide, this study introduced the surface nuclear magnetic resonance (SNMR) technology to study a representative reservoir accumulation landslide field in the Three Gorges Reservoir area (TGRA), the Baishuihe landslide, to obtain a series of relative reliable spatial measurements of Ks effectively on the basis of calibration in terms of the field tests measurements. The estimated Ks values were distributed log-normally for the overall landslide mass site with a wide range of 3.00 × 10−6∼7.80 × 10−3 cm/s, which reaches about 3 orders of magnitude. Variogram analysis indicated that the Ks values have the range (A) of 295.89 m and 65.56 m for the overall site and major cross-sectional analysis, respectively. A finite-element seepage-stress analysis associated with a Kriging-interpolated spatial Ks variable calculation model based on the best-fitted theoretical variogram was subsequently performed to study the seepage and deformation behavior of the landslide. The available monitored data and simulated results of the finite-element seepage-stress analysis indicated that the Baishuihe landslide is a progressive landslide, and the main factor influencing the deformation is rainfall and reservoir water fluctuation. This study provides an unconventional framework for studying the heterogeneous geomaterial and contributes to a better understanding of the spatial variation of the hydraulic property of accumulation reservoir landslides at a field scale.

Influence of uncertainty in the initial groundwater table on long-term stability of reservoir landslides

The seepage calculation of water fluctuation is the crucial precondition for landslide stability evaluation. It is controlled by the initial condition, boundary condition, and soil or rock structure as well as geotechnical parameters. Although the geotechnical parameters and boundary condition have greater influence on seepage and the stability of landslides, the role of the initial groundwater position cannot be ignored. To investigate the influence of an initial groundwater table on landslides, especially the influence of cyclical reservoir water fluctuation on their long-term stability, seven different methods to determine the initial groundwater table were proposed in the presented study, among which one is the actual groundwater table, and the other six are obtained with simplified methods. According to the results of the calculations, at the beginning, there is some difference in the factor of safety among different initial groundwater tables. The maximum value of relative tolerance reduces to less than 1.0 % 160 days later. After a filling–drawdown cycle, the relative tolerance of all methods reduces to less than 0.8 %, which could be ignored. It is also observed that, the closer the hydraulic gradient of the proposed initial groundwater table is to the actual condition, the smaller is the relative tolerance. Therefore, to study the influence of cyclical reservoir water fluctuation on landslide long-term stability, the initial groundwater table could be proposed as (1) equal to reservoir water level and (2) on a straight line with the hydraulic gradient equal to the weighted average of actual groundwater table for simplification.

Effect of hydraulic properties of soil and fluctuation velocity of reservoir water on landslide stability

Water fluctuation is the main triggering factor of reservoir slope failures, especially in the area of the Three Gorges Reservoir of China. Fluctuation velocity of reservoir water and hydraulic properties of soil as defined by soil–water characteristic curve (SWCC), saturated permeability coefficient and unsaturated permeability function are key potential properties that control reservoir landslide stability. The effect of reservoir water fluctuation velocity and hydraulic properties of soil on landslide stability are investigated through a series of numerical simulations with different parameters. The results of simulations show that fitting parameters in the SWCC [i.e., a, n, m for Fredlund and Xing (Can Geo J, 31(3):521–532. doi: 10.1139/t94-061 , 1994) equations] have significant effect on the stability of landslide for reservoir water’s drawdown or impounding process. The saturated permeability coefficient of soil and velocity of water level fluctuation have comprehensive (defined as Impact Factor, α) and significant influence on the stability of reservoir landslide. A relative equation: m > α > n > a has been drawn for the susceptibility of effect on the stability of reservoir landslide for the parameters “a”, “n”, “m” and “α”.

Experimental Study on the Strength Difference of Two Types of Sandstones With Different Composition of Minerals Under the Conditions of Dry and Wet Cycles

Some rock slides have taken place in Three Gorges Reservoir Area, China. Many Researches on the causes of the slides shows that the more sensitive of rock strength to the reservoir water level fluctuation, the easier to fail of the rock slopes. In order to study the strength difference of different sandstones in reservoir water fluctuation zone of Three Gorges Reservoir, the authors taken two types of sandstones with different composition of minerals as a typical case to study in detail. One type of the two sandstones (called Type I) is composed of quartz, feldspar, muscovite and calcite, argillaceous cement. The other (called Type II) is composed of quartz, feldspar, sericite, argillaceous cement. Uniaxial compression tests indicate that the compressive strength of type I sandstone decreased significantly as they underwent first wet and dry cycle, and then nearly kept constant when they underwent the following wet and dry cycles, and that the compressive strength of Type II sandstones nearly kept constant when they underwent many times of wet and dry cycles.