Reservoir Level Fluctuation Research Articles

Rainfall and water level fluctuations dominated the landslide deformation at Baihetan Reservoir, China

Understanding the deformation patterns of different types of landslides around reservoirs is crucial for precise prevention and control of related hazards. However, under the complex coupling effect of extreme rainfall and reservoir level fluctuations, the response between various types of landslides and triggering factors is still unclear. Our study employed the Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) method and wavelet analysis to undertake an early identification and quantitative analysis of deformation patterns of unstable slopes in the Baihetan Reservoir region, China, and explored the responses of different types of landslide deformation to rainfall and reservoir water level fluctuations. The findings reveal distinct differences in the deformation characteristics of unstable slopes around the reservoir. The quantitative analysis of normalized displacement indicated that the convergent-type landslide exhibits an initial rapid movement that gradually tends to be stable, following an exponential function. The steady-type landslide moves at a consistent speed along a linear trendline. The exponential-type landslide starts slowly and then progressively accelerates. The periodic-type landslide displays periodic fluctuations in displacement, which conforms to the Fourier periodic function. Furthermore, comparisons with antecedent rainfall and reservoir water levels reveal that the convergent-type landslide is significantly influenced by water level fluctuations, and both steady-type and exponential-type landslides are subject to the dual impact of rainfall and water level fluctuations, while the periodic-type landslide exhibits a notable response to rainfall. Therefore, this research aims to provide a scientific basis for the prevention and mitigation of geohazards in reservoir areas.

Phreatic Line Calculation of Reservoir Landslide under Complex Hydraulic Conditions—A Case Study

A seepage field, influenced by rainfall and reservoir water level fluctuation, is closely associated with the stability of the reservoir landslide. Understanding the phreatic line variation inside the landslide is of significant importance for the analysis and evaluation of slope stability. Currently, most of the boundaries of phreatic line analytical models and the hydrological conditions are simplified, resulting in discrepancies between the outcomes derived from these models and the actual situation. Given this, the newly proposed analytical model is refined by addressing the following two issues. Firstly, the consideration of variable-speed reservoir level fluctuations is incorporated, and secondly, the reservoir bank within the water-level fluctuation zone is treated as non-vertical. Under the combined effect of reservoir water level fluctuation and rainfall, the Boussinesq Differential Equation of unsteady seepage is established and applied to the Majiagou landslide in Three Gorges reservoir area. The results of the analytical solution are basically consistent with the measured groundwater level results, which has demonstrated the accuracy of the proposed model. Consequently, the proposed model can quickly and accurately calculate the groundwater level of landslides, which provides an effective means for the prediction and early warning of reservoir landslides.

Deformation triggers and stability evolution of landslide from multiple observations

External causes like changes in reservoir level and intense rainfall can cause reservoir landslides. Exploring the factors that govern landslide deformation and analyzing its stability evolution is essential in mitigating the associated risks. The Sanzhouxi landslide, which has experienced ongoing movements and has been implemented a professional monitoring system, is chosen for analysis in this paper. A combination of geological survey and analysis of monitoring data is utilized to explore landslide deformation characteristics. A data mining method, grey relation analysis (GRA), is subsequently performed to determine the causes of landslide deformation. Furthermore, the stability of the Sanzhouxi landslide in response to reservoir level fluctuation and rainfall for each day over an entire year is assessed using the Morgenstern-Price (MP) approach in 2D GeoStudio software. Such a process illustrates clearly how the landslide stability alters with external triggers changing. The findings reveal that the landslide deforms variably in spatial and temporal. The reservoir level rising contributes to landslide deformation primarily, while rainfall has a secondary impact. The factor of safety (FS) of the Sanzhouxi landslide drops from 1.17 to 1.07 during high reservoir water level periods and remain the same or increase in other periods except for some transitory moments while decreasing only by about 2% under the effect of rainfall. The daily FS results validate the dominant influence of reservoir level fluctuation on the stability of the landslide. The comprehensive understanding of landslide movement based on deformation characteristics, triggering factor identification, and daily stability validation, contributes to realizing nearly real-time prediction and evaluating the risk due to slope movements in similar geological settings worldwide.

Hysteresis effect and seasonal step-like creep deformation of the Jiuxianping landslide in the Three Gorges Reservoir region

Slow-moving landslides are common in the Three Gorges reservoir (TGR) region. It may evolve into massive landslide hazards due to reservoir level fluctuation and rainfall. The assessment of slow-moving reservoir landslides is critical for the prevention and control of geological hazards. A step-like deformation mechanism for slow-moving landslides is proposed. Here, we use various wavelet tools to process the time series of 16 years continuous monitoring surface displacement of the Jiuxianping landslide at TGR. Then, the methods are used to investigate the correlation and hysteresis between the trigger factors (rainfall and reservoir level fluctuation) and reservoir landslide creep displacement. Owing to the influence of reservoir level fluctuation and rainfall, the triggering factors of displacement in different regions differ and show prominent hysteresis characteristics. Furthermore, the contribution of GPS monitoring points and InSAR fusion technology to creep landslide assessment is discussed, which can effectively reduce the possibility false alarms in landslide prediction. These mechanisms can be used to explain why some sliding bodies can keep stable after very large and long-time deformation. Therefore, these results are crucial for effective and reasonable geological hazard prevention and control in the TGR region.

A novel seepage device and ring-shear test on slip zone soils of landslide in the Three Gorges Reservoir area

For the deformation and evaluation of reservoir accumulative landslide, it is of great significance to study the strength characteristics of slip zone soils under rainfall and reservoir operation. In this paper, slip zone soils from Tongjiaping landslide in the Three Gorges Reservoir area is taken as the research case, and the self-developed seepage device matching with the ring-shear test is designed and manufactured. Then, the shear strength of slip zone soils under different seepage-shear conditions is studied to reveal the strength evolution law of riverside landslide. Eventually, the creep characteristics of slip zone soils are described by the Burger model. The experimental results indicate that: (1) the weakening effect of slip zone soils will be induced by the increase of seepage cycles, change amount of seepage pressure, initial and constant seepage pressure, which decrease the residual strength of slip zone soils. (2) When the seepage cycles are <15, the weakening of residual strength of slip zone soils is not obvious. While when the cycles reach 20, the residual strength of soil samples decreases rapidly. (3) The Burger model, which connected the Maxwell model and Kelvin model in series can appropriately reflect the creep characteristics of slip zone soils of Tongjiaping landslide. The research results reveal the weakening law of mechanical strength of slip zone soils under seepage cycles, which provides a basis for the mechanism of accumulative landslide under the fluctuation of reservoir level.

Long-Term Optimal Dispatching of Hydropower Station Based on Controlling the Frequency of Reservoir Level Fluctuation

In this paper, a method for long-term optimal operation of hydropower station is proposed to control the frequency of reservoir level fluctuation. We introduce the integer variable which describes the rise and fall of the reservoir level, the number of changes, and the state transition equation for the change of the reservoir level fluctuation into the dynamic programming method. This method can obtain the global optimal solution under the control of different numbers of reservoir level rise and fall, thus improving the controllability and practicability of optimal operating results. We consider the maximum number of water level fluctuations as a constraint condition while the reservoir level, the state of fluctuation, and the number of state changes that have occurred as the three state variables to construct a dynamic programming model. Three state transition equations are the water balance, the state of the reservoir level rise and fall, and the number of fluctuations. Besides, the penalty function is used to handle minimum output and surplus water. We solve this model by using a dynamic programming reverse recursion equation. The application of this method in the Manwan Hydropower Station shows that it can effectively solve the frequent water level fluctuation problem that is generally inconsistent with the actual situation in the long-term optimal dispatch scheme of hydropower stations and improve the practicability of the optimal dispatch results.

Displacement evolution of reverse-dip rock slope considering the change of the reservoir level

The fluctuation and periodic change of reservoir level are the important incentives that affect the stability of the reverse-dip rock slope. Based on the field monitoring data, this paper investigates the topping deformation evolution characteristics of a typical reverse-dip slope containing different geological partitions considering the fluctuation of reservoir level. A typical reverse-dip rock slope was taken as an engineering case, whose geological factors including elevation, slope angle, and aspect were first obtained by a field survey. Subsequently, the factors were superimposed through ArcGIS to obtain the geological partitions. Afterwards, a spatiotemporal evolution nephogram of the topping displacement was obtained by discrete monitoring data of surface displacement of the slope. Finally, the deformation characteristic of the prone zone was analyzed by superposing the nephogram of the displacement and the geometrical partition, considering the change of the reservoir level. The results show that the largest geological and geometric characteristic zone is at the bottom elevation, medium slope, and north aspect. The zone with significant horizontal displacement is distributed in the front and middle edges of the slope, which increases with the increase of the reservoir level and vice versa. The vertical displacement mainly occurs in the trailing of the slope. The area of superimposed displacement in strong deformation zones increases as either the reservoir level rises or falls. After the superposition, zones with strong deformation increase with the variation of the reservoir level, and the area with the largest displacement is distributed at the medium gradient, low elevation, and north aspect zones.

Effects of hydrological regimes and limnological parameters on plankton community properties in tropical irrigation reservoirs: A Sri Lankan case study

AbstractWater‐level fluctuations are reported to be key processes influencing ecosystem structure and functions in lentic aquatic ecosystems such as reservoirs. The plankton community structure in reservoirs, being useful monitoring tools as reservoir trophic status indicators, are influenced by water quality parameters and water‐level fluctuations. The present study tested the hypothesis that plankton community properties in irrigation reservoirs are influenced by hydrological regimes and physical and chemical parameters. Accordingly, the effects of physical, chemical and hydrological parameters on plankton density and taxa richness were investigated for 10 selected irrigation reservoirs of Sri Lanka. The relative reservoir level fluctuation (RRLF), an index of the magnitude of water‐level fluctuation in relation to mean depth, had a positive influence on phytoplankton density. Because the RRLF positively influenced phytoplankton density, this index appeared to favour eutrophy in reservoirs. Canonical correspondence analysis (CCA) indicated both the phytoplankton and zooplankton community structure in the study reservoirs was influenced by physical and chemical characteristics. CCA also indicated the plankton taxa abundance and water quality parameters could be used for the trophic classification of irrigation reservoirs. The results of the present study highlight the need for examining attributes based on hydrological regimes in the context of reservoir water quality management.

Correlation Analysis of Influencing Factors and the Monthly Displacement Increment of a Hydrodynamic Landslide Using a Pseudo-Maximum-Likelihood-Estimation-Mixed-Copula Approach

Heavy rainfall and changes in the water levels of reservoirs directly affect the degree of landslide disasters in major hydropower project reservoir areas. Correlation analyses of rainfall- and water-level fluctuations with landslide displacement changes can provide a scientific basis for the prevention and early warning of landslide disasters in reservoir areas. Because of the shortcomings of the traditional correlation analysis based on linear assumptions, this study proposed the use of a pseudo-maximum-likelihood-estimation-mixed-Copula (MLE-M-Copula) method instead of linear assumptions. We used the Bazimen landslide in the Three Gorges Reservoir Area as a case study to carry out the correlation analysis of the rainfall, water-level fluctuations, and landslide displacement. First, we selected several appropriate influencing factors to construct four candidate Copula models and estimated the parameters using the pseudo-MLE method. After the goodness-of-fit test, we selected the M-Copula model as the optimal model and used this model to study correlations between the monthly displacement increment of the landslide and influencing factors. We then established the joint distribution functions of these correlations. We computed and analyzed the overall and tail correlations between the displacement increment and the influencing factors, and we constructed the conditional probability distribution of the monthly displacement increment for different given conditions. The results showed that the pseudo-MLE-M-Copula method effectively quantified the correlation between the rainfall, reservoir-level fluctuations, and landslide displacement changes, and we obtained the return periods and value at risk of the influencing factors of the Bazimen landslide under different rainfall conditions and reservoir-level changes. Furthermore, the tail correlations between the monthly displacement increment of the landslide and the rainfall- and reservoir-level changes were higher than the overall correlations.

Seasonal water‐level fluctuations and changes in macro‐benthic community structure in tropical reservoirs: A Sri Lankan case study

AbstractSeasonal water‐level fluctuations (WLFs) in reservoirs influence ecological processes, in turn affecting their benthic macroinvertebrate communities. The present study was carried out in 10 irrigation reservoirs of Sri Lanka to investigate the effects of seasonal WLFs on the benthic macroinvertebrate fauna. The study period was divided into two distinct phases: the drained period and the inundated period. Benthic macroinvertebrates were sampled during both periods and enumerated. Air temperature and soil quality parameters were also measured simultaneously, and hydrological data related to the Kala Oya River basin were obtained from irrigation authorities. Data analysis using non‐metric multi‐dimensional scaling revealed two distinct reservoir groups, namely, Hydrological Stress Group 1 (HSG1) and Hydrological Stress Group 2 (HSG2). A low hydrological residence time and low relative reservoir level fluctuations (RRLF) characterized HSG1, with the opposite describing HSG2. Temporal variations of macrobenthos indicated a high taxa richness and diversity in HSG1 reservoirs during the drained period, with scrapers and collector‐gatherers being the dominant functional feeding groups. Reservoirs in the lower river basin (HSG1) exhibited a high taxa richness and diversity. During the inundated periods, insect taxa colonized, particularly, chironomids and ephemeropterans. Molluscan taxa were prominent during the drained periods. These observations highlight the influence of seasonal fluctuations of reservoir water levels on benthic macroinvertebrates. Benthic macroinvertebrate communities in reservoirs were significantly influenced by the RRLF, manifesting the importance of hydrological regimes in reservoirs to develop macroinvertebrate metrics for water‐quality monitoring.

Quantitative risk analysis of the hazard chain triggered by a landslide and the generated tsunami in the Three Gorges Reservoir area

Landslides sliding rapidly into water bodies may trigger tsunamis, which can threaten not only elements at risk on the slopes but also ships and piers on the water bodies. Management of both direct risks from landslides and indirect risks from landslide-triggered tsunamis along navigation channels is thus highly challenging. In this study, a framework, including hazard and risk identification, hazard analysis, consequence analysis, and risk estimation, is proposed for risk analysis of a landslide-triggered hazard chain, through a case study of the Liangshuijing landslide in the Three Gorges Reservoir area, China. Detailed monitoring data of the landslide indicates a significant influence of the reservoir level fluctuation on the landslide stability. Then, the hazards of both the landslide and its triggered tsunami are predicted by landslide stability calculation, run-out analysis, and tsunami propagation simulation according to defined scenarios. The vulnerability of identified static and dynamic elements at risk is quantified based on hazard intensity and their resistance to the hazard. The total risk, estimated by the sum of the direct risk and the indirect risk from the hazard chain, increases during the drawdown period of the reservoir level. Risk maps are designed to present the dynamic indirect risk along the Yangtze River. Systematic risk analysis emphasizes that the indirect risk from the potential tsunami is much higher than the direct risk, which supports the practical mitigation strategy of the landslide. The framework proposed in this study can be helpful to mitigate reservoir landslide risks, and provides a reference through which entire landslide hazard chains can be analyzed.

Changes in the hydrodynamics of a mountain river induced by dam reservoir backwater

Upstream from a dam reservoir, river hydrodynamics may be directly changed by temporary inundation driven by the reservoir. This triggers morphological river changes which may additionally modify the initial hydrodynamics, even at the time when backwater inundation does not occur (indirect effects of backwater). We verified these hypotheses, applying two-dimensional hydraulic modelling of flood flows to a section of the mountainous Dunajec River upstream from the Czorsztyn Reservoir. The modelling was performed for small, medium and large floods, and hydraulic conditions were compared between the scenarios with lacking and maximum backwater inundation and between the river reaches subjected to backwater inundation and unaffected by backwater fluctuations. Direct effects of reservoir level fluctuations were limited to the reach subjected to backwater inundation during floods and comprised: significantly increased water depth and decreased flow velocity and bed shear stress in the channel and on the floodplain, as well as a re-established hydrological connectivity between the channel and floodplain during small and medium floods. Indirect effects of backwater inundation reflected channel widening and bed aggradation that triggered a positive feedback with changes in hydrodynamics, mostly by reducing the velocity of flood flows in the channel zone. These latter changes occurred on a longer distance upstream from the reservoir than the backwater reach itself, and they modified the river hydrodynamics even when backwater inundation did not occur. We propose a conceptual model which indicates that changes of mountain rivers upstream from dam reservoirs are driven by modified hydrodynamics and lead to different morphological adjustments than those induced by waters underloaded with sediment downstream from dams. Changes in hydrodynamics and the associated morphological and sedimentary adjustments of mountain rivers recorded upstream from dam reservoirs may locally mitigate impacts of channelization and channel incision on riverine and riparian ecosystems of these rivers.

Activity law and hydraulics mechanism of landslides with different sliding surface and permeability in the Three Gorges Reservoir Area, China

The Three Gorges Hydropower Station is the largest hydropower station worldwide and the largest project ever built in China. There are about 2619 ancient landslides affected by reservoir level fluctuation in the Three Gorges Reservoir (TGR) area. More than 670 landslides have been reactivated and eight landslides have failed since the impoundment of the reservoir in June 2003, which seriously threatens people's safety and property. In this study, taking a large number of re-active and failed landslides as statistical samples, the activity and displacements of the reservoir landslide with special regard to different sliding surface and permeability are analyzed and discussed. It is noted that a significant correlation between the landslide movement and the reservoir filling process. The re-active landslides are mainly concentrated in the initial stage of water storage, and the frequency of activation as well as the degree of deformation decrease gradually after the third phase of water storage (175 m). Then the four dominant combinations of the inducing factors of re-active landslide are presented: (a) drawdown of water level, straight line sliding surface, 20–40% degree of immersion, and weak permeability; (b) drawdown of water level, arc sliding surface, 40–60% degree of immersion, and medium permeability; (c) raising of water level, fold line sliding surface, 20–40% degree of immersion, and good permeability; (d) raising of water level, chair shaped sliding surface, 0–20% degree of immersion, and good permeability. Furthermore, when the rate of the reservoir level fluctuation is greater than the permeability coefficient, the shape of sliding surface is from the straight line - the arc - the fold line - the chair shaped, and the hydraulics effect of reservoir water on landslide shifts from the seepage pressure effect to the buoyant effect. Meanwhile, the impact of the reservoir water filling on the landslide reactivation changes from favorable to worse, and the impact of the reservoir water drawdown on the landslide reactivation changes from worse to favorable.

The Impact of Reservoir Fluctuations on Reactivated Large Landslides: A Case Study

Filling of Xiangjiaba Reservoir Lake in the Southwest China triggered and reactivated numerous landslides due to water fluctuation. In order to understand the relationship between reservoirs and slope instability, a typical reservoir landslide (Dasha landslide) at the right bank of Jinsha River was selected as a case study for in-depth investigations. The detailed field investigations were carried out to identify the landslide with respect to its surroundings and to find out the slip surface. Boreholes were drilled to find out the subsurface lithology and the depth of failure of Dasha landslide. The in situ geotechnical tests were performed, and the soil samples from exposed slip surface were retrieved for geotechnical laboratory analysis. Finally, stability analysis was done using the 3D strength reduction method under different conditions of reservoir water level fluctuations and rainfall conditions. The in-depth investigations show that the Dasha landslide is a bedding rockslide which was once activated in 1986. The topography of Dasha landslide is relatively flat, while the back scarp and local terrain is relatively steep. The total volume of landslides is about 580×104 m3 with an average thickness of 20 m. Bedrock in the landslide area is composed of Suining Formation of the Jurassic age. The main rock type is silty mudstone with sandstone, and the bedding orientation is 300~310° ∠ 7~22°. The factor of safety (FOS) of Dasha landslide obtained by 3D strength reduction cannot meet the minimum safety requirement under the working condition of reservoir level fluctuation as designed, with effect of rainfall and rapid drawdown.

Empirical yield predictive models for the fisheries of irrigation reservoirs in Sri Lanka

As fisheries production in reservoirs of most countries is a secondary use, challenges for improved management of fisheries should be addressed by building partnership between fisheries and other interested groups such as agriculture concerned with water management. Attempts were therefore made to develop empirical fish yield predictive models in ten irrigation reservoirs of Sri Lanka incorporating morphological, edaphic and hydrological parameters together with fishing intensity, with a view to investigating their influence on fish yields. Reservoir fish yield was found to be significantly correlated with two formulations of morpho-edaphic index (i.e., conductivity in μS cm-1/mean depth in m [MEIc] and alkalinity in m. equiv. l-1)/mean depth in m [MEIa]), and a relative reservoir level fluctuation index (RRLF), defined as the mean amplitude of the annual reservoir level fluctuations divided by the mean depth of the reservoir. Both MEIc and MEIa also had significant positive ln-ln relationships with RRWL, indicating that RRWL can be used as an independent variable in reservoir fish yield prediction. Reservoir fish yield was also related to fishing intensity (FI in boat-days ha-1, yr-1) conforming to a ln-linear regression model (p Ln FY = 3.245 + 0.327 Ln MEIa + 0.023 FI (R2 = 0.355; p Ln FY = 3.403 + 0.249 Ln MEIc + 0.019 FI (R2 = 0.369; p Ln FY = 1.330 + 0.650 Ln RRWL + 0.016 FI (R2 = 0.593; p The empirical yield predictive model based on RRWL and FI as independent variables was more robust than those based on MEIa and MEIc, and the former has significant management implications because RRWL can be manipulated by irrigation authorities whereas control of FI is under the jurisdiction of fisheries authorities. Hence, through an effective dialogue between irrigation and fisheries authorities, there is a considerable potential to optimize fish yields in irrigation reservoirs of Sri Lanka.

Influence of hydraulic retention time and amplitude of water level fluctuations on water quality in irrigation reservoirs of the Kala Oya river basin, Sri Lanka

Management of reservoir water quality is a global challenge due to the natural process of eutrophication and anthropogenic aggravation. In Sri Lanka, irrigation reservoirs support several secondary uses such as fish production, livestock farming, and many communal uses including drinking water supply. In the present study, basic limnological parameters of ten irrigation reservoirs of Sri Lanka were investigated from June 2013 to February 2016, with a view to identifying influence of hydrological regimes on reservoir water quality. Spatio-temporal similarities of water quality parameters were studied employing the self-organizing map (SOM) routine of the artificial neural network application. The sample vectors, classified on the SOM lattice, indicated 6 clusters at 50% similarity level. When reservoir that were categorized according to hydraulic retention time (HRT) and relative reservoir level fluctuation (RRWL; defined as the ratio of the mean reservoir level amplitude to mean depth), were compared with dominant water quality parameters in SOM lattice, it was evident that some productivity-related water quality parameters were influenced HRT and RRWL. The results of the study revealed that HRT and RRWL can essentially be controlled through management of hydrological regimes in irrigation reservoirs, thus, close dialogue between irrigation authorities and other users of reservoir water resources are needed to ensure desired water quality of the reservoirs.

Precedent long-term gravitational deformation of large scale landslides in the Three Gorges reservoir area, China

Large scale landslides are common in the Three Gorges reservoir region due to steep slopes and complex geological conditions, fluctuations of reservoir level, etc. Many phenomena and formation mechanisms related to these landslides are not well understood and need more research. In this study, large scale landslide evolution and formation mechanisms are thoroughly investigated in terms of precedent long-term gravitational deformation (PLTGD). Three large scale landslides in the Three Gorges reservoir region, Huangtupo landslide (HTPL), Huanglashi landslide (HLSL), and Baotaping landslide (BTPL), are taken for example to discuss their phenomena and features of PLTGD, and to investigate the correlation between the PLTGDs and landslide. Many features associated with landslides are caused by slow, downslope gravitational processes before landslide failure, and three criteria for recognition of the PLTGD features are summarized. The investigation results reveal that the PLTGDs play an important role in landslide evolution and formation mechanism. Overall, this paper presents evidences for PLTGDs of large scale landslides and their correlation with landslide evolution, which is helpful to understand the formation mechanism of large scale landslides in the Three Gorges reservoir region.

The Coupling Effect of Rainfall and Reservoir Water Level Decline on the Baijiabao Landslide in the Three Gorges Reservoir Area, China

Rainfall and reservoir level fluctuation are two of the main factors contributing to reservoir landslides. However, in China’s Three Gorges Reservoir Area, when the reservoir water level fluctuates significantly, it comes at a time of abundant rainfall, which makes it difficult to distinguish which factor dominates the deformation of the landslide. This study focuses on how rainfall and reservoir water level decline affect the seepage and displacement field of Baijiabao landslide spatially and temporally during drawdown of reservoir water level in the Three Gorges Reservoir Area, thus exploring its movement mechanism. The monitoring data of the landslide in the past 10 years were analyzed, and the correlation between rainfall, reservoir water level decline, and landslide displacement was clarified. By the numerical simulation method, the deformation evolution mechanism of this landslide during drawdown of reservoir water level was revealed, respectively, under three conditions, namely, rainfall, reservoir water level decline, and coupling of the above two conditions. The results showed that the deformation of the Baijiabao landslide was the coupling effect of rainfall and reservoir water level decline, while the latter effect is more pronounced.

Macro/Microtesting and Damage and Degradation of Sandstones under Dry-Wet Cycles

In terms of the degradation of mechanical parameters of rock mass in the hydrofluctuation belt of a reservoir bank slope arising from rainfall and the reservoir level fluctuation, the moderately weathered sandstone in a side slope of the Three Gorges Reservoir Region is selected as a research object to carry out “drying-saturation-drying” tests for disks with two thicknesses (h=25 mm,h=50 mm) in different cycles; a spiral CT machine, an ultrasonic velocity meter, and a light Schmidt hammer are utilzed to conduct nondestructive testing on dry-wet cycles; through the Brazilian splitting test, the uniaxial tensile strength of “dry” and “saturated” sandstones under different dry-wet cycles is obtained. The research shows that, with the increase of the dry-wet circles (n), the longitudinal wave velocity and the rebound strength of sandstones are linearly decreased withn; the uniaxial tensile strength of sandstones and the mean CT number of cross sections are logarithmically decreased withn; the fitting equation of macro/micromechanical parameters and dry-wet cycles (n) of sandstones is raised, which is provided as a reference basis for the weathering process of sandstones under dry-wet cycles.

Detailed hydrogeological analysis of a deep-seated rockslide at the Gepatsch reservoir (Klasgarten, Austria)

The hydrogeology of the deep-seated, slowly creeping Klasgarten rockslide in Austria is investigated in this study based on detailed surface and subsurface field data, laboratory analyses, and analytical and numerical simulations. Field data are derived from several deep exploration and monitoring boreholes, an exploration drift located within the rockslide, and geological and geomorphological mapping. Particular attention is given to the pore pressure measurements and their temporal and spatial variability. These pore pressure variations are controlled by a thin layer of clayey fault gouge (representing the basal shear zone of the rockslide), a high-permeability rockslide mass, and moderately fractured paragneissic bedrock. Variably saturated equivalent-continuum hydraulic conductivities and storage properties are derived from packer tests, laboratory tests and optical televiewer images. These data sets are used for two-dimensional numerical groundwater models to study the flow-field and pore-pressure variations caused by the reservoir water-level fluctuations, the transient groundwater infiltration from snowmelt and precipitation along the slope, and the exploration drift. The strongest pressure transients in the rockslide are caused by reservoir level fluctuations and not the natural groundwater recharge, even at substantial distances from the reservoir. The response times are very short and only a minor distance-dependent attenuation is observed. The results of this study are essential to analyse the hydromechanical control of the deformation behaviour of rockslides adjacent to hydropower reservoirs. Further, it helps to understand how the formation of a rockslide can change the original bedrock aquifer.