Reservoir Water Level Fluctuation Research Articles

Interpretasi Instrumentasi Piezometer Dalam Rangka Pemantauan Keamanan Bendungan Kedung Ombo

The embankment dam is the most widely built dam in the world, especially in Indonesia. However, embankment dams are also prone to collapse. Dam failures due to the piping process through the dam body account for 30.5% of the total dam collapses worldwide. Therefore, it is necessary to periodically monitor and evaluate the condition of pore water pressure and seepage in a dam which is usually carried out using installed instrumentation. Very little has been done on instrumentation interpretation of earthfill dams in Indonesia, which is a very worrying condition. It is possible that old or even new dams have shown behavior that leads to a decrease in safety. This condition can be monitored by instrumentation in the dam if interpreted properly. Kedung Ombo Dam as an old embankment dam but has a fairly complete instrumentation can be evaluated for safety related to pore water pressure and phreatic line (seepage line). Pore water pressure evaluation is carried out by collecting piezometer readings and reservoir water level fluctuations over a period of several years. The results of the research on the interpretation of piezometer readings indicate that the overall safety of the Kedung Ombo dam is still good in terms of pore water pressure conditions. However, there are some anomalous conditions that should be investigated further

Diversity and distribution of freshwater molluscan fauna in reservoirs and headwater streams of the Kala Oya river basin in Sri Lanka

In this study, the variation of aquatic molluscan diversity concerning seasonal water level fluctuations (WLF) and sediment texture was investigated in some perennial irrigation reservoirs and the associated head headwater streams in the Kala Oya river basin in Sri Lanka. Altogether 11,752 molluscan specimens belonging to 10 gastropod taxa (96.6%) and 2 bivalve taxa (3.4%) were identified. Of these, 11,282 specimens (96.0%) were from reservoir sampling sites and the remainder 470 (4.0%) was from the associated headwater streams. Of the gastropods, the individuals of the genus Melanoides showed the highest distribution index (DI) of 0.75 followed by Bellamya (DI = 0.63) and Thiara (DI = 0.60). The DI of the gastropod molluscs showed a significant positive relationship with their shell size (p < 0.05). Although molluscan diversity and taxa richness were comparatively lower in headwater streams than in reservoir sampling sites, Viviparidae (Bellamya; 0.06±0.03), Bithyniidae (Bithynia; 0.21±0.07) and Thiaridae (Thiara; 4.8±1.9 and Melanoides; 1.1±0.8) showed higher relative abundance (expressed as individuals per dm3) in the headwater streams. The reservoir water level fluctuation showed a significant negative relationship with molluscan taxa richness (p < 0.05), but not with the Shannon-Weaver diversity index (p = 0.073). The distribution of molluscs was also found to be related to the sediment texture where the most abundant gastropod genera Bellamia, Bithynia, and Thiara were widely distributed in sandy substrates in reservoirs and associated streams in the Kala Oya river basin.

Sensitivity Analysis of Anchored Slopes under Water Level Fluctuations: A Case Study of Cangjiang Bridge—Yingpan Slope in China

This paper presents an improved slope stability sensitivity analysis (ISSSA) model that takes anchoring factors into consideration in umbrella-anchored sand and clay slopes under reservoir water level fluctuation. The results of the ISSSA model show that the slope inclination and the layout density of anchors are the main controlling factors for sand slope stability under fluctuation of the water level, while the slope inclination and water head height are the main controlling factors for slope stability in the Cangjiang bridge—Yingpan slope of Yunnan province in China. Moreover, there is an optimum anchorage angle, in the range of 25–45 degrees, which has the greatest influence on slope stability. The fluctuation of the reservoir water level is an important factor that triggers slope instability; in particular, a sudden drop in the surface water level can easily lead to landslides; therefore, corresponding measures should be implemented in a timely manner in order to mitigate landslide disasters.

Three-dimensional landslide evolution model at the Yangtze River

Continuous river incisions, heavy precipitation events, reservoir water-level fluctuations, and changes in groundwater flow are the main driving factors of extensive landslide activities in the Three Gorges area of the Yangtze River in China. Although the triggers for these major landslide events can be technically detected, predicting and mitigating them remains challenging. This is especially the case where ancient, deep-seated, multi-stage landslides have created complex geological structures that make it difficult to uncover their evolutionary processes and to determine slip surfaces. This study, based on elaborate investigation of the Outang landslide in the Three Gorges Reservoir area, proposes a general framework for analyzing the spatial and temporal evolution of a multi-stage riverbank landslide. The framework applies three-dimensional geological modeling to integrate large amounts of data from earth surface investigations, subsurface explorations, in-situ monitoring and geological dating. The results indicate that the Outang landslide has a total volume of 8.3 × 107 m3 and a maximum thickness of 114 m. It consists of four individual sliding bodies that have been formed consecutively since 130 ka BP. Furthermore, the original slip surfaces of the sliding bodies are found to be interconnected, forming one large active landslide continually creeping towards the Yangtze River. While the entire landslide is in motion, the western, eastern and up-slope portions of the sliding mass are moving at a faster velocity of up to 12.6 cm per year. Our analysis of the Outang landslide reveals that its evolution can be subdivided into three sliding modes. These modes could serve as a reference for analyzing the spatial and temporal evolution of similar multi-stage landslides along riverbanks.

ANALYSIS OF DEFORMATION AND FAILURE MECHANISM OF BANK SLOPES WITH DIFFERENT STRUCTURES UNDER RESERVOIR WATER LEVEL FLUCTUATION—TAKING QIANJIANGPING LANDSLIDE AND SHUPING LANDSLIDE AS EXAMPLES

Since the impoundment of the Three Gorges Reservoir in 2003, different types of landslides have taken place in the main stream and tributaries of Yangtze River. Based on the structure of reservoir bank slope, taking Qianjiangping landslide and Shuping landslide as examples, this paper attempts to analyze the deformation and failure mechanism of slopes with different structures under the condition of reservoir water level fluctuation through the field investigation, long-term observation and simple model tests. It aims to provide scientific insight for the prevention and control of landslide disasters in the operation process of reservoir area. The results show that the dip-structure slope is easy to lose its stability and cause rapid landsliding in the process of water level rising, while the loose structure slope is easy to produce obvious deformation in the process of water level drawn-down due to the influence of seepage force. The deformation rate is positively correlated with the speed of water level drawn-down.

Impacts of Reservoir Water Level Fluctuation on Measuring Seasonal Seismic Travel Time Changes in the Binchuan Basin, Yunnan, China

An airgun source in a water reservoir has been developed in the past decade as a green active source that had been proven effective to derive short-term subsurface structural changes. However, seasonal water level fluctuation in the reservoir affects the airgun signal, and thus whether the airgun signals can be used to derive robust seasonal variation in subsurface structure remains unclear. We use the airgun data observed in the Binchuan basin to estimate the seasonal variation of seismic travel time and compare the results with those derived from ambient noise data in the same frequency band. Our main observation is that seasonal change δt/t from airgun is negatively correlated to the variation of dominant frequency and water table fluctuation in the reservoir. One possible explanation is that water table fluctuation in the reservoir affects the dominant frequency of the airgun signal and causes significant phase shift. We also compute the travel time changes in P-wave from the empirical Green’s function after deconvolving the waveforms from a reference station that is 50 m from the airgun source. The dominant frequency after deconvolution still shows seasonal variation and correlates inversely to the travel time changes, suggesting that deconvolution cannot completely eliminate the source effect on travel time changes. We also use ambient noise cross-correlation to retrieve coda waves and then derive travel time changes in monthly stacked cross-correlations relative to a yearly average cross-correlation. We observe that seismic travel time increases to its local maximum in the end of August. The travel time changes lag behind the precipitation for about one month. We apply a poroelastic physical model to explain seismic travel time changes and find that a combined effect from precipitation and evaporation might induce the seasonal changes as shown in the ambient noise data. However, the pattern of travel time changes from the airgun differs from that from ambient noise, reflecting the strong effects of airgun source property changes. Therefore, we should be cautious to derive long-term subsurface structural variation from the airgun source and put more attention on stabilizing the dominant frequency of each excitation in the future experiments.

Effects of reservoir water level fluctuations and rainfall on a landslide by two-way ANOVA and K-means clustering

Effects of reservoir water level fluctuations and rainfall on a landslide by two-way ANOVA and K-means clustering

The study on the time lag of water level in the Three Gorges Reservoir under the regulation processes

Abstract The identification of the water level time lag (WLTL) under the regulation processes is of great significance for environmental impact, flood control, and sediment transport of huge reservoirs. The traditional hydrodynamic method can calculate the flood inflow process and the water level change process along the river channel, but it is difficult to estimate the time difference of the reservoir water level fluctuation to the dispatching process. To quantitatively evaluate the reservoir regulation effect on the WLTL in the Three Gorges Reservoir (TGR), the daily water level data from 2011 to 2017 of five stations in the TGR are analyzed in this paper. The results revealed that there is a significant water level difference along the reservoir from April 1 to October 31. The gap between the end of the reservoir and the Three Gorges Dam (TGD) is the largest, reaching 23.67 m on July 2. The longer the distance from the TGD, the longer the time lag. Furthermore, the WLTL is also different at the four different operating periods of the reservoir in a year. During the low water level operation period and high water level operation period, the time lag is 3 days which is the greatest, while in the water level decline period and water level rise period, the time lag is within 2 days.

Improvement of transfer coefficient method under the consideration of hydrodynamic pressure

Hydrodynamic pressure is an indispensable load influencing stability of a bank slope exposed to reservoir water level fluctuations. However, the Transfer Coefficient Method(TCM), one of the limit equilibrium methods, only considers seepage force in the slope but not the hydrodynamic pressure. To calculate the stability of the bank slope more accurately, hydrodynamic pressure is redefined through indoor permeation experiment, based on which, mathematical expressions of hydrodynamic pressure are put forward and the TCM is improved. Taking Shuping landslide as an example, the stability coefficients of Shuping landslide under the condition of reservoir water level fluctuations are calculated by using the modified TCM. The results agree with the field deformation monitoring of the landslide. Therefore, compared with the TCM, the modified one in this study could be more suitable to calculate stability coefficient of bank slopes under reservoir operations.

Towards on Slope-Cutting Scheme Optimization for Shiliushubao Landslide Exposed to Reservoir Water Level Fluctuations

Bank slopes with huge accumulative sliding masses in a reservoir area suffer from landslide risks subjected to reservoir water fluctuations, and slope-cutting is an effective measure for the slope reinforcement. In this paper, a suitably and practicably integrated approach was put forward to the optimization design of the slope-cutting measure on the Shiliushubao landslide in Three Gorges Reservoir, China. It includes the determination of the most unfavorable reservoir water level variation condition according to the Three Gorges operation process, the mainly slope-cutting parts based on calculated residual sliding force curves, the main controlling factors of slope-cutting and their optimization ranges. The optimization analysis of the slope-cutting scheme for the Shiliushubao landslide was performed by taking advantage of the uniform design, transfer coefficient method, GA and ANN. The optimized layout of slope-cutting measure for Shiliushubao landslide after optimization study was to set the three main controlling factors of slope-cutting as i1 = 2.11, xb = 279.6 m and i2 = 2.01, which satisfied the objectives of both economy and landslide stability. The research results are helpful for the optimization design of slope-cutting scheme on reservoir landslides with large-scale accumulations.

Deformation Process and Mechanism Analyses of a Rock Slope Based on Long-Term Monitoring at the Pubugou Hydropower Station, China

This paper presents a typical 450 m high rock slope in a highly jointed and fractured rock mass at Pubugou (PBG) hydropower station on the Dadu River. We established a set of multiphase field geological survey combined with GPS, inclinometers, and piezometer monitoring system to analyze the deformation and failure mechanism of rock slope. The results show that small-scale excavation in road construction disrupted the balance of the Pubugou rock slope (PBGRS), and several local retrogressive failures occurred at the toe. Monitoring data regarding surface and subsurface movements show that the PBGRS is stable as a whole. The deformation concentrated mainly in the loosened fractured zone, which was a feature with sliding-compression cracking. Highly loosened rock mass was the predominant factor affecting the stability of the PBGRS, while the role of reservoir water level fluctuation, though positive, was not significant. Overall, the PBGRS still has a high potential for further development, especially in the slope’s upper zone. To reinforce the slope, measurements mainly consist of the concrete frame combined with anchor cables constructed on the slope. In this study, the analysis was carried out of pre- and postreinforcement measure slope stability with numerical simulation, and safety factor increased from 1.09 to 1.21. This study’s findings have important implications to the analytical method and reinforcement design with geological settings like that of the PBGRS.

Deformation characteristics, mechanisms, and influencing factors of hydrodynamic pressure landslides in the Three Gorges Reservoir: a case study and model test study

Hydrodynamic Pressure landslides are the most typical landslides affected by the water level in the Three Gorges Reservoir. These types of landslides are large and cause severe deformation. Therefore, they may significantly affect the safe operation of the Three Gorges Reservoir once losing stability. Taking the Shuping landslide in the Three Gorges Reservoir as a typical case, this study explored the deformation characteristics and influencing factors of the Hydrodynamic Pressure landslide using monitoring data of its surface deformation, 17 years of GPS displacement data, automatic displacement metre of surface cracks, and groundwater level. To determine the deformation mechanism of the Hydrodynamic Pressure landslide, the model of Hydrodynamic Pressure landslide was designed and carried out to simulate the fluctuation of reservoir water level. The results showed that the hydrodynamic pressure landslides deformation was mainly affected by the overall deformation of the front edge of the landslide, and the amount of deformation was relatively large. The back part of the landslide mainly encountered tensile deformation. The Hydrodynamic Pressure landslides are a typical retrogressive deformation. The deformation of Hydrodynamic Pressure landslide was affected by the periodic change in the reservoir water level and the overall deformation trend is increasing. The intrinsic factor influencing the deformation of the hydrodynamic pressure landslide is the low permeability coefficient of the sliding mass, and the extrinsic factor is the drawdown of the reservoir water level. When the reservoir water table drawdown occurred, there was a noticeable water level difference with the underground water level in the landslide mass and generated hydrodynamic pressure. The Hydrodynamic Pressure landslide model results showed that the pore-water pressure, effective stress, and groundwater level in the landslide were consistent with the reservoir water level but with noticeable hysteresis. The key hydrodynamic factor for the deformation of this type of landslide was the hydrodynamic pressure towards the outside of the slope, formed when the reservoir water level dropped. Moreover, it was found that the faster reservoir water-level drawdown rates led to an increased influence on the stability of the landslide.

Soil anti-scourability enhanced by herbaceous species roots in a reservoir water level fluctuation zone

Revegetation is one of the successful approaches to soil consolidation and streambank protection in reservoir water level fluctuation zones (WLFZs). However, little research has been conducted to explore the impact of herbaceous species roots on soil anti-scourability during different growth stages and under different degrees of inundation in this zone. This study sampled two typical grasslands (Hemarthria compressa grassland and Xanthium sibiricum grassland) at two elevations (172 and 165 m a.s.l.) in the water level fluctuation zone (WLFZ) in the Three Gorges Reservoir (TGR) of China to quantify the changes in soil and root properties and their effects on soil anti-scourability. A simulated scouring experiment was conducted to test the soil anti-scourability in April and August of 2018. The results showed that the discrepancy in inundation duration and predominant herbaceous species was associated with a difference in root biomass between the two grasslands. The root weight density (RWD) values in the topsoil (0-10 cm) ranged from 7.31 to 13 mg cm−3 for the Hemarthria compressa grassland, while smaller values ranging from 0.48 to 8.61 mg cm−3 were observed for the Xanthium sibiricum grassland. In addition, the root biomass of the two herbs was significantly greater at 172 m a.s.l. than that at 165 m a.s.l. in the early recovery growth period (April). Both herbs can effectively improve the soil properties; the organic matter contents of the grasslands were 128.06% to 191.99% higher than that in the bare land (CK), while the increase in the water-stable aggregate ranged from 8.21% to 18.56%. Similarly, the topsoil anti-scourability indices in both the herbaceous grasslands were larger than those in the CK. The correlation coefficients between the root length density (RLD), root surface area density (RSAD) and root volume density (RVD) of fine roots and the soil anti-scourability index were 0.501, 0.776 and 0.936, respectively. Moreover, the change in the soil anti-scourability index was more sensitive to alternations in the RLD with diameters less than 0.5 mm. Overall, the present study showed that the perennial herbaceous (H. compressa) has great potential as a countermeasure to reduce or mitigate the impact of erosion in the WLFZ of the Three Gorges Reservoir.

Stability Analysis of the Shiliushubao Landslide Based on Deformation Characteristics and External Trigger Factors in the Three Gorges Reservoir

There exists the problem of landslide reactivation due to the seasonal fluctuation of rainfall and reservoir water level annually. Based on a large number of GPS monitoring data of the landslide mass after impoundment of the Three Gorges Reservoir in Shiliushubao landslide area, the relationship between the external trigger factors and slope stability could be obtained. A finite element calculation model has been established for the stability analysis of the Shiliushubao landslide after impoundment from January 2004 to October 2009. Through the deformation characteristics of the landslide, it is shown that the landslide exhibited a stepwise pattern on the whole, which developed faster after impoundment and slowed down in rainy seasons. The trend of the curve kept roughly opposite to the fluctuation of the safety factor. It suggested that the stability of the landslide mass was closely related to the seasonal fluctuation of the rainfall and the reservoir level, and the landslide deposits demonstrated to be reactive with them. The subject provides a certain reference value on the landslide stability analysis and the risk assessment within a similar engineering geological condition.

Slope stability analysis considering seepage and stress coupling under water level fluctuation

The reservoir water level fluctuation is an important factor inducing the reaction of pore-water pressure, seepage and at last resulting in instability and failure of the slope. A typical homogeneous slope is conducted as an example in this paper, the seepage and stress coupling effect is considered, and the slope stability calculation and analysis are carried out by using the finite element stress method. The results demonstrate that the factor of safety increases with the reservoir water level rises, and then gradually changes from decrease to stabilization. It should be noted that the factor of safety decreases slightly during the initial stage of water level rising at the speed of 0.2 m/d, which the slope will probably lose its stability. On the other, the factor of safety changes from decrease to increase along with the reservoir water level drawdown, and then gradually tends to stabilization. There is a minimum factor of safety when the water level is at about 1/4 of the slope height, and the minimum factor of safety decreases with increasing drawdown speed, just as the factor of safety decreases from 0.83 to 0.73 when the drawdown speed is increased from 0.20 m/d to 5.0 m/d.

Mpact Analysis of Reservoir Water-level Fluctuation Speed on Reservoir Bank Building

mpact Analysis of Reservoir Water-level Fluctuation Speed on Reservoir Bank Building

Numerical Analysis of Slope Stability under Reservoir Water Level Fluctuations Using a FEM-LEM-Combined Method

Large-scale slopes at the banks of reservoirs pose a serious threat to the safety of hydropower stations. The fluctuation of the reservoir water level is a key factor in the slope stability. However, the parameters to describe the relationship among water content, matric suction, and soil strength are difficult to measure using unsaturated soil strength theory. To solve this problem, a simple FEM-LEM-combined scheme considering pore pressure, seepage force, and strength weakening is presented to calculate the safety factor. A numerical study on the impact of reservoir water level fluctuations on stability of a glaciofluvial deposit slope is implemented. Two typical profiles are used to estimate the stability of the glaciofluvial deposit slope in response to rising and lowering water levels. The results indicate that this method proposed a simple and efficient tool for water level-induced slope stability analysis.

Impact Analysis of Reservoir Water-level Fluctuation on Building Foundations on Bank Slopes

Impact Analysis of Reservoir Water-level Fluctuation on Building Foundations on Bank Slopes

Influence of human activity on landslide susceptibility development in the Three Gorges area

Human activities are important factors that trigger frequent occurrences of landslides; thus, for landslide control, it is critical to determine the influence of human activity on landslide occurrence probability. The Three Gorges area is a region in the world that typically experiences serious landslide disasters and frequent human activities. The objective of this work is to employ the Three Gorges area as an example to reveal the impact of human activity on the dynamic development of landslide susceptibility from 2010 to 2019. Some new viewpoints are suggested for the five aspects: (1) High-precision landslide susceptibility maps are generated by a combination of multiresolution segmentation and convolutional neural network algorithms. Moreover, the dynamic development rules of landslide susceptibility from 2010 to 2019 are revealed. (2) The change in landslide susceptibility in the study area from 2010 to 2019 was mainly caused by the combined action of rainfall and human activity. The fluctuation of reservoir water level had a less influence on the development of landslide susceptibility. (3) Some human activities, especially road construction, farmland appropriation for building construction, agricultural reclamation, farmland cultivation and irrigation, initiation of commercial planting, urban expansion, and large-scale deforestation, may dramatically increase landslide occurrence probability. (4) Human activities, e.g., conversion of farmland to forestry, artificial recovery of natural vegetation, and later periods of artificial planting, may obviously reduce landslide susceptibility. (5) The human activity causes and mechanisms influencing landslide susceptibility in the study area are proposed, including transpiration and anchorage of plants, slope reinforcement by plant roots, destruction of slope stress equilibrium, and soil erosion.

Study on the Deformation Mechanism of Reservoir Landslides Considering Rheological Properties of the Slip Zone Soil: A Case Study in the Three Gorges Reservoir Region

Reservoir water level fluctuation is one of the main extrinsic factors that could change the stress field in landslides, as well as the mechanical strength of geomaterials, hence affecting the deformation and stability of landslides. The largest reservoir landslide in the Three Gorges Reservoir area was selected for a case study. The impact of reservoir water level fluctuation is represented by the dynamic change in the underground seepage field and was thereby analyzed with numerical modeling. The deformation behavior considering the rheological properties of the slip zone soil was studied. The sudden change in the displacement–time curve was selected as the failure criterion for the investigated landslide. The evolution process of the accelerated deformation stage was divided into slow acceleration, fast acceleration, and rapid acceleration stages. The Huangtupo landslide is characterized by a retrogressive landslide and is currently in the creep deformation stage; the deformation mechanism and deformation characteristics are closely related to the reservoir water level fluctuation. Research was carried out by means of field investigation, in situ monitoring, and numerical simulation to provide a true and reliable result for stability evaluation.