Impoundment Stage Research Articles

Determination of the optimum sealing method for Azad pumped storage dam considering seepage analysis

Seepage analysis of the upper reservoir of the Kurdistan Azad pumped storage dam with a volume of 3.8E+5 m3 is a key step for selection of the optimized sealing method. More than 60% of the Lugeon test results show very permeable behavior for the pit and abutments of the reservoir. In this study, regarding the permeability value of the reservoir abutments and pit obtained by means of Lugeon tests, seepage rate was computed using various analytical and numerical methods. Reservoir total seepage discharge was computed in steady-state regime by means of analytical and numerical methods (SEEP/W finite element software) as 1.14E+05 and 1.15E+05 m3/day, respectively. Distinct element method (UDEC software) showed variable behavior for the seepage flow. In the reservoir initial impounding stages, the amount of seepage was very high (1.70E+06 m3/day). Then, the seepage rate decreased gradually and reached to a constant value (1.12E+05 m3/day). For the reservoir 3D modeling, Seep3D commercial software was used and has shown water seepage discharge of about 1.18E+05 m3/day, means 3% of total reservoir volume. Based on the above-mentioned results and regarding behavior of seepage in the initial impounding stages, sealing element is necessary to prevent from seepage phenomenon. Clay blanket, concrete lining, asphaltic concrete, and geosynthetic are the proposed methods in a large water reservoir. After a feasibility study on various sealing methods, geomembrane was suggested as the best sealing method with the reasonable implementation cost.

Mechanisms of Interaction Between an Arch Dam and Abutment Slope Using Physical Model Tests

In southwestern China, the stability of high-steep slopes in large-scale hydropower projects has become a key technical challenge that constrains the safety of construction and operation. Based on a geological survey of the large-scale rock block in the Jinping-I Hydropower Station left bank, the entire system of the dam and its abutment slope is defined as the study subject. The mechanisms of interaction between the arch dam and the abutment slope during the construction stage, the impoundment stage and the structural plane strength-weakening stage are investigated using physical model tests. (1) During the excavation stage, the early-stage excavation has a significant impact on the huge rock block, whereas the impact of later-stage excavation is relatively small. (2) During the impoundment stage, the dam foundation is under hydraulic load. Therefore, the huge rock block moves away from the slope due to the arch thrust. (3) During the structural plane strength-weakening stage, both sides of the structural planes develop a relative displacement, and the massive rock block slips slightly. Moreover, the strain of the dam is slightly different from the situation in the normal impoundment stage. The majority of the downstream plane is under tension, indicating that a decline in the bedrock strength of the left bank dam abutment results in deformation of the dam towards the mountain body, the riverbed and the top part of the dam crest.

Seasonal variations of carbonic anhydrase activity in Chongqing urban section of Jialing River and its influencing factors

Carbonic anhydrase (CA) is an enzyme in algal carbon-utilization that plays an important role in the formation of algal blooms. A year-long monitoring program in the shore area of Chongqing Urban Section of the Jialing River (JR) was launched to determine the variations in carbonic anhydrase activity (CAA) and its change mechanism in the hydro-fluctuation belt of the tributaries in the Three Gorges Reservoir (TGR) area. The variations in basic water quality parameters, different carbon forms, and CAA were investigated from November 2013 to October 2014. Results showed that the mean CAA value in JR was 0.67 ± 0.31 EU/106 cells. CAA was high during the flood stage, low during the impounding stage, and peaked on April 3, 2014 during the discharging stage. No significant difference was observed in the CAA of different sampling sites in JR. However, a significant difference was observed between the CAA of JR and that of the Yangtze River. Correlation analyses showed that water temperature, pH, algal cell density, and dissoluble organic carbon were positively correlated with CAA, whereas CO2 and dissoluble inorganic carbon were negatively correlated with CAA. A model for CAA and related parameters was built through principal component regression. The equation was expressed as follows: CAA = 0.116T + 0.00746Cells+0.0156pH−0.0157CO2−0.0150DIC+0.0135DOC+0.565. Results revealed that CAA in JR was controlled by multiple factors, which could be used for CAA monitoring. The model demonstrated a potential value in controlling algal blooms.

Stability of macroinvertebrate communities in a newly formed large reservoir with recurrent impoundment events

Limited knowledge was known about the stability of newly formed large reservoirs for laking long-time datasets. We used a decade-long monitoring dataset to examine the stability of macroinvertebrate community in the Three Gorges Reservoir and the impacts of water level fluctuations caused by recurrent impoundment events. We found that the macroinvertebrate community experienced a weak directional change over the ten years. More specifically, the directional change only happened during the initial impoundment stages and the community became relatively stable since the third impoundment stage. The communities were significantly different among the three impoundment stages when the annual water level fluctuation increased consecutively. The temporal variation of the community in the former phase was on account of the increasing water level fluctuation and the intrinsic succession process. The species richness, evenness and production all showed slight increase trends since the third impoundment stage, which implied the stabilization of the community. Nevertheless, influenced by the huge annual water level fluctuations (30 m) and vagaries seasonal floods, the community experienced high stochastic year-to-year variation. Our study suggests that the macroinvertebrate community in the Three Gorges Reservoir has become relatively stable and will keep the stability with high stochastic variation for a long time.

Reservoir-induced landslides and risk control in Three Gorges Project on Yangtze River, China

The Three Gorges region in China was basically a geohazard-prone area prior to construction of the Three Gorges Reservoir (TGR). After construction of the TGR, the water level was raised from 70 m to 175 m above sea level (ASL), and annual reservoir regulation has caused a 30-m water level difference after impoundment of the TGR since September 2008. This paper first presents the spatiotemporal distribution of landslides in six periods of 175 m ASL trial impoundments from 2008 to 2014. The results show that the number of landslides sharply decreased from 273 at the initial stage to less than ten at the second stage of impoundment. Based on this, the reservoir-induced landslides in the TGR region can be roughly classified into five failure patterns, i.e. accumulation landslide, dip-slope landslide, reversed bedding landslide, rockfall, and karst breccia landslide. The accumulation landslides and dip-slope landslides account for more than 90%. Taking the Shuping accumulation landslide (a sliding mass volume of 20.7 × 106 m3) in Zigui County and the Outang dip-slope landslide (a sliding mass volume of about 90 × 106 m3) in Fengjie County as two typical cases, the mechanisms of reactivation of the two landslides are analyzed. The monitoring data and factor of safety (FOS) calculation show that the accumulation landslide is dominated by water level variation in the reservoir as most part of the mass body is under 175 m ASL, and the dip-slope landslide is controlled by the coupling effect of reservoir water level variation and precipitation as an extensive recharge area of rainfall from the rear and the front mass is below 175 m ASL. The characteristics of landslide-induced impulsive wave hazards after and before reservoir impoundment are studied, and the probability of occurrence of a landslide-induced impulsive wave hazard has increased in the reservoir region. Simulation results of the Ganjingzi landslide in Wushan County indicate the strong relationship between landslide-induced surge and water variation with high potential risk to shipping and residential areas. Regarding reservoir regulation in TGR when using a single index, i.e. 1-d water level variation, water resources are not well utilized, and there is also potential risk of disasters since 2008. In addition, various indices such as 1-d, 5-d, and 10-d water level variations are proposed for reservoir regulation. Finally, taking reservoir-induced landslides in June 2015 for example, the feasibility of the optimizing indices of water level variations is verified.

Analysis of phosphorus import characteristics of the upstream input rivers of Three Gorges Reservoir

The phosphorus import of upstream rivers of Three Gorges Reservoir (TGR) significantly affects water environment of TGR. To recognize phosphorus import characteristics of the Yangtze River, the Jialing River, and the Wu River, the accumulated 10-year statistic data (2004–2013) of total phosphorus concentration were analyzed. Two water sampling campaigns at the critical sites in three upstream rivers were carried out in October 2014 and January 2015 to determine phosphorus fractions in water and suspended particulate. The results showed that there were different import characteristics of phosphorus component in three upstream rivers. The phosphorus concentration in water of Wulong site in the Wu Rivers exhibited a sharply increasing trend from 2004 to 2011, and it was much higher than that in the Yangtze River and the Jialing River after 2005. Besides agricultural nonpoint pollutions, these were greatly attributed to phosphorus mine exploitations in the upstream basin of Wu River. In addition, the import of phosphorus fractions from three upstream rivers also showed significant temporal variations. During impounding stage of TGR (October 2014), total particulate phosphorus in water accounted for more than 50 % of total phosphorus (TP); meanwhile, 51 % of phosphorus in suspended particulate were in the form of bioavailable phosphorus, meaning that the potential impact of inputted particulate phosphorus from three upstream rivers on the water environment of TGR cannot be ignored. However, total dissolved phosphorus was the predominant phosphorus fractions in water which accounted for more than 61 % of TP during high water level stage of TGR (January 2015). During this period, large amount of reservoir backwater would flow into the tributaries of TGR; consequently, the inputted dissolved phosphorus could be accumulated in the tributaries and then may provide sufficient nutrients for algal bloom in spring.

Three Gorges Dam alters the Changjiang (Yangtze) river water cycle in the dry seasons: Evidence from H-O isotopes

As the largest hydropower project in the world, the Three Gorges Dam (TGD) has attracted great concerns in terms of its impact on the Changjiang (Yangtze) River and coastal marine environments. In this study, we measured or collected the H-O isotopic data of river water, groundwater and precipitation in the mid-lower Changjiang catchment during the dry seasons of recent years. The aim was to investigate the changes of river water cycle in response to the impoundment of the TGD. Isotopic evidences suggested that the mid-lower Changjiang river water was ultimately derived from precipitation, but dominated by the mixing of different water masses with variable sources and isotopic signals as well. The isotopic parameter “deuterium excess” (d-excess) yielded large fluctuations along the mid-lower mainstream during the initial stage of the TGD impoundment, which was inherited from the upstream water with inhomogeneous isotopic signals. However, as the reservoir water level rising to the present stage, small variability of d-excess was observed along the mid-lower mainstream. This discrepancy could be explained that the TGD impoundment had significantly altered the water cycle downstream the dam, with the rising water level increasing the residence time and enhancing the mixing of reservoir water derived from upstream. This eventually resulted in the homogenization of reservoir water, and thus small fluctuations of d-excess downstream the dam after the quasi-normal stage (2008 to present). We infer that the retention effect of large reservoirs has greatly buffered the d-excess natural variability of water cycle in large river systems. Nevertheless, more research attention has to be paid to the damming effect on the water cycle in the river, estuarine and coastal areas, especially during the dry seasons.

Study on the phosphorus-algal ecological modelling during high water level period in Lake Gaoyang of Pengxi River, Three Gorges Reservoir

The article set up model of phosphorus-algae on the basis of establishing total phosphorus model in early period. From the start of inorganic salts represented by orthophosphate and organophosphorus represented by algal biomass, it analyses at high water level stages, kinds of form transformation and cycle mechanism of accumulated phosphorus due to impounding stage in order to explain the source of the phosphorus which is consumed by the outbreak of water bloom at the end of winter from fixed quantity and fixed nature two parts. The research shows that the total phosphorus of phosphorus pool in the three phases of impounding stage, stable stage and algae bloom stages at high water level in Lake Gaoyang is totally different. Water-level-fluctuating zone with phosphorus release is a major source of solubility reactive phosphorus at high water level in Lake Gaoyang (72.69% of the total input flux), which is related to the area of water-level-fluctuating zone and the phosphorus exchange rate in the soil and water interface of water-level-fluctuating zone. More flooded area, the higher exchange rate of phosphorus, more phosphorus release, the greater contribution of the phosphorus cycle. And the maximum synthetic ratio of phosphorus-algae was only 14.4%. However, the amount of utilized phosphorus at algal bloom stage was small. © 2016 by Journal of Lake Sciences.

The Analysis of Stress, Deformation and Arch Effect of the Lianghekou Earth-rockfill Dam

Deformation, stress and arch effect are problems of interest for high earth- rockfill dams. Deformations and stresses during construction, impoundment and operation stages of Lianghekou earth-rockfill dam were studied through numerical methods. The filling materials were modeled by using the Mohr- Coulomb and Burgers models. As a result, the maximum vertical displacement is located in the middle of the dam height during every stage. The vertical displacement increases evidently during operation stage due to the time dependent behavior of the dam materials. The dam moves in the downstream direction after impoundment. The horizontal displacements of upstream rockfill and downstream rockfill increase during operation stage. The level of arch effect increases evidently after 10 years of operation due to the time dependent behavior of dam materials. The possibility of horizontal cracks and hydraulic fracturing is little during construction stage and impoundment stage, but increases evidently after operation.

Safety evaluation of replacement reinforcement quality in abutment contact zones of ultra-high arch dam in first impoundment period based on prototype monitoring

Reinforcement quality evaluation at the abutment is an important research direction. Prototype monitoring and theoretical derivation were integrated to study the replacement reinforcement quality in abutment contact zones of the Xiaowan ultra-high arch dam. The principles of monitoring layout and design are introduced in detail. Prototype monitoring shows that the increment of the interfacial compressive stress is much larger in the impoundment stage than in the regulating stage. The water pressure and time-effect are two main factors affecting the interfacial stress. The time-effect is the key factor in the initial impoundment stage, and the water pressure is the key factor after impoundment. The contact properties are significantly improved by grouting. This study shows that there are three typical stages in the joint opening hydrographs, namely the compression stage, opening stage, and stable stage. There is a nonlinear relationship between the joint opening and temperature, which can be well described by the S-function. In conclusion, the reinforcement effect is satisfying, and the abutment is safe.

Macroinvertebrate community succession in the Three-Gorges Reservoir ten years after impoundment

The Three-Gorges Reservoir (TGR) is one of the world's largest reservoirs, whose ecological effects have attracted much attention. Focusing on the macroinvertebrate community dynamics and its relationship with hydrological factors ten years after impoundment, we provide an overview of the macroinvertebrate community succession in the TGR including determining factors. Pioneer species in the TGR was Polypedilum scalaenum while Nais inflata became dominant during non-flooding seasons commencing the second impounding year with extremely high relative abundance (up to 97%). An increase of water-level fluctuation range in the third impoundment stage did not significantly alter the steady seasonal pattern of macroinvertebrate community which formed following the second impounding year. MRPP (Multi-response Permutation Procedure) analysis showed significant differences between-season (A<0.3, P < 0.01) except between summer and autumn (A = −0.0165, P = 0.773). Macroinvertebrate assemblages were evidently correlated with inflow discharge during flood seasons and water retention time during non-flood seasons. Macroinvertebrate density showed severe reduction in summer following high velocity inflow current, and disappeared in autumn following vast sedimentation. The macroinvertebrate community gradually became reestablished following reduction of inflow discharge and sedimentation and increase of water retention time in winter and spring. Our analyses suggest that macroinvertebrate community in the TGR is regulated by the subtropical monsoon climate, commencing with seasonal cycles of destruction followed by reestablishment.

Characterization of chromophoric dissolved organic matter and trihalomethane formation potential in a recently constructed reservoir and the surrounding areas – Impoundment effects

Summary The effects of the dam impoundment on the distribution of chromophoric dissolved organic matter (CDOM) were evaluated for a dam reservoir (the Gunwi reservoir) at an early impoundment stage by comparing the characteristics of CDOM and trihalomethane (THM) precursors among the upstream catchment areas, the dam reservoir, and a downstream site. Sampling was conducted for two separate sampling periods of a non-storm event in May and a storm event in August, 2012. The dam reservoir had experienced long-term enrichment of non-biodegradable organic matter since its construction in February, 2010. In May, significant differences were observed in several selected CDOM properties between the upstream catchments and the locations affected by the impoundment (i.e., within the reservoir and the downstream sites). For the storm event, however, such impoundment effects became much less pronounced likely due to elevated input of CDOM with terrestrial origin into the reservoir. Specific THM formation potential (STHMFP) did not show the same spatial distinction as those of CDOM for both sampling periods. Three fluorophore groups were identified from fluorescence excitation–emission matrices (EEMs) of the collected samples by parallel factor analysis (PARAFAC) modeling. Protein-like and microbial humic-like components were relatively more enriched for the impoundment-affected sites compared to the upstream locations, in which terrestrial humic-like component was more dominant. Principal component analysis (PCA) demonstrated that the accumulation of non-biodegradable organic matter in the dam reservoir might be attributed to microbial humification of the algal-derived organic substances originated from either periphytons flushed from upstream stream beds or decomposing algae settled on the bottom of the reservoir, or both.

Reservoir Induced Seismicity Types in the Three Gorges Project

Reservoir Induced Seismicity(RIS) is a common phenomenon needed to be focused in the construction and operation of water conservancy project. The Three Gorges reservoir has a digital telemetry seismic network to monitor the earthquakes in this region. According to the correlation between water impoundment and earthquakes, the reservoir induced seismicity can be divided into rapid response and delayed response. The two types can be found in the Three Gorges area as well. In 2003, soon after the first stage of water impoundment, micro earthquake swarm occurred, which is so called rapid response type and water loading is the main factor. And delayed effect is the most observed phenomenon in RIS, in which pore diffusion controls the earthquakes. Double difference relocation results show that the earthquakes can be generally divided into three regions. And the earthquakes controlled by the active faults are called tectonic type RIS, while those related with karst, landslide, etc are nontectonic type. In region A, some earthquakes are related with the Gaoqiao active fault, and some have relationship with karst. The earthquakes in region B are controlled by some coalmines, landslide, and so on. And the earthquakes in region C belong to tectonic type RIS, which have certain relationship with the Xiannvshan fault and Jiuwanxi fault. Different RIS types have different mechanisms and controlling factors, furthermore have different earthquake trending.

Evaluation of the performance of the face slab of a CFRD during earthquake excitation

The primary goal of this study was to examine the cracking behavior of the face plate of a CFRD during earthquake excitation. Analyses of the impounding stage and earthquake loading were conducted in sequential phases using a 2-D plane-strain model with the appropriate non-linear constitutive relationships for the dam constituents. The effect of rockfill stiffness and the face plate design properties on the seismic performance of the face plate was investigated. The crack widths on the plate increased with earthquake shaking. Settlement of the fill during intense seismic excitation counteracted this phenomenon by causing compression on the plate at some locations.

Prediction of and early Warning for Deformation and Stress in the Xiaowan Arch Dam during the First Impounding Stage

A hybrid prediction model based on the simulation of the complete process in high arch dams is proposed because of capacity shortage in the prediction of and early warning for deformation and stress in such dams during the first impounding stage. An early warning system for dam body deformation as well as dam heel and dam toe stress is established in this model. The warning thresholds are also clarified. Applications in the first impounding stage of the Xiaowan Arch Dam show that the model is practical and effective, and can provide highly accurate predictions. Early warning indicator thresholds for deformation and stress are reasonably set to provide warnings for abnormal situations. The model provides accurate predictions and effective warning methods for the safe impounding and operation of high arch dams.

Behaviour of the reinforced concrete face slabs of concrete faced rockfill dams during impounding

The primary goal of this study was to examine the relative effects of various factors that affect the cracking of the face slab of a concrete faced rockfill dam (CFRD). Rigorous simulation of the construction and impoundment stages were conducted in sequential phases during which the rockfill and the rockfill-face slab interface were modelled with elasto-plastic models that were calibrated to existing test data. The face slab was modelled using embedded reinforcements with a total strain crack model. The results of the analyses showed that the stiffness of the rockfill significantly changed the crackwidth on the face slab, but not the extent of cracking. Increasing the reinforcement ratio was the most effective remedy for decreasing the average crack width on the slab. The properties of the rockfill-slab interface and the location of the reinforcement within the slab did not significantly affect the cracking on the slab.

Using artificial neural network (ANN) in prediction of collapse settlements of sandy gravels

Collapse settlement is one of the main geotechnical hazards, which should be controlled during first impoundment stage in embankment dams. Imposing large deformations and significant damages to dams makes it an important phenomenon, which should be checked during design phases. Also, existence of a variety of contributing parameters in this phenomenon makes it difficult and complicated to well predict the potential of collapse settlement. Thus, artificial neural networks, which are commonly applied by majority of geotechnical engineers in predicting various perplexing problems, can be efficiently used to calculate the value of collapse settlement. In this paper, feedforward backpropagation neural networks are considered. And three-layered FFBPNNs with the architectures of 4–6–2 and 4–9–2 accurately predicted the coefficient of stress release and collapse settlement value, respectively. These networks were trained using 180 datasets gained from large-scale direct shear test, which were carried out on gravel materials. High correlation between measured and predicted values for both collapse settlement and coefficient of stress release can be easily understood from the coefficient of determination and root mean square error. It is shown that sand content and normal stress applied to the specimens, respectively, are most effective parameters on the collapse settlement value and coefficient of stress release.

Spatial Distribution of Macroinvertebrate Community along a Longitudinal Gradient in a Eutrophic Reservoir‐Bay during Different Impoundment Stages, China

AbstractThe longitudinal patterns of the macroinvertebrate community in the Xiangxi Bay of the Three Gorges Reservoir (TGR) were investigated during the second (2nd) and third (3rd) impoundment stages (October 2006–July 2010), to test the effects of increased water level fluctuations (WLF) on the macroinvertebrates. By comparing to the former reports of the first (1st) impoundment stage (inter‐annual WLF 4 m), we found that oligochaetes dominated in three different stages in the Xiangxi Bay. However, the total abundance of macroinvertebrates showed a dramatical decline from the 1st to 2nd stage (inter‐annual WLF 11 m), but changed slightly from the 2nd to 3rd stage (inter‐annual WLF 30 m). This indicated that higher WLF in the 2nd stage had already greatly reduced the macroinvertebrates abundance, thereby the disturbance in the 3rd stage could only slightly affect the already reduced abundance. Three longitudinal zones (the mainstream zone, the lacustrine zone and the transitional zone) were found based on the macroinvertebrate density, biomass, and taxa richness, combined with the geographical location of each site. Significant differences in density and biomass of macroinvertebrate were found among different zones (P &lt; 0.05), yet no significant difference was found in taxa richness (P &gt; 0.05). Two‐way indicator species analysis showed that the community type in most sites varied in different seasons from the 2nd stage, exhibiting a dynamic zonation pattern, which differed with the stable pattern of the 1st stage. This seasonal feature was coupled to the seasonal changes of the WLF. (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Investigation and treatment of post-construction incidents at Satpara Dam

During the initial 5 years, spanning over the partial impounding stages of the Satpara Dam project, two independent post-construction incidents were observed at the project. This paper describes in detail the methods of investigation and treatment conducted for the unusual development of depressions observed slightly upstream of the main dam axis, and sinkholes observed upstream of the project area. The former incident was limited within the shell/shoulder zone and rehabilitated subsequently. The second incident was interconnected with a subsurface subsidence and its subsequent treatment was considered to induce self-healing within the natural foundations over time.

Changes in water types under the regulated mode of water level in Three Gorges Reservoir, China

The creation of a reservoir is often the most serious impact of damming on upstream river ecosystems, which may cause the dramatic change of water types. A giant subtropical reservoir (Three Gorges Reservoir, TGR) formed by the construction of Three Gorges Dam (TGD) has experienced three impoundment stages. According to the combined classification criterion of reservoir water quality management, a study of monthly change of water types was conducted in the mainstream and Xiangxi Bay of TGR from Jun. 2003 to Dec. 2009. Due to the rise of water level from the first stage to the last stage of impoundment, dramatic changes of water types were found during non-flood season for the mainstream, and during most months of the year for Xiangxi Bay. Under the planned mode of water operation, the mainstream would still be characterized by full mixing during the season of algal growth, which prevents the development of algal blooms, even though it experiences extreme drought events. However, Xiangxi Bay is characterized as a stable system similar to natural lakes (e.g., thermal stratification), which may contribute to the development of algal blooms, especially in years of extreme drought.