01 July 2023, Volume 40 Issue 7

    

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  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 0-0.

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River-Lake Protection and Regulation
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  Ecological Flow Involving Water Quantity and Water Quality: Case Study on Xinzhou Segment of Jushui River

  ZHANG Yun-chao, CHAI Zhao-hui, WANG Jia-sheng, ZHU Kong-xian, MIN Feng-yang

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 1-7. https://doi.org/10.11988/ckyyb.20220483

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  The governance and protection of lake and river water environment require the consideration of both the quantity and quality of water to preserve ecological flow. In this study we examine the Xinzhou segment of the Jushui River, a tributary of the Yangtze River, using the MIKE11 software to develop a water quantity and quality model. The model was calibrated using measured data and data from pollution source investigations. The model measured the main pollutants including COD, NH₃-N, TN, and TP, and established the water demand for control sections to meet water quality standards on a monthly basis with consideration of current sewage discharge levels. In addition, we utilized the Tennant method and flow frequency curve method to calculate the ecological water demand to ensure the basic stability of the river ecosystem. By comparing and analyzing the results of Tennant method, flow frequency curve method, and the proposed model, we obtained the monthly ecological water flow for the Xinzhou segment of Jushui River.
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  Variation of Bed-forming Discharge and Its Influencing Factors in the Inner Mongolia Reach of the Yellow River

  WANG Ke-zhi, LIU Xiao-min, ZHANG Hong-wu, ZHANG Xiao-hua

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 8-15. https://doi.org/10.11988/ckyyb.20220317

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  Bed-forming discharge is an important index characterizing the erosion and deposition of river beds, and is also a key parameter for river management. Based on measured data from 1960 to 2019, we calculated and analyzed the bed-forming discharge at four hydrological stations, namely, Shizuishan, Bayangol, Sanhuhekou, and Toudaoguai, using the improved Makaviev method, bank-full level method, and geomorphology work method. In 1960-1989 and 2010-2019, the bed-forming discharge ranged between 2 100 m³/s and 3 540 m³/s, indicating medium scouring, while in 1990-2009, the bed-forming discharge was 740-1300 m³/s, reflecting severe deposition. In spatial scale, bed-forming discharge was larger in the upper reach stations compared to the lower reach stations. Bed-forming discharge is significantly influenced by the amount of incoming water. When the water inflow during flood season is less than 10.5 billion m³, properly increasing the inflow by jointly dispatching the three reservoirs in Liujiaxia, Longyangxia, and Haibowan during flood season could appropriately augment bed-forming in the Inner Mongolia reach of the Yellow River. Results manifest that the physical meaning of the improved Makaviev method is clear and the calculation results are relatively reasonable.The research results provide important implications for determining the alluvial river bed-forming flow and channel management in the Inner Mongolia reach of the Yellow River.
Water Resources
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  Discussion on Transprovincial Horizontal Ecological Compensation Mechanism of the Mainstream Yangtze River

  YIN Zheng-jie, ZHUANG Chao, CHEN Jin

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 16-21. https://doi.org/10.11988/ckyyb.20221394

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  The Yangtze River, known as the mother river of the Chinese nation, plays a crucial role in establishing a trans-provincial ecological compensation mechanism in the Yangtze River Basin. This mechanism holds great significance in harmonizing the interests between the ecological protection areas and the beneficiary regions, thereby fostering high-level ecological conservation and promoting sustainable development within the basin. Focusing on the mainstream of the Yangtze River, we propose a conceptual framework for trans-provincial ecological compensation based on water quality and quantity. We delve into the essential components, compensation standards, fund allocation, monitoring and assessment indicators, as well as the safeguarding system of trans-provincial ecological compensation. Furthermore, we conduct a case study to illustrate the application of trans-provincial ecological compensation in the main stream of the Yangtze River using the 2018 data. The findings reveal that the primary contributing provinces (autonomous regions, municipalities) to the trans-provincial ecological compensation in the main stream of the Yangtze River are Jiangsu, Shanghai, and Anhui, while the provinces (autonomous regions, municipalities) receiving the compensation include Sichuan, Qinghai, Yunnan, Tibet, and Jiangxi. These results demonstrate the compensation relationship between downstream provinces, benefiting from the protective measures taken by upstream provinces in the Yangtze River main stream. We suggest that a comprehensive trans-provincial ecological compensation mechanism should be established at the basin-wide level, involving the simultaneous participation of multiple provinces (autonomous regions, municipalities). Initially, water quality and quantity can be considered as fundamental compensation factors, and over time, the range of compensation factors can be gradually expanded, alongside the enhancement of compensation evaluation standards and the refinement of the ecological compensation safeguarding system.
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  Simulation on the Impact of Large-scale Eucalyptus Plantation on Runoff in Watershed

  HUANG Feng-hua, HUANG Ben-sheng, HONG Chang-hong, QIU Jing

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 22-26. https://doi.org/10.11988/ckyyb.20220214

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  Eucalyptus is widely planted as an economic forest in the humid regions of southern China due to its fast growth rate, adaptability, and high economic benefits. However, the impact of large-scale eucalyptus plantations on water resource amout and floods has become a major concern. To examine this issue, a distributed hydrological model with physical mechanisms was constructed for the Liuxihe reservoir watershed in Guangdong Province. Scenario analysis method was applied to simulate the impact of land surface pattern under different eucalyptus plantation scenes on water resource amout in the watershed. The study found that large-scale eucalyptus plantation reduces annual water resource amout compared to common tree species such as natural mixed forest. For every additional 10 000 hectares of eucalyptus plantation, the annual water resource amout can be reduced by approximately 22 million m³. Although the impact on floods is less pronounced and the flood process under different eucalyptus planting scenes are basically the same, the flood peak flow changes are relatively significant. For every 10 000 hectares of eucalyptus plantation, the flood peak flow can be increased by approximately 10 m³/s. Overall, the large-scale planting of eucalyptus aggravates the loss of water resources, increases the peak flow of floods, and raises the risk of flood and drought disaster prevention.
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  Correlation Analysis of Karst Groundwater Level, Precipitation and Yellow River Water Level in Changqing District, Jinan City

  QI Huan

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 27-31. https://doi.org/10.11988/ckyyb.20220176

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  To explore the correlation between karst groundwater level, precipitation, and Yellow River water level in Changqing District, Jinan City, we utilized long-term monitoring data of four karst groundwater levels in the Changqing-Xiaolipu hydrogeological unit from 2007 to 2019, alongside data on precipitation and Yellow River water level during the same period. By applying wavelet coherence and multiple wavelet coherence methods to analyze the data, we found the following results: 1) There are significant continuous or discontinuous one-year and half-year high-frequency main oscillation cycles in the dynamics of karst groundwater level. 2) The average wavelet coherence (AWC) and percent area of significant coherence (PASC) mean values between karst groundwater level and precipitation are 0.47 and 20.64%, respectively. The mean AWC and PASC between groundwater level and Yellow River water level are 0.42 and 13.00% respectively. Precipitation has a greater impact on groundwater level than the Yellow River water level. 3) The multiple wavelet coherence (MWC) between karst groundwater level and precipitation and Yellow River water level in Guangli Village of Xiaoli Town and Guide Town-Wenchang Street area increased by at least 5% compared to AWC, indicating that the karst groundwater level in this area is affected by both precipitation and Yellow River water level. These research findings are highly significant for further understanding the transformation relationship among precipitation, surface water, and groundwater. Furthermore, our findings could potentially benefit spring protection and water supply along the Yellow River in Jinan.
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  Evaluating the Ability of CMIP6 Models in Simulating Precipitation and Temperature in Wanzhou City in the Three Gorges Reservoir

  LI Jia-wen, ZHOU Yu-lin, WEI Xing, FANG Zu-jin

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 32-40. https://doi.org/10.11988/ckyyb.20221072

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  To accurately predict the hydrometeorological trends of the Three Gorges reservoir area and provide a scientific basis for rational allocation of water resources, we evaluate the adaptability of 12 CMIP6 (Coupled Model Intercomparison Project Phase 6) global climate models and a multi-model ensemble (MME) to the city of Wanzhou. The evaluation includes analysis of seasonal monthly average precipatation and air temperature, mutation years, and comprehensive simulation abilities using mean value analysis, Mann-Kendall tests, Taylor diagrams and Taylor scores. Our results show that: (1) ACCESS-CM2 models yield better precipitation simulation results prior to impoundment, while MME models show superior performance post-impoundment. (2) MME produces superior temperature simulation results before impoundment, while ACCESS-CM2 exhibits better performance after impoundment. (3) Overall, ACCESS-CM2 demonstrates the best temperature and precipitation simulation results both before and after impoundment.
Water Environment and Water Ecology
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  Hydrogen and Oxygen Isotopes and Hydrochemical Characteristics of Water in Pingzhai Reservoir

  XIE Jiang-ting, ZHOU Zhong-fa, WANG Cui, KONG Jie, LI Yong-liu, WEN Chao-cheng

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 41-49. https://doi.org/10.11988/ckyyb.20220235

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  To investigate the influence of upstream rivers on the water body in Pingzhai Reservoir, water samples were collected from the inlet river and the reservoir area of Pingzhai Reservoir, as well as in the Sancha River Basin, in January and July 2020. The hydrochemical parameters and stable isotopes of the water samples were analyzed by using mathematical statistics, Durov plots, correlation analysis, and spatial interpolation. The spatiotemporal distribution characteristics and their causes were preliminarily explored. The study show that: (1) The hydrochemical characteristics of the reservoir water are highly influenced by the supply rivers, and the hydrochemical pattern of reservoir water is consistent with that in the basin, mainly HCO^-₃-Ca²⁺, with the ion concentration being higher during dry season than wet season. (2) The δD and δ¹⁸O of the water were linearly related, and the isotopes exhibit high values in summer and low values in winter. The reservoir water is supplied by precipitation on one hand, and is affected by karst groundwater on the other, thus displaying different seasonal variation characteristics from those of precipitation. (3) The hydrogen and oxygen isotopes of the water in both the reservoir and the basin are mostly distributed along the meteoric water line; however, the slope and interception values are smaller than global meteoric water line and local meteoric water line, indicating strong evaporation fractionation despite dominant supply from precipitation. (4)During wet season, the hydrogen and oxygen isotopes of the basin and the reservoir water are significantly correlated with ion concentration, while in dry season, the water bodies in the lower reaches and the reservoir are notably influenced by precipitation, and the upper reaches by evaporation.
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  Simulation of Non-point Source Pollution in Danjiangkou Reservoir Basin Based on Coupled Improved Output Coefficient Method and SWAT Model

  ZHAI Wen-liang, TANG Jian, WANG Cheng-gang, LI Xiao-meng, ZHAO Ke-feng

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 50-58. https://doi.org/10.11988/ckyyb.20220184

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  This study aimed to evaluate more accurately the characteristics of non-point source pollution in the Danjiangkou Reservoir basin following the water supply of the middle route of the South-to-North Water Transfer Project. The aim was also to improve the accuracy of SWAT model in simulating non-point source pollution. To accomplish this, we coupled the improved output coefficient method and SWAT model to conduct a comprehensive simulation on the process of multi-type non-point source pollution entering the river. First, the improved output coefficient method estimated the load of TP, TN, and other pollutant indicators related to livestock and poultry, rural life, and aquaculture pollution in three stages from generation, loss, to entering the river. Second, the SWAT hydrological model comprehensively simulated and analyzed the temporal and spatial distribution characteristics of non-point source pollution in the Danjiangkou Reservoir basin in 2019. The pollution from livestock and poultry breeding, rural life, and aquaculture industries was generalized at the county level and added to the SWAT Model in the form of point sources. The model's hydrological parameters were calibrated and verified for accuracy with Hanjiang River, Danjiang River and Laoguan River basins as reference basins. Results reveal that, in the Danjiangkou Reservoir basin in 2019, the loss of TN and TP was 275 600 tons and 18 600 tons, respectively. The inflow of TN and TP into the river was 33 100 tons and 2 400 tons, respectively. The planting industry was the primary contributor to both TN and TP inflow, accounting for 72.45% and 64.97%, respectively. The amount of TN and TP entering the river was greatest in Hanbin District, Xunyang County, Yunyang District, Yangxian County, and Xixiang County, while the smallest was recorded in Shangzhou District, Fengxian County, Zhangwan District, Taibai County, Lueyang County, and Liuba County. The contribution rate was the highest in May and the lowest in October. The research findings provide scientific basis for the comprehensive management and control of non-point source pollution in the Danjiangkou Reservoir basin.
Soil and Water Conservation and Ecological Restoration
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  Analysis of Soil Erosion Control Based on China Soil and Water Conservation Bulletin in the Past Two Decades

  WANG Yi-feng, QU Li-qin, LI Jian-ming, LI Li

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 59-65. https://doi.org/10.11988/ckyyb.20220681

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  Soil and water conservation plays a crucial role in the construction of ecological civilization. It is also an important indicator that reflects the balance between economic and social development and ecological environment quality. Based on the China Soil and Water Conservation Bulletin published over the past two decades, we analyze the current status of soil and water loss in China, summarize the progresses made in soil and water conservation, and scrutinize the causes of dynamic changes in soil and water loss as well as the effectiveness of soil and water conservation efforts. Our research reveals that: 1) in 2020,the soil erosion area in China reduced by 26.6% from the late 1980s and 24.4% from the beginning of the 20th century; 2) before 2011, soil erosion was moderate or severe, but from 2018, the erosion intensity significantly decreased, and the mild loss area accounted for more than 60%; 3) comprehensive treatment of soil erosion is the primary contribution to the reduction of soil erosion area. Over the past 20 years, the annual sediment discharge of eleven major rivers decreased by 72.4%, and the annual sediment load was significantly negatively correlated with the cumulative soil erosion control area (R²=0.90). At present, China's soil and water conservation efforts are advancing from “surface” to “point” and are moving towards high-quality development. The research results provide quantitative data and theoretical foundations for evaluating soil and water conservation work and promoting high-quality development of soil and water conservation in China.
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  Spatio-temporal Evolution of Net Primary Productivity in Beijing-Tianjin-Hebei Region Based on MOD17A3 Data

  GUO Hao, YUAN Jin-guo, WANG Jing-zhi, WANG Xiao-xin, LI Yan-cui, LIU Bo-han

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 66-72. https://doi.org/10.11988/ckyyb.20220164

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  This study explores the spatio-temporal changes in vegetation net primary productivity (NPP) across the Beijing-Tianjin-Hebei region based on MOD17A3 data. Univariate linear regression method was employed to analyze the temporal and spatial evolution of vegetation NPP in 20 years (2000-2019). Additionally, this study analyzed the correlation between NPP and climate factors. The results show that vegetation NPP in the Beijing-Tianjin-Hebei region mainly falls within the range of 200-400 gC/(m²·a). The mean and maximum values of NPP exhibited gradual increase from 2000 to 2019, with a peak in both mean and maximum values occurring in 2016 at 385.10 gC/(m²·a) and 908.40 gC/(m²·a), respectively. The area with significantly increased NPP in the region from 2000 to 2019 was found to account for 97.12% of the study area, while the area with NPP decrease mainly occurring in areas surrounding urban centers. Furthermore, the four types of vegetation cover in the region ranking from smallest to largest in terms of NPP mean were as follows: cropland, shrub, grassland, and forest. The study also found that from 2000 to 2019, the stability of NPP in the region was characterized by high-low fluctuations, with lower fluctuations being dominant. Finally, NPP was found to be lowly correlated with the average annual temperature and highly correlated with annual precipitation. The findings can serve as reference for ecological civilization construction, ecological environmental restoration, and management and protection in Beijing-Tianjin-Hebei region.
Water-related Disasters
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  Research Framework and Prospect for Monitoring and Early Warning of Rainstorm-induced Mountain Torrent Disaster Chain

  TANG Wen-jian, FAN Zhong-jie, DONG Lin-yao, LIU Ji-gen, ZHANG Ping-cang, LI Tong-lu, TONG Guan-jun, DU Jun, WANG Lin

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 73-79. https://doi.org/10.11988/ckyyb.20220469

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  Rainstorm-induced flash floods and their associated chain disasters pose a common threat in mountainous areas. Their wide distribution, complex causes, and characteristics of abrupt, localized, and hidden occurrence increase the difficulty of disaster identification, monitoring, and prediction in the early stages. At present, research on the transformation mechanism and monitoring and early warning systems of mountain torrent disaster chains is an international frontier and hotspot issue in the field of disaster prevention and mitigation, which demands comprehensive interdisciplinary approaches. To address this challenge, we summarize the status and trends of domestic and foreign research on rainstorm-induced mountain torrent disaster chains, analyze the key scientific and technical issues that require breakthroughs, and proposes corresponding research directions and prospects. Key scientific and technical issues that urgently need to be tackled include: revealing the homologous chain transformation mechanism between rainstorm, flood, landslide (collapse), and debris flow; establishing accurate monitoring and stable transmission technology for disaster chains; and constructing an early warning index system and dynamic warning platform for disaster chains. Proposed research directions are as follows: identifying disaster-causing factors, developing monitoring and early warning technologies for key elements of the disaster chain, building monitoring and early warning platforms for mountainous small watersheds, and integrating and demonstrating monitoring and early warning technologies. Research prospects involve a multidisciplinary and multi-method approach, targeting “disaster-causing factor identification, key technology development, software platform construction, and integrated application demonstration” as the main research thread, and ultimately achieving breakthroughs and innovations in driving and evolving mechanisms of disaster chains, precise monitoring, and dynamic warning technology. The expected results can provide scientific and technological support for improving the defense capability against mountain torrent disaster chains and promoting sustainable ecological development and high-quality development of watersheds.
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  Temporal and Spatial Evolution Characteristics and Influencing Factors of Mountain Torrents in Chongqing

  ZHANG Qian-zhu, LU Yang, YAN Tong-jin, XIE Qian, ZHAO Cha, HU Yue

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 80-87. https://doi.org/10.11988/ckyyb.20220249

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  Based on investigations of mountain torrents in 2013-2015 and 2016-2019, this study analyzes the temporal and spatial characteristics of 831 historical mountain torrent disasters in Chongqing. The spatial changes of mountain torrent disasters are researched using an ArcGIS gravity model and the standard deviation ellipse model, while the driving factors are identified using the geographic detector model. The frequency of disasters can be divided into three stages based on statistical analysis of disaster frequency over time: a low-frequency period from 1926 to 1977, a low-frequency fluctuation period from 1977 to 2006, and a high-frequency fluctuation period from 2006 to 2017, which is related to literature records, rainfall conditions, and social and economic development. Wavelet analysis shows that the mountain flood disasters in recent years change periodically every 3.7 years. Despite of increased frequency of disasters since 2000, the number of deaths and missing persons due to disasters has stabilized, reflecting the effectiveness of mountain torrent prevention and control measures. The disasters concentrated in the Pengshui and Wulong areas in Southeast Chongqing in May and moved northward in June. After July, the focus of disasters moved westward to west Chongqing and then gradually forward to northeast Chongqing from August to September. The geographic detector model analysis shows that the river network density and elevation factors have a significant impact on mountain flood disasters. After the superposition of each factor, the release force increases non-linearly. This study comprehensively summarizes the historical patterns of mountain torrents in Chongqing, providing important insights into the temporal and spatial evolution pattern of mountain torrents and their driving factors in Chongqing. The results could provide technical support and theoretical guidance for mountain torrent prevention and control.
Agricultural Water Conservancy
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  Simulation of Groundwater Level in Irrigation Area Based on Sky-Earth Cooperation and Deep Learning

  CHEN Wen-long, YANG Yun-li, ZHANG Yu, HU Zu-kang

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 88-95. https://doi.org/10.11988/ckyyb.20220061

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  In this study, we aim to simulate the groundwater level in irrigation area by utilizing sequential observation data from ground-based and remote sensing platforms. A deep learning model based on a multi-layer GRU network was developed for this purpose. Precipitation, soil moisture, historical measurements of groundwater levels, and Sentinel-2 remote sensing observations were used as simulation factors. Furthermore, groundwater level simulation experiments and result analyses are conducted for two irrigation areas located in North and South China. The experimental findings reveal that the groundwater level simulation model, which incorporates the synergy between sky-earth observations and deep learning, effectively establishes the intrinsic relationship between external environmental factors and groundwater levels within the irrigation area. The model is apparently superior to comparative models that merely considers groundwater level as it demonstrates impressive simulation performance, exhibits applicability in diverse geographical environments, and holds promising potential for practical applications. It can provide valuable decision-making support for crop cultivation and water resources management in irrigation area.
Rock-Soil Engineering
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  Experimental Study on Three Point Bending of Granite after High Temperature Quenching and Thermal Cycling

  ZHANG Fan, LÜ Dun-bo

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 96-103. https://doi.org/10.11988/ckyyb.20220153

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  High temperatures have a significant impact on the mechanical properties of rocks in geothermal reservoirs. To investigate the influence of high temperature on the fracture toughness of Type I granite, three-point bending tests were conducted on semi-circular bending (SCB) samples of granite subjected to cyclic high-temperature quenching at 400 ℃ for different numbers of cycles (1, 3, 5, and 7 cycles). The failure characteristics, load-displacement curves, and fracture toughness of the granite specimens after cyclic high-temperature quenching were also analyzed. Results demonstrate that as the number of thermal cycles increases, the mass and density of granite gradually decrease, the peak load continuously declines, the roughness of the fracture surface progressively intensifies, and the fracture toughness noticeably reduces. These findings provide a theoretical basis for the development of geothermal energy and the safety of underground engineering structures.
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  Calculation of Frost-Heaving Deformation and Internal Force for Trapezoidal Canal on Pasternak Frozen Soil Foundation

  XIAO Min, WANG Zheng-zhong, WU Lang, YANG Xiao-song, CUI Hao, GE Jian-rui

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 104-109. https://doi.org/10.11988/ckyyb.20220158

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  To address the limitations of the existing Winkler model which fails to account for the continuity of frozen soil in the channel bed, we introduce the Pasternak shear layer to describe the interaction between independent soil springs, and further develop a novel analytical method for analyzing the mechanics of frost heave in trapezoidal channels with a frozen permafrost foundation. Analytical formulas are derived for the normal stress on contact surface, the frost heave displacement of lining plates, and the internal force distribution within the cross-section of a trapezoidal channel with uniformly frozen foundation soil and no top cover constraint. With a trapezoidal channel in Gansu Province as a case study, we compare the calculated results of frost heave displacement of the lining plates and the distribution of normal stress on the contact surface obtained from our proposed model with those from the Winkler model. The results demonstrate a good agreement between our model and the observed values, indicating that our model provides a more accurate representation and is closer to the actual observations compared to the Winkler model. This highlights the rationality and reliability of our proposed model. Moreover, the model effectively captures the dynamics of normal frost heave force, including its release and attenuation in response to the deformation of the lining plates. It also accounts for the non-linear and differential distribution of the normal frost heave force on the middle and lower parts of the slope plate, the tendency for detachment and uplift in the middle and upper parts due to the action of normal freezing force, and the exclusive impact of normal frost heave force on the bottom plate. These research findings offer valuable insights and serve as a practical reference for the design of frost heave resistance in trapezoidal channels.
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  Numerical Manifold Method for Unbounded Domain Problems

  WANG Fang-yi, ZHENG Hong

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 110-117. https://doi.org/10.11988/ckyyb.20220114

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  Since its invention, the Numerical Manifold Method has been applied to the analysis of a wide variety of problems, including the analysis of structures, seepage flow, and crack propagation. These problems typically involve bounded domains, or interior problems. However, for problems such as underground and surface structures, wave propagation, and other unbounded domain problems or exterior problems, the behavior of field variables in the far field needs to be considered in the numerical solution process. In this study, we constructed a finite element cover and weight functions suited to unbounded domain problems using the Numerical Manifold Method. With consideration of the asymptotic behavior of field variables at infinity, a local approximation was constructed to approach the behavior of the infinite domain. Unlike the shape function of infinite elements in the finite element method, the weight function in our proposed method only needs to satisfy the partition of unity, while the local approximation needs to approximate the behavior of the field variables, which makes the approximation of field variables more reasonable. The results from numerical examples demonstrate that the proposed method is effective and yields accurate results with fewer elements.
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  A Seepage Model for Slopes with Soft Interlayers in Consideration of Equivalent Fracture Surfaces

  ZHONG Zhuo-xi, SHENG Jian-long, HU Bin, LI Jing, WANG Ting-yuan

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 118-124. https://doi.org/10.11988/ckyyb.20220019

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  The key to researching the seepage characteristics and stability of slopes containing soft interlayers is to construct a reasonable seepage model. On the basis of saturated-unsaturated seepage-stress coupling theory, we established a slope seepage model by assuming that the intersection surface between soft interlayers and upper rock mass is equivalent to a single fracture surface of certain width. The modelling result is in general consistent with the simulation results of classical saturated-unsaturated model in terms of the seepage characteristics of slopes with soft interlayers under rainfall conditions. The permeability coefficient of the equivalent fissure surface at the foot of the slope grows rapidly, which is more consistent with the actual growth of the slope permeability coefficient. By comparing the curve of stability coefficient between the proposed model and classical model, we found that the inflow of the equivalent fissure surface has a significant influence on the stability coefficient of slopes with soft interlayers. The model offers a basis and reference for the design of slopes with soft and weak inclusions in practical projects.
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  Influence of Salt Solution on Drying Shrinkage Characteristics of Bentonite

  LI Jing, LIU Qing-bing, ZHENG Peng-ling

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 125-131. https://doi.org/10.11988/ckyyb.20220160

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  As a major buffering backfill material for high-level radioactive waste disposal repository, bentonite is affected by soluble salts in groundwater and thermal energy generated by nuclear waste decay, leading to drying shrinkage. Studying the drying shrinkage characteristics of bentonite under the influence of salt solutions is crucial to rationally evaluate its engineering performance. Constant-temperature drying shrinkage tests were carried out on bentonite from Gaomiaozi under the exposure of NaCl and CaCl₂ solutions with concentrations of 0.5, 1.0 and 2.0 mol/L, respectively. The influence of salt solutions on the drying shrinkage process of compacted bentonite was analyzed. Results show that the higher the salt solution concentration, the lower the initial saturated water content and the higher the residual water content of the sample, indicating a lower water evaporation rate. Meanwhile, the effect of Ca²⁺ on water evaporation is greater than that of Na⁺. During the drying process, the surface fissures of compacted bentonite exhibit four stages, namely fissure opening, fissure maintenance, fissure closure, and fissure stability. Salt solutions could inhibit the cracking of soil mass, and the higher the concentration, the smaller the surface crack ratio of the sample. Salt solutions can change the microstructure of bentonite from a dispersed viscous particle form to an aggregated structure, thereby reducing the shrinkage strain and weakening the anisotropy of the shrinkage. As the concentration and cation valence of salt solutions increase, the volume shrinkage strain ε_vf induced by the decrease of unit water content increases.
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  Strength and Micromechanism of Arsenic-bearing Sandstone-Steel Slag Powder Cement Composite Soil under Alkali Excitation

  WANG Chong-yang, LI Xiao-li, ZHAO Xiao-ze, YANG Jian

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 132-138. https://doi.org/10.11988/ckyyb.20220928

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  The study aims to reduce soil and water loss in arsenic-bearing sandstone areas and promote the effective utilization of steel slag powder and arsenic-bearing sandstone in practical engineering applications. The effects of substitution rates and alkali equivalents of steel slag powder on the macro-mechanical properties and microstructure of arsenic-bearing sandstone-steel slag powder cement composite soil were investigated using unconfined compressive strength tests, X-ray diffraction (XRD), scanning electron microscopy, high-resolution three-dimensional microscopy and mercury intrusion porosimetry tests. Results show that under high-temperature alkali excitation, the gel and ettringite generated by the hydration of steel slag powder contribute less to the enhancement of composite soil than the cement does, which leads to a reduction in compressive strength of the composite soil with increasing substitution rate of steel slag powder. Increasing the dose of alkali activator promotes the generation of hydration products from steel slag powder, making it more effective in binding soil particles and filling internal pores. This results in a more uniform surface structure and a denser internal structure of the composite soil, which enhances its compressive strength. The best effect was observed when the alkali equivalent was 2%. The results provide a theoretical basis for the practical application of arsenic-bearing sandstone-steel slag powder cement composite soil in engineering.
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  Mechanical Characteristics of Soft and Hard Interbedded Rock Mass under Dynamic Load

  YAO Zhong-shao, LI Long-qi, HU Zhong-liang, XU Lei, HUANG Yang, HE Chuan

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 139-145. https://doi.org/10.11988/ckyyb.20220287

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  This study investigates the failure behavior of soft-hard interbedded rock mass under dynamic loading conditions in the Shuimogou landslide area of Wenchuan, using soft-hard interbedded rock specimens created according to the similarity theory. Cyclic loading tests involving uniaxial compression and variable upper and lower limits were carried out to explore the dynamic characteristics and failure process of the specimens. The results show that the failure modes include tensile failure (0°-30°), shear failure (45°-75°), and cleavage failure (90°), depending on the dip angle of the rock layer. For specimens with the same inclination angle, strength increases with loading frequency and confining pressure, while strain decreases with the former but increases with the latter. In addition, higher loading frequency leads to the transfixion of vertical tension cracks and the decrease of fracture degree.
Engineering Safety and Disaster Prevention
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  Early Warning Criterion for Debris Flow Based on Iterative Approximation of Rainfall

  HOU Yan-jun, TIAN Wan-ting, KANG Yong-qiang

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 146-151. https://doi.org/10.11988/ckyyb.20220156

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  In this research we aim to obtain a more reliable early warning criterion for debris flow universal equipment, improve the early warning accuracy of monitoring equipment for hidden dangers of geological disasters at single point, reduce false alarm rate, and improve the capability of grassroots organization to prevent and respond to geological disasters. We propose a rainfall iterative approximation method and its steps. According to the measured rainfall values measured by monitoring equipment that have been installed in the debris flow gullies, we can gradually revise the warning criterion set last time by comparing the monitored values and analyzing whether debris flow happens,and eventually reach or approach the accurate early warning value. The first step is to collect the measured or existing rainfall data,and analyze the relationship between the initial value and the occurrence of debris flow disaster; subsequently, we can obtain the early warning value by using the proposed iterative approximation method, and finally determine the early warning criteria of different levels according to the early warning standards. We applied this method to determine the early warning criteria of different levels of rain gauges for Qiangba main gully debris flow in Wenxian County, Longnan City as an example. The research findings offer reference and guidance for the monitoring and early warning of debris flow with universal equipment in Gansu Province, and has practical significance.
Hydraulic Structure and Material
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  Moisture Distribution During Water Saturation and Freeze-thaw Deterioration of Hydraulic Concrete

  LIU Fang, JIANG Wei, FU Shao-jun, ZHANG Guo-xin

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 152-157. https://doi.org/10.11988/ckyyb.20220095

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  To investigate the water migration and freeze-thaw deterioration of hydraulic concrete, water absorption and rapid freeze-thaw tests were conducted on low-heat cement concrete (LHCC) and moderate-heat cement concrete (MHCC). The testing process was monitored using nuclear magnetic resonance and industrial computerized tomography (CT) to explore and analyze the water migration and distribution in hydraulic concrete during water absorption, as well as the changes in internal pore structure under freeze-thaw action. The findings indicate that both LHCC and MHCC exhibit continuous increase of total water content during water absorption, with saturation being reached after 48 hours, and LHCC shows significantly higher water absorption capacity than MHCC. The proportion of moisture in 0-0.1μm range is higher in MHCC compared to LHCC, while all other larger sizes contain lower proportions of moisture compared to LHCC. During freezing and thawing, the total porosity in LHCC and its increment are notably higher than those in MHCC. Moreover, the percentage of pores larger than 10 mm³ in MHCC is lower than that in LHCC, while the percentage of pores of other smaller sizes is greater than that in LHCC.
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  Mix Proportion Design and Properties Analysis of Micro-expansion Grouting Material for Secondary Lining of Tunnel

  MA Li-gang, QIAO Jin-li, SUN Yong-tao, ZHU Xiang-rui, ZHANG Wen-bin, XUE Gui-xiang

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 158-166. https://doi.org/10.11988/ckyyb.20221070

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  Hollows in the secondary lining vault often leads to the failure of tunnel lining, posing a serious threat to driving safety. Current grouting materials fail to adequately adapt to the characteristics of mold grouting construction, thereby limiting the effectiveness and the further promotion of this technique. This study aims to address the limitations of traditional grouting materials, such as high water leakage, low solid setting rate, and poor bonding with the secondary lining concrete. To this end, micro-expansion materials were tested and investigated for use in mold grouting construction. On the basis of commonly used ratios in grouting engineering, the optimal mechanical properties of mortar were explored by varying the ratios of sulphoaluminate cement (SAC) and ordinary Portland cement (OPC) and water-binder ratios. The dosage of admixtures was then adjusted to improve working performance, and the influence of air-entraining agent dosage on mechanical properties and frost resistance was studied. Experimental results indicate that an OPC∶SAC ratio of 91∶9 and a water-binder ratio of 0.30 enable the best early and late strength development of mortar. Meanwhile, the optimal dosages of water reducing and thickening agents are found to be 0.4% and 0.34% of cementitious material, respectively, to achieve desirable working performance. In addition, the resulting grouting material exhibits good frost resistance, as well as maintained mechanical properties. Finally, the developed grouting material was applied to a mold grouting project, where its applicability and effectiveness were verified.
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  Experimental Study on the Effect of Adjusting pH Value with Alkali on Properties of Naphthalene Highly Effective Water Reducer and Concrete Performance

  LIU Zhan-ao, SUN Ming-lun, WANG Wei, LÜ Xing-dong, HU Hong-tao, XIAO Kai-tao, LI Jiang-wei, ZHANG Bing-liu

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 167-171. https://doi.org/10.11988/ckyyb.20220178

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  The degradation of naphthalene highly effective water reducer (NHWR) in the concrete mixing system of a large-scale hydraulic project situated in dry and hot river valley area of Jinsha River is a critical problem which considerably shortens the concrete setting time. This study investigates the effectiveness of adding alkali to adjust the pH value on NHWR storage quality and the properties of fresh and hardened concrete. A productive experiment on concrete was conducted to examine the consolidation effect at the project site. Results show that a pH level of 9.5 or higher can significantly inhibit the putrefaction of NHWR solution, and remarkably lengthen the setting time of fresh concrete, leading to a decrease in slump and the hourly loss rate of air content. Importantly, there is no detrimental effect on the mechanical property and durability of hardened concrete. Moreover, the concrete mixture produced for the placing area exhibits good workability, and its initial setting time has risen to 13 hours from the previous nearly 7 hours. Consequently, it is now possible to consolidate concrete in three or four placing areas at the same time, which enhances the efficiency and quality of dam concrete placing and produces high comprehensive benefits.
Special Column of Scientific Expedition and Research in the Headwaters of the Changjiang River
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  Seasonal Runoff Variation in Source Region of the Yangtze River and Its Multi-scale Correlation with Influencing Factors

  SHAO Jun, WU Qiong, QIAN Xiao-yan, BU Hui

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 172-178. https://doi.org/10.11988/ckyyb.20220432

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  Climate change has greatly impacted the runoff conditions in the source region of the Yangtze River in the past two decades. We analyzed the seasonal runoff variation, seasonal precipitation, and temperature variation based on measured hydro-meteorological data from the Tuotuo River hydrological station and meteorological station from 1960 to 2019. The cross wavelet transform is applied to examine the time-frequency variation and correlation among runoff, precipitation, and air temperature. Results reveal that the runoff of Tuotuo River in spring, summer, and autumn exhibited a significant increasing trend, with abrupt change points concentrated around 2006-2008. The increasing trend of seasonal precipitation was not significant, but the seasonal temperature displayed a marked rise that continues to the present. The correlation between summer runoff and precipitation was the most apparent, followed by autumn and spring. Temperature had a positive correlation with runoff, but it manifested differently on various time scales. Summer and autumn temperatures had the most significant effect on runoff. These findings provide important insights into the evolution law of seasonal runoff and hydrological response in the source region of the Yangtze River under the impacts of climate change.
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  Extracting the Dynamic Change of Lake Area in the Three-River Headwaters Region Based on Google Earth Engine

  QI Chang-xian, REN Yan, PENG Hai-yue, WEI Jia-hua, WANG Yong-qiang, LI Qiong

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 179-185. https://doi.org/10.11988/ckyyb.20220806

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  Based on Google Earth Engine (GEE) remote sensing cloud computing platform and Landsat TM, ETM+ and OLI satellite image data, a comprehensive water body identification algorithm with multiple indices such as Modified Normalized Difference Water Index (MNDWI), Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) was used to extract the area of lakes larger than 1 km² in the Three-River Headwaters region (source region of the Yangtze River, the Yellow River, and the Lancang River) from 1990 to 2020. In association with meteorological, glacier cataloguing and permafrost distribution data, the changes of lake area along with their influencing factors were analyzed. The findings of the study reveal a 15% increase in the overall lake surface area from 10 811.8 km² to 12 449.53 km², with 46 new lakes in the Three Rivers area since 1990. Specifically, the increase in lake area differed across sources, with more visible changes observed in the Yangtze River source area (29%) compared to the Yellow River source area (10%). Rising average temperature and increased precipitation were identified as the primary factors behind the increase in lake area. Specifically, increasing temperature caused glacier retreat and permafrost degradation, resulting in a faster increase in the area of glacier-replenished lakes and lakes located in permafrost areas. Precipitation was more closely related to the increase of lake area in the Yellow River source area.
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  Evolution Characteristics of Abrupt Drought-Flood Alternation Events in the Source Region of the Changjiang River

  WANG Yong-feng, FAN Li-juan

  Journal of Changjiang River Scientific Research Institute. 2023, 40(7): 186-190. https://doi.org/10.11988/ckyyb.20221407

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  According to runoff data from the Zhimenda hydrological station from 1957 to 2021, we analyzed the abrupt alteration between drought and flood in the Changjiang River source area by using the Long Runoff Drought-Flood Area Index (LRDFAI) and the Short Runoff Drought-Flood Amplitude Index (SRDFAI). We also investigated the periodical change of the intensity of the alteration events by the Hilbert-Huang Transform method. Results reveal that short-term alteration events in the study area mainly occur from March to September with comparable frequencies of “drought to flood” and “flood to drought” events. The frequencies of these events fluctuate considerably in different years and exhibit an overall trend of more-less-more-medium-more-more. The intensity of short-term “drought-to-flood” events displays a weak increasing trend, while the intensity of “flood-to-drought” events shows a weak decreasing trend. Both types of events exhibit main cycles of 7.1 years and 12.3 years. The area witnessed 20 long-term runoff alteration events with 8 and 12 occurrences of “drought to flood” and “flood to drought” events, respectively, and cycles of 8.3 and 14.2 years.