The physical habitat of the middle and lower reaches of the Yangtze River has experienced significant changes after the impoundment of the Three Gorges Reservoir, thereby affecting river functions. Based on data analysis and literature review, this paper examined the alterations in typical physical habitats such as the hydrological condition, river morphology, and vegetation after the TGR operation and their subsequent impacts on flood prevention, navigation, water supply, and typical aquatic organisms. Key areas for further research were identified as follows: 1) monitoring, including systematic and long-term monitoring programs, and the assessment of the effectiveness of river (waterway) management projects and ecological regulation measures; 2) laws and mechanisms of changes in river morphology, vegetation in the main stream and shoals, and the responses and thresholds of flood levels and benthic animals to variations in the physical habitat; 3) methods for predicting medium and long-term trends of hydrological conditions under the influence of multiple factors, channel regulation technologies that adapt to changes in the physical habitat and meet demands, as well as reservoir operation schemes that align with water supply objectives, benthic animal and fish breeding needs. Additionally, integrated research efforts focusing on physical habitat changes, their impacts, and improvement strategies and technologies require increased attention.
The maximum and minimum water levels are crucial constraints in the calculation of cascade reservoir operations and the economic operation of hydropower stations. Traditional iterative methods for multi-period predictions lack credibility due to error accumulation. This study employs a Long Short-Term Memory (LSTM) model which is effective in handling time series problems to predict the maximum and minimum water levels of the Three Gorges Reservoir over the next four days. Two LSTM-based deep learning models incorporating different characteristic variables are developed, and a conventional forecast model based on the water balance framework is also constructed for comparison. Results demonstrate that the deep learning model, which considers the propagation law of water surface profiles in the Three Gorges Reservoir area, delivers accurate and stable predictions, achieving an absolute error of less than 40 cm for 99% of the predictions.
Dongting Lake is located in the middle reaches of the Yangtze River, and its hydrological characteristics have an important impact on the middle reaches of the Yangtze River. According to the evolution characteristics and driving factors of Dongting Lake water level in flood season under changing environment, this paper analyzes the lowest water level, highest water level and average water level of Dongting Lake in flood season in East Dongting Lake (Chenglingji Station), West Dongting Lake (Nanzui Station) and South Dongting Lake (Yangliutan Station). The Mann-Kendall method and Pettitt method were used to test the variation of the three types of water level series, the frequency change characteristics of the three types of water level series was analyzed based on the GAMLASS model, and the contribution rate of climate change and human activities was quantified by the cumulative slope change rate method, so as to comprehensively analyze the driving factors of water level change in Dongting Lake during flood season. The results show that under the same design frequency, the design values of the three kinds of water level series have different degrees of reduction. In addition, the water storage of Gezhouba, the bending of Lower Jingjiang River and the increase of precipitation were the main reasons for the rise of Dongting Lake water level during the A2 period (1978-2002). During A3 period (2003-2022), the water level of East Dongting Lake decreased due to the influence of the Three Gorges Reservoir, the main stream of the Yangtze River and the inflow of three mouths and four rivers. The West Dongting Lake and the South Dongting Lake are mainly affected by the decrease of precipitation, which leads to the decrease of incoming water volume and the decrease of water level. This study can provide reference for flood control safety and water resources utilization in Dongting Lake area under changing environment.
Optimizing the dispatching mode during flood season is a crucial step in enhancing the comprehensive benefits of Wuqiangxi Reservoir. On the premise of ensuring flood control safety, we employed the method of forecast and pre-discharge to investigate the range and starting conditions for dynamic control of water level, and the operation mode of pre-discharge for Wuqiangxi Reservoir during the main flood season. Additionally, we calculated the comprehensive benefits of uplifting operational water level in flood season. Case studies on the flood season operations in 1996 and 2019 demonstrate that dynamic control of operating water level during flood season increased power generation head by 0.48 and 0.54 meters, reduced wasted water by 853 million and 956 million cubic meters, and boosted power generation by 126 million and 134 million kW·h, respectively. The results indicate that under controllable risk conditions, dynamic control of operating water level in Wuqiangxi Reservoir during flood season significantly improves power generation efficiency while reducing the likelihood of unit output blockage and water waste.
Luoshan hydrological station serves as a crucial flood control base in the middle reaches of the Yangtze River as it is located at the confluence of mainstream Yangtze River and the outflow of Dongting Lake with complex stage-discharge relationship. We analyzed the trends and influencing factors of stage-discharge relationship at Luoshan Station under erosion conditions by employing the M-K test method, Theil-Sen Median method, and a comprehensive correction approach for stage-discharge relationship based on measured water level and discharge data from 1990 to 2021 and typical river section data for selected years. Our key findings are as follows: 1) The water levels at Luoshan Station for low and medium discharges significantly decreased, which was consistent with the decline of the centroid elevation of low water-level channel and basic channel. Conversely, the water level at flood discharges exhibited large fluctuation range, yet with a non-significant upward trend. 2) The operation of the Three Gorges Reservoir has narrowed the fluctuation range of water level differences between Luoshan Station and Hankou Station, leading to an overall increase in the average water level difference. However, after 2013, the water level difference within flood flow intervals reduced, potentially exacerbating topwater conditions at Luoshan station during the flood season. During continuous flooding events in 2016 and 2020, contributions from topwater elevation, fluctuation rate, and other influencing factors at Luoshan Station averaged 34.8%, 23.8%, 41.4% and 31.4%, 50.6%, and 18.0% respectively; indicating that topwater elevation and fluctuation rate are primary influencing factors on water levels while other contributing factors may have larger proportions in certain years.
To explore the treatment model for farmland drainage pollutants, this study conducted an experimental investigation from July to September 2023 on the interception and purification effects of ecological drainage ditches, constructed wetlands, and their combined system in the Hetao Irrigation District. The findings demonstrate that various treatment modes in ecological drainage ditches and constructed wetlands effectively remove nitrogen and phosphorus pollutants. Specifically, the reduction efficiency of total nitrogen (TN) and total phosphorus (TP) in ecological drainage ditches treated with skew stem Astragalus membranaceus, yellow sweet clover, alfalfa, bio-ball matrix, and bio-sheet matrix was 21.09% and 23.84%, 12.06% and 26.67%, 20.08% and 34.15%, 23.65% and 20.56%, and 19.92% and 25.83%, respectively. In the emergent and submerged aquatic plant areas, the reduction efficiency of TN and TP was 24.28% and 17.89%, and 26.85% and 10.21%, respectively. The ecological drainage ditches treated with alfalfa and bio-ball matrix showed superior performance in TP and TN removal, respectively. Similarly, emergent and submerged plant areas exhibited better TP and TN removal efficiencies. The combined system of ecological drainage ditch and constructed wetland achieved TN and TP removal rates of 37.55% and 11.47%, respectively, effectively realizing step-by-step interception, adsorption and purification of pollutants. This system significantly enhances the removal and purification of nitrogen and phosphorus pollutants, thus mitigating agricultural non-point source pollution.
As one of the regions with the most concentrated distribution of freshwater lakes in China, the middle and lower reaches of the Yangtze River has seen significant improvements in water ecological environment in the past decade. However, the trend of lake eutrophication has not been fundamentally contained; the water environment quality and eutrophication of some lakes continue to deteriorate. Current analyses of lake pollution are limited by inadequate samples, making it challenging to discern regional characteristics among lake groups. In this paper, the characteristics of nitrogen and phosphorus pollution in surface sediments of 23 major lakes in middle and lower Yangtze River were analyzed. Results reveal that the average total nitrogen (TN) concentration in river-connected lakes and half-connected lakes are the highest, with no significant differences observed, followed by suburban lakes and urban lakes in descending order. Conversely, the mean total phosphorus (TP) concentration features notable differences, with urban lakes ranking the highest, followed by suburban lakes, river-connected lakes, and half-connected lakes in descending order. Although improvements have been made in the eutrophication status of regional urban and suburban lakes, the comprehensive pollution degree classification suggests that most lakes in the area still face severe pollution challenges. Therefore, there is still an urgent need to strengthen efforts in controlling nitrogen and phosphorus eutrophication. The results provide an overall understanding of the eutrophication of lakes in the middle and lower reaches of the Yangtze River, and support the prevention and control of eutrophication of lakes in the Yangtze River basin.
Topography significantly affects soil erosion, and topographic factors are key parameters in water erosion models. Topographic factors in existing modelling of regional soil erosion are mostly extracted from medium and low resolution DEMs,resulting in under-estimated slope gradient and over-estimated slope length,significantly affecting water erosion estimations. This study reviews the research progresses in the scaling effects of topographic factors and the associated effects on water erosion estimations. Results showed that the scaling effect of topographic factors widely exists in different terrain type areas,but the laws of slope attenuation and slope length expansion are quite different. These scaling effects are influenced by terrain complexity,spatial frequency of terrain information,calculation methods,and truncation techniques. The sensitivity of slope gradient and slope length factors to digital elevation model(DEM) resolution varies by region,leading to differential impacts on water erosion estimations. While scientists have made considerable achievements in elucidating the fundamental laws of slope gradient attenuation and slope length expansion,several critical areas need to be further explored,including the mechanisms underlying slope gradient attenuation and slope length expansion,the coupling mechanisms of slope gradient and slope length factor scaling effects,the impact of topographic alterations caused by human activities on scaling effects,the regional applicability,geomorphological principles,and the uncertainty analysis of topographic factor transformation models.
Understanding the impact of land use and landscape patterns on river carbon cycling is crucial for improving the watershed environment. This study utilized the landscape index method, redundancy analysis (RDA), and Pearson correlation analysis to analyze the effects of landscape factors on river carbon cycling in the Three Gorges Reservoir area. The findings reveal that: 1) Within a buffer zone scale of 1 500 m, the land use and landscape patterns have a substantial impact on the concentration of dissolved carbon in water and the fluxes of CO2 and CH4 at the water-air interface. 2) The dissolved carbon within the 1 500 m buffer zone is influenced by several key variables, including built-up land, and forest land. For CO2 and CH4 fluxes at the water-air interface, influential variables include built-up land, forest land, grassland, arable land, bare land, Shannon’s diversity index (SHDI), and patch richness density (PRD).
The influence of soil and gravel on the infiltration and sediment yield on engineering spoil heaps was investigated via artificial simulated rainfall experiments. Three soil types (sand, loam, and clay) and gravel mass fractions (10%, 20%, and 30%, with bare slope as control) were evaluated under three rainfall intensities (1.0, 1.5, and 2.0 mm/min). The findings are summarized as follows: 1) sandy soils exhibited a continuous decrease in infiltration rate, whereas loam and clay showed stable infiltration at 6 min and 3-18 min, respectively. Gravel inhibited the infiltration of sandy soils but promoted it in clay soils. The initial and stable infiltration rates of loam increased with higher gravel mass fraction. 2) The average infiltration rate of sandy soil was 0.88-2.40 times and 1.04-2.18 times those of loam and clay, respectively. The Horton infiltration model effectively predicted the infiltration rates of loam and clay during rainfall, with errors ranging from 0.61% to 6.82%. 3) Erosion in sandy soils occurred throughout the entire rainfall process, becoming more severe in the later stages. In contrast, initial erosion in loam and clay was significantly greater than in the later stages. The average erosion rate of sandy soil was 4.74 times and 2.84 times those of loam and clay, respectively. 4) Gravel significantly inhibited erosion in sandy soil and loam at rainfall intensities of 1.5 and 2.0 mm/min, but increased erosion in sandy soil and clay at 1.0 mm/min. These results provide data foundation for developing soil erosion models for engineering spoil heaps, offering both theoretical and practical values.
At present, the evaluation of fishway effectiveness primarily relies on methods such as net fishing and PIT (Passive Integrated Transponder) tracking to directly assess the quantity and efficiency of fish passage. However, these approaches have limitations, including long cycle, heavy workloads, and the inability to diagnose or identify abiotic engineering issues. Based on existing monitoring data of fishway effectiveness in China, we constructed an evaluation index system that encompasses abiotic indicators such as hydraulic condition suitability, environmental factor adaptability, and internal structure conformity, as well as biological indicators like fish passage effectiveness. Canonical correlation analysis reveals that hydraulic and structural indices, including the inlet velocity index, slot width index, and energy dissipation index, significantly influence fishway effectiveness, with respective weights of 0.23, 0.16, and 0.15. By integrating fuzzy evaluation theory, we developed a fishway effectiveness evaluation model based on abiotic indices. Case analysis demonstrates that the model’s results align with direct monitoring conclusions, indicating that the model can provide more reliable scientific and technological support for fishway operations in China.
Affected by corner centrifugal force and inertial force, stilling pool at the turning section of spillway often exhibits unfavorable flow conditions characterized by uneven water depth and flow velocity distribution. To address this complex flow issue, we conducted simulations on stilling pool at the turning section of the spillway of XBT reservoir in Xinjiang. We designed 17 simulation schemes and selected flow pattern, water depth, average flow velocity, and energy dissipation rate as evaluation indices. Results indicate that the hydraulic characteristics of the turning-section stilling pool vary in different simulation schemes. To mitigate adverse hydraulic phenomena in the stilling pool, deepening the pool depth to 6.55 m, adopting a rectangular open outlet type, and equipping 9 staggered rough strips can achieve optimal flow condition. This configuration resolves the backwater problem in the middle and rear sections and eliminated overflow along the walls. Notably, the water depth at concave bank declined by 30.22% compared to the original scheme, with a marginal water level difference of only 0.02 m between the two sides. According to calculation results of the average water depth and kinetic energy of typical section in the stilling pool, the average water depth at the outlet section decreased by 49.97% from the original scheme, while energy dissipation rate enhanced from 18.97% to 62.63%.
In this study, we analyzed the distribution patterns and ranges of expansive soil indices through an engineering case study in Ankang, Shaanxi Province. By utilizing mathematical statistical models, specifically the Normal, Gamma, Weibull, and Lognormal distributions, we aimed to gain a deeper understanding of these indices. To validate our findings, we conducted the Kolmogorov-Smirnov (K-S) test, which allowed us to confirm the distribution of the indices and further elucidate the physical and mechanical properties of expansive soil. Our results revealed notable trends: the dry density index exhibited minimal deviation with a right skew, closely aligning with the Normal distribution. Conversely, the expansion rate demonstrated the greatest deviation and a left skew, indicating its heightened sensitivity to other indices. We also observed that the Lognormal distribution adeptly captured the patterns of water content and void ratio, while the Normal distribution provided an accurate representation of dry density. The Weibull distribution, on the other hand, excelled in describing the distributions of liquid limit, plastic limit, plasticity index, expansion rate, and expansion force in expansive soil. When compared to the traditional average method, our approach by utilizing the peak parameter values from the optimal distribution functions of various indices offers a more precise evaluation of the physical and mechanical properties of expansive soil. The findings serve as valuable guidance for comprehending regional expansion deformation and enhancing engineering design and construction practices.
The water conveyance and power generation system of pumped storage power stations is generally buried deeply,and the three-dimensional seepage field distribution of the plant’s chamber group is complex due to external seepage in the water diversion system. Drainage measures are crucial in controlling the seepage field of water transmission and power generation system. Using the three-dimensional seepage field finite element method, we constructed a numerical calculation model of Zhangye pumped storage power station’s water delivery and power generation system, integrating the water conveyance system, underground plant system, and seepage prevention and drainage systems. Based on the distribution law of seepage field within the power generation system, we analyzed the impact of the drainage system beneath the pressure pipeline and the plant’s drainage system on the seepage field. Results indicate that under normal operating conditions, most of the underground plant is above the wetting line, and seepage flow is maintained within a reasonable range under the designed seepage control plan. Seepage overflows occur near the bottom of the plant chamber group, the pipeline exhibits characteristics of internal water seepage, and the seepage flow of the tailwater system is relatively large. The lower drainage gallery of the pressure pipe significantly influences the seepage field of the pressure pipe and the upstream side of the plant. A smaller drainage hole spacing results in a lower wetting line and larger seepage flow in the corresponding area, with a drainage hole spacing of 3 m proving more reasonable. The drainage system in the plant area significantly affects the seepage field of the underground plant. As the drainage hole spacing increases, the drainage effect diminishes, the flow into the collection well decreases, the wetting line rises slightly, and a drainage hole spacing of 3 m is deemed more reasonable.
The development of green and low-carbon chemical solidification technology is crucial for rapid solidification of soft ground under the “Dual Carbon” context. This study introduces an innovative synergistic technology that combines active nano-SiO2with microbial induced carbonate precipitation (MICP) for sludge solidification. Through unconfined compressive strength tests, pH monitoring, Ca2+ utilization rate analysis, and scanning electron microscopy, the reinforcement efficiency and micromechanisms of this technology are examined. Key findings include: 1) An increase in compressive strength of nano-SiO2-MICP solidified sludge is observed with increasing nano-SiO2 content up to 0.1%. 2) Samples treated with 0.1% nano-SiO2at Ca2+ concentrations of 0.5, 1, and 2 mol/L exhibit compressive strength enhancements of 64.21%, 10.28%, and 75.98%, respectively, compared to those without nano-SiO2. 3) Nano-SiO2 provides new nucleation sites for MICP, fills pores, induces aragonite-to-calcite transformation, and forms cementitious gels, thereby boosting sample strength. 4) The presence of nano-SiO2enhances Ca2+ utilization and pH regulation within the pore solution. Together, microbial-induced bio-CaCO3 processes (cementation, filling, bridging) and nano-SiO2-induced physicochemical effects (new nucleation sites, micro aggregate filling, and gelling products) synergistically improve the mechanical properties of solidified sludge and optimize the microscopic structural construction.
In this paper we addressed and elaborated on three critical issues concerning the Laplace transform solution of the Richards equation: the convergence of the original function, the steps for inverse transform, and the applicability of the equation. By presenting theoretical counterexamples, employing integral transformations and substitution schemes as well as real engineering cases, we demonstrated that assuming the convergence of the original function can lead to significant errors. Therefore, it is necessary to assess the convergence of the infiltration function before applying the Laplace transform. We also elucidated the steps for solving the Laplace inverse transform, theoretically addressing a gap in geotechnical literature. Furthermore, we reveal an anomaly where, in certain applications, the Laplace solution may show higher moisture content in lower soil layers than in upper layers. We analyzed this phenomenon from both physical and mathematical perspectives, highlighting inherent limitations in this solution. The findings of this study may help to theoretically strengthen the framework of unsaturated soil theory.
The numerical manifold method is a promising numerical method which uses a dual coverage system consisting of both mathematical and physical coverages. It has the advantages of flexible handling of boundary problems, efficient meshing and convenient improvement of approximation accuracy. Different from the traditional numerical manifold method which cuts the mathematical coverage to form the physical coverage according to the interface, a new weight function is constructed by using the refraction law in the manifold element to establish the local approximation based on the weak discontinuous physical coverage, and it is applied to the steady seepage problem. The accuracy and convenience of the method in solving discontinuous interface problems is demonstrated through the analysis of the calculation of typical seepage flow problems.
This paper presents an improved concentric arches model using the equivalence method for pile caps. The load transfer efficiency of geosynthetic-reinforced piled embankments with a triangular arrangement of piles is investigated. The pile cap with circular or square cross-sections is considered equivalent to a regular hexagon. The model is composed of three two-dimensional semicircular soil arches formed over the strip area between adjacent piles. A three-dimensional hemispherical soil arch is developed over the triangular area between three adjacent piles. Considering the geogrid deflects in a parabolic shape and the consolidation coefficient of the soil reaction, the frictional and adhesive tensions between the soil and the geogrid are obtained. The load transfer efficiency of the pile is investigated by considering the effects of the soil arch and the tensile membrane. Comparisons of the present solution results with those from available analytical methods and standards ensure its accuracy and feasibility. Parametric studies show that the load transfer efficiency decreases exponentially with an increase in the subgrade reaction coefficient and increases slightly with an increase in the consolidation coefficient of the soil. The effects of the soil arch and membrane tension increase sharply at first and then become constant as the embankment height increases.
Cement, currently a widely utilized soil reinforcement material, elevates soil pH and poses potential risks of groundwater contamination during application. This study employed three environmentally friendly materials, namely, γ-polyglutamic acid (γ-PGA), β-glucan, and a cross-linked γ-PGA-β-glucan mixture (γ-PGA-β-G crosslinker), to reinforce silty soil. The mechanism by which cross-linked biopolymers enhance the compressive and shear strength of silty soil was examined through unconfined compressive strength tests, direct shear tests, Fourier transform infrared spectroscopy (FTIR) characterization, and scanning electron microscopy (SEM) observations before and after reinforcement. Results indicated that the compressive and shear strengths of the silty soil reinforced with cross-linked biopolymers outperformed those reinforced with single biopolymers. The dosage of the cross-linked biopolymer and the age of maintenance significantly influenced the improvement effect. Longer maintenance periods better enhanced silty soil. Within a certain dosage range, the strength of silty soil positively correlated with the dosage. Specifically, a 1.5% ratio provided optimal unconfined compressive strength for γ-PGA-β-G-improved silt, with the 28-day maintenance strength reaching 47.07 kPa, a 1.43-fold increase over untreated silt. The γ-PGA-β-G cross-linked biopolymers effectively augmented the cohesion and internal friction angle of silt. This enhancement mechanism is attributed to the three-dimensional mesh structure formed by the crosslinks, which exhibits superior mechanical properties and envelops the silt particles, thereby significantly boosting the silt’s strength.
The intricate structure of sluice coupled with the high dosage of binder materials in pumped concrete can lead to various cracks. We examined the performance of pumped concrete mixed with fly ash, slag powder, or both in various dosages. Experimental tests include concrete mixing, mechanical properties, deformation, thermal characteristics, and durability. Findings indicate that mineral admixture combining slag powder and fly ash significantly enhances concrete mix performance. Specifically, concrete incorporating 20% fly ash and 20% slag powder exhibits nearly equivalent strength to concrete with 30% fly ash alone, while reducing the adiabatic temperature rise by 2.9 ℃ and improving crack resistance. This composite admixture could help address the cracking problem for the pumped concrete used in the sluice of the Yangtze River to Huaihe River Diversion Project.
In addressing the requirements of water resources monitoring tasks, we propose an adaptive multi-sensor performance measurement scheme by integrating time-space coverage, sensor parameters, imaging quality, and target importance based on the prototype of the monitoring task requirements. To achieve optimal benefit for water resources monitoring tasks, we constructed a combined optimization method using fuzzy greedy search decision algorithm and validated the adaptability of the proposed method by applying it to the Danjiangkou Reservoir area. Results demonstrate that the combined observation method effectively meet the requirements of reservoir water quality monitoring, reservoir bank environmental monitoring, as well as routine drought monitoring tasks within specific space-time constraints, thereby providing a sound decision-making basis for the daily monitoring of water resources.
Affected by natural factors and human activities, extreme hydrological conditions have emerged in Poyang Lake in recent years. During the flood season of 2020, Poyang Lake’s highest water level broke historical records. Conversely, in 2022, Poyang Lake experienced an unusual “drought during flood season”, with multiple stations registering their lowest water levels ever. These extreme hydrological conditions have significantly impacted flood control and drought relief in the lake area and even the downstream regions of the Yangtze River. This study summarizes and analyzes extreme flood and drought events based on hydrological and atmospheric circulation data from the Poyang Lake basin and operational records of the Three Gorges Project. The primary cause of these extreme hydrological conditions in Poyang Lake is the subtropical anticyclone, which, under the influence of El Ni o and La Ni a phenomena, affects inflow, outflow, and rainfall within the lake basin. Additionally, the regulation of main and branch reservoirs in the upper reaches of the Yangtze River also influences these extreme flood and drought hydrological situations. In response to these findings and the practical needs of Poyang Lake, this paper proposes corresponding countermeasures and recommendations to enhance the flood and drought disaster resilience of the Poyang Lake basin.
A two-dimensional (2D) hydrodynamic model is developed to investigate the dike-break flood at Tuanzhou township alongside the Dongting Lake on July 5, 2024. Integrating both lake and township into a single model, we comprehensively reconstruct the dike-break flood, capturing macroscopic flood processes and detailed flow structures. The model also assesses the flood risk associated with a potential failure of the Qianlianghu-Tuanzhou dike. The model accurately determines when the water levels inside and outside the breach reach equilibrium. It provides precise historical data on breach discharge, water levels inside and outside the breach, flood storage volume, and inundated areas in Tuanzhou township over time. Additionally, the model replicates the water surface scarp around the breach, explaining why water levels near the breach are lower than those in the downstream lake area. The water level and flow velocity distributions around the breach are plotted and analyzed. Moreover, the characteristics of concave water surface outside the breach and the convex water surface inside the breach, together with the water-level gradients are also quantitatively examined. Comparison with field data reveals that the model’s water level error is generally below 10 cm during the dike-break flood (except for the initial breach stage), and drops to less than 5 cm once equilibrium is reached. The discharge error is typically under 5%, with peak discharge error at only 2.5%. The model’s water conservation error is 0.6%, and the discrepancy in maximum flood volume between the model and hydrological department’s results obtained from flood volume versus water level curve is 6.8%. Based on the dike-break flood reconstruction, we design three breaches along the Qianlianghu-Tuanzhou dike and simulate dike-break floods with the existing breach at Tuanzhou township under both blocked and unblocked scenarios. We further quantitatively assess flood risks related to potential dike failures by analyzing the flow field, discharge processes, flood storage, and inundated areas. The findings offer technical support for flood risk assessment and levee protection. The systematic method for simulating real dike-break floods in this study includes integrated modeling of rivers/lakes and townships, detailed township modeling, and iterative calculations to determine breach topography over time. These methods enable accurate simulations of dike-break floods and can serve as a reference for similar studies on dike-break floods.
To swiftly and efficiently monitor and assess the dynamics of flood disasters under emergency conditions, this study introduces a flood disaster emergency monitoring model based on China’s Gaofen-3 satellite time-series data. This model offers a rapid and effective method for pre-disaster breach warnings, disaster response, and post-disaster loss assessment. In response to the imminent threat posed by the Tuanzhou Embankment breach on July 5, 2024, we conducted emergency remotely-sensed monitoring by using daily image time series data before and after the breach. According to water body extraction and changes detected before and after flooding, we found that the water area in farmlands surrounding the breach experienced a significant increase the day before the dike burst. From 10 a.m. on July 4, 2024, to 11 a.m. on July 5, 2024, the embankment underwent evident seepage process. By the morning of July 6, 2024, the Tuanzhou Embankment was almost entirely submerged, with only the rooftops of houses along the main road remaining above water. From July 8th to 15th, the water gradually receded. The findings indicate that Gaofen-3 data can help effectively monitor the entire disaster evolution process at high spatial and temporal resolutions before, during, and after dike breach, providing crucial data support for pre-disaster early warning, emergency rescue, and post-disaster loss assessment.
Under the background of global climate change, extreme hydrological events with increasing frequency pose severe threat to dam safety. Large floods in the Yangtze River Basin, accompanied by levee breaches, occurred in 2016 and 2020. On July 5, 2024, the embankment of Tuanzhou township in Dongting Lake area, Hunan Province, collapsed, endangering the safety of people’s lives and property. To expedite the return of residents to their homes and prevent secondary disasters, early emergency closure measures are typically implemented post-breach. At this stage, with equalized water levels inside and outside the polder, rapid emergency drainage is conducted under breach closure conditions. The impact of sudden water level drops on the safety of the main embankment and the secondary embankment has attracted significant attention, even constraining emergency rescue operations. To assess the effects of emergency drainage on embankment safety in the Tuanzhou polder of Dongting Lake area and aid in the formulation of emergency response plans, we constructed non-steady seepage and stability analysis model for the main embankment and the Qianlianghu-Tuanzhou interval embankment near the breach with Dongting Lake water level remaining unchanged. The analysis focuses on the seepage stability and slope safety of the embankment under extreme sudden water level drop rates of 0.3 m/d and 0.6 m/d during emergency drainage during breach closure. The results indicate that the maximum seepage gradient and slope stability of the embankment meet the standards for third-level embankment safety under various conditions. Additionally, we propose rapid drainage measures in comprehensive consideration of multiple factors to provide technical support for emergency rescue and shed new insights for safety analysis under similar conditions.
Based on flow and water level sequence data from six stations, we analyzed the changes in water level of floods of different frequencies, thereby obtaining the flood regime variation in the tail channel of Ganjiang River. Results revealed a general decrease in flood levels in the tail channel of Ganjiang River, with the average highest flood level in 2003-2022 dropping by 0.24 to 1.65 meters compared to 1956-2002. Flood levels at various frequencies have reduced to varying extents, with control sections for lake flood remaining stable, while control sections for river flood significantly decreasing, declining by 1.62-1.77 meters to the maximum. Such declines indicate an enhanced flood carrying capacity of the corresponding river section, which means alleviated flood control pressure and improved flood control safety. Future flood control and engineering designs should consider scenarios of encountering both river flood and lake flood at the Ganjiang River tail channel, and the impact of such extreme situations should be thoroughly examined.
