In recent years, under the combined effects of intensified human activities, climate change, and sea level rise, estuarine and coastal areas have faced increasing risks of extreme flood-tide damage, posing a serious threat to the safety of estuarine and coastal embankments. Due to the complex and rapidly changing dynamic conditions, multiple disaster-causing factors, and the abrupt and strongly destructive nature of related processes, research on embankment safety risk assessment and disaster early warning has become increasingly challenging. This represents an interdisciplinary research frontier and hotspot in the field of disaster prevention and mitigation that has attracted global attention. Focusing on international research hotspots in embankment safety risk assessment and early warning and strategic needs for disaster prevention and mitigation at the national level, this study systematically reviews the current status and trends of embankment safety risk assessment and early warning technologies both domestically and internationally. Additionally, it identifies the key scientific and technical challenges that require urgent solutions. Based on the limitations of existing research, this study proposes suggestions and future research directions. The study integrates approaches from multiple disciplines, including estuarine and coastal science, coastal dynamics, river dynamics, hydrology, meteorology, engineering geology, geophysics, information engineering, and computer engineering. By employing field surveys, dynamic monitoring, flume experiments, numerical simulation, machine learning, and theoretical analysis, it clarifies three key relationships driven by the evolution mechanism of the flood-tide disaster chains: the “fluid-structure interaction”, “causal relationship between disaster-causing factors and risk assessment”, and “coordination between habitat safety and dynamic early warning”. From the perspective of hydrometeorological conditions, disaster chain evolution, and fluid-structure interaction, this study reveals the evolution mechanism of flood-tide disaster chains under changing conditions and the response mechanism for embankment disasters. Furthermore, from the perspective of multi-element monitoring and multi-indicator dynamic early warning, the study establishes a comprehensive embankment safety risk assessment system and early warning model for estuarine and coastal areas, with technical applications to enhance the accuracy of disaster forecasting and the resilience of embankment protection. The research findings are expected to improve the safety assurance capabilities in estuarine and coastal areas, significantly enhance early warning of embankment disaster risks, and provide critical scientific and technological support for evidence-based decision-making in disaster prevention and mitigation.
[Objectives] Since the operation of the Three Gorges Project and the cascade reservoirs in the upper reaches of the Yangtze River, the new water and sediment regime has caused large-scale and high-intensity continuous erosion in the Jingjiang River section of the middle Yangtze River, resulting in recurrent bank collapse incidents at some revetment sections. To investigate the causes of recent bank collapses at revetment sections and better respond to such dangerous situations, this study examines the sudden bank collapse and its emergency treatment at the “Tianzi-1” revetment section in the lower Jingjiang River in 2023. [Methods] Measured water and sediment data at Jianli station since 1990, annual erosion and deposition data of the lower Jingjiang River since 2003, and measured data on channel topographic changes and geological drilling before and after the bank collapse at the “Tianzi-1” section were used to analyze the causes. [Results] In November 2023, continuous cave-in-type bank collapses occurred at the “Tianzi-1” revetment section in the Hunan segment of the lower Jingjiang River, with collapse lengths of approximately 100 m and 35 m, respectively. The results showed that the bank collapse primarily resulted from continuous riverbed erosion under the clear-water discharge condition, significant changes in local river regime causing deep channel and thalweg migration toward banks, poor geological conditions of the riverbank slope, and the influence of prolonged low-to-medium water levels. Based on the characteristics of the dangerous situation, an underwater stone dumping method was adopted for emergency treatment of the collapsed section and the affected upper and lower reaches. [Conclusions] This recurrent bank collapse at the revetment section highlights that the lower Jingjiang River will continue to face severe threats of bank collapse for the foreseeable future. Without timely reinforcement measures, large-scale damage can occur to existing bank protection structures, seriously threatening flood control safety. Therefore, this study proposes medium-to-long-term governance measures, including establishing institutional frameworks as soon as possible, securing construction funding, strengthening dynamic monitoring of slope toe variations at dangerous sections, enhancing the development of bank failure control technologies, and improving the monitoring, early warning, and emergency response mechanisms for bank collapse.
[Objective] Significant recent scouring of the riverbed has been observed near Biandanzhou on the right bank of the Taiziji Reach, potentially threatening dike safety, influencing river regime control nodes, and altering the flow distribution ratio of downstream branches. Meanwhile, the navigation conditions in the main channel of Donggang on the right branch remain unstable. [Methods] To ensure flood control and navigation safety, this study analyzed the recent riverbed evolution of the Taiziji Reach based on the latest original underwater topographic observation data and long-term measured records. The study also predicted river regime development trends and proposed corresponding preventive and control measures to address existing issues. [Results] The shoreline has remained generally stable over the years. Except for the straight reach from Changhekou to Xingfucun, the thalweg has shown limited variation. The most significant platform migration, with a maximum lateral migration of approximately 1.1 km, was recorded in the Biandanzhou-Xingfucun area. The thalweg elevation generally exhibited a lower upstream and higher downstream pattern, with alternating changes in elevation over time. The -5,-10, and -15 m contour lines showed a slight overall scouring trend in the deep channel. The Tietongzhou branch would continue to exhibit a pattern of left branch and right main channel, with the right branch showing a general scouring trend. Locally, severe scouring near Biandanzhou was evident inter-annually, with the right bank retreating by approximately 700 m between 1981 and 2021 and the maximum local depth of scouring in the riverbed about 12 m. [Conclusions] It is recommended to implement protective measures as soon as possible for the severely scoured sections near Biandanzhou. Continuous enhancement of hydrological and topographic monitoring and follow-up analyses is essential. Once issues are identified, engineering interventions such as river regulation works should be promptly adopted. The results of this study provide critical technical support for future river management strategies in the Taiziji Reach under new flow-sediment conditions.
[Objectives] Identification of runoff components is a key aspect of hydrological analysis and is crucial for understanding the evolution patterns of watershed water resources. Traditional runoff component models are often constructed based on the criterion of maximizing the extraction accuracy of deterministic components for the runoff series of a given length. However, a unified criterion for selecting model forms that adapt to variations in runoff series length over time is still lacking, making it difficult to determine the types of runoff components and the order of their separation during modeling. To address this, this study proposes a selection criterion for runoff component models based on the balance between benefits and risks. [Methods] Based on the diagnosis and quantitative description of evolution characteristics such as mutations, trends, and periodicities using time-series variability detection methods—the Mann-Kendall test, sliding T-test, Pettitt test, Standard Normal Homogeneity test, Buishand test, and periodogram—different forms of linear superposition models were developed by combinations and extraction sequences of the identified components, such as mutation, trend, and periodicity. These models were then employed to dynamically identify the components of runoff sequences with varying lengths. The accuracy of deterministic component identification was used to represent the “benefits” achieved by the model in runoff component recognition, while the magnitude of fluctuations in model accuracy under varying runoff sequences (i.e., stability) was regarded as the “risk”. A weighting coefficient representing the decision-maker’s preferences was introduced as a balancing variable to construct a benefit-risk balance indicator. Subsequently, runoff component models were optimized based on the criterion of minimizing this benefit-risk balance indicator. [Results] Using the runoff sequence from 1956 to 2010 at the Pingshan Station on the lower reaches of the Jinsha River as a case study, variable-length runoff sequences (with sample sizes ranging from 30 to 55) were constructed, starting from 1956 and ending in any year from 1986 to 2010. Runoff component identification was conducted under different model forms, and the proposed benefit-risk balance criterion was applied for model selection analysis. The results indicated mutual offsetting among components such as mutations, trends, and periodicities in the runoff sequence, and the same runoff sequence could be characterized by multiple models, each representing distinct compositional forms of runoff components. Runoff component identification was jointly influenced by both the model form and the sequence length; models with higher identification accuracy exhibited relatively lower stability when responding to changes in sequence length. For instance, models incorporating periodic components demonstrated superior fitting accuracy compared to those containing only trend or mutation terms, which in turn outperformed multi-year average models, while the stability of accuracy changes followed the opposite trend. If the decision-making objective was to achieve a more adequate fitting, models that sequentially separate mutations and periodic components are prioritized; conversely, if the objective was to maintain more stable accuracy with varying sequence lengths, models that identify only mutation or trend terms were more advantageous. [Conclusions] A novel approach is proposed in this study for selecting component models of variable-length runoff sequences by balancing identification accuracy (benefit) and stability (risk). Both the accuracy and stability indicators proposed in the criterion can be flexibly defined according to decision-making needs, facilitating decision-makers in comprehensively considering their preferences for model accuracy and stability under varying conditions to optimize model selection.
[Objectives] With the socioeconomic development, conflicts among the population, water resources, and the environment have become increasingly prominent. Conducting research on water quality and quantity in rivers that flow through urban areas and serve functions such as water supply and irrigation, and implementing rational scheduling, is of significance for ensuring a healthy aquatic ecosystem and enhancing the well-being of local residents. [Methods] The Nansu River Basin was selected as the research area. A one-dimensional hydrodynamic-water environment coupled MIKE11 model was constructed, utilizing chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) as key indicators. The external boundary conditions for the hydrodynamic module were defined by upstream inflow and downstream outflow, with observed hydrological data serving as model inputs. For the water environment module, the boundary conditions were established based on the water environmental characteristics at the river boundaries and pollutant discharge data entering the river. [Results] The water environmental capacity (WEC) refers to the maximum permissible pollutant load that a water body can assimilate per unit time under specified water domain boundaries, hydrological conditions, regulated sewage discharge modes, and predefined water quality targets. The monthly average WEC for COD and NH3-N showed a consistent pattern, with the highest capacity observed during the high-flow season, followed by the normal-flow season, and the lowest during the low-flow season. Water quality in the Nansu River deteriorated rapidly during the early flood season. To improve water quality, seven scheduling schemes were proposed by addressing two key aspects: controlling pollutant inflow from tributaries and increasing mainstream flow. [Conclusions] Improving water quality requires intervention in two primary areas: controlling pollutant inflow from tributaries and increasing the flow of the main stream. Based on the actual conditions of the basin and a comparison of seven regulation schemes, the Oupugou tributary is identified as the primary source of pollution affecting the mainstream. While both approaches—pollutant inflow control and mainstream flow increase—can achieve water quality improvement, the effect of pollution control is more significant than that of flow regulation. According to the comparative analysis of the scheduling schemes, the optimal scheme for improving water quality is to close the sluice gates of the Oupugou tributary to prevent pollutant inflow, and to moderately regulate water flow to further improve water quality.
[Objectives] Satellite altimetry has become a crucial method for monitoring lake water levels, yet significant challenges remain in its application to small lakes, particularly in complex urban environments. Currently, limited studies explore the effectiveness of satellite altimetry for monitoring variations of urban lake water levels. Using East Lake in Wuhan as a case study, this study evaluates the quality of Jason-3 satellite altimetry data, aiming to validate the capability of satellite altimetry in monitoring urban lake water level variations. [Methods] Based on the Jason-3 Sensor Geophysical Data Record (SGDR) products from 2017 to 2022, this study used two key parameters—pulse peakiness and waveform width—to first analyze the altimetry waveform characteristics of East Lake. In addition to the original range observations and ICE-retracked ranges provided by SGDR products, this study applied the Offset Center of Gravity (OCOG) and threshold methods for waveform retracking. Among them, the threshold retracking method selected eight threshold levels ranging from 20% to 90% (in 10% increments) to analyze the retracking performance under different thresholds. A robust coarse elimination strategy based on the Median Absolute Deviation (MAD) was employed to eliminate outliers from the water level observation data, followed by the calculation of periodic average water levels to construct the lake water level time series. To evaluate the quality of water level data by different methods, the range and standard deviation of water levels in each period, as well as the number of invalid periods, were statistically analyzed. Additionally, the accuracy of the results using different methods was verified using the measured data from hydrological stations. Finally, meteorological data (precipitation, evaporation) and a water balance model were integrated to quantify the contributions of natural and anthropogenic factors to East Lake’s water level variations. [Results] (1) Statistical analysis of pulse peakiness and waveform width from the lake surface altimetry echoes revealed that approximately 50% of East Lake’s waveforms exhibited specular reflections with distinct sharp peaks, while about 30% displayed complex shapes containing two or more peaks. (2) The results of accuracy validation using the on-site measured data of water levels showed that the 50% threshold retracking method achieved optimal performance, with a root mean square error (RMSE) of 0.108 m and a correlation coefficient of 0.87. (3) Based on the 50% threshold retracking method, and using Jason-3 data, the water level time series of East Lake from September 2017 to February 2022 was established. The results demonstrated that the lake water level remained stable around 19.5 m during this period, with annual fluctuations <0.5 m, monthly variations <0.2 m, and no pronounced seasonal pattern. Although precipitation was the primary water source, water levels showed extremely low correlation with precipitation (R=0.007), and weak negative correlation with evaporation (R=-0.44). According to the analysis of water balance, artificial regulation played a key role in the water level variations of East Lake. [Conclusions] (1) Jason-3 satellite altimetry data can effectively monitor urban lake water level variations, but requires careful data processing, including waveform retracking and outlier elimination. (2) Despite complex waveforms over urban lakes, retracking methods significantly improve altimetry accuracy. Compared with waveform retracking methods such as OCOG, ICE, and threshold method, the 50% threshold method is more suitable for urban lakes.
[Objectives] To reveal the spatiotemporal characteristics of extreme precipitation from 1981 to 2020 in the southern Gaoligong Mountain(S-GLG) and explore its relationship with strong ENSO events, this study analyses the trends of five extreme precipitation indices (EPIs) and their responses to large-scale sea surface temperature anomalies, such as the Oceanic Niño Index (ONI) and the Dipole Mode Index (DMI), providing a scientific basis for regional drought risk assessment and water resource management. [Methods] Using daily precipitation data from 8 meteorological stations, this study selected five EPIs: total wet-day precipitation (PTOT), maximum consecutive dry days (CDD), maximum 1-day precipitation (RX1day), number of heavy precipitation days (R10mm), and extreme precipitation intensity (SDII). Innovative trend analysis (ITA) and linear regression (LR) were used to analyze long-term trends, and composite analysis was employed to examine the impact of ENSO events (represented by ONI and DMI) on extreme precipitation. Seasonal-scale correlation analysis was conducted to distinguish the response differences between the western and eastern slopes. [Results] The results showed that except for a significant increase in CDD (3.9 d/(10 a) on the western slope and 0.7 d/(10 a) on the eastern slope), other EPIs exhibited decreasing trends, with PTOT decreasing most significantly (39.9 mm/(10 a) on the western slope and 46.1 mm/(10 a) on the eastern slope), indicating an intensifying drought risk in the region. ENSO correlations revealed weak to moderate negative relationships between extreme precipitation and ONI (p<0.1). During positive ONI phases (El Niño-like conditions), there was a higher probability of reduced precipitation during the rainy season. Additionally, the influence of DMI showed phase-dependent negative correlations, but with lower statistical significance. Regional seasonal differences were evident. The western slope showed a stronger negative correlation between rainy-season PTOT and CWD and simultaneous ONI during summer and autumn (r=-0.46 to -0.52), while the eastern slope exhibited a more pronounced lagged response of corresponding indices to ONI in the previous autumn and winter (r=-0.33 to -0.38), potentially indicating that topography may modulate the transmission of ENSO signals across the region. [Conclusions] The southern Gaoligong Mountain is experiencing a “drying” trend in extreme precipitation, with ENSO events (especially ONI) serving as key driving factors. Innovative findings include: (1) the first quantitative demonstration of seasonal response differences to ENSO between the western and eastern slopes, providing key parameters for improving local climate models; and (2) the proposal that early-stage ONI tracking may serve as a potential indicator for regional extreme precipitation prediction. These research findings provide important guidance for developing climate adaptation strategies in the region of Hengduan Mountains.
[Objectives] This study aims to overcome the limitations of traditional static evaluation methods by developing a multidimensional assessment framework for water resource carrying capacity with spatiotemporal continuity. It seeks to reveal the evolution patterns of regional water resources carrying capacity and propose optimized regulation schemes. [Methods] A dynamic-static analytical framework combining principal component analysis (PCA) and system dynamics (SD) modeling was applied, with Qingyang City in Gansu Province—an area relatively short on water resources—as the study area. First, using data from 21 indicators from 2012 to 2022, PCA was used to extract principal components (cumulative variance contribution rate >85%) to establish a comprehensive evaluation system for water resources carrying capacity and identify key influencing factors. Subsequently, a complex dynamic model of water resources system was established by dividing the system into socioeconomic, water supply-demand, and ecological subsystems. The dynamic changes in water supply and demand under different development scenarios were simulated. Four optimization schemes were designed: status quo development (baseline), water-saving, wastewater treatment, and integrated coordinated development. Their optimization effects on regional water resources carrying capacity were evaluated from the perspectives of water demand control, water supply efficiency improvement, and coordinated governance. [Results] (1) The water resources carrying capacity of Qingyang City significantly declined, with an annual average decrease rate of 18.78% from 2015 to 2022. PCA revealed that socioeconomic development (population growth rate, GDP per capita), water resource allocation efficiency (crude oil processing volume, water resources per capita), and ecological development level (green coverage rate in built-up areas) were the key driving factors, contributing 35.2%, 28.6%, and 19.3% to the principal component loadings, respectively. (2) Dynamic simulations showed that under the status quo development scheme (scheme 1), water shortage in 2035 increased by 47.8% compared to the baseline year (2012), with a supply-demand gap expanding to 123 million m3. The water-saving scheme (scheme 2) reduced the shortage by 11.9% through improved reuse rates, but due to the inflexible growth in water demand, the imbalance remained significant. The wastewater treatment scheme (scheme 3) reduced water shortage by 15.1% by increasing reuse rate to 55%, demonstrating a 3.2-percentage-point greater improvement compared to scheme 2. The integrated coordinated development scheme (scheme 4) implemented a synergistic “water-saving and pollution-control” strategy, optimizing demand-side control (improving industrial water-saving and agricultural irrigation efficiency) and enhancing supply-side circulation (wastewater reuse rate at 60%). This ultimately reduced the water shortage in 2035 by 16.7% compared to scheme 1, lowered total water demand by 19.4%, and narrowed the supply-demand gap to 51 million m3. [Conclusions] This study innovatively establishes an analytical paradigm integrating “historical diagnosis, dynamic early warning, and strategy optimization.” The degradation of water resources carrying capacity in oil and gas resource-based cities is essentially a manifestation of the imbalance between energy development, economic growth, and ecological protection. An integrated development strategy that includes water-saving, pollution control, and economic adjustments proves effective in alleviating water resource pressure through dual supply-demand adjustments. Future water management in Qingyang City requires curbing its current development trends promptly and regulating key guiding factors. Among the four projected schemes, the integrated coordinated development scheme performs optimally.
[Objectives] To enhance water quality prediction accuracy, this study aims to address the following challenges: (1) traditional prediction methods often rely on simple, elementary decomposition techniques, limiting their ability to extract meaningful data features. (2) Single models and basic optimization algorithms result in low prediction accuracy. (3) Most approaches fail to leverage the advantages of different networks to analyze components of varying complexity, leading to inefficient model utilization. (4) Few studies incorporate error correction after prediction. This study proposes a novel hybrid model for water quality prediction. [Methods] First, the original water quality sequence was decomposed using Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN). Next, Fuzzy Dispersion Entropy (FuzzDE) categorized the components into high-, medium-, and low-complexity subsequences. Then, an Improved Mantis Search Algorithm (IMSA) optimized three distinct models: Bidirectional Long Short-Term Memory (BiLSTM) for high-complexity components, Least Squares Support Vector Regression (LSSVR) for medium-complexity components, and Extreme Learning Machine (ELM) for low-complexity components. The predictions were combined and reconstructed, and a BiLSTM-based error correction model further corrected the errors, yielding the final prediction results. [Results] The study introduced four key innovations to the original Mantis Search Algorithm (MSA): (1) combining Logistic-Tent chaotic mapping for population initialization, ensuring uniform and random distribution of initial solutions to enhance global search capability and convergence speed; (2) nonlinear acceleration factor, refining MSA’s core update formula to transition from global exploration to local exploitation, mitigating local optima entrapment; (3) elite-guided adaptive update strategy, addressing the excessive randomness in the position update strategy when Mantis attacks fail, improving late-stage search efficiency while preserving some randomness; (4) opposition-based learning, generating individuals opposite to the current individual to enhance global optimization. IMSA’s performance was validated using benchmark functions (Rosenbrock for unimodal, Michalewicz for multimodal), confirming improved global search and convergence precision. After determining the network hyperparameters, ablation experiments were conducted to analyze the contribution of each strategy to the network model, providing a clear understanding of how each strategy impacts prediction performance. Finally, the sequence of model usage was validated by using FuzzDE to calculate the complexity of each component, creating high-, medium-, and low-complexity subsequences. The learning capabilities of different networks for these subsequences were verified, with BiLSTM used to predict high-complexity components, LSSVR for medium-complexity components, and ELM for low-complexity components. [Conclusions] This study performed a simulation verification using dissolved oxygen (DO) concentrations from two sections of Youshui River (a tributary of the Yuanjiang River) and pH values from one station in the Xiangjiang River Basin. Missing values were addressed via linear interpolation. For outlier treatment, the study considered that outliers in the data might be caused by sudden pollution events and discontinuous non-point source pollution. Directly removing them could lead to information loss, so outliers were retained. After integrating decomposition, use of entropy, algorithm optimization, and error correction models, eleven comparative experiments were established to evaluate the effectiveness of each optimization method. The hybrid model’s effectiveness was validated using RMSE, R2, and MAPE metrics. Ultimately, the R2 reached over 90%, demonstrating that the prediction accuracy of the hybrid model outperformed other comparative models.
[Objectives] Polydisperse particles are widely present in natural environments. Accurately predicting the transport and deposition of polydisperse particles in saturated media under unfavorable conditions (where repulsive forces exist between particle and medium surfaces) is crucial. [Methods] A series of constant-flow one-dimensional sand column experiments with artificial recharge were conducted using polydisperse particles (0.375-18.863 μm) under different ionic strength conditions (1, 6, 20, and 200 mM). Deposition characteristics of polydisperse particles under different ionic strengths (unfavorable and favorable conditions) were investigated. By coupling the colloid attachment efficiency model under unfavorable conditions with the polydisperse particle deposition model, a deposition model for polydisperse particles under unfavorable conditions was established, and corresponding numerical simulations were performed. [Results] Both physical experiments and numerical simulations showed that under favorable conditions, the capture probability of polydisperse particles exhibited a non-monotonic V-shaped characteristic of first decreasing and then increasing with particle size due to uneven micro-force distribution. Compared with favorable conditions, the repulsive double-layer force between polydisperse particles and the medium surface under unfavorable conditions formed an energy barrier, leading to an 8.5%-67.6% reduction in capture probability. The smaller the particle size, the greater the reduction in particle capture probability. Under favorable conditions, the final deposition profile curve of particles exhibited a hyper-exponential distribution with “upper-steep, lower-gentle”. The total deposition amount increased with increasing ionic strength, with 16.7%-24.6% of the total deposition occurring in the upper part of the sand column. A decrease in ionic strength exacerbated the uneven “upper-steep, lower-gentle” distribution of the deposition profile. [Conclusions] The research results not only further reveal the transport and deposition characteristics of polydisperse particles under natural unfavorable conditions, but also provide a scientific basis for effective watershed water quality management.
[Objectives] In the context of global climate change, studies on coastal wetlands and their carbon sink capacity face both major opportunities and challenges. Therefore, investigating their spatiotemporal distribution is crucial for achieving the “dual carbon” goals. [Methods] Taking the coastal wetlands of Chongming Island, Shanghai, as the study area, Sentinel-2 remote sensing images in 2015, 2017, 2019, and 2021 were used. Based on corrected carbon density and land use derived from supervised classification, the spatiotemporal distribution characteristics of carbon storage were obtained. The influencing factors of carbon storage were quantitatively analyzed using the geodetector method. [Results] The periphery of Chongming Island is dominated by wetlands, with natural wetlands (mainly river-lake water bodies, grasslands, reed beds, and tidal flats) primarily distributed along the shoreline, while the inner area is non-wetland. The area of both artificial and natural wetlands increased significantly, by approximately 20 000 hm2. The carbon storage of Chongming Island first increased and then decreased, but wetland carbon storage remained high, showing an overall positive trend of annual increase (approximately 600 000 tons). Conversions from non-wetland to both natural and artificial wetlands led to increases in carbon storage, indicating the high carbon sequestration potential of coastal wetlands. Natural factors had a weak influence on wetland carbon storage in Chongming Island, whereas socioeconomic development had a stronger impact. The geodetector q-values for economic added value and land use intensity reached 0.79 and 0.82, respectively. The interactive effects of natural and human factors, such as GPP combined with economic added value and population, yielded a q-value of up to 0.99, highlighting the importance of human-nature harmony in enhancing carbon sequestration in wetlands. [Conclusion] Using meteorological data from Shanghai and Chongming Island, together with a carbon density correction model, the local carbon density of Chongming District was derived. This method has low data acquisition difficulty, as most meteorological data required for local carbon density calculations can be obtained from the study area’s statistical yearbooks, and pre-correction carbon density can be retrieved from other literature. The method is applicable to coastal wetlands and other “dual carbon” focus areas, enabling accurate acquisition of localized parameters and improving the accuracy of carbon storage estimation to some extent. Additionally, directly applying geodetector to carbon storage simplifies the analysis process compared to indirect detection via land cover types and improves accuracy. The results show that wetland areas are generally increasing, with a significant growth in the proportion of natural wetlands. Carbon storage in Chongming’s coastal wetlands has increased annually, indicating initial success in wetland conservation. Dual-factor interactive effects have a greater impact on coastal wetland carbon storage than single-factor effects, and carbon storage is greatly influenced by socioeconomic factors.
[Objective] Previous studies in China on slope erosion characteristics under rainfall patterns have primarily focused on the loess region of Northwest China and red soil region of South China. Research on the purple soil region remains limited. Purple soil is the dominant cultivated soil in the Three Gorges Reservoir Region. Following the reservoir’s construction, substantial cultivated land was submerged, compelling local residents to reclaim more steep slopes for cultivation. This has exacerbated soil erosion issues in this region. Considering both rainfall patterns and land characteristics, this study conducted a comparative analysis of runoff and sediment reduction effects under different soil and water conservation (SWC) measures on purple soil slopes in the reservoir area. Understanding the response characteristics of runoff and sediment yield on purple soil slopes to SWC measures under different rainfall patterns could provide theoretical basis for evaluating the effectiveness of SWC measures in purple soil regions. [Methods] Using runoff and sediment yield data from 37 rainfall events across 10 runoff plots under different SWC measures in purple soil regions, rainfall patterns were classified using K-means clustering based on four indicators: average intensity (Iave), maximum 30-minute intensity (I30), duration (T), and erosivity (Rr). [Results] The results showed that the 37 rainfall events were classified into five patterns: Type I (low erosivity, long intensity, long duration), Type II (medium-low erosivity, medium-low intensity, medium-long duration), Type III (medium erosivity, medium intensity, medium duration), Type IV (medium-high erosivity, medium-high intensity, medium-short duration), and Type V (strong erosivity, high intensity, short duration).. Among these, Type III rainfall was identified as the primary rainfall pattern causing slope soil erosion, with runoff and sediment yields being 1.2-6.4 times and 2.7-19.4 times higher than the other four types. Narrow-terrace cultivation and platform planting exhibited optimal runoff reduction effects under light (Types I-II) and heavy (Types IV-V) rainfall patterns, respectively. [Conclusion] This was primarily because terraces effectively intercepted runoff sediment from low-intensity, small-volume rainfall, whereas under high-volume and high-intensity rainfall, terraces tended to become saturated, and platform fields were more effective in intercepting runoff sediment. Furthermore, the grass strips in forested areas demonstrated optimal runoff reduction effect under Type I rainfall pattern, primarily because the vegetation effectively slowed runoff velocity, enhanced infiltration, and facilitated sediment deposition. These findings provide a basis for further clarifying the relationship between rainfall and runoff sediment in purple soil regions.
[Objective] Current studies on the causes of water-sediment variation in the Yellow River mainly focus on the middle reaches’ hyperconcentrated sediment region or the Hekou-Longmen reach. Fewer studies have addressed the evolution of water-sediment relationships in typical tributaries of the upper reaches. Most existing research focuses on influencing factors of total water-sediment changes, with limited investigations on the driving factors behind water-sediment relationship evolution. The basin’s water-sediment effects under large-scale ecological restoration measures urgently need to be revealed. [Methods] This study took the Qingshui River Basin (QRB), the largest and most severely eroded tributary in the Ningxia section of the Yellow River, as the research object. Based on the actual water and sand data measured in the research area from 1955 to 2016, trend analysis and water-sediment relationship curves were used to reveal the characteristics of water-sediment changes. Multi-source data were employed to analyze the response of water and sediment to key influencing factors, ultimately exploring the evolution of basin water-sediment relationships under soil and water conservation. [Results] The interannual variations in runoff and sediment transport in the QRB were drastic. Annual runoff and sediment transport in Guyuan showed a significant downward trend. Annual runoff in Hanfuwang exhibited a significant decline, while annual sediment transport showed a non-significant decrease. Annual runoff and sediment transport in Quanyan Mountain showed no significant changes. Significant abrupt change years were observed in both annual runoff and sediment transport in the QRB. The abrupt change in annual runoff occurred in the 1990s, while that in annual sediment transport occurred after 2000. The periods of strong soil and water conservation measures in the Loess Plateau were close to the above abrupt change years of water-sediment factors. Sediment production in the QRB was jointly influenced by climate change (precipitation) and human activities. Drastic changes in the underlying surface caused by human activities were the primary factor leading to the sharp reduction in water and sediment in the QRB, further driving the evolution of basin water-sediment relationships. After 2000, the basin’s water-sediment relationship underwent a distinct transformation, specifically manifested as a significant decrease in the coefficient “a” of the water-sediment relationship curve and a notable increase in the downstream index “b”. Drastic changes in the underlying surface caused by human activities remained the primary factor driving water-sediment changes and the evolution of basin water-sediment relationships. [Conclusions] The water-sediment relationships in the basin have evolved as a result of large-scale soil and water conservation measures. Based on the sediment “storage-release” effect, the probability of strong sediment transport events still exists under new water-sediment conditions, necessitating strengthened preventive measures.
[Objectives] This study aims to improve the accuracy and efficiency of flash flood forecasting in the Guanshan River Basin and other similar small mountainous watersheds frequently affected by flood disasters by analyzing the runoff generation mechanisms of flash floods. By comparing the performance of saturation-excess, infiltration-excess, and hybrid runoff generation modes in simulating flash floods of different magnitudes, we also seek to overcome the limitations of single-mode simulation under complex terrain and different rainfall intensities. [Methods] The runoff generation module of the Xin’anjiang model was modified to simulate 38 flood events in the Guanshan River Basin (24 for calibration, 14 for validation) using saturation-excess, infiltration-excess, and hybrid runoff generation modes. Flood magnitudes were classified into small, medium, large, and extra-large according to the Specifications for Hydrological Information and Forecasting. Simulation results were evaluated using Nash-Sutcliffe efficiency coefficient (NSE), peak discharge error, and runoff depth error to compare the applicability and advantages of different runoff generation mechanisms. [Results] The vertical hybrid runoff generation mode demonstrated higher accuracy and stability across different flood magnitudes. It outperformed the other two modes in terms of NSE during both calibration and validation periods, with particularly strong performance in simulating extra-large floods. The saturation-excess mode performed better for small floods but was less stable for large and extra-large events. The infiltration-excess mode achieved the highest accuracy in simulating peak discharges of large floods, but performed relatively poorly in small and extra-large events. Further analysis of the runoff generation mechanisms indicated that runoff generation processes were closely related to rainfall characteristics, soil infiltration rates, and underlying surface conditions. Under intense and short-duration rainfall, infiltration-excess was the dominant mechanism, while under low-intensity and long-duration rainfall, saturation-excess prevailed. The vertical hybrid mode comprehensively integrates both mechanisms, dynamically adjusting the runoff generation approach based on varying rainfall conditions. It enabled effective simulation of flash flood processes under different rainfall scenarios. Additionally, this mode showed higher precision in simulating the recession processes, as it better reflected river basin storage states and the dynamics of interflow and groundwater runoff. [Conclusions] The vertical hybrid runoff generation mode demonstrates significant advantages in simulating flash floods in the Guanshan River Basin, providing robust support for improving the accuracy and efficiency of flash flood forecasting in this area. These findings not only provide a theoretical basis for flood prevention and disaster mitigation in the Guanshan River Basin but also offer innovative approaches for flash flood forecasting in complex mountainous watersheds. The innovation of this study lies in its comprehensive consideration of multiple runoff generation mechanisms and its validation of the hybrid mode’s adaptability under different rainfall conditions through comparative analyses. Future research will further refine the runoff generation module by incorporating more detailed physical processes and parameterization methods, while exploring the coupled applications of hydrological and hydrodynamic models to enhance the model’s capability in simulating complex hydrological processes and provide deeper insights into flood evolution in small mountainous watersheds.
[Objectives] The parameter calibration of the CASC2D hydrological model is mainly based on manual trial-and-error methods. It lacks a global sensitivity analysis of model parameters and the identification of relationships between parameters and simulation indices based on such analysis. Therefore, there remains considerable room for further exploration and discussion regarding parameter calibration methods and practices for the CASC2D hydrological model. [Methods] The CASC2D model is relatively suitable for flood forecasting in small semi-arid watersheds. This study selected the region upstream of the Suyukou hydrological station in the eastern foothills of the Helan Mountains as the study area. The Sobol index method, a representative global sensitivity analysis approach, was employed. Independent and global sensitivity analyses were conducted for eight key parameters of the CASC2D hydrological model, based on three performance indicators derived from simulation results: peak flow timing, peak discharge, and coefficient of determination. These analyses identified the correlations between model sensitive parameters and model-simulated peak discharge, peak flow timing difference, and coefficient of determination, providing references for model parameter calibration. [Results] The three parameters with the greatest global influence on the peak flow timing were saturated hydraulic conductivity (Ks), channel roughness coefficient (nc), and soil water deficit (Md). The peak flow timing of flood was mainly related to the infiltration calculation in the model. During the flow concentration process, channel routing played a controlling role, while overland flow routing played a supporting role. Additionally, the peak flow timing of flood was negatively correlated with river width (L) and vegetation interception (I), and positively correlated with nc, overland flow roughness coefficient (ns), Ks, capillary pressure head (Hc), and Md. The parameters that had the greatest global influence on peak discharge and coefficient of determination were Ks, Hc, and nc. Flood peak discharge was jointly influenced by infiltration characteristic parameters, overland flow routing parameters, and channel routing parameters. Among them, infiltration characteristics played the dominant role, while in the routing process, overland flow routing was relatively more influential. Coefficient of determination was mainly related to infiltration characteristics and channel routing parameters, with the former being dominant. Additionally, peak discharge showed positive correlations only with nc, ns, Ks, Hc, and Md. Coefficient of determination was negatively correlated with I and Ks, but positively correlated with L, ns, Hc, and Md. [Conclusions] This study further explores and supplements research on global sensitivity analysis of CASC2D hydrological model parameters. It proposes the types and sequence for adjusting eight key parameters in response to errors in peak discharge, peak flow timing, and coefficient of determination during initial calibration. The study also suggests reasonable increase or decrease ranges for each parameter based on their sensitivity to different indicators. These findings provide references for properly selecting the directions and ranges of parameter adjustments during calibration. Due to the interactions among parameters, the selection of adjustment directions and ranges during calibration should be based on each parameter’s independent sensitivity and degree of interaction obtained from the first-order and total effect indices. The research findings can provide references for manual calibration efforts and improve the efficiency of parameter calibration. Furthermore, given the current lack of research on automated calibration for this model, the findings offer strategic guidance for the development of automated calibration algorithms.
[Objective] When the water level difference between the upstream and downstream of a long-distance gravitational water conveyance system is small, gravity flow alone cannot ensure the required design flow rate. In such cases, the intake pumping station must be activated during high-flow conveyance periods to provide pressurized supply, forming a combined gravity and pressurized flow system. The hydraulic characteristics of such systems are more complex than those of pure gravity-driven systems. Accidental pump shutdowns can easily induce water column separation in the pipeline, leading to water hammer upon rejoining that poses a significant threat to project safety. [Methods] To address this issue, this study employed the method of characteristic curve to conduct one-dimensional numerical simulations of transient hydraulic processes for four water hammer protection schemes: (1) air valve, (2) air valve + terminal valve, (3) air valve + terminal valve + overflow pipe, and (4) air valve + air valve surge chamber. [Results] In long-distance gravity-pressurized water conveyance systems where the upstream elevation was higher than that of the downstream, accidental pump shutdowns without any protective measures would generate decompression waves that caused extreme negative pressure and water column separation inside the pipeline. The subsequent compression wave reflected from the downstream outlet reservoir would cause the separated water column to rejoin, potentially resulting in pipe rupture. Therefore, effective protective measures must be adopted to eliminate extreme negative pressure in the pipeline. When using an air valve alone for water hammer protection, the minimum pressure within the pipeline was effectively increased, but the range of protection was limited. In the air valve + terminal valve scheme, the compression wave generated by the closure of the terminal valve failed to effectively mitigate the negative pressure and may even result in excessive maximum pressure due to poor closure regulation of the terminal valve. Adding an overflow pipe to this combined scheme effectively reduced the maximum pressure in the pipeline. However, since the overflow pipe reflected part of the compression wave generated by the terminal valve closure, it had an adverse effect on negative pressure protection. [Conclusions] The air valve surge chamber, combining a surge pipe and an air valve with both water and air compensation functions, is used in combination with an air valve to form a protection scheme that effectively controls both positive and negative pressures in the pipeline. This solution achieves balance between engineering safety and cost-efficiency, making it the preferred protective measure for long-distance gravity-pressurized water conveyance systems.
[Objective] With the continuous expansion of China’s water conservancy infrastructure, hydraulic structures such as dams and sluice gates have obstructed fish migration routes and altered hydrological regimes both upstream and downstream. These changes have led to fragmentation of fish habitats, population declines, and even pushed some endemic fish species to the brink of extinction. To protect aquatic biodiversity and restore river connectivity, fishways have been widely implemented as critical passage facilities. Post-construction monitoring of fishway effectiveness is essential for verifying performance and identifying potential design improvements to enhance functionality and operational management. [Methods] This study evaluated the performance of the nature-like fishway at Sanghe River Secondary Hydropower Station through comprehensive monitoring. Hydrodynamic conditions were assessed using an Acoustic Doppler Current Profiler (ADCP) and 3D acoustic Doppler velocimeter (ADV) to measure water depth, temperature, and velocity parameters, ensuring they met fish passage requirements. Fish passage was monitored using infrared underwater video surveillance and capture methods during periodic dewatering, with data collected on species composition, abundance, size distribution, and movement patterns, providing references for domestic studies on nature-like fishway construction and fish passage monitoring. [Results] Results indicated all hydrodynamic parameters met design specifications. During monitoring, reservoir levels remained stable at 75 m, with fishway depths fluctuating between 0.03-1.22 m. Average velocities were 0.79 m/s in boulder crevices and 0.635 m/s in main channels, creating suitable migratory conditions. A total of 3 954 fish from 24 species (9 orders, 14 families) were recorded, dominated by Cypriniformes (75.99%). The most abundant species were Crossocheilus reticulatus, followed by Sikukia flavicaudata and Hampala macrolepidota, with most fish measuring 10-20 cm in length and 0-5 cm in width. Migration patterns showed distinct temporal variations: 68% of fish moved upstream, with significantly greater passage efficiency during daylight hours (06:00-18:00). Peak migration occurred in July-August, validating the design assumption of April-August being the primary migration season. [Conclusions] Measures to improve fish passage effectiveness include optimizing power generation-fishway coordination, removing debris in front of dam,dredging and maintaining fishway, and regular cleaning of monitoring equipment to improve reliability. The nature-like fishway at Sanghe River has successfully reestablished connectivity and created favorable hydrodynamic conditions for fish migration, demonstrating significant conservation value for the basin’s ichthyofauna.
In September 2023, the 12th International Conference on Geosynthetics (12th ICG) was held in Rome under the theme “Leading the Way to a Resilient Planet”. By reviewing and synthesizing three invited lectures,four keynote lectures, and major papers from the conference, we found that “resilience” and “sustainability” would be important future directions and they reflect the fundamental demands in the entire geotechnical engineering field. We put forward some future directions, particularly in the following areas, which were expected to become important research topics: (1) Life-cycle design will become the guiding approach for engineering design. This entails not only considering the construction phase and initial costs but also addressing the full operational lifespan and post-operational conditions and expenditures; (2) Reliability-based design methods and risk analysis, grounded in probability theory, will emerge as one of the principal methodologies for engineering design; (3) Prototype monitoring techniques will become indispensable tools for diagnosing engineering behavior and will serve as the foundation of life-cycle design. Various testing and monitoring technologies are expected to advance further; (4) More resilient and durable materials (such as geosynthetics) will continue to be developed and widely applied; (5) New and more resilient structural forms will emerge, and research into their working mechanisms will enter a new phase with enhanced simulation capabilities; (6) The intrinsic characteristics of rock masses as continuous media with structural planes and soils as particulate media will receive greater consideration in rock mechanics and soil mechanics research; (7) New numerical analysis methods(such as the Discontinuous Deformation Analysis, DDA) and artificial intelligence (AI) technologies will be increasingly integrated into geotechnical engineering, gradually transforming its design and analytical methodologies. In China, research has already begun in most of these areas, albeit to varying extents: some areas have made significant progress and are beginning to be applied in practice, such as (3), (4), and (7); Others have yielded some results but face divergent views and complicated paths forward, such as (2); Some areas have been recognized for their necessity and importance, but practical implementation is still lacking, such as (1); Others have yet to be initiated and require a renewed understanding of their significance, such as (5) and (6). This analysis inevitably reflects a limited perspective, and the author humbly invites comments and insights from readers.
[Objectives] This study focuses on the damage patterns of limestone in karst regions under acidic dry-wet cycles, aiming to explore the effects of the coupled action of acidic environment and dry-wet cycles on the mechanical properties and damage mechanisms of limestone. [Methods] Limestone from the Guilin karst region was selected as the research subject. Dry-wet cycle tests were conducted in acidic solutions with pH values of 3, 5, and 7 to simulate acid rain erosion. The number of cycles was set at 10, 20, and 30. Conventional triaxial compression tests were carried out to obtain stress-strain data and analyze the strength and deformation characteristics of the limestone. By integrating the Weibull distribution function with a composite damage variable, a geometric damage model was established. A statistical damage constitutive model for limestone was derived and its validity was verified using experimental data. [Results] (1)Mechanical degradation behavior: peak stress and elastic modulus exhibited exponential decay with increasing cycle count. The most significant degradation occurred at pH 3, where the elastic modulus decreased by 29.6% after 30 cycles. Notably, at higher cycle counts, the degradation rate in elastic modulus exceeded that of peak strength. (2)Model validation: The theoretical curves of the newly developed constitutive model showed strong agreement with the experimental data, accurately capturing the full stress-strain response of limestone under triaxial compression, including the residual strength phase. (3)Damage evolution mechanism: The total damage curve followed an “S”-shaped four-stage evolution (initial damage, rapid development, slowed development, and complete damage). Lower pH values led to an earlier onset of critical strain. After 10 cycles, the strain at the peak damage rate was significantly reduced, indicating that acidic environments induce increased brittleness in limestone. [Conclusions] The damage constitutive model developed in this study effectively reflects the mechanical behavior and damage evolution of limestone under acidic dry-wet cycles. The research reveals the complex mechanisms of acid-induced damage in limestone, offering new theoretical insights and methods for geotechnical design and slope stability analysis in karst regions, and provides an important reference for evaluating and predicting the performance of limestone materials in practical engineering applications in karst regions.
[Objective] A large number of aging earth and rockfill dams in China needs to be heightened due to seepage risks and insufficient flood control capacity. This study aims to reveal the seepage patterns of heightened dams, quantitatively evaluate the effectiveness of anti-seepage systems, and investigate the effects of two typical defects—waterstop failure at peripheral joints and cracking in cutoff walls—on seepage safety. [Methods] With a reservoir heightening project under construction as a case study, a three-dimensional finite element seepage model was established, incorporating the old dam, heightened concrete-faced rockfill dam, concrete cutoff wall, and curtain grouting system. Based on actual geological conditions and material permeability parameters, the seepage field distribution under four operating conditions—normal water level, dead water level, design flood level, and check flood level—was simulated. Defect-induced seepage was also simulated by setting different waterstop failure widths to analyze the sensitivity of these defects to seepage discharge, hydraulic head distribution, and seepage gradient. [Results] Under normal operation, the combined action of the new impermeable system effectively controlled seepage flow in the heightened dam. The free surface of seepage in the dam body remained low, with most areas in a drained state, while seepage flow primarily concentrated in the foundation; the total seepage discharge was 22.05 L/s. The hydraulic gradients of the face slab, cutoff wall, and curtain grouting were all below allowable thresholds, indicating that the anti-seepage system is reliable. When local waterstop failure occurred at the peripheral joint, reservoir water flew into the dam body through failure areas, forming a “bulging” saturation zone in the total hydraulic head contours. As the failure width increased, this zone expanded, reflecting local concentrated seepage. When local cracking occurred at the base of the cutoff wall, seepage discharge through the foundation riverbed increased markedly. As the cracking width increased, the riverbed seepage discharge rose correspondingly. However, this local leakage at the base of the cutoff wall had minimal impact on the hydraulic head distribution in the dam body and posed no threat to overall seepage safety. [Conclusion] The findings provide a theoretical basis for optimizing seepage control design in rockfill-based earth dam heightening project and offer important guidance for advancing scientific and precise anti-seepage design in old reservoir heightening projects in China.
With the acceleration of urbanization and continuous expansion of underground space, anti-floating design has become a core issue in ensuring the safety of underground structures. Based on a review of theoretical and experimental methods for the anti-floating performance of underground structures both domestically and internationally, we systematically summarize the research progresses on water buoyancy calculation methods, buoyancy model testing of underground structures, and anti-floating measures for underground structures. We also review the common scientific challenges and technical bottlenecks in current studies on the anti-floating performance of underground structures. The results show that: (1) the selection of anti-floating water levels requires comprehensive consideration of hydrogeological conditions and monitoring data, while there is currently no unified standard for multi-layer groundwater conditions. Anti-floating design for slope buildings is more complex due to significant differences in upstream-downstream water levels. Additionally, seepage significantly impacts buoyancy, particularly the overflow effect of confined water caused by vertical seepage, which can increase buoyancy to more than twice the hydrostatic pressure. Considering seepage effects, nine water buoyancy calculation models for different aquiclude structures were established based on Darcy’s law and seepage equilibrium equations, providing theoretical support for buoyancy calculations under complex geological conditions. (2) Researchers worldwide have derived buoyancy reduction coefficients for specific conditions through theoretical analysis, numerical simulation, and model box testing. Water buoyancy in sandy soils requires no reduction, while in cohesive soils, the reduction coefficient ranges from 0.41 to 0.85. (3) Anti-floating measures for underground structures can be divided into passive and active anti-floating types, with five common measures and their applicable conditions summarized. Passive anti-floating mainly increases the self-weight of the structure or the anchoring force, including methods of anti-floating (uplift) piles and anti-floating anchors (cables). Among these, floating beam capping and counterweight methods are widely used due to their convenient construction and simple operation. Anti-floating piles are suitable for deep excavations but have higher costs, while anti-floating anchors offer economic and flexible solutions but require leakage prevention at connections. Active anti-floating measures reduce water levels through interception and drainage decompression, offering quick results and low cost, though excessive drainage may cause ecological issues and foundation settlement. Practical engineering requires comprehensive consideration of geological conditions, structural characteristics, and cost-effectiveness to achieve balance between safety and efficiency.
[Objectives] The instability and failure of rock mass structures originate from the shear failure of rock joints. Therefore, understanding the shear behavior of rock joints is of great importance for understanding the mechanical properties of rock masses, evaluating the safety and reliability of rock engineering, and exploring the mechanism of geological phenomena. [Methods] To investigate the effect of deformation and failure patterns on the shear strength of rock joints, this study applied the variable cross-section beam theory to analyze stress changes during direct shear process of regular dentate joints. [Results] The possible failure patterns of dentate protrusions included shear tooth-breaking failure, tensile tooth-breaking failure, shear climbing-tooth-breaking failure, and tensile climbing-tooth-breaking failure, with transitions possible between these modes. The failure process of regular dentate rock joints was theoretically analyzed, identifying the failure patterns and corresponding horizontal displacements under different mechanical and geometric conditions. Prediction formulas for shear strength corresponding to different deformation failure patterns were derived, and the conditions for the occurrence and transition of these modes were established. Using parameter sensitivity analysis, the effects of mechanical and geometric factors (e.g., stress level, rock strength, undulation angle i, and width l of dentate protrusions) on failure patterns and shear strength were discussed. To validate the applicability and accuracy of the theoretical predictions, direct shear tests were conducted on regular dentate red sandstone joints with undulation angles of 40° and 60° under different vertical stresses (0.5, 1, 4, 6, and 8 MPa). Comparison between experimental results and theoretical calculations confirmed the correctness of the theoretical predictions. [Conclusions] This study provides theoretical support for further investigation into the generation mechanism of shear strength in natural rock joints. It should be noted that in the analysis of the stress state of the rock joints, the mechanical model of the dentate protrusions was simplified to a variable cross-section cantilever beam, and the failure surface of the protrusions was assumed to be a horizontal plane. Such simplifications may lead to deviations between the theoretical and actual stress distributions of protrusions. Future work will attempt to apply elasticity theory to determine the stress distribution of protrusions, thereby improving the accuracy of theoretical solutions.
[Objectives] This study conducts a systematic investigation into the influence of mud content on the mechanical properties and microstructure of Cemented Sand and Gravel (CSG), focusing on the low mud content range (<5%) that has not been fully addressed in previous research. The objectives include: identifying key factors affecting CSG strength through orthogonal experimental design; determining the optimal mix proportion balancing technical performance and economy; and revealing the micro-mechanism by which mud content affects CSG properties. [Methods] A four-factor (mud content, cement content, fly ash content, water-binder ratio) and four-level orthogonal experimental design (L16(44)) was used. Compressive strength, splitting tensile strength, and elastic modulus of CSG specimens were tested for 16 mix proportions at 7 days, 28 days, and 90 days. By graded washing of natural aggregates, the mud content was controlled at 0.39%, 1.28%, 2.05%, and 6.97%. Techniques such as X-ray diffraction (XRD), scanning electron microscope with energy dispersive spectrometer (SEM-EDS), and back scattered electron-image analysis (BSE-IA) were used to analyze hydration products, pore structure, and interface bonding characteristics. [Results] 1. Mechanical properties: Mud content was the most influential factor on compressive and splitting tensile strengths, with a significance ranking of: mud content > fly ash > cement > water-binder ratio. The optimal mix proportion—cement 60 kg/m3, fly ash 60 kg/m3, water-binder ratio 1.1, and mud content 2.05%—achieved a 28-day compressive strength of 7.68 MPa and an elastic modulus of 20.3 GPa. When the mud content increased to 6.97%, the elastic modulus decreased by 46.3% compared to the optimal group. Strength was age-dependent: compressive strength increased continuously (with an increase of >20% in each stage), while the growth rate of splitting tensile strength slowed after 28 days, stabilizing at 8%-11% of the compressive strength. 2. Microstructural Mechanism: In the low mud content (2.05%) group, the hydration process proceeded smoothly, promoting the formation of calcium silicate hydrate (C-S-H) gel, which effectively filled pores and cemented aggregates to form a dense structure. In contrast, high mud content (6.97%) caused unreacted mud powder to accumulate, which interfered with hydration and created interfacial cracks and large pores. XRD and EDS analyses further showed that excessive mud powder adsorbed free water, inhibited the secondary hydration of fly ash, and retained flaky calcium hydroxide (CH) crystals, ultimately reducing the overall integrity of the material. [Conclusions] This study innovatively fills the research gap on the influence of low mud content (<5%) on CSG performance. The proposed optimal mix proportion offers both economic and performance advantages, providing a practical solution for the direct use of natural aggregates with mud content in engineering (thus avoiding excessive washing). Microstructural evidence shows that appropriate mud content can improve material density through hydration products, while excessive mud content disrupts the hydration process and interfacial bonding between CSG components.
[Objectives] Traditional concrete is prone to brittle cracking under complex thermal-mechanical coupling conditions, which significantly increases the risk of gas leakage from underground gas storage reservoirs in Compressed Air Energy Storage (CAES) power stations. High-toughness cementitious composites (HTCC), due to their excellent toughness and impermeability, are considered as a potential structural lining material for CAES underground gas reservoirs. This study systematically investigates the gas permeability property and the evolution mechanism of the micro-pore structure of HTCC under thermal-mechanical coupling from an experimental perspective. A quantitative relationship between operational parameters (e.g., temperature and pressure) and gas permeability property is established, providing references for material selection in energy storage infrastructure. [Methods] Five groups of HTCC test specimens with different mix proportions were prepared. Their basic mechanical properties were evaluated through uniaxial tensile tests, and the mix with the best mechanical performance was selected to prepare ten groups of test specimens. Based on typical CAES operational conditions, nine test schemes were designed under a pressure of 10 MPa and temperature of 150 ℃. A self-developed temperature and pressure synchronized cyclic loading tester was used to simulate these operational conditions, and the ten groups of HTCC test specimens were subjected to ten cycles of loading. After the cycles, high-pressure gas permeability tests and mercury intrusion porosimetry tests were conducted to evaluate the effects of thermal-mechanical coupling on the gas permeability property and pore structure of HTCC. [Results] (1) The tensile-compressive strength ratio of HTCC reached 0.16, with a peak tensile strain exceeding 0.7% and an average crack width between 41-49 μm. HTCC demonstrated excellent tensile toughness and crack control capability, making it highly suitable for use in concrete lining structures of CAES reservoirs, and with optimized mix design, may also be applicable to the sealing layer. (2) The average gas permeability of the HTCC control group was 4.09×10-18 m2, and significant increases in permeability were observed after temperature and pressure synchronized cyclic loading. Under three pressure combinations (0-5 MPa, 0-7.5 MPa, and 0-10 MPa), when temperature increased from 25-50 ℃ to 25-150 ℃, three groups of test specimens showed maximum gas permeability increases of 112.7%, 183.6%, and 508.8%, respectively, compared to the control group. Moreover, temperature and pressure had distinct effects on permeability, with permeability being more sensitive to pressure than to temperature. (3) The gas permeability gradually decreased with increasing inlet pressure but tended to stabilize when the inlet pressure exceeded 3 MPa. (4) When the reservoir pressure was within 0-7.5 MPa, and the internal temperature reached 100 ℃, although the pore structure of HTCC changed, the critical pore diameter remained stable, and the permeability stayed within the order of 10-18 m2, which generally met the impermeability requirements of CAES reservoirs. However, when the operating pressure reached 10 MPa, the critical pore diameter increased, pore coarsening occurred, and new cracks formed, resulting in rapid degradation of impermeability. Therefore, if HTCC was to be used as the lining or sealing layer under 10 MPa pressure, it was recommended that its design compressive strength should exceed 40 MPa. [Conclusions] With excellent tensile toughness and crack control capability, HTCC can be applied to concrete lining structures of underground gas reservoirs in CAES power stations. When the operating pressure reaches 10 MPa, the impermeability of HTCC deteriorates rapidly. If HTCC is used as the sealing layer, its mix design should be optimized accordingly.
[Objective] In the context of big data from mobile internet, social media data with tags such as posting time and location has received widespread attention for its critical role in natural disaster response. In China, research on social attention and online public opinion regarding drought events remains limited, especially for the analysis of spatiotemporal and thematic characteristics of extreme drought events at the river basin scale, with no relevant reports yet. [Methods] This study used the 2022 extreme drought in China’s Yangtze River Basin as a representative case. Utilizing texts from Weibo, a mainstream social media platform in China, as data sources, this study used machine learning and artificial intelligence algorithms to collect Weibo text data throughout the drought progression process. The Latent Dirichlet Allocation (LDA) topic model was employed to perform term clustering and thematic characterization. Through this methodology, an in-depth mining of spatiotemporal and thematic characteristics of drought-related public opinion was conducted, along with sentiment analysis. [Results] (1) The temporal evolution of attention levels on social media was relatively synchronized with the progression of the drought event, with peak drought stage particularly prone to attracting heightened public attention. Across the entire Yangtze River Basin, drought-related discussions on social media remained relatively low in July 2022, rose dramatically in early August, peaked in mid-to-late August, gradually declined in mid-September, and returned to zero in early December. In terms of drought progression, an inverse correlation between the temporal variation characteristics of Weibo discussion level in severely affected provinces and municipalities including Sichuan, Chongqing, and Jiangxi and local hydrological flow data was observed. (2) The spatial characteristics of attention levels on social media basically matched the distribution of drought severity. The proportion of Weibo discussions in high-attention provinces and municipalities (e.g., Sichuan, Chongqing, and Jiangxi) exceeded 50%, reflecting widespread public concern about the drought and indirectly indicating severe socioeconomic impacts caused by the drought in these regions. In contrast, provinces and municipalities such as Yunnan, Tibet, Shanghai, and Qinghai showed relatively low levels of Weibo discussions. (3) The thematic characteristics of drought-related content on social media showed significant regional differences, with public attention levels being closely related to the severity of drought impacts. In Jiangxi and Hunan, key terms related to the drought were “shrinking of Poyang Lake” and “declining water levels” In Sichuan and Chongqing, key terms were secondary disasters such as “wildfires”, “earthquakes”, as well as drought-induced issues such as “reduced crop production by farmers” and “electricity supply shortages”. Other provinces primarily focused on “continuous high-temperature weather” and “meteorological drought”. As the drought progressed, the sentiment of public opinion on drought gradually transitioned from negative to positive. [Conclusion] Weibo texts serve as an effective data source for online public opinion analysis of sudden-onset disasters. The research findings can provide technical support for drought tracking analysis and mobilization efforts of the public for drought relief in river basins.
[Objectives] This study aims to optimize water-carbon coordinated scheduling during reservoir impoundment to improve power generation and storage rate, and to reduce greenhouse gas emissions in reservoir operation. [Methods] Given that current studies on cascade reservoir impoundment scheduling have not yet incorporated carbon reduction objectives, this study proposed a multi-objective water-carbon scheduling model for cascade reservoirs during impoundment period based on the carbon emission factor method.An early storage strategy for cascade reservoirs was developed,and three objectives—minimizing flood control risk,maximizing power generation,and minimizing greenhouse gas emissions—were established.The Non-dominated Sorting Genetic Algorithm Ⅱ (NSGA-Ⅱ) was employed to derive optimal scheduling schemes for the impoundment period.[Results] A case study was conducted on a cascade system comprising six reservoirs in the middle and lower reaches of the Jinsha River and the Three Gorges Reservoir.The results showed that the three scheduling objectives on the Pareto frontier formed a spatial surface distribution,reflecting nonlinear competitive relationships among the objectives.Compared to the current scheduling scheme,the optimal scheduling scheme—while occupying 0-4.92% of the flood control storage capacity—achieved a 0.65%-3.60% increase in multi-year average power generation (by 0.723-4.026 billion kW·h/a), a 6.45%-22.43% reduction in multi-year average spilled water volume (by 1.582-5.503 billion m3/a), an 8.33%-9.85% decrease in multi-year average greenhouse gas emissions (by 38.55-45.63 Gg CO2 e/a), and a 9.49%-11.44% reduction in carbon emission intensity (by 0.39-0.47 kg CO2 e/MW·h). Typical year scheduling analyses were conducted for a wet year (2020) and a dry year (2022). In the wet year, the selected scheme with the minimum flood risk increased power generation by 3.341 billion kW·h/a and reduced direct GHG emissions by 39.53 Gg CO2 e/a without increasing flood risk compared to the current scheme. In the dry year, the scheme with the maximum power generation raised the final storage level of the Three Gorges Reservoir by nearly 2 meters, increased available water by 1.794 billion m3, and reduced direct greenhouse gas emissions by 15.32 Gg CO2 e/a, while meeting the minimum ecological flow constraints during the impoundment period. [Conclusions] This study develops a multi-objective scheduling model for cascade reservoirs during the impoundment period and analyzes the nonlinear synergy and competitive relationships between carbon emissions and traditional water resource utilization benefits. The NSGA-Ⅱ optimization solutions significantly improv the long-term average power generation and storage rate while reducing greenhouse gas emissions without compromising flood control standards. Scheduling analyses for both wet (2020) and dry (2022) years demonstrate that the proposed model is well-suited to different hydrological scenarios, achieving a balance between carbon reduction goals and traditional reservoir functions such as flood control, storage, power generation, and drought resistance. This research provides technical support for implementing coordinated water-carbon scheduling of cascade reservoirs during the impoundment period.
[Objectives] Existing reservoir scheduling studies mainly focus on pure hydropower scheduling, with limited consideration of renewable energy integration. Traditional optimal scheduling of hydro-photovoltaic complementary systems typically prioritizes power generation benefits, which fails to meet the requirements of multi-objective comprehensive utilization. Moreover, compared with pure hydropower scheduling, the optimal scheduling of hydro-photovoltaic complementary systems is more complex to solve. This study aims to establish a multi-objective optimal scheduling model for hydro-photovoltaic complementary systems with the objectives of maximizing annual power generation benefits and maximizing the minimum output during specific periods. [Methods] To overcome the local optimum issue in the Moth-Flame Optimization (MFO) algorithm, improvements were made to the multi-objective MFO from three aspects: update formula, inspiration from moths’ linear flight paths, and flame population update strategy. To distinguish individuals that are mutually non-dominated under Pareto dominance, R-domination incorporating reference points was introduced. The combination of these two led to the development of a new high-performance multi-objective evolutionary algorithm: R-IMOMFO. A multi-objective optimization scheduling model for hydro-photovoltaic complementary systems was established, considering both power generation benefits and capacity benefits, and the model was solved using the R-IMOMFO algorithm. [Results] The R-IMOMFO algorithm demonstrated fast convergence, strong resistance to premature convergence, and high accuracy, proving to be an effective method for solving complex multi-objective optimization problems. Using the R-IMOMFO algorithm, non-dominated scheduling solution sets were obtained under three runoff scenarios—wet year, normal year, and dry year—for both power generation and capacity benefits. For each typical year, two extreme schemes and one intermediate scheme were selected for comparative analysis. This enabled scheduling operators to select more appropriate solutions based on their prioritization of different objectives. [Conclusions] The proposed multi-objective optimization model effectively coordinates the relationship between power generation benefits and capacity benefits in hydro-photovoltaic complementary systems, providing data support for decision-making in multi-objective optimal scheduling.
[Objective] To address the shortcomings of differential evolution (DE) algorithms in cascade reservoir optimization, this study proposes an intelligent algorithm that couples reinforcement learning and differential evolution (RLDE). [Methods] The RLDE algorithm improved the standard DE algorithm through three key strategies: chaotic mapping to enhance initial solution quality, Q-learning-based adaptive parameter adjustment, and a variable step-size strategy. Specifically, (1) chaotic mapping enhanced the initial solution quality. Logistic mapping with the best experimental performance was selected and applied to the population initialization of the RLDE algorithm. (2) The adaptive parameter adjustment was conducted based on the Q-learning algorithm. (3) A variable step-size strategy was designed for the actions in the Q-table, where the precision of action rows gradually increased with the number of iterations. To validate the feasibility and effectiveness of the RLDE algorithm, it was applied to optimize the power generation scheduling model for four major cascade reservoirs (Wudongde, Baihetan, Xiluodu, and Xiangjiaba) on the lower Jinsha River. [Results] (1) The chaotic initialization strategy effectively improved the initial solution quality. The adaptive parameter adjustment strategy based on the Q-learning algorithm enabled the algorithm to continuously adapt by receiving feedback from the environment. This process enhanced population diversity, greatly mitigated problems such as premature convergence or population evolutionary stagnation found in the traditional DE algorithm, thereby improving optimization performance. The variable step-size strategy allowed the algorithm to better respond to environmental feedback, further strengthening the optimization capability of the algorithm. (2) Compared with the traditional DE algorithm and adaptive genetic algorithm, the RLDE algorithm achieved an average annual power generation increase of 2.02% and 2.06%, respectively, under three typical inflow scenarios (wet, normal, and dry). Moreover, the average standard deviation of the proposed algorithm after multiple runs was reduced by an average of 729 million kW·h compared with the traditional DE algorithm, and by 844 million kW·h compared with the adaptive genetic algorithm. [Conclusions] This study proposes an intelligent algorithm that integrates reinforcement learning with differential evolution, effectively addressing issues such as premature convergence and search stagnation in the traditional DE algorithm. The proposed method provides an efficient and reliable solution for the optimal scheduling of cascade reservoirs.
