Abstract:Based on a one-dimensional salinity advection-diffusion model, an analytical expression for the salt flux transport mechanism in a regular semi-diurnal tidal estuary was derived. The effects of factors such as runoff, salinity, tidal amplitude, tidal current amplitude, phase difference between tidal current and tide, water depth, and estuary width on salinity diffusion were analyzed, quantitatively revealing the physical mechanism of the saltwater intrusion process in tidal estuaries. Furthermore, this analytical solution was utilized to explain the importance of each component of the salinity transport mechanism in Humen of the Pearl River Estuary. The results show that the Eulerian transport mechanism is controlled by upstream runoff; the Stokes drift transport mechanism is controlled by the tidal amplitude, tidal current amplitude, and their phase difference, and the tidal pumping effect is the result of the interaction among tidal pulsation, tidal current pulsation, and salinity pulsation; during the neap tide period in Humen, the semi-diurnal tidal characteristics are prominent; the advection transport is the main dynamic mechanism; the Eulerian residual flow transport is dominant, and the tidal pumping effect is not obvious; except for the mouth area, the salt flux generally shows a seaward transport trend during the tidal cycle; local areas of Humen are controlled by the tidal trapping mechanism, and between Zhangpeng and Machong stations, the downward discharge of saltwater is obstructed, which further intensifies the saltwater intrusion phenomenon in Humen.

Abstract:To study the structural characteristics of the river network in the Jinsha River Basin, river networks were extracted based on ASTER GDEMV3 data and the river network density method. By using the Horton-Stahler hierarchical method combined with indicators such as box dimension, bifurcation ratio, length ratio, and side-branch ratio, the self-similarity patterns and structural features of the Jinsha River Basin were analyzed, as well as the morphological characteristics of the main stream. The results indicate that rivers of levels 1-6 in the Jinsha River Basin exhibit structural and topological self-similarity, whereas rivers of levels 7-8 show no significant self-similarity. At the basin scale, box dimension and river network density satisfy self-similarity, with upper reaches characterized by smaller box dimensions and higher river network density, while the opposite is observed in the lower reaches. Topographic factors play a more dominant role than climatic factors in influencing box dimension and river network density in high-mountain canyon-type basins in southwestern China, such as the Jinsha River Basin. The river networks in high-altitude plateau regions generally exhibit higher bifurcation and length ratios but lower side-branch ratios. The upper reaches of the main stream of the Jinsha River feature gentle slopes and larger meander radii; the middle reaches have steep slopes and relatively straight channels, and the lower reaches show gentle slopes and smaller meander radii. As the length of the studied river segments increases, the average sinuosity, the range of sinuosity, and data dispersion all increase accordingly. Overall, an inverse relationship exists between river segment sinuosity and channel gradient.

Abstract:To improve the simulation accuracy of flow in ungauged small and medium rivers, river surface widths were inverted, and preliminary discharges were estimated using satellite imagery (Sentinel series and high-resolution images). These estimated values were then used as observed flow data and assimilated with the flow data simulated by the MIKE11 model using the Kalman filter algorithm. The assimilated flow results were fed back as updated inputs to the MIKE11 model, forming a closed-loop iteration that continuously corrected model errors and enhanced simulation accuracy. Validation results from the Huangkou Gate section in Quzhou County show that after data assimilation with the Kalman filter algorithm, the MIKE11 model achieves an R 2 of 0.820, an NSE of 0.813, and an RRMSE of 0.260 for simulated flow. Compared to pre-assimilation results, R 2 increases by 28.1%, NSE improves by 27.0%, and RRMSE decreases by 43.5%, demonstrating effective improvement in river discharge simulation accuracy.

Abstract:To improve the research system for concurrent compound disaster vulnerability, the superimposition (reduction) effects among concurrent disasters and the different characteristics of each dimension of vulnerability were considered, and the theoretical formulas for exposure index, sensitivity index, and adaptive capacity index of the concurrent compound disaster system were derived. Moreover, a assessment index system for vulnerability of the concurrent compound disaster system was established. This system used convolutional neural networks (CNNs) to evaluate sensitivity and employed the entropy weight-TOPSIS evaluation method to evaluate exposure and adaptability, and it utilized ArcGIS technology to conduct a comprehensive assessment of system vulnerability and obtained the distribution of vulnerability grade intervals. The verification results of the avalanche-landslide example in the Guangdong-Hong Kong-Macao Greater Bay Area show that this assessment system is logically reasonable and methodologically reliable, and it has accurate assessment results, with strong scientificity and applicability. It can be effectively applied to the quantitative assessment of concurrent compound disaster vulnerability. The high and medium-high vulnerability areas of avalanche-landslide in the Guangdong-Hong Kong-Macao Greater Bay Area are concentrated in the central areas of the bay such as Yuexiu District and Tianhe District, as well as in the middle and southern areas of the bay such as Nanshan District, Futian District, and Luohu District. The districts and counties with vulnerability rankings in the top ten, such as Yuexiu District and Futian District, need to particularly consider strengthening disaster-resistant infrastructure and enhancing disaster management.

Abstract:To address the problem of missing runoff data, a daily runoff prediction model (MM-LSTM-BP model) combining a long short-term memory (LSTM) neural network and a back propagation (BP) neural network based on multiple regression models was constructed. In this model, regression models were adopted to extract the linear, nonlinear, temporal, and random characteristics of runoff, and the LSTM neural network and the BP neural network were used in series for the regression simulation of the daily runoff process. The case verification results of the Weihe River Basin indicate that the MM-LSTM-BP model generally performs better than the single regression methods during the verification period; the root mean square error (RMSE) of the daily runoff data decreases by more than 50%, and the Nash efficiency coefficient (NSE) increases to 0.935; the MM-LSTM-BP model has better stability during the normal flow period and the recession period, and the simulation error of the flood peak is reduced by more than 6% during the flood period.

Abstract:The high-precision precipitation fusion products CMORPH and CMFD were used as model inputs, and 18 flood events of the Tunxi Watershed in the upper reaches of the Xin’an River Basin from 2013 to 2018 were taken as the research object. The temporal and spatial distribution characteristics of rainfall by the two precipitation fusion products in the Tunxi Watershed were analyzed, and the applicability of the WRF-Hydro model driven by two types of precipitation fusion data to the simulation of mountain torrent processes in medium- and small-sized watersheds was explored. The results show that compared with the measured precipitation at the site, the CMORPH precipitation product has higher accuracy in terms of peak precipitation values and precipitation amount, while the CMFD product generally overestimates the precipitation amount, especially the peak precipitation values. At the same time, CMORPH precipitation product has higher accuracy on different time scales. In the simulation results based on CMORPH precipitation fusion data, only the Nash coefficient of three flood simulation results is less than 0.8 (one of which is less than 0.7), and the total qualified rate is 94%, reaching the grade A accuracy. The total qualified rate of flood simulation based on CMFD precipitation fusion data is 67%, which is grade C accuracy. Moreover, the model’s simulation accuracy for large floods is better than that of small flood processes. In general, the WRF-Hydro model driven by high-resolution CMORPH precipitation fusion product can be well applied to mountain torrent process simulation in medium- and small-sized watersheds.

Abstract:To investigate the response characteristics of frozen ground’s hydrological elements to climate warming in the plateau region of the upper reaches of the Yellow River, the VIC model was established to simulate the hydrological processes in the plateau watershed of the upper reaches of the Yellow River from 2006 to 2018. The variation characteristics of runoff processes, active layer thickness (ALT), soil moisture (ice) content, and soil temperature in the study area were analyzed. The results show that permafrost can be divided into high-temperature and low-temperature types based on the average annual ground temperature. High-temperature permafrost is more widely distributed, accounting for approximately 70%, while low-temperature permafrost is mainly found in mountainous areas above an altitude of 4 000 meters. The thickening rate of ALT in low-temperature permafrost is higher, indicating a more sensitive response to climate change. The average annual unfrozen moisture content and soil ice content in the upper (0-10 cm), lower (10-30 cm), and deep (30-100 cm) soil layers exhibit a decreasing trend, with the smallest variation observed in the upper soil layer. Significant reductions in unfrozen moisture content and soil ice content are detected in the lower soil layer near Eling Lake and Zhaling Lake. The warming trend at deep soil nodes is relatively stable throughout the year, with a warming rate of approximately 0.02 ℃/a. The warming trend is more rapid and significant during autumn and winter, when the warming rate reaches 0.03 ℃/a.

Abstract:To gain further insight into the surface water and groundwater exchange process in typical salt marsh-tidal creek systems in Yancheng City, Jiangsu Province, continuous in-situ monitoring and sampling analysis of data including water volume, salinity, and isotopes were conducted, and the exchange fluxes between surface water and groundwater during both spring and neap tides were estimated, revealing the patterns of surface water and groundwater interactions. Results indicate that tides serve as the primary driving force of surface water and groundwater exchange in the salt marsh-tidal creek systems. The exchange flux is markedly influenced by tidal conditions, with exchange flux during spring tides reaching up to 26-30 times that during the neap tides. During the tidal cycles, surface water recharge and groundwater discharge are almost equivalent. Although the net water flux can be neglected, this process causes a significant discharge of stratum salts, with an average salt flux of up to 140 t/d. Furthermore, a discharge process of deeply trapped marine water with a larger space-time scale exists in the study area, which may have non-negligible impacts on water, salt, and heat exchange.

Abstract:Based on the ecological survey data in 2022, the Ecopath models of the Mulan River Estuary and its upstream and downstream control areas (river area and bay area) were constructed, and the trophic structures, energy flow characteristics, and overall system characteristics of the three ecosystems were comparatively analyzed. The results indicate that the trophic structures of the Mulan River Estuary, river, and bay ecosystems are all pyramid-shaped, and the structural complexity from low to high is river, estuary, and bay, successively; the energy flows in the three ecosystems are mainly concentrated in trophic levels Ⅰ-Ⅲ, with energy flow proportions all above 99%; the total energy transfer efficiency (TE) of the estuary ecosystem is relatively low (0.9%); benthos and phytoplankton are the key trophic communities affecting the estuary ecosystem; the ratio of primary production to respiration (3.33), Finn’s cycling index (0.085), and Finn’s mean path length (2.683) of the Mulan River Estuary are between those of the river and the bay, while the connectance index (0.32) and system omnivory index (0.051) are the smallest, indicating that the estuary ecosystem is still in an immature and unstable stage; the increases in NO₃-N and CODMn may affect the maturity and complexity of the ecosystems; it is recommended to improve water quality by implementing reasonable and effective water environment treatment measures and to improve the maturity and stability of the estuary ecosystem by moderately increasing the stock enhancement and release quantity and species of herbivorous and carnivorous fishes.

Abstract:Based on the long-term observation data of Poyang Lake, various mathematical statistical methods were used to explore the trend, mutation, and periodic characteristics of the hydrological regime evolution, and the fluctuation process of water quality was analyzed by selecting the indicators of permanganate index, ammonia nitrogen, and total phosphorus. Moreover, the driving effects of different hydrological parameters on water quality were analyzed. The results show that the water level of Poyang Lake has generally decreased from 1962 to 2022, with an average rate of change of -0.013 5 m/a, and the abrupt change year is concentrated around 2003, with a water level change cycle of about 36 years; the water quality shows a decreasing-and-then-stabilizing trend from 1988 to 2022, with total phosphorus as the main exceedance factor, and the exceedance multiples range from 0.02 to 2.31; the slight fluctuating trend of water quality indicators at each station since 2015 is expected to continue in the future at most stations; the permanganate index is weakly correlated with hydrological parameters, and ammonia nitrogen and total phosphorus are significantly correlated with many hydrological parameters. The water level is the main factor influencing the concentration of nitrogen and phosphorus. Water temperature, precipitation amount, and inflow volume of water have significant regulatory effects on water quality changes. Water level changes have a significant unidirectional effect on ammonia nitrogen and a relatively complex effect on total phosphorus.

Abstract:A time-dependent performance function for the aqueduct structure was established based on concrete carbonation depth. The first three statistical moments were obtained using the point estimate method, and the calculation results of time-dependent reliability indices by three third-moment methods were comparatively analyzed. Furthermore, remaining service life prediction method for aqueducts based on the time-dependent reliability index was proposed. By taking the Shazibei Aqueduct in Hunan Province as an example, the failure probability and reliability index under the concrete carbonation failure mode were calculated, and the remaining service life prediction formula was obtained through data fitting. The results indicate that the third-moment method based on lognormal distribution exhibits the best accuracy and applicability, which is highly consistent with the Monte Carlo simulation results, with an error of 0.42%. The third-moment methods based on the square normal distribution and exponential function have higher calculation efficiency, but the errors are 8.23% and 9.31%, respectively. The proposed method can be used for life assessment and maintenance of aqueducts under carbonation failure conditions.

Abstract:To enhance the accuracy and generalization capability of concrete dam deformation prediction models, fully utilize the topological relationships of temporal data in long time series, and consider various uncertainties, an improved Transformer (ITransformer) model and bidirectional long short-term memory neural network (BiLSTM) were integrated with the Kepler optimization algorithm (KOA) to construct the KOA-ITransformer-BiLSTM concrete dam deformation prediction model, namely KIB model. Additionally, to address uncertainties such as measurement errors, the quantile regression (QR) method was introduced, establishing the QR-KOA-ITransformer-BiLSTM concrete dam deformation interval prediction model, namely QKIB model. Experimental results demonstrate that the KIB model significantly improves prediction accuracy and iterative efficiency, reducing the mean absolute error, mean absolute percentage error, mean squared error, and root mean squared error by 77.89%, 90.37%, 93.08%, and 73.69%, respectively, compared to the LSTM models, while increasing the coefficient of determination R 2 by 23.02%. The QKIB model exhibits superior stability and accuracy, with the comprehensive evaluation metric at the 90% confidence level decreasing from 1.387 36 (QR-LSTM), 0.786 48 (GRU), and 0.543 42 (QR-BiLSTM) to 0.241 95.

Abstract:To address the operational efficiency reduction caused by sediment accumulation in the bottom corridor of storage tanks, the influence of sediment moisture content on the flushing characteristics of a hydraulic self-cleaning system in storage tanks was investigated through physical experiments, as well as its coupling effects with sediment thickness and flushing flow rates. The results demonstrate that the scouring rate exhibits a nonlinear parabolic relationship with sediment moisture content, with an optimal moisture content range of 12%-20%. Low moisture content (＜12%) inhibits scouring due to enhanced interparticle cohesion and shear strength, while high moisture content (＞20%) reduces the scouring rate owing to increased self-weight. Sediment thickness significantly affects scouring efficiency, with medium moisture content (12%-20%) showing the weakest sensitivity to thickness variations. The positive correlation between flushing flow rate and scouring rate is affected by moisture content, and the effect of increased flow rate under medium moisture content is the most significant. Structural optimization of corridor sidewalls eliminates diamond wave interference, improving the scouring rate by 15.34%-37.83% across all moisture content levels and transforming scouring morphology from wavy to strip-shaped patterns.

Abstract:To study the effect of the density current driven by temperature difference on the flow structure and mixing characteristics at the confluence of the Yangtze River and Poyang Lake, a three-dimensional hydrodynamic numerical model of the confluence channel of the Yangtze River and Poyang Lake was constructed based on field monitoring data, and the hydrodynamics and mixing processes at the confluence under conditions of different density differences were simulated and analyzed. The results indicate that the shear layer at the confluence of the Yangtze River and Poyang Lake tilts toward the side with a higher density, and a larger density difference between the two branch flows indicates a more obvious tilt of the shear layer; when the density of the Yangtze River water body is lower than that of Poyang Lake, a clockwise single-helix secondary flow is formed at the confluence, and conversely, a pair of counter-rotating double-helix secondary flows are formed; the density difference effect enhances the intrusion effect of the low-density water body into the high-density water body near the water surface, and when the density of the Yangtze River water body is higher than that of Poyang Lake, it has a promoting effect on mixing, and conversely,it suppresses mixing.

Abstract:To accurately identify the safety hazards in complex hydropower engineering construction scenes in real time, an automatic identification method of safety hazards in hydropower engineering construction based on enhanced feature representation was proposed. The feature extraction network was constructed, and the squeeze and excitation module was embedded to adaptively enhance the feature expression, enhance the identification effect of the image features of the safety hazards, and reduce the influence of background noise. The feature enhancement network was constructed, and the group-wise separable convolution module and the vision-oriented ghost spatial cross-stage partial convolution module were introduced to alleviate the loss of low-level detail information, enhance the feature fusion ability, and improve the identification accuracy of multi-scale safety hazards. The results of the engineering case verification show that the model can overcome the interference of complex scenes by strengthening the feature expression, and the average accuracy of construction safety hazard identification is up to 86.8%, which is better than the existing hydropower engineering construction safety hazard identification model and provides technical support for the intelligent and refined management of hydropower engineering construction safety hazards.

Abstract:To address the problems of difficult positioning and low detection timeliness of embankment piping points, high-precision distributed optical frequency domain reflectometry (OFDR) was introduced. Through theoretical analysis and model tests, the influence of flow velocity and piping channel diameter on the distributed strain response characteristics was studied. Relationships between strain characteristic values and key indicators such as seepage velocity and piping channel diameter were established, and the feasibility of detecting piping based on high-precision strain information was demonstrated. The results show that OFDR can sensitively detect the strain changes caused by water flow through the optical cable. With the increase of flow velocity, the strain induced in the optical cable correspondingly increases, which is consistent with the theoretical derivation trend. The correlation between flow velocity and strain can reach 0.993. An increasein piping channel diameter also causes an increase in optical cable strain.

Abstract:The Transition SST turbulence model was used to simulate and analyze the influence mechanisms of O-ring with different relative spacings and inclination angles on the mechanical characteristics of the cylinder surface, vortex shedding characteristics, and wake flow structures at a subcritical Reynolds number. The results show that the inclined O-ring with a relative spacing of 3/4 significantly controls the unsteady hydrodynamic characteristics of flow around a cylinder by extending the shear layer, disrupting the dominant frequency of vortex shedding, reducing the pressure difference between the front and rear of the cylinder, and decreasing the streamwise fluctuating velocity and turbulent kinetic energy behind the cylinder. With the increase of the inclination angle, the control effect is enhanced. Compared with the uncontrolled case, the time-averaged drag coefficient and the standard deviation of lift coefficient are reduced by about 13% and 37%, respectively, and the Strouhal number is reduced by about 7%. The inclined O-ring with a relative spacing of 3/4 and an inclination angle of 30° shows the best control effect, which is the optimal inclined O-ring structure.

Abstract:The effects of salt content and freeze-thaw cycles on the compressibility characteristics of modified saline soil in seasonally frozen regions were experimentally investigated by modifying the soil with microbial-induced calcite precipitation (MICP) combined with activated carbon. The results show that after MICP modification, the cementation effect of the generated calcium carbonate on soil particles can resist the expansion damage caused by salt-frost heave, and the compressibility is reduced. The addition of activated carbon promotes urease activity, making the MICP reaction more intense and thorough. This process generates more calcium carbonate to reinforce the soil structure. Furthermore, with the increase of activated carbon content, the reinforcement effect becomes more significant, and the compressibility is further reduced. However, with the increase of salt content, urease activity is inhibited, leading to a decrease in the urea hydrolysis rate. Consequently, the MICP effect becomes insignificant, unable to provide sufficient carbonate ions, and the calcium carbonate coverage area decreases. Therefore, MICP technology significantly improves the compression characteristics of saline soil in seasonally frozen regions.

Abstract:Salt crystallization near the injection well of deep saline aquifers for CO2 geological storage may increase engineering operation costs and pose safety risks in the near-wellbore region, and the mechanisms by which salt crystallization affects CO₂-brine two-phase flow remain unclear. To address these issues, the variation patterns of CO₂ injectivity under different salinity conditions in brine-saturated cores were investigated through laboratory CO₂ core displacement experiments. Results demonstrate that non-uniform salt crystallization occurs during the drying process regardless of salinity. In deionized water and low-salinity brine, the drying effect enhances effective gas permeability. However, higher salinity significantly increases residual water saturation, drying rates, and salt accumulation, leading to a marked reduction in gas injectivity. The core displacement process is characterized by three stages, namely displacement, entrainment, and dissolution flooding, with drying occurring during the displacement and entrainment stages after pore capillary water forms. Furthermore, the pore-scale salt crystallization interface involves a shrinkage and expansion process. The influence of crystallization on gas injectivity depends on the competition between solution shrinkage and crystal expansion; higher salinity promotes crystal expansion, causing more severe gas injectivity loss.

Abstract:To address the problem that cut-fill roadbed slopes in mountainous areas are prone to instability and sliding failure under the influence of rainfall and cracks, local reinforcement of the slopes was carried out using geosynthetic reinforced soil technology. Based on the upper bound theorem of limit analysis, a calculation formula for the stability of locally reinforced cut-fill slopes considering pore water pressure was established. Through parameter analysis, the influence laws of local reinforcement on slope stability and that of weakening coefficient on failure modes were revealed. The results show that the required reinforcement force for the stability of cut-fill slopes increases with the increase of the fill slope and pore water pressure, while it decreases with the increase of reinforcement depth and the original slope. Increasing the local reinforcement depth significantly improves slope stability, but the possibility of translational failure surface needs to be considered. When the pore water pressure is high, rotational failure should be considered.

Abstract:Unconfined compressive strength tests, direct shear strength tests, and scanning electron microscope microanalysis were conducted to investigate the improvement effect and reinforcement mechanism of the biogel and palm fiber composite on clay. The test results show that the biogel and palm fiber composite can significantly enhance the compressive strength of clay, with a maximum compressive strength of 876.4 kPa, and the optimal mixing ratio is a biogel content of 2% and a palm fiber content of 0.6%. Compared with the clay improved only by biogel, the modified soil exhibits less brittle failure; compared with that improved only by palm fiber, it presents better integrity. Under compression, palm fibers can bridge cracks in the soil, while biogel greatly increases the cohesion of the soil and reduces the outward movement of palm fibers under compression. Scanning electron microscope microanalysis reveals that biogel wraps the soil by forming a film-like structure, and the carboxyl and hydroxyl groups in its molecules bridge and form hydrogen bonds with the surfaces of clay particles, filling interparticle pores to improve soil compactness. Palm fibers mainly exert a physical reinforcement effect, sharing external loads through friction and tension with the soil. Biogel acts as a bonding agent between palm fibers and soil particles, and palm fibers fill the pores of soil particles, optimizing the arrangement structure of soil particles through stretching, interlocking, and friction effects, thereby improving the strength and overall stability of the soil.

Abstract:In view of the severe freeze-thaw damage and destruction of red sandstone in the cold and high-altitude environment of the Qinghai-Xizang Plateau, red sandstone samples with good integrity from the southeastern part of the region were selected as the research object. Multi-scale experimental methods, including freeze-thaw cycling tests, uniaxial compression tests, nuclear magnetic resonance testing, and quantitative analysis of apparent cracks, were adopted to reveal the coupled evolution laws of the physical and mechanical properties and pore-fracture damage of red sandstone under freeze-thaw action. The results indicate that as the number of freeze-thaw cycles increases, the phenomenon of particle shedding occurs on the surface of rock samples; the dry mass of samples decreases; the porosity increases linearly, and the saturated longitudinal wave velocity shows an exponential attenuation trend. The uniaxial compressive strength and elastic modulus of red sandstone decrease with the increase in the number of freeze-thaw cycles, and the deterioration rate accelerates after 70 freeze-thaw cycles. The transverse relaxation time spectrum of red sandstone shows a three-peak distribution. With the increase in the number of freeze-thaw cycles, the proportion of large pores (＞4 μm) in red sandstone increases linearly, while the proportions of small pores (＞0.1-1 μm) and medium pores (＞1-4 μm) decrease overall. Under freeze-thaw action, the rock damage gradually evolves from the microscale to the macroscale. Within the first 30 freeze-thaw cycles, the main manifestation is the expansion and connection of micro-pores, and after 30 cycles, the development of macroscopic cracks can be observed, eventually leading to rock cracking and failure. A total damage variable for sandstone is proposed by combining the elastic modulus, the volume proportion of large pores, and the fracture rate, achieving a cross-scale definition of the damage variable, which provides a theoretical basis for further understanding the freeze-thaw deterioration mechanism of sandstone in the cold and high-altitude environment of the Qinghai-Xizang Plateau.