Abstract:To address the issue that most conceptual hydrological models considering snowmelt are lumped models, a gridded Xin’anjiang model considering snowmelt and rainfall-runoff processes (iRainSnowHydro model) was constructed based on the gridded Xin’anjiang model by coupling a snowmelt module. Daily runoff simulations were conducted taking the Liyuan basin in the upper reaches of the Jinsha River and the Wunonglong basin in the upper reaches of the Lancang River as typical basins, and the results were compared with those of a lumped snowmelt runoff model (Hydromad model). The results indicate that the iRainSnowHydro model exhibits good daily runoff simulation performance in both the Liyuan and Wunonglong basins, with R2 and NSE exceeding 0.85 and the absolute value of PBIAS being less than 10% in the calibration and validation periods. The simulation performance of the iRainSnowHydro model is superior to that of the Hydromad model, and its distributed structure has significant advantages.

Abstract:To enhance the adaptability of hydrological model structures to the spatiotemporal heterogeneous characteristics of catchment runoff generation and routing and improve the applicability limitations of traditional fixed-structure models in different catchments, the fundamental principles of the SuperflexPy modeling framework based on the flexible architecture theory were systematically elaborated. By taking the Qijiang River Basin in Chongqing as the study area, a semi-distributed catchment hydrological model was constructed. A comparative test was carried out through 18 assembly schemes of hydrological process elements, and the daily runoff simulation effects of different model structures were quantitatively evaluated. The results indicate that the semi-distributed hydrological model constructed based on SuperflexPy can effectively simulate the daily runoff processes at catchment control sections; the simulation results of different element assembly schemes show significant differences, which can effectively identify and reflect the key hydrological links in the runoff formation process; SuperflexPy adopts an object-oriented paradigm to achieve the modular encapsulation of hydrological elements and generalizes the catchment topological structure through the hierarchical organization of simulation units, nodes, and networks. It can flexibly assemble different runoff generation and routing processes, possesses strong catchment adaptability, and can well depict the spatiotemporal heterogeneity of catchment runoff generation and routing.

Abstract:To address the problem of low accuracy and poor reliability of water level monitoring caused by water gauges being easily entangled by floating debris and damaged during flood periods under shore-based camera deployment, a mapping relationship between the pixel’s vertical coordinate of the waterline in an image and the actual water level was established based on monocular photogrammetry. The pyramid scene parsing network was employed to perform semantic segmentation of water and riverbank regions. Meanwhile, cross-sectional terrain data were combined to construct a virtual water gauge, through which the pixel’s vertical coordinate of the waterline was converted into the actual water level. Experimental results show that the root mean square error of waterline detection is less than 2 pixels. By properly selecting cameras to control the spatial resolution of imaging elevation, the accuracy of water level measurement can be better than 2 cm. With inclined shore-based camera deployment, the proposed method achieves fully non-contact online water level monitoring without requiring a physical water gauge or ground control points. It has the advantages of low operation and maintenance cost, strong robustness, and intuitive results and is applicable to irregular cross-sectional scenarios such as natural rivers and artificial open channels.

Abstract:Surface meteorological elements and upper-air meteorological elements under typhoon weather conditions were predicted using Pangu-Weather, and the prediction of typhoon tracks was studied combined with the tropical cyclone tracking algorithm. The SWAN model was driven based on the typhoon track prediction results of Pangu-Weather and the predicted wind field data improved by a direct correction method. The calculated significant wave height data were compared with the measured data for verification, thereby evaluating the effectiveness of the model in predicting typhoon tracks and typhoon waves in Guangdong Province and Hainan Island. The results indicate that Pangu-Weather can achieve long-term typhoon track prediction, and the results are superior to those of the high-resolution numerical atmospheric model (ECMWF-HRES), but Pangu-Weather underestimates the typhoon wind field. Combining the typhoon track predicted by Pangu-Weather with the typhoon wind field improved by the direct correction method to drive the wave field can effectively improve the prediction accuracy of typhoon wave heights.

Abstract:Based on the daily rainfall data of 79 rainfall stations in the upper reaches of the Yangtze River Basin from 1979 to 2019 and the daily runoff data at the Three Gorges, the concurrent relationship between the rainy season onset and the runoff-based flood season onset in the upper reaches of the Yangtze River Basin under different threshold discrimination conditions was explored. Based on the correlation coefficients between the rainy season onset dates and the runoff-based flood season onset dates under different thresholds, the respective thresholds for rainfall and runoff when their relationship was the most significant were determined, and accordingly, the rainy season onset index and the runoff-based flood season onset index of the upper reaches of the Yangtze River Basin were determined. The results indicate that the increase in rainfall in the upper reaches of the Yangtze River Basin precedes the rise of the inflow at the Three Gorges by 2-4 pentads. Before the flood season onset, the most significant increase in rainfall occurs at the 30th pentad, and the corresponding inflow at the Three Gorges shows an obvious rise at the 32nd pentad; the multi-year average dates of the rainy season onset and the runoff-based flood season onset are May 31 and June 11, respectively. In most years from 1979 to 2019, the rainy season onset date is earlier than the runoff-based flood season onset date, but there are eight years when the rainy season onset is slightly later than the runoff-based flood season onset, mainly because the number of rainfall stations meeting the standard in the rainy season onset index is insufficient. After optimizing the rainy season onset index using the basin rainfall volume index, the optimization effect is remarkable, and there are only two years when the rainy season onset date is later than the runoff-based flood season onset date.

Abstract:Based on the meteorological data of eight pilot cities for sponge city construction, the fully distributed surface water-groundwater coupled model ParFlow-CLM was applied to simulate long-term hydrological processes of an idealized bioretention catchment, and response characteristics of runoff, seepage, and evapotranspiration processes of a typical bioretention cell to meteorological conditions were systematically explored. The results indicate that the surface runoff volume of the bioretention cell is primarily influenced by the average rainfall intensity of rainfall events in the simulation year; the average rainfall intensity is also the main meteorological factor affecting the ratio of annual deep seepage to annual precipitation; when the seepage capacity of native soil at the bottom of the bioretention cell is zero (or the bioretention cell is treated with anti-seepage measures), the annual subsurface runoff coefficient shows a certain negative correlation with the average rainfall intensity of events within the year but is largely uncorrelated with annual precipitation and the ratio of annual potential evapotranspiration to annual precipitation( E p/ P ); as the seepage capacity of native soil increases, the correlation between the annual subsurface runoff coefficient and average rainfall intensity gradually shifts to a positive correlation, and a certain correlation with annual precipitation and E p/ P gradually emerges; the ratio of total evapotranspiration of the bioretention cell to annual precipitation of the catchment shows a strong linear correlation with E p/ P of the catchment.

Abstract:By analyzing precipitation and tide level data of the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) from 1960 to 2020, and combining the Thiessen polygon method with correlation analysis, the non-coincidence phenomena and spatial distribution characteristics of rainfall-tide compound disasters and storm surges were revealed. The results indicate that the non-coincidence of storm surges in the GBA is significant. Specifically, the variation points in the estuary regions are concentrated around 1987, whereas those in the upstream basins occur earlier, around 1975. For rainfall-tide compound disasters, the variation points are observed around 1987 in the estuary areas but are delayed to 1994 in the central basin. The non-coincidence of storm surges is primarily driven by climate change and human activities, such as upstream dam construction and estuarine sand mining. Furthermore, the variations in compound disasters are significantly influenced by the interaction between storm surges and rainfall.

Abstract:For the Gongming Reservoir-Qinglinjing Reservoir connection project in the Pearl River Delta water resources allocation project, a hydrodynamic-water quality-ecological coupled model for this connection project was established based on measured water quality and meteorological data, as well as future climate model data, by using the GOTM reservoir hydrodynamic model and the GOTM-FABM-WET reservoir ecological dynamics model. The hydrodynamic characteristics and water quality response laws of the connection project under different operation modes were simulated, and the eutrophication evolution trends of the reservoirs from 2022 to 2031 under two climate change scenarios (SSP1-2.6 and SSP3-7.0) were predicted. The results indicate that after connection, the total nitrogen mass concentration in the receiving Qinglinjing Reservoir shows a seasonal reversal characteristic of increasing from January to July and decreasing from July to December. Meanwhile, the total nitrogen mass concentration in Gongming Reservoir decreases slightly, and the changes in chlorophyll a and total phosphorus mass concentrations are relatively small. Under the background of climate warming, the chlorophyll a mass concentration in both reservoirs is expected to reach 30-40 μg/L after 10 years of the connection project operation, and the trophic level index (TLI) enters the mild eutrophication range (50-60). Moreover, under the high-emission scenario, the total nitrogen mass concentration in Gongming Reservoir faces the risk of exceeding the limit of the Class Ⅲ water quality standard.

Abstract:To address the problem of low accuracy in empirical sediment discharge ratio formulas caused by the continuous decline in effective reservoir capacity and significant changes in inflow water and sediment conditions during long-term operation of cascade reservoirs, the inflow water and sediment processes in the cascade reservoirs of the lower reaches of the Jinsha River over the next 100 years were designed. The sediment discharge ratios of the cascade reservoirs were calculated using both a one-dimensional water-sediment model and the Siyami empirical formula for sediment discharge ratio. The quantitative relationship between the results obtained by the two methods was analyzed, and the Siyami empirical formula for sediment discharge ratio was subsequently corrected. The results show that the sediment discharge ratio calculated by the one-dimensional water-sediment model exhibits greater volatility than that calculated by the Siyami empirical formula. Moreover, as the operation time of the cascade reservoirs increases, the growth rate of the sediment discharge ratio calculated by the one-dimensional water-sediment model is significantly higher than that calculated by the Siyami empirical formula. The coefficient of determination of the corrected Siyami empirical formula for the Wudongde, Baihetan, Xiluodu, and Xiangjiaba reservoirs is 0.95, 0.96, 0.87, and 0.86, respectively, indicating that the corrected formula has high accuracy.

Abstract:To address the problems of strong subjectivity in weighting by the analytic hierarchy process and insufficient research on the spatiotemporal distribution of life loss risks in traditional dam breach life loss assessment, as well as the high fuzziness and randomness of risk indicators, a risk assessment method for dam breach life loss based on a combined weighting-cloud model was proposed. This method comprehensively considered various influencing factors, established a grading standard for dam breach life loss assessment indicators, and constructed a unit population distribution model for the downstream flooded area based on dam breach flood routing results. By integrating the indicator weights determined by the combined G1-entropy weight method with the risk membership degree of each unit obtained from the cloud model, dynamic risk assessment of different spatiotemporal units during the dam breach process was achieved. The overall life loss risk level of the reservoir dam breach was determined by calculating the life loss value. The case study results demonstrate that the combined G1-entropy weight method integrates data changes during flood routing and effectively balances the subjective and objective weights of relevant indicators in dam breach life loss risk assessment; the combined weighting-cloud model method can effectively handle the randomness and fuzziness issues in the risk assessment process, achieve dynamic risk assessment of the dam breach process, better conform to the actual flood routing process, and more accurately reflect the impact of the flood on the affected population during the initial stage of the dam breach.

Abstract:For an actual water diversion project, a mechanistic model based on hydraulic principles was established, and hydraulic parameters were calibrated. Based on data such as system layout parameters, upstream reservoir’s water level, measured pressure and flow rate along the pipeline, and measured flow rate and opening of the regulating valve, a BP neural network data model was established, and GA was used to optimize the initial weights and biases to improve the accuracy of the data model. The target opening data of the regulating valve calculated by the two models were comparatively analyzed, and the applicable conditions of the two models were proposed. The results indicate that when the cosine similarity between the input data and the training data is high (≥ 0.95), the average error of the data model is 0.58%, representing a reduction of 0.11 percentage points compared with that of the mechanistic model, and the maximum error is reduced by 0.46 percentage points; however, when the cosine similarity is less than 0.95, the maximum error of the data model can reach 9.02%, while the average error of the mechanistic model does not exceed 1.13%. The data model depends on data and has high calculation speed and accuracy under conditions of high cosine similarity.

Abstract:To investigate the acid corrosion-induced deterioration law of mechanical properties of cement mortar under coupled seepage and salt attack, cement mortar erosion tests, uniaxial compression tests, and splitting tensile tests were carried out under different acidic conditions (pH=7, 3, and 1) in Na₂SO4 solution with seepage. The deterioration mechanism of the mechanical properties of cement mortar under the coupled seepage and salt attack under different acidity conditions was revealed, and a deterioration analysis model for the mechanical properties of cement mortar was established. The results show that at pH of 7 and 3, the compressive strength and tensile strength of cement mortar specimens initially increase and then decrease with increasing erosion duration, reaching their peak values at 60 d and 45 d, respectively. Specifically, the peak compressive strength and tensile strengths are 39.33 MPa and 3.12 MPa at pH of 7, as well as 36.71 MPa and 2.86 MPa at pH of 3. In contrast, at a pH of 1, the compressive strength and tensile strength of the cement mortar specimens decrease, with their maximum values being 31.00 MPa and 2.30 MPa, respectively. A higher acidity of the erosion solution indicates a lower peak compressive strength and tensile strength of cement mortar and a more pronounced deterioration effect of mechanical properties. Under coupled seepage and salt attack, as acidity increases, the deterioration of cement mortar shifts from being dominated by the coupled action of leaching erosion and sulfate attack to being dominated by acid erosion. Under the coupled seepage and salt attack, the strength damage coefficient of cement mortar exhibits a good quadratic function relationship with erosion duration, and there is a linear correlation between tensile strength and compressive strength.

Abstract:To investigate the impact of different installation conditions of rectification curtains on the crucial driving factors of algal blooms in the tributary bay of a river-type reservoir, numerical simulation methods were used. By taking the Xiangxi River, a tributary bay of the Three Gorges Reservoir, as an example, a three-dimensional hydrodynamic and water temperature model was constructed to simulate and compare the changes in flow field and water temperature characteristics of the tributary bay under conditions before and after the installation of a rectification curtain, as well as under different installation positions and submerged depths. The results indicate that the rectification curtain has a significant blocking effect on water flow. Water mass mixing occurs at the upper layer at the section where the rectification curtain is installed, resulting in a decrease in water temperature on the upstream side and a reduction in water temperature stratification. Under different installation positions of the rectification curtain, the flow velocity in the middle layer of the water body changes more significantly as affected by the rectification curtain than that in the surface and the lower layers. Furthermore, when the rectification curtain is installed closer to the upstream of the tributary bay, the influence on flow velocity at the estuary is more significant. However, the effect of the rectification curtain on water temperature has little correlation with its installation position. The average temperature difference across different layers at the rectification curtain section increases with increasing submerged depth. The upper layer exhibits the largest water temperature variation. The depth range of water temperature change also expands with increasing submerged depth, ultimately achieving a reduction in water temperature across the entire vertical section.

Abstract:Given the significant uncertainty in the sealing effectiveness of water seals for high-head gates caused by material attenuation effects, the attenuation characteristics (including stress relaxation, hysteresis effect, and plastic deformation) and time-varying laws of rubber materials were analyzed through constitutive characteristic tests of rubber water seals. A mechanical model for sealing was established by integrating the sealing mechanism of water seals filling the narrow gap space, and the constraint conditions for reliable sealing of water seals were clarified and experimentally verified. The results indicate that the compression ratio is a key factor affecting the sealing effectiveness of water seals for high-head gates; specifically, the sealing effectiveness of water seals with a compression ratio of less than 25% shows a good positive correlation with the compression ratio, whereas that of water seals with a compression ratio of greater than 25% shows a significant negative correlation with the compression ratio. The established constraint conditions for sealing effectiveness agree well with the ultimate pressure-bearing test results, which can provide an important reference for the reliable sealing of high-head gates.

Abstract:To investigate the capability of electrical resistivity tomography for characterizing heterogeneous karst conduits, laboratory model tests on the detection of heterogeneous karst aquifers were conducted under different boundary layouts and excitation source conditions. The experimental results indicate that compared to the observation mode with insulated boundaries, using controlled electrical potential boundary conditions as inversion constraints for electrical resistivity tomography detection can effectively reduce the uncertainty of estimated parameters. With the increase in the number of electrical potential boundaries, the characterization accuracy of electrical resistivity tomography for heterogeneous karst conduits gradually improves. Compared to the mode with constant current excitation sources, the mode with constant voltage excitation sources has higher imaging accuracy and inversion certainty, but the estimated conductivity is relatively high. The electrical resistivity tomography technique based on a successive linear estimation algorithm can effectively characterize the heterogeneous characteristics of the conductivity distribution in karst aquifers.

Abstract:To investigate the influence of tensile stress on the salt-freeze resistance of hydraulic concrete, salt-freeze tests were conducted under ultimate tensile stresses of 0%, 30%, and 50%. The mass loss, attenuation of dynamic elastic modulus, and chloride ion diffusion laws were analyzed, and the damage mechanism was revealed in combination with pore structure evolution. The results indicate that tensile stress significantly accelerates the deterioration process of concrete. Under ultimate tensile stress of 50%, after 200 freeze-thaw cycles, the mass loss rate of low-air-content concrete specimens increases by 21.7%; the relative dynamic elastic modulus decreases by 35.5%, and the chloride ion diffusion coefficient increases by up to 47.0%. Microcracks induced by tensile stress significantly enlarge the pore size and enhance the pore connectivity. Although increasing the air content can mitigate salt-freeze damage, the proportion of harmful pores in high-air-content concrete is relatively high, and the superimposed effect of tensile stress may affect the durability of concrete.

Abstract:To improve the connection efficiency of steel structure module units, a clamp-bolted connection joint between block units was proposed. A finite element model of the joint was established to analyze the static performance, seismic performance, and the influence laws of three parameters (side wall thickness of the welded connection surface between the corner fitting and the module steel beam (side wall thickness of corner fitting), wall thickness of the positioning clamp, and wall thickness of the module steel beam) on the mechanical performance of the joint. The results show that the clamp-bolted connection joint features a simple and reasonable structure, a clear load-transfer mechanism, and favorable seismic performance; increasing the wall thickness of the module steel beam can improve the maximum bearing capacity, as well as the overall stiffness and energy dissipation capacity of the joint to a certain extent; increasing the wall thickness of the positioning clamp can improve the initial stiffness of the joint but reduces its energy dissipation capacity, and excessive wall thickness of the positioning clamp reduces the ultimate bearing capacity of the joint; increasing the side wall thickness of the corner fitting can improve the bearing capacity of the joint, and greatly enhances its energy dissipation capacity, but weakens the stiffness of the joint.

Abstract:To address the problems of difficulty in determination and strong experience dependence of the radius of maximum wind speed and Holland- B parameter in the calculation of the Holland typhoon wind field model, the calculation methods of the radius of maximum wind speed and Holland- B parameter of the Holland typhoon wind field were optimized using the random forest algorithm, combined with the dataset of the machine learning model of satellite remote sensing inversion data. Furthermore, the wind speed of the parametric typhoon wind field model with optimized parameters was compared and verified with the measured wind speed, and the accuracy difference between the parameter values optimized by the algorithm and those calculated by empirical formulas was compared. The results indicate that the two optimized empirical parameters of typhoons fit well with the validation set data; the average errors are both less than 4%, and the prediction accuracy increases by about 50% compared with traditional empirical formulas. Based on the random forest algorithm, the empirical parameters of the parametric typhoon wind field model can be obtained quickly and effectively, and the simulated wind speed error is within 7%. This improves the accuracy and stability of the simulated wind speed of the parametric typhoon wind field model and provides a new technical approach for typhoon numerical simulation.

Abstract:By taking two typical eco-friendly wave-dissipating elements on muddy coasts, namely oyster reefs and mangroves, as research objects, a numerical simulation was conducted on the hydrodynamic characteristics of regular wave propagation and evolution over oyster reefs and mangroves based on the non-hydrostatic wave SWASH model. Furthermore, the wave dissipation variation laws of a single oyster reef, a single mangrove, and their synergy on muddy coasts under different combinations of water levels and waves were explored. The results indicate that the combined condition of oyster reefs and mangroves effectively improves the overall disaster reduction efficiency, and the wave dissipation process exhibits nonlinear variation characteristics. In the synergistic wave dissipation condition, mangroves have a significant enhancement effect on oyster reefs, and engineering layouts can prioritize increasing the planting scale of mangroves to achieve efficient disaster reduction. Under low-water-level conditions, the wave dissipation contribution rate of oyster reefs can reach more than 50%, while at high water levels, mangroves play a dominant role in wave dissipation relying on the canopy structure, and the sequential coordination of the two can achieve progressive energy dissipation and disaster reduction.

Abstract:To address the impact of large-scale offshore photovoltaic pile groups on nearshore wave fields, a generalized model method adopted SWAN model based on equivalent bottom friction coefficient was proposed to solve the bottleneck of low computational efficiency in full-grid simulation of high-density pile foundations. Based on the method, the attenuation effect of 50 000 pile foundations on wave fields under different working conditions in the offshore photovoltaic area of Qizi Bay, Qingdao, Shandong Province was simulated. The results indicate that the pile group has a significant blocking effect on wave propagation; the wave height attenuation gradually increases from sea to land, and the wave height attenuation rate on the nearshore side can reach 30% under extreme conditions. This method can effectively solve the computational difficulties in simulating large-scale pile groups and provides technical means for the wave field impact, pile foundation design, and parameter selection of offshore photovoltaic projects.

Abstract:Based on the salinity advection-dispersion equation, constant-dispersion-coefficient and variable-dispersion-coefficient analytical models for saltwater intrusion in Humen of the Pearl River Estuary were constructed under two assumptions of a constant longitudinal salinity advection-dispersion coefficient and a spatially varying longitudinal salinity advection-dispersion coefficient. With field measured runoff and salinity data, the saltwater intrusion process was simulated and reproduced; the spatiotemporal variation laws of the longitudinal salinity advection-dispersion coefficient were comparatively analyzed, and the salinity dispersion characteristics in Humen were explored. The results indicate that the variation range of the longitudinal salinity advection-dispersion coefficient in Humen is small, and the saltwater intrusion process curve presents a bell-shaped transition form, characterized by convexity in the downstream reach and concavity in the upstream reach; the salinity gradient gradually increases and then decreases along the upstream direction. The salinity dispersion characteristics of the downstream waterway in Humen are significantly affected by the incoming water from the Dongjiang River, showing obvious segmented features. During spring and neap tides, the spatiotemporal average of the longitudinal salinity advection-dispersion coefficient in the downstream waterway of Humen affected by the Dongjiang River is 1 785 m²/s, while the overall spatiotemporal average of the upstream and downstream waterways of Humen is 2 649 m²/s. Huangpuyou Station is a segmented characteristic station of the Humen Waterway. Compared with the value assignment method that comprehensively considers the upstream and downstream dispersion characteristics, adopting the longitudinal salinity advection-dispersion coefficient calibrated for the waterway downstream of Huangpuyou Station in the analytical model can improve the prediction accuracy of the model for longitudinal salinity distribution changes in the reach affected by the Dongjiang River but underestimates the actual length of saltwater intrusion in Humen to a certain extent.