To estimate the spatiotemporal characteristics of CO₂ partial pressure (p_CO2) and water-air interface CO₂ flux (F_CO2) along the Yangtze River, this study selected eight monitoring sections along the main channel of the river from upstream to downstream. Based on water quality data from 2020 to 2022, p_CO2 and F_CO2 were calculated using the CO₂ SYS software. The spatiotemporal variations of p_CO2 and F_CO2 were analyzed, and the relationships between p_CO2, F_CO2, and environmental factors were assessed using the Mantel test. The results show that from 2020 to 2022, p_CO2 in the Yangtze River ranged from 450.02 to 3 615.88 μatm, which was higher than the global atmospheric CO₂ average partial pressure of 414.78 μatm during the same period. Spatially, the distribution of p_CO2 was as follows: midstream > upstream > estuary. The average values of water-air F_CO2 during 2020-2022 were 40.25 mol/(m²·a), 74.74 mol/(m²·a), and 61.85 mol/(m²·a), respectively, with a spatial distribution of upstream > midstream > estuary. The Yangtze River is in a state of CO₂ oversaturation, and that the water-air F_CO2 flux showed an overall increasing trend from 2020 to 2022. p_CO2 exhibited a significant positive correlation with water temperature, dissolved oxygen, and pH, while F_CO2 was positively correlated with pH, dissolved oxygen, and conductivity.

Irrigation drainage is an inevitable accompanying process in agricultural irrigation, widely present in the irrigated farmlands of the northwest region of China. Due to poor water quality, if it is returned to the river channels, it will pose a threat to the water ecological environment of the basin. Taking the Huanghe South Bank Irrigation District in Hangjin Banner as the research object, a MIKE SHE distributed hydrological model was established to predict the drainage volume and available volume of the irrigation district. Cross-checking was conducted with the simulation results of hydrological models by using the water equilibrium method and the ratio of diversion to drainage method. The results show that under the current drainage system conditions, the multi-year average drainage volume is 48.21 million m³, and the available volume is 43.39 million m³; After the drainage system is upgraded and transformed, the multi-year average drainage volume is 49.20 million m³, and the available volume is 44.28 million m³. The drainage volume prediction results of each method vary slightly, but the overall difference is not significant. The simulation results by MIKE SHE's hydrological model and the average deviation is controlled within ±4%, while the relative error of the simulated drainage during the verification period is 3.7%. The MIKE SHE hydrological model performs well in simulating the drainage process of the irrigation district, which can provide reference for the resource utilization of irrigation district drainage.

The construction of fish-friendly water passage has become an inevitable demand for habitat connectivity and protection. To further optimize the hydraulic characteristics of fish-friendly channels, based on a flume experiment, large-eddy simulation (LES) is used to construct a three-dimensional hydrodynamic model. The channel flow is simulated under the influence of regular triangular baffles and permeable triangular baffles. The results indicate that the permeable triangular baffle design effectively reduces the strength of the main recirculation zone and limits its development. The turbulent kinetic energy and Reynolds stress behind the baffle are reduced due to water inflow through the permeable apertures, leading to a 34.5% reduction in maximum turbulent kinetic energy along the vertical axis. Furthermore, at two different water depths, the permeable baffle design increases the proportion of resting zones and local low-velocity zones, while significantly reducing the proportion of negative flow velocity zones that are harmful to fish.

The permeability of karst medium is affected by multiple factors such as the geological characteristics of soluble rocks, the degree of karst development, and the fluid properties. The permeability coefficient estimation model of fractured rock mass is difficult to reflect the complexity of karst development, which makes it poorly applicable. Random Forest (RF), Support Vector Regression (SVR), CatBoost machine learning algorithm combined with Bayesian optimization algorithm were used to construct the permeability coefficient estimation model of karst media. The root mean square error (R_RMSE), mean square error (M_MSE) and coefficient of determination (R²) were used to verify the evaluation accuracy of the estimation model. The SHAP algorithm was used to analyze the dominant influencing factors of the permeability coefficient of karst media in machine learning model, and the influence of each influencing factor on the permeability coefficient of karst medium was clarified. The results show that the R_RMSE of the optimized SVR model is 0.128 8, M_MSE is 0.016 6 and R² is 0.74, which are better than the random forest and CatBoost models, and can better estimate the permeability coefficient of karst media. The SHAP diagram revealed that there were obvious differences in the permeability coefficient of karst media between different eigenvalues of each dominant factor, and the karst rate (BK), depth (Z) and filling content (AFC) of the borehole line were the main influencing factors of the permeability coefficient of karst media, and had a significant impact on the permeability coefficient of karst media. The SVR model has high estimation accuracy and strong interpretability, which provides a certain reference value for engineering applications in karst areas.

Water park is an important window of ecological civilization construction. Taking 20 national water parks as examples, using the public comment data, the CES dictionary of water park was constructed to analyze the public perception frequency and satisfaction of the CES during and after the COVID-19 pandemic. And then IPA model was used to evaluate water park. The results show that the public focus on water park are consumption, transportation, scenic spot environment and water conservancy engineering, and there are differences in different stages; The frequency of aesthetic value and recreation is the highest, and the frequency of inspiration service is the lowest. The frequency of popular science education is lower during the COVID-19 pandemic; The overall satisfaction is 80.51% during the COVID-19 pandemic and 82.15% after the COVID-19 pandemic ends; The future construction of water park in Henan Province should pay attention to social relations and science education service, while fully exploiting the potential of cultural history and spiritual service. The research is of great significance to the evaluation and planning and construction of water park.

Underwater topography serves as essential foundational data for river management and reservoir scheduling. The riverbed longitudinal profile is a significant topographical characteristic and is one of the key elements determining the flow velocity and water level variation along the river or reservoir. Based on the energy equation of flow, this paper employs the width-to-depth ratio /H and the relative depth of the section centroid H_c/H as indicators to quantitatively assess the cross-sectional morphology. The correlation relationship between the cross-sectional area, hydraulic radius, and the maximum water depth for a certain power station is established. An analytical method for inverting the longitudinal profile of deep pools of underwater topography before and after reservoir siltation under the control of water surface lines was proposed. Case study results indicate that the proposed method can quickly and accurately invert underwater topography after the siltation of rivers and reservoirs, providing a new approach for rapid determination of topography before and after reservoir construction.

The stability of dam construction by tailings accumulation is closely related to the ultimate bearing capacity of geotextile used in dam construction. The fine tailings of Dayu Shilei Tungsten Mine in Ganzhou are used as the filling material. Through the uniaxial compressive strength test of the filling geotextile filled with fine tailings under different consolidation time and different filling degree, the variation law of the ultimate compressive strength of the geotextile and the failure mode of the geotextile and the strength reinforcement mechanism of the bag body are analyzed. The results show that when the geotextile reaches the ultimate compressive strength, the vertical strain is between 20% and 30%; The ultimate compressive strength of geotextile decreases with the increase of tailings filling degree (filling height), and increases with the increase of consolidation time. Under uniaxial compression, the failure position of the geotextile mainly occurs at the bottom of the intermediate geotextile, and the lower the filling degree, the greater the failure range is; The theoretical calculation value of the modified formula of ultimate compressive strength considering the influence of filling degree is compared with the experimental value of ultimate compressive strength, and the error between them is less than 4%. The conclusion can provide reference for similar fine-grained tailings geotextile dam construction.

Based on the hourly precipitation data (1980-2019) from 142 national stations in Hebei Province, Mann-Kendall (MK) trend and mutation test, K-means clustering, and hydrometeorologically homogeneous region methods were used to systematically analyze the temporal evolution characteristics and spatial distribution patterns of short-term extreme precipitation in Hebei Province. The results show that significant regional differences exist in interannual variation of short-term extreme precipitation, with an upward trend in high-altitude mountains and a downward trend in low-altitude plains/hills, marked by a 1996 change-point. Topography significantly influences patterns: the spatial extent decreases in plains and southern slopes but expands on northern slopes for 1 h and 3 h durations, indicating a shift towards mountainous areas. Seasonal differences are pronounced: winter/spring increases, while summer and autumn decreases significantly, with third-quarter Rx24h declining at 0.337 mm/a. The research results reveal the spatio-temporal differentiation law of short-term extreme precipitation in Hebei Province, providing a scientific basis for regional flood control and disaster reduction as well as adaptive management to climate change.

To ensure the timeliness of frost resistance testing of hydraulic concrete and improve the safety of construction and operation of project, the methods for testing the frost resistance of concrete were systematically reviewed. The standard differences among slow freezing method, fast freezing method, single-sided freeze-thaw method and salt-resistant erosion method were compared. Two new trends were analyzed including the rapid detection technology of frost resistance based on the rapid freezing method and the rapid detection technology of concrete relying on process parameter control. The new ideas for rapid testing methods of frost resistance were proposed based on structures parameters of hardened concrete, accelerated destructive experiment, key process parameters of freezing and thawing. The concept of dedicated curves was established, and the specific procedures of the new methods was clarified. The work of all the above could provide new ideas for the frost resistance testing of hydraulic concrete.

To clarify the first flush characteristics of particulate and dissolved pollutants in urban roof and road runoff and to scientifically determine the first flush volume (V_FF), this study investigated the typical cement roof and asphalt road runoff in Beijing using the M (V) curve method. The approach involved calculating average pollutant concentrations in specified runoff increments during rainfall events to assess water quality variations, quantify V_FF, and evaluate corresponding runoff pollution control effectiveness. The results show that the pollution levels of particulate and dissolved chemical oxygen demand (COD) and phosphorus in runoff from asphalt road are significantly higher than those from cement roof (p<0.05), but no such significant difference is observed for particulate and dissolved nitrogen. Particulate pollutants in cement roof runoff exhibit a stronger first flush phenomenon, whereas the first flush phenomenon of dissolved pollutants is more pronounced in asphalt road runoff. Except for the pollution indicators with weaker first flush phenomenon, there are significant differences between V_FF of COD, total nitrogen (TN), and total phosphorus (TP) and their particulate or dissolved indicators. According to the current national standard, the first 3 mm of runoff shall be discarded, cement roof and asphalt road can achieve SS pollution control rates of (65.26±32.40)% and (65.43±23.81)%, respectively, and COD pollution control rates of (58.17±32.49)% and (59.06±31.48)%, respectively. Higher runoff pollution control results will be obtained if V_FF is determined based on actual monitoring data. The findings will provide reference for implementing targeted control strategies and methods for particulate and dissolved pollutants in urban stormwater runoff.