The scour of seawall toe is the one of the main factors for influencing structural stability of seawall estuary. The study of the scour characteristics at seawall toe under complex hydrodynamics and prediction method is of great significance for the seawall stability. Based on the field monthly measured topographic data since 2010, the time evolution of toe scour at Xijiangtang Seawall in Qiantang Estuary was discussed and the influence of flood was identified. The research results show that the seawall toe is eroded during flood, while there is silting during tide, and the critical flood discharge for scouring is about 5 000 m³/s. Based on the theory of sediment carrying capacity and riverbed deformation, a new scour prediction method is developed and the relative error is significantly improved within 20%.

Under the condition of low flow ratio, the flow structure of the inlet area of tributaries is very complicated. Based on physical model test and PIV particle image velocimetry technology, the average velocity distribution and three-dimensional velocity spatial distribution of open channel tributaries under different intersection conditions were observed, and the variation law of the flow field of tributaries was analyzed. The results show that when the confluence is relatively small, the surface water of the tributaries will have reverse reflux phenomenon to varying degrees due to the top supporting effect of the main stream water, while the bottom water flows downstream to the main stream, and there is a relatively obvious oblique mixing interface. With the increase of the confluence ratio, the influence of the main stream on the flow structure of the left bank of the tributary decreases gradually. When the intersection angle is 30° and 90°, the water flow structure near the right bank section is most affected by the water top support of the main flow. When the intersection angle is 150°, the tributaries are basically in reverse reflux state, and the maximum reflux velocity area is formed at the intersection. The results can provide theoretical support for the study of frequent bloom caused by nutrient enrichment in tributaries of reservoir area.

Based on the daily precipitation data of 38 meteorological stations in the Huaihe River Basin from 1961 to 2020, the consecutive dry days (CDD) were selected. The variation characteristics of CDD and its response to 12 circulation index at different time scales were analyzed by using M-K trend test, principal component analysis, the lag correlation analysis and cross wavelet transform. The results indicate that the spatial distribution of CDD in Huaihe River Basin had obvious seasonal characteristics. It was high in the west and low in the east in summer, and high in the north and low in the south in spring, autumn and winter. In the past 60 years, the changes of CDD in different seasons were also different. The CDD increased in most stations and the basin tended to become dry in autumn, but the CDD decreased in all stations and drought slowed down in the basin in winter. The CDD with different time lags had good correlations with the WP, SOI and Nino4, and the strongest correlation with Nino4. The Nino4 had a significant strengthening effect on the CDD with a lag of 4 and 5 months, and a significant weakening effect on the CDD with a lag of 10 and 11 months. The significant influence of Nino4 on CDD was mainly concentrated in the resonance period of 10-15 months, and there was a significant negative correlation between Nino4 and CDD. The finding is prone to useful for drought prediction and water resources management in the future.

The groundwater level in the deep foundation pit project close to the river shows a dynamic characteristic of long-term low water level but high water level during flood season. Foundation pit dewatering leads to the complexity of the seepage field in the surrounding stratum environment, destruction of enclosure structures, accidents include piping and instability at the bottom of the pit. Therefore, this paper simulated the excavation-precipitation process of deep foundation pit project based on the HS-Small constitutive model, analyzed the sensitivity of precipitation influencing factors (precipitation depth, mode, rate and water stop curtain) to the surrounding environment deformation and their relationship. Compared the analysis results with the measured results, it can be found that the settlement of the top of the foundation pit, the soil outside the pit and the surrounding buildings gradually increases, and the dewatering has a more obvious influence on the deformation during the excavation and dewatering of the foundation pit; Fractional precipitation can effectively reduce the settlement deformation of surrounding buildings and ground surface; It is recommended that the dewatering depth of foundation pit should be controlled within 0.5-2.0 m below the bottom plate; The precipitation rate has a relatively small impact on the total settlement of the surrounding environment, but has a great impact on the settlement rate. When the precipitation rate reaches the optimal value, it is beneficial to the stability control of the foundation pit. The embedded depth of water-proof curtain in this project is more than 30 m, which has no obvious effect on controlling the settlement of surrounding buildings. The research results can provide reference for the dewatering design and construction of similar deep foundation pit projects closed to the river.

In order to study whether the original design flow can be met after the lining scheme of sections of a long distance non-pressure diversion tunnel is changed, the flow capacity of typical sections of the tunnel was analyzed by model test and theoretical calculation. There are 4 tunnel diameters and 2 roughness in the typical section of the tunnel. In order to meet the conditions of similar resistance, different materials were compared and tested, and the roughness was determined. Through testing and analyzing the flow capacity and flow characteristics at three operating conditions, it is concluded that the flow can be safely passed under operating condition 1, and the clearance margin of some tunnel sections under operating condition 2 is insufficient, with the minimum margin of 14.39%. Most tunnel sections under operating condition 3 do not meet the safety flow. Comparing the test and theoretical calculation, the results of the two are relatively close, and the test value is relatively safe, which can provide a theoretical basis for the construction and operation of the project.

In order to quantitatively analyze the impact of upstream reservoirs and the operation of the Three Gorges Project on the hydrological rhythms of the lower reaches of the Yangtze River and lakes, M-K test, cumulative anomaly method, wavelet coherence spectrum method and other hydrological time series trend analysis methods with STL time series decomposition method were used to analyze the 49-year historical water level data of Sheshan Station at Lake Shijiu. The long-term change trend and law of hydrological rhythm of Lake Shijiu under the new relationship between Yangtze River and Lake Shuijiu were analyzed. The coherent relationship between hydrological rhythm changes and local meteorological factors were analyzed along with the ecological effects under the new river-lake relationship. Under the new river-lake relationship, the dry season is earlier and longer and the averaged water level is higher, the extreme low water level is more likely to occur, the variation is gentler, and it is difficult for high water level to happen. The extreme high water level in the flood season is lower and happens later, the averaged water level is lower, ends earlier, and the amplitude is gentler. The early dry season is beneficial to increase aquatic plant biomass, but the decrease of water level variation in dry season may cause biodiversity to decrease.

Using GRACE gravity satellite data combined with GLDAS data inversion can obtain the change of groundwater reserves, which can monitor the change of groundwater reserves in the study area on a large scale, but the spatial resolution of the obtained data is only 0.25°, and it is difficult to be applied in the small scale. Based on the spatial relationship between GRACE terrestrial water storage and GLDAS shallow surface water storage and precipitation, NDVI, a downscaling method of groundwater storage change based on geographically weighted regression model (GWR model) was proposed, and the spatial resolution of groundwater storage was downscaled to 1 km. The results show that the GWR model downscaling method is successfully applied to the Haihe River Basin. The correlation coefficients between the groundwater storage data after downscaling and the measured groundwater level data at 46 verification points are all greater than 0.6, and the simulation results are reasonable and reliable. Furthermore, the temporal and spatial variation characteristics of groundwater storage in Haihe River Basin and Beijing Plain were analyzed by using the downscaling results. The results is highly consistent with the existing data, indicating that the downscaling method based on GWR model can effectively improve the spatial resolution of groundwater storage change data.

Analyzing the spatial and temporal characteristics of extreme precipitation and the response of wind speed before and after extreme precipitation are of great significance for extreme precipitation characterization, improving the understanding of the relationship between extreme precipitation and wind speed, as well as managing water-related disasters. This study defined event-based extreme precipitation by considering preceding and succeeding precipitation, and classified precipitation patterns into three types, i.e. early peak, later peak and bimodal types according to the locations of precipitation peak, after which the spatiotemporal distributions of extreme precipitation and its relationship with wind speed were analyzed. The results show that single-peak of extreme precipitation occurs more often than bimodal one, and the amount increases from northwest to southeast, with significant upward trend of extreme precipitation detected; Extreme daily precipitation threshold increases with higher wind speed over the southeast and northeast, contrary to the southwest; Moreover, wind speed tends to show anomalies before and after extreme daily precipitation, and it decreases when extreme daily precipitation occurs over the southwest; However, over other regions, it increases before extreme daily precipitation and decreases after then, reaching the peak at the extreme daily precipitation day.

The noise and nonlinear characteristics in the deformation sequence of concrete dam seriously affect the accuracy of dam deformation prediction. In this paper, ensemble empirical modal decomposition (EEMD) was used to decompose the horizontal displacement signal of the dam to mine the effective deformation information. The singular spectrum analysis (SSA) was used to extract features from the high-frequency eigenmodal components (IMF) obtained from the decomposition to reduce the loss of effective information. Considering the complex stochastic and non-linear mapping relationship between effector and environmental variables, extreme gradient boosting (XGBoost) was used to model the prediction of the noise-reduced data. Considering the significant influence of XGBoost hyperparameters on the prediction performance of the model, the Northern Goshawk algorithm (NGO) with better global search capability was introduced to perform parameter search, and an NGO-XGBoost-based dam displacement prediction model was constructed. The calculation results show that the EEMD-SSA can effectively remove the noise from the dam displacement monitoring information, and the dam deformation prediction model based on NGO-XGBoost can significantly improve the prediction accuracy.

The premise of non-conformity traceability and correction of run-off is that there is an accurate and reliable long series measured flow sequence as the calibration reference. For watersheds without long series of measured flow data, the accuracy of calculated flow can be verified through short-term and typical test data to obtain a calibration benchmark. In this study, the accuracy of NHQ curves and discharge curves of Pubugou Reservoir was analyzed and verified based on the ultrasonic flow, combined with the analysis of the level-flow relationship under stable and sudden change working conditions. The research results have proven the accuracy of the outflow calculation of Pubugou reservoir, which provided basic support for tracing and correcting the non-uniformity of cascade runoff.