A typical urban channelized (Urban) channel in Liangtan River, Chongqing, was reshaped into six types of channel by a numerical simulation tool named RiverBuilder. And then a two-dimensional hydrodynamic convection-diffusion model was constructed to study the effect of channel morphology reconfiguration on migration and diffusion index, such as water turn-over time (T_TOT), pollutant concentration curve (C_CC), pollutant reaching maximum time (M_MT) and pollutant arriving time (A_AT). The results show that the channel morphology reconfigured by changing the width (W_bf), depth (D_bf), and meandering (M_d) of the Urban channel can inhibit the migration and diffusion of pollutants to a certain extent, but the influencing effect is not as good as that of the composite channel based on the variable D_bf. Meanwhile, the near-natural (Natural) channel has the strongest anti-pollute capacity and inhibiting ability of pollutants diffusion, indicating it is more suitable for the self-purification process of pollutants. It is confirmed that the channel morphology based on disordered and complex changes in W_bf, D_bf, and M_d is closer to the Natural channel, which can provide good eco-hydraulic conditions for the improvement of river water quality.

In order to fully reflect the natural environmental conditions and effects formed and maintained by the river ecosystem, which is the basis of human life, after in-depth analysis of the river ecosystem service function, the calculation method of carbon fixation and other functions was optimized. Based on the functional value method, a scientific and reasonable river ecosystem service value (ESV) evaluation methods covering more comprehensive functions was proposed, and Nanhe River ESV in Liyang City was studied with an example. The total ESV of Nanhe River in 2019 is 1.242 billion yuan, with the value of regulation, support, supply and cultural functions accounting for 76.5%, 12.2%, 11.1% and 0.2% respectively, which can provide reference for natural resource asset accounting and ecological compensation standards.

As an important part of rural energy, small hydropower plays an important role in driving rural economic development and promoting energy saving and emissions reduction. However, there is a lack of scientific guidance in the process of optimal operation of small hydropower stations in most areas. This paper takes the Mengdong River basin as an example to establish a cascade optimal operation model of small hydropower stations based on runoff simulation. The Xinanjiang (XAJ) model is combined with Manning's formula to establish a semi-distributed hydrological model for simulating the influence of reservoir operation on runoff. The successive approximation dynamic programming method is used to achieve optimal operation by considering the actual operating characteristics of small hydropower stations. The results demonstrate that the semi-distributed hydrological model has a good performance in the river basin. The changing pattern of simulated and measured runoff processes is basically consistent, and the Nash-Sutcliffe efficiency coefficient and coefficient of determination between the measured and simulated series are 0.86. The optimal operation model can reduce the spillage water effectively, which improves the utilization efficiency of water energy. Meanwhile, the optimal operation can match the actual intra-day features of small hydropower, indicating its feasibility in applications.

To scientifically evaluate the eutrophication degree of water bodies, based on the comparison and analysis of various eutrophication evaluation methods, convolutional neural network (CNN) was introduced to establish the convolutional-eutrophication (CNN-E) model. Based on the monthly-scale water quality and algae monitoring data of Honghu Lake from 2014 to 2019, the comprehensive nutrient index method, BP neural network method and CNN-E model were used to evaluate its eutrophication degree. The mean absolute error, root mean square error, coefficient of determination and Nash-Sutcliffe efficiency coefficient were used to evaluate the performance of the neural network model. The results show that Hong Lake was in a mild eutrophic state for a long time, and the eutrophication level was increasing. In terms of model performance, the four evaluation indexes of CNN-E model are better than BP neural network 0.166, 0.098, 0.078 and 0.087, respectively. The CNN-E model can provide technical support for the prevention and comprehensive management of eutrophication in lake water bodies.

The ZM Fishway is the rare vertical slot fishway with high altitude and the long length at the domestic and foreign. The effect of fishway is particularly vital for the gene exchange and population reproduction of the upstream and downstream fish. To investigate the effectiveness of the fishway, we monitored the species, quantity and environmental factors of fish by trap and video observation method from March to July in 2021. In total, 9 species of 143 680 fish belonging to 2 orders, 4 families and 7 genera were captured. The species and quantity of fish passing through were mainly Schizothorax oconnori, Schizothorax macropogon and Racoma waltoni, which were the main objects of fishway designed. The number and species of fish showed obvious seasonal and circadian rhythms. The number and species of fish in May and June were significantly higher than those in other months, and the number of fish during the day was significantly higher than that at night. The canonical correspondence analysis (CCA) results of fishway environmental factors show that the main environmental factors affecting the effect of fishway were the water stage and water temperature. The research results could provide reference data for the optimization and effective operation of the ZM fishway, and it was of great significance to the protection of fishery resources in the middle and lower reaches of the Brahmaputra River.

Geotechnical engineering generally involves three-dimensional steady seepage problem with free surface. Traditional numerical methods for solving free surface are based on the assumption of continuum, and the pore flow is averaged over the whole area containing solid particles. In fact, water flow can only occur along the pores of porous media. Based on the equivalent principle of head and flow, the equivalent seepage velocity, continuity equation and boundary conditions of the pipe network model were derived by simplifying the pore structure of porous media into a three-dimensional orthogonal pipe network. Based on the local coordinate system, continuous penalty Heaviside function and variational principle, a three-dimensional steady seepage analysis method with free surface was established for equivalent pipe network model. Thus, the three-dimensional seepage problem was simplified to a one-dimensional form, which greatly reduces the difficulty of solving the three-dimensional steady seepage problem with free surface. The effectiveness of the equivalent pipe network model was verified by the three-dimensional free surface seepage analysis of homogeneous right-angle trapezoidal dam. The three-dimensional steady seepage analysis of the left abutment slope of Kajiwa Hydropower Station was carried out. By comparing with the variational inequality method, the equivalent pipe network model can well reflect the seepage field characteristics of the left abutment slope of Kajiwa Hydropower Station, and has strong applicability and high computational efficiency for the seepage problem of 3D complex engineering.

In order to investigate the influence of the vegetation in beach and river bottom on the water flow characteristics at different time periods, under the condition of changing the vegetation diameter (6-10 mm) only, the numerical simulation was used to study the variation of vertical velocity distribution, contoured velocity, water level and intensity of turbulence along the way at different vegetation diameter. The results show that the vertical velocity distribution shows an "S" distribution in the vegetation zone and a "J" distribution outside the vegetation zone; In general, the larger the diameter is, the lower the overall velocity is, the more obvious the upstream congestion of the water level is, and the larger the water surface slope ratio is; The turbulence intensity is proportional to the vegetation diameter; The turbulence intensity of water flowing through the vegetation is greater than that of the vegetation channel when the vegetation diameter is the same.

In order to investigate the impact of typical ecological revetment fish-nest brick on the hydrodynamic characteristics of straight water conveyance channels, a 3-D numerical model (LES) incorporating fish-nest brick was developed using large-eddy simulation technology. Periodic boundaries were employed in the longitudinal direction to allow for the repeated development of water flow within the computational domain. The reliability of the numerical model was extensively validated through experimental data from flume tests. Subsequently, the LES model was used to simulate the hydrodynamic characteristics of channels containing fish-nest brick. The results indicate that the fish-nest brick divide the channel into a high-speed main flow region and a low-speed fish-nest cavity. The time-averaged flow velocity in the main flow region is approximately 1.8 times the cross-sectional average flow velocity (U₀), and a continuous distribution of vortices exists throughout the entire water depth range. Conversely, the time-averaged flow velocity and turbulence within the fish-nest cavity are at relatively low levels, making it suitable for fish habitat and the hatching of adhesive eggs. The mixing layer at the mouth of the fish-nest cavity exhibits relatively strong vortex structures, which significantly enhances turbulence intensity and services as the primary driving force for momentum exchange between the interior and exterior of the fish-nest cavity.

To analyze the causes of turbine segmented shutdown device miloperation for a hydropower station in Central Asia, the structure of mechanical hydraulic control system of governor and its principle were described, and oil line of mechanical hydraulic control system was analyzed. It found that after the operation of the emergency pressure distribution valve, the pressure oil velocity in pipe was too fast, so the pressure of the control chamber of the segment closing device was reduced and the hydro-generator speed was too high because of the long closing time of the servomotor. The oil intake port of the control pressure oil of the stage closing device can be moved from the main pressure oil supply pipe of the emergency pressure distribution valve to the energy storage tank of the governor system. The feasibility of the scheme was verified by test.

Based on the daily precipitation data of 135 weather stations from the Yangtze river delta city during 1951-2017, spatio-temporal patterns of the extreme precipitation of the Yangtze river delta agglomeration were analyzed by the linear trend analysis, M-K trend test, wavelet cycle analysis and reverse distance weight interpolation methods. The extreme precipitation indexes were defined from the aspects of extreme precipitation amount, frequency, and intensity. The results show that except for a decrease in the continuous drought index of -0.11 d/a, the extreme precipitation indexes showed an increasing trend. The average period of change in extreme precipitation indicators was in the range of 15 a and 25 a, and the characteristic timescale was 40-50 a; The high-value area of the annual mean spatial distribution of maximum daily precipitation, maximum daily precipitation, continuous moisture index, strong rainfall, heavy rain days and annual rainy day precipitation presented in the southeast areas of the Yangtze River Delta urban agglomeration, which were distributed the opposite parts to the persistent drought index. However, the high-value areas of ordinary daily precipitation intensity were in the western part of the Yangtze River Delta urban agglomeration; The high-value areas of the changing trends of the spatial distribution and the maximum precipitation in the Yangtze River Delta urban agglomeration were all in Nanjing, Zhenjiang, Changzhou and Shanghai. The high-value areas of the spatial distribution change trend of ordinary daily precipitation intensity and annual rainy daily precipitation change trend were in Nanjing, Wuxi and Suzhou. The high-value areas of continuous moisture index, continuous drought index and heavy rain days were all in Hangzhou, Shaoxing and Wenzhou. The research findings can provide references for the prevention of rainstorm waterlogging disasters in the Yangtze River Delta Urban Agglomeration.