This article presents a stochastic splash model for analysing the artificial rainfall caused by flood discharge splash in large hydropower stations. In this model, the splash phenomenon is considered as a random process, the flight paths of the splashed droplets are tracked by solving the particle motion equations, and the volume of each droplet is accumulated into a grid on the ground corresponding to its landing coordinates. A neural network was employed to compute the wind velocity vectors and the ground elevations to control the droplet motion and flight time. Thus, the model can account for the influence of the wind field and natural terrain on the rainfall distribution. An indoor splash experiment and field measurements were conducted to compare the measured data with the numerical results, and they showed satisfactory agreement.

Due to the complex structure and the multiformity of boulder arrangements, there is currently no perfect design criterion for nature-like fishways. This paper proposes four types of nature-like fishways arranged with an impermeable partition wall (IPW), a semi-permeable partition wall (SPPW) or a fully permeable partition wall (FPPW). The hydraulic characteristics of these fishways were investigated experimentally. The results show that the discharge of the fishway arranged with a FPPW was almost twice that of an IPW fishway, and the discharge of a SPPW fishway was between the two extremes. The mean flow velocity of the FPPW fishway was larger than that of the other schemes. For the fishway arranged with an IPW, the flow information was basically consistent with that of the engineered technical fishway. In the FPPW or SPPW fishway, there was more abundant flow information and no obvious recirculation zones in the fishway pool, and these conditions are suitable for migratory fish moving up- and downstream. Notably, for the fishway arranged with two fish passages, two mainstreams were formed in the pool, which divided the flow pattern of the pool into three flow regions. A weak recirculation area was formed in the low-velocity region, which facilitates swimming for migratory fish. According to this comprehensive comparative study, the SPPW fishway with two fish passages had low discharge, abundant flow information and favorable fish migration characteristics; thus, it is the optimal fishway scheme among those studied in this paper.

For water temperature stratified reservoirs, stratified water intake structures are used to extract surface warm water to reduce the adverse effects of low-temperature discharge on river habitats and agricultural irrigation. A physical simulation method has been explored and used to conduct the comparative experimental study on the efficiency of the three types of intake structures: a traditional stoplog gate intake, a stoplog gate with a horizontal curtain and a vertical curtain upstream of the intake. In order to extend the laboratory results to the prototype, a similarity relationship for water temperature stratification was derived based on the principle of equal density stratification Froude number between the model and the prototype, as well as the functional relationship between water density and temperature. The similarity relationship makes it possible to simulate the same prototype density flow under different laboratory water temperature conditions, and this was confirmed through experiments conducted in several months with different water temperatures. Under constant water flow conditions, a stable target water temperature distribution can be formed in the experimental model through continuous stratified heating and real-time power regulation, to simulate the density flow generated by various intake operation in water temperature stratified reservoir. The relationships between the intake water temperature and the reference water temperature at intake depth in reservoir were analyzed to distinguish the difference of water intake efficiency. The experimental results showed that, the traditional stoplog gate has a relatively lower efficiency in extracting warm water affected by the lower edge expansion of the drag layer into the cold water zone below the intake elevation; by setting horizontal curtain to prevent the cold water from climbing below, it is helpful to improve the water intake efficiency; by setting vertical curtain in the upstream area of the intake, the velocity of warm water in the upper part of the drag layer increases, and the intake efficiency has been significantly improved. The above research provides a scientific approach for mechanism research and mathematical model validation of thermal density flow.

A two-dimensional water quality numerical model has been developed to analyse the influence of adsorption boundary on the variation of water pollutant degradation. The characteristic finite element method is adopted to solve the discrete pollutant concentration equations, so the time-monotonicity of concentration is ensured in the convection-dominated flow field with various adsorption conditions. The second-order Runge–Kutta method is adopted to track the upstream concentration source points along the streamline, so the precision of the calculated pollutant concentration is improved even under the streamline sharp-bending condition. The flow roughness and pollutant degradation coefficient are formulated by elements according to the actual situation, so the model can quantitatively analyse the effect of various ecological restoration schemes on purification capacity in water areas. The adaptability and robustness of the model were verified by a typical engineering case, where the calculated results coincide with the measured data.