The worldwide problem of reservoir sedimentation has perplexed the water conservancy industry. The problem of reservoir sedimentation is particularly serious in sandy rivers in China and directly affects the normal function of reservoirs. Due to its effect on the economy and environmental protection, the self-priming pipeline dredging and sediment discharge technology has broad application prospects. Nevertheless, there are pressing problems in the transportation of slurry particles in the pipeline system of this new technology. The purpose of this study is to use physical model tests to analyze the influence of the sediment transport rate and pipeline velocity on the motion state of particles (aggregation transport, jump transport, and suspension transport) when a heterogeneous flow with different particle sizes is transported in the pipeline. The results indicate that under the same pipeline velocity and sediment transport rate, the thickness of the static particle accumulation layer decreases with the increase in particle size in the state of aggregation and transportation, and the smaller the particle size, the greater the particle movement speed in the case of aggregation and suspension transportation. During jump transportation, the velocity of particles above the critical inflection point Y’ increases with the decrease in particle size. The opposite is found below the critical inflection point Y’. At the same particle size and sediment transport rate, when the pipeline velocity increases, the particle transport transits from aggregation transport to jump transport and then to suspension transport. The larger the pipeline velocity, the greater the overall movement speed of particles. When gathering and conveying, if the pipeline flow rate increases by 1.5, the maximum movement speed of particles increases by 3.3. The curvature of the vertical velocity curve of the particles during jump transportation is not affected by the pipeline velocity. The particle velocity at the highest point increases with the increase in the pipeline velocity. During suspension transportation, the difference between the maximum and minimum vertical particle distribution velocities is exponentially related to the pipeline velocity. At the same pipe velocity and particle size, the overall particle velocity decreases with the increase in sediment transport rate.

To enhance the efficiency of solving the optimal operation model for cascade reservoirs, this paper first constructed an optimal operation model of cascade reservoirs. The model comprehensively considered the ecological flow, the guaranteed output of hydroelectric power plants, and the relaxation constraints of the water level at the end of water supply and storage period. The relaxation constraints refer to two relaxation variable constraints, which are used to ensure that the water levels decline in the water supply period and rise in the water storage periods. At the same time, to avoid the challenges of “dimension disaster” and susceptibility to local optima commonly encountered in existing optimization algorithms when resolving the above model, a novel optimization algorithm, M-IWO-ODDDP, derived from the optimization principles of the Invasive Weed Optimization (IWO) and Discrete Differential Dynamic Programming (DDDP) algorithms, was proposed in this paper. The 11 cascade hydropower stations in the Wujiang River basin were used as a case study, and the results showed that the water-level dispatching process exhibited a high degree of conformity with the actual dispatching process during both the water supply and storage periods. Furthermore, the output calculation results based on the M-IWO-ODDDP algorithm were 3.94% and 0.30% higher than the actual output and ODDDP calculation results, respectively, while reducing water abandonment by 21.58% and 4.07%.

The construction of large-scale water diversion projects has effectively alleviated the current situation of the uneven distribution of water resources in China. However, due to the siltation of very fine sediment and organic matter on the side wall of an open channel, and the slow velocity of the side wall flow field, it is easy for epipelic algae to be produced, which affects water quality. Because prototype observation cannot be used to predict the series of flow in real time, and the calculation of the mathematical model is affected by parameter limitations, these two methods often cannot truly reflect the hydrodynamic characteristics of an open channel with epipelic algae. Therefore, by referring to the design parameters of the water diversion project channel, this study took the epipelic algae growing on the side wall of an open channel as the research object and used the scale of 1:30 to carry out a generalized flume experiment. Through the analysis of the physical characteristics of the prototype sample, and the simulation of the cohesive force between the oblique side wall and the epipelic algae, multi-group and multi-series hydrodynamic tests were carried out. The velocity distribution law and flow field distribution law were analyzed. The research results show that the presence of epipelic algae has a certain hindering effect on the flow velocity and significantly reduces the range of the peak velocity of the channel along the water depth. The position of the maximum velocity on the vertical line of the channel flow appears at the relative water depth of 0.6. In the case of small flow, the epipelic algae group only reduces the average flow rate of the channel by 5~6%; in the case of large flow, the effect of epipelic algae on the channel flow rate is minimal. This paper includes important scientific guiding significance and practical value for the regulation of water quantity and water quality safety, as well as the protection of long-distance projects.

This paper investigates the influence of coarse particle size on pressure characteristics through horizontal pipe transportation experiments of coarse particles and sand-laden water. As particle size increases, the thin and long grain accumulation layer forming at the pipe bottom and particle clusters above the layer vanish, most grains roll and bounce more quickly, the instantaneous pressure fluctuation intensity increases exponentially, and the time-averaged pressure decreases linearly along the flow direction. The fluctuating pressure probability density tends to obey a Gaussian distribution, and the turbulence power below 16 Hz increases. After adding fine sand constituting sand-laden water flows, the instantaneous pressure fluctuation intensity, transportation energy loss speed and fluctuating pressure amplitudes increase. With increasing particle size, the fitted Gaussian distribution of the fluctuating pressure probability density changes from thin to short and wide, and the spectral power of the measured pressure fluctuations increases within the resolvable frequency range, especially in the range from 8 to 10 Hz.

The functionality of rivers and open diversion channels can be severely impacted when the epipelic algae group that grows on concrete inclined side walls, which are typical of urban rivers, joins the water flow. This study aims to increase the long-distance transport of epipelic algae groups in urban rivers and open diversion channels through flow scheduling and to anticipate their transport capacity with respect to water flow. Current research on contaminant movement is primarily based on mathematical models with limited data on flake epipelic algae types. A sidewall epipelic algae group in a flume was modeled using a generalized hydrodynamic experimental approach. Hydraulic experiments were conducted to study the physical movement form and transport capacity of the suspended epipelic algae group. This study suggests that the epipelic algae group will create transport movement without sedimentation when the velocity reaches 80–85% of the main flow velocity and settle to the bottom when it falls below 80%. This research can support the mathematical modelling of hydrodynamic transport, provide a research foundation for long-distance transport, and estimate potential gathering places and sediment amounts under different water flow conditions.