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 differential flip bucket has efficient energy dissipation capacity, but its impact on downstream erosion cannot be ignored. In this paper, the physical model test is used to analyze the water surface line of the spillway, the flow pattern and velocity distribution of the downstream river channel, and the erosion of the downstream river channel in the form of a differential flip bucket. The influence of the discharge flow on the project is studied, and the rationality of the engineering design is verified. It is found that the flip bucket tongue of the spillway falls into the plunge pool of the downstream river channel, and the flow pattern of the downstream main river channel is gradually stable after a certain distance adjustment. The depth of the stilling basin meets the requirements of energy dissipation and erosion prevention, but local protection is required at the end of the excavation of the downstream left bank slope, or the excavation type of the left bank of the stilling basin is optimized.

Climate change is altering the water cycle and increasing drought risks in river basins. However, few studies account for minor droughts, despite their limited environmental impact. This study uses a pooling and exclusion method to remove the effects of minor droughts on the identification of drought events and analyze drought characteristics in the Daqing River Basin (DRB) using the HADGEM3-RA model within an Exposure–Resilience–Vulnerability (ERV) framework. It finds that the drought duration and the number of events are sensitive to pooling and exclusion rates. Drought severity is also sensitive to exclusion rates. Pooling and exclusion lead to fewer but longer and more severe droughts. Future droughts in the DRB are projected to become more severe, with durations averaging up to 7 months and severity increasing from 0.2 to 4.3. Drought peak severity is expected to exceed 1.28, with development and relief periods extending to 0.68 and 0.69 months, respectively. Risk levels in the basin are projected to rise from I to II–IV, with RCP4.5 scenarios showing higher risks than RCP8.5. Mountainous areas will face higher risks compared to plains. Initially, risk factors will increase then decline over time. These findings clarify drought dynamics and risk changes in the DRB under climate change. They can help in developing climate-resilient strategies for disaster reduction in similar basins.