This study evaluates the effectiveness of artificial Kandelia obovata forests in wave attenuation through physical model experiments conducted in a wave flume. The experiments meticulously replicated real-world hydrodynamic conditions and mangrove movement responses using the principles of gravitational and motion similarity, with a scaled 1:10 model of Kandelia obovata. Our approach included comparative experiments against a 1:100 gradient concrete slope to isolate the effects of seabed friction and flume wall reflections. The wave height was measured using strategically placed wave gauges. The findings indicated that the artificial Kandelia obovata forests significantly attenuated waves, with a decrease in the total attenuation capacity as the water depth increased from 2.75 m to 3.28 m under both regular and irregular waves. The elastic mangrove model with a canopy effect led to a 15% increase in wave attenuation over cylindrical models. Predictive models using multivariate nonlinear regression and back propagation neural networks showed that the latter provided a superior accuracy in estimating wave transmission coefficients

The coordinated operation of cascade reservoirs, while achieving multi-objective optimization in flood control and power generation, profoundly alters the natural hydrological rhythms of river systems. The combined effects of downstream water level backwatering and upstream flow reduction can trigger reverse flow within reservoir zones, exerting coupled impacts on environmental processes such as water exchange, nutrient transport, and algal blooms. This study focuses on the Xin’anjiang–Fuchunjiang cascade reservoir system, constructing a high-spatiotemporal-resolution model for May to July 2025 using the MIKE 21 two-dimensional hydrodynamic model. By integrating Lagrangian particle tracking, Spearman rank correlation analysis, and redundancy analysis (RDA), we systematically reveal the spatiotemporal patterns, propagation mechanisms, and driving factors of reverse flow in the Fuchunjiang reservoir area. Results show that during the study period, reverse flow occurred frequently in the middle reaches, decreased toward the upper and lower reaches, and occurred sporadically in tributaries. Reverse flow was predominantly low-intensity and intermittent, exhibiting a bimodal temporal distribution at night and in the morning. Reverse flow events were primarily driven by daily shutdowns of the Xin’anjiang hydropower station, propagating sequentially from upstream to downstream and then into tributaries; fluctuations in the Fuchunjiang reservoir water level and changes in Lanjiang inflow played only minor modulating roles. The three key driving factors—discharge from the Xin’anjiang station, Lanjiang inflow, and Fuchunjiang reservoir water level—together explained 80.1% of the total variation in reservoir current velocity, showing a segmented control pattern. Reverse flow can cause high-concentration nutrients from the Lanjiang River to be transported backward into the main stem of the Xin’anjiang River, affecting an area of approximately 2.5 km. A single reverse flow event increases average nutrient retention time by about 6 h, and the cumulative effect of daily occurrences creates favorable hydraulic conditions for cyanobacterial proliferation. Reservoir reverse flow can be classified into two types: standing wave oscillations and propagating reverse flows. The former corresponds to recurrent water level fluctuations caused by daily regulation at the power stations, with flow direction fluctuating slightly around the mean and producing minimal net transport; the latter refers to the reverse flow propagation following shutdowns at the Xin’anjiang station, advancing sequentially from upstream to downstream and then into tributaries, with a clear direction of water mass transport. The ecological impact of backflow depends not directly on its intensity, but on the extent to which it increases water retention time and, accordingly, on the source and transport direction of the nutrients it carries. Integrating hydrodynamic simulation, Lagrangian particle tracking, and driver factor analysis at time resolutions ranging from 1 to 30 min, this study applies these methods to a cascade reservoir system characterized by “peak shaving at upstream, water level control at downstream, and tributary inflow management.” It systematically quantifies the spatiotemporal patterns and driving mechanisms of reverse flow under cascade joint operation, providing scientific support for optimizing reservoir operations, managing reservoir water quality, and protecting drinking water sources.

Artificial seawater lakes constructed in estuarine environments are highly susceptible to the intrusion of water containing high concentrations of suspended sediment, which can degrade water quality and threaten ecosystem stability. To clarify the settling mechanisms and sedimentation efficiency under high-turbidity conditions, this study investigated the Baishawan Artificial Lake in the Jiaojiang Estuary, eastern China, through field observations, controlled still-water sedimentation experiments, and a multi-particle size sedimentation efficiency model. Field measurements revealed significant spatiotemporal variability in suspended sediment concentration (SSC), with higher SSC during spring tides than neap tides and a spatial gradient decreasing from the near-estuary zone to the artificial lake and offshore waters. Grain-size analysis showed that suspended sediment was dominated by clay and silt (>98%). Laboratory experiments indicated a two-stage settling process characterized by rapid initial sedimentation followed by gradual stabilization; under high concentration (1.32 kg/m³), SSC decreased by about 85% within 40 min due to concentration-enhanced flocculation, whereas under low-concentration conditions (0.24 kg/m³) approximately 14 h were required to reach the target concentration of 0.01 kg/m³. Model validation demonstrated that the multi-component sedimentation model effectively reproduced the temporal attenuation of SSC. Model application further suggested that when the initial SSC was 0.70 kg/m³ and the water depth was 5.7 m, the sedimentation tank could reduce the SSC to 0.01 kg/m³ within about 16–17 h, with an estimated annual sedimentation volume of ~65,000 m³ and a recommended dredging interval of five years. These results provide quantitative guidance for sedimentation tank operation and sediment management in estuarine artificial lakes and other high-turbidity coastal environments.