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The outer bank slump blocks play a fundamental role in modulating the rate of bank erosion, and consequently, have a profound influence on many geomorphic and ecologic processes in meandering streams, e.g., channel evolution and habitat creation. To date, no adequate research has been developed regarding how these blocks, partially strengthened by roots of herbaceous plants, impact the near-bank flow velocity, bank erosion, and migration of streambanks. This paper analyzes 246 slump blocks in a meandering stream on the Marqu Meadow, China. Aerial surveys were conducted once a year from 2018 to 2021 and the lateral migration rates (M) of streambanks are estimated by superimposing the current-year drone imagery onto its previous-year counterpart. When compared to the outer bank segments lacking slumps, our research findings indicate that the bank segments exhibiting slumps demonstrate a reduction of 57 % and 43 % in the maximum and average bank erosion rates, respectively. Overall, the wider blocks provide stronger bank protection; nevertheless, they may also introduce or enhance local scouring in their vicinity, thereby increasing the heterogeneity of bank erosion rates. To elucidate this complex influence mechanism, we simulate the three-dimensional flow velocity field of a ~100 m meandering bend containing three slump blocks using the MIKE-3 model. Furthermore, we compare one-year bank migration distance with and without the blocks by correlating the lateral migration distance of outer banks to the longitudinal gradient of near-bank velocity. The paper provides valuable insights into the complex interplay between flow dynamics and streambank behavior in real-world settings, thereby enhancing the effectiveness of future management and restoration practices. • 246 slump blocks were analyzed in a meander on Marqu Meadow, China. • Slump blocks can persist for years but may be washed away in high flows. • The outer bank slump blocks play a vital role in modulating bank erosion rates. • Slump blocks protect outer banks by redistributing the high flow and secondary flow. • Slump blocks help protect bank overall but it may introduce scour in their vicinity. [ABSTRACT FROM AUTHOR]

Habitat of fish species has been an essential component of riverine ecosystems in natural rivers. However, a series of ecological problems have posed a practical challenge on fish habitats and blocks migration routes, particularly in the upstream reach of the Yangtze River, mostly due to the construction of hydroelectric dams rapidly increased in recent years in China. Therefore, it is necessary to explore the hydrodynamic characteristics of fish habitats for the ecological management and restoration, especially for the rare and unique fish, and thereby to evaluate the habitat conditions of aquatic organisms in the upper reaches of the Yangtze River. In this study, a three-dimensional model of flow field was established, corresponding to the artificial restoration of rare fish habitats in the river section of Yangtze River upstream, in Luzhou city, Sichuan province, China. The hydrodynamic characteristics of different flow velocities were investigated, based on the Computational Fluid Dynamics (CFD) numerical simulation combined with an experimental survey. The evolution and development of the turbulence/vortex structure were analyzed, in order to obtain the influence mechanisms of several artificial dams on the abdominal flow law of the basin, compared with the experimental data, including the site topography, flow mapping of the habitats, and the survey of fish shoal. The results showed that the large vortex areas were formed in the test area of the habitat basin, where the shape of vortex was almost invariant with the change of the stream speed. The upwelling occurred obviously in the anticlockwise vortex region, of which the velocity was slightly higher than that in the clockwise vortex region. The flow velocity of the habitat basin in the test area is lower than the control area, but the uniformity of water flow is baddish. The Froude number does not increase linearly with the inflow velocity, and the variation trends of flow uniformity index on different water depth sections of the habitat basin are similar. By the field survey of fish shoal in the same mapping distance, the area outside the dam was 0.714 in 1 000 scanning times, while, the area inside the dam was 3.157 in 1 000 scanning times, revealing that the low-velocity turbulence/vortex structure in the test area of the habitat basin can gather fish better, and thereby the artificial restoration of fish habitat can provide suitable living conditions for aquatic organisms to roost, breed, and shelter. Specifically, the average flow velocity in the abdomen of the basin was about 0.5-0.8 m/s, when the flow velocity was 2 m/s. The difference between the numerical simulation results and the test data is about 10% on the same mapping path, which verify the reliability of the numerical calculation method. The findings can offer a sound theoretical reference for the hydrodynamics of large-water fishery ecological projects. [ABSTRACT FROM AUTHOR]

With the increase of mining depth, the high gassy coal mine confronts with a variety of gas problems, such as gas concentration exceeding the limit in the working face, gas outburst and gas explosion. According to the situation of gas drainage in Qinshui Basin (South of Shanxi Province, China) and enlightened by horizontal directional drillings (HDD) and multi‐branched horizontal wells, a new gas drainage pattern that inverted π‐shape km borehole layout was proposed. Verified in Yuwu Coal Mine, the gas drainage data were standardized via the unified theory of standardization. It could dropped the coal seam gas content to 7.71 m3/t, and increased the gas drainage rate to 34.2%, which conformed to the Chinese regulation (<8 m3/t, >30%, respectively). This pattern has a significant effect on coal mines with a single seam, where protective seam mining technology was unsuitable to prevent gas outburst and gas explosion. A double pressure relief circle model of gateway and borehole was proposed. Combined with traditional gas drainage technology, a new gas drainage scheme came up with – inverted π shape km boreholes group model. The novel gas drainage scheme of inverted π‐shape km boreholes arrangement has the advantage of reducing gas drainage time and expanding coverage area. It is a new tri‐dimensional space‐time gas drainage system for underground coal mines. [ABSTRACT FROM AUTHOR]

• CEFR DHRS primary system with full core CFD model is established. • The intra-subassembly flow path, inter-wrapper flow path and MVCS backflow path are identified. • The three-dimensional thermal and flow characteristics in sodium pool are analyzed. The pool-type sodium-cooled fast reactor decay heat removal system (DHRS) is an important engineered safety system to ensure the establishment of natural circulation in the case of station blackout (SBO). It is of great significance to study characteristics of DHRS for evaluating its passive residual heat removal capacity. Due to numerous core subassemblies and small scale of gaps between subassemblies, it is difficult to use the same scale grids to describe the three-dimensional flow paths in sodium pool with full core. Therefore few researches, either experiments or numerical simulation, have been performed on such complicated phenomena so far. In order to identify the natural circulation flow paths of fast reactor, an integrated three-dimensional simulation model of China Experimental Fast Reactor (CEFR) primary circuit system with full core was established, including 712 subassemblies and small gaps between subassemblies. FLUENT was used to carry out three-dimensional numerical simulation. Through the transient simulation of 5000 s, the main flow paths including the intra-subassembly flow path, the inter-wrapper flow path and the Main Vessel Cooling System (MVCS) backflow path were identified. At 5000 s, the intra-subassembly flow rate, the inter-wrapper flow rate, and the MVCS backflow rate were 3.07 kg/s, 1.53 kg/s, and −1.94 kg/s respectively. The symmetrical thermo-hydraulic characteristics of two loops were obtained to analyze thermal stratification in sodium pool. The results provided a key three-dimensional numerical reference for the safety of CEFR. [ABSTRACT FROM AUTHOR]