Fishery Machinery and Instrument Research Institute, Chinese Academy of Fishery Sciences, Shanghai, China.
PeerJ. 2022 Aug 23;10:e13943. doi: 10.7717/peerj.13943. eCollection 2022.
The hydrodynamic conditions of rivers affect fish habitats by influencing parameters such as river bottom topography. Ecological restoration projects change the water morphological characteristics of rivers. Here, water flow characteristics of the upper Yangtze River before and after the construction of a restoration project were analyzed using the computational fluid dynamics simulation method. The longitudinal diversion dam could divide the river into two flow velocity zones, and the outer flow is similar to the original river with a flow velocity of 0.75 m/s. However, flow velocity on the inner side of the river was about 0.25 m/s, forming a larger buffer area. The eddy became more diversified and stable, with a high eddy viscosity coefficient and less fluctuations, at 9 Pa·s; this was conducive to fish aggregation and spawning. At different depths, large gradient differences were observed between the inner and outer sides of the longitudinal diversion dam, and the turbulent current and upward flow of the inner side were obvious; this was more favorable to the aggregation of different fish species. The longitudinal dam body was under a pressure of about 200.2 Pa at the same flow rate; this was significantly lower than the pressure on the transverse dam body. The field flow test and fish survey data showed that the error rate of the simulation using the RNG turbulent model was less than 10% compared with actual mapping. After the restoration of fish habitats by the longitudinal diversion dam, the number of fish species in the area increased from 40 to 49; The density of fish in the water increased from 71.40 fish per 1,000 m before the project to 315.70 fish per 1,000 m after the project. These results can provide a reference for the rapid assessment of water morphology and fish habitat restoration in the future.
河流的水动力条件通过影响河底地形等参数来影响鱼类栖息地。生态修复工程改变了河流的水形态特征。本研究采用计算流体动力学模拟方法，分析了长江上游某修复工程前后的水流特征。纵向导堤将河流分为两个流速区，外侧水流类似于原始河流，流速为 0.75 m/s。然而，内侧河流的流速约为 0.25 m/s，形成了更大的缓冲区。涡流变得更加多样化和稳定，涡粘系数为 9 Pa·s，波动较小，有利于鱼类聚集和产卵。在不同深度，纵向导堤内外侧存在较大的梯度差，内侧存在强烈的湍流转流和上升流；这更有利于不同鱼类的聚集。在相同流量下，纵向坝体的压力约为 200.2 Pa，明显低于横向坝体的压力。现场流量测试和鱼类调查数据表明，RNG 湍流模型的模拟误差率低于实际映射的 10%。通过纵向导堤恢复鱼类栖息地后，该区域的鱼类物种数量从 40 种增加到 49 种；水体中鱼类的密度从项目前的每 1000 米 71.40 条增加到项目后的每 1000 米 315.70 条。这些结果可为未来快速评估水形态和鱼类栖息地恢复提供参考。
