鄱阳湖水利枢纽工程建设对草鱼江湖洄游潜在的影响

Abstract

鄱阳湖是长江四大家鱼索饵、育肥的重要场所, 近年来鄱阳湖出现了枯水季水位严重降低、枯水期延长、湿地面积缩小的现象。为解决鄱阳湖水资源、水文、水生态等问题, 建议在鄱阳湖入江水道兴建控制闸水利枢纽。然而, 拟建的水利枢纽工程将打破鄱阳湖与长江的天然连通性, 可能会对四大鱼类洄游过程产生影响。通过构建二维和三维水动力模型, 分析鄱阳湖水利枢纽建设后入江水道与枢纽洄游通道的水动力学特征, 结合实验和文献获得的草鱼幼鱼和成鱼游泳能力参数, 阐明了枢纽建设对草鱼洄游的影响。结果表明: 在设计调度模式下, 草鱼幼鱼入湖期间, 湖口段适宜通过天数达到83.74%以上, 说明湖口及入江水道的水动力条件对洄游的影响较小, 同时, 枢纽工程处在过鱼高峰期仍能保持较高的过闸效率; 草鱼成鱼出湖期间, 丰、平水年闸前水动力条件对洄游的影响较小, 仅在枯水年闸前流速几乎静止, 草鱼适宜出湖天数偏低。在该调度模式下, 水利枢纽建设运行后鄱阳湖整体水动力条件能够满足草鱼洄游需求。目前设计的鱼道在高、低水位时期均出现局部流速过大的现象, 不满足过鱼条件。从四大家鱼江湖洄游的角度为鄱阳湖水利枢纽工程设计和运行提供科学参考。;Poyang Lake serves as the main feeding and fattening venue for the four major Chinese carps. In recent years, Poyang Lake has experienced a severe drop in water level during the dry season, prolonged dry season, and reduced wetland area. To tackle the problem of water resources, hydrology and water ecology in Poyang Lake, it is suggested to build a hydro-junction project which is proposed to be located at the channel connecting the Poyang Lake and the Yangtze River. Yet the to-be-built Poyang Lake Hydro-junction Project would impede the natural connection between Poyang Lake and the Yangtze River. The migration passage of the four major Chinese carps may be affected. To study the potential impact of the prospective hydro-junction project on the migration of grass carp, analysis was conducted on the hydrodynamic characteristics of the migration channel after the construction of Poyang Lake Hydro-junction Project using two-dimensional and three-dimensional hydraulic models. The swimming ability of grass carp was determined through experiment and literature review. According to the study results, more than 83.74% of the days suitable for fish passage at the entrance to the lake. The hydrodynamic conditions at the entrance and the channel into the Yangtze River had an insignificant impact on the fish migration at the time when the juvenile grass carps entered the lake. Meanwhile, the gate chamber of hydro-junction project could still maintain a high passing efficiency during the peak period of fish migration. While under the designed scheduling mode, the hydrodynamic conditions in front of the hydraulic construction had little effect on fish migration in the years of wet and normal, but the days that were favorable for the fish departure from the lake decreased in dry years caused by almost static velocity in front of the hydraulic construction when the adult grass carps left the lake. The overall hydrodynamic conditions of Poyang Lake could meet the needs of the grass carp migration during the operation period of the Poyang Lake Hydro-junction Project. However, the current design of the fishway of the Poyang Lake Hydro-junction Project suffered the excessive flow velocity in some parts during high and low water level period, which dissatisfied the required passage conditions based on fish swimming ability under the existing scheduling mode. This study was expected to provide a scientific reference for the design and operation of the Poyang Lake Hydro-junction Project from the perspective of river-lake migration of the four major Chinese carps.