大坝泄水对鱼类洄游能力的影响研究

大坝的建设将天然河道分隔成上、下两个环境单元,改变了河道的流量、流速和水位等水文要素,使原有的水力条件及生态环境都发生了变化,对鱼类的洄游、繁殖和生长等都产生较大影响。以江河湖泊常见鱼种—成年鲤为研究对象,以0.02 m~3/s为基础流量,按照0.01 m~3/s的流量递增进行大坝泄水模拟实验;采用声学信号监测技术监测成年鲤在不同泄水量下的洄游能力及游泳轨迹,分析不同泄水量的河道流场并与鱼类游泳轨迹进行拟合,研究不同流速对鱼类洄游能力的影响。结果表明:成年鲤的洄游距离、游泳速度随着河道流速增大而逐渐减小,成年鲤洄游开始出现困难、开始出现逆流后退以及无法洄游时河道流速分别为0.42,0.48 m/s和0.62 m/s;泄水量每增加一个0.01 m~3/s流量梯度,成年鲤洄游距离约减少1.5 m,说明随着河道流速增大鱼类洄游轨迹变化是一个逐渐收敛的过程。大坝泄水过程同时还会造成氮气和氧气过饱和、改变水体温度和浊度从而对鱼类生存环境、繁殖及鱼类资源造成影响。

Influence of dam discharge on fish swimming ability

Dam project divides the natural river channel into upper and lower environmental units, which changes the hydrological factors such as flow velocity and water level of the river channel. It changes the original hydraulic conditions and ecological environment so that the fish migration, reproduction and growth are greatly impacted. The adult carp swimming ability is studied in this paper. The dam discharge is simulated based on the flow of 0.02 m3/s and increased by 0.01 m3/s per times. The acoustic signal monitoring technology is used to observe the swimming ability of adult carp and migration track under the different discharge. The flow field of different discharges are established and fitted with the fish swimming track to analyze the effects of different flow conditions on migration distance and fish swimming ability. The results show that the migration distance and swimming speed of adult carp gradually decreases with the increase of flow velocity. Adult carp began to swim difficultly at the flow velocity of 0.42 m/s,retreat along the flow at 0.48 m/s and stop migration at 0.62 m/s. The migration distance of adult carp reduced by approximately 1.5 m when the discharge rate increased by 0.01 m3/s, indicating that the fish migration track was a gradual convergence process as the flow velocity increased. Due to the change of flow velocity, the dam discharging process has an impact on the fish migration ability, brings about nitrogen supersaturation and changes the temperature and turbidity of the water body, accordingly affecting the living and breeding environment of fish.