鱼卵漂流的欧拉-拉格朗日模型与产卵量估算

从河流鱼类早期资源研究和保护的角度,立足鱼卵运动,将传统二维浅水模型与三维粒子追踪结合起来,建立了适用于天然河流鱼卵漂流的欧拉-拉格朗日模型。模型能够模拟对流和紊动扩散作用下鱼卵在河道内的三维运动和散布特性。模型效果通过模拟文献中的室内水槽PTV试验,对比实测鱼卵运动特性参数得到了验证。将模型应用于长江中游藕池河支流鱼卵野外示踪漂流试验中,模拟分析了鱼卵在河道内的平面迁移动态、垂向混合规律、断面分布特性以及河道地形和水动力的影响和作用;重点讨论了鱼卵断面浓度分布不均对产漂流性卵鱼类早期资源量(产卵规模)估算的影响,并通过模拟对传统的断面平均估算方法进行了校正,校正效果得到了示踪鱼卵漂流回捕实测数据的良好验证,鱼卵总量估算误差大大降低。此外,模拟还发现鱼卵漂流过程中的平均速度滞后于水流断面平均流速,在产卵场精确定位时须予以考虑。

Eulerian-Lagrangian modeling of riverine fish eggs drifting and improved estimation of spawning scale of fish with pelagic eggs

To examine the fish resources in rivers and its protection, this paper develops a fluvial egg drift model in the Eulerian-Langrangian approach coupling a traditional 2D shallow water model to a 3D particle tracking model. This egg drift model is capable of simulating river hydrodynamics, 3D movement of fish eggs and their dispersive patterns in natural rivers under advection and turbulent diffusion. Its performance is verified by comparing our simulations with the previously published measurements on laboratory flumes using particle tracking velocimetry (PTV), and a good agreement is achieved. Then, the model is used to simulate a field experiment of egg release and capture in the Ouchi tributary of the middle Yangtze, focusing on analysis of egg transport dynamics, vertical egg mixing, transverse distribution of egg concentration, and the influence of river geography and hydrodynamics. The inaccuracy of traditional methods using cross-sectional averages in estimating the drifting egg resources due to the non-uniformity of transverse distribution is addressed and improved through certain correction in numerical simulations. The improvement is verified against field egg capture data, showing that after correction the simulation errors are reduced significantly. Moreover, the simulations reveal that average egg drift velocities are considerably lower than those of the mean flows, which must be considered in predicting the locations of fish spawning grounds.