水库运行对汉江流域草鱼洄游影响评价研究

水库运行导致河流水文条件发生改变，对鱼类洄游及其性腺发育产生显著负面影响。为了探究丹江口水库运行对汉江草鱼（Ctenopharyngodon idella）洄游的影响，利用三维水动力模型EFDC模拟水库不同运行情景下的库区和下泄口水动力条件，建立带有外源输入的非线性自回归神经网络（NARX）模型预测下游水动力条件；通过室内试验获取草鱼洄游与水文条件响应关系，并建立草鱼洄游适宜度计算公式，评价丹江口水库上游、库区和下游的洄游适宜性。结果表明，时间上，由于4月水温升温较慢，且流速较低，草鱼洄游状况劣于5-7月；空间上，无论是水库下游还是库区，鱼类洄游状况都劣于未受丹江口水库影响的上游区域。库区极低的流速是影响草鱼上溯的限制因素，而下游降低的流速和水温对草鱼上溯和性腺发育都造成了阻碍。在鱼类洄游期间，降低库区水位、增大下泄量有利于提升库区及下游的流速和水温，改善洄游的外部环境条件。根据已有水库下泄方案（初始水位153 m），如果初始水位降至142 m、下泄增大20%，库区平均洄游适宜度可提高6.5%，下游可提高22.0%。

Impact of Reservoir Operation on Grass Carp (Ctenopharyngodon idella) Migration in the Hanjiang River Basin

Danjiangkou reservoir is located at the confluence of Hanjiang River and Danjiang River and is the key water control project for water resource development and utilization in the Hanjiang River basin. Reservoir operation alters the riverine hydrological regime and has significant negative impacts on fish migration and reproduction. In this study, grass carp (Ctenopharyngodon idella) were used to explore the impact of Danjiangkou reservoir on the migration of grass carp in Hanjiang River. A three-dimensional hydrodynamic model (Environmental Fluid Dynamics Code, EFDC) was used to simulate hydrodynamic conditions in the reservoir and discharge outlet under different operating scenarios, and a nonlinear autoregressive neural network with external input (NARX) was established to predict hydrodynamic conditions downstream of the dam. The relationship between grass carp migration and hydrological conditions were obtained using laboratory experiments, and a formula for grass carp migration suitability was established to evaluate migration suitability upstream, within and downstream of Danjiangkou Reservoir. Eight representative sites were selected to evaluate grass carp migration. Results show that the operation of Danjiangkou reservoir significantly changes water temperature and flow velocity in and downstream of the reservoir. The highest flow velocity in the reservoir was less than 0.20 m/s, and the downstream velocity ranged 0.26-0.47 m/s. Higher water temperatures primarily distributed in shallow water areas where residence time was low. Temporally, water temperatures increased slowly and flow velocity was low in April, so conditions for fish migration were less suitable in April than in May, June and July. Spatially, suitability for fish migration was lower in the reservoir and downstream than in the upper Hanjiang River, which is not affected by Danjiangkou reservoir. The extremely low flow velocities in the reservoir limit upstream movement of grass carp, and low flow velocity and water temperature below the dam hinder upstream movement and gonad development of grass carp. During the migration period, decreasing the reservoir water level and increasing the discharge will improve flow velocity and water temperature conditions in the middle and lower reaches of Hanjiang River, thereby improving fish suitability for migration. Under the existing reservoir operating scheme (with an initial water level of 153 m), when the initial water level drops to 142 m or the water discharge is increased by 20%, the average migration suitability in the reservoir increases by 6.5%, and downstream suitability increases by 22.0%.