径流量变化对长江口北槽最大浑浊带影响分析

Study on the effect of river inflow on estuarine turbidity maximum in the North Passage of the Yangtze Estuary

长江口属巨型多级分汊河口,由于受中等强度潮汐及季节性变化明显的径流共同作用,其动力-地貌物理过程十分复杂。研究了长江口北槽最大浑浊带水沙动力与大通径流量的响应特征。聚焦于径流变化对河口最大浑浊带的三重作用:一是水流起悬能力增强;二是泥沙输运能力增大;三是在河口最大浑浊带这个特殊区域,由于河流效应,还会引起河口环流增强及底部向陆方向的输运能力增加。实测资料和数学模拟结果表明:对于长江口而言,径流越大,小流速的滩地由于动力增加而含沙量会越大;但主流区由于流量增加的三重作用,最大浑浊带含沙量并非单向增大,而是最大浑浊带含沙量在上游流量为30000~40000 m^(3)/s时达到最大。本研究定量分析了不同径流条件下河口泥沙悬浮状态,可为长江口水域相关水土资源开发利用、生态环境保护及航道疏浚维护等工作提供参考。

The Yangtze Estuary is a giant multi-channel bifurcated river-tide system,which is affected by mediumintensity tides(mainly semilunar tides)and obvious seasonal variation of riverine inflow,and its hyrodynamicmorphological conditions are very complex.In this research,the response of discharge to the dynamic characteristics of water and sediment in the maximum turbidity area(North Passage)of the Yangtze Estuary is studied.The research results show that the increasing of discharge means the increasing of hydrodynamics,which first of all has two consequences:one is the enhancement of sediment resuspension capacity,the other is the increase of transport capacity;in addition,in the maximum turbidity area of the estuary,because of the river effect,there is often an increase in estuarine circulation,and the change of discharge also means that the transport capacity from the bottom to land also changes.The measured data and mathematical model jointly show that the larger the discharge is,the greater the sediment concentration of the beach with low velocity will be,however in the main flow area,due to the triple effects of the increase of discharge,the sediment concentration in the maximum turbidity area does not increase in one direction.Sediment concentration in the maximum turbidity area reaches the maximum under the discharge of 30,000-40,000 m^(3)/s.This study clarifies the sediment suspension state of the estuary under different discharge conditions,which could provide a reference for the development and utilization of soil and water resources,ecological environment protection and waterway dredging maintenance in the Yangtze Estuary.