流量调节对长江口潮流不对称的影响

Influence of Discharge Regulation on Tidal Current Asymmetry in the Changjiang River Estuary

长江上游人类工程的建设使得长江口来水来沙条件发生变化,改变了河口地区洪枯季径流量,并进一步影响潮流不对称特性。而潮流不对称对河口近岸的泥沙输运及地貌演变有着重要的影响。利用二维水动力数学模型对长江口感潮河段进行水动力模拟,研究洪枯季流量调节对潮流不对称的影响。采用非稳态调和方法(NS_TIDE)并结合偏度指标分析长江口涨落潮流速不对称和涨落憩历时不对称的变化趋势。研究结果表明:潮波在河口的上溯过程中,潮流不对称呈现先增大后减小的趋势。河口枯季径流的提高在加强中下游区域落潮流占优的趋势同时也延长河口大部分区域落憩的历时。主汛期洪峰的削弱加快了中上游区域的落潮流速,缩短了上游区域落憩历时,而潮流流速和涨落憩历时不对称在下游区域则表现出相反的趋势。

The construction of engineering projects in the upper reaches of the Changjiang River has changed the flow and sediment conditions of the Changjiang River Estuary and the river discharges in flood and dry seasons,which further affects the tidal current asymmetry.Such asymmetry exerts evident impact on offshore sediment transport and geomorphic evolution in the estuary.The influence of discharge regulation on tidal current asymmetry in flood and dry seasons was studied by applying a two-dimensional hydrodynamic numerical model of the Changjiang River Estuary.The nonstationary harmonic method(NS_TIDE)and tidal skewness method were applied to analyze the variation trend of flow velocity asymmetry(FVA)and flow duration asymmetry(FDA).Results manifest that tidal current asymmetry intensifies prior to a slight decrease as tidal propagates landward.The increase of discharge in dry season at the estuary not only strengthens the ebb tide dominance in the middle and lower reaches of the estuary,but also prolongs the duration of low-water slack in most areas of the estuary.In major flood period,the weakening of flood peak enhances the ebb current velocity in the middle and upper reaches and shortens the duration of low-water slack in the upstream region,while the asymmetry of tidal flow velocity and flow duration shows an opposite trend in the downstream region.