Abstract Due to variations in channel depth, width, and lateral bottom profile, estuarine residual flows can exhibit significant variation in magnitude and transverse structure along macrotidal and convergent estuaries. This article explores the along-channel residual flow (magnitude and transverse structure), forcing mechanisms and their variations along the Gironde estuary in France. With emphasis on the role of density gradient and the advective accelerations in the along channel momentum balance, the study outlines the along-channel residual flows and forcing mechanisms over the neap-spring tidal cycle during high and low river discharge conditions. The results demonstrate that the density-driven flow contribution to total residual flows is, approximately, 75% (along-channel averaged) during neap tide and 18% during spring tide for both high and low river discharge scenarios. Owing to the complex lateral variation in the channel depth and the constriction near the mouth, advective accelerations play a major role in altering the residual flow lateral structure. However, the relative importance of advection reduces in the main body of the estuary where the channel is widened with poor lateral variation in the bottom depth. The results suggest advection and the baroclinic pressure gradient produce a laterally sheared along-channel residual flow with inflow in the channel and outflow over the shoals during neap tide. During spring tide, this lateral structure is produced due to advection. The results show that even in a homogenous system, advection can induce a flow with a structure that mimics the density-driven flow. The article shows that along macrotidal estuaries the presence of complex morphological features can affect the residual flow dynamics. As such, the residual flow in these systems should be schematized not only by considering the lateral variation of bathymetry, but also the along channel complexity.

中文翻译：

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平流和密度梯度在驱动沿大潮汇合河口的残余环流中的作用，具有非理想化的几何形状

摘要 由于河道深度、宽度和横向底部剖面的变化，河口余流沿大潮河口和会聚河口在大小和横向结构上可能表现出显着变化。本文探讨了法国吉伦特河口沿河道剩余流（大小和横向结构）、强迫机制及其变化。该研究强调了密度梯度和平流加速度在沿河道动量平衡中的作用，概述了高低河流流量条件下沿河道剩余流量和小泉潮汐循环的强迫机制。结果表明，密度驱动的流量对总剩余流量的贡献大约为 小潮期间为 75%（沿河道平均），大潮期间为 18%（高位和低位河流排放情景）。由于通道深度的复杂横向变化和口附近的收缩，对流加速度在改变残余流横向结构方面起着重要作用。然而，在河口主体中，平流的相对重要性降低，河道加宽，底部深度横向变化较差。结果表明，平流和斜压梯度产生横向剪切的沿河道残余流，在小潮期间流入河道，流出浅滩。在大潮期间，这种横向结构是由于平流而产生的。结果表明，即使在同质系统中，平流可以诱导具有模拟密度驱动流动的结构的流动。文章表明，沿着大潮汐河口，复杂形态特征的存在会影响残流动力学。因此，这些系统中的残余流不仅应考虑水深的横向变化，而且还应考虑沿河道的复杂性。