This paper addresses the role of the phase difference between the peak discharge and the tidal level on the development of nearshore bars at river mouths during extreme river discharge events. We use a coupled hydrodynamic and morphodynamic numerical model (Delft3D) to reproduce extreme river discharge events on an idealized river mouth debouching on a nearshore shelf, characterized by a concave cross-shore profile. Different peak river discharges and lags between the peak discharge at the upstream boundary and the high tide at the offshore boundary are tested. The analysis of the water levels, currents, bed shear stresses, sediment transport rates and bed level changes shows that the lag between tidal conditions and river discharge triggers significant changes in (1) the instant in which the maximum currents at the outlet are reached, (2) the period for which the sediment is mobilized through the outlet, and (3) the maximum sediment transport rates during the events. These changes significantly modify the final characteristics of the river mouth bars, doubling their final extension and quadrupling the final bar volume for the same river discharge conditions and different phase lag, varying also their plan shape and the development of lateral subaqueous levees. These results emphasize the complex interplay between river and coastal hydrodynamics, being of major interest for researchers and managers dealing with projections of the consequences of coastal extreme events and plans to mitigate their effects.

本文讨论了在极端河流流量事件期间峰值流量和潮汐水位之间的相位差对河口近岸堤坝发展的作用。我们使用耦合的流体动力学和形态动力学数值模型 (Delft3D) 在理想化的河口上重现极端河流排放事件，该河口在近岸大陆架上泄出，其特征是凹形跨岸剖面。测试了不同的峰值河流流量以及上游边界峰值流量与近海边界高潮之间的滞后。对水位、水流、河床剪应力、泥沙输运速率和河床水位变化的分析表明，潮汐条件和河流流量之间的滞后会引发（1）出口处达到最大水流的瞬间，(2) 沉积物通过出口流动的时期，以及 (3) 事件期间的最大沉积物输送速率。这些变化显着改变了河口堤坝的最终特征，在相同的河流流量条件和不同的相位滞后下，它们的最终延伸量增加了一倍，最终坝体体积增加了四倍，还改变了它们的平面形状和侧向水下堤坝的发展。这些结果强调了河流和沿海流体动力学之间复杂的相互作用，对于处理沿海极端事件后果的预测和减轻其影响的计划的研究人员和管理人员来说，这是非常重要的。这些变化显着改变了河口堤坝的最终特征，在相同的河流流量条件和不同的相位滞后下，它们的最终延伸量增加了一倍，最终坝体体积增加了四倍，还改变了它们的平面形状和侧向水下堤坝的发展。这些结果强调了河流和沿海流体动力学之间复杂的相互作用，对于处理沿海极端事件后果的预测和减轻其影响的计划的研究人员和管理人员来说，这是非常重要的。这些变化显着改变了河口堤坝的最终特征，在相同的河流流量条件和不同的相位滞后下，它们的最终延伸量增加了一倍，最终坝体体积增加了四倍，还改变了它们的平面形状和侧向水下堤坝的发展。这些结果强调了河流和沿海流体动力学之间复杂的相互作用，对于处理沿海极端事件后果的预测和减轻其影响的计划的研究人员和管理人员来说，这是非常重要的。