Channel beds in estuaries and deltas often exhibit a local depth maximum close to the river mouth. There are two known mechanisms of large-scale (i.e., >10 river widths along-channel) channel bed scours: width constriction and draw-down during river discharge extremes, both creating flow acceleration. Here, we study a potential third mechanism: tidal scour. We use a 1D-morphodynamic model to reproduce tidal dynamics and scours in estuaries that are in morphologic equilibrium. A morphologic equilibrium is reached when the net (seaward) sediment transport matches the upstream supply along the entire reach. The residual (river) current and river-tide interactions create seaward transport. Herein, river-tide interactions represent the seaward advection of tide-induced suspended sediment by the river flow. Tidal asymmetry typically creates landward transport. Scours form when tidal flow is amplified through funneling of tidal energy. Scours simultaneously reduce the residual (river) current and the river-tide interaction contribution to sediment transport, thereby maintaining morphologic equilibrium. When tidal influence is relatively large, and when channel convergence is strong, an equilibrium is only obtained with a scouring profile. We propose a predictor dependent on the width convergence, quantified as S_B, and on the ratio between the specific peak tidal discharge at the mouth and the specific river discharge at the landward boundary (q_tide/q_river). Scours develop if (q_tide/q_river)/S_B exceeds 0.3. Scour conditions were found to occur globally across a range of scales, which allows its prediction in estuaries under future changes.

中文翻译：

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应对河口潮汐优势的大规模冲刷

河口和三角洲的河床经常在靠近河口处表现出局部最大深度。有两种已知的大规模（即，沿河道宽度大于 10 条河道）河床冲刷的机制：河床极端流量期间的宽度收缩和水位下降，两者都会产生流量加速。在这里，我们研究了潜在的第三种机制：潮汐冲刷。我们使用一维形态动力学模型来重现处于形态平衡状态的河口中的潮汐动力学和冲刷。当净（向海）沉积物输送与整个河段的上游供应相匹配时，就达到了形态平衡。残余（河流）流和河流潮汐相互作用产生向海运输。在这里，河流-潮汐相互作用代表了潮汐引起的悬浮沉积物由河流流动的向海平流。潮汐不对称通常会导致向陆运输。当通过潮汐能的漏斗放大潮汐流量时，形成冲刷。冲刷同时减少残余（河流）流和河流-潮汐相互作用对泥沙输送的贡献，从而保持形态平衡。当潮汐影响较大，河道收敛性强时，只有冲刷剖面才能达到平衡。我们提出了一个依赖于宽度收敛的预测器，量化为 只有通过冲刷曲线才能达到平衡。我们提出了一个依赖于宽度收敛的预测器，量化为 只有通过冲刷曲线才能达到平衡。我们提出了一个依赖于宽度收敛的预测器，量化为S _B，以及河口特定峰值潮汐流量与向陆边界特定河流流量之间的比值 ( q_潮汐/ q_河流)。如果 ( q_潮汐/ q_河流)/ S _B超过 0.3，就会发生_冲刷。发现冲刷条件在全球范围内发生，可以预测未来变化下的河口。