Abstract. Recent studies have drawn special attention to the significant dependencies between flood drivers and the occurrence of compound flood events in coastal areas. This study investigates compound flooding from tides, river discharge (Q) and specifically waves using a hydrodynamic model at Breede Estuary, South Africa. We quantify vertical and horizontal differences in flood characteristics caused by driver interaction, and assess the contribution of waves. Therefore, we compare flood characteristics resulting from compound flood scenarios to those in which single drivers are omitted. We find that flood characteristics are more sensitive to Q than to waves, particularly when the latter only coincide with high spring tides. When interacting with Q, however, the contribution of waves is high, causing 10–12 % larger flood extents and 45–85 cm higher water depths, as waves caused backwater effects and raised water levels inside the lower reaches of the estuary. With higher wave intensity, the first flooding began up to 12 hours earlier. Our findings provide insights on compound flooding in terms of flood magnitude and timing at a South African estuary and demonstrate the need to account for the effects of compound events, including waves, in future flood impact assessments of open South African estuaries.

中文翻译：

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调查南非布里德河口复合洪水期间波浪和河流流量的相互作用

摘要。最近的研究特别关注洪水驱动因素与沿海地区复合洪水事件的发生之间的显着相关性。本研究使用南非布里德河口的水动力模型研究潮汐、河流流量 (Q) 和特别是波浪造成的复合洪水。我们量化由驾驶员交互引起的洪水特征的垂直和水平差异，并评估波浪的贡献。因此，我们将复合洪水情景产生的洪水特征与忽略单个驱动因素的洪水特征进行比较。我们发现洪水特征对 Q 比对波浪更敏感，特别是当后者只与大潮重合时。然而，当与 Q 相互作用时，波的贡献很高，导致洪水范围扩大 10-12%，水深增加 45-85 厘米，因为波浪造成了回水效应并提高了河口下游的水位。随着海浪强度的增加，第一次洪水在 12 小时前开始。我们的研究结果提供了关于南非河口洪水规模和时间方面的复合洪水的见解，并证明了在未来对南非开放河口的洪水影响评估中考虑复合事件（包括波浪）的影响的必要性。