Coastal rivers that build deltas undergo repeated avulsion events—that is, abrupt changes in river course—which we need to understand to predict land building and flood hazards in coastal landscapes. Climate change can impact water discharge, flood frequency, sediment supply, and sea level, all of which could impact avulsion location and frequency. Here we present results from quasi-2D morphodynamic simulations of repeated delta-lobe construction and avulsion to explore how avulsion location and frequency are affected by changes in relative sea level, sediment supply, and flood regime. Model results indicate that relative sea-level rise drives more frequent avulsions that occur at a distance from the shoreline set by backwater hydrodynamics. Reducing the sediment supply relative to transport capacity has little impact on deltaic avulsions, because, despite incision in the upstream trunk channel, deltas can still aggrade as a result of progradation. However, increasing the sediment supply relative to transport capacity can shift avulsions upstream of the backwater zone because aggradation in the trunk channel outpaces progradation-induced delta aggradation. Increasing frequency of overbank floods causes less frequent avulsions because floods scour the riverbed within the backwater zone, slowing net aggradation rates. Results provide a framework to assess upstream and downstream controls on avulsion patterns over glacial-interglacial cycles, and the impact of land use and anthropogenic climate change on deltas.

中文翻译：

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河流三角洲撕裂位置和频率的气候变化控制

构建三角洲的沿海河流会经历反复的侵蚀事件——即河道的突然变化——我们需要了解这一点，以预测沿海景观中的土地建设和洪水灾害。气候变化会影响排水量、洪水频率、沉积物供应和海平面，所有这些都会影响撕裂的位置和频率。在这里，我们展示了重复三角叶构造和撕脱的准二维形态动力学模拟的结果，以探索撕脱位置和频率如何受到相对海平面、沉积物供应和洪水状况变化的影响。模型结果表明，相对海平面上升会导致更频繁的撕脱，这些撕脱发生在距由回水流体动力学设定的海岸线一定距离处。相对于运输能力减少沉积物供应对三角洲撕脱几乎没有影响，因为，尽管在上游干道上有切口，但三角洲仍会因进积而加剧。然而，增加相对于运输能力的沉积物供应可以将回水区上游的侵蚀转移，因为主干河道的加积超过了进积引起的三角洲加积。由于洪水冲刷回水区内的河床，减缓了净加成速率，因此越堤洪水频率的增加会导致发生较少的撕裂。结果提供了一个框架来评估上下游对冰川-间冰期循环中的侵蚀模式的控制，以及土地利用和人为气候变化对三角洲的影响。增加相对于运输能力的沉积物供应可以转移回水区上游的侵蚀，因为主干河道的积聚速度超过了进积引起的三角洲积聚。由于洪水冲刷回水区内的河床，减缓了净加成速率，因此越堤洪水频率的增加会导致发生较少的撕裂。结果提供了一个框架来评估上下游对冰川-间冰期循环中的侵蚀模式的控制，以及土地利用和人为气候变化对三角洲的影响。增加相对于运输能力的沉积物供应可以转移回水区上游的侵蚀，因为主干河道的积聚速度超过了进积引起的三角洲积聚。由于洪水冲刷回水区内的河床，减缓了净加成速率，因此越堤洪水频率的增加会导致发生较少的撕裂。结果提供了一个框架来评估上下游对冰川-间冰期循环中的侵蚀模式的控制，以及土地利用和人为气候变化对三角洲的影响。