Predicting the morphodynamics of sedimentary landscapes due to fluvial and aeolian flows requires answering the following questions: Is the flow strong enough to initiate sediment transport, is the flow strong enough to sustain sediment transport once initiated, and how much sediment is transported by the flow in the saturated state (i.e., what is the transport capacity)? In the geomorphological and related literature, the widespread consensus has been that the initiation, cessation, and capacity of fluvial transport, and the initiation of aeolian transport, are controlled by fluid entrainment of bed sediment caused by flow forces overcoming local resisting forces, whereas aeolian transport cessation and capacity are controlled by impact entrainment caused by the impacts of transported particles with the bed. Here the physics of sediment transport initiation, cessation, and capacity is reviewed with emphasis on recent consensus-challenging developments in sediment transport experiments, two-phase flow modeling, and the incorporation of granular physics' concepts. Highlighted are the similarities between dense granular flows and sediment transport, such as a superslow granular motion known as creeping (which occurs for arbitrarily weak driving flows) and system-spanning force networks that resist bed sediment entrainment; the roles of the magnitude and duration of turbulent fluctuation events in fluid entrainment; the traditionally overlooked role of particle-bed impacts in triggering entrainment events in fluvial transport; and the common physical underpinning of transport thresholds across aeolian and fluvial environments. This sheds a new light on the well-known Shields diagram, where measurements of fluid entrainment thresholds could actually correspond to entrainment-independent cessation thresholds.

中文翻译：

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沉积物在风成和河流环境中开始、停止和夹带的物理学

预测由河流和风成流动引起的沉积景观的形态动力学需要回答以下问题：流动是否足够强大以启动沉积物输送，流动是否足够强大以维持沉积物一旦启动，以及有多少沉积物被流动输送到饱和状态（即运输能力是多少）？在地貌学和相关文献中，普遍的共识是，河流输运的开始、停止和能力以及风成输运的开始，是由克服局部阻力的流动力引起的床层沉积物的流体夹带控制的，而风成运输停止和容量由运输颗粒与床的冲击引起的冲击夹带控制。这里回顾了沉积物运输开始、停止和容量的物理学，重点是最近在沉积物运输实验、两相流建模和颗粒物理学概念的结合方面具有挑战性的发展。突出的是密集颗粒流和沉积物运输之间的相似之处，例如称为蠕动的超慢颗粒运动（发生在任意弱的驱动流中）和抵抗床层沉积物夹带的跨系统力网络；湍流波动事件的幅度和持续时间在流体夹带中的作用；传统上被忽视的颗粒床撞击在触发河流运输中的夹带事件中的作用；以及跨越风成和河流环境的运输阈值的共同物理基础。