Meandering of river systems has been attributed to erosion and deposition of sediments along river banks, yet a universal cause of the instability has not been identified that can be applied to other meandering systems. Here, we address the conditions that lead to the meander instability, in effect “upstream” of the many previous and thorough analyses of hydraulics and morphological patterns that ensue when such conditions exist. Rivers are only one of many fluid systems that exhibit meandering behavior, and no other involves sediment. Meandering is observed in the Gulf Stream, free-falling streams of viscous fluid, derailed trains, jackknifed trucks, and other systems in one, two or three dimensions. As such, a universal criterion is needed to explain meandering in general. We propose that meandering in all systems is driven by development of an adverse pressure gradient that results from an imbalance between driving and resistive forces. A universal framework will make it possible to determine under what conditions the meandering instability will manifest in altered flow and channel morphology. Toward that end, we conducted laboratory experiments in 2- and 3-dimensions and analyzed systems with either reduction in driving forces or increase in resistive forces. We also examine the ubiquitous example of natural rivers to identify the conditions under which rivers meander or ply a more direct course to base level. Further, we define a dimensionless “Meander Number” as (driving-resistive)/resistive forces. The observations presented here support a common cause that leads to instability of a wide range of meandering systems and with further exploration, may ultimately lead to a universal theory of meandering systems.

河流系统的曲折归因于沿河岸的沉积物的侵蚀和沉积，但尚未确定可应用于其他曲流系统的不稳定的普遍原因。在这里，我们解决了导致曲流不稳定性的条件，实际上是在这种条件存在时对水力学和形态模式进行的许多先前和彻底的分析的“上游”。河流只是许多表现出蜿蜒行为的流体系统之一，没有其他流体系统涉及沉积物。在墨西哥湾流中观察到蜿蜒流动、粘性流体的自由下落流、脱轨的火车、折弯的卡车和其他一维、二维或三维系统。因此，需要一个普遍的标准来解释一般的曲折。我们提出，所有系统中的蜿蜒曲折都是由驱动力和阻力之间的不平衡导致的逆压力梯度的发展驱动的。一个通用框架将可以确定在什么条件下蜿蜒不稳定性将表现为改变的流动和通道形态。为此，我们在 2 维和 3 维中进行了实验室实验，并分析了驱动力减少或阻力增加的系统。我们还研究了普遍存在的天然河流示例，以确定河流在何种条件下蜿蜒曲折或更直接地流向基线。此外，我们将无量纲“曲流数”定义为（驱动阻力）/阻力。