Neck cutoffs are a common morphologic feature of meandering rivers though their occurrence on natural rivers is intermittent. Morphologic adjustments following cutoff initiation are typically rapid making detailed field investigations of the interactions between flow and form challenging. However, numerical models can offer insights into the hydrodynamic characteristics within the early stages of cutoff evolution. Field measurements of channel bathymetry and three‐dimensional velocities were collected during the first two years of morphologic change for a neck cutoff on the White River in Arkansas, USA. These data were used to calibrate a two‐dimensional numerical model to investigate the influence of hydrologic variability on the hydrodynamic characteristics of neck cutoffs during the early stages morphologic adjustment. The modeling results reveal complex patterns of the two‐dimensional flow field, including multiple regions of flow separation and recirculation related to strong redirection of the flow nearly 180 degrees through the cutoff. These regions of recirculation are also shown to vary depending on discharge conditions and affect hydrologic connectivity between the main channel and abandoned bend. Model results for the initial cutoff morphology show a substantial portion of discharge still conveyed by the original bend for all three discharge scenarios, resulting in a shear layer within the downstream limb of the site that limits advection of high‐momentum fluid against the bank opposite of the cutoff. The findings from this investigation are among the first detailed flow structure studies during the initiation of a neck cutoff and are used to improve conceptual models for cutoff dynamics.

中文翻译：

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不同水文条件下高弯曲主动演化截割区二维水动力数值模拟

尽管自然河流中的断流是断断续续的，但颈部断流是蜿蜒河流的常见形态特征。切断开始后的形态调整通常很快，使得对流动与形式之间相互作用的详细现场调查变得困难。但是，数值模型可以提供有关截止演化早期阶段的水动力特性的见解。在美国阿肯色州怀特河的颈部断流的形态变化的前两年中，收集了通道测深和三维速度的现场测量结果。这些数据用于校准二维数值模型，以研究水文变异性对早期形态调整过程中颈部截流的水动力特性的影响。建模结果揭示了二维流场的复杂模式，包括流分离和再循环的多个区域，这些区域与通过截流的近180度的强流重定向有关。这些回流区域也显示为根据排放条件而变化，并影响主河道和废弃弯道之间的水文连通性。初始截留形态的模型结果表明，对于所有三种排放情况，原始弯道仍会输送相当大的排放量，从而在该站点的下游分支内形成了一个剪切层，限制了高动量流体相对于河床对岸的平流。截止。