Response of Grain-Size Distribution Characteristics of a Gravel Bar to Topographic and Hydraulic Conditions: A Case Study from the Upper Yangtze River in China

Pub Date : 2024-07-10 DOI:10.1134/s0097807823602509

Rangang Zhang, Shengfa Yang, Peng Zhang

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Abstract

The characteristics of grain-size distribution on the surface of gravel bars have important implications for riverbed development and fish spawning. In this study, an unmanned aerial vehicle was used to sample 204 sites on the surface of a gravel bar in the upper reaches of the Yangtze River, China. Photogrammetry was used to generate digital elevation model data for the bar. Based on the calculation results of a two-dimensional river hydrodynamic model, clear distribution maps of the flow and grain-size fields were obtained. In addition, the correlation between the hydrodynamic and grain-size indicators was discussed, and a relational equation between the Froude number and median grain size was derived. Finally, the effect of topographic changes on the grain-size distribution was analyzed. The results showed that the grain size at the head of the gravel bar was larger than that at the tail, influenced by the scouring of the flow; coarsening of the gravel at the edge of the bar bend was also evident. A positive correlation was found between \({{D}_{{50}}}\), flow velocity, and the Froude number. The sorting coefficient, \({{S}_{0}}\), exhibited a negative correlation with the flow velocity and Froude number. A positive correlation was found between grain size variability indicator \({{C}_{{v}}}\) and topographic variability indicator \({{C}_{h}}\). The variability in the grain-size distribution was the highest near areas with more drastic topographic variations. The bar surfaces exhibited a pattern of coarse-grained tops and fine-grained pools. The results of this study contribute to further understanding the geomorphology of gravel bars and may help investigate the spawning sites of organisms on the bar surface sensitive to bottom particle size.

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砾石条粒径分布特征对地形和水力条件的响应：中国长江上游案例研究

摘要砾石条表面粒径分布特征对河床发育和鱼类产卵具有重要影响。在这项研究中，无人机对中国长江上游的一个砾石条表面的 204 个地点进行了取样。利用摄影测量法生成了砾石层的数字高程模型数据。根据二维河流水动力模型的计算结果，获得了清晰的流量和粒径场分布图。此外，还讨论了水动力指标与粒径指标之间的相关性，并得出了弗劳德数与中值粒径之间的关系式。最后，分析了地形变化对粒度分布的影响。结果表明，受水流冲刷的影响，砾石条头部的粒度大于尾部；砾石条弯曲边缘的粒度也明显变粗。发现 \({{D}_{{50}}}\)、流速和弗劳德数之间存在正相关。分选系数（{{S}_{0}}/\）与流速和弗劳德数呈负相关。粒度变化指标（{{C}_{v}}}）与地形变化指标（{{C}_{h}}}）呈正相关。在地形变化较剧烈的区域附近，粒度分布的变异性最大。条带表面呈现出粗粒顶和细粒池的模式。该研究结果有助于进一步了解砾石条带的地貌，并有助于研究对底部粒径敏感的生物在条带表面的产卵地点。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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