AI 中文总结
该研究通过水槽实验结合Stream Tomography技术，揭示了流量影响非线性沙坝增长的机制，为沙坝稳定性理论提供基准约束并改进沙坝高度对流量变化的预测。
AI 中文摘要
交替沙坝是冲积河流中普遍存在的床形，沙坝高度的过度增长会增加洪水风险并破坏生态系统。预测沙坝高度的变异性需要量化沙坝增长速率对水流量的依赖关系，但由于传统水槽测量会干扰水流且无法连续捕捉沙坝演化，这一目标很少实现。本研究在四种流量和四种河道坡度（共16种条件）下开展实验室实验，采用非侵入式、可穿过水流的测量技术Stream Tomography连续测绘床面地形。沙坝高度呈现S型增长，可由朗道方程准确描述，从而能可靠估算增长速率和平衡高度。推断出的无量纲增长速率随流量降低而趋于增加，但其敏感性弱于单一交替沙坝模式稳定性理论的预测。该差异在低流量时更为显著，表明线性化存在局限性以及多沙坝模式间相互作用的影响。此外，对实测床面地形的数值水流模拟显示，沙坝发育过程中，低流量条件下的沙坝高深比相对更大，使水流更易偏转；此时沉积区下游的输沙受限，从而限制沙坝迁移，水流和输沙因此集中在冲刷区，加剧局部冲刷并促进沙坝高度增长。这些结果为沙坝稳定性理论提供了基准约束，有助于改进沙坝高度对流量变化响应的预测。
英文摘要
Alternate bars are ubiquitous bedforms in alluvial rivers, and excessive bar-height growth can increase flood risk and disrupt ecosystems. Predicting bar-height variability requires quantifying the dependence of bar growth rate on water discharge, yet this has rarely been achieved because conventional flume measurements interrupt the flow and cannot continuously capture bar evolution. Here we conducted laboratory experiments under four discharges and four channel slopes (16 conditions) and continuously mapped bed topography using Stream Tomography, a nonintrusive, flow-through measurement technique. Bar height exhibits sigmoidal growth and is well described by the Landau equation, allowing robust estimation of the growth rate and equilibrium height. The inferred dimensionless growth rate tends to increase as discharge decreases, but its sensitivity is weaker than that predicted by stability theory for a single alternate-bar mode. This discrepancy becomes more pronounced at lower discharge, indicating limitations of linearization and the influence of interactions among multiple bar modes. Furthermore, numerical flow simulations over the measured bed topography reveal that, during bar development, lower-discharge conditions produce a relatively larger bar height-to-depth ratio, making the flow more prone to deflection. In such cases, sediment transport is restricted downstream of depositional areas, thereby limiting bar migration. Consequently, flow and sediment transport become concentrated in the scour zones, enhancing local scour and promoting the growth of bar height. These results provide benchmark constraints for bar stability theories and help improve predictions of how bar height responds to changes in discharge.
Comments38 pages, 13 figures
