Stream hydromorphology regulates in‐stream water flow and interstitial flow of water within streambed sediments, the latter known as hyporheic exchange. Whereas hyporheic flow has been studied in sand‐bedded streams with ripples and dunes and in gravel‐bedded streams with pool‐riffle morphology, little is known about its characteristics in plane bed morphology with subdued streambed undulations and sparse macroroughness elements such as boulders and cobbles. Here, we present a proof‐of‐concept investigation on the role of boulder‐induced morphological changes on hyporheic flows based on coupling large‐scale flume sediment transport experiments with computational fluid dynamics. Our results show that placement of boulders on plane beds increase the reach‐scale hyporheic median residence time, τ₅₀, by 15% and downwelling flux, q_d, by 18% from the plane bed. However, reach‐scale hyporheic exchange changes are stronger with τ₅₀ decreasing by 20% and q_d increasing by 79% once the streambed morphology reached equilibrium (with the imposed upstream sediment and flow inputs on boulders). These results suggest that hyporheic flow is sensitive to the geomorphic response from bed topography and sediment transport in gravel‐bedded streams, a process that has been overlooked in previous work.

中文翻译：

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巨石诱发的地貌变化引起的局部和达到规模的渗流响应

溪流水文形态调节溪流沉积物内的溪流水和间隙水，后者被称为低渗交换。尽管在具有波纹和沙丘的沙层流和具有池-沟形态的砾石层流中研究了流变流，但对于其平面特征却知之甚少，该形态具有柔和的河床起伏和稀疏的宏观粗糙度元素（例如巨石和鹅卵石） 。在此，我们基于大型水槽沉积物输运实验与计算流体动力学的耦合，对巨石引起的形态变化对流变流的作用进行了概念验证研究。我们的研究结果显示在平面床巨石的放置增加达到规模潜流平均停留时间，τ ₅₀下降了15％，下沉通量q _d下降了18％。然而，到达规模潜流交换的变化与更强的τ ₅₀减少了20％，q _d 79％一旦河床形态学达到平衡增加（与施加上游沉积物和上巨石流输入）。这些结果表明，流变流对砾石层流中的床形和沉积物输运对地貌响应很敏感，这一过程在以前的工作中被忽略了。