Data from Dudunake et al. (2020), Local and reach-scale hyporheic flow response from boulder induced geomorphic changes

Stream hydromorphology regulates in-stream water flow and interstitial flow of stream 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 macro-roughness 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 experiments on sediment transport with computational fluid dynamics. Our results show that placement of boulders on “fixed” plane beds increase the reach scale hyporheic median residence time, τ50, by 15% and downwelling flux, qd, 18% from the plane bed. However, reach scale hyporheic exchange changes are stronger with τ50 decreasing by 20% and qd 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 which has been overlooked in previous work.河流水文地貌学（Stream hydromorphology）调控河道内水流以及河床沉积物内部的孔隙水流，后者被称为潜流交换（hyporheic exchange）。尽管现有研究已针对发育沙纹、沙垄的砂质河床河道，以及发育深潭-浅滩地貌的砾石河床河道开展了潜流相关研究，但对于床面起伏平缓、仅分布少量大型糙率单元（如漂石和卵石）的平坦床面地貌下的潜流特征，目前仍知之甚少。本研究基于泥沙输运大型水槽实验与计算流体动力学（computational fluid dynamics）的耦合方法，开展了一项关于漂石诱导的地貌变化对潜流影响的概念验证研究。研究结果表明，在“固定”平坦床面上布设漂石，可使河段尺度的潜流中位停留时间τ50较纯平坦床面提升15%，下渗通量qd提升18%。但当河床地貌达到平衡状态（即上游输入的泥沙与水流在漂石作用下达到动态平衡）时，河段尺度的潜流交换变化更为显著：τ50降低20%，qd提升79%。上述结果表明，砾石河床河道中的潜流对床面地形与泥沙输运带来的地貌响应极为敏感，而这一过程在以往研究中常被忽视。