Effects of stream discharge, alluvial depth and bar amplitude on hyporheic flow in pool‐riffle channels
Effects of stream discharge, alluvial depth and bar amplitude on hyporheic flow in pool‐riffle channels
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DOI：
10.1029/2010wr009140
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发表时间：
2011-08
影响因子：
5.4
通讯作者：
D. Tonina;J. Buffington
中科院分区：
文献类型：
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作者：
D. Tonina;J. Buffington
潜流是河流流量与河道形态相互作用的结果，是河流生态系统的重要组成部分，因为它促进了河流与河床之间的水和溶质交换。由于三维地形跨越了部分淹没到完全淹没的条件范围，导致了静态和动态水头的变化，池纹沟道中的潜流特别复杂。因此，与之前研究的完全淹没的二维河床形式相比，这些河道表现出河床压力和低流速的过渡条件。在此，我们进行了一系列的三维模拟，研究了河床地形、冲积层深度和水流流量对不同河床形态淹没的池纹河段潜流的影响，并提出了三个经验公式来预测潜流交换的平均深度和停留时间分布的特征值（平均值和标准差）。用三维抽运模型预测了潜流交换，并将潜流模拟为达西流。我们发现，对于部分和完全淹没的水池-细沟地形，潜隐停留时间都可以很好地近似为对数正态分布，其分布参数由对数变换的停留时间的均值和方差定义。当冲积层深度小于所研究条件下河床波长的三分之一时，冲积层的深度对潜流有实质性的影响。
Hyporheic flow results from the interaction between streamflow and channel morphology and is an important component of stream ecosystems because it enhances water and solute exchange between the river and its bed. Hyporheic flow in pool‐riffle channels is particularly complex because of three‐dimensional topography that spans a range of partially to fully submerged conditions, inducing both static and dynamic head variations. Hence, these channels exhibit transitional conditions of streambed pressure and hyporheic flow compared to previous studies of fully submerged, two‐dimensional bed forms. Here, we conduct a series of three‐dimensional simulations to investigate the effects of bed topography, depth of alluvium, and stream discharge on hyporheic flow in pool‐riffle reaches with variable bed form submergence, and we propose three empirical formulae to predict the mean depth of hyporheic exchange and characteristic values of the residence time distribution (mean and standard deviation). Hyporheic exchange is predicted with a three‐dimensional pumping model, and hyporheic flow is modeled as a Darcy flow. We find that the hyporheic residence time is well approximated by a lognormal distribution for both partially and entirely submerged pool‐riffle topography, with the parameters of the distribution defined by the mean and variance of the log‐transformed residence time. Depth of alluvium has a substantial effect on hyporheic flow when alluvial depth is less than a third of the bed form wavelength for the conditions examined.