Simulated Dynamics of Mixed Versus Uniform Grain Size Sediment Pulses in a Gravel‐Bedded River
Simulated Dynamics of Mixed Versus Uniform Grain Size Sediment Pulses in a Gravel‐Bedded River
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DOI：
10.1029/2021jf006194
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发表时间：
2021-10
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影响因子：
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通讯作者：
M. Ahammad;J. Czuba;A. Pfeiffer;B. Murphy;P. Belmont
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作者：
M. Ahammad;J. Czuba;A. Pfeiffer;B. Murphy;P. Belmont
山区河流经常接受来自各种自然和人为过程的间歇性、离散脉冲形式的沉积物。沉积物一旦进入河流，其运动取决于水流、粒度分布、河道和网络几何形状。在这里，我们模拟下游河床高程的变化，导致离散输入的沉积物（10,000立方米），不同的体积和粒度分布，在中等和高流量条件下。我们特别关注比较混合和均匀粒径的沉积物脉冲之间的床响应。这项工作建立在拉格朗日，床物质输沙模型，并将其应用到一个27公里的范围内的mainstem尼斯夸利河，华盛顿，美国。我们比较观察到的床高程变化和积累率在下游湖泊模拟结果。然后，我们调查的幅度，时间，和下游的变化，由于引入合成沉积物脉冲的持续性进行比较的结果与基线条件（无脉冲）。我们的研究结果表明，床响应主要受沉积物脉冲粒度和分布的影响。中等混合尺寸脉冲（中值河床砾石尺寸的约50%）可能具有最大的下游影响，因为较细的尺寸快速转换，而较粗的尺寸（中值河床砾石尺寸和较大尺寸）分散缓慢。此外，具有比床更小的中值粒度的混合大小的脉冲比均匀大小的脉冲更多地增加床流动性。这项工作对河流管理具有重要意义，因为它使我们能够更好地了解河流地貌对沉积物供应变化的响应。
Mountain rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes. Once emplaced in the river, the movement of this sediment depends on flow, grain size distribution, and channel and network geometry. Here, we simulate downstream bed elevation changes that result from discrete inputs of sediment (∼10,000 m3), differing in volume and grain size distribution, under medium and high flow conditions. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. This work builds on a Lagrangian, bed‐material sediment transport model and applies it to a 27 km reach of the mainstem Nisqually River, Washington, USA. We compare observed bed elevation change and accumulation rates in a downstream lake to simulation results. Then we investigate the magnitude, timing, and persistence of downstream changes due to the introduction of synthetic sediment pulses by comparing the results against a baseline condition (without pulse). Our findings suggest that bed response is primarily influenced by the sediment‐pulse grain size and distribution. Intermediate mixed‐size pulses (∼50% of the median bed gravel size) are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed‐size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform‐size pulse. This work has important implications for river management, as it allows us to better understand fluvial geomorphic responses to variations in sediment supply.