A mechanistic understanding of channel evolution following dam removal
A mechanistic understanding of channel evolution following dam removal
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大坝拆除后河道演变的机制理解
DOI：
10.1016/j.geomorph.2021.107971
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发表时间：
2021
期刊：
影响因子：
3.9
通讯作者：
Rossi, Rebecca
中科院分区：
文献类型：
--
作者：
Fields, Jordan;Renshaw, Carl;Magilligan, Francis;Dethier, Evan;Rossi, Rebecca
冲积河道扰动后恢复的研究已经考虑了基于形式和/或过程的范例来描述动态平衡的途径。然而，对形式和过程之间的协变以及驱动每个恢复的机制的综合理解仍然不完整。我们使用了一个小（4米高）高地大坝拆除新英格兰作为一个自然的实验，调查的时间和弧的通道的动态平衡条件下，使用形式和过程为基础的观点。我们观察到前水库和下游渠道的快速搬迁后的调整，然后相对稳定后，2年的流量发生6个月后删除。这种模式，以前被描述为河道恢复的“两相”模型，是“满岸”流（θQ2）与临界Shields（θcr）的Shields值之比随时间变化的结果。在大坝拆除后，泥沙通量的增加是由θ Q2与θ cr的高比值驱动的，θ cr值的降低和θ Q2值的升高导致了θ Q2与θ cr的高比值。当细粒沉积物被筛出时，θ cr在几周到几个月内迅速恢复到典型值。随后通过更高的流量对通道几何形状进行调整（即，2年流量）重新分配床面切应力，有利于θ Q2的松弛，使θQ2：θcr ≥ 1，达到临界河道标准。尽管快速恢复到基于过程的平衡，近3年后删除前水库达到形态上仍然不成熟的天然河道的规模特征。我们的研究结果表明，基于过程的恢复是快速的，促进相对频繁，适度的流量，并依赖于调整的特征床粒度（d50），以反映当时的水力学。相比之下，较慢的形式为基础的平衡的实现取决于不太频繁的流量等于和/或大于平滩流量的时间，以及外在的渠道控制，如当地的山谷地形和可招募的大木材的可用性。
Studies of post-disturbance recovery in alluvial channels have considered form- and/or process-based paradigms to describe pathways to dynamic equilibrium. Yet, an integrated understanding of the covariation between form and process as well as the mechanisms that drive the recovery of each remains incomplete. We used a small (4 m tall) upland dam removal in New England as a natural experiment to investigate the timing and arc of a channel's return to dynamic equilibrium conditions, using both form- and process-based perspectives. We observed rapid post-removal adjustments in the former reservoir and downstream channels, then relative stability after a 2-year flow that occurred 6 months post-removal. This pattern, previously described as the “two-phase” model of channel recovery, was the result of temporal variations in the ratio of Shields values at the ‘bankfull’ flow (θQ2) to critical Shields (θcr). Immediately post-dam removal, elevated sediment flux was driven by the high ratio ofθQ2toθcrthat resulted from decreasedθcrvalues and elevatedθQ2values. As fine-grained sediments were winnowed,θcrquickly recovered back to typical values within weeks to months. Subsequent adjustments to channel geometry by higher flows (i.e., the 2-year flow) redistributed bed shear stress and facilitated the relaxation ofθQ2so thatθQ2:θcr≈ 1, the threshold channel criterion. Despite the rapid return to process-based equilibrium, nearly 3 years post-removal the former reservoir reach remains morphologically immature with respect to reach-scale characteristics of natural channels. Our results indicate that process-based recovery is rapid, facilitated by relatively frequent, modest flows, and dependent on the adjustment of the characteristic bed grain size (d50) to reflect prevailing hydraulics. In contrast, the slower attainment of form-based equilibrium depends on the timing of less frequent flows equal to and/or larger than the bankfull discharge as well as extrinsic channel controls such as local valley topography and the availability of recruitable large wood.
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DOI：
--
发表时间：
1967-02
期刊：
Journal of the Waterways and Harbors Division
影响因子：
--
作者：
R. Kellerhals
通讯作者：
R. Kellerhals
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影响因子：
5.4
作者：
A. Pearson;N. Snyder;M. Collins
通讯作者：
M. Collins
实验砾石床河道的宽度调整以响应溢流
DOI：
--
发表时间：
2013
期刊：
影响因子：
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作者：
J. Pitlick;J. Marr;J. Pizzuto
通讯作者：
J. Pizzuto
改良冲积流中的河道演化。
DOI：
--
发表时间：
1987
期刊：
影响因子：
--
作者：
A. Simon;C. Hupp
通讯作者：
C. Hupp
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影响因子：
3.9
作者：
Rathburn, Sara L.;Shahverdian, Scott M.;Ryan, Sandra E.
通讯作者：
Ryan, Sandra E.