Width adjustment in experimental gravel‐bed channels in response to overbank flows
Width adjustment in experimental gravel‐bed channels in response to overbank flows
复制标题
实验砾石床河道的宽度调整以响应溢流
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
J. Pizzuto
中科院分区：
文献类型：
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作者：
J. Pitlick;J. Marr;J. Pizzuto
我们进行了一系列水槽实验，以研究自生砾石河床渠道对不同量级和持续时间的洪水的响应。洪水是通过增加流入河道的流量而产生的，该河道是在中值粒径为2 mm的砂砾大小的沉积物中形成的。洪水增加了沿着河道周边的希尔兹应力，导致河岸侵蚀和河道快速加宽。由河岸侵蚀引入河道的沉积物不一定沉积在河床上，而是向下游输送，河床表面的瞬时变细可能促进了这一过程。在每个实验结束时，岸边沉积物不再运动，“部分推移质输运”的特点是河道的平床部分，希尔兹应力接近0.056的恒定值，大约是起动临界希尔兹应力的1.2倍。此外，流量完全由河道内的水流调节：稳定河道的建立完全消除了漫滩水流。我们推测，类似的过程可能会发生在自然界中，但只有当银行沉积物是非粘性和渠道收窄过程不能抵消银行侵蚀在漫滩流。我们还证明，一个简单的横向推移质输运模型可以重现观察到的渠道拓宽率，这表明简单的方法可能适用于预测宽度增加的渠道与非粘性，无植被的银行，即使在漫滩流。最后，我们提出了一个模型来预测一个稳定的砾石床通道的平衡宽度和深度与一个已知的通道形成盾应力。
We conducted a series of flume experiments to investigate the response of self‐formed gravel‐bed channels to floods of varying magnitude and duration. Floods were generated by increasing the discharge into a channel created in sand‐ and gravel‐sized sediment with a median grain size of 2 mm. Flooding increased the Shields stress along the channel perimeter, causing bank erosion and rapid channel widening. The sediment introduced to the channel by bank erosion was not necessarily deposited on the channel bed, but was rather transported downstream, a process likely facilitated by transient fining of the bed surface. At the end of each experiment, bank sediments were no longer in motion, “partial bed load transport” characterized the flat‐bed portion of the channel, and the Shields stress approached a constant value of 0.056, about 1.2 times the critical Shields stress for incipient motion. Furthermore, the discharge was entirely accommodated by flow within the channel: the creation of a stable channel entirely eliminated overbank flows. We speculate that similar processes may occur in nature, but only where bank sediments are non‐cohesive and where channel‐narrowing processes cannot counteract bank erosion during overbank flows. We also demonstrate that a simple model of lateral bed load transport can reproduce observed channel widening rates, suggesting that simple methods may be appropriate for predicting width increases in channels with non‐cohesive, unvegetated banks, even during overbank flows. Last, we present a model for predicting the equilibrium width and depth of a stable gravel‐bed channel with a known channel‐forming Shields stress.