Canyons with undulating walls
Canyons with undulating walls
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峡谷壁起伏
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
A. Miller
中科院分区：
文献类型：
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作者：
E. Wohl;D. M. Thompson;A. Miller
切入粘性基底的通道通常会形成起伏的壁，其特征是通道宽度有规则、重复的变化。具有起伏壁的斜坡可在各种岩性、气候和构造体系中发现，并且最常见于活动切口的克尼克状破碎带的下游。水槽实验和自然通道形态模式导致我们推断，壁起伏的残余物的突破，偏移坑洞或弯曲的纵向凹槽形成的切口的克尼克区。衬底特性似乎对这些起伏的影响不大。使用测量从八个渠道切入纳瓦霍砂岩南部的犹他州，我们发现，完整的岩石强度，岩体强度，联合方向和间距，层理，孔隙度没有显着不同的渠道达到直壁，起伏的墙壁，曲流。壁起伏的波长和幅度也没有与任何基板特性。这些结果使我们得出结论，主要控制形成的起伏壁是水力过程。沿着研究河道，深，狭窄的河段与起伏的墙壁与更广泛的直或蜿蜒的河段交替。使用水槽模拟和一维和二维水力模型，我们发现，墙壁起伏的作用，以减少interreach（空间）的变化，在能量消耗，并尽量减少能量消耗达到。我们建议，壁的波动和流动水力学创建一个反馈，从而壁的波动被保存以下断点切口。然后，壁的起伏以类似于底形的方式调节下游的能量消耗。这意味着，一般原则的均匀能量消耗的冲积渠道开发也适用于在到达尺度基岩渠道相对均匀的基板。
Channels incised into cohesive substrates commonly develop undulating walls characterized by regular, repetitive variations in channel width. Canyons with undulating walls are found in a variety of lithologic, climatic, and tectonic regimes, and are most commonly present downstream from a knick zone of active incision. Flume experiments and natural channel morphologic patterns lead us to infer that wall undulations are the remnants of breached, offset potholes or of sinuous longitudinal grooves formed during incision of the knick zone. Substrate characteristics seem to have little influence on these undulations. Using measurements from eight channels incised into the Navajo Sandstone of southern Utah, we found that intact rock strength, rock-mass strength, joint orientation and spacing, bedding, and porosity did not differ significantly between channel reaches with straight walls, undulating walls, and meanders. The wavelength and amplitude of wall undulations also did not correlate with any substrate characteristic. These results lead us to conclude that the primary control on formation of undulating walls is hydraulic processes. Along the study channels, deep, narrow reaches with undulating walls alternate with wider straight or meandering reaches. Using flume simulations and one- and two-dimensional hydraulic modeling, we found that the wall undulations act to reduce interreach (spatial) variability in energy expenditure, and to minimize energy expenditure within a reach. We propose that the wall undulations and flow hydraulics create a feedback whereby the wall undulations are preserved following knickpoint incision. The wall undulations then act to regulate downstream energy expenditure in a manner analogous to bedforms. This implies that generalized principles of uniform energy expenditure developed for alluvial channels may also apply at the reach scale to bedrock channels with relatively homogeneous substrates.