Channel hydraulics and geomorphic effects of an extreme flood event on the Sabie River, South Africa
Channel hydraulics and geomorphic effects of an extreme flood event on the Sabie River, South Africa
复制标题
南非萨比河极端洪水事件的河道水力学和地貌影响
DOI：
10.1016/j.catena.2004.03.004
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发表时间：
2004
期刊：
影响因子：
6.2
通讯作者：
G. Jewitt
中科院分区：
文献类型：
--
作者：
A. Large;B. P. Moon;G. Jewitt
研究了2000年2月极端洪水（6000-7000 m3−1200年回复期流量）对南非半干旱基岩影响的Sabie河108公里河道形态的影响。河流被切割成基岩，形成了一个大通道，其平台在被调查的变化时间尺度上是固定的。在大河道的范围内，河流可能被划分为不同的河道类型（池速、基岩接合等），长度在1至20公里之间，每一种类型都以较小的形态单元的独特组合为特征，从填充大部分大河道的大型横向沙洲到米尺度的背风沙洲和沙洲。每种渠道类型的形态单元组成和空间覆盖的变化，以及重建的洪水水力。这项评估是基于1:10 000比例尺的航拍照片，拍摄于灾前5个月和灾后7个月，后者经灾后实地观测证实。一些河道类型（如黏性混合吻合）表现出广泛的沉积剥蚀，而另一些河道类型（如基岩吻合）基本保持不变。在形态单元尺度上，大型黏结横向沉积物基本未受洪水影响，而与长年流动子河道相关的较小活动河道松散和固结特征则被剥离。在河道类型尺度上，变化受影响输沙的时空流能变化和支流位置等因素的复杂组合控制。在形态单元的尺度上，对侵蚀的敏感性似乎与低流量活动河道以上的海拔有关，河道中较低海拔的特征被剥离。野外观察表明，松散的、活跃的水道单元正在剥离位置重新形成。
The effects of the February 2000 extreme flood (6000–7000 m3s−1, 200 year return period flow) on channel morphology are examined over 108 km of the semiarid bedrock-influenced Sabie River, South Africa. The river is incised into bedrock forming a macrochannel with a planform that is fixed over the timescale of change being investigated. Within the confines of the macrochannel, the river may be zoned into distinct channel types (pool rapid, bedrock anastomosing, etc.) between 1 and 20 km long each characterised by a distinctive assemblage of smaller morphologic units ranging from large lateral bars filling most of the macrochannel to metre-scale lee bars and sand sheets. Changes in morphologic unit composition and spatial coverage are presented for each channel type, along with reconstructed flood hydraulics. This appraisal is based on 1:10,000 scale aerial photographs taken 5 months before and 7 months after the event, the latter verified by post-flood field observations. Some channel types (e.g., cohesive mixed anastomosing) displayed widespread sedimentary stripping, while others (e.g., bedrock anastomosing) remained essentially unchanged. At the morphologic unit scale, large cohesive lateral deposits were largely unaffected by the flood, whereas smaller active channel unconsolidated and consolidated features associated with perennially flowing sub-channels were stripped. At the scale of channel type, change appears to be controlled by a complex combination of factors including (i) spatial and temporal flow energy level change affecting sediment transport and (ii) tributary location. Susceptibility to erosion at the scale of the morphologic unit appears to be linked to elevation above the low flow active channel with features at lower elevations in the channel being stripped. Field observations suggest that unconsolidated, active channel units are re-forming at stripped locations.