Topographic, Hydraulic, and Vegetative Controls on Bar and Island Development in Mixed Bedrock-Alluvial, Multichanneled, Dryland Rivers
Topographic, Hydraulic, and Vegetative Controls on Bar and Island Development in Mixed Bedrock-Alluvial, Multichanneled, Dryland Rivers
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混合基岩冲积、多河道、旱地河流中坝和岛屿发育的地形、水力和植被控制
DOI：
10.1029/2019wr026101
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发表时间：
2020
影响因子：
5.4
通讯作者：
Milan D
中科院分区：
文献类型：
--
作者：
Milan D
我们调查过程中的基岩核心酒吧和岛屿的发展，在基岩影响的萨比河，克鲁格国家公园，南非东部的封闭河段。对于在2012年极端洪水事件（~ 4，470 - 5，630 m3 s −1）期间受到冲积层剥离的场地，洪水前和洪水后的航空照片和LiDAR数据，二维形态动力学模拟和实地观察表明，最厚的幸存冲积层往往位于基岩地形低洼处。在模拟的峰值流量（~ 4，500 m3 s −1）下，大多数沉积物（沙子、细砾石）是移动的，但可能在基岩地形高点上发生局部沉积。在较低的模拟流量（<1，000 m3 s −1）下，地形高点不会被淹没，并且在较低海拔地区发生沉积，特别是在下降阶段与主河道断开的地区。实地观察表明，除了排放，洪水之间的雨水冲刷可能重新分配沉积物从基岩地形高点到低海拔地区，也突出了酒吧的稳定性，并在捕获额外的沉积物和有机物的植被定植的关键作用。这些发现挑战了地形高点上优先沉积的假设，这些假设是克鲁格国家帕克河动力学先前分析的基础，并被合成在一个新的概念模型中，该模型演示了初始基岩地形低点如何在沉积物积累的后期阶段成为地形高点（基岩核心酒吧和岛屿）。该模型提供了特别的洞察发展的混合基岩-冲积物沉积沿着克鲁格国家公园的河流，但类似的过程酒吧/岛屿的发展可能会发生沿着许多其他基岩影响河流在旱地南部非洲和更远的地方。
We investigate processes of bedrock‐core bar and island development in a bedrock‐influenced anastomosed reach of the Sabie River, Kruger National Park, eastern South Africa. For sites subject to alluvial stripping during an extreme flood event (~4,470–5,630 m3s−1) in 2012, preflood and postflood aerial photographs and LiDAR data, 2‐D morphodynamic simulations, and field observations reveal that the thickest surviving alluvial deposits tend to be located over bedrock topographic lows. At a simulated peak discharge (~4,500 m3s−1), most sediment (sand, fine gravel) is mobile but localized deposition on bedrock topographic highs is possible. At lower simulated discharges (<1,000 m3s−1), topographic highs are not submerged, and deposition occurs in lower elevation areas, particularly in areas disconnected from the main channels during falling stage. Field observations suggest that in addition to discharge, rainwash between floods may redistribute sediments from bedrock topographic highs to lower elevation areas, and also highlight the critical role of vegetation colonization in bar stability, and in trapping of additional sediment and organics. These findings challenge the assumptions of preferential deposition on topographic highs that underpin previous analyses of Kruger National Park river dynamics, and are synthesized in a new conceptual model that demonstrates how initial bedrock topographic lows become topographic highs (bedrock‐core bars and islands) in the latter stages of sediment accumulation. The model provides particular insight into the development of mixed bedrock‐alluvial anastomosing along the Kruger National Park rivers, but similar processes of bar/island development likely occur along numerous other bedrock‐influenced rivers across dryland southern Africa and farther afield.