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Topographic, hydraulic, and vegetative controls on bar and island development in mixed bedrock‐alluvial, multi‐channeled, dryland rivers
Water Resources Research ( IF 5.4 ) Pub Date : 2020-05-01 , DOI: 10.1029/2019wr026101 D. J. Milan 1 , S. Tooth 2 , G. L. Heritage 3
Water Resources Research ( IF 5.4 ) Pub Date : 2020-05-01 , DOI: 10.1029/2019wr026101 D. J. Milan 1 , S. Tooth 2 , G. L. Heritage 3
Affiliation
We investigate processes of bedrock-core bar and island development in a bedrock-influenced anastomosed reach of the Sabie River, Kruger National Park (KNP), eastern South Africa. For sites subject to alluvial stripping during an extreme flood event (~4470-5630 m3 s-1) in 2012, pre- and post-flood aerial photographs and LiDAR data, 2D 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 (~4500 m3 s-1), most sediment (sand, fine gravel) is mobile but localized deposition on bedrock topographic highs is possible. At lower simulated discharges (< 1,000 m3 s−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.
中文翻译:
在混合基岩冲积、多渠道、旱地河流中对酒吧和岛屿发展的地形、水力和植被控制
我们调查了南非东部克鲁格国家公园 (KNP) 萨比河受基岩影响的吻合河段中基岩核心杆和岛屿发育的过程。对于 2012 年极端洪水事件 (~4470-5630 m3 s-1) 期间遭受冲积剥离的地点,洪水前后的航拍照片和 LiDAR 数据、二维形态动力学模拟和现场观测表明,现存最厚的冲积沉积物往往位于基岩地形低点。在模拟的峰值流量(~4500 m3 s-1)下,大多数沉积物(沙子、细砾石)是可移动的,但在基岩地形高处的局部沉积是可能的。在较低的模拟排放量 (< 1,000 m3 s−1) 下,地形高点不会被淹没,沉积发生在低海拔地区,特别是在下降阶段与主要通道断开的区域。现场观察表明,除了排放外,洪水之间的雨水冲刷可能会将沉积物从基岩地形高处重新分配到低海拔地区,并且还突出了植被定植在酒吧稳定性以及捕获额外沉积物和有机物方面的关键作用。这些发现挑战了先前对克鲁格国家公园河流动力学分析提供基础的地形高点优先沉积的假设,并在一个新的概念模型中进行了综合,该模型展示了初始基岩地形低点如何变成地形高点(基岩核心棒和岛屿)。沉积物堆积的后期。
更新日期:2020-05-01
中文翻译:
在混合基岩冲积、多渠道、旱地河流中对酒吧和岛屿发展的地形、水力和植被控制
我们调查了南非东部克鲁格国家公园 (KNP) 萨比河受基岩影响的吻合河段中基岩核心杆和岛屿发育的过程。对于 2012 年极端洪水事件 (~4470-5630 m3 s-1) 期间遭受冲积剥离的地点,洪水前后的航拍照片和 LiDAR 数据、二维形态动力学模拟和现场观测表明,现存最厚的冲积沉积物往往位于基岩地形低点。在模拟的峰值流量(~4500 m3 s-1)下,大多数沉积物(沙子、细砾石)是可移动的,但在基岩地形高处的局部沉积是可能的。在较低的模拟排放量 (< 1,000 m3 s−1) 下,地形高点不会被淹没,沉积发生在低海拔地区,特别是在下降阶段与主要通道断开的区域。现场观察表明,除了排放外,洪水之间的雨水冲刷可能会将沉积物从基岩地形高处重新分配到低海拔地区,并且还突出了植被定植在酒吧稳定性以及捕获额外沉积物和有机物方面的关键作用。这些发现挑战了先前对克鲁格国家公园河流动力学分析提供基础的地形高点优先沉积的假设,并在一个新的概念模型中进行了综合,该模型展示了初始基岩地形低点如何变成地形高点(基岩核心棒和岛屿)。沉积物堆积的后期。