Hitting rock bottom: morphological responses of bedrock-confined streams to a catastrophic flood
Hitting rock bottom: morphological responses of bedrock-confined streams to a catastrophic flood
复制标题
触底：基岩限制的溪流对灾难性洪水的形态响应
DOI：
10.5194/esurf-3-265-2015
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发表时间：
2014
期刊：
影响因子：
6.2
通讯作者：
J. Croke
中科院分区：
文献类型：
--
作者：
M. B. Sargood;T. Cohen;C. Thompson;J. Croke
抽象。几个世纪以来，极端事件在塑造地球表面方面的作用一直是地球科学家的兴趣所在。2011年，澳大利亚东部构造静止环境中的灾难性洪水为半冲积河道如何应对此类事件提供了宝贵的见解。现场调查数据（3个河段）和桌面分析（10个河段）（汇水面积从0.5到168 km 2不等）显示，2011年事件的预测流量从415到933 m3 s-1不等，单位流功率估计高达1077 W m-2。估计夹带关系预测的流动性的整个粒度人口，和现场数据表明，本地化的流动性巨石直径达4.8米。重复激光雷达数据的分析表明，所有河段（现场和桌面）的粗颗粒冲积层的广泛冲刷净退化与集水面积和归一化侵蚀（R2 = 0.72-0.74）之间的强正相关关系的地区。2011年洪水中的广泛冲刷显著降低了深泓线方差，去除了先前的阶梯水池和其他粗粒河道单元，形成了平面河床（卵石）河段形态。这也伴随着平面基岩表面，边缘基岩条纹和基岩台阶的暴露。洪水后的现场数据表明，由于2013年洪水规模较小，重建了具有池浅滩形成的冲积层叠印，深泓线方差略有增加。然而，目前的形态和分布的通道形态单元不符合以前的分类基岩或河源河流系统。这种洪水后形式的变化表明，在半冲积系统中，极端事件对于重新设置通道内单元的形态和暴露底层岩性进行侵蚀具有重要意义。
Abstract. The role of extreme events in shaping the Earth's surface is one that has held the interests of Earth scientists for centuries. A catastrophic flood in a tectonically quiescent setting in eastern Australia in 2011 provides valuable insight into how semi-alluvial channels respond to such events. Field survey data (3 reaches) and desktop analyses (10 reaches) with catchment areas ranging from 0.5 to 168 km2 show that the predicted discharge for the 2011 event ranged from 415 to 933 m3 s−1, with unit stream power estimates of up to 1077 W m−2. Estimated entrainment relationships predict the mobility of the entire grain-size population, and field data suggest the localised mobility of boulders up to 4.8 m in diameter. Analysis of repeat lidar data demonstrates that all reaches (field and desktop) were areas of net degradation via extensive scouring of coarse-grained alluvium with a strong positive relationship between catchment area and normalised erosion (R2 = 0.72–0.74). The extensive scouring in the 2011 flood decreased thalweg variance significantly removing previous step pools and other coarse-grained in-channel units, forming lengths of plane-bed (cobble) reach morphology. This was also accompanied by the exposure of planar bedrock surfaces, marginal bedrock straths and bedrock steps. Post-flood field data indicate a slight increase in thalweg variance as a result of the smaller 2013 flood rebuilding the alluvial overprint with pool-riffle formation. However, the current form and distribution of channel morphological units does not conform to previous classifications of bedrock or headwater river systems. This variation in post-flood form indicates that in semi-alluvial systems extreme events are significant for re-setting the morphology of in-channel units and for exposing the underlying lithology to ongoing erosion.