Center for Applied Geosciences, Faculty of Science, Eberhard Karls University of Tübingen, Hölderlinstraße, 12, 72074 Tübingen, Germany.
Center for Applied Geosciences, Faculty of Science, Eberhard Karls University of Tübingen, Keplerstraße, 17, 72074 Tübingen, Germany.
Sci Total Environ. 2018 Nov 1;640-641:315-326. doi: 10.1016/j.scitotenv.2018.05.186. Epub 2018 May 30.
This work presents a post-event survey study, addressing the geomorphic response and large wood budget of two torrents, Grimmbach and Orlacher Bach, in southwestern Germany that were affected by a flash flood on May 29, 2016. During the event, large amounts of wood clogged and damaged a bridge of a cycling path at the outlet of the Grimmbach, while the town of Braunsbach was devastated by discharge and material transported along the Orlacher Bach. The severity of the event in these two small catchments (30.0 km and 5.95 km, respectively) is remarkable in basins with a relatively low average slope (10.7 and 12.0%, respectively). In order to gain a better understanding of the driving forces during this flood event an integrated approach was applied including (i) an estimate of peak discharges, (ii) an analysis of changes in channel width by comparing available aerial photographs before the flood with a post-flood aerial surveys with an Unmanned Aerial Vehicle and validation with field observations, (iii) a detailed mapping of landslides and analysis of their connectivity with the channel network and finally (iv) an analysis of the amounts of large wood recruited and deposited in the channel. The morphological changes in the channels can be explained by hydraulic parameters, such as stream power and unit stream power, and by morphological parameters such as the valley confinement. This is similar for LW recruitment amounts and volume of exported LW since most of it comes from the erosion of the valley floor. The morphological changes and large wood recruitment and deposit are in the range of studied mountain rivers. Both factors thus need to be considered for mapping and mitigating flash flood hazards also in this kind of low range mountains.
本研究通过后事件调查，研究了 2016 年 5 月 29 日德国西南部的 Grimmbach 和 Orlacher Bach 两条河流的地貌响应和大型木材预算。在此次事件中，大量木材阻塞并损坏了 Grimmbach 出口处的自行车道桥梁，而 Braunsbach 镇则被 Orlacher Bach 携带的排放物和物质摧毁。在这两个小流域（分别为 30.0km 和 5.95km）中，相对较低平均坡度（分别为 10.7%和 12.0%）的流域中，此次事件的严重程度非常显著。为了更好地了解此次洪水事件的驱动力，采用了综合方法，包括（i）估计峰值流量，（ii）通过将洪水前的现有航空照片与洪水后的无人机航空调查进行比较，分析渠道宽度的变化，并结合实地观测进行验证，（iii）详细绘制滑坡图，并分析其与河道网络的连通性，最后（iv）分析大型木材的招募和在渠道中沉积的情况。河道的形态变化可以用水力参数（如水流功率和单位水流功率）和形态参数（如山谷约束）来解释。对于 LW 的招募量和输出的 LW 体积也是如此，因为它们主要来自谷底的侵蚀。河道的形态变化和大型木材的招募和沉积都在研究山区河流的范围内。因此，在这种低山地区，也需要考虑这些因素来绘制和减轻山洪灾害。
