On 13th August 2021 at Unzen Volcano (Japan), an 81 mm.hr-1 peak-rainfall (1486 mm in 2 weeks) triggered series of erosion and deposition features in the Tansandani and the Gokurakudani gullies, all adding up to 57,800 m³ of erosion and 39,600 m³ of deposition. Upstream of the Sabo dam located at the exit of the Tansandani Gully, a large deposit has been visually identified as a potential debris-flow front candidate. However, the absence of direct observation leaves some uncertainty on the process that deposited the material and the magnitude of the flow. In the present contribution, the authors are investigating (1) the role of the debris-flow body in constructing the deposit and (2) the role of the tail of the debris-flow in eroding the fresh deposit. To reach this objective, the authors have combined a field investigation with direct observation, UAV (Unmanned Aerial Vehicle) LiDAR (Light Detection And Ranging) and Photogrammetry, and GIS (Geographic Information System) analysis of the field data. From this data, a 2D hydrodynamic simulation and sediment transport models were applied. The results show that the debris-flow ran beyond the first Sabo dam, with part of the material trapped on both sides of the gully. Afterwards, a central channel connected to sub-channels conveyed the diluted flow, most probably < 25 cm with maximum velocities between 4 to 5 m.s-1 at peak flow. Only the debris-flow phase went over the internal shoulders of the Sabo dam. A lobe occupies the top half of the study area and its deposition has been discussed to be related to the sudden widening of the gully, while the lower half is connected to the base-level created by the check dam.

中文翻译：

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使用无人机 LiDAR、SfM-MVS 对检查坝控制沟渠（日本云仙火山）中的泥石流体沉积和尾流再动员进行 SWE 建模

2021 年 8 月 13 日，在日本云仙火山，81 mm.hr-1 的峰值降雨量（两周内 1486 mm）引发了 Tansandani 和 Gokurakudani 沟壑的一系列侵蚀和沉积特征，总计达 57,800 m ³侵蚀量和沉积量39,600 m ³ 。位于坦桑达尼沟壑出口处的萨博大坝上游，一处大型沉积物已被目视识别为潜在的泥石流前缘候选区域。然而，由于缺乏直接观察，沉积材料的过程和流量的大小存在一些不确定性。在本论文中，作者正在研究（1）泥石流体在沉积物形成过程中的作用以及（2）泥石流尾部在侵蚀新鲜沉积物中的作用。为了实现这一目标，作者将现场调查与直接观察、无人机、激光雷达（光探测和测距）和摄影测量以及现场数据的 GIS（地理信息系统）分析相结合。根据这些数据，应用了二维水动力模拟和沉积物传输模型。结果表明，泥石流超出了第一座萨博大坝，部分物质被困在沟壑两侧。随后，连接到子通道的中央通道输送稀释的流量，最有可能 < 25 cm，峰值流量时的最大速度在 4 至 5 ms-1 之间。只有泥石流阶段越过了萨博大坝的内肩。一个波瓣占据了研究区域的上半部分，其沉积被认为与沟壑的突然扩大有关，而下半部分则与淤地坝形成的基准面相连。