Flash floods can cause great geomorphological changes in ephemeral fluvial systems and result in particularly severe damages for the unprepared population exposed to it. The flash flood in the Storelva river in Utvik (western Norway) on 24 July 2017 was witnessed and documented. This study assessed the causes and effects of the 2017 flood and provides valuable information for the calibration and validation of future modelling studies. The flooded area at peak discharge, maximum wetted and dry areas during the entire event, critical points and main flow paths were reconstructed using on-site and post-event (i) visual documentation, such as photographs and videos, and (ii) aerial surveying, such as orthophotographs and laser scanning, of the lowermost reach. The steep longitudinal slope together with the loose material forming the valley and riverbed contributed to a large amount of sediment transport during this extreme event. Steep rivers such as the Storelva river have very short response times to extreme hydrologic conditions, which calls for exhaustive monitoring and data collection in case of future events, as well as modelling tools that can emulate the hydro-morphodynamics observed during events such as the 2017 flash flood.

中文翻译：

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陡峭河流的故事：2017 年 7 月 24 日挪威西部山洪暴发的原因和影响

山洪暴发会在短暂的河流系统中引起巨大的地貌变化，并对暴露在其中的毫无准备的人口造成特别严重的损害。目击并记录了 2017 年 7 月 24 日乌特维克（挪威西部）斯托尔瓦河的山洪暴发。这项研究评估了 2017 年洪水的原因和影响，并为未来建模研究的校准和验证提供了有价值的信息。使用现场和事后 (i) 视觉文件，如照片和视频，以及 (ii) 航拍重建了洪峰流量淹没区、整个事件期间最大干湿区、临界点和主要水流路径最底层的测量，例如正射影像和激光扫描。在这次极端事件中，陡峭的纵向坡度以及形成山谷和河床的松散物质促成了大量的泥沙输送。陡峭的河流（如斯托尔瓦河）对极端水文条件的响应时间非常短，这需要在未来发生事件时进行详尽的监测和数据收集，以及可以模拟在 2017 年等事件期间观察到的流体形态动力学的建模工具暴洪。