PosterPDF Available

The role of soft data to understand flood dynamics in an ephemeral mountain river (poster)

Authors:

Abstract

Watch recorded presentation here: https://youtu.be/AlfzGh1RrPo The maximum inundation area, critical locations, and flow paths in the wetted area of a flash flood in a steep river were reconstructed using remote sensing combined with post-event field investigation and soft data. The soft data contrasted with control points and used to assemble the flood extension included newspaper articles, photographs and videos taken during the flood, and witness testimonies. The soft data provided insights on the flood dynamics that were not available with remote sensing and post-event field observations alone. The outcome of this investigation could be used to calibrate and/or validate numerical models, as well as to improve the accuracy of flood early warning systems. This poster was used to present the extended abstract of the same title.
3rd IAHR Young Professionals Congress (29 November 1 December 2022)
Abstract The maximum inundation area, critical locations, and flow paths in the wetted area of a flash flood in a steep river were reconstructed using remote sensing combined with
post-event field investigation and soft data. The soft data contrasted with control points and used to assemble the flood extension included newspaper articles, photographs and videos
taken during the flood, and witness testimonies. The soft data provided insights on the flood dynamics that were not available with remote sensing and post-event field observations
alone. The outcome of this investigation could be used to calibrate and/or validate numerical models, as well as to improve the accuracy of flood early warning systems.
Keywords: field observations, flash floods, remote sensing, soft data, steep rivers.
Methods Conclusions
The role of soft data to understand flood dynamics
in an ephemeral mountain river
Adina Moraru YP1*
1Norwegian University of Science and Technology (NTNU), Trondheim, Norway *Correspondence YP: adina.moraru@ntnu.no
References
Bruland, O. (2020). How extreme can unit discharge become in
steep Norwegian catchments? Hydrology Research,51(2), 290
307.https://doi.org/10.2166/nh.2020.055
Moraru, A., Pavlíček, M., Bruland, O. and Rüther, N. (2021). The
story of a steep river: causes and effects of the flash flood on 24
July 2017 in western Norway. Water (Switzerland),13(12), 1688.
https://doi.org/10.3390/w13121688
The combined use of soft data obtained during the 2017
flash flood with aerial surveying provided information on:
critical locations,
flow paths and
maximum inundation area.
Most trace of this event disappeared with the quick
restoration work, making these findings important to
understand the flood dynamics in an ephemeral mountain
river in a Nordic region. The dataset presented in this
study can be used to calibrate and validate numerical
models, and to improve the accuracy of flood early
warning systems.
Results
Figure 1: Workflow followed to obtain the flooded area
at Qpeak (a), critical locations (b), flow paths (c) and
maximum inundation area (d) during the 2017 flash
flood (modified after Moraru et al., 2021). Extended abstract More results WoWW project
Figure 2: Maximum inundation area (blue area), critical
locations (CL14, white circles) and the flow paths
(purple lines) during the 2017 flash flood (modified
after Moraru et al., 2021).
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Article
Full-text available
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.
Article
Full-text available
This study presents results of observations and analysis of the flood event in Utvik on 24 July 2017. Observations during and after the event, hydraulic simulations and hydrological modelling along with meteorological observations, are used to estimate the peak discharge of the flood. Although both observations and hydraulic simulations of flood extremes are uncertain, even the most conservative assumptions lead to discharge estimates higher than 160 m3/s at culmination of the flood from the 25 km2-large catchment. The most extreme assumptions indicate it may have been up to 400 m3/s, but there is also strong evidence for the discharge at culmination being between 200 and 250 m3/s. Observations disclosed that the majority of water came from about 50% of the catchment area giving unit discharges up to 18 to 22 m3/s,km2. If the entire catchment contributed it would be from 9 to 11 m3/s,km2. This is significantly higher than previously documented unit discharges in Norway and in the range of the highest observed peak unit discharges in southern Europe. The precipitation causing this event is estimated to be three to five times higher than a 200-year precipitation taken from the intensity–duration–frequency curves for the studied region.