Abstract
The spatial and temporal scale of flash flood occurrence provides limited opportunities for observations and measurements using conventional monitoring networks, turning the focus to event-based, post-disaster studies. Post-flood surveys exploit field evidence to make indirect discharge estimations, aiming to improve our understanding of hydrological response dynamics under extreme meteorological forcing. However, discharge estimations are associated with demanding fieldwork aiming to record in small timeframes delicate data and data prone-to-be-lost and achieve the desired accuracy in measurements to minimize various uncertainties of the process. In this work, we explore the potential of unmanned aerial systems (UAS) technology, in combination with the Structure for Motion (SfM) and optical granulometry techniques in peak discharge estimations. We compare the results of the UAS-aided discharge estimations to estimates derived from differential Global Navigation Satellite System (d-GNSS) surveys and hydrologic modelling. The application in the catchment of the Soures torrent in Greece, after a catastrophic flood, shows that the UAS-aided method determined peak discharge with accuracy, providing very similar values compared to the ones estimated by the established traditional approach. The technique proved to be particularly effective, providing flexibility in terms of resources and timing, although there are certain limitations to its applicability, related mostly to the optical granulometry as well as the condition of the channel. The application highlighted important advantages and certain weaknesses of these emerging tools in indirect discharge estimations, which we discuss in detail.
Highlights
Flash floods are one of the most catastrophic natural hazards, inducing a wide range of tangible and intangible effects [1,2], significant economic losses [2,3,4], and a noteworthy number of fatalities [5,6,7,8]
With respect to the energy slope formed by the High water marks (HWMs) at the two reaches differences were found to be minimum between the unmanned aerial systems (UAS)-aided approach and the differential Global Navigation Satellite System (d-GNSS) survey as well (Table 1)
The findings show that a UAS-aided peak discharge estimation is an effective and practicable method able to extract with accuracy the geometric properties of the channel and the geometry of high-water surface
Summary
Flash floods are one of the most catastrophic natural hazards, inducing a wide range of tangible and intangible effects [1,2], significant economic losses [2,3,4], and a noteworthy number of fatalities [5,6,7,8]. Recent findings indicate that flash flood impacts can potentially become more significant in the future as a result of climate change [9]. Flash flood characteristics and spatiotemporal scales of occurrence limit the possibilities for systematic conventional observations [10,11,12]. The peak discharge is a key metric of flash floods and its estimation provides valuable insights into rainfall-runoff relationships and catchments’ hydrological response. Studying discharge is a crucial step to comprehend flood frequency and estimate return period, which are in turn necessary to develop effective flood mitigation procedures and infrastructure
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