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Applied Sciences
Volume 16
Issue 3
10.3390/app16031456
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Article

UAS-Based Photogrammetric Assessment of Geomorphological Changes Along the Lilas River (Evia Island, Central Greece) After the August 2020 Flood

by
Nafsika Ioanna Spyrou
1,
Spyridon Mavroulis
1,*,
Emmanuel Vassilakis
2,
Emmanouil Andreadakis
1,
Michalis Diakakis
2,
Panagiotis Stamatakopoulos
1,
Evelina Kotsi
1,
Aliki Konsolaki
2,
Issaak Parcharidis
3,* and
Efthymios Lekkas
1
1
Department of Dynamic, Tectonic, Applied Geology, Faculty of Geology and Geoenvironment, School of Sciences, National and Kapodistrian University of Athens, 15784 Athens, Greece
2
Department of Geography and Climatology, Faculty of Geology and Geoenvironment, School of Sciences, National and Kapodistrian University of Athens, 15784 Athens, Greece
3
Department of Geography, Harokopio University, 17676 Kallithea, Greece
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2026, 16(3), 1456; https://doi.org/10.3390/app16031456 (registering DOI)
Submission received: 23 December 2025 / Revised: 25 January 2026 / Accepted: 28 January 2026 / Published: 31 January 2026
Versions Notes

Abstract

Geomorphological change is a fundamental consequence of high-magnitude flood events, as extreme hydraulic forcing can rapidly reshape river channels, redistribute sediment, and alter floodplain connectivity. This study applies multi-temporal UAS-based Structure-from-Motion (SfM) photogrammetry to quantify flood-induced geomorphological changes along two representative reaches of the Lilas River (Evia Island, Central Greece) affected by the extreme August 2020 flash flood. High-resolution aerial surveys were conducted prior to the event (June 2018) and shortly after the flood (September 2020), producing Digital Surface Models (DSMs) and orthomosaics with a ground sampling distance of ~2.5 cm. Differential DSM analysis reveals pronounced spatial heterogeneity in erosion and deposition, with net erosional lowering locally exceeding 7 m and depositional aggradation reaching up to ~5 m after accounting for vegetation effects. Channel widening was the dominant response, with cross-sectional widths increasing by a factor of three to nine at selected locations, driven primarily by lateral bank erosion. The results highlight the strong interaction between extreme hydrological forcing, loose alluvial sediments, vegetation removal, and human interventions such as roads and engineered terraces. The study demonstrates how repeatable UAS–SfM workflows can provide quantitative evidence to support post-flood assessment, guide infrastructure adaptation, and inform river restoration and flood risk management in Mediterranean catchments prone to extreme events.
Keywords: geomorphological changes; flash flood; flood impact; photogrammetry; Structure-from-Motion; high-resolution mapping; UAS; UAV; GIS geomorphological changes; flash flood; flood impact; photogrammetry; Structure-from-Motion; high-resolution mapping; UAS; UAV; GIS

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MDPI and ACS Style

Spyrou, N.I.; Mavroulis, S.; Vassilakis, E.; Andreadakis, E.; Diakakis, M.; Stamatakopoulos, P.; Kotsi, E.; Konsolaki, A.; Parcharidis, I.; Lekkas, E. UAS-Based Photogrammetric Assessment of Geomorphological Changes Along the Lilas River (Evia Island, Central Greece) After the August 2020 Flood. Appl. Sci. 2026, 16, 1456. https://doi.org/10.3390/app16031456

AMA Style

Spyrou NI, Mavroulis S, Vassilakis E, Andreadakis E, Diakakis M, Stamatakopoulos P, Kotsi E, Konsolaki A, Parcharidis I, Lekkas E. UAS-Based Photogrammetric Assessment of Geomorphological Changes Along the Lilas River (Evia Island, Central Greece) After the August 2020 Flood. Applied Sciences. 2026; 16(3):1456. https://doi.org/10.3390/app16031456

Chicago/Turabian Style

Spyrou, Nafsika Ioanna, Spyridon Mavroulis, Emmanuel Vassilakis, Emmanouil Andreadakis, Michalis Diakakis, Panagiotis Stamatakopoulos, Evelina Kotsi, Aliki Konsolaki, Issaak Parcharidis, and Efthymios Lekkas. 2026. "UAS-Based Photogrammetric Assessment of Geomorphological Changes Along the Lilas River (Evia Island, Central Greece) After the August 2020 Flood" Applied Sciences 16, no. 3: 1456. https://doi.org/10.3390/app16031456

APA Style

Spyrou, N. I., Mavroulis, S., Vassilakis, E., Andreadakis, E., Diakakis, M., Stamatakopoulos, P., Kotsi, E., Konsolaki, A., Parcharidis, I., & Lekkas, E. (2026). UAS-Based Photogrammetric Assessment of Geomorphological Changes Along the Lilas River (Evia Island, Central Greece) After the August 2020 Flood. Applied Sciences, 16(3), 1456. https://doi.org/10.3390/app16031456

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