UAV-based evaluation of morphological changes induced by extreme rainfall events in meandering rivers


Akay S. S. , Özcan O., Balık Şanlı F. , Görüm T., Şen Ö. L. , Bayram B.

Plos One, vol.15, no.11, pp.1-29, 2020 (Journal Indexed in SCI Expanded)

  • Publication Type: Article / Article
  • Volume: 15 Issue: 11
  • Publication Date: 2020
  • Title of Journal : Plos One
  • Page Numbers: pp.1-29

Abstract

Morphological changes, caused by the erosion and deposition processes due to water discharge

and sediment flux occur, in the banks along the river channels and in the estuaries.

Flow rate is one of the most important factors that can change river morphology. The geometric

shapes of the meanders and the river flow parameters are crucial components in the areas

where erosion or deposition occurs in the meandering rivers. Extreme precipitation triggers

erosion on the slopes, which causes significant morphological changes in large areas during

and after the event. The flow and sediment amount observed in a river basin with extreme precipitation

increases and exceeds the long-term average value. Hereby, erosion severity can

be determined by performing spatial analyses on remotely sensed imagery acquired before

and after an extreme precipitation event. Changes of erosion and deposition along the river

channels and overspill channels can be examined by comparing multi-temporal Unmanned

Aerial Vehicle (UAV) based Digital Surface Model (DSM) data. In this study, morphological

changes in the Bu¨yu¨k Menderes River located in the western Turkey, were monitored with

pre-flood (June 2018), during flood (January 2019), and post-flood (September 2019) UAV

surveys, and the spatial and volumetric changes of eroded/deposited sediment were quantified.

For this purpose, the DSAS (Digital Shoreline Analysis System) method and the DEM of

Difference (DoD) method were used to determine the changes on the riverbank and to compare

the periodic volumetric morphological changes. Hereby, Structure from Motion (SfM)

photogrammetry technique was exploited to a low-cost UAV derived imagery to achieve riverbank,

areal and volumetric changes following the extreme rainfall events extracted from the

time series of Tropical Rainfall Measuring Mission (TRMM) satellite data. The change analyses

were performed to figure out the periodic morphodynamic variations and the impact of the

flood on the selected meandering structures. In conclusion, although the river water level

increased by 0.4–5.9 meters with the flood occurred in January 2019, the sediment deposition

areas reformed after the flood event, as the water level decreased. Two-year monitoring

revealed that the sinuosity index (SI) values changed during the flood approached the preflood

values over time. Moreover, it was observed that the amount of the deposited sediments

in September 2019 approached that of June 2018.