Impacts of an extreme flood event on the riparian vegetation of a monsoonal cobble-bed stream in southern Korea: A multiscale fluvial biogeomorphic framework

Abstract

© 2022 John Wiley & Sons Ltd.With climate change increasing the magnitude and frequency of extreme precipitation events, there is a growing demand for investigations on the impacts of extreme flooding on the hydrological characteristics and vegetation of rivers, particularly in monsoonal areas. In this study, we examined multiscale relationships between hydrology, vegetation, and geomorphology after a record-breaking flood event along the Seomjin River of South Korea in the summer of 2020. We conducted numerical modeling at the broad scale to identify the flow characteristics (e.g., depth and shear stress) of the flood event. A field survey was performed to investigate the impact of the flood on individual plants at the fine scale. The results showed widespread devastation of all vegetation types, from reed and willow communities to large, late-successional trees taller than 10 m, which typically survive under ordinary flooding conditions. A higher threshold of shear stress was estimated for these trees (124 N m−2) than for willow (120 N m−2) and reed plants (26 N m−2), indicating that a greater level of stress is required to cause vegetation damage as ecological succession progresses. In the presence of vegetation, the average water depth increased by 9%–23% compared to the absence of vegetation. Many rivers in northeast Asia have undergone substantial vegetation expansion and succession due to the infrequency of extreme flood events. Our findings indicate that dense communities of large plants in these systems can raise the maximum water levels of flood events, thereby increasing the future flood risk to surrounding areas utilized for agriculture, transportation, industry, and housing.