Spatiotemporal dynamics and present perception of gravel bars in natural and regulated environments

Gravel bars represent unique habitats in gravel bed rivers. These formations are endangered by river management affecting the channel natural behavior and flow conditions. This could result in the initial loss of gravel bar dynamic, leading to overgrowth of vegetation and degradation. The main aim of this study is to analyze spatiotemporal changes and public perception of gravel bars and their vegetation in regulated and natural river environments. We combine sociological and geomorphological research to better understand the current state of gravel bar dynamics and the public view of them, which is beneficial information for any future management of gravel bar habitat. We examined the 77 km-long fluvial corridor of the Odra River (Czechia) between 1937 and 2020 using aerial images for mapping gravel bars and assessment of morphodynamics. For the public perception, we conducted an online survey with photosimulations of different gravel bar environments and states of vegetation. Gravel bars were most frequent in natural reaches associated with intensive morphodynamics in wide channel segments and meanders of high amplitude. The length of the regulated river channel increased during the studied period and gravel bars were reduced. In 2000-2020, the trend was toward overly vegetated and stable gravel bars. The public perception data indicated a high preference for fully vegetated gravel bars in terms of naturalness, aesthetics, and vegetation cover in both natural and regulated environments. This emphasizes a misleading public view regarding unvegetated gravel bars as an unpopular feature that should be vegetated or removed for it to be perceived as natural or aesthetic. These findings should encourage better gravel bar management and change in the public's negative perception of unvegetated gravel bars.