Insights from long-term variations in gravel riverbed topography as an indicator of vegetation–morphology interactions

Abstract

Flooding shapes the fluvial landforms by interacting with the development of riparian vegetation. However, the quantitative evaluation of the effects of flooding on fluvial landscapes often relies on snapshot physical parameters regarding hydrological processes, as typified by shear stress on the bed surface. Flooding events over time regulate riparian vegetation, and introducing a long-term perspective into river environmental assessment could complement understanding the vegetation-morphology interactions. In this study, we estimated the long-term variations in channel topography (geomorphological variations) of a gravel riverbed of the Chikuma River. We used cross-sectional profiles of the river channel from 1959 to 2010 as an indicator of vegetation-morphology interactions and examined the effects of geomorphological variations on the fluvial landscape. Our results show that boreal and herbaceous vegetated areas had significant smaller geomorphological variations than those with active channels and gravel bars in the river. Temporal changes in the elevation of the river channel reduced after riparian vegetation was established and riverbed stabilisation could enable riparian forests to develop. We, therefore, identify geomorphological variations as an explanatory factor for fluvial landforms. The index could support river management with a long-term view of channel evolution with vegetation-morphology interaction.