Author(s): Mahmoud Omer Mahmoud Awadallah; Davide Vanzo; David Florian Vetsch; Robert Michael Boes; Francesco Caponi

Linked Author(s): Davide Vanzo, Francesco Caponi, David Vetsch

Keywords: Channel-network; Surface-water; Connectivity; Hydropeaking regime; 2D hydrodynamic modelling

Abstract: Braided river reaches in Alpine regions are often subject to (near) natural flood events that actively reshape their morphology. These changes can reconfigure channel networks and, in turn, directly influence key biogeomorphic characteristics, such as hydraulic variables, inundation frequency, and residence time, which are relevant to several aquatic and riparian species. Although some studies have examined how these characteristics vary with discharge-dependent surface-water connectivity, applications to highly variable, evolving channel networks remain scarce. Using 2-D hydrodynamic modelling and morphological analysis of an Alpine, braided reach in Switzerland, we link changes in riverbed topography and channel networks to inundation frequencies across three topographic surveys (Jan -20, Mar-23, and Feb-25). Our results show that although the overall riverbed morphology returned back in Feb-25 to be as incised as in Jan-20, the surface water connectivity did not. In Feb-25, the channel network transitioned to a single-thread-dominated network, with the threshold discharge required to activate secondary channels rising from about 2 m3/s to 25 m3/s, compared to ~8 m3/s in Jan -20. When comparing the inundation frequency in two contrasting flow regimes (hydropeaking-dominated and flood-dominated), this resulted in a decrease of about 50% of floodplain areas infrequently inundated (maximum total duration of 4 days per month) and an overall decrease in total wetted areas. This change may have a direct impact on the spatial distribution of fluvial habitats and their persistence over time. This evaluation framework can support a more holistic ecological assessment, a step towards promoting resilient riverine environments.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.161

Year: 2026