Riparian vegetation life stages control the impact of flood sequencing on braided river morphodynamics

Fernandez, Rocio L.; McLelland, Stuart; Parsons, Daniel R.; Bodewes, Bas

Abstract

With riverine flooding set to be more frequent in many parts of the world as a result of climate change, the interactions between fluvial morphodynamics and riparian vegetation may depend in part on the sequence of flood events. This paper describes a laboratory study of the geomorphic adjustment of a braided river to sequences of floods across five different strengths of braidplain vegetation. By using alfalfa as a proxy for braidplain vegetation, the differing plant life stages were used to represent the varying strengths of biogeomorphic feedbacks across the floods. Boundary conditions were constrained by sets of experimental runs with both equilibrium sediment loads and deficit loads. Changes in bed topography were monitored and assessed using a detailed digital elevation model, digital imagery and continuous monitoring of the transported sediment. Results demonstrate that in absence of plant colonization, vegetation placed the rivers in a non-equilibrium condition, in which riparian vegetation encouraged the development of new channels, increased the system channel width and enhanced topographic irregularity, these effects being more noticeable during the low-flow periods. The morphodynamics was found to be less sensitive to variations in flood discharges as the vegetation influence (strength) increased from minimum to maximum, until vegetation began to die back and the impacts of flood sequences became yet again evident. Although the overall sediment transport rate was reduced under full-grown vegetation conditions, the presence of the mature plants across the braid bars resulted in the greatest channel scour depths. Results are considered in light of expected changes in flood frequency with climate and likely morphodynamic responses of river systems as a result.

Citation

Fernandez, R. L., McLelland, S., Parsons, D. R., & Bodewes, B. (2021). Riparian vegetation life stages control the impact of flood sequencing on braided river morphodynamics. Earth surface processes and landforms : the journal of the British Geomorphological Research Group, 46(11), 2315-2329. https://doi.org/10.1002/esp.5177

• Journal Article Type: Article
• Acceptance Date: May 30, 2021
• Online Publication Date: Jun 22, 2021
• Publication Date: Sep 15, 2021
• Deposit Date: Sep 14, 2021
• Publicly Available Date: Jun 23, 2022
• Journal: Earth Surface Processes and Landforms
• Print ISSN: 0197-9337
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 46
• Issue: 11
• Pages: 2315-2329
• DOI: https://doi.org/10.1002/esp.5177
• Keywords: Biogeomorphology; Braided river; Climate change; Flood sequence; Vegetation
• Public URL: https://hull-repository.worktribe.com/output/3827957
• Publisher URL: https://onlinelibrary.wiley.com/doi/full/10.1002/esp.5177
• Additional Information: Raw data were generated at the Total Environment Simulator, and are available at https://doi.org/10.5281/zenodo.4917675. Derived data supporting the findings of this study are available from the corresponding author on request.