Biomorphodynamics of alternate bars in a channelized, regulated river: An integrated historical and modelling analysis. Issue 9 (7th March 2018)

• Record Type: Journal Article
• Authors: Serlet, Alyssa J.; Gurnell, Angela M.; Zolezzi, Guido; Wharton, Geraldene; Belleudy, Philippe; Jourdain, Camille
• Is Part Of: Earth surface processes and landforms. Volume 43:Issue 9(2018)
• Page Start: 1739
• Page End: 1756
• Publication Date: 2018-03-07
• Subjects: channelization -- alternate bars -- biomorphodynamics -- bar theory -- vegetation encroachment -- flow regulation -- sediment mining; Geomorphology -- Periodicals; 551.4
• DOI: 10.1002/esp.4349
• Languages: English
• ISSNs: 0197-9337

Abstract

Abstract: The development of alternate bars in channelized rivers can be explained theoretically as an instability of the riverbed when the active channel width to depth ratio exceeds a threshold. However, the development of a vegetation cover on the alternate bars of some channelized rivers and its interactions with bar morphology have not been investigated in detail. Our study focused on the co‐evolution of alternate bars and vegetation along a 33 km reach of the Isère River, France. We analysed historical information to investigate the development of alternate bars and their colonization by vegetation within a straightened, embanked river subject to flow regulation, sediment mining, and vegetation management. Over an 80 year period, bar density decreased, bar length increased, and bar mobility slowed. Vegetation encroachment across bar surfaces accompanied these temporal changes and, once established, vegetation cover persisted, shifting the overall system from an unvegetated to a vegetated dynamic equilibrium state. The unvegetated morphodynamics of the impressively regular sequence of alternate bars that developed in the Isère following channelization is consistent with previous theoretical morphodynamic work. However, the apparent triggering dynamics of vegetation colonization needs to be investigated, based on complex biophysical instability processes. If instability related to vegetation colonization is confirmed, further work needs to focus on the relevance of initial conditions for this instability, and on related feedback effects such as how the morphodynamics of bare‐sediment alternate bars may have affected vegetation development and, in turn, how vegetation has created a new dynamic equilibrium state. Copyright © 2018 John Wiley & Sons, Ltd. Abstract : Key Findings Detailed historical and modelling analysis in a 33 km reach of Isère River over 80 years Trajectories of channel planform change in morphology and vegetation and linked to potential causes Shift from unvegetated migrating alternate bars to vegetated steady bars