Crevasse splay morphodynamics near a non-vegetated, ephemeral river terminus

Crevasse splay morphodynamics near a non-vegetated, ephemeral river terminus: Insights from process-based modelling

Li, Jiaguang (China University of Geosciences; Key Laboratory of Theory and Technology of Petroleum Exploration and Development in Hubei Province)
van der Vegt, Helena (Deltares)
Storms, J.E.A. (TU Delft Applied Geology)
Tooth, Stephen (Aberystwyth University)

2023

Crevasse splays generate subtle local relief and contribute to fluvial basin sedimentary filling but controls on splay development along dryland rivers remain poorly understood owing to limited field, laboratory, and numerical modelling studies. Based on previously-acquired field data and new remote sensing observations of splay morphology and sedimentology (e.g. slope, width, length, grain size) and flooding characteristics (e.g. discharge, water depth and extent) near the terminus of the non-vegetated, ephemeral Río Colorado on the southeastern margin of Salar de Uyuni, Bolivia, we undertake process-based modelling using Delft3D to isolate the role of hydrological controls on crevasse splay morphodynamics. Holding the potential sediment supply constant, we focus on the role of discharge (outflow from trunk channel to crevasse channel during rising stage), floodplain water levels, and backflow (reflux to the trunk channel during falling stage). Using nine different model runs, each with 10 simulated flood cycles, we show that the processes associated with these hydrological controls result in various outcomes, from short crevasse splay channels that may bifurcate and develop depositional bars to longer splays with one primary channel that mainly transfers sediment across the floodplain. Results reveal that increases in flood discharge lead to more rapid splay sedimentation and stabilization of a single crevasse channel. Increases in floodplain water level lead to shorter but wider splays and facilitate the formation of multiple stable crevasse channels. High floodplain water levels probably restrict splay length owing to deceleration of outflow as floodplain water is encountered, but separate crevasse channels may form downstream as backflow breaches the trunk channel levee during falling stage. These findings support and extend previous observations from the Río Colorado and other dryland rivers worldwide. Future modelling studies that consider a wider range of hydrological, sedimentological, and floodplain topographic conditions will help develop more comprehensive numerical models of splay development. A combination of insights from field, laboratory experimentation, remote sensing and modelling will improve knowledge of the cascades of channel-floodplain dynamics that characterise many dryland endorheic basins.

Backflow
Channel-floodplain morphodynamics
Crevasse splay
Discharge
Dryland river

http://resolver.tudelft.nl/uuid:49782df5-5c10-481e-9fdb-53e88c187daa

https://doi.org/10.1016/j.jhydrol.2023.129088

2023-07-14

0022-1694

Journal of Hydrology, 617

Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.

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© 2023 Jiaguang Li, Helena van der Vegt, J.E.A. Storms, Stephen Tooth