Kasprak, A., Brasington, J., Hafen, K., Williams, R. D. and Wheaton, J. M. (2019) Modelling braided river morphodynamics using a particle travel length framework. Earth Surface Dynamics Discussions, 7, pp. 247-274. (doi: 10.5194/esurf-2018-17)
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Abstract
Numerical models that predict channel evolution are an essential tool for investigating processes that occur over timescales which render field observation intractable. The current generation of morphodynamic models, however, either oversimplify the relevant physical processes or, in the case of more physically complete codes based on computational fluid dynamics (CFD), have computational overheads that severely restrict the space–time scope of their application. Here we present a new, open-source, hybrid approach that seeks to reconcile these modelling philosophies. This framework combines steady-state, two-dimensional CFD hydraulics with a rule-based sediment transport algorithm to predict particle mobility and transport paths which are used to route sediment and evolve the bed topography. Data from two contrasting natural braided rivers (Rees, New Zealand, and Feshie, United Kingdom) were used for model verification, incorporating reach-scale quantitative morphological change budgets and volumetric assessment of different braiding mechanisms. The model was able to simulate 8 of the 10 empirically observed braiding mechanisms from the parameterized bed erosion, sediment transport, and deposition. Representation of bank erosion and bar edge trimming necessitated the inclusion of a lateral channel migration algorithm. Comparisons between simulations based on steady effective discharge versus event hydrographs discretized into a series of model runs were found to only marginally increase the predicted volumetric change, with greater deposition offsetting erosion. A decadal-scale simulation indicates that accurate prediction of event-scale scour depth and subsequent deposition present a methodological challenge because the predicted pattern of deposition may never “catch up” to erosion if a simple path-length distribution is employed, thus resulting in channel over-scouring. It may thus be necessary to augment path-length distributions to preferentially deposit material in certain geomorphic units. We anticipate that the model presented here will be used as a modular framework to explore the effect of different process representations, and as a learning tool designed to reveal the relative importance of geomorphic transport processes in rivers at multiple timescales.
| Item Type: | Articles |
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| Additional Information: | This research was supported by a grant from the National Science Foundation (no. 1147942). Rees River field data were acquired during the Natural Environment Research Council project (NE/G005427/1). |
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Williams, Professor Richard |
| Authors: | Kasprak, A., Brasington, J., Hafen, K., Williams, R. D., and Wheaton, J. M. |
| College/School: | College of Science and Engineering > School of Geographical and Earth Sciences |
| Journal Name: | Earth Surface Dynamics Discussions |
| Publisher: | Copemicus Publications |
| ISSN: | 2196-6338 |
| ISSN (Online): | 2196-6338 |
| Published Online: | 25 February 2019 |
| Copyright Holders: | Copyright © 2019 The Authors |
| First Published: | First published in Earth Surface Dynamics Discussions 7: 247-274 |
| Publisher Policy: | Reproduced under a Creative Commons License |
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