Assessment of a numerical model to reproduce event-scale erosion and deposition distributions in a braided river

Williams, R.D. , Measures, R., Hicks, M. and Brasington, J. (2016) Assessment of a numerical model to reproduce event-scale erosion and deposition distributions in a braided river. Water Resources Research, 52(8), pp. 6621-6642. (doi: 10.1002/2015WR018491)

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Abstract

Numerical morphological modelling of braided rivers, using a physics-based approach, is increasingly used as a technique to explore controls on river pattern and, from an applied perspective, to simulate the impact of channel modifications. This paper assesses a depth averaged non-uniform sediment model (Delft3D) to predict the morphodynamics of a 2.5 km long reach of the braided Rees River, New Zealand, during a single high-flow event. Evaluation of model performance primarily focused upon using high-resolution Digital Elevation Models (DEMs) of Difference, derived from a fusion of terrestrial laser scanning and optical empirical bathymetric mapping, to compare observed and predicted patterns of erosion and deposition, and reach scale sediment budgets. For the calibrated model, this was supplemented with planform metrics (e.g. braiding intensity). Extensive sensitivity analysis of model functions and parameters was executed, including consideration of numerical scheme for bedload component calculations, hydraulics, bed composition, bedload transport and bed slope effects, bank erosion and frequency of calculations. Total predicted volumes of erosion and deposition corresponded well to those observed. The difference between predicted and observed volumes of erosion was less than the factor of two that characterises the accuracy of the Gaeuman et al. bedload transport formula. Grain size distributions were best represented using two-phi intervals. For unsteady flows, results were sensitive to the morphological time scale factor. The approach of comparing observed and predicted morphological sediment budgets shows the value of using natural experiment datasets for model testing. Sensitivity results are transferable to guide Delft3D applications to other rivers.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Williams, Dr Richard
Authors: Williams, R.D., Measures, R., Hicks, M., and Brasington, J.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Water Resources Research
Publisher:American Geophysical Union
ISSN:0043-1397
ISSN (Online):1944-7973
Published Online:20 June 2016
Copyright Holders:Copyright © 2016 The Authors
First Published:First published in Water Resources Research 52(8):6621-6642
Publisher Policy:Reproduced under a Creative Commons License

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