Hydraulic validation of two-dimensional simulations of braided river flow with spatially continuous aDcp data

Williams, R.D. , Brasington, J., Hicks, M., Measures, R., Rennie, C.D. and Vericat, D. (2013) Hydraulic validation of two-dimensional simulations of braided river flow with spatially continuous aDcp data. Water Resources Research, 49(9), pp. 5183-5205. (doi:10.1002/wrcr.20391)

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Abstract

Gravel-bed braided rivers are characterized by shallow, branching flow across low relief, complex, and mobile bed topography. These conditions present a major challenge for the application of higher dimensional hydraulic models, the predictions of which are nevertheless vital to inform flood risk and ecosystem management. This paper demonstrates how high-resolution topographic survey and hydraulic monitoring at a density commensurate with model discretization can be used to advance hydrodynamic simulations in braided rivers. Specifically, we detail applications of the shallow water model, Delft3d, to the Rees River, New Zealand, at two nested scales: a 300 m braid bar unit and a 2.5 km reach. In each case, terrestrial laser scanning was used to parameterize the topographic boundary condition at hitherto unprecedented resolution and accuracy. Dense observations of depth and velocity acquired from a mobile acoustic Doppler current profiler (aDcp), along with low-altitude aerial photography, were then used to create a data-rich framework for model calibration and testing at a range of discharges. Calibration focused on the estimation of spatially uniform roughness and horizontal eddy viscosity, νH, through comparison of predictions with distributed hydraulic data. Results revealed strong sensitivity to νH, which influenced cross-channel velocity and localization of high shear zones. The high-resolution bed topography partially accounts for form resistance, and the recovered roughness was found to scale by 1.2–1.4 D84 grain diameter. Model performance was good for a range of flows, with minimal bias and tight error distributions, suggesting that acceptable predictions can be achieved with spatially uniform roughness and νH.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Williams, Dr Richard
Authors: Williams, R.D., Brasington, J., Hicks, M., Measures, R., Rennie, C.D., and Vericat, D.
Subjects:G Geography. Anthropology. Recreation > GB Physical geography
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
Copyright Holders:Copyright © 2013 American Geophysical Union
First Published:First published in Water Resources Research 49(9):5183-5205
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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