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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 acceptable predictions can be achieved with spatially uniform roughness and νH.
|Journal||Water Resources Research|
|Early online date||28 Jun 2013|
|Publication status||Published - 2013|
- braided river
- hydraulic modeling
- terrestrial laser scanning
- bed roughness
- fluvial remote sensing
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- 1 Finished
Hyperscale Modelling of Braided rivers : Linking Morphology, Sedimentology and Sediment transport
Natural Environment Research Council
01 May 2009 → 30 Apr 2011
Project: Externally funded research