Numerical Modelling of Braided Rivers with Structure‐from‐Motion‐Derived Terrain Models

Abstract

The development of three‐dimensional reconstructions of channel morphology has historically been limited by the high costs of geospatial data collection and software modelling. Advances in image processing, sensor technology and portable remote‐sensing platforms, however, now offer the opportunity to derive survey quality terrain models at significantly reduced cost and without traditional deployment and logistical constraints. There is a pressing need to establish whether new geospatial technologies such as structure‐from‐motion photogrammetry can be used to deliver topographic data products that are suitable for higher‐dimensional hydrodynamic modelling. To address this question, we evaluate the results of simulations using Delft3D that were designed to model distributed, depth‐averaged flows in a wide, shallow, gravel‐bed braided river. The topography for these simulations was derived from digital elevation models (DEMs) generated using structure‐from‐motion and optical bathymetric mapping of two linked reaches of the Ahuriri River, New Zealand. The DEM quality achieved vertical surface errors of 0.10 m in non‐vegetated areas and 0.20 m in inundated areas. Simulations with 1.5 m and 2.5 m resolution grids for low‐flow, medium‐flow and high‐flow conditions were calibrated and tested against field real‐time kinematic‐global navigation satellite system observations. Results revealed that modelled depth errors were comparable to the DEM uncertainty, while simulated and observed inundation patterns achieve a maximum of 81% agreement. Given the complexity of the braided network and shallow flow depths, these simulations provide a powerful demonstration of the suitability of these terrain models for hydrodynamic applications. Copyright © 2015 John Wiley & Sons, Ltd.

Hydrodynamic Modeling Improves Green River Reconnection with Floodplain Wetlands for Endangered Fish Species Recovery

“…Javernick et al. () showed similar results using Delft3D in 2D mode for braided river floodplains, where simulated and observed inundation patterns achieved a maximum of 81% agreement, and modeled depth errors were comparable to DEM uncertainty.…”

“…The last two issues could be important in these floodplain wetland environments where interactions with vegetation and groundwater can be difficult to model (Javernick et al. ).…”

“…Javernick et al. () applied Delft3D (in 2D mode) in combination with structure from motion‐derived terrain models to simulate flood interactions with floodplain invasive vegetation in a wide, shallow, gravel‐bed braided river in New Zealand. These studies demonstrated the utility of 2D hydrodynamic modeling to help evaluate river–floodplain/wetland flows, connectivity, and related ecological processes.…”

Linking geomorphic change due to floods to spatial hydraulic habitat dynamics

“…To reliably characterize such diversity in dynamic fluvial systems, objective, accurate, and efficient methods are needed (Woodget, Visser, Maddock, & Carbonneau, 2016). In particular, the combined approach of digital photogrammetry techniques and small unmanned aerial vehicle (UAV)-based image capture has emerged as a valuable way to measure river channel topography in three dimensions (Fonstad, Dietrich, Courville, Jensen, & Carbonneau, 2013;Javernick, Brasington, & Caruso, 2014;Javernick, Hicks, Measures, Caruso, & Brasington, 2015;Vericat, Brasington, Wheaton, & Cowie, 2008;Woodget, Carbonneau, Visser, & Maddock, 2014). In particular, the combined approach of digital photogrammetry techniques and small unmanned aerial vehicle (UAV)-based image capture has emerged as a valuable way to measure river channel topography in three dimensions (Fonstad, Dietrich, Courville, Jensen, & Carbonneau, 2013;Javernick, Brasington, & Caruso, 2014;Javernick, Hicks, Measures, Caruso, & Brasington, 2015;Vericat, Brasington, Wheaton, & Cowie, 2008;Woodget, Carbonneau, Visser, & Maddock, 2014).…”

Metric-Resolution 2D River Modeling at the Macroscale: Computational Methods and Applications in a Braided River

“…However, a number of researchers have found that a metric resolution is needed to reasonably approximate hydraulic habitat, i.e., local depth and velocity, which is relevant to river ecology and morphology (Crowder and Diplas, 2000;Cook and Merwade, 2009;Clifford et al, 2010;Williams et al, 2013;Abu-Aly et al, 2014). Furthermore, with the aid of analytical models for the vertical velocity distribution including a characterization of bed roughness, metric-resolution 2D models can reconstruct a 3D characterization of flow for a wide range of applications at far less computational expense than 3D models based on the Navier-Stokes equations (Begnudelli et al, 2010;Abu-Aly et al, 2014;Wyrick et al, 2014), although there are many examples of 3D flow phenomena that demand 3D models for an accurate description such as horseshoe vortices around bridge piers and similarly complex turbulent velocity fluctuations occurring around boulders, large bed forms, and other types of flow obstructions (Wu, 2007;Javernick et al, 2015).…”