A two-dimensional numerical model was developed to simulate relatively wide, shallow rivers with an erodible bed and banks composed of well-sorted, sandy materials. A moving boundary-fitted coordinate system was used to calculate water flow, bed change, and bank erosion. The cubic interpolated pseudoparticle method was used to calculate flow, which introduced little numerical diffusion. The sediment-transport equation for the streamline and transverse transport was used to estimate bed and bank evolution over time, while considering the secondary flow. Bank erosion was simulated when the gradient in the cross-sectional direction of the banks was steeper than the submerged angle of repose because of bed erosion near the banks. The numerical model reproduced the features of central bars well, such as bar growth, channel widening due to divergence of the flow around the bars, scour holes at the lee of the bars, and the increase of bar size with time. These features were in accordance with the observations fo...

This study examined the morphological behavior of a channel with vegetation by means of both laboratory experiments and a numerical simulation. Two sets of laboratory experiments were carried out to elucidate the influence of riparian vegetation on braided rivers with erodible banks. One was for a braided river without vegetation from an initially straight channel and the other was for a river with vegetation, where the density of alfalfa was controlled to form vegetated channels. A numerical simulation was also conducted to investigate the effects of vegetation on the channel morphology considering bank erosion, and the results were compared with those of the laboratory experiments. The experimental results showed that the water depth increased and the width decreased with vegetation. The mainstream was also developed to a high meandering channel and then bifurcated to two channels due to vegetation downstream. This was due mainly to a change of flow direction by the blockade of secondary channels near the vegetated zones and backwater effects near the vegetated banks. As the vegetation density increased, the correlation coefficient of cross-sectional data increased in both the numerical and experimental results, and good agreement between the numerical and experimental results was obtained. This indicates that the channel mobility decreased with increasing vegetation density. The numerical model generated the features of the bed topography obtained in experimental channels

Results from computational morphodynamics modeling of coupled flow–bed–sediment systems are described for 10 applications as a review of recent advances in the field. Each of these applications is drawn from solvers included in the public‐domain International River Interface Cooperative (iRIC) software package. For mesoscale river features such as bars, predictions of alternate and higher mode river bars are shown for flows with equilibrium sediment supply and for a single case of oversupplied sediment. For microscale bed features such as bedforms, computational results are shown for the development and evolution of two‐dimensional bedforms using a simple closure‐based two‐dimensional model, for two‐ and three‐dimensional ripples and dunes using a three‐dimensional large‐eddy simulation flow model coupled to a physics‐based particle transport model, and for the development of bed streaks using a three‐dimensional unsteady Reynolds‐averaged Navier–Stokes solver with a simple sediment‐transport treatment. Finally, macroscale or channel evolution treatments are used to examine the temporal development of meandering channels, a failure model for cantilevered banks, the effect of bank vegetation on channel width, the development of channel networks in tidal systems, and the evolution of bedrock channels. In all examples, computational morphodynamics results from iRIC solvers compare well to observations of natural bed morphology. For each of the three scales investigated here, brief suggestions for future work and potential research directions are offered. © 2019 The Authors Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd

In this study, we conducted multiple physical experiments to estimate the efficacy and spatial pattern of erosion by abrading sediment moving through a simple U‐shaped channel bend with erodible bed and banks. The experiments showed that in the bend, lateral abrasion followed a monotonically increasing linear relationship with sediment feed rate. However, vertical incision had a more complex relation with the sediment feed rate, with an initial increase in abrasion as the feed rate increased followed by a decrease in abrasion of the bed as cover effects became dominant at higher feed rates. Bank erosion was large in places where the width and the lateral slope of the point bar were relatively large. On the other hand, in places where the width of the point bar was smaller, the bedrock bed was eroded primarily along the boundary of the point bar, resulting in a bedrock bench near the outer bank.

This study examined the behavior of alternate bars in a channel with erodible banks by considering the effect of vegetation on bank strength. A two-dimensional model was developed to simulate the development of an initially straight channel with erodible banks composed of well-sorted sandy material. A moving boundary-fitted coordinate system was used to describe a natural shaped boundary. The flow field was calculated using the CIP method. To simulate bank erosion, it was assumed that banks eroded when the gradient in the cross-sectional direction of the banks was steeper than the submerged angle of repose, due to the bed erosion near the banks. The lateral rate of channel expansion, bar migration speed, and wavelength were studied numerically when the channel remained nearly straight. The bars migrated more slowly as the aspect ratio increased. The bars in a channel with strong banks migrated rapidly, and the dimensionless bar, expressed as bar height to water depth ratio, was higher than that of a channel with weak banks. Our numerical experiments showed that the behavior of bars differed according to bank strength under the same hydraulic conditions.