Coevolution of bed surface patchiness and channel morphology: 2. Numerical experiments

Journal of Geophysical Research F: Earth Surface
By: , and 

Links

Abstract

In gravel bed rivers, bed topography and the bed surface grain size distribution evolve simultaneously, but it is not clear how feedbacks between topography and grain sorting affect channel morphology. In this, the second of a pair of papers examining interactions between bed topography and bed surface sorting in gravel bed rivers, we use a two-dimensional morphodynamic model to perform numerical experiments designed to explore the coevolution of both free and forced bars and bed surface patches. Model runs were carried out on a computational grid simulating a 200 m long, 2.75 m wide, straight, rectangular channel, with an initially flat bed at a slope of 0.0137. Over five numerical experiments, we varied (a) whether an obstruction was present, (b) whether the sediment was a gravel mixture or a single size, and (c) whether the bed surface grain size feeds back on the hydraulic roughness field. Experiments with channel obstructions developed a train of alternate bars that became stationary and were connected to the obstruction. Freely migrating alternate bars formed in the experiments without channel obstructions. Simulations incorporating roughness feedbacks between the bed surface and flow field produced flatter, broader, and longer bars than simulations using constant roughness or uniform sediment. Our findings suggest that patches are not simply a by-product of bed topography, but they interact with the evolving bed and influence morphologic evolution.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Coevolution of bed surface patchiness and channel morphology: 2. Numerical experiments
Series title Journal of Geophysical Research F: Earth Surface
DOI 10.1002/2014JF003429
Volume 120
Issue 9
Year Published 2015
Language English
Publisher American Geophysical Union
Contributing office(s) National Research Program - Central Branch
Description 16 p.
First page 1708
Last page 1723