Experiment and computation of morphological response to a vegetation patch in open-channel flows with erodible banks

Abstract

This study describes morphological changes with a vegetation patch using both laboratory experiments and numerical simulations. Four experimental cases are carried out with two patch densities and without a patch. The patch is constructed with emergent cylinders of 5 mm in a staggered array and it is located at the mid-channel. A 2D depth-averaged model is proposed to simulate flow and morphological change with vegetation. For non-vegetation cases, channel widening occurs with bank erosion, whereas the added patch in open channels causes significant bank erosion opposite and downstream of the patch, and failed sediment is deposited downstream of the patch. Local scour is observed near the lateral edge of the patch, and its depth increases with increasing patch density. Small-scale scour occurs in the immediate vicinity of cylinders within the patch due to increased turbulence. Averaged channel width increases with increasing discharge, channel slope and the patch density. Comparisons with experimental data show the numerical model predicts spatial patterns of erosion and deposition as well as lateral bank erosion caused by the vegetation patch reasonably well, so could be a useful tool for the future design and assessment of river restoration works involving vegetation.