Effects of vegetation on the dynamics of river alternate bars: observations from flume experiments.
Abstract
The planform morphology of a river reach is the result of the combined actions of sediment motion (erosion, transport and deposition), hydrological regime, development and growth of vegetation. However, the interactions among these processes are still poorly understood and rarely investigated in laboratory flume experiments. In this work, we focus on the effects of added vegetation on morphological dynamics of alternate bars in a straight channel by means of flume experiments.The aim is evaluate the effect of rigid vegetation on the main characteristics of alternate bars (i.e. celerity, height, maximum scour and deposition). We performed flume experiments reproducing hydraulic conditions that are typical of gravel bed rivers, in terms of water depth, bed slope and bed load; these conditions led to the formation of freely migrating alternate bars. We then employed rigid vegetation that was deployed on the reproduced highest areas of bar deposit according to field observations. Various vegetation scenarios, in terms of density and spatial arrangement, were deployed in the flume experiments such to mimic different maintenance strategies that are carried out on actual rivers . Our preliminary observations highlight that the presence of vegetation acts as a forcing term for bar evolution. As in the case of forced bars induced by, for instance, channel curvature, the evolution of vegetated bars follows the dynamics of the forcing action. In our case, the presence of rigid stems positioned on the highest areas of bar deposit, representing patches of hardwood riparian forest, halts the bar migration and increases the amplitude of bed deformations. Moreover, plants increase the planimetric extension of bar deposit thus providing a positive feedback for colonization and establishment of pioneer vegetation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP41C2348S
- Keywords:
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- 0442 Estuarine and nearshore processes;
- BIOGEOSCIENCES;
- 0481 Restoration;
- BIOGEOSCIENCES;
- 1813 Eco-hydrology;
- HYDROLOGY;
- 1825 Geomorphology: fluvial;
- HYDROLOGY