Experimental characterization of the role of vegetation in the fluvial process-response system to flood sequencing

FERNANDEZ, ROCIO LUZ; STUART MACLELLAND; DANIEL PARSONS; BAS BODEWES

WASHIGTON

Conferencia; AGU meeting; 2018

Predicting hydrogeomorphic evolution on vegetated fluvial systems requires an understanding of how plants respond to floods and subsequently interact with river morphology. This knowledge is particularly important for restoration and risk management of fluvial environments when contemplating changes in flood magnitude and frequency due to climate change, land cover modifications and other long-term drivers. In the laboratory, quite a few studies have used alfalfa as a surrogate for riparian vegetation to capture the feedbacks between plants and morphodynamics on fluvial systems (Gran and Paola, 2001; Pollen and Simon, 2006; Tal and Paola, 2007, 2010; Van Dijk et al., 2013). Even so, the mechanism of bed morphology adjustment in response to changes in both vegetation growth and flood sequencing remains unclear. For this study, experiments in a 2.5 m x 10 m movable bed channel were conducted at the University of Hull, UK, to identify the diverse roles played by the vegetation (alfalfa) during the release of a sequence of low and high magnitudes flood events. Particularly, four different growth periods for the alfalfa were investigated along with a dying phase, to get insights of the relative role of the age of the plants in the geomorphic impact of the sequential flooding. Hence, the effect of the vegetation growth, and its variable control on bank reinforcement and channel migration, was quantified by looking at the change in the channel patterns of the braided rivers in digital elevation models (DEMs) along with overhead photographs collected during the successive floods. Further, the number of flood disturbances and increased potential of channel bifurcation was observed to be influenced by the characteristics of the occurring flooding event but also on the precedent floods. Overall, the study well demonstrated that the effects of the vegetation on the experimental rivers were much influenced by the flood sequencing and by the growing phase of the alfalfa plants.