Impact of vegetation on braided river morphology under changing flood conditions in a physical model.

BAS BODEWES; FERNANDEZ, ROCIO LUZ; STUART MACLELLAND; DAN PARSOSNS

Aberystwyth

Conferencia; British Society for Geomorphology Meeting; 2018

British Society for Geomorphology

Under present day climate change predictions, with both higher magnitude and an altered frequency of flood events, uncertainty exist on what will change in the behaviour of river systems in immediate and near future, in particular when addressing for the impact of vegetation in these systems. Physical modelling can prove a valuable tool to understand the processes on a smaller scale, in particular with the use of vegetation, eventually proving an indication about the quality of the impact under changing conditions. Whereas the use of surrogate vegetation in fluvial flume studies is not novel as is shown by previous experiments on braided rivers (Tal & Paola, 2007, Bertoldi et al, 2015), the interaction of vegetation under different flood sequences has not been highlighted before.In a 2.5 by 10 meter long flume we allowed a braided river system to evolve under constant conditions. On top of this braided bed, we periodically seeded Alfalfa, a cress like species, and allowed it to grow over variable periods. After each period of growing we used a sequence of low and high magnitudes flood events in order to capture the change in morphology due these events.Captured DEM?s from these experiments indicate the impact of surrogate vegetation has on both the stabilizing effect of the river system as well as on the behaviour of erosional and depositional features in the braided river systems. The distinct patterns of erosion (and deposition) not only allow us to explain the effect of a range of flow and vegetation settings have on a braided system, it as well will allow us to pinpoint these effects on the morphology and evolution of important individual morphologic features like bars and banks. Ultimately, this can give an indication how different flood events induce change on braided river systems.