Adaptation of an experimental alluvial fan to climate change

We study the effect of an increase in flow discharge on the shape and growth of an experimental alluvial fan. The fan is built by a single-thread channel in which the flow occurs near the threshold of sediment motion. We first define a criterion that predicts the conditions under which a change in discharge leaves an inprint on the morphology of a fan. We then report on experimental runs which allow us to establish the relevance of this criterion. Experiments are carried out during which climatic changes are applied to the feeding channel of a fan. By playing on the initiation time of climate change, on the duration of the rise in flow, or on the total variation in discharge, we scan a range of configurations that allow us to qualitatively and quantitatively test our incision criterion. Qualitatively, we note that the dynamics of the fan seems altered only for values of the criterion which exceed the critical value of 1.5. In these situations, the channel stops moving and entranches. Quantitatively, we extract a characteristic time by autocorrelating spatio-temporal channel migration diagrams and show that this time correlates with the value of the incision criterion.