River channel patterns adjusts to riparian vegetation: Experiments and model analysis

Abstract:

River channel patterns, the spatial plan view of a river reach, has long been attributed to the balance between grain sizes (representing bank resistance) and stream power, i.e., the product of water density, flow discharge, and channel gradient. Not until recent years field observations and laboratory experiments have evidenced that the riparian vegetation also plays a crucial role in channel pattern change. Here we explore the bio-geomorphic interactions by a series of well-controlled laboratory experiments and a cellular automaton model. First, we created a multi-threaded braided channel pattern on a fine-sand-bedded flume with a planar size of 6*20m. Then, alfalfa seeds have been scattered in batches on the flume bed. It is observed, with the growth of alfalfa sprouts, the initially braided flume channel has gradually transformed to a mildly-curved meandering channel with a single thread. We numerically replicate the process of channel pattern change by proposing a vegetation-induced flow-resistance parameter and superimposing its values to a cellular topography in which the flow path use to be merely determined by slope.