Effect of Sediment Quantity and Caliber on Braided Channel Geometry

Predicting the evolution of self-formed channels, i.e., channels that are free to modify their planform shape and width, remains an open problem. Here we present results of laboratory experiments specifically designed to study the impact of sediment supply and caliber on the geometry and formation of these self-formed alluvial channels. We analyze results obtained from two model floodplains made of uniform sand with geometric mean size equal to 0.62 mm and 0.22 mm, which represent coarse and fine sands respectively. Both floodplains are 8 m long and 2 m wide and have an initial straight channel that is 10 cm wide and 4 cm deep. The initial slope of the model floodplains is 0.015, which is a typical value for braided channel experiments. The sediment feed rate, as well as the flow rate, is kept constant during the experiment as a braided channel forms and evolves from one equilibrium state toward another equilibrium state. Equilibrium is here defined as a condition in which sediment is delivered at the downstream end of the floodplain at a rate equal to the sediment feed. Flow rates in these experiments vary between 0.8 l/s and 2 l/s while feed rates vary from 100 g/min to 400g/m. Measurements of braid plain width, active channel width, as well and number of total and active channels and sediment transport load at the downstream section of the floodplain, are taken at periodic intervals to track evolution of the channel and of the floodplain.