The braided river is a challenging test case for a numerical model. The geometry changes during the computation as a result in variations of water level and bed changes. The adaptive grid that is used for this computation will change with each time step. The current computation has 378 000 time steps, so that there are that many grids being used. Each grid has to have sufficient quality that the solution will converge and not crash. An automated grid generation algorithm has to be used with this large number of grids.
The computation replicates an experiment by Egozi and Ashmore (2007), who used a laboratory flume that was 18 meters long and 3 meter wide. A varying discharge was used: The first 70 hours had a constant discharge of 1.4 l/s. Then a discharge of 2.1 l/s was used for the next 70 hours. The last 70 hours used a discharge of 2.8 l/s. The outflowing sediments were recycled to the inflow of the flume. A straight, 0.5 m wide channel was dug in the middle of the flume before the experiment started. This channel expanded laterally and a braided river formed.
This case is a simulation of a flood wave hitting a construction located inside a flume. A time-dependent solution of the Navier-Stokes equations is used, and a continuity based method is used to change the water surface. An adaptive grid is used.
Plan view of the channel after 15 hours. The colours shows the water depth [cm].
3D view of the channel. The colours shows the water velocity [m/s].
Animation of the development of the channel over the 210 hours. The colours shows the water depth.
This page was last updated: 14. July 2023