The formation of dunes in a laboratory channel from a flat bed is discussed based on measurements and mathematical modeling. Both linear stability analysis and three-dimensional morphodynamic numerical model computations are carried out.

This paper focusses on the initial dune formation stages that can be observed only in the laboratory. In this stage of dune initiation comparatively short bed waves develop in the laboratory experiment. Nonlinear processes leading to asymmetry and the coalescence of the bed waves affect their shape and statistics very early during the first minutes of the experimental run.

Bed waves of certain wave length are amplified most during the linear initiation. This agrees well with the linear stability analysis. The nonlinear effects of dune coalescence can be modelled using the three-dimensional morphodynamic-numerical Bmor3D.

The final dune bed with statistically stationary parameters is formed only after additional nonlinear effects that split the dunes become dominant. This effect can also be modelled by nonlinear morphodynamic-numerical models.