Alternate bars of finite amplitude: spatial analysis

Federici & Seminara (2003) has recently shown that the nature of bar instability is convective rather than absolute. This implies that bar evolution observed in nature or in the laboratory is due to the spatial smplification of perturbations that are permanently present in the initial cross-section of the channel. In the present paper, we report the results of numerical simulations on the filly nonlinear equations governing the morphodynamical problem, imposing boundary conditions appropriate to the convective nature of bar instability mechanism. The results show that the bars evolve spatially and reach an equilibrium amplitude only at a certain distance (some wavelenghts) from the inlet section of the domain. This aspect may be relevant in the design of laboratory experiments because the experimental facilities could not be long enough to allow for the full development of perturbations. A comparison with the experimental observations of Fujita & Muramoto (1985) was also attempted.