This BES show the importance of the boundary conditions and initial conditions for the study of hydraulical simulation cases. Even the case studied has a simple geometrie and a classical asumptions the convergence problemes were many. We notice also that for simulating a case with the good boundary conditions we must have an idea of the regim that will be simulated, witch depend itself on the boundary conditions. so it's hard to study a precise case and thus we have to try many experiences before we got the real case we want to study.

Fourtunately this kind of simulation dont take a lot of time . If we are runing a case with the good boundary conditions the computation converge relatively quickly.

we thank Mme. M.M Maubourguet and M. O. Astruc for their help.