In this work, the study of waves in channels, taking into account the resistences, using non linear mechanics methods, has been dealt with. As a matter of fact, from the origin of the problem, from Boussinesq, De Saint Venant etc. to Bonvicini, Puppini, Massé, Lamoen, Supino, who have brought the most recent and remarkable contributions to the question, the results they attained have been drawn by means of the waves linearized theory. Only Supino has faced, by method of successive approximations, the non-linear questions connected with the unsteady flow problem, thus reaching interesting results. However by adopting modern processes of non-linear mechanics, the author thinks that he has succeeded in showing new essential characteristics of the flow which is studied, especially the possibility of the wave amplification in the case of limited shocks, even before reaching the critical limit represented by the Froude number $F = 4(F = u^{2}/gy)$.