Daniel Y. Le Roux Professeur Agrégé - Associate Professor Département de mathématiques et de statistique Université Laval, cité universitaire Québec (QC), G1K 7P4 e-mail : dleroux@mat.ulaval.ca tel : 1 (418) 656-7348 The numerical approximation of the shallow-water equations is a delicate problem and many issues regarding their spatial discretization are still open questions. Our purpose is to bring some light on some of them. We first present new dispersion analysis results concerning the propagation of Rossby waves in ocean modelling for several mixed finite element formulations. The influence of the mass lumping procedure will be analysed and discussed. Some strange and unexpected oscillating results will be explained. We then propose to improve the quality of the solutions by trying to adapt the mesh according to the deficiencies of the numerical methods, shown by analytical studies, a kind of a priori adaptation. Some interesting results are obtained for the P1NC-P1 pair and RT0 element. Finally, we prove that the P1NC-P1 pair satisfies the so-called LLB condition.