Previously, a fluid PE model called JEPE was designed, programmed and tested for numerical prediction of sound propagation in shallow water areas with range-dependent geometry and medium parameters. The results were quite satisfactory, and the model was used also for inverse problems, to estimate medium parameters from measured sound propagation data. Soon, an extension to cover situations with a layered, solid seabed was found desirable. In this report, the basic steps in the design of such a model are described, both for a range-independent stratification of the seabed and for the range-dependent case. The code produced for this model was called JEPE-S and is presented in a separate FOA report by Brodd Leif Andersson.