In this paper, we focus on the importance of conducting the necessary tests either field or laboratory in order to obtain realistic values for soil hydrodynamic parameters allowing the best result to simulate the actual situation of any engineering facility. The importance of this research highlights in earth dams and dikes which have great importance to economic, environmental and human. It is necessary to be complete accuracy when creating a mathematical model to study stability of these structures. From here comes the need to calculate these parameters rather than extracted from engineering codes, that we will use them to simulate the effect of long rainfall on the distribution of water content in the Hweez dam soil and hence its stability. We will build a mathematical model for dam using PCSiWaPro® depending on transition flow chart. concerning that, hydraulic conductivity and volumetric water content in the soil are functions of pore water pressure. These equations with their functions give a smooth transition of the studied model where the saturated state is considered as a special case of the used equations.