The seepage study through earth dams is very essential for the design and construction processes of such dams to ensure the needed safety and efficient performance. The present study focuses on the seepage flow through zoned embankment dams by introducing a numerical analysis using the Seep/w numerical model. The main objective of the study is to investigate the different effects of the dam zones' thickness and side slopes on seepage through such dams to achieve the most suitable dimensions and geometry of the different zones. First, the Seep/w is used to analyze the problem of seepage through earth dams with an internal core. The present obtained results and the results of other previous experimental and analytical studies are almost close to each other. The present work proves that the best relative thickness of the inner, transition, and outer zones (t1:t2:t3) according to the minimum seepage and cost of the used materials is 2:1.5:1.5 respectively. At the same time, it is proven that the reasonable optimum side slopes (H:V) of the inner, transition, and outer zones are 1:1.75, 1.25:1, and 3.75:1 respectively.