To satisfy increasing water demand and to palliate the scarcity of easily mobilizable resources, the construction of dams was set a solution that should be taken into consideration to give rise to an impressive number of dams constructed all over the world.

Among the different types of constructed dams, earth dams are the most widespread and the technique of their construction has greatly progressed in time, without elucidating all the phenomena, and hence developing methods which agree with the dual level technically and economically. Although empirical methods have been improved, they are not guaranteed to prevent against very destructive damages.

Seepage in earth dams represents the main cause of damage throughout the world, thus increased attention is given to means against their effects. Therefore, a water drainage systems is always provided. However, a drain cannot be effective unless it is well dimensioned and carefully laid down in the fill (embankment). This has been an impossible task to realize so far and, therefore, in this paper the authors make use of doubtful and succinct recommendation to fix the drain length.

A graph is given in this study to read directly the length of the internal blanket drain in a homogeneous earth dam. This was obtained after having carried out a simulation of a great number of earth dams by varying the total height, the embankment slopes, and the material characteristics. For each dam, the drain length is changed within the acceptable limits of the hydraulic stability and the down creep stability of the embankment is calculated.