The article presents the results of the analysis of seepage flow character in an embankment dams with impervious diaphragm made of clay-cement concrete, using the Gotsatlinskaya HPP as an example. The process of slits colmatage was considered in the clay-cement-concrete diaphragm (CCCD), that be caused in the zone of tensile forces or by seismic actions. Mathematical models build in two-dimensional and three-dimensional formulation to study the characteristics of flow in subvertical and subhorizontal cracks. By numerical simulation was received qualitative assessment of the dynamics of gradients of pressure for a non-defective impervious element, for an open crack in impervious element, for a washed-out crack in impervious element. The methods developed for designexperimental substantiation of the parameters of the transition zone (from riding and with the lower side of impervious element), parameters of transition zones for design that provide the process of cracks selfhealing in the clay cement-concrete diaphragm. The granulometric composition shall, the capacity and number of layers of the reverse filter provided for the seepage strength of the system: upstream toe – upstream transitional layer – self-healing layer – CCCD – downstream transitional layer – downstream toe, selected according to the method.