An embankment dam, as defined earlier, is one that is built of natural materials. In its simplest and oldest form, the embankment dam was constructed with low-permeability soils to a nominally homogeneous profile. The section featured neither internal drainage nor a cutoff to restrict seepage flow through the foundation. Dams of this type proved vulnerable associated with uncontrolled seepage, but there was little progress in design prior to the nineteenth century. It was then increasingly recognized that, in principle, larger embankment dams required two component elements.

(a) An impervious water-retaining element or core of very low permeability of soil, for example, soft clay or a heavily remolded ‘puddle’ clay, and

(b) Supporting shoulders of coarser earth fill(or of rockfill), to provide structural stability

As a further enhancement to the design, the shoulders were frequently subject to a degree of simple zoning, with finer more cohesive soils placed adjacent to the core element and coarser fill material towards either face. Present embankment dam design practice retains both principles. Compacted fine grained silty or clayey earth fills, or in some instances manufactured materials, like asphalt or concrete, are employed for the impervious core element. Subject to their availability, coarser fills of different types ranging up to coarse rockfill are compacted into designated zones within either shoulder, where the characteristics of each can best be deployed within an effective and stable profile.