The materials available locally control the size and configuration of the dam. Many small embankment dams are built entirely of a single type of material such as stream alluvium, weathered bedrock, or glacial till. These are homogeneous dams, constructed more or less of uniform natural material.
Larger embankment dams are zoned and constructed of a variety of materials, either extracted from different local sources or prepared by mechanical or hydraulic separation of source material into fractions with different properties.
An important element in a zoned dam is an impermeable blanket or core which usually consists of clayey materials obtained locally. In locations where naturally impermeable materials are unavailable the dams are built of rock or earth-rock aggregates, and the impermeable layers of reinforced concrete, asphaltic concrete, or riveted sheet steel are placed on the upstream face of the dam.
Embankment dams have been built on a variety of foundations, ranging from weak glacial deposits to strong rock. An advantage compared with concrete dams is that the bearing strength requirements of the foundation are much less. Minor settlement during and after construction is generally not serious because of the adjustability of the material.