Classification by Hydraulic Design.-

Dams may also be classified as overflow or non-overflow dams.

Overflow dams are designed to carry discharge over their crests or through spillways along the crest. Concrete is the most common material used for this type of dam.

Non-overflow dams are those designed not to be overtopped. This type of design extends the choice of materials to include earth-fill and rock-fill dams.

Often the two types are combined to form a composite structure consisting of, for example, an overflow concrete gravity dam with earth-fill dikes.

Figure 4-4 shows such a composite structure built by the Bureau of Reclamation.

4.4 Classification by Materials.-The most common classification used for the discussion of design procedures is based upon the materials used to build the structure. This classification also usually recognizes the basic type of design, for example, the “concrete gravity” dam or the “concrete arch” dam.