Parts of a dam

Every dam, whatever its type, has the same basic parts. The upstream face holds back the water and the downstream face slopes or steps down to the riverbed. The heel is the upstream edge of the base, where water pressure and uplift are greatest; the toe is the downstream edge, where the dam's weight and the water thrust combine into the highest foundation pressure. The crest is the top, often carrying a road.

Water levels define the vertical layout. The full reservoir level (FRL) is the normal maximum storage level. The maximum water level (MWL) is reached during the design flood, when the spillway is passing its peak. Freeboard, the margin from MWL to the top of the dam, protects against waves, wind set-up and settlement. Dead storage lies below the lowest outlet.

Spillways pass floods safely: overflow spillways on concrete dams, chute or side-channel spillways beside embankment dams, often with radial gates to control releases. Energy dissipators, stilling basins or flip buckets, protect the riverbed below. Outlets, sluices and penstocks release water for irrigation, supply and power. Galleries inside concrete dams give access for drainage, grouting and instruments.

Below and around the dam, the foundation is treated: a grout curtain under the heel reduces seepage and uplift, drainage holes behind it relieve the remaining pressure, and in embankment dams a cut-off trench and filters do the same jobs. Instruments such as piezometers, plumb lines and seepage weirs show how the dam is behaving.