Arch dams are arches (vaults) laid ‘on their side’. The stability of arch dams is mainly ensured by the transmission of the strut (normal force in the arch belts) to the banks. They withstand water head due to three important properties that together ensure their stability:
1) the resistance of its vertical structural elements (which act as consoles embedded in the base);
3) the features of the arch structure that rests at the ends on the abutments and transmits the water head through them.
If the river valley is relatively narrow, the arch as such will bear the main load of the water mass; when the channel is wide, the other two properties also play a significant role. The Stevenson Creek experimental dam, designed for a level difference of 18 m, lost its face buttress at a level difference of 6 m, but the arch was able to withstand the full load afterwards. The construction of an arch dam is economically advantageous if the terrain is suitable, therefore many such structures were built in the twentieth century. In narrow gorges, arch dams are thin-walled structures.
Pinched heels arch damp is an arch dam that connects to the banks by means of a deep incision filled with concrete in the spacing. The depth of the tie-in is at least half the thickness of the arch at the abutment.
Perimeter-seam arch dam is an arch dam supported on a saddle, separated from the dam by a perimeter-seam.
Arch-gravity dams are curved dams in concrete or masonry, the stability and strength of which is ensured by:
(mainly) by its own weight;
(partly) operation of the dam as a vault with load transfer to the rock banks.
These are dams in which the cross section can be quite massive, similar to that of a gravity dam with a downstream slope of 0.3-0.6. Installed in wide gorges.