C.Multiple arch buttress dams The dam derives its name from the construction of arches across the buttress for the deck structure. There are two types of such dams-one when the two adjacent arches abut on a common buttress and the other where the buttress is made double walled and adjacent arches abut on different walls. The two walls of the buttress are interconnected by horizontal connections for rigidity of construction. Meer Alam dam in India, is the earliest recorded example of multiple arch dam. The highest multiple arch dam in the world is Daniel Johnson dam(210 m high) in Canada.
Closely following the Meer Alam dam, an Australian Engineer J.D. Berry advocated the multiple arch dam in 1891 with the construction of 18. M high Belubala dam Australia. A remarkable multiple arch dam is Faux-La-Montagne completed in 1951 in France. It consist of 14 arches of maximum height 19 m, only 80 mm thick at the crest and 140 mm thick at the base. The Buttress are spaced at 6.6 m centre to centre and are 200 mm thick. The arches are of cement morter pneumatically applied over the two layers of reinforcement. The buttress are braced with straight beams and arched beams in alternate bays to ensure stability with flexibility, Provision is made for expansion of the crest walkway and hand-rails in the bays that are braced with the arched beams. This dam is reported to be excellent condition.
The multiple-arch dam is suited to valleys that are too wide for a single arch. It derives its economic character from the fact that its volume is slight compared with a massive or even a hollow gravity dam. As far as foundation conditions are concerned the multiple arch dam is capable of adopting itself not only to very good rock, but also to rock of medium or exceptionally, mediocre quality, by widening base of buttress or deepening the foundations.