buttress dam
Used mainly in wide valleys, it consists of an impermeable wall, which is shored up by a series of buttresses to transmit the thrust of the water to the foundation.
cross section of a buttress dam 
reservoir 
Basin formed by the construction of a dam; it holds back a very large volume of water so that the flow rate can be controlled.
foundation 
Concrete structure that supports the weight of the dam and transmits it to the ground to provide stability to the dam.
foundation blockage 
Block of concrete that anchors the foundation in the ground to prevent movement.
buttress 
Block of concrete reinforcing a wall that has to stand up to the thrust of the water; it provides stability to the dam.