Buttress Dam consists of a watertight upstream side, usually reinforced concrete, supported by triangular-shaped walls, called buttresses on the downstream side. This kind of dam uses less concrete compared to a gravity dam due to the space between the buttresses. A buttress dam’s stability relies on the bracing action from the buttress where most of the load is concentrated. Buttress Dams are suited to sites with either wide or narrow valleys but, like gravity dams, it is necessary that they are built on a solid foundation of bedrock.